Effects of the White River and Mazama Tephras on Terrestrial and Aquatic Palaeoenvironments in Western Subarctic Canada, and Implications for Past Human Populations

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2016-01-13 Effects of the White River and Mazama Tephras on Terrestrial and Aquatic Palaeoenvironments in Western Subarctic Canada, and Implications for Past Human Populations

Rainville, Rebecca

Rainville, R. (2016). Effects of the White River and Mazama Tephras on Terrestrial and Aquatic Palaeoenvironments in Western Subarctic Canada, and Implications for Past Human Populations (Unpublished doctoral thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/25836 http://hdl.handle.net/11023/2740 doctoral thesis

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Effects of the White River and Mazama Tephras on Terrestrial and Aquatic Palaeoenvironments

in Western Subarctic Canada, and Implications for Past Human Populations

Rebecca Anne Rainville

A THESIS

SUBMITTED TO THE FACULTY OF GRADUATE STUDIES

IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE

DEGREE OF DOCTOR OF PHILOSOPHY

GRADUATE PROGRAM IN ARCHAEOLOGY

CALGARY, ALBERTA

JANUARY, 2016

This study presents new information regarding the environmental impacts of the eastern White

River (WRA; 1147 cal BP) and Mazama (MZA; 7627 cal BP) tephras in the western Canadian

subarctic, and discusses their potential implications for wildlife and human populations in the

affected regions. Sediment cores were collected from two lakes (Spirit Lake, southern YT;

“Marahbodd” Lake, western NWT) within the fallout of the WRA and one (Goldeye Lake, western AB) within the fallout of the MZA. Pollen, microcharcoal, chironomids, and

sedimentary characteristics were examined to reconstruct terrestrial and aquatic environments

before and after the eruptions. The results show noticeable environmental impacts of the WRA

and MZA at the sites, including on terrestrial and aquatic community composition and

productivity, fire activity, landscape stability, and lake conditions and chemistry. Environmental

impacts were most pronounced at Spirit Lake, the site closest to the source of its eruption, where

the data suggest that the availability of water, food, material, and habitat resources would likely

have been considerably reduced for 50-150 years. The data support archaeological, ethnographic,

and linguistic evidence that suggests that the WRA might have stimulated wildlife (notably

caribou) and human population movements out of the region, and human adoption of the bow-

and-arrow and of bone and antler points. Data from “Marahbodd” Lake suggest that the

environmental impacts of the WRA were likely similar to those at Spirit Lake, but lesser in

degree – though they lingered longer. The data support archaeological and ethnographic

evidence of limited impacts of the WRA on local wildlife and human populations, which

suggests that populations did not leave the region after the eruption – or at least not on the scale

apparent in southern Yukon. At Goldeye Lake, the data indicate that the environmental impacts

of the MZA were generally slight, though long lasting. A period of reduced occupancy of Plains

ii environments after the MZA coincides with the duration of environmental disturbance at

Goldeye Lake, suggesting that the eruption and its after effects might well have been the reason behind reduced occupancy of the region at this time, and the later introduction of stone boiling and pemmican production.

iii Acknowledgements

It’s difficult to know where to begin.

I owe my deepest gratitude to my supervisor, Dr. Richard Callaghan, for the faith he has had in me, and the support he has given me since the very beginning. From my acceptance to the

program to now, I could not have done it without him.

I am also inexpressibly grateful to my other committee members, Dr. Brian Kooyman and Dr. Gerry Oetelaar, for encouraging me, challenging me, and helping me to grow into my new role as an (environmental) archaeologist. Thank you, too, to the remainder of the former

Department of Archaeology (now Anthropology and Archaeology), for your open-armed

acceptance of “The Geographer,” and for allowing and helping her to follow her star.

The comments of my additional examiners, Drs. Rolf Mathewes and Shawn Marshall for

my defense, and Drs. Pete Dawson and Len Hills for my candidacy, are also greatly appreciated,

and have made this work better by their inclusion. Len, we miss you. Thank you also to my

neutral chair, Dr. Kathryn Reese-Taylor, for keeping everyone in line during both my candidacy

and my final defense.

I am also profoundly grateful to Dr. Bill Patterson, Mikkel Winther Pedersen, and Todd

Kristensen, who generously donated the sediment cores that this work is based upon. I truly do

not know what this project would have been without their wonderful contributions. To Derek

Wilson, Farzin Malekani, Dr. Andrea Freeman, Linda Wilson, Dr. James White, and Dr. Jennifer

Galloway, I could never have completed this project without your assistance and tremendous

offerings of laboratory space, equipment, and advice, and I will be forever thankful. Thank you

also to Dr. Duane Froese and Lauren Davies for their excellent work identifying my ash layers

iv and preparing my radiocarbon dates, and to Tyler Sylvestre for his wonderful editorial nit-

picking and for helping me to fix up my maps.

I am exceptionally lucky to have been able to focus on my research throughout my

degree, thanks to funding from the Natural Sciences and Engineering Research Council of

Canada (NSERC), the University of Calgary, the former Department of Archaeology, and the new Department of Anthropology and Archaeology. Thank you also to Dr. Jack Ives for his generous contribution to my radiocarbon dating.

I am also extremely grateful to Dr. Peter Johnson, Dr. Konrad Gajewski, Dr. Charlie

Schweger, Harvey Friebe, and to all of my past lab-mates for the years of lessons, laughs, and help along the way. Thank you also to all of my friends in Calgary for making me one of you, for keeping me on track, for keeping me sane, and altogether for being pretty much the best group of people I have ever met.

To my family, thank you – as ever – for your love, support, and patience. I promise to be more receptive to visits from now on.

Luc, there are no words.

v Dedication

To the ones who came before, in the hope that we will live up to the example you’ve set for us.

And to the ones who made me laugh, when nothing else in the world could make me smile.

vi Table of Contents

Abstract ...... ii Acknowledgements ...... iv Dedication ...... vi Table of Contents ...... vii List of Tables ...... xi List of Figures and Illustrations ...... xii Epigraph ...... xviii

Chapter One: INTRODUCTION ...... 1 1.1 Problem, research objective, approach, and organization of this thesis ...... 1 1.2 Context ...... 4 1.2.1 Catastrophic disturbance events and the human-environment relationship ...... 4 1.2.2 Volcanism and human history ...... 11

Chapter Two: STUDY SITES ...... 20 2.1 The eastern White River eruption (WRA) ...... 20 2.1.1 The eruption ...... 20 2.1.2 Study sites: Spirit Lake, YT, and “Marahbodd” Lake, NWT ...... 21 2.1.2.1 Spirit Lake, YT ...... 21 2.1.2.1.1 Location and modern setting ...... 21 2.1.2.1.2 Environmental history, 2000 cal BP-present ...... 22 2.1.2.1.3 Cultural history, 2000 cal BP-contact ...... 24 2.1.2.2 “Marahbodd” Lake, NWT ...... 26 2.1.2.2.1 Location and modern setting ...... 26 2.1.2.2.2 Environmental history, 2000 cal BP-present ...... 28 2.1.2.2.3 Cultural history, 2000 cal BP-contact ...... 29 2.1.3 Environmental, wildlife, and cultural impacts of the WRA ...... 30 2.2 The Mazama eruption (MZA) ...... 36 2.2.1 The eruption ...... 36 2.2.2 Study site: Goldeye Lake, AB ...... 37 2.2.2.1 Location and modern setting ...... 37 2.2.2.2 Environmental history, 11,500-4000 cal BP ...... 38 2.2.2.3 Cultural history, 8000-4000 cal BP ...... 40 2.2.3 Environmental, wildlife, and cultural impacts of the MZA ...... 41

Chapter Three: METHODS ...... 53 3.1 Palaeoenvironmental research using lake sediments ...... 53 3.2 Field methods ...... 55 3.2.1 Spirit Lake ...... 55 3.2.2 “Marahbodd” Lake ...... 56 3.2.3 Goldeye Lake ...... 56 3.3 Laboratory and analytical methods ...... 56 3.3.1 Core logging ...... 56 3.3.2 Loss-on-ignition ...... 58 3.3.3 Pollen and microcharcoal ...... 59

vii 3.3.4 Chironomids ...... 63 3.3.5 Chronology and ash identification ...... 65 3.3.6 Data presentation and statistical methods ...... 68 3.3.6.1 Data presentation ...... 68 3.3.6.2 Ordination ...... 68 3.3.6.3 Climate reconstructions ...... 70 3.3.6.4 Comparative data ...... 72

Chapter Four: ENVIRONMENTAL RESPONSES TO THE EASTERN WHITE RIVER ASH (WRA), 1147 CAL BP, SPIRIT LAKE, YT, AND “MARAHBODD” LAKE, NWT ...... 74 4.1 Results ...... 74 4.1.1 Chronology and ash identification ...... 74 4.1.1.1 Spirit Lake ...... 74 4.1.1.2 “Marahbodd” Lake ...... 75 4.1.2 Core logging ...... 77 4.1.2.1 Spirit Lake ...... 77 4.1.2.2 “Marahbodd” Lake ...... 77 4.1.3 Loss-on-ignition ...... 77 4.1.3.1 Spirit Lake ...... 77 4.1.3.2 “Marahbodd” Lake ...... 78 4.1.4 Pollen ...... 79 4.1.4.1 Spirit Lake ...... 79 4.1.4.2 “Marahbodd” Lake ...... 82 4.1.5 Microcharcoal ...... 85 4.1.5.1 Spirit Lake ...... 85 4.1.5.2 “Marahbodd” Lake ...... 85 4.1.6 Chironomids ...... 86 4.1.6.1 Spirit Lake ...... 86 4.1.6.2 “Marahbodd” Lake ...... 90 4.1.7 Ordination ...... 93 4.1.7.1 Spirit Lake ...... 93 4.1.7.2 “Marahbodd” Lake ...... 96 4.1.8 Climate reconstructions ...... 100 4.1.8.1 Spirit Lake ...... 100 4.1.8.1.1 Pollen-based ...... 100 4.1.8.1.2 Chironomid-based ...... 101 4.1.8.2 “Marahbodd” Lake ...... 102 4.1.8.2.1 Pollen-based ...... 102 4.1.8.2.2 Chironomid-based ...... 103 4.2 Terrestrial and aquatic environments at Spirit Lake, YT, 1384-891 cal BP, and “Marahbodd” Lake, NWT, 1488-777 cal BP...... 104 4.2.1 Radiocarbon dating ...... 104 4.2.2 General trends in terrestrial and aquatic environments ...... 105 4.2.2.1 Spirit Lake ...... 105 4.2.2.2 “Marahbodd” Lake ...... 109

viii 4.2.3 Terrestrial and aquatic responses to the WRA ...... 115 4.2.3.1 Spirit Lake ...... 115 4.2.3.2 “Marahbodd” Lake ...... 118 4.2.3.3 Discussion ...... 120

Chapter Five: ENVIRONMENTAL RESPONSES TO THE MAZAMA ASH (MZA), 7627 CAL BP, GOLDEYE LAKE, AB...... 155 5.1 Results ...... 155 5.1.1 Chronology and ash identification ...... 155 5.1.2 Core logging ...... 156 5.1.3 Loss-on-ignition ...... 156 5.1.4 Pollen ...... 157 5.1.5 Microcharcoal ...... 159 5.1.6 Chironomids ...... 160 5.1.7 Ordination ...... 162 5.1.8 Climate reconstructions ...... 166 5.1.8.1 Pollen-based ...... 166 5.1.8.2 Chironomid-based ...... 166 5.2 Terrestrial and aquatic environments at Goldeye Lake, AB, 8601-6652 cal BP ...168 5.2.1 Radiocarbon dating ...... 168 5.2.2 General trends in terrestrial and aquatic environments ...... 168 5.2.3 Terrestrial and aquatic responses to the MZA ...... 173

Chapter Six: WILDLIFE AND HUMAN IMPLICATIONS OF THE TERRESTRIAL AND AQUATIC ENVIRONMENTAL IMPACTS OF THE EASTERN WHITE RIVER (WRA) AND MAZAMA (MZA) ERUPTIONS ...... 198 6.1 Environmental, wildlife, and human significance of the WRA ...... 198 6.1.1 Environmental responses to the WRA compared to regular patterns of environmental change ...... 198 6.1.1.1 Spirit Lake ...... 198 6.1.1.2 “Marahbodd” Lake ...... 200 6.1.2 Implications of the environmental response to the WRA for wildlife and human populations ...... 202 6.2 Environmental, wildlife, and human significance of the MZA ...... 212 6.2.1 Environmental responses to the MZA compared to regular patterns of environmental change ...... 212 6.2.2 Implications of the environmental response to the MZA for wildlife and human populations ...... 214

Chapter Seven: SUMMARY AND FUTURE DIRECTIONS ...... 221 7.1 Summary ...... 221 7.2 Future directions ...... 228

REFERENCES ...... 232

APPENDIX A: ASH IDENTIFICATION RESULTS ...... 261

ix APPENDIX B: COPYRIGHT PERMISSIONS ...... 266 B.1. Chapter Two ...... 266 B.1.1. Figure 2.2 ...... 266 B.1.2. Figure 2.3 ...... 268 B.1.3. Figure 2.4 ...... 274

x List of Tables

Table 4.3 Eigenvalues from PCA on a) pollen percentages; b) chironomid percentages from Spirit Lake, YT...... 128

Table 4.4 Eigenvalues from PCA on a) pollen percentages; b) chironomid percentages from “Marahbodd” Lake, NWT...... 128

Table 4.5 Species scores from PCA on a) pollen percentages; b) chironomid percentages from Spirit Lake, YT...... 129

Table 4.6 Species scores from PCA on a) pollen percentages; b) chironomid percentages from “Marahbodd” Lake, NWT...... 130

Table 5.2 Eigenvalues from PCA on a) pollen percentages; b) chironomid percentages from Goldeye Lake, AB ...... 182

Table 5.3 Species scores from PCA on a) pollen percentages; b) chironomid percentages from Goldeye Lake, AB...... 183

xi List of Figures and Illustrations

Figure 2.1: Summary map depicting source vents and approximate distributions of the WRA and MZA, and study area locations. Approximate distribution of the WRA from Robinson (2001); approximate distribution of the MZA from Sarna-Wojcicki and Davis (1991)...... 46

Figure 2.2: Spirit Lake, YT. a) map; b) photograph. Approximate distribution of the WRA from Robinson (2001). Photograph © Spirit Lake Wilderness Resort, 2007, used with permission...... 48

Figure 2.3: Marahbodd Lake, NWT. a) map; b) photograph. Approximate distribution of the WRA from Robinson (2001). Photograph © Todd Kristensen, 2014, used with permission...... 50

Figure 2.4: Goldeye Lake, AB. a) map; b) photograph. Approximate distribution of the MZA from Sarna-Wojcicki and Davis (1991). Photograph © Luc Rainville, 2012, used with permission...... 52

Figure 4.1 Age-depth chronology for Spirit Lake, YT. The solid circles are retained 14C dates, prior to correction. The open circle indicates the single rejected 14C date. Solid diamonds are retained 14C dates, after correction. The open triangle indicates the depth and age of the WRA (Clague, et al. 1995). The X indicates the depth and age of the top of the core. The dashed line is a line of best-fit used to determine whether correction was necessary (y=23.549x+3827.7, R2 = 1). The solid line is a line of best-fit used to establish the final chronology (y=-0.0016x3+0.3816x2-5.5127-56.455, R2=1). Please see the text for details...... 131

Figure 4.2 Age-depth chronology for “Marahbodd” Lake, NWT. The solid circles are retained 14C dates, prior to correction. Open circles indicate rejected 14C dates. Solid diamonds are retained 14C dates, after correction. The open triangle indicates the depth and age of the WRA (Clague, et al. 1995). The X indicates the depth and age of the top of the core. The dashed line is a line of best-fit used to determine whether correction was necessary (y=37.353x+2348.7, R2 = 1). The solid line is a line of best-fit used to establish the final chronology (y=0.0283x3-2.1826x2+86.562-63, R2=0.999). Please see the text for details...... 132

Figure 4.3 Photograph of the section of the ML core used for this analysis. The WRA appears as a light grey band approximately 23-25cm depth...... 133

Figure 4.4 Magnetic susceptibility of the section of the ML core used for this analysis. The depth of the WRA in the ML core (23-25cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. The vertical grey line indicates and X-axis value of 0...... 134

xii Figure 4.5 Sediment organic, carbonate, and silicate content from Spirit Lake, YT. The depth of the WRA in the SL core (17-18cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes...... 135

Figure 4.6 Sediment organic, carbonate, and silicate content from “Marahbodd” Lake, NWT. The depth of the WRA in the ML core (23-25cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes...... 136

Figure 4.7 Pollen a) percentages; b) influx from Spirit Lake, YT. The depth of the WRA in the SL core (17-18cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Dotted 10-times exaggeration lines have been added to a number of the curves so that the patterns are more visible. Please note scale changes...... 138

Figure 4.8 Pollen a) percentages; b) influx from “Marahbodd” Lake, NWT. The depth of the WRA in the ML core (23-25cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Dotted 10-times exaggeration lines have been added to a number of the curves so that the patterns are more visible. Please note scale changes...... 140

Figure 4.9 Microcharcoal influx from Spirit Lake, YT. The depth of the WRA in the SL core (17-18cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation...... 141

Figure 4.10 Microcharcoal influx from “Marahbodd” Lake, NWT. The depth of the WRA in the ML core (23-25cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation...... 142

Figure 4.11 Chironomid a) percentages; b) influx from Spirit Lake, YT. The depth of the WRA in the SL core (17-18cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes...... 144

xiii Figure 4.12 Chironomid a) percentages; b) influx from “Marahbodd” Lake, NWT. The depth of the WRA in the ML core (23-25cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes...... 146

Figure 4.13 Sample scores from PCA on a) pollen percentages; b) chironomid percentages from Spirit Lake, YT. Dashed lines through the sample scores are loess smoothers with spans of 0.2. A varve-inferred reconstruction of mean July temperature anomalies from Iceberg Lake, AK (Loso 2009), is provided for comparative purposes; the dashed line through this curve is a loess smoother with a span of 0.05. The depth of the WRA in the SL core (17-18cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Vertical grey lines indicate X-axis values of 0. Please note scale changes...... 148

Figure 4.14 Sample scores from PCA on a) pollen percentages; b) chironomid percentages from “Marahbodd” Lake, NWT. Dashed lines are loess smoothers with spans of 0.2; vertical grey lines indicate X-axis values of 0. A chironomid-inferred reconstruction of mean July temperature from Slipper Lake, NWT (MacDonald, et al. 2009), is provided for comparative purposes. The depth of the WRA in the ML core (23-25cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes...... 150

Figure 4.15 Pollen-inferred mean July temperature and total annual precipitation from Spirit Lake, YT, reconstructed using the MAT. The vertical grey line through the “Distance to closet modern analogue” curve indicates the 20th percentile acceptable/non-analogue cut-off (=92), as determined using the SCD metric. A varve-inferred reconstruction of mean July temperature anomalies from Iceberg Lake, AK (Loso 2009), is provided for comparative purposes. The dashed line through this curve is a loess smoother with a span of 0.05; the vertical grey line indicates an X-axis value of 0. The depth of the WRA in the SL core (17-18cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes...... 151

xiv of 0. The depth of the WRA in the SL core (17-18cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes...... 152

Figure 4.17 Pollen-inferred mean July temperature and total annual precipitation from “Marahbodd” Lake, NWT, reconstructed using the MAT. The vertical grey line through the “Distance to closet modern analogue” curve indicates the 20th percentile acceptable/non-analogue cut-off (=92), as determined using the SCD metric. A chironomid-inferred reconstruction of mean July temperature from Slipper Lake, NWT (MacDonald, et al. 2009), is provided for comparative purposes. The depth of the WRA in the ML core (23-25cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes...... 153

Figure 4.18 Chironomid-inferred mean July temperature and lake depth from “Marahbodd” Lake, NWT, reconstructed using WAPLS regression and the MAT. The dashed line through the first lake depth curve is a loess smoother with a span of 0.2. The vertical grey line through the “Distance to closet modern analogue” curve indicates the 20th percentile acceptable/non-analogue cut-off (=24.5), as determined using the SCD metric. A chironomid-inferred reconstruction of mean July temperature from Slipper Lake, NWT (MacDonald, et al. 2009), is provided for comparative purposes. The depth of the WRA in the ML core (23-25cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes...... 154

Figure 5.1 Age-depth chronology for Goldeye Lake, AB. The solid circles are 14C dates, prior to correction. Solid diamonds are 14C dates, after correction. The open triangle indicates the depth and age of the MZA (Zdanowicz, et al. 1999). The dashed line is a line of best-fit used to determine whether correction was necessary (y=92.786x+6075.9, R2 = 1). The solid line is a line of best-fit used to establish the final chronology (y=0.0001x2+9782x+5956.9, R2=1). Please see the text for details...... 185

Figure 5.2 Photograph of the section of the GDL core used for this analysis. The MZA appears as a light grey band approximately 17-19cm depth...... 186

Figure 5.3 Magnetic susceptibility of the section of the GDL core used for this analysis. The depth of the MZA in the GDL core (17-19cm) is marked with a horizontal grey shaded band. The age of the MZA (7627 cal BP; Zdanowicz, et al. 1999) is marked with a horizontal grey line and labelled; the age of the MZA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. The vertical grey line indicates an X-axis value of 0...... 187

xv Figure 5.4 Sediment organic, carbonate, and silicate content from Goldeye Lake, AB. The depth of the MZA in the GDL core (17-19cm) is marked with a horizontal grey shaded band. The age of the MZA (7627 cal BP; Zdanowicz, et al. 1999) is marked with a horizontal grey line and labelled; the age of the MZA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes. .... 188

Figure 5.5 Pollen a) percentages; b) influx from Goldeye Lake, AB. The depth of the MZA in the GDL core (17-19cm) is marked with a horizontal grey shaded band. The age of the MZA (7627 cal BP; Zdanowicz, et al. 1999) is marked with a horizontal grey line and labelled; the age of the MZA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Dotted 10-times exaggeration lines have been added to a number of the curves so that the patterns are more visible. Please note scale changes...... 190

Figure 5.6 Microcharcoal influx from Goldeye Lake, AB. The depth of the MZA in the GDL core (17-19cm) is marked with a horizontal grey shaded band. The age of the MZA (7627 cal BP; Zdanowicz, et al. 1999) is marked with a horizontal grey line and labelled; the age of the MZA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation...... 191

Figure 5.7 Chironomid a) percentages; b) influx from Goldeye Lake, AB. The depth of the MZA in the GDL core (17-19cm) is marked with a horizontal grey shaded band. The age of the MZA (7627 cal BP; Zdanowicz, et al. 1999) is marked with a horizontal grey line and labelled; the age of the MZA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes...... 193

Figure 5.8 Sample scores from PCA on a) pollen percentages; b) chironomid percentages from Goldeye Lake, AB. Dashed lines are loess smoothers with spans of 0.2. Reconstructions of mean July temperature and total annual precipitation anomalies using pollen data from sites across central Canada (50-70°N, 80-120°W; Viau and Gajewski 2009), are provided for comparative purposes. The depth of the MZA in the GDL core (17-19cm) is marked with a horizontal grey shaded band. The age of the MZA (7627 cal BP; Zdanowicz, et al. 1999) is marked with a horizontal grey line and labelled; the age of the MZA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Vertical grey lines indicate X-axis values of 0. Please note scale changes...... 195

Figure 5.9 Pollen-inferred mean July temperature and total annual precipitation from Goldeye Lake, AB, reconstructed using the MAT. Dashed lines are loess smoothers with spans of 0.3. The vertical grey line through the “Distance to closet modern analogue” curve indicates the 20th percentile acceptable/non-analogue cut-off (=92), as determined using the SCD metric. Reconstructions of mean July temperature and total annual precipitation anomalies using pollen data from sites across central Canada (50-70°N, 80- 120°W; Viau and Gajewski 2009), are provided for comparative purposes. Vertical grey lines through the comparative mean July temperature and total annual precipitation anomaly curves indicate X-axis values of 0. The depth of the MZA in the GDL core (17- 19cm) is marked with a horizontal grey shaded band. The age of the MZA (7627 cal BP;

xvi Zdanowicz, et al. 1999) is marked with a horizontal grey line and labelled; the age of the MZA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes...... 196

Figure 5.10 Chironomid-inferred mean July temperature and lake depth from Goldeye Lake, AB, reconstructed using WAPLS regression and the MAT. Dashed lines are loess smoothers with spans of 0.2. The vertical grey line through the “Distance to closet modern analogue” curve indicates the 20th percentile acceptable/non-analogue cut-off (=24.5), as determined using the SCD metric. Reconstructions of mean July temperature and total annual precipitation anomalies using pollen data from sites across central Canada (50-70°N, 80-120°W; Viau and Gajewski 2009), are provided for comparative purposes. Vertical grey lines through the comparative mean July temperature and total annual precipitation anomaly curves indicate X-axis values of 0. The depth of the MZA in the GDL core (17-19cm) is marked with a horizontal grey shaded band. The age of the MZA (7627 cal BP; Zdanowicz, et al. 1999) is marked with a horizontal grey line and labelled; the age of the MZA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes...... 197

Figure 6.1 Summary diagram detailing terrestrial and aquatic impacts of the WRA at Spirit and “Marahbodd” Lakes and evidence of wildlife and human responses to the WRA available from other publications...... 219

Figure 6.2 Summary diagram detailing terrestrial and aquatic impacts of the MZA at Goldeye Lake and evidence of wildlife and human responses to the MZA available from other publications...... 220

xvii Epigraph

If you don’t know history, then you don’t know anything. You are a leaf that doesn’t know it is part of a tree.

Michael Crichton

xviii

Chapter One: INTRODUCTION

1.1 Problem, research objective, approach, and organization of this thesis

Since the end of the Wisconsinan Glaciation in North America, there have been a number of

major volcanic eruptions, with the eruption of Mount St. Helens the most recent in 1980. While

more recent North American eruptions, such as Mount St. Helens, have been studied extensively

to determine their environmental, wildlife, and cultural significance, our understanding of the

environmental, wildlife, and human impacts of past large eruptions such as those of Mount

Churchill (1954 and 1147 cal BP; Clague, et al. 1995; Lowdon and Blake Jr 1968) and Mount

Mazama (7850 and 7627 cal BP; Smithsonian Institution National Museum of Natural History

(Global Volcanism Program) 2013; Zdanowicz, et al. 1999) has sometimes been based more on

speculation and comparison with modern eruptions than on evidence of the effects of the

eruptions in question. Although several studies have presented evidence of the environmental,

wildlife, and cultural impacts of these large eruptions (e.g. Abella 1988; Beierle and Smith 1998;

Bennett, et al. 2001; Birks 1980; Blinman, et al. 1979; Bradbury, et al. 2004; Bunbury and

Gajewski 2013; Clark 1991; Derry 1975; Egan 2013; Hallett, et al. 1997; Hallett and Walker

2000; Hare, et al. 2004; Hare, et al. 2012; Heinrichs, et al. 1999; Hickman and Reasoner 1994;

Ives 1990; Johnson and Raup 1964; Kuhn, et al. 2010; Letts, et al. 2012; Long, et al. 2011; Long, et al. 2014; Mack, et al. 1983; MacNeish 1964; Matson and Magne 2007; Mehringer, et al. 1977;

Minckley, et al. 2007; Moodie, et al. 1992; Mullen 2012; Oetelaar and Beaudoin 2005, 2014;

Power, et al. 2011; Slater 1985; Workman 1974, 1979), numerous gaps remain in our

understanding how these events may have shaped the history of our continent.

The volcanic ash (tephra) layers deposited by the 1147 calibrated years Before Present

(cal BP, where Present is equal to AD 1950) eastern White River (WRA) eruption and the 7627

cal BP Mazama (MZA) eruption are commonly encountered at sites in western Canada.

Considerable short and long-term environmental, wildlife, and cultural effects have been

suggested to have followed from both the WRA and MZA, however evidence of these impacts is

still relatively limited and confined to a small number of studies, and substantial further

investigation will be required before the environmental, wildlife, and human consequences of

these eruptions will be able to be understood with confidence (Bunbury and Gajewski 2013;

Egan 2013; Hare, et al. 2012; Long, et al. 2011; Mullen 2012; Oetelaar and Beaudoin 2014). The objective of this study is to reconstruct terrestrial and aquatic responses to the deposition of the eastern White River and 7627 cal BP Mazama tephras at several sites in the western Canadian subarctic, and to examine the possible implications of these impacts for wildlife and human populations living nearby at the time of the eruptions.

This research is presented from an environmental archaeological perspective, whose traditional focus has been the provision of “archaeological context” (Butzer 1982:4), with the ultimate goal of determining “the interrelationship between culture and the environment” (Butzer

1982:5). Three sites – two from within the range of the eastern White River ashfall, and one within the range of the 7627 cal BP Mazama (hereafter called simply “Mazama” or “MZA”) ashfall – are examined. All of the sites are located in areas previously unexamined for ash impacts, and are located in environmentally sensitive areas where the deposition of the ashes is likely to have produced more noticeable effects. To provide the necessary palaeoenvironmental information, this study employs a palaeoecological approach, incorporating the high-resolution analysis of pollen, microcharcoal, chironomid head capsules, and sedimentary characteristics from lake sediment cores to qualitatively and quantitatively reconstruct the terrestrial and aquatic environments of the study sites – including climate, terrestrial and aquatic community

composition and productivity, fire activity, landscape stability, and lake conditions and chemistry

– both before and after the eruptions. This multi-proxy information allows this study to present

an informed discussion of the environmental consequences of the WRA and MZA ashfall events

at the sites, and of the potential influence of these effects on the responses of wildlife and human

populations, as reflected by linguistic, ethnographic, and archaeological evidence.

Following this general introductory chapter, Chapter Two outlines our current knowledge

of the eastern White River and Mazama eruptions, the suggestions that have been made in the

past about their potential influence on the environment and on wildlife and human populations, and the environmental, linguistic, ethnographic, and archaeological evidence that is currently available to inform our understanding of the environmental, wildlife, and cultural consequences of these events in general. Chapter Two also specifically describes the three study sites, and outlines our current knowledge of the environmental and human history of their surrounding regions, as well as any information we have about environmental, wildlife, and/or human

responses to the eruptions in the vicinity of each site. Chapter Three then outlines the

methodology used to produce the palaeoenvironmental data employed to reconstruct past

environments at the study sites. Chapters Four and Five present and discuss the results of

palaeoenvironmental proxy analyses at the two WRA sites and one MZA site, respectively.

Chapter Six draws together the new information presented in Chapters Four and Five with

previously available palaeoenvironmental, linguistic, ethnographic, and archaeological

information to discuss the potential consequences of the environmental effects of the WRA and

MZA ashfalls on wildlife and human populations. Lastly, Chapter Seven summarizes the

previous chapters and presents ideas for future work.

1.2 Context

1.2.1 Catastrophic disturbance events and the human-environment relationship

Humanity has influenced and been influenced by the surrounding environment since the beginning of our species (Butzer 1971; Dincauze 2000; Head 2000). Long-term environmental conditions and changes have had substantial and long-term effects on human culture (Butzer

1971; Dincauze 2000). In addition to potentially substantial short-term effects such as causing mobility, subsistence, and health issues – potentially causing increased incidence of illness and/or mortality, and/or forcing populations to temporarily abandon affected regions – abrupt climatic changes and catastrophic disturbance events such as volcanic eruptions, drought, floods, fires, and earthquakes are also likely to have had long-term effects on human culture. These impacts potentially served as driving factors behind large-scale human migrations, altering

languages, inspiring the development and adoption of new technologies, rousing social change,

and/or becoming incorporated into our mythologies (e.g. Clark 1991; D'Andrea, et al. 2011;

Derry 1975; Dillehay and Kolata 2004; Hare, et al. 2004; Hare, et al. 2012; Ives 1990; Johnson and Raup 1964; MacNeish 1964; Matson and Magne 2007; McMichael 2012; Mellars 2006;

Moodie, et al. 1992; Mullen 2012; Munoz, et al. 2010; Oetelaar and Beaudoin 2005, 2014;

Workman 1974, 1979; Zhang, et al. 2011).

While examinations of the environmental, wildlife, and cultural impacts of modern catastrophic events are often capable of providing excellent analogues for understanding similar events in the past, the uniqueness of each event’s circumstances in temporal, geographical, environmental, and human terms argues for the application of palaeoenvironmental and archaeological techniques and site-specific studies. These types of analyses allow for a greater understanding of each

individual event and its consequences, and help to provide insight into the history of particular areas and peoples. Multiple studies of specific past events allow us to understand their overall consequences, and to see the varying ways in which catastrophic disturbances are capable of influencing environment and culture depending on circumstances with a greater time-depth than is available from modern studies. Taken together, such studies provide a broader range of information for the interpretation of the effects of other past disturbance events around the world, and valuable information that might be used to guide human responses to current and future environmental change.

Understanding past human-environment relationships is the particular interest of a number of branches of archaeology, including – but not limited to – environmental archaeology. Though

Branch et al. (2005) suggest that environmental archaeology has developed with “little or no theoretical discourse” (1), the approach has drawn substantial theoretical guidance from developments in anthropological theory related to the human-environment relationship, and from processual theory in archaeology, as well as from disciplines such as geology, biology, and environmental science (Branch, et al. 2005; Butzer 1971, 1982; Dincauze 2000; Erickson and

Murphy 2003; Evans and O'Connor 1999; Head 2000; Moran 2008; Shackley 1981; Trigger

1996).

Though environmental archaeology as a named discipline is only approximately 40 years old, the field has its theoretical origins in the much older concept of environmental determinism

– a theory of anthropological thought espoused since Greco-Roman times that argues that human culture is passively influenced by the environment, which plays a deterministic role in shaping

cultural characteristics (Moran 2008). In the 19th and 20th Centuries, geographers such as

Freidrich Ratzel and Ellsworth Huntington argued that human culture reacts to nature just as any

other animal (Helm 1962; Huntington 1915; Moran 2008). This results in the development of

particular cultural traits under given environmental circumstances, under the assumption that

when faced with a number of alternatives, humans will respond to the conditions of their

environment just like other animals, and will naturally take the path of least resistance (Helm

1962; Huntington 1915; Moran 2008).

With the rise of cultural anthropology in the late 19th Century, the notion that the

characteristics of human societies are decided by the characteristics of the surrounding

environment began to fall into disfavour, and concepts such as history and culture gradually came to the fore as explanations for the similarities and differences visible in past and present

human groups (Erickson and Murphy 2003; Moran 2008; Trigger 1996). These new perspectives

suggested that rather than determining the way in which a culture will develop, the environment is only able to provide limitations on, and opportunities for, cultural development, and that ultimately it is the history of the people in question that determines the choices that will be made.

These perspectives regarding the human-environment relationship came to be categorized under the heading of “cultural determinism” or “historical possibilism,” supported and expanded upon by researchers such as Franz Boas, Clark Wissler, and Alfred Kroeber (Boas 1986; Kroeber

1939; Moran 2008; Wissler 1926).

Cultural neo-evolutionism, developing beginning in the 1950s during the modern environmental movement in part as a reaction to the historical possibilist perspective, was an attempt to re-incorporate ideas of environmental adaptation into theories of cultural development

(Erickson and Murphy 2003). In his “Science of Culturology,” Leslie White utilized the

thermodynamic concept of entropy to understand cultural evolution. Both biological and cultural evolution, he argued, reduce entropy by evolving into more complex forms; cultural evolution will occur as more energy is harnessed per capita, or the efficiency of its use is increased

(Erickson and Murphy 2003; White 1959). White divided what he saw as the general path of cultural evolution into four stages based on the ability of a culture to harvest and use energy, beginning with the invention of tools, and progressing through domestication, the use of fossil fuels, and finally to the use of atomic energy (Erickson and Murphy 2003; White 1959). Julian

Steward, a contemporary of White, found the application of the laws of thermodynamics to human culture to result in over-generalization, in which the influence of specific historical and/or environmental circumstances on the evolution of a culture is all but ignored (Erickson and

Murphy 2003; Steward 1955). Instead, Steward proposed his own theory of “Cultural Ecology,” under which human culture might evolve in a number of different ways depending on circumstances – a concept that he termed “multilineal evolution” (Erickson and Murphy 2003;

Steward 1955). Steward’s cultural ecology was particularly interested in the relationship between the environment and subsistence, and the way in which the practice of a given subsistence method might influence other aspects of culture (Moran 2008; Steward 1955). In the late 1960s, dissatisfaction with cultural ecology’s focus on subsistence at the expense of other potential influences on culture – such as political or religious factors – led to the development of ecological anthropology, associated especially with the work of Andrew Vayda and Roy

Rappaport (Moran 2008; Vayda and Rappaport 1968). The theory was strongly influenced by the biological ecosystem concept, and also by the functionalist ideas of theorists such as

Malinowski, who argued that all of the elements of a culture will act together to meet the needs of the population (Erickson and Murphy 2003). Much as some cultural determinists and cultural

neo-evolutionists had done before them, ecological anthropologists emphasized the biological nature of the human species, suggesting that humanity – like any other species – is subject to ecological principles. In the case of ecological anthropology, Vayda, Rappaport, and their followers argued that societies function in order to maintain a balance between the population and the carrying capacity of the environment, leading culture to develop in ways such that this equilibrium is maintained (Moran 2008; Vayda and Rappaport 1968). This belief led to a focus on how cultural traits function to maintain populations in balance with their resources, and placed an emphasis on concepts of homeostasis and homeostatic regulation as underlying factors shaping human action.

The way in which cultures perceive the environment gained gradually more importance with the development of cultural anthropology and postprocessual archaeology in the 1960s-

1990s, with the work of Clifford Geertz, Ian Hodder, Christopher Tilley, and others (Erickson and Murphy 2003; Geertz 1973; Hodder 1986; Tilley 1994; Trigger 1996). This new perspective on human-environment relationships focused on the study of the meanings individuals and cultures give to the environment, how they understand the place of society and individuals in relation to it, and how these factors might guide activity.

Modern anthropology and archaeology now consider a variety of potential influences on human culture and behaviour, including environmental conditions and change, which are typically understood as having both influenced and been influenced by humanity throughout our history (Head 2000; Trigger 1996). Various sub-fields of anthropology and archaeology – including ethnoecology, historical ecology, political ecology, environmental archaeology, and

landscape archeology – provide multiple approaches through which the characteristics of human- environment relationships may be examined (Moran 2008; Trigger 1996).

Drawing particularly from cultural neo-evolutionism, cultural ecology, and ecological anthropology, environmental archaeology developed largely from the framework outlined by the

Binfordian New Archaeology/processualist paradigm (Binford 1972; Branch, et al. 2005).

Binford argued that culture is in essence a means for humanity to adapt to its environment, allowing generalizable principles to be sought out to explain culture and human behaviour

(Binford 1972; Trigger 1996). Binford did not consider historical factors to be relevant, representing an insubstantial influence on behaviour in comparison to functional and/or adaptational needs. Likewise, Binford also considered psychological factors to be unimportant, developing as a result of functional and/or adaptational requirements, rather than exerting any influence themselves. Binford’s approach was highly positivist, arguing for the rigorous application of the scientific method to the study and interpretation of the archaeological record

(Binford 1972; Trigger 1996). Modern environmental archaeology has since grown to embrace the influence of historical and/or psychological factors on human-environment relationships.

Nevertheless, the concepts and principles of positivism, systems theory, functionalism, ecology/ecosystem theory, evolution and natural selection, and adaptation have played a substantial role in shaping the approach, such that its primary interests typically lie in developing an understanding of the functional/adaptational relationships that have existed between culture and the environment (Branch, et al. 2005; Butzer 1971, 1982; Dincauze 2000; Evans and

O'Connor 1999; Head 2000; Shackley 1981). Though it has been criticized for oversimplification of the human-environment relationship and its study as a result of these tendencies – leading to the development of landscape archaeology, with its interest in the meanings individuals and

cultures gave to the environment, how they understood the place of society and individuals in

relation to the environment, and how these factors might have guided behaviour, often from a

more idealist perspective – environmental archaeology has grown in significance over the four

decades of its formal history, and is now an important part of most archaeological studies

(Branch, et al. 2005; Butzer 1971, 1982; Darvill 2008; David and Thomas 2008; Dincauze 2000;

Evans and O'Connor 1999; Head 2000; Shackley 1981; Trigger 1996).

In addition to drawing from anthropological and archaeological theory, environmental

archaeology relies heavily on the geological principle of uniformitarianism, which suggests that

processes that can be observed today were also occurring in the past, produced the same effects,

and interacted according to the same principles, allowing past environments and cultures to be

reconstructed by drawing analogies with modern systems (Branch, et al. 2005; Butzer 1971,

1982; Dincauze 2000; Evans and O'Connor 1999; Head 2000; Shackley 1981). The focus of environmental archaeological studies may be either synchronic or diachronic, and – for example

– might focus on developing an understanding of land use patterns at a particular point in prehistory, the way in which a culture responded to a particular instance of environmental change, or the way in which political or religious factors might have led to anthropogenic environmental change (Darvill 2008).

Environmental archaeology employs a diverse range of methodologies drawn from the modern earth, biological, and environmental sciences, archaeology, palaeoclimatology, and palaeoecology, which are used to reconstruct past environments and cultural behaviours towards them (Branch, et al. 2005; Butzer 1971, 1982; Dincauze 2000; Evans and O'Connor 1999; Head

2000; Shackley 1981). Environmental archaeologists utilize both palaeoenvironmental and archaeological techniques to try to identify and better understand the human-environment

relationship as it has existed in the past, often with the hope of providing information with which

modern society might improve this relationship in the future (Head 2000; Shackley 1981).

Advances in our understanding of human history around the world have been invaluable to these

studies, as have advances in our ability to reconstruct past environments using

palaeoenvironmental proxies, in geomorphological and geochemical analysis, in radiocarbon and

other absolute dating techniques, in Geographic Information Systems (GIS) and remote sensing,

and in statistical analysis and modeling (e.g. multivariate ordination analyses such as Principle

Components Analysis; Branch, et al. 2005; Head 2000). The utility of these techniques for

environmental archaeological research also continues to progress with further application

(Branch, et al. 2005; Head 2000).

1.2.2 Volcanism and human history

Volcanic eruptions are among the most catastrophic disturbance events on Earth, capable of

causing substantial both short and long-term environmental, wildlife, and cultural impacts even

when the eruptions themselves are relatively short-lived. Volcanic eruptions may be broadly

classed into conventional eruptions, which do not involve water, and hydrovolcanic eruptions,

which do (Francis and Oppenheimer 2004). Conventional eruptions are further sub-classed based

on explosivity; from weakest to strongest, these are: Hawaiian, Strombolian, Vulcanian, Pelean,

Plinian, and finally, Ultra-Plinian (Francis and Oppenheimer 2004). The explosivity of volcanic

eruptions may also be classified using the Volcanic Explosivity Index (VEI; Newhall and Self

1982). Using the VEI, eruptions are classed from 0-8 on a logarithmic scale, in which a VEI of

0-1 corresponds to the weakest, Hawaiian-type eruptions, with ash plumes less than 0.1 km in

height and up to 100,000 m3 of ejecta (Decker and Decker 2006). The largest, Plinian and Ultra-

Plinian eruptions correspond to a VEI of 4-8, with plumes greater than 10 km in height, and over

10,000 km3 of ejecta (Decker and Decker 2006).

Kiluea, HI is a characteristic example of Hawaiian-type eruptions, and has been erupting

continuously since 1983. In such eruptions, low gas content results in the slow eruption of

magma forming shield volcanoes and lava lakes (Francis and Oppenheimer 2004). Magma flows from these types of eruptions are capable of causing environmental, wildlife, and human repercussions, however the slow movement of the magma typically allows time for relocation and results in limited disturbance (Zeilinga de Boer and Sanders 2002). Still, explosive eruptions do occasionally occur, as well as landslides that sometimes trigger tsunamis (Zeilinga de Boer and Sanders 2002). Unsurprisingly, volcanism has played a substantial role in Hawaiian culture.

Hawaiians explain volcanism as the work of the goddess Pele, whose volatile temper might

cause her to shake the earth, send forth destructive lava, or create new land (Zeilinga de Boer and

Sanders 2002). The tradition of leaving offerings for Pele in an attempt to convince her to be

kind continues on the islands to this day (Zeilinga de Boer and Sanders 2002).

In Strombolian eruptions, such as those typical of Mount Etna, Italy, higher gas pressures result

in short-lived explosive eruptions in which magma is ejected high into the air (Francis and

Oppenheimer 2004). These types of eruptions are relatively safe and non-disruptive, however,

due to their minimal force and the small spread of ejecta (Francis and Oppenheimer 2004).

Vulcanian eruptions, such as those typical of Sakurajima, Japan, are similar to Strombolian-

types, except that the higher viscosity of the magma results in greater explosive force (Francis and Oppenheimer 2004).

