PALEOLIMNOLOGICAL ASSESSMENT OF HOLOCENE CLIMATIC AND

ENVIRONMENTAL CHANGE IN TWO LAKES LOCATED IN DIFFERENT

REGIONS OF THE CANADIAN ARCTIC TUNDRA

by

C. Alyson Paul

A thesis submitted to the Department of Biology

in conformity with the requirements for

the degree of Master of Science

Queen's University

Kingston, Ontario, Canada

October 2008

Copyright © C. Alyson Paul, 2008 ABSTRACT

Paleoclimatic research in the Canadian Arctic has increased in recent decades;

however, there is still much to learn about the nature and extent of past climate change in

this vast and environmentally sensitive region. This thesis uses primarily diatom

assemblages in dated lake sediment cores as proxy indicators to infer how climate has

changed over the Holocene in two very different lakes in the central Canadian Arctic: one

located in a poorly-studied geographical region, and another possessing limnological

characteristics that are unusual in an Arctic context.

Lake TK-2 is located in the low Arctic tundra. Paleolimnological studies from

this region are lacking, as most have centered on sites in the High Arctic Archipelago or around Subarctic treeline. Marked changes in the diatom assemblages in TK-2 throughout the Holocene included potential evidence for the 8.2k cooling event, which has not been previously reported from other Canadian Arctic paleolimnological studies.

In addition, diatom shifts occurring ~7000 and ~3500 cal yr BP are indicative of mid-

Holocene warming and subsequent Neoglacial cooling, respectively, the timings of which

agree with those from other studies farther south. Finally, shifts in the diatom

assemblages in the upper sediment layers, beginning in the early-to-mid 19th century, are

consistent with reduced ice cover, related to recent warming.

Stygge Nunatak Pond, a small, closed-basin pond located on a nunatak in the

High Arctic on Ellesmere Island, is characterized by water with unusually high ionic

concentrations for an inland Arctic pond. As in TK-2, Stygge’s diatom assemblages

changed substantially throughout the Holocene, but especially in the most recent

sediments. Diatom shifts near ~10,500 cal yr BP suggest an early onset for the Holocene

ii Thermal Maximum (as well as for the successive Neoglacial cooling trend) in this region,

consistent with previous studies from the High Arctic. Marked changes in diatom assemblages occurred in the most recent sediments, and, like those in TK-2, are

indicative of climate warming and reduced ice cover, as well as increased ionic

concentration due to enhanced evaporative concentration. The dynamic nature of the

diatom assemblage changes at the Stygge site suggests that sediments from these rare

athalassic ponds represent an especially sensitive archive of Arctic climatic and

environmental change.

iii ACKNOWLEDGEMENTS

First, I would like to thank John Smol for putting up with me through both of my

University degrees here at Queen’s. Thank you for your kindness, patience, and

thoughtful supervision over these several years. Thanks are also due to Kathleen

Rühland, for her tireless help with everything from microscopy to taxonomy (and

beyond), and for maintaining a sense of humour through it all. Without her, this thesis

would certainly not have been possible. Thank you to Marianne Douglas for her co-

supervision, and her company during the Arctic Field Season, as well as to Brian

Cumming and Scott Lamoureux for being on my committee and providing helpful

insights into my research.

A special thank you to Dr. Wes Blake, Jr., who played an instrumental role in the

development of the Stygge Nunatak Pond project, and who has gone above and beyond in

his efforts to share his knowledge and expertise with me. Similarly, thanks to Robert

Gilbert for helping me work through the conundrum that was Stygge’s ice. I would also

like to thank my fellow PEARLites (past, present and honourary) for their help and companionship along the way. Thanks for sharing in my insanity and reminding me that

I was never alone.

Finally, a huge, heartfelt thank you is in order for my wonderful family and

friends, both near and far, for your unconditional love and support throughout this experience. Thank you for helping me to keep things in perspective. I love you all so

much.

iv TABLE OF CONTENTS

Abstract...... ii

Acknowledgments...... iv

Table of Contents...... v

List of Tables...... vi

List of Figures...... vii

List of Appendices...... viii

Chapter 1: General Introduction and Literature Review...... 1 Recent Climate Change in the Arctic...... 1 Paleolimnology and Diatoms as Paleoindicators...... 3 Paleolimnology in the Canadian Arctic...... 5 References...... 8

Chapter 2: Diatom-inferred Holocene climatic and environmental change in a lake from the continental Canadian Low Arctic, Nunavut...... 13 Abstract...... 14 Introduction...... 16 Methods...... 22 Results...... 27 Discussion...... 33 Summary and Conclusions...... 51 References...... 54 Figure Captions...... 64 Figures...... 65 Tables...... 70

Chapter 3: Diatom-inferred Holocene climatic and environmental change in an unusually saline high Arctic nunatak pond on Ellesmere Island (Nunavut, Canada)...... 72 Abstract...... 73 Introduction...... 75 Methods...... 79 Results...... 85 Discussion...... 91 Summary and Conclusions...... 108 References...... 110 Figure Captions...... 118 Figures...... 120 Tables...... 128

Chapter 4: General Discussion and Conclusions...... 131

Appendices...... 138

v LIST OF TABLES

Chapter 2

Table 2.1…….……………………………………………………………………………………70 Summary of the key modern surface water chemistry and other limnological measurements from Lake TK-2, collected on August 7, 1996.

Table 2.2…….……………………………………………………………………………………71 AMS radiocarbon dates from the Lake TK-2 sediment core.

Chapter 3

Table 3.1…….…………………………………………………………………………………128 Summary of the key modern surface water chemistry and other limnological measurements from Stygge Nunatak Pond, taken during five different field seasons.

Table 3.2…….…………………………………………………………………………………129 Unsupported 210Pb activity for 12 intervals from the short sediment core from Stygge Nunatak Pond, as well as 210Pb dates determined using the CRS (constant rate of supply) model.

Table 3.3…….…………………………………………………………………………………130 AMS radiocarbon dates from the short and long cores from Stygge Nunatak Pond.

vi LIST OF FIGURES

Chapter 2

Figure 2.1….……………………………………………………………………………...………65 Map of the location of Lake TK-2 in the low Arctic tundra, Nunavut.

Figure 2.2….……………………………………………………………………………...………66 Age-depth profile for the Lake TK-2 core.

Figure 2.3….……………………………………………………………………………...………67 Parts I and II. Stratigraphic profile of the percent relative abundances of the most common diatom taxa in the TK-2 sediment core.

Figure 2.4….……………………………………………………………………………...………69 DCA axis 1 scores and Hill’s N2

Chapter 3

Figure 3.1….……………………………………………………………………………...……..120 Map of the location of Stygge Nunatak Pond.

Figure 3.2….……………………………………………………………………………...……..121 Photos of Stygge Nunatak and Stygge Nunatak Pond.

Figure 3.3….……………………………………………………………………………...……..122 Profile of unsupported 210Pb activity for the upper 20 cm of the short sediment core from Stygge Nunatak Pond.

Figure 3.4….……………………………………………………………………………...……..123 Plot of all radioisotopic dates (both 210Pb and calibrated 14C) from Stygge Nunatak Pond. Incorporates dates from both the short and the long core.

Figure 3.5….……………………………………………………………………………...……..124 Stratigraphic profile of the percent relative abundances of the most common diatom taxa in the short core (taken in 2004) from Stygge Nunatak Pond.

Figure 3.6….……………………………………………………………………………...……..125 Stratigraphic profile of the percent relative abundances of the most common diatom taxa in the long core (taken in 1984) from Stygge Nunatak Pond.

Figure 3.7….……………………………………………………………………………...……..126 Stratigraphic profile of the percent relative abundances of the most common diatom taxa in the modern microhabitat samples from Stygge Nunatak Pond, demarcated by sampling year.

Figure 3.8….……………………………………………………………………………...……..127 Stratigraphic profile of the percent relative abundances of the most common diatom taxa in the modern microhabitat samples from Stygge Nunatak Pond, demarcated by type of microhabitat.

vii LIST OF APPENDICES

Appendix A………...……………………………………………………………………...……..138 Raw diatom count data for the sediment core from Lake TK-2.

Appendix B………….……………………………………………………………………...……..192 List of the most common diatom taxa, including their taxonomic authorities and modern synonyms, from the Lake TK-2 and Stygge Nunatak Pond sediment cores, as well as from modern microhabitat samples taken over five different field seasons from Stygge Nunatak Pond.

Appendix C………...……………………………………………………………………...……..195 Complete list of surface water chemistry measurements taken from Stygge Nunatak Pond over five different field seasons.

Appendix D………...……………………………………………………………………...……..197 Raw diatom count data from the short sediment core from Stygge Nunatak Pond.

Appendix E………...……………………………………………………………………...……..204 Raw diatom count data from the long sediment core from Stygge Nunatak Pond.

Appendix F………...……………………………………………………………………...……..218 Raw diatom count data from the modern microhabitat samples from Stygge Nunatak Pond, taken over five different field seasons.

viii

CHAPTER 1

General Introduction and Literature Review

Recent Climate Change in the Arctic

The study of human influences on recent changes in climate has become a major

area of research over recent years (IPCC 2007). For example, over the past three

decades, global average surface temperature has increased rapidly, by approximately

0.2ºC per decade (Hansen et al. 2006). However, compared with the globe as a whole,

Arctic regions are especially sensitive to climate change (ACIA 2004; Furgal and Prowse

2008; Hinzman et al. 2005), as warming effects are amplified here due to various positive-feedback mechanisms, such as the snow-ice albedo effect (e.g. Serreze and

Francis 2006). Over the past century, average temperatures in the Arctic have increased almost twice as fast as the global average (IPCC 2007). Accordingly, annual average

Arctic sea ice extent has undergone marked recent declines (ACIA 2004; IPCC 2007), decreasing by ~8% over the past three decades, with the summer average decreasing by

~15-20% over the same period. The thickness of sea ice has also decreased, on average by 10-15% between the 1960s and late 1990s (ACIA 2004). Furthermore, permafrost is thawing in many regions (Hinzman et al. 2005; IPCC 2007), with the top-most layer having warmed as much as 3ºC since the 1980s, and the areal extent of permafrost has decreased by ~7% since 1900 in the northern hemisphere. In addition, since approximately the 1960s, there has been an overall reduction (accelerating in the 1990s) in the mass balance of glaciers and ice caps (ACIA 2004; Hinzman et al. 2005); for example, ice caps on Baffin Island have decreased in area by more than 50% since 1958

1

(Anderson et al. 2008), and between 1979-2002, the melt area on the Greenland Ice Sheet increased by 16% (ACIA 2004). Moreover, weather in recent decades has become more variable and less predictable (Hinzman et al. 2005), and northward expansions in the range of some plant and animal species is already being recorded in areas of the northern hemisphere (Chapin et al. 2005; Hinzman et al. 2005).

Many of the above scientific records are supported by the observations of indigenous people from across the Arctic, who have noticed substantial changes to their environment within the span of recent memory (e.g. ACIA 2004; Hinzman et al. 2005).

These changes include thinning sea ice, more unstable and less predictable weather patterns, changes in the quality and characteristics of snow, increased rain in winter, declining lake-water levels, changes in the distribution of vegetation and animals, increased storm surges and coastal erosion, and an increase in the intensity of the sun, with sunburns and related skin problems becoming more prevalent.

Numerous studies combining various paleoclimate proxy data with recent observed and instrumental data confirm that the warming we are now experiencing has been unprecedented over the past several centuries, and maybe even millennia (e.g.

ACIA 2004; Bradley 2000; Douglas et al. 1994; Furgal and Prowse 2008; Gajewski and

Atkinson 2003; Jansen et al. 2007; Mann et al. 1998; Overpeck et al. 1997; Serreze et al.

2000; Smol et al. 2005;). Based on a wealth of global climate models, this global warming trend is expected to continue and even intensify (ACIA 2004; Furgal and

Prowse 2008; IPCC 2007;), with the greatest and earliest temperature increases occurring in the Arctic (ACIA 2004). For example, even the most conservative of climate models predict that warming in the Arctic over the next century will be over twice the magnitude

2

of the past century’s warming (ACIA 2004). The implications of this warming for the sensitive and complex Arctic ecosystems will, no doubt, be substantial.