Pelean eruptions are named for Mount Pelée, Martinique, which erupted in 1902, devastating the northern end of the island and killing almost the entire population of the city of St. Pierre

(Francis and Oppenheimer 2004; Zeilinga de Boer and Sanders 2002). Eruptions of this type eject large volumes of gas and dust resulting from the collapse of the previous lava dome

(Francis and Oppenheimer 2004). The collapsed material mixes with super-heated gases emitted from the volcano, creating fast-moving pyroclastic flows with extreme destructive power

(Francis and Oppenheimer 2004). The 1902 eruption of Mount Pelée was the first identification of pyroclastic flows resulting from a volcanic eruption (Francis and Oppenheimer 2004). The eruption was preceded by steam and gas emissions and small earthquakes (Zeilinga de Boer and

Sanders 2002). Magma gradually began to force its way up past the cool, solid plug of the volcano’s lava conduit, forming a “spine” of rock which projected from the floor of Pelée’s caldera (Francis and Oppenheimer 2004; Zeilinga de Boer and Sanders 2002). As pressure built, fractures began to form in the mountain’s sides, expelling gas, steam, and mud (Zeilinga de Boer and Sanders 2002). Ash and gases killed wildlife or drove it down from higher elevations, killed vegetation and domestic animals, contaminated water, and made people ill and travel difficult

(Francis and Oppenheimer 2004; Zeilinga de Boer and Sanders 2002). Streams overflowed with water from heavy rains and groundwater that welled up through the fissures in the mountain

(Zeilinga de Boer and Sanders 2002). The eruption of Mount Pelée began with a vertical eruption of ash and smoke, followed by a lateral explosion that released a pyroclastic flow that flowed down the flank of the mountain, setting vegetation on fire and ultimately hitting St. Pierre, killing

its population and destroying the city along with several ships in the harbour (Francis and

Oppenheimer 2004; Zeilinga de Boer and Sanders 2002). The volcano continued to erupt

sporadically, depositing additional ash and debris, until 1905 (Zeilinga de Boer and Sanders

2002).

Plinian and Ultra-Plinian eruptions, such as those of Mount St. Helens, Washington, in 1980, and

Pinatubo, Philippines, in 1991, are the most explosive type of eruption (Francis and

Oppenheimer 2004). In these eruptions, magma is forced through a narrow conduit before

breaking through to the surface in a sustained column, often causing substantial damage to the

vent that enhances the velocity of the eruption (Camp 2006). Eruptions may last for days, with

large amounts of ash and debris being carried into the air by expanding gases and resulting in

widespread ashfalls, while magma and heavier debris form pyroclastic flows (Camp 2006).

Deposited ash mixes with water from rain, hail, and/or snowmelt to form destructive lahars

(mudflows) that cause further destruction (Camp 2006). The lingering influence of recent large

Plinian/Ultra-Plinian eruptions, such as that of Tambora, Indonesia, in 1815, Krakatau,

Indonesia, in 1883, and Mount St. Helens, WA, in 1980, continues to be felt even in the 21st

Century.

The eruption of Tambora, Indonesia, in 1815, devastated the island of Sumbawa with ash, debris, and pyroclastic flows, killing people, wildlife, vegetation, and even sea life near the coast, destroying villages, and contaminating fields and water, leading to famine, disease, and mass migration out of the affected area (Zeilinga de Boer and Sanders 2002). Yet the most substantial effect of this eruption resulted from the injection of ash high into the atmosphere, where it encircled the globe and resulted in the “Year Without A Summer” – a global reduction in solar

radiation and temperature, and change in precipitation patterns, which actually lasted

approximately three years, causing crop failure and the death of people and animals in North

America, Europe, and Asia (Zeilinga de Boer and Sanders 2002). The influence of the eruption

lingers to this day in literature inspired by the gloom cast by the changed climate, including

Byron’s “Darkness” and Mary Shelley’s “Frankenstein” (Zeilinga de Boer and Sanders 2002).

The effects of the eruption of Krakatau, Indonesia, in 1883, also continue to be felt. The

eruption lasted three days, ejecting ash and dust high into the stratosphere, where it encircled the

globe within two weeks, and killed plant and animal life on the island and its neighbours

(Zeilinga de Boer and Sanders 2002). In some cases, tsunamis triggered by pyroclastic flows

completely obliterated islands that had previously existed, while debris created new, temporary

islands that eventually eroded away (Francis and Oppenheimer 2004; Zeilinga de Boer and

Sanders 2002). Ecological recovery began quickly with sprouting of new plants from rhizomes

and buried seed banks and the arrival of other plants and animals by sea and air, however this process continues to this day (Thornton 1996; Zeilinga de Boer and Sanders 2002).

The impeding eruption of Mount St. Helens, WA, on May 18, 1980, was foreshadowed by a 4.1 magnitude earthquake a few months earlier, on March 18 of the same year (Zeilinga de

Boer and Sanders 2002). In the following weeks, sensors installed to monitor the mountain detected continued low-magnitude earthquakes and magmatic activity, prompting officials to warn people to keep away from the mountain, and eventually to begin evacuating nearby populations by the end of March (Decker and Decker 2006; Zeilinga de Boer and Sanders 2002).

At the same time, a plume of steam and ash began to issue from the mountain, and a state of emergency was declared soon after (Decker and Decker 2006; Zeilinga de Boer and Sanders

2002). At this time, the United States Geological Survey (USGS) established an observation post

10 km northwest of the volcano to observe a bulge that was forming on the northern side of the mountain (Decker and Decker 2006; Zeilinga de Boer and Sanders 2002). On May 18, a 5.1 magnitude earthquake collapsed this bulge in a landslide, releasing gases, ash, and debris that

formed a pyroclastic flow (Decker and Decker 2006; Francis and Oppenheimer 2004; Zeilinga

de Boer and Sanders 2002). A vertical eruption followed. All life unable to escape the

pyroclastic flow – including USGS geologist David Johnson, who was manning the observation

post – was killed (Decker and Decker 2006; Zeilinga de Boer and Sanders 2002). Melted snow

mixed with dirt, debris, and ash to form destructive mudflows, clogging the Columbia River;

increased sediment loads continued to be recorded in the North and South Fork Toutle rivers

even 20 years later (Decker and Decker 2006; Zeilinga de Boer and Sanders 2002). Ash was

deposited as far away as Montana, causing short circuits, disabling cars and trucks, and causing

widespread breathing difficulty in the human population (Zeilinga de Boer and Sanders 2002).

The subsequent ecological and cultural impacts of the Mount St. Helens eruption have been

extensively studied. Ecological regeneration was begun relatively quickly by survivors of the

eruption, however even today the ecosystem is still in flux (Dale, et al. 2005; Zeilinga de Boer

and Sanders 2002). Social issues in human populations that have been attributed to the eruption

include the effects of forced relocation, such as job loss, as well as generally increased stress

levels, incidence of illness, and mortality rates. The eruption has also inspired poems, art, and

film (Zeilinga de Boer and Sanders 2002).

In Canada and the United States, there are 174 volcanoes that have been active in the last 10,000

years (Smithsonian Institution National Museum of Natural History (Global Volcanism Program)

2013). Major eruptions of Plinian/Ultra-Plinian type have occurred a number of times, including

of the Fisher Caldera, AK (ca. 9370 and 5120 cal BP, VEIs 6 and 5, respectively), Mount

Mazama, OR (ca. 7850 and 7627 cal BP, VEIs 6 and 7, respectively), Mount Aniakchak, AK (ca.

7200 and 3595 cal BP, VEIs 6), Black Peak, AK (ca. 3850 cal BP, VEI 6), Mount St. Helens,

WA (ca. 4290, 3720, 3810, and 2480 cal BP and AD1480, 1482, 1800, and 1980, VEIs 5, 5, 6, 5,

5, 5, 5, and 5, respectively), Mount Meager, BC (ca. 2630 cal BP, VEI 5), Okmok Caldera, AK

(ca. 2050 cal BP, VEI 6), Mount Churchill, AK (ca. 1954 and 1147 cal BP, VEIs 6), and

Novarupta, AK (AD1912, VEI 6; Smithsonian Institution National Museum of Natural History

(Global Volcanism Program) 2013). Of these, ash deposits from the 7627 cal BP Mount

Mazama, 3810 cal BP Mount St. Helens, 2630 cal BP Mount Meager (Bridge River), and 1954 and 1147 cal BP Mount Churchill (White River) eruptions may be found in the western Canadian subarctic. Of these, the 1147 cal BP Mount Churchill, 3810 cal BP Mount St. Helens, and 7627 cal BP eruption of Mount Mazama were the largest with VEIs of 6, with the Mount Churchill and Mount Mazama ashes covering the most extensive areas within Canada.

The 1147 cal BP eruption of Mount Churchill and the 7627 cal BP eruption of Mount

Mazama were both of Plinian type, with high volumes of ejecta and widespread ashfall areas

(Lerbekmo 2008; Lerbekmo and Campbell 1969; Robinson 2001; Smithsonian Institution

National Museum of Natural History (Global Volcanism Program) 2013; Zdanowicz, et al.

1999). Substantial environmental effects have been suggested to have resulted from both

eruptions, including terrestrial and aquatic productivity and community changes, changed fire

regimes, increased landscape instability and erosion, and changed water conditions and

chemistry. Wildlife and cultural impacts as a direct result of the eruptions and indirectly as a

result of their environmental effects have also been suggested to have been substantial,

potentially causing increased incidence of illness and/or mortality, stimulating the abandonment

of affected regions by wildlife and human populations, encouraging human technological

innovation, and/or leading to the incorporation of tales of the eruptions into human oral histories.

Evidence supporting such effects, however, remains limited to a relatively small number of

studies given the broad temporal, geographical, environmental, and human context of the

eruptions and the suggested significance of their consequences (e.g. Abella 1988; Beierle and

Smith 1998; Bennett, et al. 2001; Birks 1980; Blinman, et al. 1979; Bradbury, et al. 2004;

Bunbury and Gajewski 2013; Clark 1991; Derry 1975; Egan 2013; Hallett, et al. 1997; Hallett and Walker 2000; Hare, et al. 2004; Hare, et al. 2012; Heinrichs, et al. 1999; Hickman and

Reasoner 1994; Ives 1990; Johnson and Raup 1964; Kuhn, et al. 2010; Letts, et al. 2012; Long, et al. 2011; Long, et al. 2014; Mack, et al. 1983; MacNeish 1964; Matson and Magne 2007;

Mehringer, et al. 1977; Minckley, et al. 2007; Moodie, et al. 1992; Mullen 2012; Oetelaar and

Beaudoin 2005, 2014; Power, et al. 2011; Slater 1985; Workman 1974, 1979). This study will add to our understanding of these events by providing new information detailing their terrestrial and aquatic environmental effects at several sites in the western Canadian subarctic, and by utilizing this new evidence – in combination with the results of previously available palaeoenvironmental, linguistic, ethnographic, and archaeological studies – to discuss the potential impacts of the ashes on wildlife and human populations in the affected regions with greater confidence than has been possible in the past. In combination with other similar studies, this study will also improve our understanding of the impacts of these eruptions in general, and of the varying potential consequences of events such as these for different environments and populations, providing a broader range of information for the interpretation of the effects of other past disturbance events around the world. Finally, it is hoped that the new information presented in this study will aid modern society in its attempts to understand and cope with current and

future environmental change, and contribute to the development of a more informed human- environment relationship in years to come.

Chapter Two: STUDY SITES

2.1 The eastern White River eruption (WRA)

2.1.1 The eruption

The White River Ash consists of two lobes of volcanic ash deposited in two events ca. 1954 and

1147 cal BP (Clague, et al. 1995; Lerbekmo 2008; Lerbekmo and Campbell 1969; Lowdon and

Blake Jr 1968). Ash from the first eruption spreads northward from the source in the St. Elias

Mountains along the Yukon-Alaska border, while ash from the second, larger eruption spreads eastwards across southern Yukon and parts of northern British Columbia, northwestern Alberta,

and far western Northwest Territories (Figure 2.1; Lerbekmo 2008; Robinson 2001). A number of possible vents have been proposed, centering around Mount Churchill, AK, in Wrangell-St.

Elias National Park and Preserve (Lerbekmo 2008; Richter, et al. 1995). Due to the known seasonality of prevailing winds in the region, it has been suggested that the first eruption occurred in the summer, when prevailing winds blow to the north, while the second occurred in the winter, when prevailing winds blow eastward (West and Donaldson 2002; Workman 1979).

The eruption which produced the eastern lobe produced 47 km3 of ejecta in an eruption that is

estimated to have been ca. 45 km high, making the eruption of Plinian type, with a Volcanic

Explosivity Index (VEI) of 6 (Lerbekmo 2008; Smithsonian Institution National Museum of

Natural History (Global Volcanism Program) 2013). The ash from the WRA is composed of a

blend of glass, plagioclase, hornblende, hypersenthe, and magnetite (Lerbekmo and Campbell

1969). Ash from the eruption has been discovered as far as Greenland and northern Europe,

suggesting potentially global significance (Jensen, et al. 2014).

2.1.2 Study sites: Spirit Lake, YT, and “Marahbodd” Lake, NWT

2.1.2.1 Spirit Lake, YT

2.1.2.1.1 Location and modern setting

Spirit Lake (60°15’07"N, 134°44'22"W; surface area = 67 ha; Barker 2015) is a marl lake located in the Southern Lakes region of southern Yukon, ca. 400 km from the source of the

WRA (Figure 2.2). The lake is long and narrow, oriented approximately N-S, and has a complex bathymetry, with a shallow shelf at its southern end and several deep basins at its northern end.

The lake was once connected to another lake, called Blue Lake, at its northern end, but the two lakes are now separated by Highway 2, which passes between. The lake is groundwater fed, and has an outlet that flows southward from its southern end to join with the Watson River. The region is underlain by primarily Mesozoic sedimentary bedrock consisting largely of limestone, dolomite, and conglomerate (Yukon Geological Survey 2015). Surface material is composed of glaciofluvial sands and gravels (Yukon Geological Survey 2014). Regional climate is primarily influenced by air masses from the Gulf of Alaska in the North Pacific (Wahl, et al. 1987). The region has a continental subarctic climate, with a mean annual daily air temperature of ca. -1°C

(Oswald and Senyk 1977). Annual precipitation is quite low at ca. 230 mm/yr, resulting in particular sensitivity of the environment to changes in moisture availability (Anderson, Abbott,

Finney and Burns 2005; Anderson, et al. 2007; Anderson, Abbott, Finney and Edwards 2005;

Oswald and Senyk 1977). Permafrost is sporadic discontinuous in the region (Atlas of Canada

5th Edition 1995). The lake lies in the valley of the Watson River, and is surrounded by hills of predominantly open boreal forest dominated by Picea glauca and Populus tremuloides, with

Pinus contorta common in valley bottoms (Cwynar 1988). Larix laricina, Picea mariana, and

Picea glauca may also be found in low-lying or more poorly-drained areas (Cwynar 1988). Abies

lasiocarpa is abundant at higher elevations (Cwynar 1988). Artemisia and Poaceae are common

on drier sites (Anderson, Abbott, Finney and Edwards 2005). Alnus crispa, Betula, and Salix are

also common components of the vegetation, particularly in more poorly-drained areas (Cwynar

1988). The region supports a wide variety of wildlife, including woodland caribou, moose,

thinhorn sheep, mountain goats, wood bison, elk, mule deer, black and grizzly bears, wolves, 169

species of resident and migratory birds, two amphibian species, and a variety of small mammals

(Southern Lakes Wildlife Coordinating Committee 2012).

2.1.2.1.2 Environmental history, 2000 cal BP-present

Though southern Yukon has been subject to extensive palaeoenvironmental study overall, only

two lakes have been studied from the Southern Lakes region in particular: Kettlehole

Pond/Marcella Lake (Anderson, et al. 2007; Anderson, Abbott, Finney and Edwards 2005;

Cwynar 1988), and “Jellybean” Lake (unofficial name; Anderson, Abbott, Finney and Burns

2005). Gajewski et al. (2014) summarize the overall environmental history of southern Yukon, including the Southern Lakes. Isotope, pollen, charcoal, and palaeolimnological proxies all

indicate climate and environmental conditions similar to the present day in the region during the

last 2000 years. Oxygen isotope data from Mount Logan, YT, and pollen-based temperature and precipitation reconstructions from southwestern and eastern Beringia, YT and AK, indicate slightly warmer and wetter conditions until ca. 700 cal BP, followed by a gradual shift to slightly cooler and drier conditions to the present day, corresponding with the timing of the Medieval

Warm Period (MWP) and Little Ice Age (LIA; Fisher, et al. 2008; Gajewski, et al. 2014; Viau, et al. 2008). Forests have generally been dominated by Picea glauca or Pinus, with Populus, Picea

mariana, Abies, Larix, Artemisia, Poaceae, Alnus, Juniperus, Betula, Salix, and Cyperaceae also

forming important components of the vegetation (Gajewski, et al. 2014). Charcoal records from

Upper Fly Lake, Sulphur Lake, Keyhole Lake, and Lake “WA01” (unofficial name) suggest

approximately stable fire frequency, though variability was higher during the MWP until ca. 700

cal BP than from ca. 700 cal BP-present (Bunbury and Gajewski 2009; Gajewski, et al. 2014;

Lacourse and Gajewski 2000; Rainville and Gajewski 2013). Several available tree-ring studies document reduced growth – associated with lower summer temperatures – at most sites until the end of the LIA ca. 100 years ago, followed by increased growth, suggesting warming conditions in the 20th Century (Ayotte 2002; Gajewski, et al. 2014; Zalatan and Gajewski 2005).

In the Southern Lakes region, only Kettlehole Pond/Marcella Lake and “Jellybean” Lake

have been subjected to palaeoenvironmental study. Cwynar (1988) documents increased

abundance of Pinus contorta at Kettlehole Pond/Marcella Lake starting ca. 2000 cal BP,

coincident with reductions in Picea glauca and P. mariana, as well as Alnus crispa, Salix, and

Juniperus. Using lacustrine isotopic data, Anderson et al. (2007) and Anderson, Abbott, Finney

and Edwards (2005) reconstruct gradually decreasing lake levels from ca. 3000 to 1200 cal BP,

followed by approximate stability at or just below modern values to the present. At “Jellybean”

Lake, Anderson, Abbott, Finney and Burns (2005) reconstruct similar wetter than average

conditions lasting until ca. 1200 cal BP, followed by generally drier than average conditions to

the present. Anderson, Abbott, Finney and Burns (2005) and Anderson et al. (2007) relate

variations in water depth at “Jellybean” and Kettlehole Pond/Marcella Lakes to variations in the

strength/position of the Aleutian Low (AL) pressure system in the North Pacific, suggesting that

a stronger/more easterly AL tends to correspond to periods of drier conditions in the Yukon

interior due to increased rainout on the windward side of the St. Elias and Coast Mountains,

while a weaker/more westerly AL corresponds to lesser rainout over the coast and mountains,

and wetter conditions in the interior. A similarly-timed pattern in sediment carbonate content was

also found at Lake “WA01,” providing further evidence that the AL has a substantial influence

on the climate and environment of the region (Rainville and Gajewski 2013; Spooner, et al.

2003).

2.1.2.1.3 Cultural history, 2000 cal BP-contact

Spirit Lake is located within the traditional territory of the Carcross/Tagish First Nation

(McClellan 1975, 1981, 1987). The Tagish language falls within the Northern Athapaskan

language group, though substantial contact with coastal Tlingit has resulted in the general

adoption of that language (McClellan 1975). The Tagish had little contact with Europeans until

late in the 19th Century, as a result of the careful management of trade routes to the coast by

Tlingit groups, however the region was directly on the path of prospectors on their way to the

Klondike during the Gold Rush of AD 1898, which brought massive change to ways of life in the

region (McClellan 1975). McClellan (1975, 1981, 1987) describes the traditional lifeways of the

population in her detailed ethnographic accounts. Prior to the Gold Rush, the traditional yearly

round consisted of the seasonal exploitation of available natural resources by small groups of 1-2

families. Summer and fall were important times for resource gathering, preparation, and storage,

however despite the great effort placed into setting aside stores, supplies were often insufficient

for families to make it through the winter. Familial ties between groups served in part as a safety

mechanism, ensuring that resources were shared and that none were left to starve (McClellan

1975:97). The many lakes and rivers of the region dominate and characterize the environment,

and served not only as sources of fresh water and food, but also as transport routes and meeting

places (McClellan 1975, 1981, 1987). Freshwater fish such as grayling, ling cod, whitefish, pike,

herring, and lake trout were fished throughout the year, while caribou, sheep, and moose were pursued from late summer to early winter (Hare, et al. 2004; McClellan 1975, 1981, 1987).

Recent archaeological discoveries of faunal and cultural remains in ice patches in the region have led to the investigation of the role that these environments played as hunting areas (Alix, et al.

2012; Bowyer 2011; Dove, et al. 2005; Farnell, et al. 2004; Greer and Strand 2012; Hare 2011;

Hare, et al. 2004; Hare and Thomas 2010; Hare, et al. 2012; Helwig, et al. 2008; Kuhn, et al.

2010; Yukon Ice Patch First Nations 2010a, b). The materials recovered lack any sign of longer- term inhabitation such as caches, domestic artifacts, or domestic structures, and are often located within 10-15 km of lakeside sites at lower elevations, leading Hare et al. (2004) to suggest that the ice patches were used as specialized caribou and sheep hunting sites for stays of only a short duration. Salmon also formed an important resource for the Tagish, who had a large salmon camp on the McClintock River and at Marsh Lake for catching and drying the fish during their run in the late summer (McClellan 1975). Berrying, including blueberries, cranberries, currants, and raspberries, was also an important activity of the late summer.

The archaeological sequence of the region is generally considered to follow that of

Workman (1978). Workman (1978) envisioned cultural continuity in the region as of ca. 5000

radiocarbon years Before Present (BP, uncalibrated, where Present is equal to AD 1950), with

the sudden arrival of the Northern Archaic tradition (Taye Lake phase), characterized by notched

points with straight or concave bases, heavy bifaces, unifaces, endscrapers, and a lack of the

microblades particularly characteristic of the previous Little Arm phase (ca. 7100-5400 BP).

Workman (1978) suggested that the Northern Archaic tradition ultimately originated in the

northern Plains, having followed a circuitous route through the Mackenzie Valley and

northwestern Alaska, however this has been questioned by other authors since. Clark and Morlan

(1982) have argued that the Northern Archaic in southern Yukon was actually a late phase of

MacNeish’s (1964) Northwest Microblade tradition, with characteristic microblades simply absent from some sites – similar to MacNeish’s (1964) original definition in which the Taye

Lake phase was included under the Northwest Microblade umbrella. Regardless, the Northern

Archaic in southern Yukon is generally accepted as being continuous with the later Late

Prehistoric tradition (Aishihik Phase), characterized by comparable material culture as Taye

Lake, with the addition of smaller side-notched points similar to Prairie side-notched points from

the northern Plains, small stemmed Kavik points, copper, and increased use of bone and antler

(Workman 1978). In southern Yukon, Workman (1978) dated the transition from the Taye Lake

to the Aishihik phase to the time of the WRA. More recent archaeological investigations in the

region have provided additional evidence for the temporal association of the WRA with

increased use of bone and antler, and the beginning of copper use, as well as with the adoption of

the bow-and-arrow, and with increased use of birch versus spruce for weapon shafts (Hare, et al.

2004; Moodie, et al. 1992; see section 2.1.3). The Aishihik phase was finally succeeded by the

Bennet Lake phase after European contact (Workman 1978).

2.1.2.2 “Marahbodd” Lake, NWT

2.1.2.2.1 Location and modern setting

“Marahbodd” Lake (unofficial name; 62°58'35"N, 129°08'54"W) is a ca. 86 hectare lake located

in the Selwyn Mountains of western NWT, ca. 1550 km from the source of the WRA (Figure

2.3). The lake is long, narrow, and slightly arced in shape, lying in a roughly NE-SW orientation.

It has a simple bathymetry, and is ca. 6 m deep at its deepest point in the centre of the lake along

both its length and width. A small inlet stream flows from the west into the lake on its western

side approximately 1/3rd of the way from its northernmost end. The lake’s outlet flows eastward from the eastern side of the northern end of the lake, eventually feeding into O’Grady Lake and the Natla River, which flows NW-SE through the study region. The study lake is underlain by

Paleozoic sedimentary rock, with large areas of Precambrian and Mesozoic intrusives (Blusson

1971). Surface material is composed of Quaternary glacial till and alluvial deposits (Blusson

1971). Regional climate is continental subarctic, with a mean annual daily air temperature of ca.

-7°C and total annual precipitation of ca. 750-800 mm (Crowe, et al. 1979). Permafrost in the region is extensive and generally continuous (Atlas of Canada 5th Edition 1995). The lake itself is located in a region of relatively flat topography, characterized by oxbow lakes, meandering streams, and shrub birch (Betula glandulosa) tundra vegetation (MacDonald 1983). Cladonia is a common component of the ground cover. The lake is close to the forest-tundra transition, resulting in terrestrial and aquatic environments that are particularly sensitive indicators of environmental change (MacDonald 1983). Higher elevations (ca. 1500-2000 m) border the site to

the west, north, and east, while to the south the South Nahanni River runs in an approximately

NW-SE direction. Salix is common at higher elevations (MacDonald 1983). Former channels are often occupied by areas of bog dominated by Sphagnum and Carex, while open coniferous forests of predominantly Picea glauca are characteristic of the river valley (MacDonald 1983).

Picea mariana replaces Picea glauca on more poorly-drained sites (MacDonald 1983). Wildlife

in the region is diverse, consisting of more than 40 mammal, 175 bird, and 16 fish species

(Andrews, MacKay and Andrew 2012).

2.1.2.2.2 Environmental history, 2000 cal BP-present

Palaeoenvironmental records from the Mackenzie and Selwyn Mountains and Tuktoyaktuk

Peninsula suggest generally stable climate and environment in the region over the last ca. 2000 years, with only a slight trend towards cooler and wetter conditions leading to the present beginning ca. 5000-3500 BP. Slater (1985) notes generally stable climate and environmental conditions at Eildun Lake, NWT, beginning ca. 2400 BP to the present. MacDonald (1987) also identifies generally stable conditions at Lac Mélèze and Lac Demain, NWT, beginning ca. 5000

BP. At Natla Bog in the central Selwyn Mountains, MacDonald (1983) records decreasing total pollen production, as well as decreasing representation of Picea in favour of Alnus and Ericales, suggestive of cooling conditions, starting ca. 5400 BP. At Andy, Keele, and Bell’s Lakes in the central Mackenzie Mountains, Szeicz et al. (1995) also note a gradual climatic cooling record, suggested by decreased Picea relative to Alnus and Cyperaceae, and a shift from Picea mariana to Picea glauca beginning ca. 5000 BP. Ritchie and Hare (1971) identify Betula-Salix shrub tundra on the Tuktoyaktuk Peninsula starting ca. 4000 BP, following a period of shrub-forest tundra which lasted from ca. 5500-4000 BP. Spear (1993) also reconstructs gradually cooler and wetter conditions at Reindeer Lake, Sleet Lake, and Bluffer’s Pingo in the Tuktoyaktuk

Peninsula, starting ca. 3500-3000 BP. The gradual development of wetter conditions is also inferred at Lac Mélèze, and at several sites in the Doll Creek area, northern YT, from increases in Alnus and Betula neoalaskana (at the Doll Creek sites), beginning ca. 6000 BP (MacDonald

1987; Ritchie 1982).

2.1.2.2.3 Cultural history, 2000 cal BP-contact

The area surrounding “Marahbodd” Lake is located within the traditional homeland of the

Shútagot’ine (Mountain Dene; Andrews, MacKay, Andrew, et al. 2012; Gillespie 1981).

Ethnographic accounts suggest that prior to European contact, the inhabitants of the region would spend most of the year in the mountains, only rarely coming down to lower elevations

(Andrews, MacKay, Andrew, et al. 2012; Gillespie 1981). Results from archaeological studies of perennial ice patches in the region seem to provide support for this notion, though investigation of the NWT ice patches is at an earlier stage than the Yukon ice patches (Andrews, MacKay and

Andrew 2012; Andrews, MacKay, Andrew, et al. 2012). As the fur trade developed in the 19th

Century, land use patterns are suggested to have shifted so that summers were more commonly spent at lower elevations in the Mackenzie Valley (Andrews, MacKay, Andrew, et al. 2012;

Gillespie 1981). The traditional diet was dominated by sheep and caribou; moose were also caught, but were more difficult to kill and thus less commonly sought (Gillespie 1981). Fish were also consumed, but were less desirable than these other sources of meat. Before the arrival of guns, sheep, caribou, and moose were caught with snares, and killed using throwing-darts and/or the bow-and-arrow (Andrews, MacKay, Andrew, et al. 2012). Archaeological and ethnographic evidence suggests a preference for Saskatoon berry, birch, and spruce for both throwing-dart and bow-and-arrow shaft construction, which were tipped with points of caribou bone or stone (Andrews, MacKay and Andrew 2012; Andrews, MacKay, Andrew, et al. 2012).

The archaeological sequence in the Mackenzie Valley as of ca. 2000 BP is characterized by Millar’s (1968) Mackenzie complex, in which the microblades characteristic of previous complexes of MacNeish’s (MacNeish 1953, 1954, 1955) Northwest Microblade tradition largely drop from the record, to be replaced by increased abundance of more finely made bifaces.

Broadly side and corner-notched, stemmed, and lanceolate points present in previous

assemblages are still present (Clark 1981). MacNeish’s (1954) Spence River phase (a.k.a. Spence

River complex; Clark 1981; Millar 1968) arrives in the region after the WRA, representing the

beginning of the Late Prehistoric tradition. The Spence River phase shares similarities with both

the Aishihik phase to the west, and the Taltheilei tradition to the east, and is characterized by a lack of microblades, and by the introduction of bone and horn tools, and of smaller, more narrowly-notched points similar to Prairie side-notched points (Clark 1981; Morrison 1984).

Morrison (1984) has suggested the term “technocomplex” to describe the relationship between

the Spence River phase, Aishihik phase, and Taltheilei tradition at this time in history. The

addition of European goods introduces the Fort Liard complex, which then carries the region into

the historic period (Clark 1981).

2.1.3 Environmental, wildlife, and cultural impacts of the WRA

Beginning in the 1970s, Workman (1974, 1979) hypothesized regarding the potential cultural

consequences of the WRA in southern Yukon, developing on the propositions made by

MacNeish (1964), who initially hypothesized a substantial temporal gap between his Taye Lake

and Aishihik phases corresponding to the WRA and the years following. Based on observations

of the environmental, wildlife, and human impacts of volcanic eruptions in Iceland (Malde

1964), Washington (Ray 1954), Alaska (Wilcox 1959), and Russia (Suslov 1961), Workman

(1974, 1979) suggested that the WRA had likely had a substantial immediate impact on human populations in the region. This would have begun with the sight and sound of the eruption, and

the development of heavy clouds, potentially bringing toxic rain or hail. Ash and debris would

also have been distributed across the landscape (Workman 1974, 1979). Workman (1974, 1979)

hypothesized that long-term physical effects of the eruption and ash on the environment and on human populations would include inhibited grazing for lowland mammals, and a “disastrous early spring” (1974:249), bringing enhanced flooding, intensified erosion and landscape instability, tree breakage and damage from windblown ash, and the death of herbaceous plants.

Workman (1974, 1979) suggested that water sources would likely have been severely contaminated, causing problems for humans and terrestrial animals in search of drinking water, and for aquatic life. Workman (1974, 1979) hypothesized a substantial impact of the ash on game and fish as a result of these environmental effects. In addition to physical impacts,

Workman (1974, 1979) suggested that the psychological effects of the eruption on human populations might have been severe, citing detrimental psychological effects recoded after a small recent eruption in Washington, in which the ash is described as “snow” that fell several inches deep and caused great fear among human populations (Workman 1974:248, quoting Ray

1954:108). Ray’s (1954:108) informant goes on to describe how as a result, the whole summer was spent praying and dancing, rather than gathering food, and many died of starvation the following winter (Workman 1974:248, quoting Ray 1954:108). Workman (1974, 1979) also cites the transition from the Taye Lake to the Aishihik phase at approximately the time of the WRA as possible evidence of the substantial impact of the ash on human populations in the region.

Workman (1974, 1979) also cites instances of site abandonment recorded by Johnson and Raup

(1964), again approximately coincident with the WRA, as possible evidence of the eruption’s substantial human consequences, and links the spread of the Athapaskan language group to the

Pacific Coast and what is now the American Southwest to the movement of Northern

Athapaskan-speaking populations out of affected regions after the WRA.

Though the environmental impact of the WRA in southern Yukon has been subject to a

deal of speculation, surprisingly few studies have specifically addressed the question, and the

majority of palaeoenvironmental evidence of the terrestrial and aquatic consequences of the

eruption comes from just a few recent studies. Based on DNA analysis of caribou remains

uncovered from perennial ice patches in southern Yukon, Kuhn et al. (2010) have discovered genetic replacement of local caribou populations ca. 1000 BP, following a ca. 400-year period from which no remains were recovered. The authors note that these occurrences are approximately coincident with the WRA and the MWP, providing two possible explanations for the apparent abandonment of the ice patches by caribou during this time, and for the genetic replacement ca. 1000 BP (Kuhn, et al. 2010). At Gull Lake, YT, Birks (1980) documents the sequence of plant colonization around the site after the WRA, beginning with Cyperaceae-

dominated herbaceous vegetation, followed by Alnus-Betula-Salix shrub tundra, and finally by

open Picea glauca forest similar to what is present in the region today. Bunbury and Gajewski

(2013) have also specifically examined the impacts of the WRA on aquatic environments in

Yukon. Using magnetic susceptibility (MS), biogenic silica (BSi), and chironomid head

capsules, the authors reconstruct the short and long-term effects of the ash at three lakes with

varying ash thicknesses and in different environments. At Upper Fly Lake, with 0.1 cm of ash

and located in alpine tundra, the ash appeared to have little effect, though it is noted that air

temperatures may have played an important role influencing chironomid productivity. At Jenny

Lake, with 0.3 cm of ash and located in the boreal forest, the immediate effect of the ash is

determined to have lasted ca. 20 years, with decreased lake productivity indicated by decreased sediment BSi and chironomid influx, and alterations to chironomid community structure suggestive of decreased lake water pH. At Lake WP02, located in the alpine tundra with a thick

but unspecified amount of ash, and at Donjek Kettle, located in the boreal forest with 44 cm of

ash, the immediate impact of the ashfall again caused decreased chironomid productivity and

changes in community structure to favour taxa suggestive of decreased lake water pH. Primary

productivity at Lake WP02 also decreased after the ash, while it increased at Donjek Kettle; the authors attribute this to increased Si:P ratios in the lake after the deposition of the ash, which would favour diatom production. After ca. 60 years of short-term response, the lakes then took an additional ca. 40 years to return to their pre-ash conditions (Bunbury and Gajewski 2013).

DNA analysis of caribou remains from ice patches in Northwest Territories has revealed no similar abandonment of the region corresponding to the MWP and/or the WRA as has been discovered by Kuhn et al. (2010) in Yukon (Letts, et al. 2012). At Eildun Lake, NWT, Slater

(1985) notes increased representation of Picea, Cyperaceae, and Sphagnum relative to Alnus and

Betula at the time of the ash, though these results are questioned by the author given Malde’s

(1964) assertion that coniferous taxa are more susceptible to ash than are deciduous taxa, and the issue is not discussed further. Decreased pollen concentrations and sediment organic content are also noted after the ash at Eildun Lake, suggesting reduced terrestrial and/or aquatic productivity.

All of these changes occur over a relatively short time-span, before returning to pre-ash conditions. Finally, it has been suggested that ash thickness in southeast Yukon and southwest

Northwest Territories was insufficient to have affected peat development (Crowley, et al. 1994;

Zoltai 1988).

Evidence for technological replacement among human populations approximately coincident with the WRA and the Taye Lake-Aishihik phase transition has been uncovered in recent years from perennial ice patches in southern Yukon, where radiocarbon dating has

indicated the general replacement of the atlatl with the bow-and-arrow ca. 1100-1200 BP (Hare,

et al. 2004). Projectile point shaft material also changed from primarily spruce to birch at

approximately this time, and points from primarily stone to antler (Hare, et al. 2004). Discussing

these finds, Hare et al. (2004) suggest that populations might have moved temporarily out of the

area following the WRA, returning some time later with bow-and-arrow technology. Based on

radiocarbon dates of projectile point shafts and faunal remains of caribou, Hare et al. (2004)

suggest that this period of abandonment lasted for ca. 200 years. Matson and Magne (2007) have

also provided evidence suggesting that the WRA might have been an influential factor in

stimulating population movement from southern Yukon to the Pacific Coast and American

Southwest ca. 1200 years ago, as Workman (1974, 1979) hypothesized. Based on linguistic

evidence presented by Hoijer (1971) suggesting the divergence of Pacific Coast Athapaskan and

Apachean Athapaskan from Northern Athapaskan at approximately the time of the WRA,

Matson and Magne (2007) suggest that the WRA was the principal cause of movement of

Northern Athapaskan populations out of the region at that time, with the earliest effects of climatic change at the beginning of the MWP potentially exacerbating those of the eruption. The authors also cite substantial archaeological evidence of rectangular structures, Kavik points, side- notched points with concave bases, and microblades – all potentially suggestive of Athapaskan occupations – in central British Columbia and dated to the last ca. 1200 years as additional

evidence in support of their suggestion (Matson and Magne 2007). Using the Canadian

Archaeological Radiocarbon Database (CARD; Gajewski, et al. 2011), Mullen (2012) also notes

substantially decreased frequency of cultural radiocarbon dates in the fallout area of the WRA

lasting for ca. 200 years, with lingering effects for an additional ca. 300 years, and slightly

increased frequency of dates in the area surrounding. Mullen (2012) suggests that this might be

indicative of population movements out of the affected area after the eruption, though the author

is also careful to note that that these results are tentative due to the paucity of available dates, and

to the potential influence of research, discovery, taphonomic, and calibration biases on the

radiocarbon dates.

The cultural impact of the WRA on populations in NWT has not been subject to as

intensive study as in southern Yukon. Moodie et al. (1992) note that large Plinian eruptions can

last many hours, producing huge amounts of ejecta in plumes many kilometres high, and can

cause extreme immediate devastation and short and long-term effects including cloud cover, acid

precipitation, and lightning, which may be seen and heard from great distances (100s of

kilometres). Because the WRA occurred during the winter, even otherwise routine events such as

lightning storms – which are typical of the summer months – would have been unusual. Moodie

et al. (1992) present evidence of oral traditions from the Mackenzie Valley describing eruptions

and their after effects, such as population movements and the development of new languages, as

have been suggested of the WRA. Stories such as “The Collapse of the Mountain” (Moodie, et

al. 1992:152-153) describe smoking mountains to the west, falling ash, widespread fire,

exploding rocks, and fields of debris, as well as the fear of the population and the movement of

groups away from the affected area where they eventually formed nations that no longer spoke

the same language. Moodie et al. (1992) also describe stories that link the discovery of copper

with volcanism at approximately the time of the WRA, and note a possible link between the

WRA and the beginning of copper use, as has been noted in southern Yukon archaeological record in the distinction between the pre-ash Taye Lake and post-ash Aishihik phases.

2.2 The Mazama eruption (MZA)

2.2.1 The eruption

The eruption of Mount Mazama (now Crater Lake, OR) ca. 7627 cal BP was a Plinian-type

eruption with a VEI of 7 (Smithsonian Institution National Museum of Natural History (Global

Volcanism Program) 2013). The eruption produced ca. 50 km3 of ash, which covered over 1

million km2 primarily to the north and east of the vent, and which has been discovered in visible layers as far away as Saskatchewan (Figure 2.1; David 1970; Sarna-Wojcicki, et al. 1983).

Discoveries of other Mazama-like ash layers below the MZA have indicated that the volcano was active for some time before the 7627 cal BP eruption (Sarna-Wojcicki, et al. 1983). Based on patterns of ash accumulation in sediments, it has been suggested that the 7627 cal BP eruption itself lasted for ca. three years, though the occurrence of several separate eruptions in a short space of time has also been proposed (Mehringer, et al. 1977; Zdanowicz, et al. 1999). Based on the thicknesses of compressed ash deposits and comparison with data from the eruption of Mount

St. Helens, Oetelaar and Beaudoin (2005) have estimated that the original depth of the ash on the

northwest North American Plains was ca. 15 cm. Based on high abundances of Artemisia, and

low abundances of Pinus, Botryococcus, and Pediastrum found in the lowest levels of the ash in a core from Lost Trail Pass Bog, MT, Mehringer et al. (1977) have suggested that the ash fell in

Autumn, when Artemisia is in flower, Pinus is not, and algal populations have begun to die off with declining water temperatures. This is supported by evidence of fires in the Kootenay Valley,

BC, at the time of the ash, suggesting a late summer or early autumn eruption (Hallett, et al.

1997). The ash is composed primarily of glass, plagioclase, horneblende, orthopyroxene, and augite (Powers and Wilcox 1964).

2.2.2 Study site: Goldeye Lake, AB

2.2.2.1 Location and modern setting

Goldeye Lake (52°26’45"N, 116°11'30"W; surface area = 15 ha) is located in the Rocky

Mountain Foothills of central Alberta, ca. 1150 km from the source of the MZA (Figure 2.4).

The lake is roughly teardrop-shaped, oriented approximately N-S. It has a simple bathymetry, with a maximum depth in the centre of the lake of ca. 13.5 m. The lake’s inlet flows in from the north to the lake’s northern tip, while the outlet flows southward from the lake’s southern end, eventually meeting Black Canyon Creek and the North Saskatchewan River. The lake is underlain by sedimentary bedrock of Paskapoo sandstone (Schweger 2014). Surface material is composed of late Wisconsinan glacial till from the Jackfish Creek advance (Fenton, et al. 2013;

Schweger 2014). Regional climate is continental subarctic, with a mean annual daily air temperature of ca. 3°C and total annual precipitation of ca. 540 mm (Environment Canada 1993).

Permafrost occurs in isolated patches (Atlas of Canada 5th Edition 1995). The location of

Goldeye Lake in the Rocky Mountain Foothills places it in a transitional zone between Plains environments found to the east and alpine environments to the west, potentially making it a sensitive indicator of environmental change. The lake is surrounded by low hills of dense boreal forest, dominated by Pinus contorta and Picea glauca (Schweger 2014). Larix laricina and

Picea mariana may also be found in low-lying or more poorly-drained areas, while Picea engelmanii and Abies lasiocarpa occur at higher elevations (Schweger 2014). Betula papyrifera and Populus tremuloides are common on drier sites (Schweger 2014). Alnus, Salix, and

Shepherdia canadensis are common components of the understory (Schweger 2014). A wide variety of wildlife can be found in the region, including many species found in both the Rocky

Mountain and Boreal Forest regions found nearby, such as elk, moose, woodland caribou,

various other large and small mammal species, and a variety of species of birds and fish (Natural

Regions Committee 2006). The lake is the centrepiece of the Goldeye Lake Provincial

Recreation Area. The region surrounding Goldeye Lake is part of the traditional territory of the

Ĩyãħe Nakoda (Stoney Nakoda) of the Rocky Mountain Foothills and northwestern Plains

(Rocky Mountain Nakoda 2015).

2.2.2.2 Environmental history, 11,500-4000 cal BP

The early to mid-Holocene environmental history of the Rocky Mountain Foothills and

northwestern Plains has been extensively studied. After deglaciation, the early Holocene was characterized by the warm and dry conditions of the Holocene Climatic Optimum (HCO), peaking ca. 9000-8000 BP in this region (Beierle and Smith 1998; Elias 1996; Hickman and

Schweger 1993, 1996; Hutton, et al. 1994; Luckman and Kearney 1986; Schweger and Hickman

1989). This period of heat and aridity is marked by indicators of warm summer temperatures, glacial retreat, altitudinal and latitudinal extension of boreal forest and grassland ecozones, increased fire frequency, increased evaporation, increased productivity, decreased lake depth,

and increased lake water salinity throughout the region (Beaudoin and King 1990; Beierle and

Smith 1998; Beierle, et al. 2003; Elias 1996; Hickman and Reasoner 1998; Hickman and

Schweger 1991, 1993, 1996; Hutton, et al. 1994; Kearney and Luckman 1987; Luckman and

Kearney 1986; MacDonald 1982, 1989; Schweger and Hickman 1989; Vance 1986a, b; Vance,

et al. 1983). Following this period of peak warmth and aridity, conditions in the region became

cooler and wetter, leading to changes in vegetation communities as conditions became

appropriate for the establishment of new species, the contraction of vegetation zones, the

reduction fire activity, and the flooding of previously dry basins – though in some cases warm

and dry conditions persisted for up to several thousand years longer before undergoing any

noticeable change (Beaudoin and King 1990; Elias 1996; Hickman and Schweger 1993, 1996;

Hutton, et al. 1994; Luckman and Kearney 1986; MacDonald 1989; Schweger and Hickman

1989; Vance 1986a, b; Vance, et al. 1983). The beginning of peatland development is also recorded at some sites following the end of the HCO, indicating the development of cooler and wetter environmental conditions (Kubiw, et al. 1989). Conditions similar to the modern day were generally established by ca. 4000 BP, though some studies have recorded continuing environmental change lasting until ca. 3000 BP (Elias 1996; Hickman and Schweger 1993,

1996; Hutton, et al. 1994; Luckman and Kearney 1986; MacDonald 1989; Schweger and

Hickman 1989; Vance 1986a, b; Vance, et al. 1983).

Previous study of Goldeye Lake has identified a saline period during the initial ca. 1000 years of the lake’s history until ca. 10,400 BP, after which freshwater conditions developed

(Hickman and Schweger 1993). Diatom-based inferences regarding lake conditions suggest minimal variability from that point; despite the lake’s location in a transitional area between two ecozones, Hickman and Schweger (1993) suggest that the influence of the Rocky Mountains might have had a stabilizing influence on the regional climate relative to Plains environments further to the east, where heat and reductions in moisture availability during the HCO would likely have been more severe. Similar limited response to early to mid-Holocene warmth and aridity has also been recorded at nearby Fairfax Lake, AB, 60 km north of Goldeye Lake, where diatoms indicated only a slight reduction in lake levels ca. 11,255-7000 BP (Hickman and

Schweger 1991).

2.2.2.3 Cultural history, 8000-4000 cal BP

Beginning ca. 8600 BP and lasting to ca. 7500 BP, Peck (2011) identifies a transitional period between the Early and Middle Prehistoric periods in Alberta, encompassing the Plains/Mountains and Lusk complexes, and characterized by the transition from spears to darts in the

Foothills/Mountains and Plains. The adoption of atlatl/dart technology on the northwestern

Plains marks the beginning of the Middle Prehistoric period in the region, ca. 7500 BP (Peck

2011). A lack of sites in the early portion of the period has been attributed variously to sampling

bias, misidentification of materials, arid conditions during the HCO – leading to the general or

partial abandonment of the region and/or to changes in subsistence and settlement patterns with

increased use of refugia – and/or abandonment of the region as a result of the MZA (Bamforth

1997; Buchner 1980; Hurt 1966; Meltzer 1999; Oetelaar and Beaudoin 2014; Sheehan 1994,

2002). Archaeological assemblages dated to the centuries before the MZA are characterized by

materials of the Mummy Cave complex, including Bitterroot side-notched points with square

notches, sharp shoulders, and well-defined bases (Kooyman 2000; Peck 2011; Reeves 1969).

The Mummy Cave complex is sometimes considered to extend through the MZA to as late as ca.

4500 BP (Dyck 1983; Kooyman 2000), when it is succeeded by Oxbow, but this has been questioned by some authors. Peck (2011), for example, identifies the Maple Leaf complex from

ca. 6300-5200 BP, characterized by Gowan/Salmon River side-notched points, which are similar

to Bitterroot side-notched points, but different in certain essential details, with more open

notches, obtuse shoulders, and concave bases (Kooyman 2000; Swanson Jr and Sneed 1966); and

the Calderwood complex from ca. 5200-4700 BP, which exhibits a wide range of variability in

points styles. Following his Calderwood complex, Peck (2011) places the beginning of an

Oxbow tradition at ca. 4700 BP, and splits it into the Estevan phase, ca. 4900-4500 BP,

characterized by Oxbow-like points with block-shaped ears, and the Oxbow phase, ca. 4500-

4100 BP, with its characteristic round-eared points. Though other sources of food were exploited, communal hunting of bison dominated subsistence activities throughout (Reeves

1990). Stone boiling to extract bone grease and marrow for the production of pemmican became common by the end of this period ca. 5000-4000 BP – an important development allowing the long-term storage and easy transport of nutritious food (Peck 2011; Reeves 1990). Reeves (1990) has suggested that the introduction of pemmican production on the Plains came about as a result of decreased environmental productivity during the HCO, as a method of compensating for reduced and/or less reliable resources. Alternatively, Oetelaar and Beaudoin (2014) have associated the introduction of stone boiling to the Plains with the MZA, suggesting that the technique was brought back from the Eastern Woodlands when Plains populations returned to the region after having retreated from the effects of the ash several centuries earlier (see section

2.2.3).

2.2.3 Environmental, wildlife, and cultural impacts of the MZA

Oetelaar and Beaudoin (2005, 2014) have described the likely immediate and long-term environmental, wildlife, and cultural impacts of the Mazama eruption, which would have included the noise of the eruption itself, darkness, clouds, lightening, fires, and falling ash, as well as – in succeeding years – reductions in temperature, reduced productivity and death of plants, contamination of water sources, changed runoff and erosion patterns, increased landscape instability, and the consequences of these for animal and human populations. Impacts on wildlife would have included direct effects of the ash, including physical damage, illness, and/or death from mechanical damage and/or chemical toxicity, and indirect effects owing to reduced access

to appropriate food and/or habitat as a result of the ash causing their inaccessibility, damage, or

destruction. Oetelaar and Beaudoin (2005, 2014) hypothesize that human groups might have had substantial difficulties in coping with the MZA, as their usual methods of managing resource

shortages through diversification, storage, intensification, mobility, and exchange within the

region would be rendered ineffective because of the large area impacted by the ash and their long

duration. The authors suggest that taboos to control resource use and demand might have been

established, that land management may have increased, and that technological innovation might

have been encouraged as a way to increase the efficiency of resource use.

Terrestrial and aquatic environmental impacts resulting from the MZA have been noted at

sites throughout the northwestern United States and parts of western Canada. Decreased

productivity of terrestrial and aquatic environments has been identified at several sites in the

central Cascade Mountains, WA, lasting ca. 40-100 years after the ashfall (Long, et al. 2011;

2014), as well as in the immediate aftermath of the MZA at Lost Trail Pass Bog, MT, and for ca.

200 years at Foy Lake, MT (Mehringer, et al. 1977; Power, et al. 2011). Increased representation

of herbaceous taxa such as Artemisia and Poaceae has also been noted for up to ca. 40 years after the ash at Lost Trail Pass Bog (Blinman, et al. 1979; Mehringer, et al. 1977), as well as immediately after the ash at Teepee Lake, MT (Mack, et al. 1983), and at Kilpoola Lake, BC

(Heinrichs, et al. 1999). Minckley et al. (2007) relate long-term increases in the representation of

Pinus at Dead Horse Lake, OR, after the MZA to the development of lower-nutrient soils near the site as a result of the deposition of the ash. Increased fire frequency after the MZA has also been noted at some sites in the central Cascades (Long, et al. 2011; 2014), at Foy Lake (Power, et al. 2011), and at Johnson Lake, AB (Beierle and Smith 1998). Increases in fire frequency do

not occur at all of the sites examined by Long et al. (2011; 2014), indicating the importance of

regional conditions in determining the frequency of fire. Increased rates of peat formation have

also been noted at Johnson Lake after the MZA (Beierle and Smith 1998). A number of authors

have also noted a substantial response of lake environments to the MZA. Palaeoenvironmental

proxies such as diatoms have indicated changed water chemistry and decreased pH in lakes

following the MZA at sites in Montana (Foy Lake; Power, et al. 2011), Washington (Wildcat

Lake; Blinman, et al. 1979), and Oregon (Wildhorse Lake, Upper Klamath Lake; Blinman, et al.

1979; Bradbury, et al. 2004). Increased salinity after the MZA and lasting up to ca. 1000 years

has also been indicated by diatom and chironomid records from Upper Klamath Lake, OR

(Bradbury, et al. 2004), and Kilpoola Lake, BC (Heinrichs, et al. 1999); at Kilpoola Lake, this

increase amounted to some 450 % above pre-ash salinity values. Increases in diatom productivity

at Opabin and Mary Lakes, BC, and Lake Washington, WA, lasting several hundred years, have been suggested to have occurred as a result of increases in available silica after the deposition of

the ash (Abella 1988; Hickman and Reasoner 1994). Increased turbidity lasting ca. 600 years is

also suggested to have occurred at Lake Wabamun, AB as a result of the ash, which combined

with the results of climatic change to produce rapid infilling and decreased lake primary

productivity (Hickman, et al. 1984). Hickman et al. (1984) also note decreased water levels and

increased salinity prior to the MZA relative to after at Wabamun Lake. At Big Lake, BC, Bennett

et al. (2001) have identified several peaks in pigments immediately above the MZA, but attribute

these to the direct effects of the ash, rather than to any changes in the lake environment.

A record of the MZA is present in Klamath oral histories that tell of a great battle that occurred between the Chief of the Above World at Mount Shasta, CA, and the Chief of the

Below World at Mount Mazama (Clark 1953:53-55). The stories describe how the Chief of the

Below World – spurned by a Klamath woman – swore revenge on the people. The Chief of the

Above World came to their defense, and two chiefs fought from their mountain tops, causing

mountains to crumble, rock and ash to fall from the sky, and fires that destroyed forests and

forced the people to flee. Eventually, the Chief of the Below World fell and his mountain (Mount

Mazama) collapsed on top of him (Clark 1953:53-55). Though the frequency of archaeological

sites on the Plains dated to within the HCO is limited in general, Oetelaar and Beaudoin (2014)

have identified a brief period of abandonment (ca. 500 years) at the Stampede site, AB (DjOn-

26), a longer period (ca. 1500 years) at the Tuscany site, AB (EgPm-377), and particularly low site occurrence in southern Alberta generally beginning after the MZA. Based on this finding,

Oetelaar and Beaudoin (2014) suggest a brief period of abandonment of the region as a result of the MZA, followed by the return of the population ca. 500 years later. The authors suggest that increased evidence of Early Archaic (spanning ca. 8000-5500 BP (Frison 2007), approximately coincident with the latter half of the HCO in the region, and with the first half of Vickers’ (1986) and Peck’s (2011) Middle Prehistoric period) points on the eastern margins of the Plains is indicative of the movement of the population in that direction at this time, possibly stimulated or at least encouraged by the MZA. Citing evidence of fire-broken rock (FBR) indicative of stone

boiling from the Gowen, SK (FaNq-25 and FaNq-32; Walker 1992), and Stampede (Vivian, et al.

2008) sites, dated to ca. 6000 BP, Oetelaar and Beaudoin (2014) also suggest that this technique

– used in the Eastern Woodlands for the production of nut oil and butter, among other things –

was introduced on the Plains after the return of the population. The Eastern Woodlands process

of stone boiling to produce nut oil and butter involved immersing cracked nuts in water, and

once the floating shells were removed, heating the water with hot stones for several hours. The

nut meat and oils would congeal on the water’s surface once cooled, and was then skimmed off and stored for later use (Oetelaar and Beaudoin 2014). Oetelaar and Beaudoin (2014) suggest that populations returning to the Plains brought this new technology with them, and adapted it to suit their needs. On the Plains, the technique was used for the production of bone grease, a necessary ingredient for making pemmican – a long lasting, easily transported, highly nutritious food composed of bone grease mixed with dried berries and meat, which Oetelaar and Beaudoin

(2014) suggest would have provided a reliable food-source to mitigate the effects of food shortages after the MZA. Stone boiling and pemmican production gradually increased in importance following the MZA, particularly after ca. 5000-4500 BP, ultimately becoming a dietary staple and important trade item for Plains populations (Oetelaar and Beaudoin 2014; Peck

2011; Reeves 1990).

b) Figure 2.2: Spirit Lake, YT. a) map; b) photograph. Approximate distribution of the WRA from Robinson (2001). Photograph © Spirit Lake Wilderness Resort, 2007, used with permission.

b) Figure 2.3: Marahbodd Lake, NWT. a) map; b) photograph. Approximate distribution of the WRA from Robinson (2001). Photograph © Todd Kristensen, 2014, used with permission.

b) Figure 2.4: Goldeye Lake, AB. a) map; b) photograph. Approximate distribution of the MZA from Sarna-Wojcicki and Davis (1991). Photograph © Luc Rainville, 2012, used with permission.

Chapter Three: METHODS

3.1 Palaeoenvironmental research using lake sediments

This study uses the analysis of palaeoenvironmental proxies from cores of lake sediment to

reconstruct past environments. Lake sediments have become an important source of information

for the reconstruction of past environmental conditions both within lakes themselves and of their

surrounding terrestrial environments (Birks and Birks 1980; Smol 2002). Both autochthonous

and allochthonous materials will gradually accumulate as a part of a lake’s sediments over time,

and are often preserved and can be extracted from the sediments and analyzed (Lowe and Walker

1997). Micro and macro remains such as pollen, charcoal, insects, diatoms, and plant fragments

may all be used as proxies for past environmental conditions, and the sediments themselves are

also sources of valuable palaeoenvironmental information, for example via the analysis of

sediment organic, carbonate, and inorganic content, particle size, or biogenic silica content

(Smol, et al. 2001a, b). These proxies can be used to inform both synchronic and diachronic

reconstructions of a wide variety of factors, including air and water temperature, precipitation,

terrestrial and aquatic productivity, vegetation composition, fire activity, landscape instability

and erosion, lake depth, lake turbidity, lake pH, and others. The ability of such archives to

provide diachronic information makes them particularly valuable for studies of environmental

responses to and recovery after disturbance events.

Lake selection for palaeoenvironmental analysis is driven by a number of factors. First and

foremost are the goals of the study, which might require that a specific lake or a lake with

particular characteristics be selected for analysis. Lake size, for example, may be a an important

factor, as larger lakes tend to source inputs of allochthonous material from a wider area than

smaller lakes (Faegri and Iverson 1989). If a number of lakes might be appropriate to the study,

the conditions of the lakes and their surroundings will generally be used to make a selection,

with the goal of ensuring that as complete and reliable a record is recovered as possible. Lakes

located in environmentally sensitive areas will typically yield proxy records in which changes will be more distinct. To minimize the possibility that the sedimentary sequence has been disturbed, ideally the lake that is chosen will be deep enough not to freeze to the sediment-water interface (where freezing is a concern), dry completely during drought, or allow the sediment to be disturbed by wind, but will be shallow enough that sampling will not be too difficult (Smol

2002). Lakes with complicated bathymetry, open-basin lakes with surface inlets or outlets, and lakes with steep surrounding slopes may have irregular sedimentation patterns or be subject to the effects of mass movements such as slides, and are best avoided if possible – though these factors can sometimes be compensated for with careful selection of the sampling location within the lake (Smol 2002).

Lake sediments intended for palaeoenvironmental analysis are typically collected as cores from the deepest, central portion of the chosen lake. Various studies have shown that this location produces a representative sample of the sediments overall, and is the least likely to suffer from any disturbance (Charles, et al. 1991). Depending on the goals of the study, core collection may focus on the retrieval of a particular section of sediment (for example, only the topmost sediments for a study of recent conditions, or the bottommost sediments for a study of the early history of the lake and its surroundings), but in many cases the aim of sampling is to retrieve a core that extends from the youngest surface sediments to the oldest bottommost sediments, so that the entire palaeoenvironmental record of the lake is available for study should it be wanted. The coring itself may be done either from a boat or raft anchored to the shore, or

from the ice surface in cases where the lake freezes over. A variety of coring equipment is

available, each with its own advantages and disadvantages. Some typical coring devices used for

taking sedimentary sequences from lakes include gravity or modified gravity corers such as

percussion corers, piston corers such as modified Livingstone square-rod piston corers,

Vibracorers, freeze-corers, and chamber corers such as Russian peat corers (Glew, et al. 2001).

Once a core has been collected, the topmost unconsolidated sediments are sampled

immediately (if they are being retained) to ensure that their sedimentary sequence remains intact.

This is often done by pushing the core gradually out of the core tube through a sampling

platform, and sectioning measured sections of sediment into labelled plastic bags (Glew, et al.

2001). This process is continued until the sediments are solid enough to remain intact, whereupon the core is sealed into its core tube for transport to the field station or lab. On

reaching the field station and/or lab, the sediments are kept refrigerated at ca. 4°C to discourage

the growth of mould or bacteria while analysis is underway.

3.2 Field methods

3.2.1 Spirit Lake

An 11 m core of lake sediment (Core SL01) was collected from Spirit Lake, YT (60°15’07"N,

134°44'22"W; surface area = 67 ha; Barker 2015), in summer 2009 by Dr. William Patterson,

Saskatchewan Isotope Laboratory, Department of Geological Sciences, University of

Saskatchewan. The core was collected using a Vibracorer (Smith 1998), from a raft anchored at three points to the shore. The core was sealed within the core tubing for transport to the

University of Saskatchewan and kept in a cold room. The core was collected for transport to

Calgary in winter 2012 and stored in a refrigerator at 4°C.

3.2.2 “Marahbodd” Lake

A 2 m core of lake sediment (Core ML01) was collected from “Marahbodd” Lake (unofficial

name; 62°58'35"N, 129°08'54"W; surface area = 86 ha), in summer 2013 by Todd Kristensen,

Department of Anthropology, University of Alberta. The core was collected using a percussion corer (Gilbert and Glew 1985), from a raft anchored at three points to the shore. The core was

sealed within the core tubing for immediate transport to Calgary, and stored in a refrigerator at

4°C.

3.2.3 Goldeye Lake

A 4 m core of lake sediment (Core GDL01) was collected from Goldeye Lake, AB (52°26’45"N,

116°11'30"W; surface area = 15 ha), in summer 2012 by Mikkel Pedersen, Natural History

Museum of Denmark. The core was collected using a percussion corer (Gilbert and Glew 1985),

from a raft anchored at three points to the shore. The core was sealed within the core tubing for

transport to the University of Alberta for storage and kept refrigerated. The core was collected for transport to Calgary in fall 2012 and stored in a refrigerator at 4°C.

3.3 Laboratory and analytical methods

3.3.1 Core logging

The “Marahbodd” Lake and Goldeye Lake core tubes were opened in Calgary using a handheld

Dremel Trio 6800, and the cores themselves then split open using 20 gauge stainless steel wire to allow their stratigraphy to be photographed and to allow for easier sampling. The two cores were immediately measured and photographed before being wrapped in plastic wrap and aluminum

foil and returned to the refrigerator to await sampling. The Spirit Lake core had previously been opened, split, measured, and photographed at the University of Saskatchewan. A single layer of volcanic ash was visually apparent in each of the three cores.

Magnetic susceptibility (MS) is a non-destructive logging method that measures the ability of a material to be magnetised (Dearing 1999). Magnetic susceptibility data is useful for associating cores and core sections taken at different times and/or places at the same site, providing a quick and inexpensive method of relating cores to each other. MS data is also useful for identifying layers of volcanic ash in cores, which are often apparent as brief, sharp peaks in susceptibility, even when the layers themselves are not visible. It has also been suggested that fluctuations in magnetic susceptibility might be indicative of changes in catchment erosion, with higher susceptibility indicating increased landscape instability and minerogenic inputs to the lake (Lowe

and Walker 1997). Magnetic susceptibility was logged on the “Marahbodd” Lake and Goldeye

Lake cores using a Bartington MS2C core scanning sensor, at continuous 1 cm intervals for the

10 cm above, 10 cm below, and centimeters within the ash layer in each core. Magnetic

susceptibility was not logged on the Spirit Lake core, as the core’s long exposure to air by that

time would have caused oxidation of the iron-bearing minerals in the sediment and so would

have compromised the results of the analysis.

All three cores were visually examined for any macrobotanical remains for use in radiocarbon

dating. The depth and thickness of the volcanic ash in each core was also noted, prior to being

sampled for identification by Lauren Davies and Dr. Duane Froese, Department of Earth and

Atmospheric Sciences, University of Alberta.

3.3.2 Loss-on-ignition

Loss-on-ignition (LOI) is a method for estimating the proportion of organic, carbonate, and silicate material in sediments (Dean 1974; Heiri, et al. 2001). It has been suggested that variations in LOI might be used as a method of estimating lake water pH, catchment productivity, variations in landscape instability/erosion/lake water turbidity, and regional palaeoclimate (Birks and Birks 2006; de Klerk, et al. 2008; Fortin and Gajewski 2009, 2010;

Kaplan, et al. 2002; Willemse and Törnqvist 1999). Sediment organic content as measured using the LOI technique has also been found to be an influential variable in chironomid distribution and abundance (Bunbury 2009; Fortin 2010). Bunbury and Gajewski (2013) have noted changes in LOI in response to the WRA at three sites in southwest Yukon. Effects of the WRA on the sediment composition at these sites ranged from negligible change to ca. 80 years of reduced organic and carbonate content, which the authors interpret as being indicative of reduced terrestrial and/or aquatic productivity and lake water pH, respectively (Bunbury and Gajewski

2013). Changes in LOI in response to the MZA have also been identified by a number of lake sediment studies in the northwestern United States (Egan 2013).

Using a modified syringe, 0.5 cc of sediment was sub-sampled from the 10 cm above, 10 cm below, and centimeters within the ash in each core at continuous 1 cm intervals. The sub- samples were placed into crucibles of known weight and then weighed again to obtain the wet weight of the sediment (WW; the difference between the weight of the empty crucible and its weight with the wet sample). The samples were then dried in an oven for 24 hours at 105°C, and were weighed again to obtain their dry weights (DW105). Following this, the samples were placed into a muffle furnace and ignited at 550°C for 4 hours before being weighed again to obtain their

weights after ignition of organic materials (DW550). Finally, the samples were returned to the muffle furnace, ignited for a further 2 hours at 950°C, and then weighed to obtain weights after ignition of carbonate materials (DW950). The organic (LOI550) and carbonate (LOI950) content was calculated as follows:

LOI550=((DW105-DW550)/DW105)*100

LOI950=((DW550-DW950)/DW105)*100

The residual material after final ignition is taken to represent the silicate content of the sediment

(Heiri, et al. 2001).

3.3.3 Pollen and microcharcoal

Pollen is the male gametophyte of angiosperms and gymnosperms. The cell wall of pollen grains is composed of cellulose and a substance called sporopollenin. Sporopollenin is extremely resistant to degradation (except by oxidation), allowing pollen to be preserved in a wide variety of environments, including lake sediments (Bennett and Willis 2001). Pollen grains are transported to lakes in a variety of ways, including by wind (anemophily), water (hydrophily), insects (entomophily), and animals (zoophily), though anemophilous types tend to be produced and represented in the greatest quantities (Faegri and Iverson 1989). Anemophilous pollen grains are taken up into the air where they are mixed, before being deposited again as the "pollen rain"

(Faegri and Iverson 1989). A large number of studies have shown that the pollen rain that falls on a lake’s surface is generally representative of the regional vegetation, though a precise source area is difficult to determine; the area of the receiving surface, the surrounding topography, the direction and strength of the prevailing wind, variations in pollen morphology and ability to remain airborne, and other factors may all have an influence on the source area of a lake’s pollen

rain (Birks and Birks 1980; Faegri and Iverson 1989). Other complications to the determination

of a precise source area for a lake’s pollen inputs include the influence of inputs of pollen from

surface running water, which may come from distant sources, as well as from insects and

animals – though as has been mentioned, these latter two types tend to be less well represented in

pollen assemblages than anemophilous types (Birks and Birks 1980; Faegri and Iverson 1989).

These concerns can often be addressed via careful selection of the sampling location within the

lake (e.g. by keeping sampling sites away from surface running water inlets and the lake shore

whenever possible; Faegri and Iverson 1989; Smol 2002). In areas with low regional pollen

production, long-distance transport of pollen by wind may also be a concern, though in such

instances taxa brought in by long-distance transport often can be identified. Once deposited, pollen tends to preserve well in a lake’s sediments, though some grains whose cell walls have lower sporopollenin content (e.g. Populus) are more susceptible to degradation. Anemophilous pollen tends to be very small and to be produced in large quantities, however, and so the influx of pollen grains to a lake’s sediments is often substantial enough to ensure the representation of rare pollen types even in small samples (Birks and Birks 1980). The pollen grains of different taxa are morphologically distinct to varying degrees, allowing the pollen grains recovered from lake sediments to be identified and the regional vegetation to be reconstructed.

Palynological analysis has been used extensively to provide insight into the past composition and productivity of vegetation communities at sites in North America and around the world (e.g. Anderson and Brubaker 1994; Cwynar 1982, 1988; Dyke 2005; Jensen, et al.

2007; Lacourse and Gajewski 2000; Lichti-Federovich 1970; Lotter, et al. 1995; MacDonald

1983, 1987, 1989; MacDonald, et al. 1991; Moser and MacDonald 1990; Peros, Gajewski, et al.

2010; Pisaric, et al. 2001; Rainville and Gajewski 2013; Ritchie 1982; Ritchie and Hare 1971;

Schweger and Hickman 1989; Strong and Hills 2005; Szeiz and MacDonald 2001). Pollen

assemblages have also been demonstrated to be valuable indicators of regional temperature and

precipitation, and have been used to generate both qualitative and quantitative temperature and

precipitation reconstructions at sites in North America and elsewhere (e.g. Bunbury and

Gajewski 2009; Davis, et al. 2003; Herzschuh, et al. 2004; Minckley, et al. 2007; Nakagawa, et

al. 2002; Seppä and Birks 2001; Tonello, et al. 2009; Viau and Gajewski 2009; Viau, et al. 2006;

Webb III and Bryson 1972; Zabenskie and Gajewski 2007). Relating to the effects of volcanic

ash deposition, Mehringer et al. (1977) have noted changes in pollen influx in response to the

MZA in Montana, and suggest that the deposition of the ash enhanced the productivity of steppe genera such as Artemisia. Long et al. (2014) have also noted 50-100 years of decreased representation and accumulation of non-arboreal pollen types after the MZA in Oregon. Changes to pollen assemblages and the introduction of new species in response to the MZA have also been identified on Vancouver Island by Lucas and Lacourse (2013). At Gull Lake, YT, Birks

(1980) has recorded the development of the vegetation after the WRA, beginning with species- rich treeless vegetation, progressing to birch-alder-willow shrub tundra, and finally to Picea glauca forest similar to what occupies the region today. Lacourse (1998) has also noted changes in pollen assemblages at Sulphur Lake, YT, in response to the WRA, in the form of increased representation of Pinus. Noticeable changes to pollen assemblages and accumulation rates have also been identified in response to other volcanic events, for example as a result of the European

Laacher See eruption, ca. 11,000 BP (Lotter, et al. 1995).

Microcharcoal (charcoal <125 µm in size) is transported, deposited, and preserved much like pollen, and is retained in pollen samples after processing (Patterson III, et al. 1987; Whitlock and

Larsen 2001). Microcharcoal counts are conducted on the same slides as pollen, and have been

used to provide information regarding regional fire history at sites in North America, Europe,

Africa, Asia, and elsewhere (e.g. Bunbury and Gajewski 2009; Innes, et al. 2004; Innes and

Simmons 2000; Lacourse and Gajewski 2000; MacDonald, et al. 1991; Rainville and Gajewski

2013; Scott 2002; Tinner, et al. 2006; Turner, et al. 2010). The relationship between ash

deposition events and the occurrence of fire remains unclear. At four sites in Oregon, Long et al.

(2014) have noted inconsistent changes in fire activity associated with the MZA (two of four), suggesting that while in some cases the deposition of volcanic ash might facilitate the occurrence of fire, this is not always the case.

For this study’s pollen and microcharcoal analyses, 2 cc of sediment were sub-sampled from the

10 cm above, 10 cm below, and the centimetres within the ash in each core at continuous 1 cm intervals. Chemical preparation of the sediments for analysis followed Faegri and Iversen (1989), and was conducted at the Geological Survey of Canada (Calgary office). Pre-acetolyzed

Lycopodium tablets were added to each sub-sample to allow the calculation of pollen and microcharcoal concentrations. Chemical processing included digestion with 10 % HCl, heated

10 % KOH, heated concentrated HF, glacial acetic acid (GAA), heated acetolysis solution (9:1 mixture of acetic anhydride and concentrated sulphuric acid), GAA (repeated after acetolysis),

95 % ethanol, and tert-butyl alcohol (TBA). Saffranin stain was added at the ethanol step to make the pollen more clearly visible during later identification on slides. Between each step, the samples were washed at least one time with de-ionized water. Final storage was in silicone oil

(Faegri and Iverson 1989).

For identification, small aliquots of processed material were placed on slides and covered with coverslips that were fixed into place with clear nail varnish. Pollen, Lycopodium spike, and

microcharcoal were counted together under transmitted light at 400-1000x magnification, to a

minimum total of 300 identifiable pollen grains/level (Bennett and Willis 2001). Pollen

identifications were based on comparison with modern reference material, as well as on the

identification keys of Faegri and Iversen (1989), Kapp (1969), McAndrews et al. (1973), and

Moore and Webb (1978).

3.3.4 Chironomids

Chironomids (Diptera: Chironomidae) are the larval stage of non-biting midges. While the adults

are airborne, chironomid larvae inhabit aquatic environments, including lake sediments. As the

larvae develop, they go through a series of four developmental stages known as instars. Between

each instar, the chitinous cuticle and head capsule of the larvae is shed. The shed head capsules

are then preserved in the lake’s sediments, and can be recovered, isolated, and identified as a part

of palaeoenvironmental studies (Walker 2001). The value of chironomids as both qualitative and

quantitative palaeoenvironmental proxies – particularly of air temperature, lake water salinity,

lake depth, and environmental hydrological balance – has been demonstrated many times (e.g.

Antonsson, et al. 2006; Barley, et al. 2006; Fortin 2010; Heinrichs and Walker 2006; Heinrichs,

et al. 2001; Heinrichs, et al. 1999; Heinrichs, et al. 1997; Porinchu, et al. 2003; Rosenberg, et al.

2004; Smith, et al. 1998; Walker 1995; Walker and Mathewes 1987). Generally, chironomid

larvae are primary or secondary consumers, feeding on plants and organic detritus or small

animals, with diatoms a particularly important food source; they are also important sources of

food for fish and other secondary and higher-level consumers (Oliver and Roussel 1983). As a

result of these associations, chironomid influx may be an excellent indicator of overall within-

lake productivity (Walker 2001). Changes in chironomid community composition and decreased influx in response to the WRA have been noted at three sites in Yukon by Bunbury and Gajewski

(2013). The authors interpret these changes as being indicative of lake disturbance and decreased

lake water pH after the deposition of the ash (Bunbury and Gajewski 2013). Changes in

chironomid community composition in response to the MZA have also been described from two

sites in British Columbia by Smith (1997). At Kilpoola Lake, BC, Heinrichs et al. (1999) have

inferred at 450 % increase in lake water salinity following the MZA, based on increases in the

representation of chironomid taxa tolerant of saline environments. Changes in chironomid

community composition, abundance, and diversity after ash deposition have also been identified

in a number of South American studies (e.g. Araneda, et al. 2007; Massaferro, et al. 2005;

Urrutia, et al. 2007).

For this study’s chironomid analyses, an initial 5 cc of sediment were sub-sampled from

the 10 cm above, 10 cm below, and the centimetres within the ash in each core at continuous 1

cm intervals. Sample preparation followed Walker (2001). Samples were treated with hot 10 %

KOH for 30 minutes before being sieved through 90 µm Nitrex sieve screen with de-ionized

water. Chironomid head capsules (HC) were then hand-sorted with forceps under stereo-

microscopes at 100-400x magnification, and transferred onto coverslips. Each sample was sorted

in its entirety to allow head capsule concentrations to be calculated. The cover slips were left to

dry and then affixed to slides using Entellan.

Chironomid head capsules were identified under transmitted light at 400-1000x

magnification, using the identification keys of Oliver et al. (1978), Oliver and Roussel (1983),

and Walker (1988, 2007). A minimum of 35 head capsules were identified at each level (Quinlan

and Smol 2001). If less than 35 head capsules were identified from the first 5 cc sub-sample, the sub-sampling/preparation/identification process was repeated until sufficient head capsules had been identified, or until no sediment remained. Four levels did not achieve the minimum count out of the three cores (SP01 Level 71, 31 HC; GDL01 Level 16, 21 HC; GDL01 Level 17, 15

HC; GDL01 Level 18, 27 HC).

3.3.5 Chronology and ash identification

A sub-sample of volcanic ash from each core was sent for identification to Lauren Davies and

Dr. Duane Froese, Department of Earth and Atmospheric Sciences, University of Alberta. Once at the University, the samples were wet-sieved into 250, 150, 75, and 45 µm size fractions before being dried and examined to determine which size fraction was most suitable for further analysis.

In each case, the 75-150 µm size fraction was selected. The volcanic glass in each sample was then separated from heavier minerals using Lithium Sodium Polytungstate with a density of 2.43 g/cm3, mounted, polished, carbon coated, and finally analyzed on a JEOL superprobe by wavelength dispersive spectrophotometry. The major element geochemistry of each sample was then compared to previously analyzed samples of the eastern White River and Mazama Ashes to establish identifications (Lauren Davies, personal communication 2014).

A total of 17 samples were taken from the three cores for accelerator mass spectrometer

(AMS) radiocarbon dating – four from Spirit Lake (two above and two below the WRA), eight from “Marahbodd” Lake (three above and five below the WRA), and four from Goldeye Lake

(three above and one below the MZA). The samples were wet-sieved at the University of

Calgary with a 0.177 mm sieve and de-ionized water to remove the finest materials before being sent to the Department of Earth and Atmospheric Sciences, University of Alberta, for additional

pre-treatment. At the University of Alberta, the samples were hand-picked for terrestrial and

aquatic macrofossils (e.g. plant parts, chironomid head capsules). Samples that contained

sufficient organic matter (13 of the original 17) were then sent to the Keck Carbon Cycle AMS

Facility, Earth System Science Department, UC Irvine, for AMS radiocarbon dating. Three

additional samples were discarded at this stage because of insufficient gas production for 14C measurement, leaving 10 dates (four from Spirit Lake, four from “Marahbodd” Lake, and two from Goldeye Lake; Lauren Davies, personal communication 2014). The results were calibrated using OxCal 4.2 and the IntCal13 calibration curve (Bronk Ramsey 2009; Reimer, et al. 2013).

The calibrated dates from each core were then plotted on separate core-specific age-depth graphs. Dates that were substantially different from the others in a core were rejected. This amounted to one date from “Marahbodd” Lake, which despite being from near the top of the core, was dated to ca. 29,000 cal BP, while the other dates clustered ca. 4000-2500 cal BP. Dates that might have caused age reversals if included in age-depth interpolations were also considered for rejection; ultimately, such dates were retained or rejected based on comparison with the other dates in the core, such that the retained dates created as linear an age-depth sequence as possible, providing the most parsimonious model for combination with the depths and ages of the ashes in the cores, and the depths and ages of the tops of the cores (not available for GDL) for calculation of the final chronology. This amounted to one from Spirit Lake and one from “Marahbodd”

Lake, leaving three and two dates, respectively, plus the ages and depths of the ashes and tops of the cores at these sites. The established age of the WRA (1147 cal BP; Clague, et al. 1995) was assigned to the midpoint of the ash in each core (80.5 cm in SL, 24cm in ML). For each of the three cores, best-fit lines (determined based on R2 values, once any line that would have given a

negative sedimentation rate was rejected) were plotted to the retained date sets and interpolated

to assign ages to the sediments at 0.5 cm intervals. Correction of the retained 14C dates was

considered necessary if the difference between the interpolated and established age of the ash in

each core was larger than the smallest error of that core’s calibrated radiocarbon dates.

Corrections were applied to both the Spirit Lake and “Marahbodd” Lake radiocarbon dates based

on this criterion. The difference between the interpolated and established age of the ashes was

used as the correction factor in each case; this approach is similar to that previously used, for example, by Bunbury and Gajewski (2013) and Peros and Gajewski (2009). The corrected dates were then re-plotted, and new best-fit lines were drawn for each core including each core’s corrected dates, the depth and known age of each core’s ash layer, and the depth and age of the top of each core. In this case, lines of best-fit were selected so that the difference between the interpolated ash age and real ash age, and the interpolated origin age and real origin age was minimized, and so that R2 values were maximized, after any line that would have given a negative sedimentation rate was rejected. Once selected, the best-fit lines were interpolated to

assign ages to the necessary sample depths, and the sedimentation rate in cm/yr was calculated

for each lake. The Goldeye Lake dates were initially deemed not to be in need of correction,

however a best-fit line plotted to the two radiocarbon dates and the ash layer in the core resulted

in an interpolated date for the MZA that was greater than the smallest error of the dates (error of

-181 years, compared to 133 years), and so the dates were ultimately subjected to correction

using the same method as was used for the Spirit and “Marahbodd” Lake dates. Again, the

established age of the MZA (7627 cal BP; Zdanowicz, et al. 1999) was assigned to the midpoint

of the ash in the core (18 cm). The distance from the top of the Goldeye Lake core section that

was analysed to the top of the core was not known, and so this point was not plotted or used in

the establishment of the core’s final chronology.

3.3.6 Data presentation and statistical methods

3.3.6.1 Data presentation

The results of MS, LOI, pollen, charcoal, and chironomid analysis are presented in stratigraphic

diagrams made using the program C2 (Juggins 2014). Pollen data are presented as percentages of

the sum of all identifiable pollen grains and spores. The arboreal:non-arboreal (AP:NAP) pollen

ratio is presented along with the pollen percentage data, and was calculated using standard

techniques (Faegri and Iverson 1989), with the total percent of the pollen assemblage represented by all tree and shrub taxa at each level counted as “arboreal,” and that of all herbaceous taxa

counted as “non-arboreal.” Spores are not included in this calculation. Chironomid data are

presented as percentages of the sum of all identifiable head capsules. Pollen, microcharcoal, and

chironomid influx was calculated by multiplying each proxy’s concentration by the

sedimentation rate at each level. Influx data is also presented in stratigraphic diagrams made with

C2.

3.3.6.2 Ordination

Principle Components Analysis (PCA) is a linear indirect ordination technique commonly used

to reveal patterns in multivariate datasets by creating a set of synthetic variables in which each

successive new variable explains as much of the variance within the original dataset as possible

(Legendre and Birks 2012). The result is a series of “axes,” each comprised of a different linear

combination of the original variables, with gradually decreasing representation of the variability

present in the entire original dataset (Legendre and Birks 2012). Eigenvalues give the fraction of

the variability of the original dataset explained by each new axis. In palaeoecological analyses

using taxonomic data, “species scores” for each taxon in the original dataset detail the

combinations of these which were used to create each new component, and their relative

contributions (“loadings” or “weights”), while “sample scores” give the same for each sample.

Patterns in the species scores may then be used to help in the interpretation of the sample scores:

for example if Taxa X, Y, and Z are all heavily positively loaded (i.e. have a strong positive weight, or value) on Axis 1, a shift in Axis 1 sample scores from heavily positive to heavily negative would indicate a reduction in the abundance of all of these species between these

samples. The appropriateness of using unimodal (e.g. correspondence analysis, CA) versus linear

ordination techniques is determined using Detrended Correspondence Analysis (DCA), via the

variable gradient length, which is recorded in standard deviation (SD) units. If the gradient

length is less than two SD units, linear techniques such as PCA are appropriate (Smol 2002). In

this study, DCA was performed on the percentage pollen and chironomid data from each lake

using the open-source statistical program R, and the accompanying Vegan package (CRAN

2014; Oksanen, et al. 2015). The results of the DCAs indicated that linear ordination techniques

were appropriate in all cases. PCA was then used to visualize trends in the pollen and

chironomid percentage data from each core, using the program C2. Five components (axes) were

extracted in each PCA. Taxa were organized in the same way as for quantitative climate

reconstruction (see section 3.3.6.3) for comparability. The chironomid percentage data were also

square-root transformed for analysis to reduce the influence of dominant taxa. Each PCAs five

axis species scores are presented in table format, while sample scores are presented in

stratigraphic diagrams.

3.3.6.3 Climate reconstructions

Percentage pollen data from each lake were used to generate quantitative reconstructions of

mean July air temperature and total annual precipitation using the Modern Analogue Technique

(MAT). In the MAT, fossil assemblages are compared to a number of potential modern

“analogue” assemblages, each of which has accompanying modern environmental data

(Overpeck, et al. 1985). Modern pollen and environmental data for this study was obtained from

the North American Modern Pollen Database (NAMPD; Whitmore, et al. 2005). The squared-

chord distance (SCD) metric is used to determine the dissimilarity of the fossil assemblage from

each of the possible modern analogue assemblages. The analyst then selects the number of “best analogues” that will be used to assign environmental data to the fossil assemblage (typically between five and ten; Juggins and Birks 2012). For this study’s pollen reconstructions, a series of temperature and precipitation reconstructions were created using 1, 3, 5, and 9 modern analogues. The most appropriate number of analogues for the reconstruction of each variable was chosen by comparing the bootstrapped r2 and root mean square error of prediction (RMSEP)

values of the training set for each variable and under each of the four analogue set options, with

the goal of maximizing r2 and minimizing the RMSEP. The aquatic taxa Nymphaea and Typha

did not appear in the training set and so were not included in the reconstructions. The five best modern analogues obtained from the NAMPD (r2=0.91, RMSEP=5.49) were ultimately used to

reconstruct mean July temperature using the MAT. Nine analogues (r2=0.80, RMSEP=317.49)

were used to reconstruct total annual precipitation. The results are presented in stratigraphic

diagrams. The squared-chord distance of each fossil assemblage to its closest modern analogue

was used in order to evaluate the overall reliability of the reconstructions. Analogues were

considered to be acceptable if the SCD of the fossil assemblage to its closest modern analogue

was less than the 20th percentile of the observed distribution of pair-wise dissimilarities in the

training set, which represents the non-statistical likelihood of two assemblages within the

training set being similar to each other (Simpson 2012). The 20th percentile of this distribution

gives the SCD value within which 20 % of assemblage pairings in the training set will find their

best analogues.

The MAT was also used to reconstruct mean July temperature and lake depth using the

percentage chironomid data and the Northwest North American (Chironomid) Training Set

(Barley, et al. 2006). Species data were square-root transformed for analysis as in the original

paper. The taxa Micropsectra, Paratanytarsus, and Stenochironomus were not included in the reconstructions, as they did not appear in the training set. Stichtochironomus spp. A and B were also combined into one grouping (Stichtochironomus undiff.), as were Tanytarsina – other,

Tanytarsus group C, and Tanytarsus lugens (into Tanytarsina – other). Temperature and lake

depth reconstructions were created using 1, 3, 5, and 10 modern analogues; the ten best

analogues in the modern data were ultimately used to reconstruct temperature (r2=0.8,

RMSEP=1.58), and the three best to reconstruct lake depth (r2=0.42, RMSEP=0.67), again based

on the principle of maximizing the bootstrapped r2 and minimizing the RMSEP of the training set for each variable and under each of the four analogue set options. In addition to the

reconstructions created using the MAT, weighted-averaging partial least squares (WAPLS)

regression was used to create a second set of temperature and lake depth reconstructions using

the percentage chironomid data and the Barley et al. (2006) dataset. WAPLS is a combination of

weighted-averaging (WA) and partial least squares (PLS) regression, and tends to produce more

reliable reconstructions than the MAT when training datasets are small (Juggins and Birks 2012).

Predictive components are extracted using weighted averages of both the biological and

environmental data in the training set, with the goal of maximizing the covariance between the

variable being reconstructed and each subsequent component (Juggins and Birks 2012; ter Braak

and Juggins 1993). The component selected to provide the reconstruction is based on comparison

of the bootstrapped r2 and RMSEP values of the extracted components, once again with the goal

of maximizing r2 and minimizing the RMSEP. In this study, the third component of WAPLS

regression (r2=0.83, RMSEP=1.50) was used to reconstruct mean July temperature, and the

fourth to reconstruct lake depth (r2=0.40, RMSEP=0.62). Species data were once again square-

root transformed for analysis. Results of chironomid-based MAT and WAPLS reconstruction are

presented together in stratigraphic diagrams for each lake.

3.3.6.4 Comparative data

Because the goals of this study are primarily to examine the effects of the WRA and MZA on the terrestrial and aquatic environments of the study sites, and to explore the potential implications

of those effects for nearby wildlife and human populations, it is vitally important that changes in

sediment characteristics, vegetation, fire, and chironomid communities that occurred as a result

of the ashes be distinguished from changes that may have occurred as a result of other factors,

such as climatic change. For this reason, a number of independent quantitative climate

reconstructions are presented alongside the results of this study, which will be used to help in the

differentiation of climatic and ash effects at the study sites. These are: 1) a southeast Alaskan

varve-based reconstruction of mean summer air temperature (Loso 2009), for comparison with

the Spirit Lake data; 2) a chironomid-based reconstruction of mean July air temperature from a

lake in central NWT (MacDonald, et al. 2009), for comparison with the “Marahbodd” Lake data;

and 3) a pollen-based reconstruction of mean July temperature and total annual precipitation

using data from sites across central Canada (50-70°N, 80-120°W; Viau and Gajewski 2009), for comparison with the Goldeye Lake data. The Loso (2009) curve is presented as °C anomalies from the reconstructed mean temperatures of the last 1000 years, while the MacDonald et al.

(2009) curve is presented simply as °C. The Viau and Gajewski (2009) curves are presented as anomalies from the reconstructed temperature and precipitation values for the modern-day.