Paleolimnology and Diatoms as Paleoindicators

Despite the growing evidence for recent climate change in the Arctic, still very little is known about how climate has changed in these regions in the past. Knowledge of past changes is critical, as it provides a longer temporal context in which to place current trends, so that it can be determined whether they exceed the range of natural variability, or are merely part of a natural climate cycle. Additionally, knowing how ecosystems have responded to past environmental change offers potential insights into how they might respond to future changes. However, historical environmental and climate monitoring data are often sparse or nonexistent (Smol and Cumming 2000), especially in harsh, remote regions like the Arctic. Fortunately, this crucial information can be obtained using paleolimnology.

Paleolimnology uses the physical, chemical and biological information preserved in lake sediments to reconstruct past limnological conditions, and thus infer the environmental conditions under which the sediments were deposited (Smol et al. 2001).

Because lakes and ponds are often a dominant feature of Arctic landscapes, paleolimnology is an ideal tool with which to study environmental change in this region.

Numerous biological paleoindicators exist, including plant microfossils, chitinous remains of invertebrates, and the remains of certain groups of microscopic algae (Smol

2008). Diatoms (class Bacillariophyceae) belong to the latter category, and are the most extensively used indicators in paleolimnological studies (Douglas et al. 2004; Smol and

Cumming 2000).

3

Diatoms are single-celled, photosynthetic algae. They are ubiquitous, living in

virtually every type of aquatic habitat, including marine environments (e.g. Battarbee et

al. 2001; Dixit et al. 1999; Smol and Cumming 2000; Stoermer and Smol 1999). They are extremely diverse, with estimates of species numbers ranging in the tens of thousands or higher (Stoermer and Smol 1999). Diatoms are an important component of freshwater algal communities (Hall and Smol 1999), and are ideal paleoenvironmental indicators for several reasons. Their siliceous cell walls (frustules) are resilient, preserving well in aquatic sediments, and have intricate, taxonomically distinct ornamentations that allow them to be identified to low taxonomic levels (species and often variety). Many taxa have well-defined optima for various environmental variables (Stoermer and Smol 1999), and because they are autochthonous, they represent the local conditions of the environment in which they originate (Smol 1988; Smol and Cumming 2000). Finally, their short generation times mean that there is little to no temporal lag between the timing of a disturbance and the resultant response from the diatom community (Smol 1988;

Smol and Cumming 2000). Diatoms have been shown to be sensitive indicators of various limnological variables, including salinity (Fritz et al. 1999), nutrients and water quality (Cremer et al. 2001; Dixit et al. 1999), pH (Battarbee et al. 1999; Psenner and

Schmidt 1992), conductivity, ice cover and water level (Cremer et al. 2001). They are particularly useful in high-latitude environments, such as the Canadian Arctic, where lakes and ponds are abundant, and where other indicators commonly employed in lower latitudes, such as pollen grains and tree-rings, are often absent or rare (Douglas et al.

2004; Smol and Cumming 2000).

4

Paleolimnology in the Canadian Arctic

Paleolimnology and diatoms are commonly implemented in studies of high-

latitude environments (Douglas et al. 2004). They have been successfully used in the

circumpolar Arctic to track past changes in various climate-related variables, including

lake ice cover and associated limnological variables. In high latitude (Smol 1988) and

high altitude (Lotter et al. 1999) lakes, many of which remain frozen for most of the year,

ice cover extent and duration has been found to be the dominant factor determining

diatom community structure, largely through its effects on habitat availability (e.g.

Keatley et al. 2008). A change in the extent of ice cover can dramatically alter lake water

properties (Douglas and Smol 1999). For example, an increase in temperature due to

climate warming can lead to a longer ice-free period, which provides a substantially

longer photosynthetic period and growing season for aquatic macrophytes and algae in

the lake (Douglas et al. 1994; Smol and Cumming 2000). A prolonged open-water period

also allows increased light penetration, establishment or enhancement of thermal

stratification, and increased nutrient distribution and cycling, among other changes in water chemistry. All of these changes ultimately serve to transform the aquatic habitat,

and can therefore have a profound impact on diatom community composition (Douglas

and Smol 1999; Keatley et al. 2008; Smol 1983, 1988).

Although the number of Arctic paleolimnological studies has greatly increased in

recent decades, still very little is known about the climate history of the central Canadian

Arctic, including both the mainland and the archipelago (Seppä et al. 2003). Moreover,

few long-term, millennial-scale records exist for the Canadian High Arctic. The overall

objective of this thesis is to examine how the diatom assemblages in two different

5

freshwater systems, located in different regions of the central Canadian Arctic, have

responded to climate change over the Holocene. In doing so, I will attempt to bridge

certain gaps that exist in the paleolimnological data from this region. In Chapter 2, I will

examine the diatom profile from a lake that is located far north in the Canadian low

Arctic tundra, but still on the mainland. Most Arctic paleolimnological studies have

focused on sites located in or around Subarctic treeline, or in the archipelago in the High

Arctic. The diatom profiles from lakes and ponds in the High Arctic generally have

recorded relatively stable, coldwater assemblages starting in the early Holocene and

continuing until marked recent (19th and 20th-century) changes occur that are suggestive of climatic warming and reduced ice cover (e.g. Douglas et al. 1994). In contrast, lakes in the more southerly regions have tended to record some notable changes in the diatom assemblages throughout the Holocene, including evidence for mid-Holocene warmth (i.e.

the Holocene Thermal Maximum, or HTM; Kaufman et al. 2004) and subsequent

Neoglacial cooling (e.g. MacDonald et al. 1993; Moser and MacDonald 1990; Rühland

2001; Rühland and Smol 2005; Wolfe and Smith 2004). The latter studies also generally show evidence for dramatic recent (mid-19th century) shifts in life strategy, from

assemblages dominated by benthic and/or tychoplanktonic diatoms, to those dominated

by planktonic taxa; these recent shifts are also suggestive of a warming trend. My study

site in Chapter 2 presents an opportunity to determine the nature of Holocene diatom

assemblage dynamics in the under-studied intermediate region.

In Chapter 3, I will examine the sediment profile of a high Arctic nunatak pond that has an unusually high ionic concentration. The vast majority of Arctic

paleolimnological studies have been undertaken on very dilute, oligotrophic lakes and

6

ponds, a fact that is to be expected given the extreme commonness of this type of freshwater system in polar regions. However, inland, closed basin lakes that have higher ionic concentrations (unrelated to marine influences), although very rare in the Arctic, present a potentially highly sensitive archive of past climatic change. In such systems, small changes in the balance between precipitation and evaporation (P-E, or effective precipitation), which is ultimately controlled by climate, can change the lake or pond

volume dramatically, in turn impacting ionic concentration through evaporative

concentration or dilution (Fritz et al. 1999; Gasse et al. 1997; Roberts et al. 2006).

Diatoms are known to respond sensitively to changes in salinity and salinity-related

variables (e.g. Fritz et al. 1999), and have been successfully used to infer past changes in

salinity, indirectly tracking past P-E, and ultimately climate (e.g. Fritz 1990; Fritz et al.

1991, 1999; Gasse et al. 1997; McGowan et al. 2003; Roberts et al. 2006; Wilson et al.

1994). However, most of these studies are from temperate or tropical latitudes, where

saline systems are more abundant. The nunatak pond in Chapter 3 of this thesis provides

a novel opportunity to examine how the diatom assemblages in a rare, high Arctic

athalassic “saline” system have responded to Holocene climate and environmental

change.

7

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Rühland, K. 2001. Diatom Assemblage Shifts Relative to Changes in Environmental and Climatic Conditions in the Circumpolar Treeline Regions of the Canadian and Siberian Arctic. Ph.D. Thesis, Queen’s University, Kingston, Ontario, Canada, 265 pp.

Rühland, K. and J.P. Smol. 2005. Diatoms shifts as evidence for recent Subarctic warming in a remote tundra lake, NWT, Canada. Palaeogeography, Palaeoclimatology, Palaeoecology 226: 1-16.

Seppä, H., L.C. Cwynar and G.M. MacDonald. 2003. Post-glacial vegetation reconstruction and a possible 8200 cal. yr BP event from the low arctic of continental Nunavut, Canada. Journal of Quaternary Science 18: 621-629.

Serreze, M.C. and J.A. Francis. 2006. The Arctic amplification debate. Climatic Change 76: 241-264.

Serreze, M.C., J.E. Walsh, F.S. Chapin III, T. Osterkamp, M. Dyurgerov, V. Romanovsky, W.C. Oechel, J. Morison, T. Zhang and R.G. Barry. 2000. Observational evidence of recent change in the northern high-latitude environment. Climatic Change 46: 159-207.

Smol, J.P. 1983. Paleophycology of a high arctic lake near Cape Herschel, Ellesmere Island. Canadian Journal of Botany 61: 2195-2204.

Smol, J.P. 1988. Paleoclimate proxy data from freshwater arctic diatoms. Verhandlungen der Internationalen Vereinigung für Limnologie 23: 837-844.

Smol, J.P. 2008. Pollution of Lakes and Rivers: A Paleoenvironmental Perspective, Second Edition. Blackwell Publishing, Ltd., Oxford, United Kingdom, 383 pp.

Smol, J.P., H.J. Birks, and W.M. Last. 2001. Using biology to study long-term environmental change. p. 1-3 In: Smol, J.P., Birks, H.J.B. and W.M. Last (eds.). Tracking Environmental Change Using Lake Sediments, Volume 1: Basin Analysis, Coring and Chronological Techniques. Kluwer Academic Publishers, Dordrecht, Netherlands.

11

Smol, J.P. and B.F. Cumming. 2000. Tracking long-term changes in climate using algal indicators in lake sediments. Journal of Phycology 36: 986-1011.

Smol, J.P., A.P. Wolfe, H.J.B. Birks, M.S.V. Douglas, V.J. Jones, A. Korhola, R. Pienitz, K. Rühland, S. Sorvari, D. Antoniades, S.J. Brooks, M.A. Fallu, M. Hughes, B.E. Keatley, T.E. Laing, N. Michelutti, L. Nazarova, M. Nyman, A.M. Paterson, B. Perren, R. Quinlan, M. Rautio, E. Saulnier-Talbot, S. Siitonen, N. Solovieva, and J. Weckström. 2005. Climate-driven regime shifts in the biological communities of arctic lakes. Proceedings of the National Academy of Science 102: 4397-4402.

Stoermer, E.F. and J.P. Smol. 1999. Applications and uses of diatoms: prologue. p. 3-8 In: Stoermer, E.F. and J.P. Smol (eds.). The Diatoms: Applications for the Environmental and Earth Sciences. Cambridge University Press, Cambridge, United Kingdom.

Wilson, S.E., B.F. Cumming and J.P. Smol. 1994. Diatom-salinity relationships in 111 lakes from the Interior Plateau of British Columbia, Canada: the development of diatom- based models for paleosalinity reconstructions. Journal of Paleolimnology 12: 197-221.

Wolfe, A.P. and I.R. Smith. 2004. Paleolimnology of the Middle and High Canadian Arctic. p. 241-268 In: Pienitz, R., M.S.V. Douglas and J.P. Smol. (eds.). Long-term environmental change in Arctic and Antarctic Lakes. Springer, Dordrecht, Netherlands.

12 CHAPTER 2

Diatom-inferred Holocene climatic and environmental change in a lake from the continental Canadian Low Arctic, Nunavut

C. Alyson Paul

13 ABSTRACT

Although the number of paleolimnological studies in the Canadian Arctic has increased in recent years, the majority have been from lakes located in either the High

Arctic or in (or near) the forest-tundra ecotone in the Subarctic. Studies from the intermediate geographical region are lacking. A 14C-dated, 198 cm-long sediment core was examined for shifts in diatom assemblages over the Holocene in Lake TK-2, a small lake located far north in the tundra of the central continental Canadian Low Arctic. The diatom assemblages record notable changes throughout the core, suggesting that the

Holocene in this region has been environmentally and climatically dynamic. The earliest assemblages were dominated by small, benthic Achnanthes and Navicula taxa (A. impexa,

A. nitidiformis, N. schmassmannii), which is atypical of most early post-glacial assemblages from lakes and ponds in the Arctic. Although the ecologies of these taxa are poorly understood, this study suggests that their presence may be indicative of relatively warm conditions, possibly resulting from air circulation patterns generated by the presence of the retreating Laurentide Ice Sheet. A shift to a dominance of small, benthic, alkaliphilous Fragilaria taxa followed, indicative of colder, more alkaline conditions more typical of most post-glacial diatom assemblages. An abrupt and short-lived dramatic increase in the Aulacoseira lirata complex ca. 8500 cal. yr BP, with corresponding changes in other physical and chemical indicators, provides potential evidence for the 8.2k cooling anomaly, an event first noted in the Greenland ice cores and generally absent from other paleolimnological studies in the Canadian north. The largest shift in diatom assemblage composition occurred at ca. 7000 cal. yr BP (DCA score = 1.5

SD units), when a new, more structurally diverse assemblage was established consisting

14 of a number of slightly more acidic to circumneutral taxa, and an increase in the number and relative abundance of planktonic taxa. This shift likely indicates a natural, long-term loss of alkalinity in the lake, and marks the onset of warming during the mid-Holocene

(ca. 7000 cal. yr BP) that is consistent with the timing of the Holocene Thermal

Maximum for this region. Evidence of Neoglacial cooling followed around 3500 cal. yr

BP in the form of concurrent further increases in a number of taxa known to prefer slightly more acidic to circumneutral environments. In the most recent sediments, the post-industrial expansion of the small, planktonic Cyclotella stelligera complex, and a concurrent decline in the heavily-silicified Aulacoseira lirata complex, are in accordance with what is increasingly being recognized as a geographically widespread diatom response to recent climate warming.