Chapter Four: ENVIRONMENTAL RESPONSES TO THE EASTERN WHITE RIVER ASH (WRA), 1147 CAL BP, SPIRIT LAKE, YT, AND “MARAHBODD” LAKE, NWT

4.1 Results

4.1.1 Chronology and ash identification

4.1.1.1 Spirit Lake

A single layer of volcanic ash was identified in the Spirit Lake (SL) core at approximately 80-81

cm depth. Identification by wavelength dispersive spectrophotometry and comparison with

reference samples positively identified the ash as coming from the eastern White River eruption

(WRA), 1147 cal BP (Appendix A; Lauren Davies, personal communication 2014; Clague, et al.

1995).

Construction of the SL chronology was based on three accelerator mass spectrometer (AMS) radiocarbon dates, the depth and age of the WRA (Clague, et al. 1995), and the depth and age of

the top of the core. Results are presented in Table 4.1 and Figure 4.1. A single AMS date from

62-64 cm depth was rejected before chronology construction began because it was younger than

the date above it, and its inclusion would have caused age reversal in the age-depth interpolation.

Rejection of the above 47-49 cm date would also have corrected this issue, however rejection of

this date and retention of the 62-64 cm date would have resulted in a significant curve in the

slope of the resulting age-depth sequence. Removal of the 62-64 cm date resulted in a linear age-

depth sequence between the retained dates, providing the most parsimonious model for

combination with the depth and age of the ash in the core, and the depth and age of the top of the

core for calculation of the final chronology. A best-fit line was then plotted to the remaining

three AMS dates and interpolated to 0.5 cm intervals to determine if correction was necessary.

Correction was considered necessary if the difference between the interpolated and established 74

age of the ash was larger than the smallest error of the calibrated radiocarbon dates. In the case

of Spirit Lake, the difference between the interpolated and established age of the WRA equaled

4756 years; the smallest error of the three retained calibrated radiocarbon dates was 117 years.

Correction was therefore considered necessary, and the difference between the interpolated and

established age of the WRA (4756 years) was subtracted from each retained radiocarbon date to

establish a set of corrected dates for use in chronology construction. A 3rd-order polynomial best-

fit line was then plotted using the three retained corrected radiocarbon dates, the depth and age of

the WRA, and the depth and age of the top of the core to give the final age-depth curve. Ages were then interpolated for the necessary sample depths and sedimentation rates calculated. The resulting record is 493 years long, spanning 1384-891 cal BP, with a sedimentation rate of 0.04-

0.05 cm/yr.

4.1.1.2 “Marahbodd” Lake

A single layer of volcanic ash was identified in the “Marahbodd” Lake (ML) core at

approximately 23-25 cm depth. Identification by wavelength dispersive spectrophotometry and

comparison with reference samples identified the ash as coming from the eastern White River

eruption, 1147 cal BP (Appendix A; Lauren Davies, personal communication 2014; Clague, et

al. 1995).

The ML chronology was constructed based on two AMS radiocarbon dates, the depth and age of

the WRA (Clague, et al. 1995), and the depth and age of the top of the core. Results are

presented in Table 4.2 and Figure 4.2. Two of the initial four AMS dates were rejected prior to

beginning chronology construction: the date from 4-7 cm depth because it was substantially

older than dates below it (see section 3.3.5), and the date from 36-38 cm depth because it was younger than the date above it, and its inclusion would have caused age reversal in the age-depth interpolation. Rejection of the above 9-12 cm date would also have corrected this issue, however would have resulted in a significant slope in the resulting age-depth sequence, implying a very fast sedimentation rate. As there was only one other date available, retention of either date would have resulted in a linear age-depth sequence, making an additional standard necessary for the determination of which date to retain and which to reject. Ultimately, given the low-productivity nature of the tundra/forest-tundra environment at “Marahbodd” Lake, the lower sedimentation rate implied by the age-depth sequence that retained the 9-12 cm date and rejected of the 36-38 cm date was determined to be the most realistic, and the 9-12 cm date was retained for calculation of the final chronology, while the 36-38 cm date was rejected. A linear best-fit line was plotted to the remaining two AMS dates and interpolated to 0.5 cm intervals to determine if correction was needed. The difference between the interpolated and established age of the WRA in this case equaled 2098 years, while the smallest error of the two retained calibrated radiocarbon dates was 127 years. The difference between the interpolated and established age of the WRA (2098 years) was thus subtracted from the two retained radiocarbon dates to establish a set of corrected dates for use in chronology construction. A 3rd-order polynomial best-fit line was plotted using the two retained corrected radiocarbon dates, the depth and age of the WRA, and the depth and age of the top of the core to give the final age-depth curve, and ages were interpolated for the necessary sample depths and sedimentation rates calculated. The ML record is 711 years long, spanning 1488-777 cal BP, with a sedimentation rate of 0.014-0.033 cm/yr.

4.1.2 Core logging

4.1.2.1 Spirit Lake

The SL core was collected, opened, and logged in 2009 by Dr. William Patterson and colleagues,

Saskatchewan Isotope Laboratory, Department of Geological Sciences, University of

Saskatchewan. The core was transported to the University of Calgary as a part of this study in

2012. By this time, oxidation had altered the colour and magnetic properties of the core, so that photography and magnetic susceptibility (MS) analysis would not have produced a true representation of the core’s original state. The log data from the Saskatchewan Isotope

Laboratory remains unpublished, and so no photograph or MS record is presented here for the SL core.

4.1.2.2 “Marahbodd” Lake

A photograph of the ML core is presented in Figure 4.3. The WRA appears as a light grey band

from approximately 23-25 cm depth.

The results of MS analysis on the ML core are presented in Figure 4.4. MS remains stable at SI

values near 0 for the majority of the record, with the sole exception of at and above the depth of the WRA, where values deviate substantially first to high (ca. +56 SI) and then to low (ca. -62

SI) values over the course of ca. 100 years.

4.1.3 Loss-on-ignition

4.1.3.1 Spirit Lake

The results of loss-on-ignition (LOI) analysis from Spirit Lake are presented in Figure 4.5.

After an initial increase at the beginning of the record from ca. 2 to ca. 7 % by 1350 cal

BP, sediment organic content in the core begins to follow a cyclic pattern of increasing and

decreasing values ranging from ca. 5-8 %, which lasts until the WRA. This pattern has an

approximately 100-year periodicity. Organic content remains at ca. 5 % through the WRA.

Approximately 1100 cal BP, organic content increases sharply to ca. 11 %, and then declines

rapidly to ca. 1 % by 1000 cal BP. Values begin to rise again after this, reaching ca. 12 % by the

end of the record.

Carbonate content remains approximately steady throughout the majority of the Spirit

Lake record, varying from ca. 34-40 %. Values decrease sharply to ca. 16 % at the depth of the

WRA, but recover rapidly to ca. 40 % by ca. 1100 cal BP. Values are slightly elevated ca. 1000

cal BP (45 %), followed by a return to values ca. 34-40 % to the end of the record.

Like carbonate content, residual (silicate) content remains relatively stable throughout the

SL record, varying from ca. 55-60 %. The sole exception to this trend again occurs at the depth of the WRA, where silicate content increases to ca. 75 %, before decreasing again sharply to ca.

54 % by ca. 1100 cal BP.

4.1.3.2 “Marahbodd” Lake

The results of LOI analysis on the ML core are presented in Figure 4.6.

Sediment organic content varied from ca. 5-10 % for the first approximately 100 years of

the record. Organic content stabilizes at ca. 8 % at ca. 1350 cal BP, remaining at approximately

this level until ca. 1275 cal BP. It then increases substantially to near 20 % at ca. 1225 cal BP,

before decreasing sharply at the depth of the WRA to ca. 4 %. A slight increase occurs ca. 1100

cal BP (ca. 8 %), but values remain generally low after the WRA ca. 2-5 % until ca. 1000 cal BP,

when organic content begins to gradually increase, reaching ca. 13 % by ca. 950 cal BP. A brief

decrease in organic content occurs ca. 900 cal BP (ca. 4 %), followed by a return to higher values

ca. 15 % at the end of the record.

Sediment carbonate content exhibits no notable long-term trend and substantial centennial-scale variability in the early portion of the record, varying from ca. 0-8 % until the

WRA. Carbonate content rapidly declines to 0 % at the depth of the WRA, and remains at

somewhat lowered levels relative to earlier in the record until ca. 1100 cal BP, when it begins to gradually increase. Carbonate content is generally higher in the second half of the record than in the first, ranging from ca. 4.5-8 % from ca. 1000-850 cal BP, after which it declines again to values ca. 0-3 % to the end of the record.

Residual (silicate) content averages ca. 86 % for the first ca. 200 years of the record, with the only substantial variation a single-point decrease ca. 1450 cal BP to ca. 81 %. Silicate content decreases substantially ca. 1250 cal BP (to 77 %), before increasing sharply at the depth of the

WRA to ca. 94 %. Values remain generally elevated after the WRA until ca. 975 cal BP, when silicate content begins to decrease sharply to near its pre-ash levels, reaching ca. 78 % by ca. 900 cal BP. Values briefly increase to ca. 90 % once again ca. 900 cal BP, before decreasing to ca.

80-85 % ca. 850 cal BP to the end of the record.

4.1.4 Pollen

4.1.4.1 Spirit Lake

Pollen percentage and influx graphs from Spirit Lake are presented in Figure 4.7.

Percent representation of Pinus remains at ca. 60 % during the early portion of the record.

Percentages begin to decrease ca. 1200 cal BP and continue through the WRA to ca. 1100 cal

BP, reaching a minimum of ca. 40 %. Pinus then recovers ca. 1050-950 cal BP to ca. 60-80 %, before declining again at the end of the record. Picea follows similar trends to Pinus, but is less variable with values ca. 0-15 %, and lower rather than higher values for a brief period ca. 1000-

975 cal BP. Percentage representation of Betula, Juniperus, and Populus increases gradually

from the beginning of the record to ca. 1200 cal BP, each reaching values of approximately 10

%. Betula increases to ca. 15 % at the depth of the WRA, while Juniperus and Populus decline to near 0 %. Both Juniperus and Populus recover to ca. 10 % by ca. 1100 cal BP, while Betula decreases to ca. 10 %. Percent representation of Alnus varies between values of ca. 5-20 % for

the majority of the record; values are slightly lower from ca. 1050 cal BP to the end of the

record, remaining below ca. 15 %. Salix remains at low percentages throughout the record, with

a slight peak at the depth of the WRA to ca. 7 %. Artemisia and Cyperaceae also peak slightly at the depth of the WRA, each to approximately 5 %. Polypodiaceae has elevated percentages both early (ca. 20 %) and late (ca. 15 %) in the record and at the depth of the WRA (ca. 10 %), but otherwise remains at low levels. The ratio of arboreal pollen (AP) to non-arboreal pollen (NAP) increases slightly through the first quarter of the record, reaching a peak ca. 1250 cal BP. The

AP:NAP ratio then declines from this point through the WRA, reaching a minimum ca. 1100 cal

BP, before rapidly increasing to its highest values of the record by ca. 1050 cal BP. AP:NAP ratio then rapidly declines once again to near previous levels, which continue to the end of the record.

Patterns in total influx are mirrored closely by that of both Pinus and Picea, though patterns in Picea are less distinctive than those in Pinus. Total influx remains approximately stable for the first half of the record at ca. 800 grains/cm2/yr. This is followed by a sharp decline

in influx at the depth of the WRA to ca. 200 grains/cm2/yr, and then by a rapid increase to ca.

700 grains/cm2/yr, where it stabilizes until ca. 1050 cal BP. A single-point increase at this time to

ca. 1600 grains/cm2/yr is followed by a decline to ca. 600 grains/cm2/yr. Total influx increases

again to ca. 800 grains/cm2/yr at the end of the record. Taxon-specific influx of Betula begins low early in the record, but rises gradually to ca. 80 grains/cm2/yr by ca. 1200 cal BP. Influx of

Betula is highly variable from this point to the end of the record, varying from ca. 0-100

grains/cm2/yr. Influx of Juniperus and Populus also increases ca. 1200 cal BP to ca. 70 and 60 grains/cm2/yr, respectively, but decreases sharply at the depth of the WRA. Influx of both taxa

recovers to previous levels by ca. 1100 cal BP. Influx of Juniperus then gradually declines to the end of the record, while Populus decreases to ca. 20 grains/cm2/yr at ca. 1050 cal BP and remains at levels ca. 20-50 grains/cm2/yr until the end of the record. Influx of Alnus shows a

slight decreasing trend over the course of the record from values ca. 300 grains/cm2/yr to values

ca. 50 grains/cm2/yr. Influx of Alnus also decreases sharply at the depth of the WRA from ca.

180 grains/cm2/yr to ca. 15 grains/cm2/yr, as well as at ca. 1250, 1050, and 950 cal BP. These

rapid declines are followed by equally rapid recoveries to near previous levels in each case. After

an initial peak early in the record, influx of Artemisia remains low through the first half of the

record at values ca. 10 grains/cm2/yr. Influx increases slightly after the WRA to ca. 20

grains/cm2/yr, before declining to 0 grains/cm2/yr by ca. 1050 cal BP. Influx increases again to

ca. 20 grains/cm2/yr ca. 1000 cal BP, followed by another decline to 0 grains/cm2/yr ca. 950 cal

BP, and then by another increase to the end of the record. With the exception of at the depth of

the WRA, where its influx is slightly lower (ca. 0-5 grains/cm2/yr), Poaceace remains at levels ca. 15 grains/cm2/yr until ca. 1000 cal BP, when it drops entirely from the record. Influx of

Tubuliflorae remains low throughout much of the record, with the exception of a period of elevated influx ca. 1300-1250 cal BP. Influx of Cyperaceae is low both early and late in the

record at ca. 10 grains/cm2/yr, while values are elevated ca. 1250-1050 cal BP at ca. 20

grains/cm2/yr. Polypodiaceae has elevated influxes both early (ca. 125 grains/cm2/yr) and late

(ca. 110 grains/cm2/yr) in the record and at the depth of the WRA (ca. 100 grains/cm2/yr), but

otherwise remains at low levels throughout.

4.1.4.2 “Marahbodd” Lake

Pollen percentage and influx graphs from “Marahbodd” Lake are presented in Figure 4.8.

Percentage representation of Alnus increases gradually over the first half of the record

from ca. 5-10% until the WRA. Betula exhibits a gradually decreasing trend over the same

period, from ca. 10-5%, with a sudden return to higher values ca. 15% at the depth of the ash.

Percentage representation of both of these taxa decreases abruptly following the WRA to 0 % ca.

1100-1000 cal BP, before returning to near-previous levels and patterns ca. 1000 cal BP. Salix

follows a similar trend, with generally lower average percentage values (ca. 5 %), and slightly

elevated percentages in the latter half of the record (ca. 5-10 % vs. ca. 0-5 %). Percentage

representation of Juniperus and Populus remains relatively stable throughout the record (ca. 5-10

% each), with notable decreases to near 0 % only at the depth of the WRA, lasting until ca. 1075

cal BP. Cyperaceae also exhibits a similar trend, averaging ca. 10 % for much of the record with

the exception of at the depth of the WRA, where it declines to 0 %. A single-point increase also

occurs in Cyperaceae at ca. 1050 cal BP, where it reaches 40 %. Populus shows a very slight

decreasing trend over the course of the record (from ca. 10 % on average to ca. 5 %). Picea also

shows a slight decreasing trend over the course of the record from ca. 50 % to ca. 40 %, and

gradually increasing centennial-scale variability. After an initial decline from ca. 20 % to near 0

% by ca. 1350 cal BP, Pinus remains at generally low values ca. 0-5 % until the WRA. Percent

representation of Pinus increases slightly to ca. 10 % at the depth of the WRA, followed by a

sudden decrease to near 0 % immediately after, ca. 1100 cal BP. and a sharp increase to ca. 20 % ca. 1050-1025 cal BP. Values of Pinus after the WRA stabilize at a level somewhat higher than the majority of the first portion of the record – ca, 10-15 % – before declining slightly in the final ca. 75-100 years of the record to ca. 5%. Percent representation of Artemisia remains low throughout the record, increasing gradually from near 0 % early in the record to ca. 10-15 % by the WRA. Values of Artemisia show a strong decreasing trend following the WRA, reaching ca.

2 % by ca. 1075 cal BP, and remain at or below 5% after this through the remainder of the record, with the exception of a single point ca. 900 cal BP where values reach ca. 7%.

Polypodiaceae increases substantially from ca. 5 % to ca. 20 % after the WRA, and declines to previous levels by ca. 1000 cal BP. The AP:NAP ratio shows a very slight decreasing trend over the course of the record. The ratio increases slightly ca. 1400-1350 cal BP, followed by decreased values lasting until ca. 1250 cal BP, when they increase again. The AP:NAP ratio decreases through the WRA, increasing again rapidly in a single-point peak ca. 1050 cal BP.

Values decrease to previous levels ca. 1075 cal BP, before increasing once again and remaining approximately stable to the end of the record.

Total influx increases gradually in the first half of the record from ca. 300-700 grains/cm2/yr until the WRA, when influx decreases suddenly to ca. 200 grains/cm2/yr. Total influx increases rapidly again after ca. 1100 cal BP to ca. 800 grains/cm2/yr by ca. 1050 cal BP.

Values vary from ca. 400-900 grains/cm2/yr from this point to the end of the record. Patterns in

the influx of Picea and Juniperus are approximately similar to those of total influx. Influx of

Pinus is low at ca. 10-60 grains/cm2/yr for the first half of the record. Values fall sharply to near

0 grains/cm2/yr after the WRA, followed by a sharp increase to ca. 80 grains/cm2/yr at ca. 1050

cal BP. Influx of Pinus remains elevated to near the end of the record, when values decrease

gradually but substantially to ca. 20 grains/cm2/yr. Influx of Alnus increases gradually over the

course of the record from ca. 25-50 grains/cm2/yr, with the exception of after the WRA, when

values decline steeply to 0 grains/cm2/yr, lasting until ca. 1050 cal BP. Influx of Betula is also

elevated in the second half of the record in comparison to the first prior to the WRA, and is more

variable; influx values of Betula range from ca. 25-50 grains/cm2/yr in the first half of the record,

and from ca. 30-130 grains/cm2/yr in the second. Influx of Populus shows substantial centennial-

scale variability in the first half of the record, varying from ca. 6-45 grains/cm2/yr. Values are

generally lower around the WRA, declining sharply to 0 grains/cm2/yr before increasing once

again to ca. 6 grains/cm2/yr by ca. 1075 cal BP. Values remain at approximately this level for the remainder of the record, with the exception of a single-point increase to ca. 45 grains/cm2/yr at ca. 900 cal BP. Influx of Salix also decreases from values ca. 20-25 grains/cm2/yr to 0

grains/cm2/yr after the WRA. Influx values recover to values ca. 20-25 grains/cm2/yr once again by ca. 1000 cal BP, and remain stable to the end of the record, with the exception of a single- point increase to ca. 80 grains/cm2/yr at ca. 900 cal BP. The influx of Poaceae is also

approximately stable at ca. 10 grains/cm2/yr throughout the record, with the exception of an

extended decrease at the depth of the WRA (0 grains/cm2/yr) and sharp increase ca. 900 cal BP

(ca. 35 grains/cm2/yr). Influx of Artemisia increases from low values ca. 10 grains/cm2/yr early

in the record to ca. 40 grains/cm2/yr by ca. 1250 cal BP, where it remains until the WRA. Influx

then decreases rapidly, reaching ca. 6 grains/cm2/yr by ca. 1075 cal BP. Values recover to ca. 30

grains/cm2/yr by ca. 1000 cal BP, and vary from ca. 10-30 grains/cm2/yr to the end of the record, with the sole exception of a single-point increase to ca. 70 grains/cm2/yr at ca. 900 cal BP. Influx

of Cyperaceae varies from ca. 20-50 grains/cm2/yr throughout much of the record. Exceptions

are a single-point increase to ca. 300 grains/cm2/yr at ca. 1050 cal BP, and a decline to 0

grains/cm2/yr at the depth of the WRA, which lasts until ca. 1100 cal BP. Influx of

Polypodiaceae increases substantially from values averaging ca. 30-50 grains/cm2/yr prior to the

WRA to ca. 100 grains/cm2/yr by ca. 1075-1025 cal BP, returning rapidly to more typical values

by ca. 1000 cal BP.

4.1.5 Microcharcoal

4.1.5.1 Spirit Lake

The results of microcharcoal analysis from Spirit Lake are presented in Figure 4.9.

Microcharcoal influx shows no notable long-term trend and only slight variability over the

course of the record, with the exception of a large increase at the depth of the WRA from values

ca. 800 to ca. 2800 particles/cm2/yr. Influx returns to previous levels by ca. 1100 cal BP. For the

remainder of the record, microcharcoal influx varies from ca. 350-900 particles/cm2/yr, with

peaks at ca. 1350, 1250, and 950 cal BP.

4.1.5.2 “Marahbodd” Lake

The results of microcharcoal analysis from “Marahbodd” Lake are presented in Figure 4.10.

Microcharcoal influx at “Marahbodd” Lake shows a gradually decreasing long-term trend with

noticeable centennial-scale variability. Peaks in the record occur at ca. 1400 cal BP (1350

particles/cm2/yr), 1250 cal BP (1500 particles/cm2/yr), 1000 cal BP (1000 particles/cm2/yr), and

900 cal BP (850 particles/cm2/yr), and troughs at ca. 1400-1300 cal BP (700 particles/cm2/yr),

950 cal BP (550 particles/cm2/yr), and 850 cal BP (200-400 particles/cm2/yr). A substantial decrease in microcharcoal influx also occurs at the depth of the WRA, where values decline from

their previous high point of ca. 1500 particles/cm2/yr at ca. 1250 cal BP to a minimum of 250

particles/cm2/yr by ca. 1125 cal BP.

4.1.6 Chironomids

4.1.6.1 Spirit Lake

Chironomid percentage and influx graphs from Spirit Lake are presented in Figure 4.11.

Percent representation of Chironomus decreases gradually over the first half of the record

from ca. 30-2 %. Representation remains low through the WRA, increasing to ca. 20 % ca. 1050

cal BP. Values remain elevated to ca. 1000 cal BP when they then decrease to ca. 5 %, with a

final increase at the end of the record. Dicrotendipes represents ca. 15-20 % of the assemblage

early in the record, but rapidly decreases to ca. 2 % at ca. 1200 cal BP, where it remains for the

remainder; values reach 0 % at the depth of the WRA and from ca. 1025-975 cal BP.

Paratendipes and Polypedilum both remain at low values until after the WRA, when their relative abundances increase. Paratendipes increases somewhat after the WRA, starting ca. 1050

cal BP, rising to ca. 8 % before decreasing once again to ca. 2 % to the end of the record.

Polypedilum increases almost immediately after the WRA, starting ca. 1100 cal BP, and rises to

ca. 10 %, where it remains for the remainder of the record. The relative abundance of Sergentia

is highly variable through the first 400 years of the record, varying from ca. 0-25 %. Sergentia

declines in abundance gradually beginning ca. 1000 cal BP, reaching 0 % by ca. 925 cal BP.

Highest values of Sergentia are reached just after the WRA ca. 1100 cal BP. Tanytarsina group

C and Tanytarsus lugens both increase gradually in abundance over the first half of the record, to

ca. 20 % and ca. 8 %, respectively. Tanytarsina group C then rapidly declines to ca. 2 %

immediately after the deposition of the ash, followed by a gradual increase to ca. 11 % by ca.

950 cal BP. Tanytarsus lugens decreases to 0 % abundance by ca. 1050 cal BP, and appears only

sporadically thereafter at low abundances. Parakeifferiella sp. B also increases gradually from the beginning of the record to the WRA (from ca. 5-10 %) before decreasing to 0 % at the

WRA. Values remain between approximately 0 and 4 % for the remainder of the record.

Tanytarsus chinyensis declines gradually over the course of the record from ca. 20-5 %.

Abundances decline at the depth of the WRA by 10 %, and recover by ca. 1100 cal BP. A single- point increase reaching ca. 30 % also occurs near the end of the record. After an initial decline from ca. 20-10 % by ca. 1275 cal BP, Tanytarsina – other begins to increase in abundance until the WRA, reaching ca. 25 %. This is followed by a sharp decrease to ca. 10 % abundance immediately after the ash, and recovery to ca. 25 % once again by ca. 1050 cal BP. Values decline to ca. 12 % by ca. 950 cal BP, before increasing in a single-point peak at the end of the

record. Percent representation of Cricotopus/Orthocladius is generally stable in the first third of

the record, with a gradual slight increase from 5-10 % by ca. 1250 cal BP. Values gradually

decrease from this point to 0 % by the depth of the WRA, followed by a sharp increase to ca. 15

% at ca. 1100 cal BP. Abundances decrease rapidly to ca. 2 % by ca. 1075 cal BP and remain

stable at approximately this value until the end of the record. With the exception of high values

in the initial parts of the record, Psectrocladius undiff. decreases in abundance during the first

third of the record, from ca. 15-0 % by ca. 1225 cal BP. Abundances increase through the WRA

to ca. 8 % by ca. 1050 cal BP. Abundances are variable from this point, before declining to 0 %

by ca. 950 cal BP. Procladius remains approximately stable at ca. 10-15 % throughout much of

the record. Peak values are slightly higher early in the record at ca. 18 %. A slight decline in

abundance at the end of the record (values generally less than 10 %) is also apparent. Both

Micropsectra (0 % to ca. 5 %) and Paratanytarsus (0 % to ca. 10 %) peak slightly immediately

after the WRA. Micropsectra remains elevated until ca. 1100 cal BP, while abundances of

Paratanytarsus remain slightly higher until ca. 1050 cal BP, before declining once again.

With the exception of a single-point decrease to low values of ca. 0.2 head capsules/cm2/yr early in the record, total chironomid influx at Spirit Lake gradually declines over the course of the record from ca. 0.5-0.7 head capsules/cm2/yr to ca 0.1 head capsules/cm2/yr.

Low values ca. 0.1 head capsules/cm2/yr also occur ca. 1175 cal BP, before recovering to ca. 0.5

head capsules/cm2/yr by ca. 1100 cal BP and continuing their gradual decline. Chironomus

influx shows generally stable values ca. 0.3-0.5 head capsules/cm2/yr over the course of the

record, with slightly elevated values ca. 0.6 head capsules/cm2/yr early and late in the record, and

slightly decreased values ca. 0.1-0.2 head capsules/cm2/yr starting ca. 1250 cal BP and continuing through the WRA, before increasing again ca. 1100 cal BP. Cyphomella/Harnischia/

Paracladopelma shows a gradual decrease from peak values 0.05 head capsules/cm2/yr ca. 1300

cal BP to near 0 head capsules/cm2/yr by the end of the record. Influx is slightly elevated after

the WRA, at ca. 0.02 head capsules/cm2/yr, until ca. 1075 cal BP. Influx of Dicrotendipes and

Glyptotendipes also declines over the course of the record: Glyptotendipes gradually, and

Dicrotendipes in a single decrease from 0.08-0.01 head capsules/cm2/yr ca. 1250 cal BP.

Paratendipes and Polypedilum both increase substantially after the WRA: Paratendipes at ca.

1050 cal BP, and Polypedilum at ca. 1100 cal BP, both from near 0 to ca. 0.2-0.3 head capsules/cm2/yr. With the exception of a single-point increase ca. 1275 cal BP, influx of

Sergentia remains at values ca. 0.01-0.06 head capsules/cm2/yr prior to the WRA. Influx decreases to 0 head capsules/cm2/yr ca. 1175 cal BP, and then increases through the ash to a peak

of ca. 0.1 head capsules/cm2/yr by ca. 1100 cal BP. Influx then gradually decreases, until the

taxon drops from the record ca. 900 cal BP. Influx of Psectrocladius undiff. also follows a

similar pattern. Influx of Micropsectra and Paratanytarsus are both largely absent from the

record, with the exception of at the depth of the WRA, where Micropsectra peaks to influxes of

ca. 0.02 head capsules/cm2/yr, and Paratanytarsus to values ca. 0.04 head capsules/cm2/yr.

Micropsectra remains elevated until ca. 1100 cal BP, when it again drops from the record, while

Paratanytarsus remains elevated until ca. 1050 cal BP. Influx of Tanytarsina group C gradually

increases over the first half of the record, peaking at ca. 0.07 head capsules/cm2/yr at the depth of the WRA. Influx then rapidly decreases to ca. 0.01 head capsules/cm2/yr, and remains

approximately stable to the end of the record. With the exception of a single-point decrease early

in the record, influx of Tanytarsus lugens is approximately stable for the first half of the record,

at values ca. 0.01-0.02 head capsules/cm2/yr. Influx decreases slightly at the depth of the WRA

from ca. 0.02-0.01 head capsules/cm2/yr, and increases again to ca. 0.03 head capsules/cm2/yr by ca. 1100 cal BP. Influx decreases sharply after this to 0 head capsules/cm2/yr by ca. 1050 cal BP,

and the taxon appears only intermittently from this point to the end of the record. Influx of

Tanytarsina – other remains generally stable at ca. 0.06 head capsules/cm2/yr over the course of

the record, with some slight variability at the depth of the WRA and elevated values early in the

record. Cricotopus/Orthocladius, Tanytarsus chinyensis, and Procladius all exhibit substantial decreases in influx at or leading up to and through the depth of the WRA, followed by rapid increases to previous or higher than previous values. In the case of Tanytarsus chinyensis and

Procladius, this decrease occurs in the middle of a gradual decline which occurs over the course of the record, from 0.08-0.01 head capsules/cm2/yr. Influx of Tanytarsus chinyensis reaches 0

head capsules/cm2/yr at the depth of the WRA and recovers to ca. 0.06 head capsules/cm2/yr by ca. 1100 cal BP, while that of Procladius reaches near 0 head capsules/cm2/yr just before the

WRA ca. 1175 cal BP, and begins to increase slowly from that point. The decline in

Cricotopus/Orthocladius follows a gradual increase from early in the record to ca 1225 cal BP.

Influx peaks after the ash in a single-point increase ca. 1100 cal BP, before declining to near 0

head capsules/cm2/yr, where it remains to the end of the record. Influx of Parakeifferiella sp. B ranges from values near 0 head capsules/cm2/yr to ca. 0.02 head capsules/cm2/yr over the course of the record, with higher values on average from ca. 1250-1050 cal BP than at the beginning and the end of the record. Influx decreases briefly to 0 head capsules/cm2/yr before recovering to

previous values by ca. 1100 cal BP.

4.1.6.2 “Marahbodd” Lake

Chironomid percentage and influx graphs from “Marahbodd” Lake are presented in Figure 4.12.

Percentages of the majority of taxa remain below ca. 10 % over the course of the record

and show few long-term trends and limited centennial-scale variability. The record is dominated

by a few taxa: Corynocera ambigua, Tanytarsys chinyensis, Tanytarsus lugens, and Tanytarsina

– other. Corynocera ambigua shows a gradual increasing trend from ca. 8 % at the beginning of the record to ca. 40 % on average. Centennial-scale variability is substantial, with higher values

occurring at the beginning of the record (ca. 20 %), ca. 1300-1200 cal BP (ca. 30 %), ca. 1100

cal BP (40 %), ca. 900 cal BP (60 %), and at the end of the record (ca. 40 %). Lower values

occur from early in the record to ca. 1300 cal BP (ca. 10 %), at the WRA (ca. 15 %), ca. 1000 cal

BP (ca. 20 %), and ca. 850 cal BP (ca. 20 %). After an initial decline early in the record,

Tanytarsus chinyensis varies from 10-15 % through the first half of the record. Abundances are increased at and after the depth of the WRA at ca. 20-25 %, before declining to previous levels by ca. 1050 cal BP. Values continue to decline from this point, reaching a minimum of ca. 2 % by ca. 950 cal BP, when values once again increase, reaching ca. 15 % by the end of the record.

With the exception of a single-point peak to ca. 30 % at ca. 1350 cal BP, Tanytarsus lugens

decreases gradually over the first half of the record from ca. 20 % to ca. 5 % by the WRA.

Values increase slightly thereafter to ca. 15 % by ca. 1100 cal BP, and remain at approximately

this level to the end of the record. Tanytarsina – other also shows a gradual decreasing trend

until the depth of the WRA, from ca. 25 % to near 0 %. Values gradually increase to ca. 20 % by

ca. 1000 cal BP, but then decrease rapidly to ca. 5 % by ca. 950 cal BP, where they remain to the

end of the record. Other taxa with lesser abundances than the above, but still noticeable trends

are Sergentia, Paratanytarsus, and Procladius. Sergentia remains at generally low and stable

values ca. 5-10 % over the whole of the record, with the exception of a peak at ca. 1000 cal BP,

where values reach ca. 15 %. Paratanytarsus also has generally low abundances, with a peak to

ca. 12 % at the depth of the WRA; values decrease to previous levels ca. 5-8 % by ca. 1050 cal

BP. Finally, Procladius also remains approximately stable at ca. 15 % for the first half of the

record, and decreases rapidly after the WRA to ca. 2 %. Values increase to ca. 15 % by ca. 950

cal BP and remain at approximately this level to the end of the record.

Total chironomid influx at “Marahbodd” Lake cycles between higher (ca. 1.4 head capsules/cm2/yr) and lower (ca. 1.0 head capsules/cm2/yr) values over the course of the record,

with peaks ca. 1400, 1225, and 1000 cal BP. Times of reduced influx occur ca. 1350, 1200, and

950 cal BP. Decreased total influx values ca. 1200 cal BP last until after the WRA –

approximately 50 years – before beginning to rise once again. Dicrotendipes, Corynocera

ambigua, Tanytarsina – other, Tanytarsina group C, Tanytarsus lugens, Parakeifferiella sp. B,

Psectrocladius undiff., Pseudosmittia/Smittia, and Procladius all follow similar general trends as

total influx, though patterns in Tanytarsina group C and Tanytarsus lugens are somewhat more

stable during early portion of the record until ca. 1250 cal BP, and Pseudosmittia/Smittia drops

almost entirely from the record after ca. 1050 cal BP. Influx of Sergentia remains approximately

stable throughout the record at ca. 0.02-0.05 head capsules/cm2/yr, with the exception of a

single-point increase ca. 1000 cal BP to ca. 0.15 head capsules/cm2/yr. Glyptotendipes follows

similar patterns, but at lower values (0-0.02 head capsules/cm2/yr), and drops entirely from the

record from ca. 1225-1050 cal BP. Cladopelma and Chironomus both show gradually declining

influxes over the course of the record, from 0.05-0.02 head capsules/cm2/yr in the case of

Cladopelma, and from 0.03-0 head capsules/cm2/yr by ca. 975 cal BP in that of Chironomus.

Tanytarsus chinyensis, and Paratanytarsus both show declining influxes early in the record (ca.

0.05-0.004 head capsules/cm2/yr and ca. 0.2-0.04 head capsules/cm2/yr, respectively), followed by elevated values from ca. 1300-950 cal BP (ca. 0.05 head capsules/cm2/yr and ca. 0.15 head

capsules/cm2/yr, respectively), and then stable values thereafter to the end of the record.

Olivideria/Hydrobaenus group, Cryptochironomus, and Corynocera olivieri all follow similar trends to each other, with low or intermittent influx prior to the ash (ranging from ca. 0-0.01 head capsules/cm2/yr), and somewhat higher or more consistent influx after (up to ca. 0.03 head

capsules/cm2/yr), beginning ca. 100 years after the ash at ca. 1050 cal BP. Micropsectra,

Pseudochironomus, and Parachironomus show the opposite trend, with higher influxes before

the WRA (up to ca. 0.03 head capsules/cm2/yr), and lower or more intermittent influxes after the

deposition of the ash (ranging from 0-0.02 head capsules/cm2/yr). Finally, Limnophyes,

Stichtochironomus sp. B, Polypedilum, and Corynoneura/Thienemanniella all show increased influxes at or near to the WRA (up to 0.01 head capsules/cm2/yr), with only intermittent

appearances in the remainder of the record. Heterotrissocladius also appears at the depth of the

WRA, having dropped from the record suddenly ca. 1400 cal BP; the taxon only appears once

more in the remainder of the record, ca. 975 cal BP.

4.1.7 Ordination

4.1.7.1 Spirit Lake

Detrended correspondence analysis (DCA) of percentage pollen data revealed a gradient length of 1.0 standard deviation (SD) units, both with and without down-weighting of rare taxa, indicating linear ordination methods were appropriate. Principle Components Analysis (PCA) was performed on un-transformed pollen percentage data, as a method of visualizing temporal trends. The results are presented in Table 4.3, Table 4.5, and Figure 4.13. A varve-based reconstruction of mean July temperature anomalies from Iceberg Lake, AK (Loso 2009), is also presented in Figure 4.13 for comparative purposes. The Loso (2009) curve indicates gradually and slightly increasing temperatures over the course of the record. Centennial-scale trends indicate that temperatures were slightly elevated at the beginning and end of the record (ca.

+0.1°C at approximately 1350 cal BP; ca. +0.1-0.15°C at approximately 950-900 cal BP), with lower values (ca. -0.3-0°C) from ca. 1300-950 cal BP. Temperatures appear to increase and decrease with an approximately 200-year periodicity from ca. 1300 cal BP to the end of the record; the periodicity of the earliest portion of the record, prior to ca. 1300 cal BP, is somewhat faster at approximately 100 years.

As given by the Axis 1 eigenvalue, Axis 1 of the pollen-based PCA from Spirit Lake explains approximately 25 % of the variability in the data. Axis 1 sample loadings show a cyclic pattern of increasing and decreasing values, with a periodicity of ca. 100 years, and a slight positive association to the Loso (2009) temperature curve. Loadings are slightly elevated ca.

1200-1000 cal BP, with consistently positive values, while values prior to and after this period are typically negative. Axis 2 explains ca. 17 % of the variability in the dataset, but shows little

long-term trend in the sample scores, with loadings near 0. A single-point increase to positive values at the end of the record is the only occurrence of strong loadings. Axis 3 (explains ca. 13

% of the variability in the dataset) also shows generally stable samples scores, with loadings near or just under 0 throughout much of the record; positive loadings occur at the beginning and end of the record, and at the depth of the WRA. Axis 4 (explains 12 % of the variability in the dataset). Like Axis 1, Axis 4 sample scores appear to show a slight positive association with the

Loso (2009) temperature curve, exhibiting a centennial-scale trend of cyclic variation with a periodicity of ca. 200 years. The Axis 4 sample scores also display a slightly decreasing long- term trend in loadings from the beginning to the end of the record. Axis 5 (explains ca. 8 % of the variability in the dataset) sample score loadings remain generally near 0 throughout the record, with slightly lower values for a period of ca. 100 years ca. 1200 cal BP, as well as at the end of the record. Species scores of Alnus, Betula, Juniperus, Equisetum, Populus, and

Shepherdia are all strongly positively loaded on Axis 1, while Pinus is strongly negatively loaded. Corylus, Ericaceae, and Picea are all strongly loaded on Axis 2, while Artemisia,

Cyperaceae, and Salix are all strongly negative. On Axis 3, Artemisia, Betula, Cyperaceae, and

Salix are all strongly positive, while Pinus and Rosaceae are all strongly negative. Strongly positive on Axis 4 are: Artemisia, Tubuliflorae, and Salix, while Lycopodium, Poaceae, and

Polypodiaceae are all strongly negative on this axis. Finally, on Axis 5, Cyperaceae, Ericaceae, and Poaceae are all strongly positive, while Equisetum, Lycopodium, and Shepherdia are all strongly negative.

DCA of percentage chironomid data revealed a gradient length of 1.4 and 1.3 SD units, with and without down-weighting of rare taxa, respectively, indicating linear ordination methods were

appropriate. PCA was performed on square-root transformed chironomid percentage data. The results are presented in Table 4.3, Table 4.5, and Figure 4.13. The Loso (2009) varve-based reconstruction of mean July temperature anomalies from Iceberg Lake, AK, is also presented in

Figure 4.13 for comparative purposes. As given by the Axis 1 eigenvalue, Axis 1 of the

chironomid-based PCA from Spirit Lake explains ca. 17 % of the variability in the chironomid

dataset. Sample scores for Axis 1 display a long-term trend towards increasingly positive

loadings over the course of the record, with slight centennial-scale variability with a period of ca.

100 years. Following a peak ca. 1300 cal BP, sample score loadings on Axis 2 (explains ca. 14 %

of the variability in the data) decline gradually to ca. 1200 cal BP, when they once again begin to

increase. Loadings reach their highest values ca. 1000 cal BP, before declining to the end of the

record. Sample scores for Axis 3 (explains ca. 12 % of the variability in the dataset) show a

gradually decreasing trend following initially high values early in the record. Loadings decrease

steadily to ca. 950 cal BP, before a single-point increase near the end of the record, ca. 900 cal

BP. Sample scores for Axis 4 (explains 12 % of the variability in the record) show generally

stable loadings near 0, with the exception of a single-point increase ca. 1250 cal BP. Sample

scores for Axis 5 (explains 8 % of the variability in the dataset) also show generally stable

loadings near 0 throughout; values are slightly higher in the first half of the record to the depth of

the WRA than in the second half of the record. Species scores of Cryptochironomus,

Limnophyes, Paratendipes, Polypedilum, Pseudosmittia/Smittia, and Tanytarsina – other are all strongly positively loaded on Axis 1, while Dicrotendipes, Procladius, Psectrocladius undiff.,

and Sergentia are all strongly negatively loaded. Cladotanytarsus mancus type,

Cyphomella/Harnischia/Paracladopelma, Limnophyes, Polypedilum, and Procladius are all strongly positively loaded on Axis 2, while Corynocera ambigua, Dicrotendipes,

Parakeifferiella sp. B, Stempellina, and Stichtochironomus undiff. are all strongly negative. On

Axis 3, Parakeifferiella sp. B, Procladius, and Tanytarsus chinyensis are all strongly positive, while Chironomus, Corynocera ambigua, Glyptotendipes, Pseudosmittia/Smittia, Sergentia, and

Stempellina are all strongly negative. Cyphomella/Harnischia/Paracladopelma, Pagastiella,

Parachironomus, and Stichtochironomus undiff. are all strongly positive on Axis 4, while

Psectrocladius undiff. is strongly negative. On Axis 5, Corynoneura/Thienemanniella,

Cyphomella/Harnischia/Paracladopelma, Glyptotendipes, and Stichtochironomus undiff. are all strongly positive, while Chironomus, Cladopelma, Parakeifferiella sp. B, and Stempellina are strongly negative.

4.1.7.2 “Marahbodd” Lake

Detrended correspondence analysis (DCA) of percentage pollen data from “Marahbodd” Lake

revealed a gradient length of 1.3 standard deviation (SD) units, both with and without down-

weighting of rare taxa, indicating linear ordination methods were appropriate. Principle

Components Analysis (PCA) was performed on un-transformed pollen percentage data. The

results are presented in Table 4.4, Table 4.6, and Figure 4.14. A chironomid-based reconstruction

of mean July temperature from Slipper Lake, NWT (MacDonald, et al. 2009), is also presented in Figure 4.14 for comparative purposes. Temperatures in the beginning of the MacDonald et al.

(2009) record remain at ca. 10°C, before decreasing to ca. 8°C approximately 1350 cal BP.

Temperatures increase to a peak of ca. 14°C following this, until ca. 1250 cal BP, when they decrease to ca. 10°C once again. Temperatures remain approximately stable for the remainder of the record, with the exception of a brief decrease to 8-9°C from ca. 1050-1000 cal BP.

As given by the Axis 1 eigenvalue, Axis 1 of the pollen-based PCA from “Marahbodd”

Lake explains approximately 19 % of the variability in the data. Sample score loadings on Axis 1

decrease gradually over the course of the record. There is little centennial-scale variation in the early portion of the record, followed by a rapid and substantial increase after the WRA. The overall decreasing trend continues at an accelerated rate following this to the end of the record, where loadings then increase slightly to near 0. Sample scores for Axis 2 (explains 16 % of the variability in the dataset) show little centennial-scale variability, but a long-term trend towards slightly increased values. Centennial-scale variability increases in the latter half of the record, beginning with a large single-point increase ca. 1050 cal BP. Sample scores for Axis 3 (explains

ca. 12 % of the variability in the dataset) increase from negative to positive loadings in the first

half of the record, up until the WRA. A sharp decrease after the WRA is followed by a rapid

increase ca. 1050 cal BP. The long-term trend in the second portion of the record is one of

gradually decreasing values. Sample scores for Axis 4 (explains ca. 11 % of the variability in the dataset) show a cyclic pattern with a long periodicity, though the record is not sufficiently long to capture it in its entirety. Sample score loadings on Axis 4 move from positive early to negative in the first third of the record, from positive to negative in the second third, and from negative to positive in the final third. Sample scores for Axis 5 (explains ca. 9 % of the variability in the data) show a generally negative association with Axis 4, with increasing values in the first third of the record, and decreasing values second, followed by increasing values once again in the last third of the record. Species scores of Cyperaceae, Dryas, and Polypodiaceae are all strongly positively loaded on Axis 1, while Alnus, Artemisia, Betula, Salix, and Sphagnum are all strongly negative. On Axis 2, Cyperaceae, Dryas, Ericaceae, and Lycopodium are all strongly positive, while Tubuliflorae and Picea show strongly negative loadings. On Axis 3, Alnus and Artemisia

are strongly positive, while Juniperus, Pinus, Poaceae, and Populus are strongly negative.

Strongly positive on Axis 4 are: Tubuliflorae, Pinus, and Sphagnum, while Betula, Ericaceae, and Epilobium are strongly negative. Finally, Shepherdia is strongly positively loaded on Axis 5, while Pinus and Polypodiaceae are strongly negative.

DCA of percentage chironomid data revealed a gradient length of 1.4 SD units, both with and without down-weighting of rare taxa, indicating linear ordination methods were appropriate.

PCA was performed on square-root transformed chironomid percentage data. The results are presented in Table 4.4, Table 4.6, and Figure 4.14. The chironomid-based reconstruction of mean

July temperature from Slipper Lake, NWT (MacDonald, et al. 2009), is also presented in Figure

4.14 for comparative purposes. As given by the Axis 1 eigenvalue, Axis 1 of the chironomid- based PCA from “Marahbodd” Lake explains ca. 13 % of the variability in the chironomid dataset; sample scores for this axis show a long-term trend towards increasingly negative loadings, with little centennial-scale variability. Sample scores for Axis 2 (explains 12 % of the variability in the dataset) appear to be slightly positively associated with the MacDonald et al.

(2009) temperature curve, and show a long-term trend towards more negative loadings. A sharp decrease ca. 1250 cal BP is followed by elevated values through the WRA, and another sharp decrease ca. 1000 cal BP. Sample scores for Axis 3 (explains 11 % of the variability in the data) show generally stable loadings near 0 throughout much of the record, with the exception of a sharp decrease to negative loadings near the end of the record, followed by a rapid increase to positive values at the end of the record. Sample scores for Axis 4 (explains ca. 10 % of the variability in the data) show generally stable loadings near 0 throughout the record; values are slightly lower before and slightly increased after the WRA. Finally, sample scores for Axis 5

(explains ca. 8 % of the variability in the data) also show generally stable loadings near 0

throughout the record. Variability increases in the second half of the record after the WRA, with

a period of increased values ca. 1000-900 cal BP, and decreased values from ca. 900 cal BP to

the end of the record. Species scores of Chironomus, Dicrotendipes, Microtendipes,

Parachironomus, Parakeifferiella sp. B, Paracladius, Procladius, and Pseudochironomus are all strongly positively loaded on Axis 1, while Corynocera ambigua is the only taxon to be strongly negative. On Axis 2, Chironomus, Cladopelma, Cladotanytarsus mancus type,

Corynoneura/Thenemanniella, Heterotrissocladius, Limnophyes, Polypedilum,

Pseudosmittia/Smittia, and Tanytarsus chinyensis are all strongly positively loaded, while

Dicrotendipes, Glyptotendipes, Parakeifferiella sp. B, and Sergentia are all strongly negative.

Strongly positive on Axis 3 are: Cricotopus/Orthocladius, Glyptotendipes, Limnophyes, and

Zalutschia, while Cladotanytarsus mancus type, Paratendipes, Procladius, Pseudochironomus,

Sergentia, and Stempellina are all strongly negative. Cladopelma, Corynocera olivieri,

Cryptochironomus, Glyptotendipes, and Olivideria/Hydrobaenus group are all strongly positively loaded on Axis 4, while Cladotanytarsus mancus type, Cyphomella/Harnischia/

Paracladopelma, Stichtochironomus undiff., and Tanytarsus chinyensis are all strongly negative.

Finally, Corynoneura/Thenemanniella, Cryptochironomus, Parakeifferiella sp. B, Procladius,

and Psectrocladius undiff. are all strongly positive on Axis 5, while Olivideria/Hydrobaenus

group, Limnophyes, Paracladius, Paratendipes, Pseudosmittia/Smittia, Pseudochironomus, and

Tanytarsina – other are strongly negative.

4.1.8 Climate reconstructions

4.1.8.1 Spirit Lake

4.1.8.1.1 Pollen-based

The results of pollen-based temperature and precipitation reconstruction at Spirit Lake using the

Modern Analogue Technique (MAT) are presented in Figure 4.15. Reconstruction of mean July temperatures shows no notable long-term trend, with temperatures remaining at approximately

17°C for the majority of the record. Temperatures are somewhat higher in the earliest portion of

the record at ca. 20°C, but decline to ca. 16°C by ca. 1300 cal BP, before increasing to ca. 17°C

by ca. 1275 cal BP. Temperatures remain approximately stable at ca. 17°C from this point until

the WRA. At the depth of the WRA, temperature undergoes a sharp single-point decrease to ca.

14°C, before increasing back to ca. 17°C ca. 1100 cal BP, where it remains for the remainder of

the record. Reconstructed total annual precipitation is more variable than reconstructed mean

July temperature over the course of the record, but also displays little long-term trend. As in the

temperature reconstruction, total annual precipitation is higher at the start of the record with

values of ca. 1000 mm, but declines rapidly to ca. 400 mm by ca. 1300 cal BP. Precipitation also

decreased sharply at the depth of the WRA to ca. 375 mm, before increasing again to ca. 700 mm

by ca. 1100 cal BP. Precipitation remains slightly elevated for the next ca. 75 years to ca. 1025

cal BP, reaching a maximum of ca. 925 mm. This is followed by a decline to ca. 1000 cal BP,

and then a gradual increase to ca. 1000 mm by the end of the record. Acceptable vs. non-

analogues were determined using the 20th percentile of the observed distribution of pair-wise

dissimilarities in the training set, equal to a squared-chord distance (SCD) value of 92. SCD

values remain below 92 throughout the record, indicating a generally reliable reconstruction.

SCDs are particularly low from the depth of the WRA to ca. 1050 cal BP.

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4.1.8.1.2 Chironomid-based

The results of chironomid-based mean July temperature and lake depth reconstruction at Spirit

Lake using weighted-averaging partial least squares (WAPLS) regression and the MAT are

presented in Figure 4.16.

Reconstructions of mean July temperature using both WAPLS and the MAT show similar

patterns, though the values reconstructed using WAPLS are somewhat more variable, ranging

from ca. 16-13.5°C, in comparison to the MAT’s ca. 14.5-13°C. Temperatures increase from ca.

14°C (WAPLS) and ca. 13.5°C (MAT) in the beginning of the record to ca. 16°C (WAPLS) and

ca. 14.5°C (MAT) ca. 1300 cal BP, before declining to ca. 14°C (WAPLS) and 13°C (MAT) ca.

1300-1200 cal BP. Temperatures briefly increase once again (WAPLS, ca. 15.5°C; MAT, ca.

14°C) ca. 1200 cal BP, but decline (WAPLS, ca. 13°C; MAT, ca. 13.5°C) after the WRA until

ca. 1100 cal BP. Temperatures then begin to rise gradually until the end of the record. A single-

point decrease to ca. 13°C (from ca. 14°C) occurs at ca. 900 cal BP in the MAT reconstruction,

but does not appear in the WAPLS reconstruction.

No notable long-term trend is apparent in either WAPLS or MAT reconstruction of lake

depth at Spirit Lake. WAPLS reconstructed lake depth values range from ca. 2.2-1.4 m for the

majority of the record, while MAT reconstructed values range from ca. 2.4-1.6 m. Lake depth

decreases immediately prior to the WRA (WAPLS, ca. 2.2 to 1.6 m; MAT, ca. 2.4 to 1.5 m). An

increase in lake depth from ca. 1.6 to 2.6 m ca. 1000-900 cal BP appears in the WAPLS reconstruction, but is not reconstructed by the MAT. SCDs from the MAT remain below the acceptable/non-analogue cut-off (SCD of 24.5) throughout most of the record, only exceeding it

at the end of the record ca. 900 cal BP, with a value of ca. 27.

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4.1.8.2 “Marahbodd” Lake

4.1.8.2.1 Pollen-based

The results of pollen-based temperature and precipitation reconstruction at “Marahbodd” Lake using the MAT are presented in Figure 4.17. Reconstructed mean July temperature shows a slight increase from the beginning of the record to ca. 1350 cal BP, from ca. 8.5 to 10.5°C.

Temperatures decreases once again to ca. 9°C by ca. 1225 cal BP, before increasing substantially at the depth of the WRA to ca. 13°C. Temperatures remain generally elevated until ca. 1075 cal

BP, when they decrease sharply to ca. 6°C at ca. 975 cal BP. Temperatures return briefly to higher values of ca. 10-11°C by ca. 950-900 cal BP, before decreasing sharply again to ca. 6.5°C at ca. 850 cal BP. Temperatures finally increase to ca. 10°C at ca. 800 cal BP, where they remain to the end of the record. Patterns in reconstructed total annual precipitation are generally similar to those of mean July temperature, with gradually increasing values at the beginning of the record (from ca. 500 to 800 mm by ca. 1350 cal BP), followed by gradually decreasing values (to ca. 500 mm) until ca. 1225 cal BP. A period of slightly increased precipitation values of ca. 850 mm, beginning ca. 1200 cal BP, is interrupted by a sharp decrease at the depth of the WRA to ca.

550 mm. Precipitation returns to values ca. 850 mm by ca. 1100 cal BP and remains above ca.

600 mm until ca. 975 cal BP, when values decrease sharply to ca. 300 mm. A single-point increase to a value of ca. 750 mm occurs at ca. 925 cal BP, followed by a return to lower values ca. 400 mm ca. 900 cal BP. Precipitation increases again at the end of the record to a value of ca.

650 mm. SCD values reach just under the acceptable/non-analogue cut-off of 92 at ca. 1075 cal

BP, but remain well below this point for the remainder of the record.

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4.1.8.2.2 Chironomid-based

The results of chironomid-based mean July temperature and lake depth reconstruction at

“Marahbodd” Lake using WAPLS and the MAT are presented in Figure 4.18.

WAPLS reconstruction of mean July temperature suggests generally stable temperatures

before the WRA of ca. 13.5-13°C. There is a slight decrease in temperatures immediately before the WRA at ca. 1225 cal BP to ca. 12.5°C, but temperatures return to ca. 13°C by ca. 1150 cal

BP. Temperatures begin to decline ca. 1100 cal BP, reaching a minimum of ca. 12°C by 1000 cal

BP. This is followed by increasing temperatures for the next ca. 150 years to a maximum of ca.

14.5°C. Temperatures decline again from this time, reaching ca. 13°C by the end of the record.

MAT reconstructed temperatures indicate a gradually decreasing trend from values ca. 14°C to

12°C by the end of the record. Centennial-scale variability is limited, with the exception of a single-point decrease at ca. 850 cal BP to a temperature of 11.5°C (from ca. 13°C), which is followed by an increase to ca. 12°C at the end of the record, in keeping with the long-term trend.

Reconstructions of lake depth at “Marahbodd” Lake using both WAPLS and the MAT show similar trends, though once again the WAPLS curve shows more variability than the MAT reconstruction; lake depth values reconstructed using WAPLS range from ca. 2.5-1.0 m, while those of the MAT range from ca. 2.5-1.5 m. Lake depth increases at the beginning of the record from initial values of ca. 1.2 (WAPLS) and 1.8 m (MAT) to ca. 1.8 (WAPLS) and 2.4 m (MAT) by ca. 1400 cal BP. Reconstructed lake depth remains at these levels until ca. 1200 cal BP, when it decreases once again (WAPLS, ca.1.0 m; MAT, ca. 1.8 m). Lake depth increases at the depth of the WRA to ca. 2.2 (WAPLS) and 2.5 m (MAT). Beginning ca. 1100 cal BP, lake depth begins to follow a cyclic pattern of decreasing and increasing values, which continues to the end of the record. These cycles have a ca. 150 year periodicity. WAPLS-reconstructed lake depth

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ranges from ca. 1.2-2.4 m during this time, while that of the MAT ranges from ca. 1.5-2.4 m.

SCDs exceed the acceptable-non-analogue cut-off of 24.5 below the WRA ca. 1200 cal BP

(SCD=ca. 27.5), at ca. 850 cal BP (SCD=ca. 29.5), and at the end of the record (SCD= ca. 27).

4.2 Terrestrial and aquatic environments at Spirit Lake, YT, 1384-891 cal BP, and “Marahbodd” Lake, NWT, 1488-777 cal BP

4.2.1 Radiocarbon dating

The radiocarbon dates obtained from both Spirit and “Marahbodd” Lakes were determined to be too old when compared to the depth of the WRA in each core and its established age (1147 cal

BP; Clague, et al. 1995). Both sets of radiocarbon dates included organic sediments and aquatic

macrofossils in the absence of sufficient terrestrial macrofossils, and so were likely subject to

hard-water error (HWE). This is likely particularly true of the dates from Spirit Lake, which is a

carbonate marl lake located in predominately limestone bedrock. While the estimated HWE is

substantial in both lakes, such values are not unprecedented. Errors of up to 8000 years have

been found in highly inorganic sediments, for example from Cottonwood Lake, IL, and Lost

Lake, MT (Grimm, et al. 2009). HWEs at a series of other lakes with varying carbonate contents

ranged from 500-2000 years (Grimm, et al. 2009). Karrow and Anderson (1975) have also reported HWEs of 1000-4000 years at a series of marl lakes in southwestern Ontario, while

Deevey et al. (1954) found an HWE of 2200 years at Queechy Lake, NY, located in a region of

limestone bedrock. The method of date correction used to remove the effects of HWE in this study is similar to that used by Bunbury and Gajewski (2013) and Peros and Gajewski (2009).

Correction of the Spirit and “Marahbodd” Lake dates resulted in simple, near-linear age-depth interpolations that minimized the difference between the interpolated ages of the WRA and tops

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of the cores and their accepted/known ages. This suggests that the corrections applied to the

dates are potentially quite reasonable. Dates have been given above in reflection of this,

however, the relatively large errors of the dates themselves, and the large corrections required

nevertheless demand that the dating be considered with extreme caution.

4.2.2 General trends in terrestrial and aquatic environments

4.2.2.1 Spirit Lake

Pollen data from Spirit Lake indicate the presence of a boreal forest environment similar to that

of the modern day at the site throughout the period of record. Long-term decreasing trends in the representation and influx of Alnus and Betula are suggestive of a gradual shift towards drier climatic conditions leading into the Medieval Warm Period (MWP; ca. 1150-700 cal BP).

Centennial-scale (100-yr) variations in the influx of taxa such as Alnus, Juniperus, and Populus,

often showing a negative association to that of Pinus, are also indicative of variability in wet vs.

dry conditions on a centennial-scale. Centennial-scale shifts between wetter and drier conditions

at the site are also visible in the MAT reconstructed record of total annual precipitation. The

overall stability of MAT reconstructed mean July temperature suggests that changes in mean

July air temperature over the course of the record tended to be slight enough to have limited

effect on the vegetation surrounding the lake, though the long-term trend towards slightly

increased temperatures does parallel that of the Loso (2009) temperature anomaly curve. The

results of PCA on the Spirit Lake pollen data also indicate long and short-term trends in

vegetation community composition likely related to patterns in temperature and precipitation.

The one hundred-year cycles between Pinus – a dry-adapted taxon – and Alnus, Betula,

Juniperus, Populus, Shepherdia, and Equisetum – typically more wet-adapted taxa – noted above

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are also visible on Axis 1 of the pollen-based PCA, and once again are suggestive of shifts between dry vs. wet conditions at the site over the course of the record. Slightly warming

climatic conditions are also suggested by Axis 2, which displays a long-term trend towards

increased representation of Picea versus cooler-adapted taxa such as Salix, Artemisia, and

Cyperaceae, and positive association with the Loso (2009) temperature curve. The microcharcoal

record indicates generally stable regional fire frequency over the course of the record, the only

exception being at the time of the WRA.

Proxies for aquatic conditions at Spirit Lake are generally indicative of similar long and short-

term trends as the terrestrial proxies. Axis 2 of the chironomid-based PCA shows a slight long-

term trend towards increased representation of Cladotanytarsus mancus type,

Cyphomella/Harnischia/Paracladopelma, Limnophyes, Polypedilum, and Procladius, relative to

Corynocera ambigua, Dicrotendipes, Parakeifferiella sp. B, Stempellina, and Stichtochironomus,

and generally positive association with the Loso (2009) curve, suggesting a slight change in the

chironomid community in response to long-term increases in regional temperature. Many of

these taxa have similar environmental tolerances (warmer, shallower, and/or plant-associated),

however, implying that these changes were limited. Limited indication of any long-term trend in

temperature in the results of WAPLS and MAT reconstruction also suggests that long-term

increases in temperature were slight enough to have had little effect on the chironomid

community, though WAPLS estimated mean July temperatures do display an increasing trend

near the end of the record. SCDs are elevated at this time, however, and so the results of the

reconstruction should be interpreted with caution at these levels. Total chironomid influx

decreased gradually over the course of the record, suggesting gradually decreasing lake

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productivity associating with gradually drying conditions as inferred from the pollen data.

Increased influx of shallow water chironomid taxa such as Polypedilum and Limnophyes is also suggestive of gradually decreasing water depth over the course of the record, while increased

relative abundance of resistant, generalist, and low-pH tolerant taxa such as Chironomus and

Tanytarsina – other suggests gradually harshening environmental conditions and potentially

increased lake water acidity (Brooks 1997; Brooks, et al. 2007; Olander, et al. 1999). In

combination, these data are suggestive of gradually drying conditions leading to lower lake

depth, decreased lake productivity, and changes in lake conditions and chemistry. Total

chironomid influx varies on a 100-year cycle that parallels patterns apparent in the pollen data,

suggesting that centennial-scale variability in wet vs. dry conditions played a role in influencing

within-lake productivity. Periods of wetter conditions as indicated by the pollen data tend to

correspond with periods of increased lake productivity in these cycles. Relative abundances of

chironomid taxa and Axis 1 of the chironomid-based PCA also suggest gradually drying

conditions with superimposed centennial-scale variability between drier and wetter conditions,

represented by increased abundances of Cryptochironomus, Paratendipes, Polypedilum,

Tanytarsina – other, Limnophyes, and Pseudosmittia/Smittia, and Dicrotendipes, Sergentia,

Psectrocladius undiff., and Procladius, respectively. Larvae of Cryptochironomus, Polypedilum,

Limnophyes, and Pseudosmittia/Smittia are all typical of shallow water or even terrestrial

environments, while Procladius and Sergentia are generalists or are more typical of deeper

water, suggesting that drier conditions also corresponded to periods of reduced lake depth.

Limited variability in lake depth captured by WAPLS and MAT reconstruction suggests that

these variations were slight. Centennial-scale patterns in sediment organic content are also

visible, with periods of higher organic content suggestive of increased overall productivity

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within the catchment generally associated with periods of wetter conditions and increased

chironomid-inferred within-lake productivity and lake depth. Centennial-scale variability in

mean July temperature is captured by Axis 2 of the chironomid-based PCA and by chironomid-

based WAPLS and MAT reconstruction, which was less clear in the pollen data. Shifts between

cooler and warmer conditions do not occur synchronously with variability in wet vs. dry

conditions, resulting in periods of wetter conditions and low temperature, drier conditions and

high temperature, wetter conditions and high temperature, and drier conditions and low

temperature. Highest within-lake and general catchment productivities as indicated by the

chironomid and sediment organic content data were reached during periods of wetter conditions

and higher temperature, while times of lowest productivity occurred during periods of drier

conditions and higher temperature. Periods of wetter conditions and low temperature, and drier

conditions and low temperature fell in between, with periods of wetter conditions and low

temperature corresponding with slightly higher productivity. This suggests that variability in wet

vs. dry conditions played a more important role in determining productivity than did

temperature; given the dry climate of the study region, the influence of variability in wet vs. dry

conditions on productivity is unsurprising.

Indications of generally stable environmental conditions at Spirit Lake with a slight long-term

trend towards gradually warming and drying conditions are consistent with previous work.

Pollen studies from central and southern Yukon indicate the presence of boreal forest on the

landscape for the last ca. 10,000 years, with only slight spatial and temporal variability

(Gajewski, et al. 2014). Slightly warming/drying conditions after ca. 1300 BP are suggested by increases in the relative abundance of herbaceous taxa relative to Picea mariana and Alnus at

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Two Horsemen Pond and Long Last Lake, YT (Keenan and Cwynar 1992). Bunbury and

Gajewski (2012) also reconstruct gradually warming conditions with increased centennial-scale

variability at Jenny Lake, YT, leading into the MWP. Anderson, Abbot, Finney and Burns

(2005), Anderson, Abbott, Finney and Edwards (2005), and Anderson et al. (2007) reconstruct a

stronger/more easterly Aleutian Low (AL) since ca. 1200 cal BP at “Jellybean” and Marcella

Lakes, YT, leading to drier conditions in southwest Yukon as rainout is enhanced on the

windward side of the mountains and at higher elevations. Increased fire frequency during the

MWP has also been suggested by Yalcin et al. (2006) from records from the Eclipse Icefield.

Centennial-scale variability in wet vs. dry conditions at low elevations has been noted by

Anderson et al. (2011) at Marcella and Seven Mile Lakes, YT, in the years after the WRA, lasting until ca. 350 cal BP. The authors note that periods of drier conditions at the lakes are typically associated with periods of glacial advance in the St. Elias Mountains, and suggest that these patterns might be related to short-term variations in the strength and position of the AL over time. Though the dates of Anderson et al.’s (2011) study only slightly overlap with the

Spirit Lake record, the period that does suggests a positive association between patterns of drier vs. wetter conditions inferred by Anderson et al. (2011) and those inferred from the Spirit Lake data, making it possible that this same mechanism is responsible for the centennial-scale patterns in wetter vs. drier conditions observed at Spirit Lake.

4.2.2.2 “Marahbodd” Lake

The pollen data from “Marahbodd” Lake suggest the presence of Betula-Artemisia shrub tundra

at the site with nearby Picea-dominated boreal forest throughout the period of record. A long-

term trend in total influx and also apparent on Axes 1 and 2 of the pollen-based PCA from

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“Marahbodd” Lake suggests gradually increasing terrestrial productivity over the course of the

record, with gradually increasing Alnus, Betula, Salix, and Artemisia, and decreasing Picea, suggestive of gradually opening vegetation, and wetter conditions and/or decreasing temperatures. Patterns on Axis 1 of the PCA and in AP:NAP also indicate the presence of a ca.

200-year cycle between increased AP vs. NAP, with increased AP represented by lower loadings and higher abundance of Alnus, Betula, Salix, Artemisia, and Sphagnum, and NAP by higher loadings and abundance of Polypodiaceae, Cyperaceae, and Dryas. Typical preferences of these taxa suggest that periods of increased AP may be representative of wetter and/or warmer climatic conditions, and the 200-year cycle of a pattern of centennial-scale cyclic variability in wet vs. dry conditions and/or temperature at the site superimposed over the long-term trend. Both the long-term and centennial-scale climatic variations appear to have been minor, however, and are not captured in the pollen-based climate reconstructions. Patterns in microcharcoal also identify a long-term gradual decrease in fire frequency that corresponds with the long-term trend in the pollen record towards wetter/cooler conditions, and a superimposed ca. 200-year cycle between periods of higher and lower incidence of fire, in which periods of higher fire frequency approximately correspond to periods of wetter and/or warmer conditions inferred from the pollen. Increased fire frequency may be associated with increased availability of fuel under wetter and/or warmer conditions, when AP was increased.

Proxies for aquatic conditions at “Marahbodd” Lake also indicate a pattern of centennial-scale climatic variability with a periodicity of ca. 200-300 years. Periods of increased sediment organic content, suggestive of increased catchment productivity, correspond to periods of increased carbonate and decreased silicate content, suggesting calm, shallow water, and perhaps

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decreased landscape instability and erosion. These phases last ca. 100-150 years before

tendencies reverse to become indicative instead of conditions of decreased catchment

productivity, deeper water, and increased landscape instability/erosion/lake turbidity. These alternate phases last for ca. 100-150 years before returning to previous conditions once again, and this pattern continues for the duration of the record. Periods of increased organic and carbonate content also correspond to periods of higher total chironomid influx (further suggesting increased within-lake productivity during these phases), and to higher influx and abundance of shallow water chironomid taxa such as Corynocera ambigua, while the influx of generalist and deeper water taxa such as Paratanytarsus and the various Tanytarsina declines at these times (further suggesting calm, shallow water). Conversely, total influx and the influx and

abundance of shallow water chironomid taxa is reduced during periods of reduced sediment

organic and carbonate content and increased silicate content, while the influx of generalist and deeper water taxa such as Paratanytarsus and the various Tanytarsina increases, again suggesting decreased catchment and within-lake productivity, deeper water, and increased landscape instability/erosion/lake water turbidity during these alternate phases. Sample loadings on Axis 2 of the chironomid-based PCA are generally negative during higher productivity/shallow water periods, indicating increased abundance of negatively-loaded

Dicrotendipes and Glyptotendipes – both typically plant-associated and/or found in shallow

water – while several generalist and deeper water taxa such as Chironomus and Sergentia are heavily positively loaded, indicating reduced abundance during these times. These trends once again support the presence of alternating periods of increased general catchment and within-lake productivity and shallow water versus lower productivity and deeper water at the site over the course of the record. Chironomid-based lake depth reconstructions also reconstruct somewhat

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lower water depths during periods of increased organic content, carbonate content, total

chironomid influx, and influx and abundance of Corynocera ambigua, and decreased silicate

content and loadings on Axis 2 of the PCA, and higher water depths when these are reversed. It

is likely that higher productivity/shallow water periods also corresponded to periods of higher

water pH, suggested by increased carbonate content and decreased abundance of low pH-

resistant taxa such as Chironomus and Sergentia during these times, while lower

productivity/deeper water periods correspond to periods of decreased pH. Periods of lower lake

depth and increased productivity correspond well to periods of wetter and/or warmer conditions, increased AP, and increased fire activity inferred from the pollen and microcharcoal. General

stability of the chironomid-based temperature reconstruction from “Marahbodd” Lake suggests that centennial-scale variations in regional temperature were generally slight enough to have had

limited effect on the chironomid community, particularly in comparison to variations in water depth. A long-term trend towards increased abundance of Corynocera ambigua at the expense of

a number of other taxa, such as Microtendipes, Parachironomus, Pseudochironomus,

Tanytarsina – other, and Paracladius, appears in Axis 1 of the PCA, but appears to have had

little influence on either the temperature or depth reconstructions, suggesting that changes in neither temperature nor depth played a role in this change; in fact, with the exception of generalist Tanytarsina – other, all of these taxa are typical of shallow water environments. A possible explanation is that Corynocera ambigua was a relatively new introduction to the lake environment at the start of the record, where it originally appeared at relatively low abundances, but was able to gain a foothold and out-compete previously established taxa within the lake once it had arrived. A period of particularly increased general catchment and within-lake productivity appears to have occurred ca. 1325 cal BP, lasting for approximately 50 years. Higher sediment

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organic content and total chironomid influx, and particularly low lake depth is apparent at

“Marahbodd” Lake at this time. This period corresponds to a period of increased temperatures in

the MacDonald et al. (2009) curve, suggesting that these warmer temperatures might have played

a role in producing this period of enhanced productivity. Kaislahti Tillman et al. (2010) have also

reconstructed a period of high temperatures ca. 1300 cal BP at Selwyn and Misaw Lakes, NWT,

based on the analysis of stable carbon isotope ratios derived from peat profiles. The authors

suggest that these increased temperatures might have been related to briefly influence of more

southerly air-masses. If this is the case, it is possible that the effects of these southern air-masses were responsible for the increase in overall productivity at “Marahbodd” Lake at approximately this time.

Indications of generally stable environmental conditions at “Marahbodd” Lake with a slight long-term trend towards wetter and/or cooler conditions are consistent with previous work done in the region. At Natla Bog, located ca. 15 km to the east of “Marahbodd” Lake in the central

Selwyn Mountains, NWT, MacDonald (1983) notes decreased total pollen production – particularly of Picea – beginning ca. 5400 BP, while Alnus and Ericales increase slightly – all

suggestive of the development of gradually cooler and wetter conditions after this time. Szeicz et

al. (1995) also infer cooling conditions at this time from gradually decreasing representation of

Picea at Andy and Keele Lakes in the central Mackenzie Mountains, NWT. Increased

representation of Alnus and Cyperaceae at Andy Lake, and a shift from Picea mariana to Picea

glauca at Bell’s Lake, central Mackenzie Mountains, NWT, beginning ca. 5000 BP, are similarly interpreted (Szeicz, et al. 1995). Increases in the representation of Alnus, as well as tree-form

Betula neoalaskana at Lac Mélèze, also in the central Mackenzie Mountains, NWT, and at

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several sites in the Doll Creek area, northern YT, also suggest the development of gradually

wetter conditions as of ca. 6000 BP (MacDonald 1987; Ritchie 1982). On the Tuktoyaktuk

Peninsula, NWT, Ritchie and Hare (1971) reconstruct the replacement of shrub-forest tundra

with Betula-Salix shrub tundra beginning ca. 4000 BP and lasting until the present, further

suggesting cooling conditions in the region. Spear (1993) also reconstructs gradually cooler and

wetter conditions at Reindeer Lake, Sleet Lake, and Bluffer’s Pingo in the Tuktoyaktuk

Peninsula, starting ca. 3500-3000 BP. Gradual increases in total pollen influx and decreases in

microcharcoal influx at “Marahbodd” Lake are likely related more to the gradual development of

wetter conditions, leading to enhanced productivity and decreased fire frequency, than to long- term decreases in temperature, which would more likely decrease overall productivity.

Subordinate to long-term trends in temperature, centennial-scale variations in AP:NAP,

fire, sediment organic, carbonate, and silicate content, and chironomid community composition

and productivity at “Marahbodd” Lake suggest alternating periods of warmer and cooler

temperatures, with warmer temperatures associated with increased AP, fire, and productivity, and decreased lake depth. The alternative that these centennial-scale variations might be reflective of variations between wetter and drier conditions presents a less parsimonious interpretation, wherein wetter conditions would be associated with increased AP and productivity, but also with increased fire, and decreased lake depth. Increased within-lake

productivity during warmer time periods might be related to these warmer temperatures directly, and/or to decreased lake depths at these times, allowing increased light penetration (Wetzel

2001). Centennial-scale variations in temperature, however, appear to have had little effect on chironomid community structure; instead, the taxonomic composition of the chironomid community at “Marahbodd” Lake appears to have been closely tied to variations in lake depth.

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This is indicated by the general stability of the MAT and WAPLS temperature reconstructions, and the variability of WAPLS reconstructions of lake depth. Centennial-scale cycles in temperature of ca. 200-300 years have been noted in palaeoclimatic studies from the Seymour-

Belize Inlet Complex of British Columbia and central Northwest Territories, and have been associated with the deVries solar cycle (Galloway, et al. 2013; Prokoph, et al. 2011). The deVries cycle is considered to be one of the most climatically influential cycles of solar variation during the Holocene, and provides a possible explanation for the centennial-scale warmer/cooler climatic cycles observed at “Marahbodd” Lake (Raspopov, et al. 2008).

4.2.3 Terrestrial and aquatic responses to the WRA

4.2.3.1 Spirit Lake

Axis 3 of the pollen-based PCA suggests a substantial impact of the WRA on the vegetation surrounding Spirit Lake, with increased abundances of Betula, Salix, Artemisia, and Cyperaceae lasting for approximately 50 years. These conditions are noticeably different from those typical of both before and after the ash, characterized by increased abundance particularly of Pinus, with comparable conditions occurring only for very brief periods at the very beginning and end of the record, corresponding to particularly dry periods in the region’s centennial-scale climate cycle, visible on Axis 1 (see section 4.2.2.1). The degree of difference from the general trend of the axis is lesser in these early and late periods than at the depth of the WRA. Total and taxon- specific pollen influx decreased sharply at the immediate depth of the ash, suggesting a strong immediate impact in the form of substantially reduced vegetation productivity overall, largely as a result of reductions to the productivity of particular important taxa, such as Alnus, Betula,

Juniperus, Picea, Pinus, and Populus. These reductions were generally rapid, often occurring in

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the midst of otherwise high influxes of these taxa, and often reaching values equal or lower to any other point in the record. A brief and substantial increase in fire activity also occurred at the depth of the WRA, with a rapid return to pre-ash conditions within 50 years. Lasting impacts of the WRA on the vegetation community are suggested by particularly low AP:NAP ratios and relative abundance and influx of Pinus after the WRA, which lasted for approximately 100 years.

These low AP:NAP ratio values slightly exceeded those of any other time in the record, while the only other occurrence of such low values of Pinus is a single-point decrease ca. 950 cal BP surrounded by higher values; while being a single point does not necessarily invalidate this low value (Pinus populations may have been reduced because of disease, for example), the significance of the point should be interpreted with caution. The substantial decrease in both reconstructed mean July temperature and reconstructed total annual precipitation at the depth of the WRA is likely attributable to the direct effects of the ash resulting in changes to the vegetation community composition that mimicked those which might have been caused by reductions in temperature and precipitation, rather than to any actual notable climatic changes – though it is possible that climatic effects resulting from the eruption did play a role in the vegetation changes that occurred at this time.

Evidence suggests that the WRA had a noticeable impact on the aquatic environment of Spirit

Lake. Sediment carbonate content was substantially reduced at the WRA in favour of increased silicate content for ca. 50 years, suggesting disturbed conditions within the lake, and/or increased terrestrial landscape instability and erosion. The chironomid community experienced some noticeable longer-term changes, characterized by an overall decline in productivity lasting ca.

100 years, and considerable declines in the influx of most taxa. These declines occurred rapidly

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at the immediate depth of the ash, often in the midst of extended periods of higher influx,

suggesting that the deposition of the WRA was the likely cause of these changes. This rapidity

makes the community changes that occurred at the time of the WRA noteworthy at least in this

respect compared to the remainder of the record. Declines often also exceeded the range of

variability present in any other prortion of the record and/or lasted longer than other comparable

decreases, further supporting the uniqueness of the impacts of the ash on the aquatic community.

After the deposition of the ash, the lake environment gradually recovered, first with increased

influx and relative abundance of a few resistant, generalist taxa – namely Micropsectra,

Paratanytarsus, and Tanytarsina group C – in the initial ca. 25 years after the deposition of the ash. This was followed by the gradual resurgence of other taxa, dominated by generalist and shallow water taxa such as various Tanytarsina, Parakeifferiella sp. B, Procladius, and

Cricotopus/Orthocladius ca. 50 years after the eruption, and Sergentia, Polypedilum, and

Paratendipes within ca. 75-150 years. These taxa all rise rapidly to peaks in influx that match or exceed any other point in the record immediately after their re-introduction, before declining equally rapidly to at or near their pre-ash levels. Few long-term changes in the chironomid community are apparent in the post-ash data. The most notable change that occurred was increased influx and relative abundance of Polypedilum (often plant-associated) and

Paratendipes (generalist), which both were near-absent from the community prior to the deposition of the ash. It is unlikely, however, that the increased influx of these two taxa is indicative of any substantial change in the lake environment, as other taxa with similar habitat preferences were present prior to their increase (e.g. generalist

Cyphomella/Harnischia/Paracladopelma, Procladius, Tanytarsus chinyensis, and T. lugens, and plant and/or shallow water-associated Dicrotendipes and Glyptotendipes). It is instead more

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likely that Polypedilum and Paratendipes took advantage of the niche space temporarily vacated

by other taxa after the ash, and managed to establish populations within the lake.

4.2.3.2 “Marahbodd” Lake

Axes 1, 2, 3, and 5 of the pollen-based PCA from “Marahbodd” Lake indicate a noteworthy impact of the WRA on the vegetation surrounding the site, primarily in the form of increased representation of herbaceous taxa, ferns, and mosses relative to shrub taxa, lasting up to 200 years, and somewhat increased variability of community composition to the end of the record.

Polypodiaceae increased substantially in both influx and relative abundance beginning immediately after the WRA and peaking ca. 75 years after the ash. This was shortly followed by a large and brief peak in Cyperaceae ca. 125 years after the ash. After ca. 200 years, both

Polypodiaceae and Cyperaceae returned to approximately pre-ash levels, while taxa that had decreased in influx after the WRA also returned to at or near their pre-ash levels in most cases, and the vegetation community returned to approximately pre-ash conditions. Noticeably increased influx and representation of Pinus beginning ca. 100 years post-ash is likely indicative of increased representation of long-distance pollen resulting from both reduced productivity of the landscape post-ash, and from the long-term trend towards more open vegetation cover discussed above (see section 4.2.2.2). Increases particularly in Polypodiacedceae and decreases particularly in Alnus and Betula occurred rapidly after the deposition of the ash (and returned

equally rapidly to at or near pre-ash levels on their recovery), reached values that exceeded those

of any other time in the record, and remained at these levels for an extended period of time,

making the post-ash conditions unique over the period of the reconstruction. Increased variability in vegetation community composition post-ash is also suggested by the pollen-based climate

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reconstructions, which appear to show increased climatic variability after the ash, but it is

perhaps more likely that this is not representative of climate patterns, but rather of changes in the

vegetation community post-ash towards inceased representation of herbaceous, fern, and moss

taxa, which mimicked those which might have been caused by reductions in temperature and

precipitation. The limited similarity of the pollen-based climate reconstructions to the

MacDonald et al. (2009) temperature curve supports this interpretation. Rapid and substantial

decreases occur in the influxes of many taxa at and after the WRA, which exceed the variability of any other point in the record in either degree, duration, or both, in some cases lasting for up to ca. 200 years, suggesting a considerable reduction in the productivity and diversity of the vegetation at the site after the WRA which lasted for some time. Fire frequency decreases to some of its lowest values of the record in the years after the WRA, for a period of approximately

100 years. This reduction corresponds to decreases in total and taxon-specific influxes of a number of pollen taxa – including Picea, Pinus, Alnus, Betula, Juniperus, Populus, Salix,

Artemisia, and Cyperaceae – after the WRA, suggesting that this low fire frequency may simply have been a result of limited fuel due to reduced vegetation productivity after the deposition of the ash.

The influence of the ash on chironomid community structure within “Marahbodd” Lake appears on Axes 2, 3, and 4 of the PCA, lasting ca. 100 years. Indications of this influence are slight, however, suggesting that chironomid community changes as a result of the ash were minor in degree, though recovery took some time. The temperature and lake depth reconstructions using both the MAT and WAPLS also show no noteworthy changes at the depth of the WRA, further suggesting limited impact of the ash on chironomid community structure. Elevated relative

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abundances of resistant Tanytarsina group C and Paratanytarsus at the depth of the ash are

indicative, however, of at least some disturbance to the chironomid community, as are rapid,

substantial, and extended decreases in total chironomid influx and the taxon-specific influxes of

a number of taxa for a period of ca. 100 years following the WRA, which generally exceed the

variability of any other point in the record on at least one (and often multiple) of these points.

Sediment organic content also decreased to some of its lowest values for the record and for an

extended period of time (ca. 100 years) post-ash, suggesting generally decreased catchment

productivity that endured for a particularly long time, though limited disruption to chironomid

community structure and productivity suggests that decreased sediment organic content in the

“Marahbodd” Lake core may be reflective more of decreased terrestrial rather than aquatic productivity as a result of the WRA. Carbonate content also decreased to its lowesat values of

the record for a period of ca. 100 years post-ash – a longer duration than any other decline that

occurred – and silicate content increased to its highest values of the record, again for a extended

period (ca. 150 years), suggesting continued landscape disturbance and perhaps increased

erosion long after the deposition of the ash itself that was unique compared to the the remainder of the period of record. Patterns in magnetic susceptibility are also indicative of disturbed conditions within and/or surrounding the site and of increased minerogenic inputs after the WRA

lasting ca. 100 years.

4.2.3.3 Discussion

Studies of volcanic ash effects on terrestrial and aquatic environments have shown substantial

variability in the kind and degree of ash impacts, and in the lengths of time taken for recovery,

which may range from only a few years to many centuries (e.g. Abella 1988; Baillie and Munro

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1988; Beierle and Smith 1998; Bennett, et al. 2001; Birks 1980; Blinman, et al. 1979; Bradbury,

et al. 2004; Bunbury and Gajewski 2013; Crowley, et al. 1994; D'Arrigo and Jacoby 1999;

Heinrichs, et al. 1999; Hickman and Reasoner 1994; Hickman, et al. 1984; LaMarche Jr and

Hirschboeck 1984; Long, et al. 2011; Long, et al. 2014; Mack, et al. 1983; Mehringer, et al.

1977; Minckley, et al. 2007; Power, et al. 2011; Scuderi 1990; Seymour, et al. 1983; Slater 1985;

Zoltai 1988). This great variability is not only related to variations in ash thickness, composition,

and season of deposition, but also to the physical, chemical, and biological conditions of a site’s

environment prior to ash deposition. Complex interactions between all of these factors will influence both the ability of terrestrial and aquatic environments to buffer the effects of volcanic ash deposition and their ability to recover, resulting in the wide range and duration of impacts that may be seen. Comparison of the environmental responses of sites across the fallout zone of a volcanic ash layer provides the only method of identifying general trends.

Previous study of the palaeoenvironmental impacts of the WRA in southwest Yukon by Bunbury and Gajewski (2013) has demonstrated varying kinds, degrees, and durations of environmental responses to the ash in aquatic environments. Four sites were examined by the authors: two with thick layers of ash (tens of cms) and two with thin (less than 1 cm). In each category, one site was located in alpine tundra, while the other was located in the boreal forest. Aquatic responses to the WRA were determined through the analysis of biogenic silica and chironomid head capsules. Ash impacts were found to be greatest in both degree and duration at sites with thicker ash layers, regardless of environment, while the kind of response which occurred varied dependent on the precise characteristics of each lake and its surroundings. At Donjek Kettle

(thick ash layer – 44 cm), located in the alpine tundra, primary production was found to increase

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after the ash, while chironomid production decreased and community structure altered to show

increased abundances of low pH and/or ash-resistant taxa such as Chironomus, Sergentia, and

Tanytarsina – other. Increased primary productivity was attributed to an increase in Si:P after the

WRA, which contributed to an increase in diatom concentrations. At Lake WP02 (thick ash layer

– exact cms unknown), located in the boreal forest, both primary production and chironomid

community productivity decreased after the ash. Decreased pH was once again inferred based on

increased relative abundance of Tanytarsina – other and Olivideria/Hydrobaenus. Short-term ash

impacts on the aquatic environment were found to last ca. 60 years, with longer-term impacts

lasting an additional ca. 40 years. At sites with thin ash layers, aquatic responses to the ash were

absent or negligible, with no impact at all observed at Upper Fly Lake (alpine tundra, 0.1 cm

ash), and only limited change observed at Jenny Lake (boreal forest, 0.3 cm ash), with decreases in productivity and changed chironomid community structure lasting ca. 20 years.

Aquatic responses to the WRA at Spirit and “Marahbodd” Lakes compare well with those

of Bunbury and Gajewski (2013), suggesting decreased lake productivity in both cases, and

recovery times of ca. 100 years. As might be suggested by Bunbury and Gajewski’s (2013)

results, the degree of aquatic response to the WRA was also lesser at “Marahbodd” Lake, at a

greater distance to the vent and with a thinner ash layer than Spirit Lake. Chironomid taxa found

at increased abundances after the ash were similar in both study lakes (Tanytarsina group C and

Paratanytarsus), though chironomid community composition within the lakes diverged

thereafter as they recovered. Increased landscape instability and erosion after the WRA at both

sites is also suggested by patterns in magnetic susceptibility and sediment carbonate and silicate content.

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Responses of terrestrial vegetation communities to the deposition of volcanic ash may also be

quite variable in kind, degree, and duration. Plant colonization after the WRA at Gull Lake, YT,

began with the development of Cyperaceae-dominated herbaceous tundra. This was followed

within ca. 200 years by Alnus-Betula-Salix shrub tundra, which persisted for another ca. 200

years, after which the shrub tundra communities were finally replaced by open Picea glauca

forest typical of the region today (Birks 1980). Alternatively, results of palynological analysis

from Eildun Lake, NWT, show brief increases in the relative abundance of Picea, Cyperaceae,

and Sphagnum at the depth of the WRA (0.7 cm thick), and coincident decreases in Betula and

Alnus (Slater 1985). These changes are accompanied by decreased pollen concentrations and

sediment organic content, however conditions return to previous very rapidly (within ca. 5 cm,

corresponding to ca. 15 14C years). The author does not delve deeply into the examination of these effects, except to note that coniferous taxa have been found to be more susceptible to the impacts of volcanic ash than deciduous taxa (Slater 1985, citing Malde 1964). Reduced growth rates in Abies have also been observed as a result of the eruption of Mount St. Helens (Seymour,

et al. 1983). Ash on branches and needles was observed to form a crust, changing the geometry

of the needles and resulting in increased boundary layer thickness, causing increased heat loads

as the needles’ capacity for energy exchange was reduced, and leading to needle mortality and

reduced photosynthetic ability (Seymour, et al. 1983). Decreased growth rates in both coniferous

and deciduous plant taxa have also been related to climatic changes resulting from decreases in incoming solar radiation caused by increased concentrations stratospheric sulphuric aerosols and

fine ash particles from volcanic eruptions (Baillie and Munro 1988; D'Arrigo and Jacoby 1999;

LaMarche Jr and Hirschboeck 1984; Scuderi 1990).