15 INTRODUCTION

Polar environments are particularly sensitive to the effects of climate change (e.g.,

ACIA 2004; Furgal and Prowse 2008; Hansen et al. 2006; Rouse et al. 1997; Serreze and

Francis 2006; Smol 1988), primarily resulting from positive feedback mechanisms that serve to amplify those effects (ACIA 2004). Even very small alterations to climatic and environmental conditions can have striking effects on biological communities, as

organisms here are often living at their environmental limits (Rühland and Smol 2002;

Smol 1988; Smol et al. 2005). Because of these characteristics, high latitude regions are particularly important in studies of climate change.

Scientific evidence for recent warming across the circumpolar Arctic is mounting.

Numerous studies, using a wide range of paleoclimate proxies, substantiate the claim that

temperatures have increased since pre-industrial times to magnitudes greater than they

have been for at least several centuries past, if not longer (e.g., Bradley 2000; Douglas et

al. 1994; Gajewski and Atkinson 2003; Jansen et al. 2007; Mann et al. 1998; Overpeck et

al. 1997; Serreze et al. 2000; Smol et al. 2005;). However, in order to fully understand

recent climate change (and to be able to predict potential impacts of future change), it is

important to have a more thorough understanding of how climate has changed over the

long-term past (Smol and Cumming 2000). With this information, it is possible to place

current trends in a longer temporal context and thus determine whether they exceed the

range of natural variability, or are simply part of a natural climate cycle. Unfortunately,

reliable instrumental data are typically only available for the past century or so in

temperate regions (Smol and Cumming 2000), and in remote, less accessible

16 environments like the Arctic, these data are much fewer. Fortunately, paleolimnology

provides a means of obtaining this historical climate information.

Paleolimnology reconstructs past limnological and environmental conditions

using physical, chemical and biological indicators preserved in lake sediments (Smol et

al. 2001). Of the many biological paleoindicators, diatoms (class Bacillariophyceae) are the most commonly employed (Douglas et al. 2004; Smol and Cumming 2000). These single-celled, photosynthetic algae are a part of almost every aquatic environment, and are very diverse (Hall and Smol 1999; Stoermer and Smol 1999). Their silicious cell walls display intricate, taxon-specific patterns, making them identifiable to low taxonomic levels, and allowing them to preserve well in aquatic sediments. Furthermore, many diatom taxa have well-defined optima for various environmental variables

(Stoermer and Smol 1999), and have accordingly been shown to be sensitive indicators of those variables. Because they are autochthonous, they represent the local conditions of the environment in which they originate (Smol 1988; Smol and Cumming 2000).

Diatoms are of particular use in Arctic regions, where lakes and ponds are widespread and often very abundant, and where other indicators commonly used at lower latitudes are not always available (Smol and Cumming 2000; Douglas et al. 2004).

Although paleoclimatic investigations are increasing, the climate history of the

central Canadian Arctic, for both the mainland and the archipelago, is still largely

unknown (Seppä et al. 2003). Of the existing paleolimnological climate studies

undertaken in this region, the vast majority have been done on lakes located in the

Subarctic, in or near the forest-tundra ecotone, or in the tundra of the High Arctic (Pienitz

et al. 2004). Though the timing is geographically quite variable, most of the lower-

17 latitude Arctic studies have found evidence for some notable changes over the longer- term Holocene, especially a mid-Holocene warming trend (the Holocene Thermal

Maximum, or HTM; Kaufman et al. 2004), followed by Neoglacial cooling (e.g.

MacDonald et al. 1993; Moser and MacDonald 1990; Rühland 2001; Rühland and Smol

2005; Wolfe and Smith 2004). Many of these studies have also inferred substantial recent (post-industrial) community changes indicative of climate warming. In contrast, diatom studies of lakes and ponds in the High Arctic have generally recorded relatively stable assemblages throughout the longer-term Holocene, but with very dramatic post- industrial changes attributed to climate warming (e.g. Douglas et al. 1994). However, paleolimnological studies investigating Holocene climate and environmental change in lakes located far north in the continental Canadian Arctic are lacking. The subject of this chapter, Lake TK-2, is located high in the central continental Arctic tundra, but still in the low Arctic region. It therefore provides an interesting opportunity to begin to bridge this gap and study how the diatom response in this under-studied intermediate region will compare to those in previous studies from both higher and lower Arctic latitudes.

Previously, Seppä et al. (2003) analyzed pollen from the sediments of Lake TK-2 in order to track Holocene climate change based on latitudinal shifts in the distribution of vegetation. However, from its location high in the tundra, Lake TK-2 did not register

Holocene treeline shifts that are evident in the pollen stratigraphies of lakes located farther south, proximal to modern treeline. The authors suggested that the lake is located too far north of the forest-tundra ecotone to have been affected by treeline advance during mid-Holocene warming (evident in other lakes farther south), which is therefore not reflected in the lake’s pollen profile. A similar investigation of climate change in this

18 lake using diatoms should not be limited in the same way, because diatoms are

autochthonous and thus reflect the local conditions of the lake in which they are

preserved. In this chapter, I use the same sediment core as Seppä et al. (2003) to examine

the nature and patterns of diatom assemblage changes in Lake TK-2 over the Holocene,

and compare these changes to those observed in lower latitude Arctic lakes, including

Lake TK-20 (Rühland 2001), Slipper Lake (Rühland and Smol 2005), and Queen’s and

McMaster lakes (MacDonald et al. 1993; Moser and MacDonald 1990).

The only notable change that Seppä et al. (2003) detected in the pollen record of

TK-2 occurred between ca. 8100-7900 cal. yr BP, and consisted of an abrupt decline in

Betula glandulosa (dwarf birch) accompanied by increases in other shrubby species. The

authors speculated that these changes may be linked to a dramatic cold event known as

the 8.2k event. Also referred to as the 8k event, or the Finse event in Scandinavia, it is

recorded as an anomalous cooling evident in the Greenland ice cores that peaks at

approximately 8200 cal. yr BP. The event is manifested as an abrupt and dramatic

decline in δ18O in the ice cores to its absolute minimum over the past 10,000 years (i.e.

the Holocene) (e.g. Alley et al. 1997; Alley and Águstsdottir 2005; Rohling and Pälike

2005; Thomas et al. 2007). Combined with a similarly dramatic minimum in snow

accumulation rate, this indicates a substantial local cooling (as much as 6˚C; Alley et al.

1997), with important changes in local-to-regional atmospheric circulation patterns

(Alley et al. 1997; Alley and Águstsdottir 2005; Thomas et al. 2007). Synchronous with these local signals in the ice cores are indications that the event was expressed more distally. For example, an increase in calcium derived from wind-blown continental dust suggests increased dryness, dustiness and transport vigor from distant continental

19 regions; increased levels of chloride similarly indicate increased vigor of atmospheric

circulation; decreased methane is suggestive of lower wetland cover (and thus increased dryness); and increased forest-fire smoke is an indication that distant forested regions likely experienced enhanced dryness (Alley et al. 1997; Alley and Águstsdottir 2005).

Although these other proxies provide compelling evidence that the 8.2k event was likely a widespread (and potentially global) phenomenon, unlike the local signals, the magnitudes of their deviations are not the most extreme of their kind throughout the pre- anthropogenic Holocene record (Alley and Águstsdottir 2005).

Beyond the evidence extracted from the Greenland ice cores, potential evidence

for the 8.2k climate anomaly has also been found in numerous paleoclimate records from

various locations within the North Atlantic Ocean. Summarized by Alley and

Águstsdottir (2005) and Rohling and Pälike (2005), this evidence includes maximum

Holocene abundances of cold-adapted species of foraminifera in deep sea sediment cores,

as well as minimum δ18O levels in the shells of these and other groups of foraminifera,

and sharp maxima in ice-rafted debris indicative of increased sea ice, all possibly

correlative with the 8.2k event. Additionally, large and abrupt changes in the

geochemistry and sedimentary composition of a deep sea sediment core from the

northwest Atlantic Ocean are indicative of a change in the deepwater circulation patterns

around the time of this cooling event (Kleiven et al. 2007).

Some evidence potentially correlative with the 8.2k event has also been presented from regions outside the North Atlantic, such as indications of increased dryness and reduced monsoon intensity in the monsoonal regions of Africa, the Arabian peninsula,

India and Asia (summarized by Alley and Águstsdottir 2005 and Rohling and Pälike

20 2005), as well as evidence for dryness in various coastal regions of Central and South

America (summarized by Alley et al. 1997 and Alley and Águstsdottir 2005). However,

the evidence from these areas remains weak relative to data presented for the Northern

Hemisphere and especially the North Atlantic region (Alley and Águstsdottir 2005;

Rohling and Pälike 2005; Thomas et al. 2007). Finite sampling, insufficient sampling resolution of existing records, and the commonness of dating uncertainties may all

contribute to the apparent absence of the 8.2k anomaly from many regions (e.g. Alley and

Águstsdottir 2005).

It is widely accepted that the ultimate cause of the 8.2k cooling event was most

likely the catastrophic outburst flooding of super-lake Agassiz into the North Atlantic

Ocean (Clarke et al. 2003, 2004) approximately 8.479k cal. yr BP (Barber et al. 1999),

the only known potential culprit. Lake Agassiz, a coalescence of two proglacial lakes,

Agassiz and Ojibway, was located at the southwest margin of the receding Laurentide Ice

Sheet (just south of contemporary Hudson Bay), and had a volume estimated at approximately 200,000 km3 (Barber et al. 1999). Flooding of the lake likely occurred

through subglacial tunneling beneath the ice sheet, similar to the mechanism behind

modern jokulhaups (Clarke et al. 2003, 2004). The flood is estimated to have lasted for

about half a year, with a magnitude of around 5 Sv (Clarke et al. 2004), and with respect to the volume of water released, it is the largest known freshwater outburst flood into the

North Atlantic over the past 100,000 years (Clarke et al. 2003, 2005; Kleiven et al. 2005).

Summarized by Barber et al. (1999), evidence for the flood includes glacial-marine sediments directly overlying the proglacial lake sediments in the Hudson and James Bay lowlands, as well as a “red bed”, or layer of varying thickness of hematite-rich sediment,

21 believed to have originated in the basin of Lake Agassiz, extending up to 700 km throughout the Hudson Strait and deposited simultaneously.

Such an immense input of freshwater would have freshened the surface waters of

the North Atlantic Ocean (Alley and Agustsdottir 2005; Barber et al. 1999; Rohling and

Pälike 2005). This freshening would likely have hindered the formation at the ocean’s

surface of cold, salty North Atlantic Deep Water (NADW), which sinks upon formation

and flows southward, with warm surface water from the south flowing north to replace it.

This conveyor system, also known as thermohaline circulation (THC), plays a large role

in moderating the Earth’s climate (Broecker 1997; Clark et al. 2002). According to

climate models, a disruption of this process by North Atlantic freshening would result in

colder and dryer conditions across the northern hemisphere (especially pronounced over

the North Atlantic), and potentially a slight warming trend in the southern hemisphere

(Alley and Agustsdottir 2005; Rohling and Pälike 2005).

Although Seppä et al. (2003) tentatively link the changes in their pollen record

with the 8.2k event, their results are inconclusive, and no other paleoecological records

from northern Canada have shown evidence for this important, potentially global climate

event. In this chapter I also focus on this critical time period to determine whether the

diatoms of TK-2 track any significant ecological excursions therein.