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Terrestrial responses to the WRA at both Spirit and “Marahbodd” Lakes were generally

more substantial in kind, degree, and duration, than those of the aquatic environments of the

study lakes. Responses were not the same between the two sites, and showed both similarities

and differences to previous studies. Vegetation communities at both sites showed decreased productivity in the years after the WRA, however changes to the vegetation community were

somewhat more dramatic at Spirit Lake, located within the boreal forest, with noticeably

decreased representation and/or influx of many deciduous tree and coniferous tree and shrub taxa

– particularly Pinus – and increases in certain other shrub and herbaceous taxa such as Salix,

Artemisia, and Cyperaceae. At “Marahbodd” Lake, located in shrub tundra, changes to the vegetation community were rather less dramatic, showing noticeable but lesser reductions in

shrub taxa, and increases in herbaceous taxa, ferns, and mosses. Increased susceptibility of

coniferous taxa to damage from volcanic ash compared to deciduous taxa, as suggested by Malde

(1964) and observed by Slater (1985) and Seymour et al. (1983), might help to account for the

decreases in coniferous taxa such as Pinus, which may be observed in the Spirit Lake record. At

both sites, the immediate damage to deciduous plant taxa would also have been reduced as a

result of the eruption’s having occurred in winter, when these taxa would have been dormant,

while coniferous taxa would likely have suffered more substantial effects as a result of ash

damage to needles. Changes to vegetation community composition and productivity lasted longer

at “Marahbodd” Lake than at Spirit Lake (ca. 200 years at “Marahbodd” Lake, versus ca. 50-100

years at Spirit Lake), however, despite their lesser degree, suggesting that the harsher

environmental conditions of the tundra at “Marahbodd” Lake might have slowed the pace of

recovery. The response of the regional fire regimes also differed between the sites, showing a

brief increase at Spirit Lake, and a more extended decrease at “Marahbodd” Lake. It is possible

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that increased mortality of coniferous taxa such as Pinus at Spirit Lake resulted in increased

incidence of fire as a result of their high abundance at the site and generally high combustibility.

Were this the case, a large, brief peak in fire activity would be observed until the fuel load was reduced to its previous state, much as is seen in the Spirit Lake microcharcoal record. Volcanic eruptions also often bring increased lightning activity, providing a possible ignition source, however lightning strikes also account for the majority of naturally-started fires in southern

Yukon in the absence of volcanic activity, making it difficult to determine whether increased

lightning strikes as a result of the eruption were indeed a factor in the fires. Decreased fire

activity after the WRA at “Marahbodd” Lake occurred within a period of already lowered fire

frequency, resulting in particularly low microcharcoal influx for a period of ca. 100 years.

Centennial-scale cycles in fire at the site have been linked above to periods of decreased

AP:NAP, and cooler conditions, potentially related to variations in solar activity (see section

4.2.2.2). These conditions likely resulted in a decreased fuel load at the site, reducing the

incidence of fire during these cool periods. Reduced terrestrial productivity as a result of the

WRA potentially caused even further reductions to the fuel load, possibly accounting for the

especially decreased fire frequency at the site in the decades after the WRA.

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Table 4.1 AMS radiocarbon ages from Spirit Lake, YT. The depth of the WRA in the core is also given, along with its established age (from Clague, et al. 1995), as is the depth and age of the top of the core. Calibration was performed using OxCal 4.2 and the IntCal13 calibration curve (Bronk Ramsey 2009; Reimer, et al. 2013). The AMS date from 62-64cm depth was not used in the construction of the core chronology. Please see the text for details. Mean Conventional cal BP cal BP Relative area Depth Lab code cal ± 2σ Corrected Source of date depth radiocarbon age ± 2σ 2σ under calibrated (cm) (UCIAMS-) BP error cal BP* (cm) BP lower upper age curve top of core 0-1 0.5 -59 terrestrial & aquatic 47-49 48 136468 4400 15 5040 4995 0.287 4957 82 381 plant parts, 4986 4877 0.667 chironomids terrestrial & aquatic 62-64 63 150840 3970 25 4523 4461 0.455 4460 82 plant parts, 4456 4406 0.493 chironomids 4367 4360 0.006 WRA (Clague et al. 109 80-81 80.5 1147 1995) 133 126 terrestrial & aquatic 91-93 92 136465 5250 15 6172 6160 0.036 5997 117 1420 plant parts, 6107 6083 0.094 chironomids 6018 5938 0.824 terrestrial & aquatic 108- plant parts, 108.5 150841 5615 25 6446 6316 0.954 6381 65 1805 109 chironomids * Correction factor =

4576.395 cal yrs

Table 4.2 AMS radiocarbon ages from “Marahbodd” Lake, NWT. The depth of the WRA in the core is also given, along with its established age (from Clague, et al. 1995), as is the depth and age of the top of the core. Calibration was performed using OxCal 4.2 and the IntCal13 calibration curve (Bronk Ramsey 2009; Reimer, et al. 2013). The AMS dates from 4-7cm depth and 36-38cm depth were not used in the construction of the core chronology. Please see the text for details. Mean Conventional cal BP cal BP Relative area Depth Lab code cal ± 2σ Corrected Source of date depth radiocarbon age ± 2σ 2σ under calibrated (cm) (UCIAMS-) BP error cal BP* (cm) BP lower upper age curve top of core 0-1 0.5 -63 terrestrial & aquatic plant parts, 4-7 5.5 150839 25070 160 29511 28736 0.954 29124 388 chironomids terrestrial & aquatic 9-12 10.5 136470 1215 40 2635 2844 0.945 2741 127 643 plant parts, 2881 2888 0.009 chironomids WRA (Clague et al. 109 23-25 24 1147 1995) 133

127 terrestrial & aquatic 36-38 37 136459 2550 100 2844 2823 0.015 2582 244 plant parts, 2800 2356 0.939 chironomids terrestrial & aquatic plant parts, 40-44 42 136467 3605 15 3974 3861 0.954 3918 57 1819 chironomids * Correction factor

= 2098.172 cal yrs

Table 4.3 Eigenvalues from PCA on a) pollen percentages; b) chironomid percentages from Spirit Lake, YT. a) Axis Eigenvalue b) Axis Eigenvalue Axis 1 0.171 Axis 1 0.252 Axis 2 0.140 Axis 2 0.169 Axis 3 0.122 Axis 3 0.133 Axis 4 0.117 Axis 4 0.124 Axis 5 0.081 Axis 5 0.084

Table 4.4 Eigenvalues from PCA on a) pollen percentages; b) chironomid percentages from “Marahbodd” Lake, NWT. a) Axis Eigenvalue b) Axis Eigenvalue Axis 1 0.132 Axis 1 0.187 Axis 2 0.129 Axis 2 0.164 Axis 3 0.111 Axis 3 0.119 Axis 4 0.097 Axis 4 0.112 Axis 5 0.084 Axis 5 0.093 128

Table 4.5 Species scores from PCA on a) pollen percentages; b) chironomid percentages from Spirit Lake, YT. Axis Axis Axis Axis Axis a) Taxon Axis 1 Axis 2 Axis 3 Axis 4 Axis 5 b) Taxon 1 2 3 4 5 Alnus 1.139 -0.522 -0.743 0.983 0.501 Chironomus 0.032 0.994 -1.747 -0.294 -1.804 Betula 1.278 0.274 1.664 0.247 0.213 Cladopelma -0.659 0.109 0.388 0.669 -1.431 Corylus 0.892 1.794 0.339 -0.070 0.566 Cryptochironomus 1.896 -0.926 0.732 0.375 0.220 Juniperus 1.753 0.041 -0.109 -0.925 -0.049 Cyphomella/Harnischia/Paracladopelma -0.261 1.128 0.257 1.538 1.068 Picea -0.283 2.034 0.368 0.322 -0.680 Dicrotendipes -1.047 -1.388 -0.336 1.520 -0.210 Pinus -1.287 -0.592 -1.540 0.529 0.515 Glyptotendipes -0.721 -0.611 -1.341 -0.936 1.232 Populus 1.670 0.425 0.401 -0.785 -0.268 Pagastiella 0.245 -0.514 0.015 2.573 -0.705 Salix 0.396 -1.323 1.265 1.038 0.250 Parachironomus -0.696 0.204 0.044 2.180 -0.867 Shepherdia 1.104 -0.750 -0.920 0.193 -1.944 Paratendipes 1.998 0.848 0.369 -0.144 -0.222 Artemisia 0.006 -1.041 1.395 1.202 -0.296 Polypedilum 1.265 1.180 0.340 -0.065 -0.628 Cyperaceae 0.316 -1.325 1.673 -0.161 1.226 Sergentia -1.009 0.949 -1.517 0.041 0.682 Ericaceae 0.682 1.510 -0.148 -0.211 1.747 Stichtochironomus undiff. 0.898 -1.004 -0.918 1.010 1.892 Poaceae -0.304 -0.694 -0.734 -1.662 1.686 Pseudochironomus -0.640 -0.110 0.844 0.111 0.453 129 Tubuliflorae 0.318 0.778 -0.683 1.744 -0.841 Cladotanytarsus mancus type -0.496 1.473 -0.803 0.180 0.163 Rosaceae 0.931 -0.646 -1.131 -0.909 0.363 Corynocera ambigua 0.700 -1.409 -1.890 0.074 -0.666 Equisetum 1.346 -0.841 -0.684 -0.985 -1.252 Tanytarsus chinyensis -0.112 -0.639 1.657 -0.732 -0.745 Lycopodium -0.950 0.340 0.985 -1.432 -1.398 Tanytarsina - other 1.433 -0.617 0.604 -0.975 0.944 Polypodiaceae -0.979 -0.021 0.975 -1.682 -0.944 Stempellina -0.199 -1.257 -1.643 -0.863 -1.494 Corynoneura/Thienemanniella -0.270 -0.817 -0.320 0.115 2.058 Cricotopus/Orthocladius -0.836 0.161 0.488 0.969 0.068 Limnophyes 1.001 1.757 -0.261 -0.345 -0.594 Parakeifferiella sp. B 0.212 -1.803 1.154 0.075 -1.103 Psectrocladius undiff. -1.608 -0.367 -0.097 -1.465 -0.028 Pseudosmittia/Smittia 1.316 0.607 -1.230 0.886 0.720 Procladius -1.393 1.083 1.374 -0.253 0.722

Table 4.6 Species scores from PCA on a) pollen percentages; b) chironomid percentages from “Marahbodd” Lake, NWT. Axis Axis Axis Axis Axis a) Taxon Axis 1 Axis 2 Axis 3 Axis 4 Axis 5 b) Taxon 1 2 3 4 5 Alnus -1.668 0.568 1.278 -0.970 -0.476 Chironomus 1.120 1.207 0.012 -0.129 0.060 Betula -1.388 0.334 -0.550 -1.473 0.672 Cladopelma 0.335 1.551 -0.606 1.626 0.519 Dryas 1.041 1.521 0.656 0.942 0.978 Cryptochironomus -0.718 0.442 0.762 2.121 1.196 Juniperus -0.118 0.298 -1.241 0.276 0.920 Cyphomella/Harnischia/Paracladopelma 0.907 -0.071 0.946 -1.449 -0.132 Picea 0.732 -1.945 0.739 -0.360 0.790 Dicrotendipes 1.142 -1.722 -0.852 -0.241 0.268 Pinus -0.351 0.163 -1.412 1.727 -1.193 Glyptotendipes 0.155 -1.104 1.272 1.152 -0.621 Populus 0.645 -0.305 -1.915 -0.884 0.717 Microtendipes 1.978 0.611 0.264 0.835 0.270 Salix -1.750 0.145 -0.621 -0.578 0.119 Parachironomus 1.684 0.068 0.521 -0.180 -1.419 Shepherdia -0.265 0.724 -0.729 0.895 2.261 Paratendipes -0.784 0.301 -1.478 -0.213 -1.338 Artemisia -1.589 0.185 1.171 0.583 -0.341 Polypedilum 0.199 1.137 -0.422 0.928 0.331 Cyperaceae 1.177 1.752 0.681 0.323 0.619 Sergentia -0.110 -1.346 -1.124 -0.654 -0.850 Epilobium 0.827 -0.812 0.551 -1.635 0.769 Stichtochironomus undiff. -0.343 -0.181 0.875 -1.975 0.530 Ericaceae -0.172 1.300 -0.240 -1.107 -0.839 Pseudochironomus 1.458 -0.384 -1.014 0.534 -1.287 130 Poaceae -0.765 0.294 -1.656 0.400 -0.230 Cladotanytarsus mancus type -0.276 1.051 -1.071 -1.016 -0.135 Tubuliflorae -0.114 -1.198 0.603 1.169 -0.170 Corynocera ambigua -2.007 -0.774 0.988 0.613 0.313 Lycopodium 0.440 1.906 0.743 -0.544 -0.309 Corynocera olivieri -0.026 -0.526 0.916 1.279 -0.178 Polypodiaceae 1.185 0.013 -0.377 0.178 -2.301 Tanytarsus chinyensis -0.714 1.662 -0.217 -1.700 0.145 Sphagnum -1.078 -0.325 0.986 1.643 0.751 Tanytarsina - other 1.866 -0.849 0.079 0.309 -1.347 Stempellina -0.838 -0.379 -2.072 0.111 -0.479 Corynoneura/Thenemanniella -0.353 1.306 -0.828 0.543 1.259 Cricotopus/Orthocladius 0.434 0.249 1.506 0.948 -0.483 Heterotrissocladius 0.819 1.497 -0.061 0.678 0.465 Limnophyes -0.665 1.565 1.532 -0.527 -1.113 Olivideria/Hydrobaenus group -0.485 0.297 -0.900 1.227 -1.511 Paracladius 1.547 0.364 0.239 -0.868 0.265 Parakeifferiella sp. B 1.003 -1.186 -0.056 0.673 1.712 Psectrocladius undiff. 0.865 -0.099 0.797 -0.810 2.411 Pseudosmittia/Smittia 0.667 2.002 0.712 -0.122 -1.551 Zalutschia -0.458 -0.394 1.863 -0.962 -0.712 Procladius 1.024 0.361 -1.398 -0.910 1.297

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Figure 4.1 Age-depth chronology for Spirit Lake, YT. The solid circles are retained 14C dates, prior to correction. The open circle indicates the single rejected 14C date. Solid diamonds are retained 14C dates, after correction. The open triangle indicates the depth and age of the WRA (Clague, et al. 1995). The X indicates the depth and age of the top of the core. The dashed line is a line of best-fit used to determine whether correction was necessary (y=23.549x+3827.7, R2 = 1). The solid line is a line of best- fit used to establish the final chronology (y=-0.0016x3+0.3816x2-5.5127-56.455, R2=1). Please see the text for details.

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Figure 4.2 Age-depth chronology for “Marahbodd” Lake, NWT. The solid circles are retained 14C dates, prior to correction. Open circles indicate rejected 14C dates. Solid diamonds are retained 14C dates, after correction. The open triangle indicates the depth and age of the WRA (Clague, et al. 1995). The X indicates the depth and age of the top of the core. The dashed line is a line of best-fit used to determine whether correction was necessary (y=37.353x+2348.7, R2 = 1). The solid line is a line of best- fit used to establish the final chronology (y=0.0283x3-2.1826x2+86.562-63, R2=0.999). Please see the text for details.

Figure 4.3 Photograph of the section of the ML core used for this analysis. The WRA appears as a light grey band approximately 23-25cm depth.

133

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Figure 4.4 Magnetic susceptibility of the section of the ML core used for this analysis. The depth of the WRA in the ML core (23-25cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age- depth estimation/interpolation. The vertical grey line indicates and X-axis value of 0.

) te a c ili (S ate ic n al o u rb sid rgan O Ca Re

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e 1150 WRA g A

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Figure 4.5 Sediment organic, carbonate, and silicate content from Spirit Lake, YT. The depth of the WRA in the SL core (17- 18cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes.

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e m ae a u ceae a dia ia e ae e em rus s c e lor t dia ae a us e i a ea if e odi o s l s x m c is p l tul ry ea u i epher cac a bul op ha a e n h i o u t Alnu B Co Junip Pic Pi Populus Sal S Arte Cyper Er P Rosaceae T Equ Lyc Poly Nymph Typ To

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e a ia ae e m m s a e e a u u um di P S iflor o s la s peru a s cea podiace A u u a i ix emisi lobi ca y :N len ry ce inu al rt P Aln Bet D Jun Pi P Populus S ShepherdA Cyperac Epi Eri Poaceae Tubul Lycop Pol SphagnumA Pol

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e a e e ia a e m c s d e e ra iu a m u r ia c m a e i u r s e s iu e a lo d d n e lu h i ra if o o g s la s a s b c e l p p l u u a ip u u ix p m e lo a c u o y a t y n e p l e te p i ic a b c l h ta ln e r u ic in o a h r y p r o u y o p o A B D J P P P S S A C E E P T L P S T

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Chironominae (Pseudochironomini) Chironominae (Tanytarsini - Zavreliina) Tanypodinae (Macropelopiini) Chironominae (Chironomini) Chironominae (Tanytarsini - Tanytarsina) Orthocladiinae

lma

dope e lla yp e aracla t ni ia/P . A s man t sp ncus si e B n sp. B a C n n ladius diff. ittia u nisch us m igua s er n us r s b up ye n hie sp. u m a u m s o in e th thoc Co o o omus sus m g o /T s e H es m s omus n a a su gr - a p n on ro ch a iella ul us lla/ no m i a tr r s s lm lu a c us eura fe p m ndipes ti nytar s pus/Or me e ndipe chir ta se r rsina o ope tochiron o tochironomus o p arsina dosmittia/Sm ono p ho ot astiella ht h udoch ynocer ro atanytar yt yta ytarsus luyta ynon u cladiu d Ca ir d y g rachiro rate rgen c c d r c r n n r icot rakief a h la r yp icr olypedi tenochiroti i la o i a a a tempellino r a ro e C C C C D Glyptotendi Pa Pa Pa P Se S S St Pse C C M P T Tan T Tan S C C LimnophyesP Psectrocladiu Pse P H

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% 143 a)

Chironominae (Pseudochironomini) Chironominae (Tanytarsini - Zavreliina) Tanypodinae (Macropelopiini) Chironominae (Chironomini) Chironominae (Tanytarsini - Tanytarsina) Orthocladiinae

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Head capsules/cm2 /yr b)

Figure 4.11 Chironomid a) percentages; b) influx from Spirit Lake, YT. The depth of the WRA in the SL core (17-18cm) is 144 marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes.

Chironominae (Pseudochironomini) Chironominae (Tanytarsini - Zavreliina) Tanypodinae (Macropelopiini) Chironominae (Chironomini) Chironominae (Tanytarsini - Tanytarsina) Orthocladiinae

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Chironominae (Pseudochironomini) Chironominae (Tanytarsini - Zavreliina) Tanypodinae (Macropelopiini) Chironominae (Chironomini) Chironominae (Tanytarsini - Tanytarsina) Orthocladiinae

a lm pe o clad e la p p el u ara ty gro /P B s s a . u anni u s p m i s nc a d nu f. ia s a C sis r a . B if itt s s igu ri p n s ius ae rnischi s u u mu s m b ie n hiene ocl d sp und u th rob Sm s om o rou /T la /Ha om am oliv a g hinye luge - othe c s a onomus tr rsus a c a e Hyd riella dius us on hiron ra c s s / ius mittia/ dipes lum ir c e in u in llina eura us/Or hy om elm chir n di tia h chiron o anytars c se nyta s rs e n p trisso p ria ad effe ocla os ia dius n d t tars ta to r a op homella pe en hto yno y tarsu ytar no ide ud sh p rachironomu rate noc rop rata n mp tero u al hiro lad y icrotendipe a a oly erg te tic seu lado orynocera or ic a te oryno rico e im liv sect se rocl ot C C Crypto C D Glyptotendipes MicrotendipesP P P S S S P C C C M P Tan Tan Ta Tany S C C H L O Paracl Paraki P P Zal P T

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2 Head capsules/cm /yr

Figure 4.12 Chironomid a) percentages; b) influx from “Marahbodd” Lake, NWT. The depth of the WRA in the ML core (23- 25cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth 146 estimation/interpolation. Please note scale changes.

ed h 9) ot 00 o 2 m s so o L ( filter y

omal an e r low-pass

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est analogues est analogues s os e ue tur og ) ra of 5 cl of 9 clo hed e ge anal age n mooto 2009 temp er s Los ter ( mod fil y t tion by aver ion by avera ses at lo c anomal d mean July d total annual precipitation o low-pass e valida e valid t re - - e u c ear timat timat y perat Es Es stan 24- y cross cross m b by Di te

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1150 WRA Age (cal BP) (cal Age

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16 20 600 840 1080 75 85 95 -0.2 0.0 0.2

°C mm SCD °C

Figure 4.15 Pollen-inferred mean July temperature and total annual precipitation from Spirit Lake, YT, reconstructed using the MAT. The vertical grey line through the “Distance to closet modern analogue” curve indicates the 20th percentile acceptable/non- analogue cut-off (=92), as determined using the SCD metric. A varve-inferred reconstruction of mean July temperature anomalies from Iceberg Lake, AK (Loso 2009), is provided for comparative purposes. The dashed line through this curve is a loess smoother with a span of 0.05; the vertical grey line indicates an X-axis value of 0. The depth of the WRA in the SL core (17-18cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes.

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es s u ue log g e alo r ana n u st a st se e erat o p l os cl tem re 0 c u 3 d ) ly f 1 th f u rat o p o 09 e nalogue othe J ge a o 20 n p a ) m rage r n so 3 te 4) e sm meat lake de v r n nt a lte (Lo uly y ave e y i J b epth b f ly atedone ated on d st moder s a m an e as ti e ion tim tion s p s omp at ake e c m es comp ( lid ( lida e anom ted a S a to clo r trap LS a rap -v tu ts m tst ear low- ti o timated l -y oo s pera B E cross-v Bo Es stance 24 y cross i m by WAP by by WAPL b D te

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950

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1150 WRA Age (cal BP) (cal Age

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1350

14.0 15.0 16.0 13.5 14.0 14.5 2.0 3.0 2.0 3.0 17.5 22.5 27.5 -0.2 0.0 0.2 °C m SCD °C

Figure 4.16 Chironomid-inferred mean July temperature and lake depth from Spirit Lake, YT, reconstructed using WAPLS regression and the MAT. The dashed line through the first temperature curve is a loess smoother with a span of 0.2. The vertical grey line through the “Distance to closet modern analogue” curve indicates the 20th percentile acceptable/non-analogue cut-off (=24.5), as determined using the SCD metric. A varve- inferred reconstruction of mean July temperature anomalies from Iceberg Lake, AK (Loso 2009), is provided for comparative purposes. The dashed line through this curve is a loess smoother with a span of 0.05; the vertical grey line indicates an X-axis value of 0. The depth of the WRA in the SL core (17-18cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes.

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s s e e u u g g lo lo a a n n t a t a s s se se lo n lo e c c e r 5 tio 9 u tu f a f g a o it o lo r ip a re e e c e n u p g g a t m ra re ra n ra e e l p e r e t v a v e p ) ly a u a d 9 u y n y o m 0 J b n b m te 0 a t r 2 n n l n s i l. a io a io e a a e t t t s y t m a to a o l e d id cl u d li d l J ld te a te a to e a a -v a -v g n s s e ra o im s im s c e D st ro st ro n v c E c E c ta A a y y is b b D (M

750

850

950

1050

1150 WRA Age (cal BP) Age (cal

1250

1350

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10 14 400 600 800 1000 75 100 10 15

°C mm SCD °C

Figure 4.17 Pollen-inferred mean July temperature and total annual precipitation from “Marahbodd” Lake, NWT, reconstructed using the MAT. The vertical grey line through the “Distance to closet modern analogue” curve indicates the 20th percentile acceptable/non-analogue cut-off (=92), as determined using the SCD metric. A chironomid- inferred reconstruction of mean July temperature from Slipper Lake, NWT (MacDonald, et al. 2009), is provided for comparative purposes. The depth of the WRA in the ML core (23-25cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes.

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logues ogue al re by ana u t ses lo mperat c losest an e 0 c 3 ue f 1 log rature pth e o e of a n July t pe g de g an ra ra n ea em e rature t ake 4) ve er e ) ly l a d m y av nt pth od 09) e t 3 ed e temp 0 Ju b at ne t m r mat en po on by s l. 2 i n ean tion tim i a st po m at e m es d et m close July dai ted rap to e trap (co LS (co -vali e nal ts S ma tst P s o ti o timated lake d nc oo ros veragcD B Es Bo Es c A a y WAPL by cross-valida by WA b Dista (M

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1150 WRA Age (cal BP)

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13.0 15.0 12.0 13.0 14.0 1.5 2.0 2.5 2.0 3.0 20.0 25.0 30.0 10.0 15.0 °C m SCD °C Figure 4.18 Chironomid-inferred mean July temperature and lake depth from “Marahbodd” Lake, NWT, reconstructed using WAPLS regression and the MAT. The dashed line through the first lake depth curve is a loess smoother with a span of 0.2. The vertical grey line through the “Distance to closet modern analogue” curve indicates the 20th percentile acceptable/non- analogue cut-off (=24.5), as determined using the SCD metric. A chironomid-inferred reconstruction of mean July temperature from Slipper Lake, NWT (MacDonald, et al. 2009), is provided for comparative purposes. The depth of the WRA in the ML core (23-25cm) is marked with a horizontal grey shaded band. The age of the WRA (1147 cal BP; Clague, et al. 1995) is marked with a horizontal grey line and labelled; the age of the WRA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes.

Chapter Five: ENVIRONMENTAL RESPONSES TO THE MAZAMA ASH (MZA), 7627 CAL BP, GOLDEYE LAKE, AB

5.1 Results

5.1.1 Chronology and ash identification

A single layer of volcanic ash was identified in the Goldeye Lake (GDL) core at approximately

17-19 cm depth. Identification by wavelength dispersive spectrophotometry and comparison with

reference samples positively identified the ash as coming from the Mount Mazama eruption,

7627 cal BP (Appendix A; Lauren Davies, personal communication 2014; Zdanowicz, et al.

1999).

Construction of the GDL chronology was based on two accelerator mass spectrometer (AMS)

radiocarbon dates and on the depth and age of the MZA, as determined by Zdanowicz et al.

(1999). Results are presented in Table 5.1 and Figure 5.1. A linear best-fit line was plotted to the

two radiocarbon dates and interpolated to 0.5 cm intervals to determine if correction was

necessary. Correction was considered necessary if the difference between the interpolated and

established age of the MZA was larger than the smallest error of the calibrated radiocarbon dates.

In the case of the GDL core, the difference between the interpolated and established age of the

MZA amounted to 119 years, while the smallest error of the two calibrated radiocarbon dates was 133 years. Correction was therefore originally not considered necessary, however, the best- fit line (2nd-order polynomial) plotted to the two radiocarbon dates and the ash layer in the core

resulted in an interpolated date for the MZA that was greater than the smallest error of the dates

(error of -181 years), and so the dates were ultimately subjected to correction. The difference

between the interpolated and established age of the MZA obtained from the original best-fit line

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between the two GDL radiocarbon dates (119 years) was subtracted from the ages of the dates to produce corrected ages for use in chronology construction. A linear best-fit line was then plotted using the corrected radiocarbon dates and the depth and age of the MZA to give the final age- depth curve, and ages were interpolated for the necessary sample depths and the sedimentation rate calculated. The resulting record is 1949 years long, spanning 8601-6652 cal BP, with a sedimentation rate of 0.011 cm/yr.

5.1.2 Core logging

A photograph of the section of the GDL core used in this analysis is presented in Figure 5.2. The

MZA appears as a light grey band from approximately 17-19 cm depth.

The results of magnetic susceptibility (MS) analysis are presented in Figure 5.3. The MS record shows substantial variability in the sediments surrounding the MZA, beginning with a sharp increase from ca. 3 SI to ca. 6.5 SI at approximately 7850 cal BP. This is followed by gradually decreasing values until ca. 7300 cal BP (minimum value ca. -3 SI). A sharp increase (2 SI) at ca.

7200 cal BP is followed by relatively stable MS at ca. -1.5 SI until the end of the record.

5.1.3 Loss-on-ignition

The results of loss-on-ignition (LOI) analysis are presented in Figure 5.4.

Sediment organic content ranges from 30-40 % in the earliest portions of the record, and then decreases slightly ca. 8150-7950 cal BP to approximately 20 %. This is followed by a sharp increase to ca. 55 % peaking ca. 7750 cal BP. Organic content decreases to ca 10 % at the depth

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of the MZA, recovering to near previous values by ca. 7200 cal BP. Organic content decreases again to ca. 15 % ca. 7100-6950 cal BP before increasing again at the end of the record.

Sediment carbonate content begins in the record at values of approximately 5 %. At ca.

8250 cal BP, carbonate content increases sharply to 30 %, before declining again to ca. 5 % by ca. 8050 cal BP. Carbonate content decreases to 0 % in the depths surrounding the MZA, and increases to slightly above its former values (ca. 10 %) by approximately 7125 cal BP.

The residual (silicate) fraction of the sediment comprises approximately 60 % of the record for its first 300 years. At ca. 8250 cal BP, silicate content decreases to ca. 20 %, parallel to the measured increase in carbonate content. Silicate content then recovers to values ca. 70 %, before decreasing again to ca. 40 % ca. 7750 cal BP. Silicate content increases to ca. 90 % at the depth of the MZA, and decreases gradually from that point until ca. 7200 cal BP, where it reaches a value of 50 %. Silicate content then increases again to ca. 80 % at ca. 7025 cal BP, and then decreases to the end of the record.

5.1.4 Pollen

Pollen percentage and influx graphs are presented in Figure 5.5.

Alnus and Betula both decrease over the first quarter of the record from ca. 6-7 % to ca.

1-3 %, before increasing again during the second quarter of the record to near previous values by approximately the depth of the MZA. The increase in Alnus occurs immediately after the MZA, while that of Betula occurs just before ca. 7750 cal BP, and extends through the ash to ca. 7550 cal BP. Both taxa then decrease to values near 0 % by ca. 7200 cal BP, and remain at this level until the end of the record. Representation of Picea and Pinus display long-term, reciprocal trends towards increased and decreased values, respectively, over the course of the record, with

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no notable changes at the depth of the MZA. Percent representation of Picea ranges from

ca. 20-30 % over the course of the record, while Pinus ranges from ca. 45-70 %. The remaining

identified taxa all remain below ca. 10 % representation for the duration of the record, and

variations are slight. Juniperus, Populus, Salix, Poaceae, and Tubuliflorae all decrease to values

of 0 % at the depth of the ash. Slight increases in Artemisia, Polypodiaceae, Tubuliflorae,

Chenopodiaceae/Amaranthaceae (Cheno/Am), and Poaceae occur after the MZA; with the

exception of Polypodiaceae, these somewhat elevated values last ca. 200-500 years before

returning to previous levels. The increase in Polypodiaceae lasts to the end of the record.

Variations in the proportion of arboreal (AP) to non-arboreal (NAP) pollen types are reflected in

the AP:NAP ratio. Initially high values decrease gradually starting ca. 8325 cal BP, reaching

their lowest point ca. 7750 cal BP. A brief and sharp increase in AP:NAP then occurs at the depth of the MZA, followed by a decline which lasts until ca. 7300 cal BP. A single-point increase is then followed by reduced values ca. 7125-6850 cal BP. Values increase again from this time to the end of the record.

Influxes of all taxa are generally high (total influx ca. 5000 grains/cm2/yr) in the earliest

portions of the record, ca. 8600-8500 cal BP. This is followed by a decline in influx values (total

influx ca. 2000 grains/cm2/yr) lasting until ca. 8050-7950 cal BP in most cases, though Alnus and

Juniperus remain at low values (ca. 40 and 10 grains/cm2/yr, respectively) for the remainder of

the record. Total influx, as well as taxon-specific influxes of Betula, Picea, Pinus, Populus,

Salix, Artemisia, Cheno/Am, Cyperaceae, and Poaceae increase sharply at ca. 7850 cal BP (total

influx ca. 2000 to 6000 grains/cm2/yr; Betula ca. 40 to 170 grains/cm2/yr; Picea ca. 400 to 1100

grains/cm2/yr; Pinus ca. 1200 to 4100 grains/cm2/yr; Populus ca. <10 to 30 grains/cm2/yr; Salix

ca. 10 to 50 grains/cm2/yr; Artemisia ca. 0 to 30 grains/cm2/yr; Cheno/Am ca. 0 to 10

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grains/cm2/yr; Cyperaceae ca. 20 to 70 grains/cm2/yr; Poaceae ca. 0 to 30 grains/cm2/yr), before

decreasing to near 0 grains/cm2/yr ca. 7750 cal BP. Betula, Picea, Pinus, Lycopodium,

Polypodiaceae, and to a lesser extent Alnus, Artemisia, and Cheno/Am increase sharply again

within the MZA to values near their previous peaks. This is followed by declines to 0 or near 0

grains/cm2/yr shown by total and taxon-specific influxes of all of the taxa. Total and taxon-

specific influxes of Picea, Pinus, Populus, and Cyperaceae then begin to gradually recover to

their former values, reaching their 8600-8500 to 8050-7950 cal BP values by ca. 7200-7000 cal

BP. Poaceae increases slightly more rapidly, reaching its 8600-8500 to 8050-7950 cal BP value

by ca. 7475 cal BP. Betula and Salix both remain at reduced influxes (ca. 30 grains/cm2/yr and ca. 10 grains/cm2/yr, respectively) from the ash to the end of the record, while influx of

Tubuliflorae, Polypodiaceae, and to a lesser extent Lycopodium increase and remain elevated (ca.

5 grains/cm2/yr, ca. 120 grains/cm2/yr, and ca. 10 grains/cm2/yr, respectively) from the

deposition of the ash to the end of the record. Artemisia reaches its peak influx of ca. 40

grains/cm2/yr at ca. 7300 cal BP, followed by a decrease to values of ca. 10 grains/cm2/yr that

lasts to the end of the record. Chemo/Am also reappears briefly ca. 7300 cal BP with an influx of

ca. 5 grains/cm2/yr, only to disappear from the record thereafter.

5.1.5 Microcharcoal

The results of microcharcoal analysis are presented in Figure 5.6. From high values at the very

beginning of the record of ca. 2800 particles/cm2/yr, charcoal influx decreases rapidly to values

ranging from ca. 800-1400 particles/cm2/yr by ca. 8500 cal BP. Values vary slightly over the course of the record, but display few trends, with the exception of a brief and sharp increase at

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the depth of the MZA to a value of ca. 2000 particles/cm2/yr. This increase is both preceded and

followed by slight reductions in charcoal influx, to values of ca. 100-200 particles/cm2/yr.

5.1.6 Chironomids

Chironomid percentage and influx graphs are presented in Figure 5.7.

Percentage representation of Chironomus decreases steadily over the course of the record

from ca. 50 % to ca. 10 %. Values increase slightly ca. 7750 cal BP to ca. 40 %, before

continuing to decline. The data show few other long-term trends. Cladopelma, Dicrotendipes,

Cladotanytarsus mancus type, Micropsectra, Parakeifferiella sp. B, Tanytarsina group C, and

Tanytarsus chinyensis all decrease to values near 0 % at the depth of the MZA following a

period of stable or increased representation leading up to the ash. Values recover ca. 100-250 years later, with the exception of Cladotanytarsus mancus type, which remains absent until the very end of the record. Both Endochironomus and Glyptotendipes show increases ca. 7750 cal

BP, which last to ca. 7300 cal BP. Endochironomus increases from less than ca. 5 % to ca. 5-10

% representation during this time, while Glyptotendipes increases from ca. 5 % to ca. 10-15 %.

The representation of both Polypedilum and Cricotopus/Orthocladius increases slightly after the

MZA, from less than ca. 5 % on average to ca. 6 %. Polypedilum remains elevated until ca. 7000

cal BP, while Cricotopus/Orthocladius returns to near previous values by ca. 7400 cal BP.

Parakeifferiella sp. B also shows increased representation after the MZA, increasing from 0 % at

the immediate depth of the ash to ca. 10 % by ca. 7500 cal BP, before returning to pre-ash levels

of ca. 5-8 %. Representation of Tanytarsus lugens and Tanytarsina – other also increases slightly at and above the ash, from ca. 5 % to 15 % in the case of Tanytarsus lugens, and from ca. 10 %

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to 15 % in the case of Tanytarsina – other. Tanytarsus lugens remains elevated until ca. 7400 cal

BP, while Tanytarsina – other remains slightly elevated on average to the end of the record.

With the exception of a sharp, single-point increase in influx at ca. 8150 cal BP (from ca.

0.1 to 0.2 head capsules/cm2/yr) and a slight decrease during and after the MZA (ca. 0.08 to 0.01

head capsules/cm2/yr, lasting to ca. 7400 cal BP), total chironomid influx remained

approximately stable throughout the record at values of approximately 0.1 head capsules/cm2/yr.

Patterns in the influx of Chironomus are generally similar to those of total influx, with a sharp, single-point peak (from ca. 0.03 to 0.08 head capsules/cm2/yr) at ca. 8150 cal BP, and a decrease

through and after the MZA (to ca. 0.002 head capsules/cm2/yr) which lasted for ca. 250 years.

Similar peaks in taxon-specific influx at ca. 8150 cal BP occur in Dicrotendipes (to ca. 0.02 head

capsules/cm2/yr), Glyptotendipes (to ca. 0.008 head capsules/cm2/yr), Tanytarsina group C (to ca. 0.02 head capsules/cm2/yr), Tanytarsus chinyensis (to ca. 0.03 head capsules/cm2/yr),

Tanytarsus lugens (to ca. 0.01 head capsules/cm2/yr), Cricotopus/Orthocladius (to ca. 0.006 head

capsules/cm2/yr), Parakeifferiella sp. B (to ca. 0.01 head capsules/cm2/yr), and Procladius (to ca.

0.01 head capsules/cm2/yr). Influx of the majority taxa decreases through and after the MZA,

with recovery to pre-ash values within 200-500 years in most cases. Chironomus and

Polypedilum remain at low values (ca. 0.01 and 0.002 head capsules/cm2/yr, respectively) from

the MZA to the end of the record. A brief increase in the influx of Endochironomus and

Glyptotendipes (from 0 to ca. 0.008 head capsules/cm2/yr, and from ca. 0.001 to 0.01 head capsules/cm2/yr, respectively) occurs starting ca. 7400 cal BP. This increase lasts until ca. 7200

cal BP in the case of Endochironomus, when it returns to its previous values, while

Glyptotendipes remains elevated to the end of the record. Tanytarsina – other also experiences a

notable increase in influx after the MZA, rising from ca. 0.002 head capsules/cm2/yr prior to the

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ash to a brief and sharp peak ca. 0.04 head capsules/cm2/yr at ca. 7400 cal BP. Influx then

declines to ca. 0.03 head capsules/cm2/yr on average, lasting to the end of the record where there is another sharp peak to ca. 0/04 head capsules/cm2/yr.

5.1.7 Ordination

Detrended correspondence analysis (DCA) of percentage pollen data from Goldeye Lake revealed a gradient length of 0.8 standard deviation (SD) units, both with and without down-

weighting of rare taxa, indicating linear ordination methods were appropriate. Principle

Components Analysis (PCA) was performed on un-transformed pollen percentage data, as a

method of visualizing temporal trends. The results are presented in Table 5.2, Table 5.3, and

Figure 5.8. The Viau and Gajewski (2009) reconstructions of mean July temperature and total

annual precipitation anomalies are also presented in Figure 5.8 for comparative purposes. With

the exception of increased values ca. 8600-8100 cal BP, the Viau and Gajewski (2009) mean

July temperature anomaly curve shows a long-term trend towards decreased temperatures over

the course of the record (from ca. +1.5 °C to +0.5 °C). The mean July temperature anomaly ca.

8600-8100 cal BP varies from ca. 1.5 to 2 °C. The Viau and Gajewski (2009) total annual

precipitation curve shows a generally increasing trend, from anomalies of ca. -15 mm to +25

mm. Precipitation was particularly low ca. 8700-8200 cal BP, reaching a minimum of ca. -50

mm, and shows a slight increase immediately after the MZA to ca. +25 mm.

As given by the Axis 1 eigenvalue, Axis 1 of the GDL PCA explains approximately 23 %

of the variability in the pollen data. Axis 1 sample score loadings gradually move from more

negative to more positive values over the course of the record, and appear to be generally

positively associated with the Viau and Gajewski (2009) temperature curve before the MZA, but

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are not after, showing a more negative association. Axis 1 sample loadings also show a negative

association with centennial-scale patterns in precipitation reconstructed by Viau and Gajewski

(2009), but positive association with the long-term trend towards wetter conditions exhibited by

the Viau and Gajewski (2009) reconstruction. Like Axis 1, Axis 2 sample scores show gradually

more positive loadings on average over the course of the record. A notable decrease occurs at the immediate depth of the MZA where values briefly become strongly negative, before returning to their previous positive values and continuing their gradual increase. Axis 4’s sample loadings remain close to 0 throughout the record, with only slight variations to the negative and positive.

With the exception of the immediate depth of the MZA on Axis 2, sample scores for both Axis 2 and Axis 4 are also negatively associated overall with the Viau and Gajewski (2009) temperature curve, though the association is less apparent on Axis 4; these axes explain 16 and 10 % of the variability in the dataset, respectively. Sample scores from Axis 3 (explains 11 % of the

variability in the dataset) are largely positively loaded in the beginning of the record, becoming

more negatively loaded at approximately the depth of the MZA, and recovering to more positive

values ca. 250 years later. Finally, sample scores from Axis 5 (explains 8 % of the variability in

the dataset) remain at loadings near 0 prior to the ash, but exhibit substantial change after with

strong both positive and negative loadings. Species scores of Alnus, Betula, Juniperus,

Cyperaceae, Poaceae, and Salix are all strongly negatively loaded on Axis 1, while Lycopodium,

Picea, and Polypodiaceae are all strongly positively loaded. On Axis 2, Cheno/Am and Pinus are

both strongly negatively loaded, while Corylus, Juniperus, Poaceae, Polypodiaceae, Populus,

and Tubuliflorae are all strongly positive. Artemisia and Betula are both strongly negatively loaded on Axis 3, while Cornus, Pinus, Rosaceae, and Shepherdia are strongly positively loaded.

Pinus is strongly negatively loaded on Axis 4, white Artemisia, Cheno/Am, Cornus, Ericaceae,

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Picea, and Shepherdia are strongly positively loaded. Finally, Betula, Cheno/Am, Corylus,

Cyperaceae, and Populus are strongly negatively loaded on Axis 5, while Ericaceae, Poaceae,

Rosaceae, and Tubuliflorae are strongly positively loaded.

DCA of percentage chironomid data from Goldeye Lake revealed a gradient length of 1.4 SD units, both with and without down-weighting of rare taxa, indicating linear ordination methods were appropriate. PCA was performed on square-root transformed chironomid percentage data.

The results are presented in Table 5.2, Table 5.3, and Figure 5.8. The Viau and Gajewski (2009) reconstructions of mean July temperature and total annual precipitation anomalies are also presented in Figure 5.8 for comparative purposes. Axis 1 explains 14 % of the variance in the chironomid dataset, as given by the Axis 1 eigenvalue. Sample scores from Axis 1 are generally positively associated with patterns in precipitation reconstructed by Viau and Gajewski (2009), though this association appears closer prior to the MZA than after. Sample loadings on this axis gradually increase from negative to positive values over the first ca. 1300 years of the record, reaching a peak after the MZA at ca. 7400 cal BP. High loadings last until ca. 7300 cal BP, and then begin to decline once again, reaching minimum values ca. 7000 cal BP, before returning to more positive values by the end of the record. Axis 2 explains 13 % of the variance in the data.

Sample scores on Axis 2 are generally positively associated with the Viau and Gajewski (2009) mean July temperature curve prior to the MZA, however after the MZA, sample scores from

Axis 2 no longer associate well with the temperature record. Loadings on this axis are somewhat elevated following the MZA compared to other times in the record, reaching a peak ca. 7600 cal

BP. Values remain elevated until ca. 7500 cal BP, but then decline gradually to the end of the record. Sample scores from Axis 3 (explains 12 % of the variability in the dataset) remain near 0 164

throughout the record, but begin to exhibit somewhat more variability after the ash and more

positive loadings, with elevated values after the MZA for a period of approximately 250 years,

and again ca. 6900 cal BP. Axis 3 sample scores are are also generally positively associated with

the Viau and Gajewski (2009) precipitation curve. Sample scores from Axis 5 (explains 9 % of

the variability in the dataset) exhibit less variability and more negative loadings. Sample scores

from Axis 4 shows a long-term shift from more positive to more negative loadings. Species

scores of Chironomus, Microtendipes, Sergentia, Stichtochironomus undiff., Tanytarsus

chinyensis, Limnophyes, and Psectrocladius undiff. are all strongly negatively loaded on Axis 1,

while Endochironomus, Glyptotendipes, Tanytarsina – other, and Procladius are all strongly

positively loaded. On Axis 2, Cladopelma, Cryptochironomus, Dicrotendipes, Pagastiella,

Cladotanytarsus mancus type, and Corynocera ambigua are all strongly negatively loaded, while

Polypedilum, Stichtochironomus undiff., Cricotopus/Orthocladius, Limnophyes, and

Parakeifferiella sp. B are all strongly positively loaded. Negatively loaded on Axis 3 are:

Cladopelma, Dicrotendipes, Labrundinia, Lauterborniella/Zavreliella, Parachironomus, and

Pseudochironomus, while Corynocera ambigua, Limnophyes, Microtendipes, Stichtochironomus

undiff., and Tanytarsina – other are positively loaded. Cladopelma, Cricotopus/Orthocladius,

Lauterborniella/Zavreliella, Psectrocladius undiff., Pseudosmittia/Smittia, and

Pseudochironomus are all strongly negatively loaded on Axis 4, while Chironomus,

Cryptotendipes, and Labrundinia are strongly positive. Finally, Corynocera ambigua,

Pseudochironomus, and Tanytarsina – other are strongly negatively loaded on Axis 5, while

Cladotanytarsus mancus type, Corynoneura/ Thienemanniella,

Cyphomella/Harnischia/Paracladopelma, and Tanytarsus chinyensis are strongly positively loaded.

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5.1.8 Climate reconstructions

5.1.8.1 Pollen-based

The results of pollen-based temperature and precipitation reconstruction using the Modern

Analogue Technique (MAT) are presented in Figure 5.9. Reconstructed mean July temperature

from GDL shows little variation overall and no notable long-term trend, varying from ca. 14-

16°C throughout the entirety of the record in a cyclic pattern with a periodicity of approximately

500 years, oscillating between higher and lower values. Reconstructed total annual precipitation from GDL shows a similar pattern, with generally stable values averaging ca. 500 mm and a ca.

500-year cyclic pattern of oscillation between higher and lower values. Exceptions to this general pattern in the precipitation are slightly increased values (ca. 600-650 mm) from beginning of the record to ca. 8300 cal BP and a sharp, single-point increase at the depth of the MZA to a value of ca. 800 mm. Acceptable vs. non-analogues were determined using the 20th percentile of the

observed distribution of pair-wise dissimilarities in the training set, equal to a squared-chord

distance (SCD) value of 92. All of the analogues fall within the acceptable range of SCDs of 92

or less, with the exception of at ca. 7200 cal BP and at the end of the record, where they exceed

the cut-off. SCDs are also generally slightly higher in the second half of the record after the

MZA than prior to its deposition.

5.1.8.2 Chironomid-based

The results of chironomid-based mean July temperature and lake depth reconstruction using weighted-averaging partial least squares (WAPLS) regression and the MAT are presented in

Figure 5.10.

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Patterns in reconstructed mean July temperature are generally similar using both WAPLS

and the MAT, though the variations in the record are somewhat more pronounced in the WAPLS

reconstruction. Higher temperatures (WAPLS, ca 17 °C; MAT, ca. 14.5 °C) in the earliest

portion of the record give way to decreased temperatures in both reconstructions ca. 8400-8100 cal BP (WAPLS, ca 14 °C; MAT, ca. 13.5 °C). A brief increase in mean July temperature at ca.

8050 (WAPLS, ca 16 °C; MAT, ca. 14.5 °C) is then followed by stable temperatures of ca. 15 °C

(WAPLS) to 14 °C (MAT) until after the MZA. After a slight decrease ca. 7500 cal BP

(WAPLS, ca 14 °C; MAT, ca. 13.5 °C), temperatures then return to their previous values. A

substantial decrease in temperatures occurs at ca. 7025 cal BP (WAPLS, ca 13 °C; MAT, ca. 13

°C), followed by recovery to previous values once again by ca. 6950 cal BP, which continues to the end of the record.

Both WAPLS and the MAT suggest gradually decreasing lake depth at GDL over the course of the record, though the specific patterns reconstructed by the two techniques are somewhat different. Once again, WAPLS produces a reconstruction with greater variability than the MAT, with values ranging from ca. 2.5-1.0 m, compared to the MAT’s ca. 2.0-1.5 m.

Centennial-scale patterns reconstructed using WAPLS are also more closely associated to those of the Goldeye Lake mean July temperature reconstructions discussed above than are those of the

MAT. Reconstruction using the MAT indicates an increase in lake depth immediately after the

MZA (from ca. 1.6 to ca. 2.0 m), however a similar increase does not appear in the WAPLS reconstruction. SCDs from the MAT remain well below the acceptable/non-analogue cut-off

(SCD of 24.5) throughout, but are generally slightly higher early in the record and immediately after the MZA than later in the record.

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5.2 Terrestrial and aquatic environments at Goldeye Lake, AB, 8601-6652 cal BP

5.2.1 Radiocarbon dating

The radiocarbon dates obtained from Goldeye Lake were ultimately subjected to relatively minor

correction as a result of being slightly too old when compared to the depth of the MZA in the

core and its established age (7627 cal BP; Zdanowicz, et al. 1999). In the absence of more

appropriate terrestrial material, both of the two radiocarbon dates from the core included organic

sediments and aquatic macrofossils, and so were likely subject to some hard-water error (HWE).

Corrections greater than what was applied to the Goldeye Lake dates are not uncommon, even

when based solely on macrofossils; Bunbury and Gajewski (2013), for example, applied a

correction of 690 years to their macrofossil-based dates from Upper Fly Lake, YT. Correction of

the Goldeye Lake dates resulted in a simple, linear age-depth interpolation that minimized the difference between the interpolated age of the MZA and its accepted age, suggesting that the

correction applied to the Goldeye Lake dates is likely quite reasonable. Dates have been given

above accordingly, however some caution is warranted because of these corrections, as well as as

a result of the relatively large errors of the dates themselves.

5.2.2 General trends in terrestrial and aquatic environments

The pollen data from Goldeye Lake indicate the presence of a boreal forest environment similar to that currently at the site throughout the period of record. Similarities between long and short-

term variations in the pollen data from Goldeye Lake and the Viau and Gajewski (2009)

temperature and precipitation reconstructions suggest that variations in climate had a substantial

influence on the composition of the vegetation at the site over the course of the record. Axes 1, 2,

and 4 of the PCA, gradually increasing representation of Picea, and gradually decreasing

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representation of Pinus are indicative of a long-term trend towards cooler and wetter conditions.

The microcharcoal record is also suggestive of a long-term trend towards decreased fire activity

in the region, corresponding with the gradual development of cooler and wetter climatic

conditions and the decreasing abundance of fire-susceptible Pinus. When analyzed using the

MAT, the pollen percentage data from Goldeye Lake also reconstruct a cyclic pattern of

centennial-scale (500-year) variability between cooler/wetter and warmer/drier conditions, with

increased abundance of non-arboreal plant taxa suggestive of a more open terrestrial

environment during warmer/drier phases. These patterns correspond to periods of increased and

decreased vegetation productivity, respectively, indicated by the pollen influx data. Centennial-

scale variability in the microcharcoal record indicates periods of lower fire activity during

periods of cooler/wetter conditions.

Proxies for aquatic conditions at Goldeye Lake also identify a pattern of centennial-scale

climatic variability at the site with a periodicity of ca. 500 years. General association of

centennial-scale patterns in the aquatic proxy data with the Viau and Gajewski (2009)

temperature and precipitation curves suggests that – as was the case for the terrestrial

environment – climatic factors had substantial influence on the aquatic environment of the lake

at this time-scale, particularly in the first half of the record prior to the MZA. Lack of association

between Axis 2 of the chironomid-based PCA and the Viau and Gajewski (2009) curves after the

MZA suggests that the importance of centennial-scale patterns in climate in determining chironomid community structure was reduced after the eruption. Slightly elevated SCD values

after the MZA might be indicative of unconventional composition of successional communities

after the ash. Variations in sediment organic content indicate periods of increased and decreased

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catchment productivity that positively associate with variations in total pollen influx, vegetation community composition, and microcharcoal indicative of a cyclic pattern between periods of cooler/wetter climatic conditions. Times of higher inferred catchment productivity, increased terrestrial productivity, more closed vegetation, and decreased fire frequency were also generally associated with cooler conditions reconstructed by the chironomid percentage data and the MAT and WAPLS. Small variations are also visible in total chironomid influx that correspond with this pattern, indicating slight increases in aquatic productivity during cooler/wetter periods, as well. Quantitative lake depth reconstruction using the chironomid data indicates that periods of reduced lake depth were also associated with these times of cooler/wetter climatic conditions. A centennial-scale cyclic pattern is also apparent in variations in chironomid community structure, though distinction between the phases is slight, with periods of cooler/wetter climate associated with increased representation of generalist taxa such as Procladius, and taxa typically found associated with aquatic plants such as Glyptotendipes, Endochironomus,

Cricotopus/Orthocladius, and Polypedilum. These patterns are more apparent in the sample score curves from the chironomid-based PCA, particularly on Axes 1 and 2. Variations in sediment silicate content also indicate a pattern of increasing and decreasing landscape instability with a periodicity of ca. 500 years, with periods of lower instability corresponding to cooler/wetter climate.

Quantitative lake depth reconstruction using the chironomid data captures a slight long- term trend towards decreased lake depth corresponding to the long-term trend towards cooler/wetter conditions demonstrated by the pollen and microcharcoal data. Patterns in magnetic susceptibility also suggest gradually increasing landscape stability, beginning ca. 7950 cal BP, punctuated by brief periods of increased instability ca. 7850 and 7200 cal BP. Beyond

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this, however, the aquatic proxy data from Goldeye Lake give little indication of any aquatic

response to long-term climatic changes. This observation is supported by the results of previous diatom-based studies of Goldeye Lake and of nearby Fairfax Lake, AB, which have identified little or no response of aquatic environments to long-term changes in climate over the course of the Holocene (Hickman and Schweger 1991, 1993).

The long-term trend towards cooler and wetter conditions present in the Goldeye Lake pollen and chironomid data corresponds well to the results of previous studies from the region indicating deteriorating climatic conditions beginning ca. 8000 years ago, as summer insolation began to decline in the latter half of the Holocene Climatic Optimum (HCO; Beierle and Smith

1998; Elias 1996; Hickman and Schweger 1993, 1996; Hutton, et al. 1994; Kutzbach and Guetter

1986; Luckman and Kearney 1986; Schweger and Hickman 1989). Gradually decreasing drought stress and increasing moisture availability at the end of the warm, dry HCO, also provides a reasonable explanation for long-term decreases in fire activity over the course of the record by

suggesting gradually decreasing susceptibility of the vegetation to ignition, and for increasing

landscape stability as a result of decreased erosion from increased plant cover. Similar long-term climatic changes have been inferred at a series of sites in Alberta and the northwestern United

States, resulting in alterations in vegetation community structures, contraction of vegetation zones, reduced fire activity, and flooding of previously dry lake basins (Beaudoin and King

1990; Elias 1996; Hickman and Schweger 1993, 1996; Hutton, et al. 1994; Luckman and

Kearney 1986; MacDonald 1989; Schweger and Hickman 1989; Vance 1986a, b; Vance, et al.

1983).

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A cyclic pattern in solar irradiance with a ca. 500-year periodicity has been identified in tree ring and ice core studies, including in the GISP2 oxygen isotope record, as well as in circulation and climate patterns in the North Atlantic, Alaska, and the northern Great Plains

(Chapman and Shackleton 2000; Hu, et al. 2003; Steinhilber, et al. 2012; Stuiver and Braziunas

1993; Stuiver, et al. 1995; Yu and Ito 2010). The timing of this cycle approximately corresponds to that of the ca. 500-year cycles between cooler/wetter and warmer/drier conditions inferred

from the Goldeye Lake proxies, providing a possible explanation for these patterns at the site.

Periods of weaker insolation indicated by proxies for total solar irradiance tend to correspond to

cooler phases indicated by the GISP2 isotopes, and to cooler/wetter periods at Goldeye Lake

with increased AP and thus more closed vegetation, and decreased landscape instability likely

because of increased vegeation cover. As in the case of the long-term trend, reductions in fire

activity during cool/wet phases at Goldeye Lake might have resulted from reduced susceptibility

of the vegetation to ignition at these times. Increased productivity during cooler/wetter periods at

Goldeye Lake may also be explained by decreased heat stress and increased moisture availability

during cooler/wetter phases, under the otherwise warm and dry conditions of the HCO.

Chironomid-based reconstruction of shallower lake depths during periods of increased moisture

availability as indicated by the other proxies is counter-intuitive. A possible explanation is that

variations in chironomid-based reconstructed lake depth are actually indicative of in within-lake

productivity and in the abundance of aquatic plants within the lake, rather than of actual changes

in water depth. Higher abundances of chironomid taxa often found associated with aquatic plants

(such as Glyptotendipes, Endochironomus, Cricotopus/Orthocladius, and Polypedilum) during

these periods would lead to the reconstruction of shallower lake depths due to the tendency for

aquatic plants to occur in shallow water, where conditions are typically more favourable for plant

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growth than in deep water (Wetzel 2001). Instead, it is likely that lake depths at Goldeye Lake remained approximately stable – or even increased somewhat – during wetter periods in the region’s centennial-scale climate cycle, providing better growing conditions for aquatic plants and associated chironomid taxa compared to warmer, drier periods during the already warm and dry HCO, when heat and/or drought stress might have increased water temperatures and/or reduced water levels such that plant growth was inhibited.

5.2.3 Terrestrial and aquatic responses to the MZA

Axes 2, 3, and 5 of the pollen-based PCA indicate a noteworthy impact of the MZA on the vegetation surrounding Goldeye Lake, primarily in the form of rapid and significant increases in the representation of shrub and herbaceous taxa that match or exceed the variability of the remainder of the record. Rapid, substantial, and extended decreases in the influx of numerous taxa immediately following the MZA, and lasting for ca. 100-150 years, also suggest a considerable impact on the overall productivity of the vegetation surrounding the lake unique to the period of record. Long lasting increases to higher-than-usual values in the influx and representation of herbaceous taxa such as Artemisia and Poaceae are indicative of a longer-term impact of the MZA in the form of a more open environment at the site, lasting up to ca. 500 years, while somewhat increased variability of community composition relative to prior to the ash is indicative of ongoing impacts lasting to the end of the record and possibly beyond. Lack of association between Axis 1 of the pollen-based PCA and the Viau and Gajewski (2009) temperature and precipitation records after the MZA is likely indicative of decreased importance of climate in determining vegetation community structure after the eruption relative to successional processes. Unconventional successional communities after the MZA are also

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suggested by increased SCDs, indicating poor or non-analogue community compositions. The

microcharcoal record indicates a brief (ca. 50-year) increase in fire activity at the depth of the

MZA – though it should be noted that this is a single point, and so must be interpreted with

caution – followed by a period of particularly decreased fire activity that lasted ca. 200 years,

before returning to approximately pre-ash conditions.

The chironomid community at Goldeye Lake demonstrated noticeable immediate and long-term

changes resulting from the MZA, with reductions in total influx and in the influx of many taxa in

the immediate aftermath of the deposition of the ash that often exceeded the variability present in

the remainder of the record in both degree and duration, lasting for up to ca. 250 years.

Particularly high loadings beginning after the MZA on PCA Axes 1, 2, and 3 are indicative of

immediately increased representation of taxa such as Stichtochironomus undiff., Corynocera

ambigua, Tanytarsina – other, Limnophyes, and Parakiefferiella sp. B lasting up to ca. 250 years,

and later of Glyptotendipes, Endochironomus, Procladius, Cricotopus/Orthocladius, and

Polypedilum. These patterns are suggestive of a period of noticeable disturbance and potentially decreased lake water pH in the immediate aftermath of the MZA characterized by the presence of resistant taxa such as Tanytarsina – other, followed by a period of particularly elevated representation and productivity of a variety of generalist and plant-associated taxa ca. 250 years later. This period of elevated abundance of generalist and plant-associated taxa lasted ca. 250 years, and corresponds with the return of total chironomid influx to approximately pre-ash levels.

Considerable long-term changes also occurred in chironomid community structure after the ash, with relatively stable, but decreased abundance of formerly highly variable, but strongly dominant Chironomus, and generally increased average values of Polypedilum and Tanytarsina –

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other relative to prior to the ash, lasting to the end of the record. Generally higher loadings on

Axes 2 and 3 after the MZA, and generally lower loadings on Axis 5 reflect these long-term community changes. Particularly decreased general catchment productivity after the MZA is also indicated by rapid and substantial decreases in sediment organic content lasting for ca. 500 years after the ash. Sediment organic content reaches its lowest values for the record during this time, suggesting atypically low productivity within the catchment in the ca. 500 years after the eruption. Sediment carbonate content also reaches its lowest values in the ca. 500 years after the

MZA, while silicate content reaches its highest values, suggesting potentially increased lake water acidity, and increased landscape instability/erosion/lake disturbance compared to typical patterns for ca. 500 years after the eruption.

Palaeoenvironmental studies of the impacts of volcanic ash on terrestrial and aquatic environments have revealed the great variability of responses that may occur dependent on a wide range of factors, including the characteristics of the eruption and ash itself, the thickness of

the ash, the season of the eruption, and the characteristics of the environment upon which the ash

is deposited (e.g. Birks 1980; Bunbury and Gajewski 2013; Slater 1985). Power et al. (2011)

have identified changes in water chemistry and decreased pollen and charcoal accumulation rates

lasting ca. 200 years at Foy Lake, MT, in response to the MZA. Changed aquatic environments

and decreased productivity after the MZA have also been identified at Lost Trail Pass Bog, MT,

inferred from decreased occurrence of Botryococcus and Pediastrum (Mehringer, et al. 1977).

The authors also found that the MZA resulted in increased influx of Artemisia, possibly

indicative of a positive impact on steppe vegetation; changes in the influx of other pollen taxa

were minimal (Mehringer, et al. 1977). Heinrichs et al. (1999) have also noted an increase in

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Artemisia immediately following the MZA at Kilpoola Lake, BC, as have Mack et al. (1983) at

Teepee Lake, MT, while Blinman et al. (1979) have identified increased Poaceae at Lost Trail

Pass Bog after the MZA, lasting ca. 40 years. In the central Cascades, WA, Long et al. (2011;

2014) have noted decreased NAP lasting ca. 40-100 years after the MZA, as well as increased fire frequency at some – but not all – sites. Increased fire frequency, as well as increased rates of peat formation after the MZA have also been identified by Beierle and Smith (1998) at Johnson

Lake, AB. Minckley et al. (2007) have attributed the dominance of Pinus at Dead Horse Lake,

OR, after the MZA to its influence on soils in the region, resulting in lower-nutrient soils that favoured the establishment of lodgepole pine.

Hickman and Reasoner (1994) have identified several hundred years of increased diatom productivity after the MZA, as a result of increases in available silica, at Opabin and Mary

Lakes, BC. Abella (1988) has also interpreted increases in Si:P ratios from community shifts in diatoms in Lake Washington, WA, for ca. 300 years after the MZA. Decreased pH and increased salinity after the MZA at Upper Klamath Lake, OR, has also been inferred by Bradbury et al.

(2004), again based on diatoms. The authors suggest that ash impacts on the lake may have lasted up to ca. 1000 years (Bradbury, et al. 2004). Increased lake water turbidity as a result of the MZA has also been recognized at Lake Wabamun, AB, lasting ca. 600 years (Hickman, et al.

1984). Hickman et al. (1984) also note decreased water levels and increased salinity at the site prior to the MZA relative to after. At Kilpoola Lake, Heinrichs et al. (1999) have inferred a 450

% increase in salinity after the MZA, based on the analysis of chironomid head capsules.

Decreased pH at and after the MZA has also been identified in cores from Wildcat Lake WA, and Wildhorse Lake, OR, based on increases in the concentration of acid-resistant algae

(Blinman, et al. 1979). At Big Lake, BC, Bennett et al. (2001) have also identified several peaks

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in pigments immediately above the MZA, but attribute these to the direct effects of the ash,

rather than to any changes in the lake environment.

Terrestrial and aquatic responses to the MZA at Goldeye Lake show similarities to previous

studies in some, but not all, aspects. The duration of ash impacts at the site, with immediate

effects lasting at least ca. 50 years and long-term effects lasting up to ca. 500 years, is similar to

that found in some other studies, though not all identified such long lasting consequences (Abella

1988; Bennett, et al. 2001; Blinman, et al. 1979; Hickman and Reasoner 1994; Long, et al. 2011;

Long, et al. 2014; Mack, et al. 1983; Mehringer, et al. 1977; Power, et al. 2011).

Increased abundance of Artemisia and Poaceae at Goldeye Lake suggests similar disturbance to the vegetation as occurred at Teepee Lake and Lost Trail Pass Bog, MT (Mack, et

al. 1983; Mehringer, et al. 1977), and Kilpoola Lake, BC (Heinrichs, et al. 1999), however no

change in the representation of Pinus, as occurred at Dead Horse Lake, OR (Minckley, et al.

2007), is visible in the Goldeye Lake record. NAP also increases after the MZA at Goldeye

Lake, rather than decreasing, as was noted at by Long et al. (2011; 2014) in the central Cascades,

WA. Decreased pollen influx at Goldeye Lake is indicative of decreased plant productivity and a

more open forest environment in the years after the ash at the site; similar decreases in

productivity have been identified by Power et al. (2011) at Foy Lake, MT. Together, the

palaeoenvironmental data from this series of lakes is suggestive of site-specific responses of terrestrial environments to volcanic ashfalls, substantially influenced by regional conditions and vegetation types. Trends in fire from Goldeye Lake show some similarities to previous studies, with increased fire activity immediately after the MZA followed by decreased activity, and then

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a return to previous patterns. As at Spirit Lake, YT, it is possible that elevated fire activity

immediately after the MZA at Goldeye Lake resulted from increased abundance of dead

vegetation leading to increased combustibility of the fuel load, and/or from increased lightning

activity as a result of atmospheric disturbance caused by the eruption and ash. After this

intensified period of fire activity, a period of reduced activity might have occurred as a result of

the decreased fuel load (after it had all burned), and/or temporarily decreased landscape

productivity.

Patterns in sediment organic content suggest substantially decreased general catchment

productivity after the MZA, lasting for many years. Particuarly increased sediment silicate content in the Goldeye Lake core above the ash is also suggestive of somewhat increased landscape instability/erosion/lake disturbance after the MZA relative to regular patterns over the period of record. Similar disturbed lake conditions have been inferred from data from Lake

Wabamun, AB (Hickman, et al. 1984). Previous studies have also identified both increases and decreases in within-lake productivity following the deposition of volcanic ashes (Hickman and

Reasoner 1994; Mehringer, et al. 1977). At Goldeye Lake, noticeable disturbance and immediately decreased lake productivity is demonstrated by particularly and immediately increased representation of resistant taxa such as Tanytarsina – other, and reduced chironomid influx, indicating an initial negative response of the lake environment to the deposition of the ash that exceeded the variability of the remainder of the record. This is followed by a period of particularly increased within-lake productivity – suggested by increased chironomid influx and representation of generalist and plant-associated chironomid taxa – and finally a return to approximately pre-ash levels and patterns. Increased lake primary productivity of diatoms after

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ashfalls has been attributed to increased Si:P ratios resulting either from chemical weathering of the ash itself or from decreased phosphorus recycling as a result of thick ash layers, and has been observed at Lake Washington, WA, in response to the MZA (Abella 1988). Bunbury and

Gajewski (2013) also identify a similar phenomenon at Donjek Kettle, YT, in response to the

WRA. Diatoms form a major food source for chironomid larvae, and so increased diatom productivity might reasonably be expected to lead to increased productivity of the chironomid population as occurred at Goldeye Lake – though additional analyses would be required to discover whether diatom productivity really did increase at the site after the deposition of the ash. Increased productivity of diatoms and chironomids would also be beneficial to other lake organisms that might feed off them, leading to further enhancements to lake productivity.

Tanytarsina – other is a generalist taxon that has been found to be resistant to the deposition of volcanic ash in other studies (Bunbury and Gajewski 2013). The taxon is also tolerant of decreased lake water pH, which has been interpreted in number of lakes as a result of volcanic ash deposition (Blinman, et al. 1979; Bradbury, et al. 2004). Increased abundance of

Tanytarsina - other after the MZA in the Goldeye Lake records might therefore have resulted from its increased ability to survive under disturbed and/or acidic conditions after the deposition of the ash. Long-term changes in chironomid community structure after the MZA towards decreased abundance of Chironomus and increased abundance of Tanytarsina – other are not suggestive of any long-term change in the lake environment, however, as these taxa are more-or- less tolerant of the same environmental conditions. Rather, it is perhaps more likely that

Tanytarsina – other was able to gain increased footholds within the lake after the MZA when

Chironomus decreased in abundance, which allowed for them to continue at elevated abundances in the long-term. Increased abundance of Polypedilum after the ash may be suggestive of

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increased abundance of aquativc plants, however, no substantial long-term increases in the abundance of other plant-associated taxa (such as Glyptotendipes, Endochironomus, Procladius, and Cricotopus/Orthocladius) pre vs. post-ash suggests that Polypedilum may also have simply moved into niche space vacated by other taxa after the ash, and was able to establish a larger population within the lake as a result.

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Table 5.1 AMS radiocarbon ages from Goldeye Lake, AB. The depth of the MZA in the core is also given, along with its established age (from Zdanowicz, et al. 1999). Calibration was performed using OxCal 4.2 and the IntCal13 calibration curve (Bronk Ramsey 2009; Reimer, et al. 2013). All dates were used in the construction of the core chronology. Please see the text for details. Mean Conventional cal BP cal BP Relative area Depth Lab code cal ± 2σ Corrected Source of date depth radiocarbon age ± 2σ 2σ under calibrated (cm) (UCIAMS-) BP error cal BP* (cm) BP lower upper age curve terrestrial & aquatic plant parts, 1-3 2 150842 5430 300 6931 5592 0.954 6262 670 6142 chironomids MZA (Zdanowicz 17-19 18 7627 150 et al. 1999) terrestrial & aquatic plant parts, 29-31 30 136461 7975 25 8993 8726 0.954 8860 134 8740 chironomids * Correction factor

181 = 119.048 cal yrs

Table 5.2 Eigenvalues from PCA on a) pollen percentages; b) chironomid percentages from Goldeye Lake, AB a) Axis Eigenvalue b) Axis Eigenvalue Axis 1 0.230 Axis 1 0.140 Axis 2 0.165 Axis 2 0.131 Axis 3 0.110 Axis 3 0.121 Axis 4 0.102 Axis 4 0.105 Axis 5 0.084 Axis 5 0.091

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Table 5.3 Species scores from PCA on a) pollen percentages; b) chironomid percentages from Goldeye Lake, AB. a) Taxon Axis 1 Axis 2 Axis 3 Axis 4 Axis 5 Alnus -1.021 -0.477 -0.591 0.466 0.764 Betula -1.286 -0.645 -1.373 -0.269 -1.081 Cornus -0.828 0.456 1.726 1.435 0.094 Corylus -0.187 1.478 -0.539 -0.691 -1.188 Juniperus -1.068 1.742 -0.417 -0.555 -0.039 Picea 1.497 0.838 -0.369 1.241 -0.576 Pinus -0.902 -1.269 1.035 -1.513 0.581 Populus -0.071 2.095 0.686 0.082 -1.209 Salix -1.603 0.818 0.285 -0.734 0.489 Shepherdia -0.410 0.798 1.985 1.154 -0.267 Artemisia -0.943 -0.498 -1.106 2.001 0.565 Chenopodiaceae/Amaranthaceae -0.499 -1.029 -0.569 1.872 -1.150 Cyperaceae -1.531 0.512 -0.449 0.285 -1.545 Ericaceae 0.643 0.432 -0.997 1.121 1.486 183 Poaceae -1.150 1.247 -0.654 0.068 1.383 Ranunculaceae 0.170 -0.684 0.174 -0.762 -0.099 Rosaceae -0.810 -0.236 1.878 0.928 1.235 Tubuliflorae -0.315 1.001 -0.881 -0.523 2.060 Lycopodium 1.220 0.243 0.935 -0.586 0.070 Polypodiaceae 1.468 1.012 -0.498 0.495 0.672

b) Taxon Axis 1 Axis 2 Axis 3 Axis 4 Axis 5 Chironomus -1.404 -0.079 -0.963 1.907 0.796 Cladopelma 0.124 -1.286 -1.163 -1.951 -0.374 Cryptochironomus -0.547 -1.709 0.569 -0.719 -0.038 Cryptotendipes -0.647 -0.323 -0.799 2.099 -0.566 Cyphomella/Harnischia/Paracladopelma -0.062 -0.642 -0.140 -0.347 2.462 Dicrotendipes -0.888 -1.719 -1.483 -0.360 -0.208 Endochironomus 1.195 0.197 -0.974 0.633 -0.939 Glyptotendipes 2.311 0.044 0.339 -0.010 0.999 Microtendipes -1.196 -0.110 1.892 -0.515 -0.620 Pagastiella 0.009 -1.015 0.287 0.099 0.320 Parachironomus 0.059 0.395 -1.488 -0.993 0.944 Polypedilum 0.272 1.906 -0.731 0.653 0.125 Sergentia -1.260 0.813 -0.755 -0.636 -0.070 Stichtochironomus undiff. -1.539 1.179 1.168 0.084 -0.027 Pseudochironomus 0.258 0.620 -1.314 -1.237 -1.541

184 Cladotanytarsus mancus type 0.635 -1.469 0.609 0.185 1.184 Corynocera ambigua -0.438 -1.184 1.156 -0.620 -1.077 Lauterborniella/Zavreliella -0.490 0.315 -1.090 -1.233 -0.868 Tanytarsus chinyensis -1.290 -0.701 0.492 -0.851 1.687 Tanytarsina - other 1.240 -0.454 1.544 -0.280 -1.620 Corynoneura/Thienemanniella -0.109 0.429 -0.413 0.097 2.113 Cricotopus/Orthocladius -0.693 1.466 -0.061 -1.221 0.620 Limnophyes -1.160 1.297 1.383 -0.288 0.097 Parakeifferiella sp. B 0.723 2.035 0.546 -0.691 0.135 Psectrocladius undiff. -1.501 0.066 -0.908 -1.280 -0.301 Pseudosmittia/Smittia 0.470 0.045 -0.876 -1.218 -0.152 Labrundinia -0.429 -0.299 -1.322 1.697 -0.828 Procladius 1.775 0.164 -0.404 -0.741 0.827

9000

8000 BP)

7000 (cal

Age 185

6000

5000 0 5 10 15 20 25 30 35 Depth (cm)

Figure 5.2 Photograph of the section of the GDL core used for this analysis. The MZA appears as a light grey band 186 approximately 17-19cm depth.

6600

7100

7600 MZA Age (cal BP) 187

8100

8600

048

Figure 5.3 Magnetic susceptibility of the section of the GDL core used for this analysis. The depth of the MZA in the GDL core (17-19cm) is marked with a horizontal grey shaded band. The age of the MZA (7627 cal BP; Zdanowicz, et al. 1999) is marked with a horizontal grey line and labelled; the age of the MZA falls slightly off from the midpoint of the ash as a result of age- depth estimation/interpolation. The vertical grey line indicates an X-axis value of 0.

s) e licat (Si e l ic ua onat d rb Organ Ca Resi

6600

7100 ) P

7600 MZA cal B 188 ( e g A

8100

8600

25 45 12 24 36 60 100

Figure 5.4 Sediment organic, carbonate, and silicate content from Goldeye Lake, AB. The depth of the MZA in the GDL core (17-19cm) is marked with a horizontal grey shaded band. The age of the MZA (7627 cal BP; Zdanowicz, et al. 1999) is marked with a horizontal grey line and labelled; the age of the MZA falls slightly off from the midpoint of the ash as a result of age- depth estimation/interpolation. Please note scale changes.

Spores AP NAP

ae eae e diacea ia ace e cea d po uac e a a us th ae ul i um s r sia n e c dium P u us a c n liflor o od A s nus eraceae u nipe us emi Cheno p b u n hepher rt mar rica osacea u Alnu Betula Cor Coryl J Picea Pi Popul Salix S A A Cy E PoaceaeRanu R T Lycop Polyp AP:N Pollen S

6600

7100

7600 MZA Age (cal BP) Age (cal

8100 189

8600

10 10 10 10 10 25 50 20 40 60 80 10 10 10 10 10 10 10 10 10 10 10 10 20 100 200 600 900 1200

% a)

AP NAP Spores

/ e a e e odiacecea e aceae e ia p a u m cea s d o tha e iu ia ru s n n ce a e ae d e lu her a a ce o od us p s u p r ra l us tula rn rylus i Che a e buliflora n n inu op m u cop olyp Al Be Co Co Ju Picea P P Salix She Artemisia A Cyp Ericace Poace Ranuncul Rosa T Ly P Tota

6600

7100

7600 MZA Age (calBP)Age

8100

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160 320 180 360 6 15 45 90 800 1600 2400 4800 36 72 30 60 10 20 30 60 16 50 100 4 15 30 12 8 10 20 15 30 120 240 3000 6000

Grains/cm2 /yr b) 190 Figure 5.5 Pollen a) percentages; b) influx from Goldeye Lake, AB. The depth of the MZA in the GDL core (17-19cm) is marked with a horizontal grey shaded band. The age of the MZA (7627 cal BP; Zdanowicz, et al. 1999) is marked with a horizontal grey line and labelled; the age of the MZA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Dotted 10-times exaggeration lines have been added to a number of the curves so that the patterns are more visible. Please note scale changes.

6600

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7600 MZA Age (cal BP) 191

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1500 3000

Particles/cm2 /yr

Tanypodinae (Macropelopiini) Chironominae (Pseudochironomini) Tanypodinae (Pentaneurini) Chironominae (Chironomini) Chironominae (Tanytarsini - Tanytarsina) Orthocladiinae

e lla ie typ n la n a/Paracladopelma a s i cus liel m iu . n a e sis d f tia sp. B u C n a . B dif t us ma ig p n s us m s b u ye ther sp u mus u m s ro in a Count m no su g gens - o ll le no omus es m o r su s e us a o pes n ip o n iro r s lu ri a su m ir i o dipes d lla o rniella/Zavr ina s/Orthocl e p m d n n ilum ir nyta o su u smittia/Smi ius a o el ch tendipes n te e d tia och cera a b sectra nyta rsina rsus ch r rs neura/Thienep phye o d p te chir o e n ch d ta o r p o to o d a C on o to to o o t astie chiron u o te o ta yta yta yta yta o kieff ctrocladiusu rundini ir d d g ra lyp d ryn u r ra ryn c n ra b cl ad h la ryp ryp icr n yp icrot erge la o a ic n n n n ri se se o e C C C C Cyphomella/HarnischD E Gl M Pa Pa Po S Sticto Pse C C L M Pa Ta Ta Ta Ta Co C Lim Pa P P La Pr H

6600

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7600 MZA Age (cal BP) (cal Age

8100

8600

20 40 60 10 10 10 10 20 20 20 10 10 10 10 10 10 10 10 10 10 10 10 20 20 20 20 40 10 10 10 10 10 10 10 20 60 120

% 192 a)

Tanypodinae (Marcopelopiini) Chironominae (Pseudochironomini) Tanypodinae (Pentaneurini) Chironominae (Chironomini) Chironominae (Tanytarsini -Tanytarsina) Orthocladiinae

dopelma a la racl type niel la n el li ius . B ncus e s . ia p a r t s gua v C nsi r lad diff us s us m i a p e e c n rnischia/Pa s s m s b u y th sp. B u m a u u u m ro n o tho /Smit es H s m es s m mu g ugens - lla us a s / e o p e o ono iella/Z ra l e i ono dip ip a n r tars ra a n t arsus a i ia ir d ll ono lum a o y e r c t ina in er lad mitti s h en ndip iron endi n ie ir i c e y s sus chi s pus/Or c s iu omu c t mella e h t h di nt ochi tan o bo s n r rsus r oneura/Thienema o d n to to o t c tot s c d o n p ta a ta n to tro d a p p o rote tochir u ter ro y y o keiff c u rundin y p c ga lype rge e u c n ic a e e b hiro r icr ly i a ara o e tic s lad ory a i anytar an ory r s rocl C CladopelmaC Cry Cyph D Endo G M P P P S S P C C L M Parata T T Tanyt Ta C C LimnophyesPar Ps P La P Total

6600

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7600 MZA Age (cal BP) Age (cal

8100

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0.05 0.10 0.005 0.003 0.002 0.002 0.03 0.01 0.02 0.015 0.002 0.003 0.01 0.004 0.002 0.01 0.002 0.003 0.003 0.008 0.015 0.03 0.03 0.015 0.04 0.003 0.008 0.002 0.02 0.01 0.003 0.002 0.015 0.1 0.2 0.3

Head capsules/cm2 /yr

b) 193

n ) tio re ita tu p i 2009 ci re l p jewsk a ly tempera Ga nu Ju an and and Gajewski 2009) ion gion g e re l al r tr tra n n 1 3 4 5 is is s x xi Ce Ce A Axis 2 Axis Ax A anomaly (Viau anomaly (Viau

6600

7100 194

7600 MZA Age (cal BP)

8100

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0.0 1.0 0.0 1.0 0.0 1.0 0.0 1.0 0.0 1.0 0.5 1.5 2.5 -50 0 50

Sample score °C mm

n ) o ) e 9 ti 9 r 0 a 0 tu 0 it 0 ra 2 ip 2 e ki c i p s re sk m w l p w te je a je y a u a l G n G Ju d n n a d n a n n io io a g u g u e ia e ia l r V l r V a ( a ( tr ly tr ly 1 4 5 n a n a 2 3 e m e m is is is is is C o C o x x x x x n n A A A A A a a

6600

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7600 MZA Age (cal BP) 195

8100

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0.0 1.0 0.0 1.0 0.0 1.0 0.0 1.0 2.0 0.0 1.0 0.5 1.5 2.5 -50.0 0.0 50.0

Sample score °C mm

es u g lo a n a t ses lo n e e c n r 5 gu tio tu f tatio a a alo it 09) r pi n p 0 e ci raturei 2009) i 2 age o re age of 9 closest analogues a e k mp r p r rn rec te e e ws p wski ave e e ly av aj u y mod J t G nnual Gaj n July temp a a ion b es t s n and n me a o u lid a alidation by i ted v to clo l regi(V l regio e a a (Viau and s-va y tr ly ma ntr al a sti ros e en E c Estimated total annual C C om istanc n by by cross- D anom a

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7600 MZA Age (cal BP)

8100

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14 16 18 600 840 88 104 0.5 1.5 2.5 -50 0 50

°C mm °C mm SCD

Figure 5.9 Pollen-inferred mean July temperature and total annual precipitation from Goldeye Lake, AB, reconstructed using the MAT. Dashed lines are loess smoothers with spans of 0.3. The vertical grey line through the “Distance to closet modern analogue” curve indicates the 20th percentile acceptable/non-analogue cut-off (=92), as determined using the SCD metric. Reconstructions of mean July temperature and total annual precipitation anomalies using pollen data from sites across central Canada (50-70°N, 80-120°W; Viau and Gajewski 2009), are provided for comparative purposes. Vertical grey lines through the comparative mean July temperature and total annual precipitation anomaly curves indicate X-axis values of 0. The depth of the MZA in the GDL core (17-19cm) is marked with a horizontal grey shaded band. The age of the MZA (7627 cal BP; Zdanowicz, et al. 1999) is marked with a horizontal grey line and labelled; the age of the MZA falls slightly off from the midpoint of the ash as a result of age-depth estimation/interpolation. Please note scale changes.

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s logues a logue n a a t an s e st ) lose t 3 c n re 0 clos on u 1 3 i ly ne e at u o of alogue ur it J n at ip 2009) mp depth ge i e a n a er rec ean co er r p m ( temperatverage of lak 4) a h av ode ed LS y ed pt y P July t b m nnual at A n n b de m o ima on ea t ti sest n July and temp Gajewski 2009) n a and Gajewsk m lake a o io esti by W idati es d e d l (component d eg iau r e S e ali r l regioV trap tu -va trap L at -v (Viau a ( s ra s s P ral e timat ot tim oss nt aly ntr aly oot p s s ance to cl m m B E cros Bo WA E cr t Ce Ce o y tem by by b Dis ano an 6600

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7600 MZA 197 Age (cal BP)

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14.0 16.0 18.0 14.0 15.0 1.5 2.0 2.5 1.8 2.0 15.0 20.0 25.0 0.5 1.5 2.5 -50.0 0.0 50.0 °C m SCD °C mm

Chapter Six: WILDLIFE AND HUMAN IMPLICATIONS OF THE TERRESTRIAL AND AQUATIC ENVIRONMENTAL IMPACTS OF THE EASTERN WHITE RIVER (WRA) AND MAZAMA (MZA) ERUPTIONS

6.1 Environmental, wildlife, and human significance of the WRA

6.1.1 Environmental responses to the WRA compared to regular patterns of environmental change

6.1.1.1 Spirit Lake

At Spirit Lake, the WRA extended and intensified many of the effects of the then ongoing warmer/drier phase of the region’s 100-year climatic cycle, resulting in particularly low terrestrial productivity and increased fire activity that lasted for ca. 50 years. Contrary to the regular pattern, the WRA also caused noticeably reduced representation of Pinus and increased representation of certain shrub and herbaceous taxa such as Salix, Artemisia, and Cyperaceae, indicating generally reduced plant cover and a more open environment after the ash. These impacts on the composition of the vegetation community lasted ca. 100 years to the end of the cooler/wetter phase that followed the warmer/drier phase during which the ash fell. Pinus in particular was substantially reduced during the ca. 50 years after the WRA, when it ought to have been elevated as a result of the ongoing warmer/drier phase. Representation of Pinus reached its lowest point in the record ca. 50 years after the WRA, when the short-term effects of the ash combined with those of the new cooler/wetter climatic phase to reduce its abundance still further.

Many shrub and herbaceous taxa reached their highest values for the record during this period, under the combined influence of the WRA and suitable wetter/cooler climatic conditions.

Representation of Pinus recovered to previous levels by the next warmer/drier phase, ca. 100 years after the deposition of the ash. The short-term effects of the ash on the aquatic environment were limited primarily to increased lake disturbance as a result of increased landscape instability/erosion, which – like short-term effects on the terrestrial environment – lasted ca. 50 198

years to the end of the warmer/drier phase during which the ash fell. Increased representation of

various resistant, generalist chironomid taxa such as Micropsectra, Paratanytarsus, and

Tanytarsina group C lasted up to ca. 150 years, and was not typical of the region’s regular

centennial-scale climatic cycle. Long-term effects on chironomid community productivity lasted to the end of the cooler/wetter phase that followed the ash – ca. 100 years, as occurred in the terrestrial environment – before returning to previous patterns with the end of cooler/wetter conditions and the onset of the next warmer/drier period.

The terrestrial and aquatic impacts of the WRA at Spirit Lake were often unique in kind, degree, and/or duration relative to regular patterns, causing considerable both short and long- term changes. Short-term reductions to terrestrial productivity, and increases in fire activity and landscape instability were substantially greater than typical of the region at the time. Short-term increases in fire activity and landscape instability might also have exacerbated conditions of reduced terrestrial productivity by causing additional disturbance to the environment. Long-term changes to vegetation community composition also resulted in reduced abundance of Pinus – the dominant tree present in the region – relative to certain shrub and herbaceous taxa such as Salix,

Artemisia, and Cyperaceae, and thus to more open terrestrial environments in the ca. 50 years following the WRA, when the abundance of Pinus would normally have been increased, and the boreal forest landscape would generally have hosted a more closed vegetation canopy. This resulted in a ca. 100-year long period of more open vegetation at the site atypical of the regular pattern. Long-term decreases in aquatic productivity were also of sufficient significance to negate the effects of the cooler/wetter climatic phase that began ca. 50 years after the eruption, which would typically have brought increased within-lake productivity. This resulted in a ca.

100-year period characterized by conditions of decreased productivity within the lake that was

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also not typical of the regular pattern. Disturbed conditions within the lake lasted for up to ca.

150 years, as indicated by altered chironomid community structure in favour of resistant and generalist taxa. Short-term increases in landscape instability might have exacerbated these conditions by causing additional disturbance to the aquatic environment. These terrestrial and aquatic effects of the WRA would likely have had a substantial impact on wildlife and human populations by causing reductions to the availability of terrestrial and aquatic food, material, and habitat resources both generally (as a result of decreased productivity) and particularly (as a result of reductions in the abundance of certain taxa) of a greater degree and/or duration than was typical of the region at the time.

6.1.1.2 “Marahbodd” Lake

At “Marahbodd” Lake, the WRA led to particularly increased representation of herbaceous plant

taxa, decreased fire activity, decreased terrestrial productivity, and increased landscape

instability/erosion/lake turbidity during a warm phase of the area’s 200 to 300-year centennial- scale climate cycle, when these tendencies would generally have been inverted. The effects of the WRA on the environment at “Marahbodd” Lake thus caused the reversal of terrestrial environmental conditions from those which might have been expected in the region at the time, despite the distance of the site from the source of the eruption and its relatively thin ash layer.