METHODS

Site Description

Lake TK-2 (unofficial name; 66˚20’54”N, 104˚56’45”W) is located in the low

Arctic tundra in Nunavut, Canada, approximately 265 km north of the current treeline

(Figure 2.1). It is a relatively small and shallow lake, with a surface area of

22 approximately 2.8 ha and a coring depth of 7.5 m. Its waters are alkaline, oligotrophic and dilute, with a pH of 8.0, TPUF (total phosphorus unfiltered) of 3.1 μg/L and specific conductivity of approximately 9.8 μS/cm (Table 2.1). It currently has no inflow or outflow. The surrounding region is located on Canadian Shield bedrock, consisting of

Precambrian intrusive igneous rocks as well as metamorphic volcanic rocks and sedimentary rocks from the Slave Province (Padgham and Fyson 1992). Where it is not exposed, the bedrock lies beneath a thin cover of glacial till. Temperature and precipitation are presently relatively cold and dry, with mean July and January surface air temperatures of ca. 10 ºC and -35 ºC, respectively, and annual mean precipitation of ca.

200 mm (Rouse 1993). Lake TK-2 lies in a region of continuous permafrost, with poorly developed soil supporting highly discontinuous vegetation characteristic of a lichen-heath tundra, scattered with predominantly Betula glandulosa (dwarf birch) shrubs, Salix

(willow) species and Arctostaphylos, Ledum and Vaccinium heath shrub species. Peat deposits grow in poorly drained areas, where mosses, sedges, shrubs and cotton grasses dominate (Ritchie 1993). Retreat of the Laurentide Ice Sheet likely occurred in the region between 9500 and 8980 cal yr BP (or 8500 and 8000 14C yr BP) (Dyke et al.

2003).

Field Methods

In early August of 1996, a 198 cm sediment core was retrieved from the centre of

Lake TK-2 using a modified Livingstone piston corer with a diameter of 5 cm. The core was extruded at 1 cm intervals. Temperature, specific conductivity and pH were measured on site using a handheld thermometer, a Yellow Springs Instrument (YSI) model 33 conductivity meter, and a handheld Hanna pHEP pH meter, respectively. In

23 addition, water chemistry samples were taken from approximately 30 cm below the water

surface, and were treated according to procedures outlined by Environment Canada

(1994). These samples were sent for analyses to the National Water Research Institute in

Burlington, Ontario. Water chemistry and other limnological measurements are listed in

Table 2.1.

Laboratory Methods

Seven radiocarbon dates were determined from the core using Accelerator Mass

Spectrometry (AMS) (see Seppä et al. 2003, who examined the pollen profile of the sediment core used in the present study). Because the top half of the core lacked terrestrial macrofossils, dates were derived from bulk sediment samples from the intervals 32-34, 60-62 and 96-98 cm (Table 2.2). These samples were analyzed at Beta

Analytic, Inc., Miami, Florida. Some terrestrial macrofossils (twigs) were present in the lower half of the core; these were retrieved via sieving and dated from the depths 132,

137, 142 and 174 cm at IsoTrace Radiocarbon Laboratory, Toronto, Ontario. Dates were calibrated using CALIB 4.3 (Stuiver and Reimer 1993) and INTCAL 98 (Stuiver et al.

1998) calibration data (see Seppä et al. 2003). For comparison, I also calibrated the 14C

dates using the online Cologne Radiocarbon Calibration and Paleoclimate Reasearch

Package (CalPal-2007online, Danzeglocke et al. 2007). Unless otherwise stated, dates

referred to in the text will be calibrated dates.

Percent loss-on-ignition (LOI) was also determined for the core by Seppä et al.

(2003) by igniting 121 subsamples at 1-2 cm intervals at 550ºC for 4 hours. The raw data from this analysis were unfortunately not available to me; however, the resulting LOI profile presented in the pollen study provides useful additional insights.

24 Diatom slides were prepared using the standard procedures for diatom samples,

outlined by Battarbee et al. (2001). A total of 62 sediment samples (1 cm intervals from the top 32 cm, and from every 4-6 cm for the remainder of the core) were digested in 15

mL of a 1:1 molar ratio solution of concentrated nitric (HNO3) and sulphuric (H2SO4)

acids to remove any organic matter. The resulting slurries were then rinsed with

deionized water and allowed to settle overnight, after which the supernatant was

removed, and the samples were rinsed again. This process was repeated until the slurries

reached a neutral pH (about 6 rinses). A small amount of each of the slurries was then

spread over glass coverslips (at four different dilutions) and allowed to evaporate at room

temperature on slide warmers. Once dry, the coverslips were mounted onto glass microscope slides using Naphrax® mounting medium (refractive index = 1.74).

For each interval, a minimum of 400 diatom valves (where possible) was

identified and enumerated along several complete transects of the slide using a Leica

DMR microscope at 1000x magnification, with differential interference contrast (DIC)

and a 100x oil immersion objective and oil immersion condenser lens. Identification was

carried out to the lowest possible taxonomic level (i.e., species or variety) using

numerous taxonomic sources, including Camburn et al. (1984-1986), Krammer and

Lange-Bertalot (1986, 1988, 1991a, 1991b), Krammer (1992), Lange-Bertalot and

Metzelin (1996), Camburn and Charles (2000), and Fallu et al. (2000). Chrysophycean

stomatocysts were enumerated (though not identified), and the ratio of cysts to diatom

valves counted (C:D) was calculated (Smol 1985). Photomicrographs of various diatom

taxa were taken using the Leica microscope and an attached Retiga 1300 camera. These

photographs aided in diatom identification, and helped to ensure taxonomic consistency.

25 Raw diatom counts were converted to percent relative abundances, and these data were

then used to generate a stratigraphical profile for the core using the computer program C2

version 1.3 (Juggins 2003). Biostratigraphical zones were delineated by cluster analysis using constrained incremental sum of squares (CONISS); this was done using the computer programs TILIA and TILIA-GRAPH (Grimm 1991).

Statistical Analyses

Hill’s N2 diversity index (Hill 1973) was used as one estimate of diatom diversity

(i.e. the effective number of diatom taxa in each sample, or N2) for each sediment

interval. This index is one of the most commonly used diversity indices in ecological

studies (Ludwig and Reynolds 1988); however, the results must be interpreted with

caution, as changes in sedimentation rates over the length of the core may result in

differential representation of time periods amongst sediment intervals from different

depths in the core (Smol 1981). The data obtained with the N2 index are used here

simply to supplement the primary diatom data, as they may provide valuable additional

ecological insights. In addition to Hill’s N2, a detrended correspondence analysis (DCA)

was run using CANOCO version 4.5 (ter Braak and Šmilauer 2002) in order to present an

overall summary of changes in the diatom assemblage data. The relative abundance data

for all taxa were included in the analysis, and were square-root transformed with no

downweighting of rare taxa. Both Hill’s N2 values and DCA Axis 1 sample scores were

plotted against core depth to facilitate comparison with the diatom stratigraphy.

26 RESULTS

Radioisotopic dating

The results of the radiocarbon dating (Seppä et al. 2003) are listed in Table 2.2.

The oldest date, taken at 174 cm, indicates that the core dates back to more than

approximately 8550 cal yr BP, and therefore encompasses the majority of the Holocene

and thus most, if not all, of the lake’s history. For example, deglaciation of the region occurred between approximately 9500-8980 cal yr BP (or 8500-8000 14C yr BP) (Dyke et

al. 2003). All dates are chronologically consistent, except for one inversion at 137 cm.

This anomalous date was excluded from the age-depth model (Figure 2.2), which was

generated following the method of Seppä et al. (2003) in order to facilitate comparisons

between our diatom record and their pollen record from the same core. The model was

produced by fitting a second-order polynomial curve to the calibrated dates, and

assuming a modern age (1996, or -46 cal yr BP) for the top-most sediments.

Diatoms

A total of 221 taxa belonging to 23 genera make up the species-rich diatom flora

recorded in the TK-2 core (Appendix A). The assemblages are composed predominantly

of benthic taxa, with only a few planktonic and tychoplanktonic taxa present. A

stratigraphic profile of the percent relative abundances of the most common taxa (as well

as the chrysophycean cyst to diatom ratio, or C:D) throughout the core is shown in Figure

2.3 (for a list of all identified taxa, their authorities, and their modern synonyms, see

Appendix B). For the sake of simplicity, taxa displaying similar trends and/or that are

known to have similar ecological preferences were grouped together for stratigraphic

display (Figure 2.3), resulting in a total of 12 taxonomic groupings. Eight diatom

27 biostratigraphic zones were determined using CONISS (total sum of squares = 24).

Substantial changes in the diatom assemblage composition were recorded in the TK-2

core throughout the last ca. 9000 years, and these will be described below.

The results of the detrended correspondence analysis (DCA) and Hill’s N2

analysis of sample diversity are shown in Figure 2.4a and b, respectively. To facilitate

comparison with the diatom profile, these figures are also divided by the eight diatom biostratigraphic zones. Notable trends in DCA and N2 will be described below, in parallel with the diatom assemblage changes seen in the corresponding zones. Age estimates for each zone are derived from the age-depth model following Seppä et al.

(2003), and are approximate.

Zone 1 (199-196 cm; ca. 9056-9048 cal yr BP)

The diatom assemblages at the base of the core are dominated by small, benthic

Achnanthes taxa (collectively ~60%), together with a few small Navicula species (~30%)

(Figure 2.3). Achnanthes nitidiformis and A. impexa co-dominate the relatively low-

diversity (N2 ~20; Figure 2.4b) assemblage at relative abundances of approximately 22-

25% and 25-28%, respectively. Smaller but notable contributions also come from

Navicula jaernefeltii and N. digitulus. Although the assemblage composition of this zone

is predominantly periphytic, the presence of one planktonic group, the Cyclotella

stelligera complex, is notable (~8-10%). The Cymbella complex (~5%), A. minutissima

(~2.5-7%), N. radiosa (~5%), and the Nitzschia perminuta and Achnanthes marginulata/scotica/lacus-vulcani groups (both ~2.5%) are present but at low

abundances.

28 Zone 2 (193-174 cm; ca. 9028-8850 cal yr BP)

Similar to Zone 1, the assemblage in Zone 2 consists predominantly of

Achnanthes and Navicula taxa, but diversity is greater (N2 reaches 40; Figure 2.4b). The

small, periphytic, possibly aerophilic N. schmassmannii replaces A. nitidiformis and A.

impexa as the dominant taxon, reaching abundances greater than 45%, although it briefly

shares this dominance with A. minutissima (~25%), the A. curtissima/stolida complex

(~20%) and N. kulebsii (~20%) in the early part of the zone. The virtual disappearance of

the C. stelligera complex between Zones 1 and 2 makes the assemblage in the latter zone

almost entirely periphytic, until the top of the zone, where the tychoplanktonic

Aulacoseira lirata complex appears for the first time in notable abundance (~10%). Also

at this time, the small, benthic, alkaliphilous Fragilaria taxa, which were previously

absent, now represent nearly 10% of the relative abundance (Figure 2.3). Subdominants

in this zone include the Diploneis complex, N. radiosa and the Cymbella complex.

Zone 3 (167-154 cm; ca. 8727-8490 cal yr BP)

The beginning of Zone 3 is marked by a dramatic increase in the small benthic

Fragilaria group to a relative abundance of nearly 55% (Figure 2.3). It then abruptly decreases to less than 10% over the next two intervals (160-161 and 154-155 cm), with a corresponding marked increase in the tychoplanktonic Aulacoseira lirata complex (~72% to >95%). Diversity drops greatly here (N2 nearly zero; Figure 2.4b), reflecting this dramatic expansion of A. lirata at the expense of all other taxa. C:D also decreases to its lowest level in the core. However, it is important to note that five intervals (166-167,

160-161, 154-155, 148-149, and 142-143 cm; i.e. all of Zone 3 as well as the 2 basal intervals of Zone 4) had extremely sparse diatoms and were very high in siliciclastic

29 material relative to the rest of the core; in fact, there is a striking increase in sediment accumulation rate in this part of the core (~0.64 cm/yr) compared with in the strata above

(~0.01-0.03 cm/yr). This resulted in unavoidably low diatom counts (<200 valves) for these intervals. The two intervals at the top of Zone 3 (154-155 and 160-161 cm) were

especially sparse and high in siliciclastic content, with exhaustive diatom counts of only

54 and 25 valves, respectively. Interpretation of these intervals must therefore be

undertaken with caution.

Zone 4 (149-110 cm; ca. 8348-7091 cal yr BP)

Zone 4 coincides with an abrupt and dramatic decline in the once-dominant A. lirata complex (~15%), and a return to high relative dominance by small, benthic, alkaliphilous Fragilaria taxa (~50-60%) (Figure 2.3). Diversity increases again to values similar to those in Zone 2 (Figure 2.4b), with taxa from the genera Achnanthes, Navicula,

Cymbella, Diploneis, Pinnularia, and Nitzschia providing notable contributions to the assemblage. Although no longer dominant, the Aulacoseira lirata complex remains relatively important throughout this zone (~20%). Navicula schmassmannii gradually increases to ~15% relative abundance towards the top of the zone, where the benthic

Fragilaria group begins a sharp decline.

Zone 5 (105-50 cm; ca. 6836-3843 cal yr BP)

The transition between Zones 4 and 5 is characterized by an abrupt and marked

decline in the previously dominant small, benthic, alkaliphilous Fragilaria taxa, and a shift to dominance (~20-55%) by large, heavily-silicified, tychoplanktonic Aulacoseira

species (Figure 2.3). As these Fragilaria species decline to <5% (remaining absent or at

trace levels for the rest of the core), the A. lirata and A. perglabra complexes both

30 increase in this zone, and the A. distans complex appears for the first time. Additionally,

after having been present at only very low abundances, the somewhat acidophilic

Fragilaria virescens var. exigua also becomes a dominant taxon, reaching abundances of

~15-30%. This shift in assemblage composition marks the largest (almost complete)

species turnover throughout the core, which is reflected in the DCA axis 1 scores with a change of more than 1.5 SD units over 5 sediment intervals (Figure 2.4a). Taxa considered to be circumneutral to slightly acidophilic, such as the Achnanthes

marginulata/scotica/lacus-vulcani group and the Cymbella complex, each exceed 5%

relative abundance, becoming a more important component of the diatom assemblage.

Additionally, the Frustulia rhomboides and Eunotia groups, Stauroneis anceps, and

Pinnularia cf. viridis (the former three of which are also associated with circumneutral to

slightly acidic environments), become notably more prominent here, although in low

relative abundances. Finally, the Cyclotella stelligera complex reappears around ca. 102

cm, though also at very low abundances (e.g. 1.5-2%). Compared to the changes

recorded in the lower half of the core, the diatom assemblage remains relatively stable

throughout this zone, and, despite some fluctuations, so does diversity (Figure 2.4b).

Zone 6 (45-13 cm; ca. 3434-1069 cal yr BP)

Zone 6 is characterized by notable fluctuations in the relative abundances of

dominant, heavily-silicified Aulacoseira taxa, which experience a decline early on in the

zone and two peaks at around 33 cm and 15 cm, both of which correspond to small

declines in diversity (Figure 2.4b). In addition, F. virescens var. exigua gradually

increases from approximately 15% at the base of this zone to ~25% at the top. Besides

31 these most prominent changes, there are also some fluctuations evident among the sub- dominant taxa, although no clear trends are apparent.

Zone 7 (13-4 cm; ca. 1069-306 cal yr BP [or 881-1644 AD])

Zone 7 is marked by the abrupt appearance and expansion of the small-celled

Achnanthes biasolettiana var. subatomus, which peaks at ~15% in the middle of the zone

(around 9 cm), and then declines again to ~5% for the rest of the core (Figure 2.3). The

heavily-silicified Aulacoseira lirata and A. perglabra complexes, as well as F. virescens var. exigua, all undergo a steep decline in relative abundance from Zone 6 to Zone 7, increasing again in the second half of Zone 7. The small-celled Achnanthes curtissima/stolida and A. marginulata/scotica/lacus-vulcani groups also increase relative to their abundances in Zone 6, and Navicula digitulus and N. schmassmannii undergo gradual declines. Diversity shows an overall increasing trend from the base of this zone to the top of the core (Figure 2.4b).

Zone 8 (4-0 cm; ca. 306 cal yr BP [or 1644 AD] – present [1996])

The most pronounced change in the diatom assemblage in the top-most zone is a

striking expansion of the small, planktonic Cyclotella stelligera complex in the top 5 cm

from trace levels to abundances exceeding 10% (Figure 2.3). This is paralleled by an

equally striking decline in the heavily-silicified Aulacoseira lirata complex, from 15%

down to trace abundances. Fragilaria virescens var. exigua also decreases over this

zone, but remains a dominant component of the assemblage at ~15%. Small increases in

the Achnanthes curtissima/stolida group and Nitzschia perminuta are also evident at the

top of the core.

32 DISCUSSION

The species composition of the diatom assemblages in Lake TK-2 overlaps

markedly with those from two other nearby Canadian Arctic lakes from which detailed

paleolimnological studies have been completed: Slipper Lake (Rühland and Smol 2005) and Lake TK-20 (Rühland 2001), located approximately 200 km south-west of TK-2 in the forest-tundra ecozone. Dominance by benthic taxa is typical of Arctic lakes and

ponds, and is an indication of TK-2’s relative shallowness and, perhaps more

importantly, the fact that it is extensively ice-covered for the majority of the year (Smol

1988; Smol and Cumming 2000), limiting the growth and development of planktonic taxa

(Smol 1983; Smol et al. 2005; Smol and Douglas 2007).

Early Holocene

In the earliest strata in the TK-2 sediment core (Zones 1 and 2), starting at

approximately 9000 cal. yr BP, the diatom assemblages are characterized by an

abundance of predominantly small, periphytic Achnanthes and Navicula taxa. Ecological

interpretation of this portion of the core presents somewhat of a challenge. The small,

periphytic Achnanthes species A. impexa and A. nitidiformis co-dominate Zone 1,

together comprising approximately 50% and higher of the assemblage. These diatoms are poorly known ecologically and are not taxonomically well-defined (D. Antoniades, personal communication). To my knowledge, they have not been noted in any substantial abundances in any other Arctic diatom study, making ecological inferences for the period in which they dominate difficult. Interestingly, in this first zone there is also a notable presence (~10%) of the Cyclotella stelligera complex. Increases in this small, planktonic diatom have been associated with increased open-water (ice-free) periods and associated

33 changes to the water column (Rühland et al. 2003, 2008; Smol et al. 2005; see below).

The presence of this group at the very bottom of the core may therefore be an indication

that the open-water period in summer was sufficiently long at this time to allow for their

development. If this is the case, perhaps these dominant Achnanthes species also

flourished in response to advantageous conditions related to a longer open-water season,

such as an expansion of the littoral zone resulting in an increase in their preferred substrate.

In Zone 2, Navicula schmassmannii replaces these Achnanthes species as the dominant taxon in a notably more diverse assemblage (Figure 2.4b), reaching nearly 50% relative abundance. This species has been commonly found in diatom studies throughout the Canadian Arctic (e.g. Bouchard et al. 2004; Fallu et al. 2002; Joynt and Wolfe 2001;

Michelutti et al. 2003; Pienitz et al. 1995; Rühland and Smol 2002; Rühland et al. 2003a), but it is generally a very small component of the diatom assemblage. As such, the ecological preferences of this diatom are also poorly understood. However, in lakes on

Victoria Island in the Canadian High Arctic, Michelutti et al. (2003) found it exclusively on moss habitats (though again at low relative abundances), and it is believed by some to be aerophilic (John P. Smol, Dermot Antoniades and Paul Hamilton, personal communications). In a Slovakian alpine lake, it reached abundances of nearly 40% post-

1900 (Šporka et al. 2002), and the authors postulate that climate warming may have been an important driver of this change. Furthermore, the recent (post-1950) appearance and expansion of this taxon in a Norwegian alpine lake has been linked to recent measured climate warming (Larsen et al. 2006). Additionally, it increased notably in relative abundance with the onset of the Holocene Thermal Maximum in a lake on Baffin Island

34 (Briner et al. 2006), though the authors do not indicate the magnitude of the increase. It is possible, then, that the dominance of N. schmassmannii in Zone 2 of the TK-2 core is indicative of conditions warm enough to have provided an ice-free period of sufficient duration to support a substantial growth of mosses in the littoral zone, thus enabling the proliferation of this potentially moss-dwelling diatom.

The above observations for the first two zones do not corroborate with conditions inferred from the pollen record from the same core by Seppä et al. (2003), who deduced that climatic conditions during this part of the lake’s history were colder than present, much like the climate of the modern mid Arctic tundra, north of TK-2’s low Arctic location. Furthermore, the diatom assemblage composition differs notably from most

Arctic Holocene cores, wherein early postglacial assemblages are commonly characterized by low diversity and a dominance of small, benthic, alkaliphilous

Fragilaria taxa (e.g. Douglas et al. 1994; Lemmen et al. 1988; Lotter and Bigler 2000;

Michelutti et al. 2007; Rühland and Smol 2005; Smith 2002; Smol 1983, 1988; Sorvari and Korhola 1998). Such an assemblage is more consistent with conditions that would intuitively be expected in a newly-formed lake following deglaciation; namely cooler temperatures and extended ice cover resulting from the localized effects of the retreating ice sheet, as well as relatively alkaline waters from the leaching of soluble base cations from the undeveloped, newly deglaciated catchment (Bradshaw et al. 2000; Engstrom et al. 2000; Fritz et al. 2004; Smol 1983; Wolfe 1996).

However, studies involving the reconstruction of paleo-wind patterns (from dune fields formed during deglaciation, for example; Wolfe et al. 2007) have inspired speculations regarding the potential local warming effects of air circulation patterns

35 generated by the retreating Laurentide ice sheet (Glen MacDonald, personal

communication). In the pollen profile of the TK-2 core (Seppä et al. 2003), there are

visible peaks in certain arboreal pollen types (Pinus and Picea species) in the earliest

strata. It is possible that this pollen was transported from the south via warm air drawn

northward by anticyclonic winds generated by a stationary high-pressure system centred over the Laurentide ice sheet (Glen MacDonald, personal communication). This warm

southern air could have contributed to a transient period of relative warmth, which would

have diminished as the ice sheet retreated farther away, taking the anticyclonic winds

with it. Although it remains highly speculative, this scenario would reconcile the

apparent warm conditions inferred from the diatom assemblages for this early part of the

core.

8.2k cold event?

Although the small, benthic Fragilaria taxa typical of early post-glacial

assemblages are virtually absent from the earliest layers of the core, they become

dominant (>50% relative abundance) in Zones 3 and 4, suggesting a shift to colder conditions with more extended ice cover sometime between approximately 8550 and

8500 cal yr BP. However, this dominance is interrupted at the top of Zone 3 by the dramatic increase in the tychoplanktonic Aulacoseira lirata complex. As mentioned earlier, this apparent increase must be viewed with caution, as a marked increase in the amount of siliciclastic material in the slides for these and the surrounding intervals necessitated very low diatom counts. However, the observed increase in siliciclastic content and accompanying scarcity of diatom valves here may, in itself, be an important paleoenvironmental signal. The timing of these changes in the core corresponds closely

36 to the timing of the catastrophic outburst flood from glacial Lake Agassiz (approximately

8,479 cal yr BP, Barber et al. 1999), widely accepted as the likely trigger for the so-called

8.2k cooling event (Clarke et al. 2004). Also referred to as the 8k event, or Finse event in

Scandinavia, it is an anomalous cooling event evident in the Greenland ice cores as an

abrupt, dramatic decline in δ18O and snow accumulation rate to their Holocene minima,

with most extreme lows in these parameters occurring at approximately 8200 cal yr BP

(e.g. Alley et al. 1997; Alley and Águstsdottir 2005; Rohling and Pälike 2005; Thomas et

al. 2007). Freshening of the North Atlantic surface waters as a result of the immense

outburst flood from Lake Agassiz would have inhibited the formation of sinking North

Atlantic Deep Water (NADW), which flows southward and is replaced by warmer surface water from the south in a process known as thermohaline circulation (THC), an integral process in moderating climate (Broecker 1997; Clark et al. 2002). A disruption

of this system would ultimately result in a colder, dryer climate across the northern

hemisphere, but especially pronounced over the North Atlantic (Alley and Agustsdottir

2005; Rohling and Palike 2005). Numerous widespread paleoclimate records using

various paleoindicators have put forth potential evidence in support of this event

(summarized by Alley and Agustsdottir (2005) and Rohling and Palike (2005)). It is a

distinct possibility that the diatom record from TK-2 is similarly showing evidence for

this anomalous cooling.