Alterations to terrestrial environmental conditions as a result of the WRA were also slightly greater in degree than experienced under the region’s regular climate cycle, though impacts were certainly of a lesser degree than at Spirit Lake. Impacts to the terrestrial environment lasted through the warm period that was ongoing at the time of the eruption before returning to normal

with the following cool period, leading to conditions of more open vegetation, decreased fire,

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decreased terrestrial productivity, and increased landscape instability/erosion/lake turbidity

which lasted ca. 200 years – 50-100 years longer than typical. Changes to chironomid

community structure were minor, however, with slightly increased representation of only a few

resistant taxa, suggesting limited impact of the ash on aquatic communities. Patterns of

chironomid community productivity were also generally unaffected by the WRA. Shorter-term aquatic impacts of the WRA lasted ca. 100-150 years, to the end of the warm phase that was ongoing when the ash fell.

Despite the increased distance of “Marahbodd” Lake from the source of the eruption in

comparison to Spirit Lake, the impacts of the WRA – particularly on the terrestrial environment

– lasted longer at “Marahbodd” Lake than at Spirit Lake, though they were lesser in degree. In

general, the impacts of the ash at both sites were similar, with decreased productivity, increased

representation of herbaceous plant and generalist/resistant chironomid taxa, and increased

landscape instability/erosion/lake turbidity – though fire activity at “Marahbodd” Lake

decreased, whereas it increased at Spirit Lake. It is possible that this difference was a result of

the increased fuel load at Spirit Lake relative to “Marahbodd” Lake prior to the WRA, as a result

of its forested environment and increased abundance of fire-susceptible coniferous taxa such as

Pinus. High mortality and the increased combustability of dead plant material would have

increased the susceptibility of the Spirit Lake vegetation to ignition still further. Despite their

lesser degree, the effects of the WRA at “Marahbodd” Lake were nonetheless substantial enough

to reverse the conditions that would otherwise have been in place under the ongoing warm phase

of the region’s centennial-scale climate cycle, and to extend the duration of these conditions

through to the next cool period. They were also substantial enough to slightly intensify these

conditions beyond their usual range. It is possible that the extended duration of WRA impacts at

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“Marahbodd” Lake occurred as a result of the general difficulty of low-energy tundra/forest-

tundra environments such as that of “Marahbodd” Lake in recovering from disturbances, resulting in a longer successional period.

6.1.2 Implications of the environmental response to the WRA for wildlife and human populations

A summary diagram detailing the terrestrial and aquatic impacts of the WRA at Spirit and

“Marahbodd” Lakes and evidence of wildlife and human responses to the WRA available from

other publications is presented in Figure 6.1. In combination, the direct and short and long-term

indirect impacts of the WRA on wildlife and human populations within the fallout zone of the

ash are likely to have been quite severe. Modern studies of the wildlife and human consequences

of volcanic eruptions in the aftermath of the 1980 eruption of Mount St. Helens have

demonstrated substantial direct impacts of volcanic ash itself on the physical and mental health

of wildlife and human populations (Decker and Decker 2006; Francis and Oppenheimer 2004;

Zeilinga de Boer and Sanders 2002). While these impacts were certainly more severe closer to

the source, the sound of the explosion carried at least 800 km, while ash was deposited as far

away as western Montana, resulting in a relatively large area within which direct effects of the

eruption might have been felt (Decker and Decker 2006; Francis and Oppenheimer 2004;

Zeilinga de Boer and Sanders 2002). These include stress from the eruption and associated noise

and storms, the onset of strange conditions, and uncertainty regarding the future, and physical

ailments including respiratory illness from breathing airborne ash, eye irritation, and digestive

complaints and mechanical damage to teeth from ingestion (Francis and Oppenheimer 2004;

Zeilinga de Boer and Sanders 2002). Volcanic ash also causes transportation concerns, directly

damaging equipment and blocking transport routes (Francis and Oppenheimer 2004; Zeilinga de

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Boer and Sanders 2002). Ash from volcanic eruptions also clogs and contaminates watercourses,

causing flooding and reduced access to usable drinking water, and may cause trees to fall, causing further damage or disruption to resources, injury, or death (Francis and Oppenheimer

2004; Zeilinga de Boer and Sanders 2002). If rained upon, ash may slide or slump, or it may form a hard crust covering whatever it has settled upon, causing injury, death, or damage

(Decker and Decker 2006; Francis and Oppenheimer 2004). Ash may also be entrained by wind, potentially causing damage when blown into objects or living things (Decker and Decker 2006;

Francis and Oppenheimer 2004). Direct effects such as these would be substantial and disruptive, but would be unlikely to last very long – eventually, perhaps within a season or two, the ash would settle out of the air and water and be washed off the landscape or stabilized, and come

(more-or-less) to rest. Though the precise kind, degree, and duration of indirect ash effects is highly variable from eruption to eruption and from site to site, the indirect effects of volcanic ash deposition – on terrestrial and aquatic community composition and productivity, fire activity, lake and river water chemistry and turbidity, landscape stability, and erosion – would likely have far more insidious consequences for both wildlife and human populations by potentially impacting the availability of clean water, food, material, and habitat resources, perhaps for centuries.

At Spirit Lake, the short and long-term impacts of the WRA caused considerable both short and long-term changes that were unique in kind, degree, and/or duration relative to regular patterns, including particularly reduced forest cover, decreased terrestrial and aquatic productivity, increased fire activity, and increased landscape instability/erosion/lake disturbance lasting ca. 50-

150 years. While decreased forest cover, increased representation of certain shrub and

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herbaceous taxa, and increased fire may have increased the abundance of certain important edible resources such as berries, atypically decreased productivity of both terrestrial and aquatic environments would likely have led to particular scarcity of plant and aquatic food, material, and habitat resources for both wildlife and human populations. Particularly disturbed lake environments might also have resulted in markedly reduced access to usable water sources.

Unusually increased landscape instability and erosion would have exacerbated these effects, and would also have made travel specially difficult and caused terrestrial landscapes and processes to behave in unconventional and unpredictable ways (e.g. by increasing the possibility of mass movements and/or altering the conditions under which they would occur), leading to increased stress and increasing the possibility of injury or death as a result of misjudgment.

At “Marahbodd” Lake, the short and long-term impacts of the WRA decreased the representation particularly of shrub taxa, decreased terrestrial productivity, decreased fire activity, and increased landscape instability/erosion/lake disturbance beyond typical levels for ca. 100-200 years. Direct impacts of the WRA at the site were likely somewhat lesser than at Spirit Lake due to its increased distance from the source of the eruption and thinner ash layer. Though lesser in degree than at Spirit Lake, the short and long-term indirect effects of the WRA at “Marahbodd”

Lake are nevertheless likely to have caused changes to the availability particularly of terrestrial plant food, material, and habitat resources for wildlife and human populations that were out of the ordinary relative to regular patterns of environmental change. While specially increased representation of herbaceous plant taxa may have been beneficial in some respects by increasing the availability of certain resources, particularly decreased representation and productivity of arboreal taxa would have reduced the availability of other resources in turn. Generally decreased

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terrestrial productivity relative to regular patterns would also have led to specially increased

scarcity of plant resources in general in the already low-productivity environment in the region

of the lake. Particularly decreased fire activity might have led to somewhat increased landscape

stability relative to normal patterns, but would also have slowed already slow regeneration rates

by reducing the rate of recycling of dead plant material. The aquatic environment at the site was

largely unaffected by the deposition of the ash, however, and thus it and its resources would have

remained available for wildlife and human populations able to take advantage. As at Spirit Lake,

particularly increased landscape instability at “Marahbodd” Lake might have caused increased

erosion and/or lake disturbance and turbidity relative to normal patterns, making movement

across the landscape especially difficult, and leading to further changes in the availability of

terrestrial and aquatic food, material, and habitat resources, and to reductions in the availability

of usable water. Increased landscape instability and erosion relative to normal would also have

led to generally and uniquely unconventional and unpredictable landscapes, increasing the

possibility of injury or death as a result of misjudgment, and likely leading to increased stress in

wildlife and human populations. While certainly still more challenging than typical, conditions at

“Marahbodd” Lake in the aftermath of the WRA were thus perhaps less insurmountable than at

Spirit Lake where impacts were more severe, though the slow recovery time of the environment

at “Marahbodd” Lake resulted in their enduring for a longer period.

Evidence from Spirit and “Marahbodd” Lakes suggests that Workman (1974, 1979) was correct in many of his suggestions regarding the physical impacts of the WRA on the environment. The data from Spirit and “Marahbodd” Lakes supports his suggestion that the eruption and deposition of the ash would have been followed by a “disastrous early spring” (Workman 1974:249), with

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enhanced landscape instability and erosion, contamination of water sources, and reduced productivity of terrestrial and aquatic environments relative to regular patterns of environmental change. At Sprit Lake, however, Workman’s (1974, 1979) suggestion of a special reduction in the representation of herbaceous plants is not supported, and herbaceous plants actually increased in relative abundance at the site relative to pre-ash conditions, while Pinus experienced the most noticeable decline. The relative abundance of herbaceous taxa did increase at

“Marahbodd” Lake relative to pre-ash conditions, illustrating the wide variability of environmental responses to even the same event that are possible in different environments.

Workman’s (1974, 1979) suggestion that environmental recovery might have taken an extended period of time is supported by palaeoenvironmental evidence from both sites, where recovery of the environment from the short-term effects of the ash took a minimum of ca. 50 years (at Spirit

Lake), while recovery from long-term effects took up to 200 years (at “Marahbodd” Lake). The results from Spirit Lake in particular support the possibility of substantial impacts of the ash upon wildlife and human populations suggested by linguistic, ethnographic, and archaeological evidence from the region.

Genetic replacement of local Southern Lakes caribou populations ca. 1000 BP, following an apparent ca. 400-year abandonment of the region, has been suggested to have occurred as a result of the WRA and/or the MWP (Kuhn, et al. 2010). The Spirit Lake data support the possibility that the WRA was the principal stimulus behind the departure of local caribou populations at the time, as the availability of water, food, and habitat resources in the area of the Southern Lakes was likely severely compromised during at least the first 50 years after the eruption. The continued absence of caribou from the region for an additional 200 years – after even the long-

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term environmental impacts of the deposition of the ash had dissipated – however, cannot be explained by the WRA. Kuhn et al.’s (2010) suggestion that environmental change resulting from the Medieval Warm Period (MWP) might account for the disappearance of caribou for such an extended period is also not supported by the Spirit Lake data, where indications of substantial environmental change as a result of the MWP are lacking. Further, no mention of noticeable effects of the MWP appears in other palynological and isotopic studies from the area (Anderson, et al. 2007; Anderson, Abbott, Finney and Edwards 2005; Cwynar 1988). Interestingly, Farnell et al. (2004) have noted a period of no net ice accumulation of the region’s ice patches from ca.

1440-1030 BP. Genetic replacement of caribou populations occurs almost immediately after this period. It is thus possible that reductions in the availability of ice patch habitat played a role in delaying the return of caribou to the region after it was abandoned (Kuhn, et al. 2010).

Conversely, caribou appear not to have abandoned Northwest Territories ice patches after the WRA or as a result of the MWP (Letts, et al. 2012). Though the terrestrial environmental impacts of the WRA at “Marahbodd” Lake were certainly noteworthy and relatively long lasting, they were lesser in degree than at Spirit Lake. Combined with limited aquatic impacts, it is possible that the reduced severity of ash effects on the terrestrial environment resulted in water, food, material, and habitat resources remaining generally available to wildlife and human populations at “Marahbodd” Lake after the eruption, and that populations were therefore able to remain. Increased disturbance and decreased terrestrial productivity may, however, have reduced population sizes.

At Spirit Lake, the uniqueness of the direct and indirect environmental impacts of the WRA on the availability of water, food, material, and habitat resources would certainly have caused

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substantial disruption to human populations for at least the first 50 years after the eruption, and

potentially for up to 150 years. Probable reductions in wildlife populations as a result of

increased mortality and/or emigration during this time would have enhanced this disturbance,

and may have encouraged human populations to move out of the region in search of resources or

aid. The data from Spirit Lake thus supports the evidence of archaeological, ethnographic, and

linguistic studies that suggests that human occupancy of southern Yukon was at least reduced

after the WRA (Hare, et al. 2004; Johnson and Raup 1964; MacNeish 1964; Matson and Magne

2007; Moodie, et al. 1992; Mullen 2012; Workman 1974, 1979). Hare et al. (2004) and Mullen

(2012) have suggested that this period of reduced occupancy lasted for ca. 200-500 years, based

on absent or decreased cultural radiocarbon dates from the region during this period, however,

this period is again longer than the period of even long-term environmental impacts that occurred

at Spirit Lake as a result of the WRA. Ethnographic and archaeological evidence of caribou

hunting indicates that caribou have been important to subsistence in the region for many years

(Hare, et al. 2004; McClellan 1975, 1981, 1987). The continued absence of caribou from the region (and potentially of other species important to subsistence) may thus have played a role in lengthening the period that human populations stayed away. The area over which the ash was deposited is also quite substantial, and likely played host to a relatively large human population

(Matson and Magne (2007) estimate a group size of ca. 400-1000), whose immigration into new regions may well have triggered substantial rippling population movements suggested by archaeological, ethnographic, and linguistic evidence of the eventual dispersal of Northern

Athapaskan populations far to the east and south (Johnson and Raup 1964; MacNeish 1964;

Matson and Magne 2007; Workman 1974, 1979). Linguistic evidence of this dispersal is

provided by evidence presented by Hoijer (1971) suggesting the divergence of Pacific Coast

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Athapaskan and Apachean Athapaskan from Northern Athapaskan at approximately the time of

the WRA. Matson and Magne (2007) link these events, suggesting that the WRA may have been

the initial stimulus of the population movements that ultimately resulted in this linguistic

divergence. Workman (1974, 1979) also hypothesized about this potential linkage in his

examination of the potential human impacts of the WRA. Evidence of Athapaskan occupations

in central British Columbia since the WRA, including rectangular structures, Kavik points, side-

notched points with concave bases, and microblades, provides additional support for the WRA

having stimulated population movements out of the affected region, with lasting consequences

(Matson and Magne 2007).

Radiocarbon dating of cultural remains recovered from ice patches in the Southern Lakes

region has dated the replacement of the atlatl with the bow-and-arrow in southern Yukon to ca.

1100-1200 BP, providing evidence for technological replacement among human populations

approximately coincident with the WRA (Hare, et al. 2004). Given the considerable

environmental impacts of the WRA identified in the Spirit Lake palaeoenvironmental record, and

their likely consequences for water, food, material, and habitat resources, it is not unreasonable

to suppose that populations would have adopted new hunting technologies as a means of

adapting to these unique circumstances. Hare et al.’s (2004) and Mullen’s (2012) proposition that

human populations largely abandoned the region for ca. 200-500 years following the eruption would suggest that the introduction of the bow-and-arrow did not occur as an adaptation to the environmental effects of the WRA on their return, however, as conditions had by then returned to regular patterns. It is possible that any groups that remained in the area impacted by the ash and/or that returned earlier might have adopted this new technology to assist them in their subsistence efforts. A number of potential reasons have been identified as influencing the choice

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of a bow-and-arrow for hunting over other forms of projectile weapon such as the atlatl,

including terrain, vegetation, range, accuracy, and/or force requirements, and/or the cost of production (Kelly 2007). Kelly (2007) also relates a shift towards increased use of the bow-and- arrow to a change in game type and/or hunting strategy, suggesting that because of its typically larger points, the increased distance it can be thrown, and its consequent increased force, the atlatl might be more useful for the pursuit of large game than the bow-and-arrow. Kelly (2007) also suggests that the increased movement involved in throwing an atlatl might be valuable in communal drive hunting, where the movement might help to scare and direct animals. In contrast, the reduced force of a bow-and-arrow and reduced movement required to use it might be more suited to the pursuit of smaller game and/or to stalking of game by individuals (Kelly

2007). Use of bone, horn, and antler for points has also been linked to the pursuit of smaller game, and also appears in the region of southern Yukon after the WRA at the Taye

Lake/Aishihik phase transition (Ellis 1997; Hare, et al. 2004; Workman 1978). The adoption of the bow-and-arrow and of bone and antler points after the WRA might thus be related to a shift towards increased pursuit of smaller game and/or to increased frequency individual rather than communal hunting. Evidence of the at least partial abandonment of the region by caribou after the WRA suggests that reductions in the availability of large game may indeed have been a factor in the technological change (Kuhn, et al. 2010). Changes in hunting strategies may have followed from changes in game types, or may have occurred in response to the reduced productivity of the landscape requiring populations to spread themselves more thinly after the deposition of the ash. From material recovered from southern Yukon ice patches, Hare et al.

(2004) have also identified a shift from spruce to birch for the construction of weapon shafts after the WRA. Though representation and influx of Picea do decrease as a result of the ash,

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these changes are minimal in comparison to conditions immediately previous, suggesting that this change was probably not related to reduced availability of Picea after the WRA; instead, it is also possible that Betula was more suitable for the construction of antler-mounted arrow shafts than spruce, and this is why the change was made. Oral traditions recorded by Moodie et al.

(1992) in the Mackenzie Valley also link the discovery of copper with volcanism at approximately the time of the WRA; use of copper as appears in southern Yukon after the WRA with the onset of the post-ash Aishihik archaeological phase (Workman 1978).

The palaeoenvironmental data from “Marahbodd” Lake suggests that living conditions for human populations in the region would have been rendered more difficult than usual for a number of years. The reduced severity of the environmental impacts of the WRA at

“Marahbodd” Lake relative to those at Spirit Lake, however, supports faunal, ethnographic, and archaeological evidence that does not suggest that the environmental consequences of the eruption were sufficient to cause large human population movements out of the area. Indeed, ethnographic and archaeological evidence indicates movement of refugees into the region from more severely affected areas to the west. Moodie et al. (1992) have suggested that oral traditions from the Mackenzie Valley describing a recent eruption and its after effects – including population movements and the development of new languages – are in fact tales of the WRA. If this suggestion is true, descriptions of falling ash and debris present in “The Collapse of the

Mountain” (Moodie, et al. 1992:152-153) are likely based on firsthand experiences of such events by local populations in the Mackenzie Valley, however descriptions of increased fire activity in the region are not supported by the “Marahbodd” Lake data. It is possible that populations fleeing more severely affected regions instead told local populations about the

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occurrence of widespread fire. In addition, accounts of several impacts of the (WRA) eruption

that are not likely to have occurred at that distance from the vent – such as exploding rocks –

suggest that other aspects of the descriptions were borrowed from the accounts of refugees.

Increased frequency of cultural radiocarbon dates outside the fallout area of the WRA, in

combination with decreases within the fallout area of the ash, are also suggestive of population movements from areas closer to the source of the WRA such as southern Yukon, to regions at greater distances such as the Mackenzie Valley (Mullen 2012). The long duration of the environmental impacts of the WRA in the region of “Marahbodd” Lake may have eventually led some to leave the region for improved conditions beyond the fallout area of the ash, but if this occurred, evidence of these movements (or rather, lack thereof) would indicate that they were substantially lesser in scale than those triggered from where the eruption’s impacts were more severe.

6.2 Environmental, wildlife, and human significance of the MZA

6.2.1 Environmental responses to the MZA compared to regular patterns of environmental change

At Goldeye Lake, the most notable terrestrial impacts of the MZA were a slight change in the

composition of the vegetation community suggesting a more open environment after its

deposition relative to prior, atypically decreased productivity of the vegetation, and a brief peak

followed by an extended decrease in fire activity. With the exception of decreased fire activity –

likely a result of decreased fuel load after substantial burning, and of decreased terrestrial

productivity in the years after the ash – these conditions paralleled changes already occurring as

a result of the then ongoing warm/dry phase of the region’s centennial-scale climate cycle. The

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result was an intensifying effect producing conditions of opened vegetation, decreased terrestrial productivity, and increased fire activity after the ash that exceeded those experienced at any other time in the record, however these differences were only slight. Changes in aquatic proxies after the MZA also tended to parallel changes already occurring under the influence of cyclic climatic change. Conditions of already increased landscape instability/erosion/lake water turbidity, decreased aquatic productivity, and decreased productivity and representation of many generalist and plant-associated chironomid taxa were slightly intensified in the years after the

MZA relative to their regular patterns. Reduced productivity within the catchment in general also

paralleled regular patterns of climatic change, leading to particularly low values in the years after

the eruption. Changes to the vegetation community and to landscape stability/erosion/lake water

turbidity after the ash endured through the cooler/wetter climate phase that began ca. 125 years

after the eruption, before returning to normal patterns during the next warm/dry period. After ca.

50 years of elevated values, conditions of reduced fire activity lasted through the remainder of

the warm/dry period during which the ash fell (when fire activity should have been generally

increased) and into the following cooler/wetter phase. Reduced general catchment productivity,

aquatic productivity, and productivity and representation of generalist and plant-associated taxa

also endured into the cooler/wetter climatic phase that followed ca. 125 years after the eruption,

when they would typically have increased, while terrestrial productivity returned to normal

patterns at approximately the time of the transition from warmer/drier to cooler/wetter

conditions. Aquatic productivity and the productivity and representation of generalist and plant-

associated chironomid taxa increased partway through this cooler/wetter phase; the productivity

and representation of generalist and plant-associated chironomid taxa was somewhat elevated

from usual at this time, potentially as a result of the combined influence of generally more

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favourable lake conditions under the cooler/wetter climate, and increased availability of silica after the ash relative to normal conditions, leading to particularly increased productivity of diatoms and thus also of chironomids. Conditions of specially elevated productivity and representation of generalist and plant-associated chironomid taxa extended ca. 250 years into the next warm/dry climate phase, before returning to approximately their pre-ash levels and patterns.

The MZA also produced unique short-term increases in the abundance of disturbance-resistant and acid-tolerant chironomid taxa at and immediately after the ash, suggesting particularly disturbed conditions and perhaps increased lake water acidity, and lasting changes in chironomid community composition that extended for the remainder of the record – though as has been discussed, similar environmental tolerances of the old and new taxa make it unlikely that these lasting changes reflect any substantial alteration to the lake environment in the long-term (see section 5.2.3). Substantial and unparalleled reductions to sediment carbonate content for ca. 250 years after the ash may also be indicative of especially increased acidity of the lake water during that time.

6.2.2 Implications of the environmental response to the MZA for wildlife and human populations

A summary diagram detailing the terrestrial and aquatic impacts of the MZA at Goldeye Lake and evidence of wildlife and human responses to the MZA available from other publications is presented in Figure 6.2. The direct physical and mental impacts of the MZA on wildlife and human populations are likely to have been generally similar to those which occurred as a result of the eruption of Mount St. Helens, and which have been supposed for the WRA. The great distance of Goldeye Lake from the source of the MZA at Mount Mazama, OR, however, might have resulted in these effects being of lesser severity than at sites closer to the source and/or with

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thicker ash layers. The subsequent short-term environmental impacts of the MZA were generally

slight in kind and degree, paralleling and marginally intensifying the conditions already present

under the ongoing warm/dry phase of the region’s centennial-scale climate cycle. Due to their limited difference from regular environmental conditions in the region, the effects of ash-induced environmental disturbance on wildlife and human populations in the region were likely relatively limited, with water, food, material, and habitat resources remaining comparatively unchanged relative to normal, though living conditions were likely rendered somewhat more difficult, and disturbed conditions endured for up to 500 years. Immediate and outstanding increases in fire activity may have aggravated already difficult conditions post-ash by causing increased disturbance and destruction, though the increased fire activity would also speed the recycling of dead vegetation and clear the way for new growth. Particularly disturbed lake conditions and decreases in aquatic productivity would likely also have made living conditions in the years after the eruption somewhat more difficult than normal by reducing the availability of usable water and aquatic food, material, and habitat resources beyond what was typical of the region. Atypical increases in lake water acidity may also have further reduced the availability of usable water resources for wildlife and human populations. Finally, particular decreases in forest cover and terrestrial productivity would have reduced the availability of certain terrestrial food, material, and habitat resources somewhat beyond what was normal, and atypically increased landscape instability would have increased the unpredictability of the landscape relative to normal conditions, and so potentially may have increased the difficulty of travel within the region and/or caused further damage to terrestrial and aquatic environments as a result of increased erosion, lake turbidity, mass movements, watercourse blockages, and so on.

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Evidence from Goldeye Lake suggests that Oetelaar and Beaudoin (2005) are generally correct

in their suggestions about the likely environmental impacts of the MZA within the fallout area of the ash. The data from Goldeye Lake supports their suggestion that the deposition of the ash increased landscape instability and erosion, decreased the productivity of plant life, and caused changes to water chemistry in ways that were unique to the period. If temperature was indeed reduced in the region of the site as they suggest, however, it is not captured by the Goldeye Lake temperature reconstructions, suggesting that any temperature-induced change to the environment that occurred was insufficient to counter successional changes resulting from the ash’s disturbance. In their previous diatom-based study of Goldeye and Fairfax Lakes, Hickman and

Schweger (1993) noted that Foothills environments appear to have been less sensitive to climatic changes during the Holocene than Plains sites, potentially as a result of the moderating influence of the mountains. It is possible that these same influences reduced the sensitivity of Goldeye

Lake to the effects of the MZA. While environmental conditions at the site were certainly impacted by the deposition of the ash, and subsistence was likely rendered more difficult as a result of decreased availability of water, food, material, and habitat resources, the limited degree of ash impacts at Goldeye Lake relative to regular patterns of environmental change may not have been severe enough to trigger movement of wildlife or human populations out of the region as has been suggested for the Plains, where environmental responses to the ash were likely more severe as a result of the increased sensitivity of Plains environments, and strain from already warm and dry conditions during the HCO. The long duration of environmental disturbance at

Goldeye Lake, however, may have resulted in reduced population sizes, and/or may have finally stimulated movement to other regions and/or the development of new strategies to increase the efficiency of resource use, as archaeological evidence suggests occurred on the Plains.

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Substantial consequences of the MZA on the Plains are suggested by particularly reduced archaeological site frequency in southern Alberta after the eruption, lasting ca. 500 years, and disuse of sites such as Stampede (DjOn-26) and Tuscany (EgPm-377), for ca. 500-1500 years

(Oetelaar and Beaudoin 2014). While reduced archaeological site frequency during the early

Middle Prehistoric on the Plains has also been attributed to sampling bias, misidentification of materials, and/or arid conditions during the HCO (Bamforth 1997; Buchner 1980; Hurt 1966;

Meltzer 1999; Oetelaar and Beaudoin 2014; Sheehan 1994, 2002), the timing of reoccupation of the Plains ca. 500 years after the eruption suggested by Oetelaar and Beaudoin (2014) coincides with the timing of essentially complete environmental recovery at Goldeye Lake. This suggests that the eruption and its after effects might very well have been the reason behind reduced occupancy of Plains environments during this time, as Oetelaar and Beaudoin (2014) have proposed. Oetelaar and Beaudoin (2014) also suggest that increased evidence of Early Archaic points on the eastern margins of the Plains is indicative of the movement of the population in that direction at this time. It is not unreasonable that the importation of stone boiling from Eastern

Woodlands populations and its adaptation for the production of bone grease for pemmican would have occurred as a strategy to increase the efficiency of resource use and mitigate the effects of shortages after the MZA, as Oetelaar and Beaudoin (2014) suggest. Evidence of fire-broken rock

(FBR) indicative of stone boiling from the Gowen, SK (FaNq-25 and FaNq-32; Walker 1992), and Stampede (Vivian, et al. 2008) sites occurs ca. 300 years after environmental conditions at

Goldeye Lake returned to normal, however, ca. 6000 BP. This delay might suggest that stone boiling was not introduced as an adaptation to continuing disturbed environmental conditions after the MZA, as Oetelaar and Beaudoin (2014) have suggested, but simply as a result of its utility as a technique for efficient food preparation and storage. However, it is possible that

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disturbed conditions lingered longer on the Plains than at Goldeye Lake, and/or earlier evidence may have yet to be discovered that would bring the introduction of stone boiling closer in time to the MZA, making a stronger case for its introduction as an adaptation to difficult subsistence conditions after the deposition of the ash.

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Figure 6.2 Summary diagram detailing terrestrial and aquatic impacts of the MZA at Goldeye Lake and evidence of wildlife and human responses to the MZA available from other publications.

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Chapter Seven: SUMMARY AND FUTURE DIRECTIONS

7.1 Summary

Palaeoenvironmental studies of changes in terrestrial and aquatic environmental proxies

following catastrophic events provide valuable information for understanding the environmental

impacts of these events within the study region. When multiple studies are available, comparison

of the environmental impacts of catastrophic events at multiple sites and from multiple events

also allows a deeper understanding of the variability of impacts that may occur, with a time-

depth not available from modern studies. When used to provide context for archaeological

studies, studies of the environmental impacts of past catastrophic events such as volcanic

eruptions may also help to guide the interpretation of archaeological evidence and the

reconstruction of the human consequences of these events, giving insight into human history, and

also valuable information that might be used to guide human responses to future environmental

change.

This study has presented new information regarding the environmental impacts of the 1147 cal

BP eastern White River (WRA) and 7627 cal BP Mazama (MZA) tephras – the results of two of the largest volcanic eruptions to occur in North America in the last 10,000 years – and has discussed the implications these impacts might have had for wildlife and human populations.

Cores of lake sediment were collected from three lakes in the western Canadian subarctic, within the fallout areas of the ashes. To study the impacts of the WRA, cores were collected from two sites at different distances from the source of the eruption. Spirit Lake, YT, is located ca. 400 km from the source of the WRA in open boreal forest, while “Marahbodd” Lake, NWT, is located close to the edge of the WRA’s distribution at ca. 1550 km from the source, in shrub-birch

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tundra near to the forest-tundra transition. To study the impacts of the MZA, a core of sediment

was collected from Goldeye Lake, AB, located in dense boreal forest in the Foothills region of

the Alberta Rockies, at the northwestern edge of the distribution of the MZA, ca. 1150 km from

its source. All of the sites were located in environmentally sensitive areas where the deposition

of the ashes is likely to have produced noticeable impacts, and that had not been previously

examined for ash effects. The cores were radiocarbon dated and the sediments above and below

the ashes were examined at high resolution for pollen, microcharcoal, magnetic susceptibility, loss-on-ignition, and chironomid head capsules. The results of proxy analysis were interpreted and subjected to statistical analysis to give insight into climate, and terrestrial and aquatic environmental conditions before and after the eruptions, and into changes in these resulting from

the deposition of the ashes.

The results showed both similarities and differences to previous palaeoenvironmental studies of

the environmental impacts of the WRA and MZA.

Proxy evidence from Spirit Lake indicated a long-term trend towards drier conditions

over the course of the record associated with the onset of the Medieval Warm Period (MWP),

with decreased representation of more wet-adapted deciduous and shrub plant taxa such as Alnus

and Betula, decreased lake productivity and depth, increased landscape instability leading to

increased erosion and lake turbidity, and possible increases in lake water acidity. Superimposed

over this long-term trend were centennial-scale cycles between wetter and drier conditions with a

ca. 100-year periodicity, associated with patterns and changes in the strength/position of the

Aleutian Low pressure system. Wetter periods in this cycle were generally characterized by decreased representation of Pinus and increased representation of various deciduous and shrub

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taxa, increased catchment and within-lake productivity and lake depth, and increased landscape stability resulting in decreased erosion and lake turbidity, while drier conditions typically produced the reverse effects. Some indications of long and short-term changes in air temperature were also present in the data, but these were not as pronounced as signs indicating variations in moisture availability at the site through time. Temperatures increased slightly in the long-term, with centennial-scale increases and decreases in temperature corresponding to the region’s 100- year climate cycle superimposed non-synchronously with wetter/drier periods; periods of increased temperature tended to intensify the effects of the current wet or dry phase. The longer- term impacts of the WRA, including decreased representation of Pinus, decreased aquatic productivity, and changes in aquatic community structure relative to regular conditions resulting from normal patterns of environmental change, lasted approximately 100-150 years, while short- term effects, including increased representation of certain shrub and herbaceous plant taxa, decreased terrestrial productivity, increased fire activity, and increased landscape instability/erosion/lake turbidity relative to regular conditions lasted ca. 50 years.

Results from “Marahbodd” Lake indicated a long-term trend towards wetter conditions, characterized by increased productivity, decreased fire activity, and more open vegetation, corresponding to the results of previous palaeoenvironmental studies conducted in the region. A superimposed 200-300 year pattern of cooler and warmer conditions is proposed to be associated with variations in solar activity under the deVries solar cycle. Warmer conditions under this pattern were generally characterized by increased arboreal pollen (AP), fire activity, catchment productivity, and lake water pH, and decreased landscape instability, erosion, lake turbidity, and lake depth. The WRA led to specially decreased terrestrial and aquatic productivity lasting ca.

100-200 years, elevated representation of herbaceous taxa lasting up to ca. 200 years, decreased

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fire activity lasting ca. 100 years, decreased lake productivity also lasting ca. 100 years, and

increased landscape instability/erosion/lake turbidity lasting ca. 100-150 years.

At Goldeye Lake, results indicated a long-term trend towards cooler/wetter conditions

associated with the latter half of the Holocene Climatic Optimum (HCO), with increased

representation of Picea vs. Pinus, decreased fire, and increased landscape stability. A

superimposed 500-year cycle between cooler/wetter and warmer/drier conditions is suggested to

be associated with a 500-year cycle in solar activity that has also been identified in the GISP2 ice

core and various other palaeoenvironmental studies from North America and elsewhere

(Chapman and Shackleton 2000; Hu, et al. 2003; Steinhilber, et al. 2012; Stuiver and Braziunas

1993; Stuiver, et al. 1995; Yu and Ito 2010). Cooler/wetter phases in this cycle tended to be associated with increased terrestrial and aquatic productivity, changes to chironomid community

structure suggesting increased abundance of aquatic plants, and decreased fire activity. The MZA

resulted in increased representation of shrub and herbaceous taxa relative to regular conditions

resulting from normal patterns of change, suggesting the precense of an uncharacteristically open

environment lasting ca. 500 years after the deposition of the ash, and atypically decreased

terrestrial productivity lasting ca. 100-150 years. Fire activity at the site experienced an

immediate and substantial increase lasing ca. 50 years, followed by a decrease to especially low

values lasting ca. 200 years. Aquatic productivity experienced an immediate and substantial

decrease after the MZA, lasting ca. 250 years, followed by an increase ca. 250 years after the

ash, with particularly increased representation of plant-associated taxa that lasted for an

additional ca. 250 years. Long lasting disturbance to the lake environment and potentially

increased acidity after the MZA was also indicated by distinctive changes to chironomid

communities, with particularly increased representation of disturbance and acid-resistant taxa,

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and by changes to the sediment carbonate and silicate content of the lake sediment unmatched at any other point in the record, lasting ca. 500 years.

The direct effects of the WRA and MZA eruptions on wildlife and human populations might have included physical and/or mental impacts such as increased incidence of stress, illness, injury, or mortality, and/or damage or disruption to resources (Decker and Decker 2006; Francis and Oppenheimer 2004; Zeilinga de Boer and Sanders 2002). In addition to these, the results of proxy analysis suggest potentially substantial indirect impacts of the WRA and MZA ashfalls on wildlife and human populations, via their consequences for terrestrial and aquatic environments.

At Spirit Lake, the direct and indirect terrestrial and aquatic environmental impacts of the

WRA are likely to have reduced the availability of clean water, food, and suitable habitat beyond typical for wildlife for at least 50 years. These findings support evidence of at least partial abandonment of the Southern Lakes region by caribou after the WRA, though the proposed period for this abandonment (lasting to ca. 200 years after the WRA) cannot be completely accounted for by either the short or long-term environmental impacts of the ash, or by changed environmental conditions as a result of the MWP (Kuhn, et al. 2010). Instead, it is proposed that though environmental conditions in the region returned to approximately normal patterns within ca. 50-150 years, reduced availability of ice patch habitat lasting until ca. 1030 BP resulted in a delayed return of caribou to the region.

The impacts of the WRA on the regional environment and wildlife at Spirit Lake would likely have had a substantial impact on human populations as well, whose water, food, material, and habitat resources would have been affected by all of the above exceptional direct and

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indirect ash effects, as well as by changes in wildlife populations. Unique conditions of terrestrial

and aquatic environmental disturbance lasting at least ca. 50 years, and the absence of caribou

(and likely other wildlife) for up to ca. 200 years was likely more than enough to have

encouraged the movement of human populations out of the region as has been suggested by

linguistic, ethnographic, and archaeological evidence (Hare, et al. 2004; Johnson and Raup 1964;

MacNeish 1964; Matson and Magne 2007; Moodie, et al. 1992; Mullen 2012; Workman 1974,

1979). Archaeological evidence also indicates changes in material culture after the WRA –

including the introduction of the bow-and-arrow, bone and arrow points, and of copper – that

might be related to changes in the types of game being pursued and/or to hunting strategies after

the WRA. Increased usage of Betula rather than Picea for weapon shafts after the WRA is not

likely to have been related to specially decreased availability of Picea in the region after the

ashfall; instead, it is possible that Betula was simply better suited for the construction of the new

arrow shafts than was Picea.

At “Marahbodd” Lake, the proxy evidence suggests that the direct and indirect impacts of

the WRA on wildlife and human populations would likely have been similar, but lesser in degree

than at Spirit Lake – though recovery of the environment took somewhat longer. Reduced

severity of the wildlife and human consequences of the ashfall at “Marahbodd” Lake relative to

Spirit Lake is supported by ethnographic evidence from the Mackenzie Valley that describes an

eruption in the west, but which focuses more on the arrival of refugees than on hardships felt

locally as a result of the eruption. The long time taken for the environment to recover may have

promoted some movement of populations into regions even further removed from the effects of

the ashfall, however if this occurred, lack of evidence for large movements out of the region

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indicates that they would certainly have been lesser in scale than those suggested by evidence from southern Yukon.

At Goldeye Lake, the short and long-term environmental impacts of the MZA slightly intensified and in some cases extended changes already occurring as a result of the then ongoing warm/dry phase of the region’s 500-year climatic cycle, causing atypical conditions of open vegetation, increased fire activity, increased landscape instability/erosion/lake turbidity, and decreased terrestrial and aquatic productivity. Additional consequences also included especially disturbed lake conditions and potentially increased lake water acidity relative to regular conditions resulting from normal patterns of environmental change. These impacts would likely have decreased the availability of usable water, food, and suitable habitat for wildlife and human populations in the region of the site beyond what was typical of the region at the time for a period of up to 500 years, though the degree of these impacts in the Foothills region was likely less severe than in the more ecologically-sensitive Plains, where warm and dry climate conditions during the HCO had already put strain on terrestrial and aquatic ecosystems (Hickman and Schweger 1993). Conditions in the region of Goldeye Lake would likely still have been generally less hospitable than usual while the region was suffering under these effects, however, and might have been exacerbated by their long duration, potentially leading wildlife and/or human populations to move to other regions and/or to develop new strategies to increase the efficiency of resource use. Reduced site frequency on the Plains after the MZA lasting ca. 500 years, and disuse of sites such as the Stampede and Tuscany sites in Alberta lasting at least 500 years corresponds to the timing of ash-induced environmental effects at Goldeye Lake, suggesting that the MZA may well have been the reason for the reduced occupancy of the Plains

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at this time (Oetelaar and Beaudoin 2014). Movement of human groups eastward away from the

ash is also suggested by increased abundance of Early Archaic points on the eastern margins of

the Plains at this time, and by the eventual introduction of new, Eastern Woodlands-origin, food

preparation techniques – namely, of stone boiling used on the Plains for the production of bone

grease for pemmican (Oetelaar and Beaudoin 2014). If developed as an adaptation to continuing

disturbed environmental conditions after the MZA, pemmican production would have provided a

long lasting, easily stored, and easily transportable food to help ensure food security in an

environment still recovering from the effects of the ashfall (Oetelaar and Beaudoin 2014). The

importation of stone boiling to the Plains ca. 800 years after the MZA eruption and its adaptation for the production of bone grease currently appears to have occurred ca. 300 years after the environment of Goldeye Lake recovered to normal conditions, however (Oetelaar and Beaudoin

2014), suggesting that its introduction might not have been related to the need to adapt to lingering disturbed environmental conditions, and may simply have been introduced because of its utility as a food preparation and storage technique. It is possible that recovery of the environment took longer on the Plains than in the Foothills around Goldeye Lake, or that earlier evidence may have yet to be discovered that will account for the delay.

7.2 Future directions

Multiple studies examining the environmental impacts of catastrophic events such as volcanic eruptions have illustrated the extreme variability that is possible in the kind, degree, and duration of responses that may occur. While studies of the environmental impacts of catastrophic disturbances are thus useful as indicators of potential impacts and as guides for understanding proxy evidence, this variability makes it important not to rely on modern or even other

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palaeoenvironmental studies for particulars of the environmental effects of such events on a specific region, as even the same event may have widely diverse environmental consequences.

Though studies of the environmental effects of past volcanic eruptions and their associated ashfalls are becoming increasingly common, volcanic ash layers are still generally considered only as chronostratigraphic markers, rather than as the focus of high-resolution study.

Palaeoecologists should make a greater effort to incorporate examination of the disruptive impacts of such catastrophic events into their analyses; in doing so they will provide a larger network of sites so that specific information is available regarding these events for the use of archaeologists and others who might be interested in their impacts on particular regions. In the particular cases of the WRA and MZA, focus should be on producing palaeoenvironmental studies in regions to the north and east of the eruptions, where large gaps remain in the network of sites. Studies should focus on environmentally sensitive sites that will be more likely to show noticeable impacts. Multiple proxies should also be examined from both terrestrial and aquatic environments, in particular those indicative of overall ecosystem structure, fire activity, and water chemistry such as pollen, charcoal, loss-on-ignition, and chironomids, as well as diatoms and biogenic silica. Studies should be conducted at as high a resolution as possible – ideally from varved sediments or from lakes with high sedimentation rates – so that short-term changes are captured.

Many archaeologists are also guilty of neglecting the significance of volcanic ashes, where the tendency has also been to consider them simply as convenient chronostratigraphic markers.

Given the potential significance of such events for human populations, one might hope to see more studies taking the human consequences of such events into serious consideration in the future. Any change occurring after a catastrophic event – for example in site organization or size,

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in material culture, or in the type and frequency of other remains (e.g. faunal remains) – may

give clues regarding the impact of that event on the environment, wildlife, and/or people in the

region. Nearby palaeoenvironmental studies meeting as many of the above criteria as possible

will be necessary to these studies to provide context for the interpretation of sites and for the

identification of any causal relationships that may be present. Additional modern studies of the impacts of catastrophic disturbances on different environments and on human populations would also give increased context for the interpretation of palaeoenvironmental and archaeological data.

Site-specific studies – whether palaeoenvironmental or archaeological – can only provide so much insight into the environmental, wildlife, and/or human consequences of catastrophic events, however, as the information they provide is geographically and also often temporally limited. The value of databases as sources of large amounts of geographically and temporally varied information is becoming gradually clearer with the increasing number of studies that have employed such repositories to search for patterns and changes in environmental and archaeological data across wide areas and at different points in time. Palaeoenvironmental databases allow the examination of continental or even global-scale patterns and changes in environmental conditions through time and/or at specific times in history, and have been used to identify potential drivers of human cultural change (e.g. Munoz, et al. 2010). Radiocarbon-based archaeological database studies have also proven to be a fruitful area of research, giving insight into broad-scale patterns and changes in human populations and culture across space and time

(e.g. Mullen 2012; Munoz, et al. 2010; Oetelaar and Beaudoin 2014; Peros, Munoz, et al. 2010).

Data sharing and broad-scale analyses using databases are thus perhaps our best ways forward to understand general patterns in environmental, wildlife, and human responses to catastrophic events such as volcanic eruptions. Database studies of the impacts of specific events across space

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will improve our understanding of their overall consequences, as some palaeoenvironmental and

archaeological database studies have already demonstrated (e.g. Mullen 2012; Munoz, et al.

2010; Oetelaar and Beaudoin 2014; Peros, Munoz, et al. 2010). Increased use of databases will

also facilitate the performance of comparative studies of the impacts of the same eruption in

different locations, and of different eruptions across space and time, which will allow us to

develop a better understanding of the wide variety of ways in which catastrophic disturbances are

capable of influencing environment and culture. Such studies would not only inform the

interpretation of the effects of other past disturbance events around the world, but might also be used to guide human responses to modern catastrophic events, future environmental change, and the development of a more harmonious human-environment relationship.

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Anderson, L., M. B. Abbott, B. P. Finney and S. J. Burns 2005 Regional atmospheric circulation change in the North Pacific during the Holocene inferred from lacustrine carbonate oxygen isotopes, Yukon Territory, Canada. Quaternary Research 64(1):21-35.

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APPENDIX A: ASH IDENTIFICATION RESULTS

Ash identifications were performed by Lauren Davies and Dr. Duane Froese, Department of

Earth and Atmospheric Sciences, University of Alberta.

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265 APPENDIX B: COPYRIGHT PERMISSIONS

B.1. Chapter Two

B.1.1. Figure 2.2

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