Although the very low diatom counts at the top of Zone 3 may be a potential

result of dilution by increased siliciclastic sedimentation, they may also reflect cooler

conditions at this point in the TK-2 core. This is suggested by the fact that virtually the

only diatom taxa present here are Aulacoseira species, a group of typically heavily-

37 silicified, tychoplanktonic taxa that require a certain degree of turbulence to remain suspended in the photic zone, and which thus bloom under well-mixed conditions (e.g.

Kilham et al. 1996; Pannard et al. 2008; Ptacnik et al. 2003; Rühland and Smol 2005).

Furthermore, there are certain physical and chemical characteristics of the sediment here that lend support to a cooling scenario. For example, in addition to the qualitative observation of increased siliciclastic material, it is clear from trends in % LOI over time

(Seppä et al. 2003) that there is also a marked decrease in organic matter corresponding to the timing of the apparent increase in the Aulacoseira lirata complex. Furthermore, there is a striking increase in sedimentation rate around this depth in the core that is apparent both visually and mathematically (0.64 cm/yr here compared with 0.013 - 0.029 cm/yr everywhere above this). These sedimentological changes are consistent with a potential climate cooling, which could have resulted in the deterioration of the vegetation cover in the lake’s catchment, destabilizing the soils and resulting in an enhanced influx of minerogenic sediment to the lake via wind and melt water (e.g. Andresen et al. 2006;

Spooner et al. 2002). Decreased organic content (i.e. LOI) could also potentially signal decreased productivity in the lake from an extended period of ice cover (Spooner et al.

2002). A few studies on cores from lakes in North America and northern Europe have noted similar abrupt shifts in the minerogenic properties of the sediment that are consistent with cooling and correlative with the timing of the 8.2k event. These changes include marked decreases in LOI and increased siliciclastic content (Dean and Schwalb

2000; Kurek et al. 2004; Spooner et al. 2002), increased sedimentation rate (Andresen et al. 2006; Dean and Schwalb 2000; Spooner et al. 2002) and magnetic susceptibility

38 (Dean and Schwalb 2000; Spooner et al. 2002), and increased mean sediment grain size

(Andresen et al. 2006; Spooner et al. 2002).

The increased influx of minerogenic sediment into TK-2 could have easily enhanced mixing and turbidity in the lake, inhibiting light penetration and creating an environment that was detrimental to the growth of most diatoms. However, the same conditions could have lent a selective advantage to the heavily-silicified Aulacoseira taxa, which are known to be competitive under turbid, turbulent, and low-light conditions

(Bradshaw et al. 2000; Gibson et al. 2003; Interlandi et al. 1999; Spooner et al. 2002).

Aulacoseira species were also found to strongly dominate (~95%) the diatom assemblage of a Nova Scotia lake coeval with the timing of the outburst flood, and coincident with many of the same sedimentological changes mentioned above (Spooner et al. 2002). The authors hypothesized that this may indicate colder and perhaps windier conditions, with increased turbulence in the lake.

Although the dating resolution for the TK-2 core is relatively coarse, all of the observed physical, chemical and biological changes mentioned above can be constrained to between approximately 8550 and 8500 cal yr BP, which, as noted above, is correlative with the timing of the Lake Agassiz outburst flood (Barber et al. 1999). Thus, the marked increases in sedimentation rate and siliciclastic content, and decreased LOI in the

TK-2 core, combined with the very low counts of diatoms consisting of almost entirely

Aulacoseira species, may provide new evidence for the 8.2k cooling event in this region of the Canadian Arctic. These findings support the conclusions of the Seppä et al. (2003) pollen study on the same core, in which the overall stable pollen assemblage profile is interrupted only once, at approximately 8100 cal. yr BP (which is based on dates

39 interpolated from the age-depth model; based on the calibrated 14C dates, the onset of

their event falls slightly after 8500 cal. yr BP), with a dramatic and abrupt drop in the

otherwise dominant Betula (dwarf birch) pollen, and corresponding increases in some

heath, grass and sedge pollen. The inferred vegetation change is indicative of a transient

cooling (Seppä et al. 2003), which the authors tentatively linked to the 8.2k cooling

event. However, a lack of paleoecological evidence for this event elsewhere in northern

Canada made them hesitant to draw any firm conclusions.

The above changes in the diatom record precede the changes in the pollen record by approximately 20 cm, or approximately 90-100 years (based on the calibrated radiocarbon dates). This time lag between the response of these two different proxies is to be expected when one considers the very rapid life cycle of diatoms relative to terrestrial vegetation, which can take years to become established and to reach reproductive age. Because of this, it is not uncommon for the vegetation response to a given disturbance to lag that of diatoms (e.g. Rühland et al. 2006). Furthermore, models simulating the effects of a freshwater outburst flood to the North Atlantic predict recovery times of over 200 years (Clarke et al. 2003); thus, a lag of 90-100 years between the response of diatoms and that of pollen does not seem unreasonable.

Based on the nature and likely cause of the 8.2k cooling event, one might expect

evidence of its occurrence to be more abundant and widespread. Why, then, has there

been no other paleoecological evidence for this event reported in northern Canada? It has

been suggested that this could result from a combination of limited sampling, dating

uncertainties, and the fact that many paleoecological studies do not go back far enough in

time or lack sufficient temporal resolution to detect such an abrupt and potentially quite

40 brief event (Alley et al. 1997; Alley and Águstsdottir 2005; Kleiven et al. 2007; Seppä et

al. 2003; Spooner et al. 2002; Thomas et al. 2007). Indeed, if the present interpretation is

correct and we are, in fact, seeing evidence for the 8.2k event, these results corroborate

other records suggesting that the event was quite short-lived (from decades to a few

centuries; e.g. Alley et al. 1997; Alley and Águstsdottir 2005; Kleiven et al. 2007;

Spooner et al. 2002; Thomas et al. 2007), its effects appearing to have lasted for a period

of less than 50 years in the present case. Given the typically low sedimentation rates in

Arctic lakes and ponds, high temporal resolution is very difficult to attain, and it is easy to see how a short-lived signal could be diluted or passed over in the sampling process.

Holocene Thermal Maximum

From Zone 4 and upward, the TK-2 stratigraphy is consistent with previous

findings from other detailed diatom analyses from the central Canadian Arctic. In fact,

some of the major diatom trends bear a striking resemblance to certain elements of the

cores from Slipper Lake (Rühland and Smol 2005) and Lake TK-20 (Rühland 2001) to

the south. In Zone 4, close to approximately 8500 cal yr BP, the heavily-silicified,

tychoplanktonic Aulacoseira lirata complex drops markedly in relative abundance, and

the small, benthic, alkaliphilic Fragilaria species, which can bloom under cold, harsh

conditions (e.g. Lotter and Bigler 2000), once again increase and resume dominance at

nearly 60%. This is a good indication that conditions were relatively cold and alkaline

during this time, possibly with extended periods of ice cover. This lasts until the end of

Zone 4, around 7000 cal yr BP, when the alkaliphilous Fragilaria species decline, never

to reach more than 2.5 - 5% again, and the possibly aerophilic N. schmassmannii

increases notably. It is at this point in the core, at the transition between Zones 4 and 5,

41 where the largest species turnover occurs, with many of the species that were important in the bottom half of the core virtually disappearing, and with a very different assemblage dominating from Zone 5 onward. This compositional change is summarized in the DCA axis 1 curve (Figure 2.4b), which at this transition shows a change of approximately 1.5 standard deviation units over 5 sediment intervals. The changes here clearly indicate an important change in the aquatic environment of Lake TK-2, and likely represent the

initiation of the local Holocene thermal maximum (HTM), a climatic interval widely

recognized in paleoclimate records from across the Arctic (Kaplan and Wolfe 2006;

Kaufman et al. 2004).

During the above period of marked compositional change (ca. 7000 cal yr BP),

concurrent with the decline in small, benthic, alkaliphilous Fragilaria taxa, diatoms that are known to be less alkaline, or more circumneutral to slightly acidophilic, such as

Fragilaria virescens var. exigua, Eunotia species, varieties of Frustulia rhomboides,

Stauroneis anceps, the Achnanthes marginulata/scotica/lacus-vulcani and A.

curtissima/stolida complexes, A. carissima, the Cymbella complex (consisting primarily

of C. gaeumannii), and the Aulacoseira lirata, A. distans and A. perglabra complexes,

become noticeably more common (some appearing for the first time in any notable

abundance), constituting the majority of the assemblage. The timing of this shift to a less

alkaline assemblage corresponds very closely with a similar shift in Lake TK-20 (ca 7210

cal yr BP; Rühland 2001), where many of the same species are involved. The marked

decline in alkaliphilous Fragilaria taxa, in concert with the appearance or expansion of

circumneutral to acidophilic taxa, is likely a result of a natural loss of alkalinity as lake

ontogeny proceeded. Over time, the base cations from the catchment that contributed

42 alkalinity to the newly-formed lake would have been depleted from the developing soils,

and a developing vegetation cover could have further enhanced alkalinity loss by

contributing organic acids to the system (Bradshaw et al. 2000; Engstrom et al. 2000;

Fritz et al. 2004; Rühland and Smol 2005). This type of natural, long-term alkalinity loss

is seen in most Arctic lakes that, like TK-2, are located on slow-weathering, granitic

bedrock, which has a low buffering capacity (e.g. Pienitz et al. 1999; Rühland and Smol

2005; Smol 1983).

In addition to indicating a natural loss of alkalinity, the changes recorded thus far

are also suggestive of ameliorating climatic conditions. For example, the number of

planktonic diatom taxa increases here with the appearance of the Aulacoseira distans and

A. perglabra complexes, as well as the reappearance, albeit in very low abundances, of

the Cyclotella stelligera complex. A similar increase in planktonic taxa also occurred

around this time in Lake TK-20 (Rühland 2001), which was attributed to warming

conditions, because an increase in planktonic taxa would be expected with an increased open-water period and longer growing season (Smol 1988). A coincident notable

increase (>10%) in organic matter content recorded by Seppä et al.’s (2003) LOI profile for TK-2 further supports a warming scenario at this transition, with an increase in

productivity in the lake and/or a decrease in siliciclastic input. A similar trend in % LOI

was also recorded in Lake TK-20 (Rühland 2001). Further support for warming is

evidenced by an increase in Alnus (alder) in TK-2’s pollen profile (Seppä et al. 2003), a

trend that is apparently widespread over northwestern Canada (and also occurs in Lake

TK-20; Huang et al. 2004). As Alnus prefers relatively warm, moist environments

(Moser and MacDonald 1990; Seppä et al. 2003), its notable increase indicates that

43 conditions became warmer and wetter around this time (Huang et al. 2004). In Lake TK-

20, there was an increase in Picea (spruce) pollen coincident with the rise in Alnus, but to abundances low enough to suggest long distance transport from an advancing treeline to the south rather than direct invasion of TK-20’s catchment (Huang et al. 2004). No similar rise in Picea is recorded in the TK-2 pollen assemblage at this time, likely because treeline did not migrate far enough north for this shift to be detected (Seppä et al.

2003). As noted by Rühland (2001), this warming in TK-20 (and TK-2) corresponds approximately with the timing of mid-Holocene treeline advances seen in the pollen records of lakes located to the south of TK-2 near the current treeline, west of TK-20, where between approximately 5000-3500 14C yr BP (or roughly 5700-3800 cal yr BP; calibrated using CalPal-2007online), forest-tundra vegetation was established in catchments that had previously been tundra environments (Queen’s and McMaster lakes: Moser and

MacDonald 1990; MacDonald et al. 1993; Pienitz et al. 1999). Coincident with these inferred changes in vegetation, dramatic increases in diatom-inferred DOC and the concentration of diatom valves in Queen’s Lake are also suggestive of increased productivity in a warmer environment (MacDonald et al. 1993; Pienitz et al. 1999).

Taking into consideration all of the above evidence, the transition from Zone 4 into Zone 5 likely corresponds to a period of climate amelioration, with warmer, moister conditions supporting a more productive aquatic environment, and providing a slightly longer growing season that is more amenable to planktonic diatoms. This warming is correlative with the timing of the Holocene thermal maximum recorded in records from other regions of the central continental Canadian Arctic (Kaufman et al. 2004).

Furthermore, natural loss of alkalinity from the lake is apparent at this time, and likely

44 represents the continued development of the catchment’s soil and vegetation as lake

ontogeny proceeded.

Neoglacial Period

The next section of the TK-2 core (Zone 6 and 7), beginning at around 3500 cal yr

BP, corresponds to a climatic interval known as the Neoglacial Period, a widely recognized occurrence that is generally characterized by a gradual overall cooling trend

following the Holocene Thermal Maximum (e.g. Bradley 1990; Grove 2001; Kaufman et

al. 2004; Overpeck 1997). The timing of the onset of this period (like that of the

Holocene Thermal Maximum) is spatially variable, but is generally recorded between

approximately 4000-2000 cal. yr BP in continental Arctic Canada (Bradley 1990; Grove

2001; Kaufman et al. 2004). The diatom assemblages in TK-2 are supportive of a

Neoglacial cooling, manifested in concurrent notable increases over this time period in

the prominence and relative abundances of taxa known to prefer slightly more acidic to

circumneutral waters, including Fragilaria virescens var. exigua, the Achnanthes

curtissima/stolida and A. marginulata/scotica/lacus-vulcani complexes, A. carissima, the

Eunotia and Frustulia rhomboides complexes, and Stauroneis anceps. In Arctic lakes with poor buffering-capacity, pH is modulated primarily by the effects of ice cover on dissolved inorganic carbon (DIC) dynamics and primary production within the lake

(Wolfe 2002). In a cooling scenario, prolonged ice cover prevents the escape of dissolved CO2 to the atmosphere, in addition to inhibiting light penetration and thus the

drawdown of CO2 through photosynthetic activity. The resultant increase in the

concentration of CO2 in the lake causes a decline in pH through the production of carbonic acid, or H2CO3 (Wolfe 2002), which would provide conditions more amenable

45 to the slightly acidophilous to circumneutral diatom taxa mentioned above. Indeed,

studies of other Arctic lakes, such as Lake TK-20 and Queen’s and Toronto lakes

(Rühland 2001 and Pienitz et al. 1999) record similar Neoglacial diatom assemblage

changes to those described here for the TK-2 core, involving increases in many of the

same diatom taxa, and occurring around roughly the same time. The authors similarly

attribute these changes to a decrease in pH driven ultimately by a cooling climate.

In addition to the above assemblage changes, there are marked fluctuations in the

Aulacoseira lirata complex in the Neoglacial portion of the TK-2 core that bear a striking

resemblance to changes recorded over a similar timeframe in the Aulacoseira complex in

the more southerly Slipper Lake (Rühland and Smol 2005). Although the low resolution

of the TK-2 core combined with very approximate dating estimates makes it difficult to

correlate these changes with any known climatic events, the peaks and valleys in the A.

lirata complex could indicate periods of even further cooling and relative warming,

respectively, as these heavily-silicified taxa have been known to thrive under cooler

conditions, and conversely are less successful under warmer, more thermally stable

conditions (see below).

Interestingly, the sudden expansion in Zone 7 of Achnanthes biassolettiana var.

subatomus, which had been previously virtually absent, appears to occur at

approximately 1100 cal yr BP, and therefore may correspond to the timing of the so-

called “Medieval Warm Period” (MWP). The MWP is an interval between approximately the 9th and 14th centuries (Overpeck et al. 1997) during which the overall

cooling trend of the Neoglacial Period was interrupted by an anomalous general warming

trend (Grove 2001; Overpeck et al. 1997). Although the autecology of A. biasolettiana

46 var. subatomus is not well established, the decline in the Aulacoseira lirata and A.

perglabra complexes occurring in concert with the expansion of this small Achnanthes

species supports a relative warming (as mentioned above).

Finally, the period between approximately 550-100 cal yr BP is often cited as the

culmination of the Neoglacial Period, termed the ‘Little Ice Age’ (LIA), with anomalous

cooling evident in the melt records and oxygen isotope ratios of ice caps, as well as in widespread evidence of glacial expansions (e.g. Bradley 1990; Grove 2001; Overpeck et al. 1997). In the TK-2 core, as Achnanthes biasolettiana var. subatomus declines, a final

peak in the Aulacoseira lirata complex in the TK-2 core occurs at the top of Zone 7, at

approximately 560 cal yr BP. As mentioned above, this is a possible indication of

cooling, and it is potentially correlative with the timing of the LIA. However, the interval

of time encompassing both the MWP and LIA is particularly difficult to date accurately,

as it lies just beyond the ranges of the half-lives of both 210Pb and 14C, necessitating extrapolation. For this reason, any interpretation during this period is somewhat speculative.

Recent changes

In the most recent strata of the TK-2 core (Zone 8), the most notable and perhaps

most ecologically pertinent changes are recorded in the dramatic expansion of the

Cyclotella stelligera complex in the top 3-4 cm (approximately the early- to mid-19th century) to values exceeding 10%, before which time it had been either absent or only present at very low levels for many millennia. Coincident with this expansion is an equally dramatic decline in the once dominant Aulacoseira lirata complex to near trace abundances at the top of the core. Furthermore, there is a dramatic increase in percent

47 organic matter (%LOI) to unprecedented levels (72.9%) at the top of the core (Seppä et

al. 2003), which is reflective of a marked increase in primary productivity within the

lake. These trends are in parallel with what is becoming increasingly recognized as a

geographically widespread response to recent climate warming (Rühland et al. 2008;

Smol et al. 2005). Warming in Arctic environments impacts the physical, chemical and

ultimately biological properties of lakes and ponds, largely through its effects on ice

cover. Lakes in these regions are generally extensively ice-covered for most of the year,

with only a short period of open-water conditions in the summer season, during which

some lakes or ponds never become completely ice-free; thus, even a slight increase in

temperature can substantially decrease the amount of ice-cover and prolong the ice-free

period (Douglas and Smol 1994, 1999; Smol 1988; Smol et al. 2005; Smol and Douglas

2007). A longer open-water period provides a longer growing season, and results in

changes in thermal stability of the water column, often strengthening and increasing the

duration of thermal stratification (Rühland et al. 2008; Winder and Hunter 2008; Winder

et al. 2008). This, in turn, alters the aquatic habitat through changes in lake water

chemistry, nutrient distribution, as well as light dynamics and quality within the water

column (e.g. Rühland et al. 2003, 2008; Winder and Hunter 2008; Winder et al. 2008).

Both empirical and paleolimnological evidence suggest that these changes ultimately result in conditions under which small planktonic taxa with rapid growth rates and high surface area-to-volume ratios, such as Cyclotella species, enjoy a competitive advantage

(Lotter and Bigler 2000; Rühland and Smol 2005; Rühland et al. 2008; Winder and

Hunter 2008; Winder et al. 2008) over benthic taxa as well as heavier, rapidly-sinking tychoplanktonic Aulacoseira species that require some turbulence to remain in the photic

48 zone (e.g. Kilham et al. 1996; Pannard et al. 2008; Ptacnik et al. 2003; Rühland et al.

2008).

In accordance with the above process, past studies from the circumpolar Arctic have recorded notable 19th-century increases in planktonic Cyclotella species that are very similar to those seen in TK-2 (summarized by Smol et al. 2005). In all cases, these expansions were accompanied by compensatory decreases in benthic taxa (most commonly small Fragilaria taxa, e.g. Rühland et al. 2003), and/or, in some cases, in tychoplanktonic Aulacoseira species (e.g. Slipper Lake, Rühland and Smol 2005; Lake

TK-20, Rühland 2001; Lakes Saanäjarvi and Tsahkaljavri in Finnish Lapland, Sorvari et al. 2002; and now Lake TK-2). In all of these studies, the authors attribute these recent assemblage shifts to 19th-century climate warming and its resultant effects on the aquatic habitat. Although this phenomenon appears to be widespread across most of the circumpolar Arctic (Smol et al. 2005), it is not exclusive to northern regions; similar trends are also being found in the more recent (post-1950) sediments of temperate lakes, and can often be correlated with measured increases in temperature from meteorological records, as well as with historical lake-ice records (e.g. Rühland et al. 2008).

Because these most recent changes in the diatom assemblages of TK-2 (early- to- mid-19th century) and other Arctic lakes occur within a period of time in which anthropogenic impacts on the environment have vastly increased, there are some alternative drivers (besides climate warming) that could be considered. As summarized by Rühland et al. (2003) and Smol and Douglas (2007), these include more direct anthropogenic impacts such as atmospheric acid deposition and anthropogenically- derived nutrient deposition. Lake acidification as a result of acid deposition has been

49 well-documented, and could potentially cause dramatic changes in diatom assemblage

composition, especially in lakes situated over bedrock with poor buffering capacity, as is

Lake TK-2. However, Cyclotella species generally do not survive well in acidic

environments, and are commonly lost or severely reduced in acidified lakes (e.g.

Battarbee et al. 1999). Furthermore, in their analysis of over 200 paleolimnological

records, Rühland et al. (2008) found that all lakes that experienced a recent increase in

Cyclotella species were nutrient-poor and non-acidified. Thus, the expansion of the

Cyclotella stelligera complex in the upper strata of the TK-2 core is contrary to what would be expected under an acidification scenario. This, coupled with the lake’s currently more alkaline nature (pH 8.0), makes acid deposition an unlikely driver of these recent changes. As Rühland et al. (2003) note, anthropogenically-derived nutrients and other pollutants are also improbable explanations. Firstly, in the 50 lakes they surveyed

(some of which were located near TK-2), nutrient levels showed no correlation with the abundances of any of their common taxa (including Cyclotella species), many of which are also common in TK-2. In addition, the expansion of Cyclotella species in TK-2 (and other circumpolar Arctic lakes) begins in the early- to mid-1800s, pre-dating the initiation of anthropogenic deposition of nutrients and other pollutants by approximately a century

(Smol et al. 2005). Furthermore, TK-2 is presently ultra-oligotrophic, thus making it unlikely that it has acquired any substantial amount of nutrients in the recent past.

Strong evidence against nutrient deposition as a driver for the recent Cyclotella expansion was also recently put forth by Rühland et al. (2008), who found no correlation between a

30-year instrumental record of inorganic nitrogen deposition and the Cyclotella increase in Whitefish Bay, Lake of the Woods. Finally, in lakes from a region of the eastern

50 Canadian Subarctic where there is no evidence for recent warming, diatom assemblages

have changed very little over time, even since the commencement of anthropogenic

pollutant deposition (Laing et al. 2002; Paterson et al. 2003). If nutrients or other

pollutants were the cause of the recent changes in TK-2 and other lakes, one would expect these eastern subarctic lakes to have registered similar diatom changes (Smol et al.

2005). Thus, 19th-century climate warming and its resultant changes to the aquatic habitat remains the most plausible explanation for the changes in the top-most strata of lake TK-2’s sediment.

Summary and Conclusions

The diatom assemblages of Lake TK-2 have undergone notable changes over the

course of the lake’s history, suggesting that the Holocene in this region of continental

Arctic Canada has been environmentally and climatically dynamic. The early Holocene

diatom record is not typical compared to that of other lakes and ponds studied in the

Arctic; although the environmental implications of the assemblage are difficult to

interpret, it may indicate relatively warm conditions in the earliest part of the core, as

opposed to the more common indications of a cooler post-glacial environment. One

potential explanation for this atypical warmth, though still speculative, may lie in the

possible effects of anticyclonic circulation patterns generated by the presence of the

retreating Laurentide Ice Sheet, which could have drawn air northward from warmer,

more southerly regions, creating transient warmer conditions that would have dissipated

with the retreat of the ice sheet from the region (Glen MacDonald, personal

communication).

51 An assemblage dominated by small, benthic, alkaliphilous cold-water Fragilaria

taxa followed, indicating cooler, more alkaline conditions typical of early post-glacial

lakes and ponds in the Arctic. This assemblage was punctuated early on by abrupt and

dramatic changes in physical, chemical and biological indicators, providing potential evidence for the 8.2k cooling anomaly first noted in the Greenland ice cores.

Paleoecological evidence for this climate event in northern Canada is rare, potentially as

a result of limited sampling and, in existing samples, dating uncertainties as well as

temporal resolution too coarse to detect such an abrupt and brief occurrence.

The largest species turnover in TK-2 occurred at approximately 7000 cal. yr BP, when the cooler, more alkaline diatom assemblage was replaced by a very different and more structurally diverse assemblage, which included a larger number of planktonic taxa

(as well as increased relative abundance of those already present) and the appearance and/or increased importance of several slightly more acidophilic to circumneutral taxa.

These changes are consistent with a natural, long-term decrease in alkalinity as lake ontogeny progressed and the catchment developed, as well as with the onset of a mid-

Holocene warming, the timing of which is congruent with that found in other paleolimnological studies from the central Canadian Arctic. This warming was succeeded in the later Holocene by Neoglacial cooling, evident in concurrent relative increases in numerous taxa known to inhabit slightly more acidic to circumneutral waters.

This trend is suggestive of cooling temperatures because a prolonged period of ice-cover causes slight declines in pH driven by a shift in DIC dynamics, and similar patterns in many of the same diatom taxa as in TK-2 have been observed in other Arctic lakes.

Furthermore, though coarse sampling resolution and dating uncertainties make it difficult

52 to attribute them to known climate events, fluctuations in certain diatom taxa can

potentially be correlated with the so-called “Medieval Warm Period” and subsequent

“Little Ice Age”, though these associations remain tentative.

Finally, a dramatic expansion in the small, planktonic Cyclotella stelligera

complex and a corresponding decline in the heavily-silicified Aulacoseira lirata complex

in the most recent strata of the core (ca. the early to mid 19th century) are unprecedented

over the past eight millennia or longer. This observation is consistent with the ever- growing body of paleolimnological and neolimnological literature recording similar recent 19th century shifts in the diatom assemblages of lakes and ponds from across the

circumpolar Arctic, as well more recent shifts recorded in lakes in temperate regions.

This widespread ecological trend is increasingly being attributed to recent (19th-century)

climate warming, which increases the duration of the summer ice-free period, resulting in

a longer growing season, increased nutrient cycling and light within the lake, and/or

longer and stronger thermal stratification of the water column, providing conditions that

are favourable to the small, rapidly-growing planktonic Cyclotella taxa, while detrimental

to the heavily-silicified, rapidly-sinking Aulacoseira taxa.

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63 FIGURE CAPTIONS

Figure 2.1. Map showing the location of Lake TK-2 in the low Arctic tundra, Nunavut, Canada.

Figure 2.2. Age-depth model for the TK-2 core (198 cm long), produced using a second- order polynomial curve fitted to six radiocarbon dates, and assuming a modern age (1996, or -46 cal yr BP) for the top sediment layer.

Figure 2.3. Parts I and II. Stratigraphic profile of the relative abundances (%) of the most common diatom taxa, as well as the chrysophycean cyst:diatom frustule ratio (C:D), in the Lake TK-2 core. Diatom taxa displaying similar trends and/or that are known to have similar ecological preferences were grouped together, resulting in a total of 12 taxonomic groupings: the Cyclotella stelligera complex (C. stelligera, C. pseudostelligera); the Aulacoseira lirata complex (A. lirata, A. lirata v. biseriata); the A. distans complex (A. distans, A. distans v. nivalis); the Frustulia rhomboides complex (F. rhomboides, F. rhomboides v. saxonica, F. rhomboides v. satelles); the Eunotia complex (E. arculus, E. arcus, E. bidentula, E. bilunaris, E. bilunaris v. mucophila, E. pectinalis v. undulata, E. circumborealis, E. denticulata, E. diodon, E. exigua, E. faba, E. flexuosa., E. incisa, E. meisteri, E. minor, E. monodon, E. nymanniana, E. praerupta, E. rhychocephala , E. rhychocephala v. satelles, E. serra); the Achnanthes curtissima/stolida complex (A. curtissima & A. stolida); the A. marginulata/scotica/lacus-vulcani complex (A. marginulata, A. scotica, A. lacus-vulcani); the A. suchlandtii/laterostrata complex (A. suchlandtii, A. laterostrata); the Cymbella complex (C. cesatii, C. cf. angustata, C. cf. descripta, C. cf. ehrenbergii, C. cf. norvegica, C. cf. tynnii, *C. gaeumannii, C. gracilis, *C. hebridica, C. lapponica, C. mesiana, C. microcephala, *C. silesiaca, C. sinuata, C. naviculiformis); the small benthic Fragilaria group (*F. brevistriata, *F. brevistriata v. papillosa, F. cf. parasitica, *F. pinnata, *F. construens, F. construens v. binoda, F. construens v. pumila, *F. construens v. venter, *F. pseudoconstruens); and the Diploneis complex (*D. marginestriata, D. parma, *D. smithii v. dilatata). Asterisks (*) denote taxa with dominant contributions to a given grouping. 14C dates (cal. yr BP) are included, as are some estimated dates derived from an age-depth model. Hatched horizontal lines delineate biostratigraphic zones determined using CONISS.

Figure 2.4. a) Axis 1 sample scores for a Detrended Correspondence Analysis (DCA) of the sediment core from Lake TK-2, measured in standard deviation units of species compositional turnover and plotted against depth in the core (cm). b) Hill’s N2 sample diversity for each interval of sediment, plotted against depth (cm).

64 Figure 2.1 65

10000

2 9000 y = -0.2149x + 88.514x - 46 R2 = 0.9949

8000

7000

6000

5000

(cal BP)Age yr 4000

3000

2000

1000

0 0 20 40 60 80 100 120 140 160 180 200 Depth (cm)

Figure 2.2

66

24 CONISS

Total sum of squares Total sum

4 8 12 16 20

s s s i i i

m m

m 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1

difor difor difor

iti iti iti

n n n

C:D C:D C:D

ima ima ima

ss ss ss

0.0

nuti nuti nuti nanthes nanthes nanthes nanthes i i i

ch ch ch

s m m m s s s A A A

e e e

th th th

an an an xiformis xiformis xiformis 020

e e e

imp imp imp Achn Achn Achn

tii tii tii l l l

020

hnanthes hnanthes hnanthes hnanthes

c c c

jaernefe jaernefe jaernefe A A A

la la la

iosa iosa iosa

cu cu cu d d d x x

x 020

le le le ra ra ra

p p p

a a a a l l l Navi Navi Navi

com com com

vicu vicu

vicu 020

s s s

a a a

bsii bsii bsii / / / l l l

N N N

a a a 010 t t t

la kue kue kue la la la

Diplonei Diplonei Diplonei

a a a

cu cu cu

n n

n 010

rostra rostra rostra suchlandtii suchlandtii suchlandtii

ria ria ria

s s s s te te te

u u u Navi Navi Navi

e e e

la la la

o o o

f f f th th th

s s s 020 bal bal bal

nan nan nan a a a

ch ch ch

lari lari lari

i i i A A A

020

nnularia nnularia nnularia nnularia

i i i Frag Frag Frag

P P P c c c c

010 Relative Abundance (%) Abundance Relative thi thi thi

en en en

b b b l l l

al al al

m m m

annii annii annii S S S

sm sm sm

0204060

schmas schmas schmas

la la la

s s s

lu lu lu

vicu vicu vicu

itu itu itu

P) P) P)

Na Na Na

ig ig ig

B B B d d d

r r r

l y y y l l l

) )

) 02040

m m m

(ca (ca (ca

e e e

Navicula Navicula Navicula Navicula g g g

d A A d d

d A d 020

e e e

Depth (c (c (c Depth Depth Depth

lat lat lat

0 o o

o 10 20 30 40 50 60 70 80 90

200 100 110 120 130 140 150 160 170 180 190

terp terp terp

n n n I I I

649 131

1639 2111 2567 3008 3434 3843 4238 4617 4980 5328 5661 5978 6279 6565 6836 7091 7331 7555 7830 8018 8191 8348 8490 8616 8727 8850 8925 8984 9028 9056 1152 e (cal. yr BP) BP) BP) yr yr yr (cal. (cal. (cal. e e e

g g g

A A A 2540 4290 6440 8160 8500 8550

Figure 2.3. Part I

67

inuta inuta inuta inuta

m m m m

/ / /

per per per per

ica ica ica t t t

chia chia chia chia chia ex ex ex

ex 8 7 6 5 4 3 2 1

s s s s cani cani cani seminulum seminulum seminulum seminulum

pl pl pl pl

ul ul ul a a a a a itz itz itz itz

m m m m

v v v

- - - N N N

N 10 co co co co cul cul cul cul

vi vi vi

vi 0

da da da da a a a a

a a a a i i i i

lacus lacus lacus

N N N N m m m m

marginulata/sco marginulata/sco marginulata/sco 010

a/stol a/stol a/stol a/stol

Cymbella Cymbella Cymbella Cymbella es es es es

carissi carissi carissi carissi

010 ssim ssim ssim ssim i i i i

hnanth hnanth hnanth

s s s s

di di di di Ac Ac Ac

i i i i

r r r r 020

i i i i

v v v v

Achnanthes Achnanthes Achnanthes Achnanthes Achnanthes

cf. cf. cf. cf.

cf. cf. 010

ex ex ex ex

20 pl pl pl pl Achnanthes curt curt curt curt Achnanthes Achnanthes Achnanthes Achnanthes

omplex omplex omplex omplex

c c c c

0 com com com com

Pinnularia Pinnularia Pinnularia Pinnularia Pinnularia

anceps anceps anceps s s s

anceps s 010

ei ei ei ei

n n n n

Eunotia Eunotia Eunotia Eunotia o o o o

010 rhomboides rhomboides rhomboides rhomboides

a a a a

lex lex lex lex Staur Staur Staur Staur

s s s s

p p p

p 010

stuli stuli stuli stuli

u u u u

r r r r gua gua gua gua scen scen scen scen com com com com

i i i i

F F F F

010 ire ire ire ire

ex ex ex ex

v v v v

a a a a a

ar. ar. ar. ar. i i i i

v v v v

ar ar ar ar l l l l complex complex complex complex

s s s s

agi agi agi agi

perglabra perglabra perglabra perglabra a a a a r r r r

an an an an

t t t t F F F F

er er er er s s s s

di di di di 02040 osi osi osi osi

eira eira eira eira eira

Aulac Aulac Aulac Aulac

cos cos cos cos 020

Aula Aula Aula

Aula (%) Abundance Relative 010

irata irata irata irata ex ex ex ex

pl pl pl pl

a l l l l a a a a

r r r r

m m m m

co co co co

osei osei osei osei

ex ex ex ex Aulac Aulac Aulac Aulac

pl pl pl pl

m m m m

subatomus subatomus subatomus subatomus biasolettiana biasolettiana biasolettiana biasolettiana

co co co co

s s s s s

e e e e

var. var. var. var. var. h h h h

gera gera gera gera

i i i

i 0 20406080100

nant nant nant nant

tell tell tell tell

a s s s s a a a a Ach Ach Ach Ach

yr BP) BP) BP) yr yr yr

yr BP) yr 020

cal cal cal cal

Cyclotell Cyclotell Cyclotell Cyclotell

020 pth (cm) (cm) (cm) (cm) pth pth pth pth

e e e e

D D D

D 0 ated Age ( ( ( Age Age Age ated ated ated

ated Age ( Age ated 10 20 30 40 50 60 70 80 90

100 110 120 130 140 150 160 170 180 190 200 ol ol ol ol

p p p p

BP) BP) BP) BP)

r r r r

er er er er

y y y y

. . . .

Int Int Int Int 649 131

1639 2111 2567 3008 3434 3843 4238 4617 4980 5328 5661 5978 6279 6565 6836 7091 7331 7555 7830 8018 8191 8348 8490 8616 8727 8850 8925 8984 9028 9056 1152

Age (cal (cal (cal Age Age Age Age (cal Age 2540 4290 6440 8160 8500 8550

Figure 2.3. Part II

68

Age (cal yr BP) 0 8 7 10

20 (a) (b)

30 6 2540 40

50

60 4290

70 Biostratigraphic Zones 5 80

90

6440 100 110 Depth (cm) 120

130 4 8160

140 8500

150

160 3 170 8550 180 2 190 1 200 0 1.0 2.0 3.0 010203040 50 DCA Axis 1 Hill’s N2 (SD units)

Figure 2.4

69

Table 2.1. Surface water chemistry and other limnological measurements for Lake TK-2, collected on August 7, 1996.

Variable Value Variable Value

Cl (mg/L) 0.64 TN (μg/L) 135.0 SO4 (mg/L) 0.7 TPUF (μg/L) 3.1 SiO2 (mg/L) 0.27 TKN (μg/L) 93.0 DOC (mg/L) 2.0 CHLa (μg/L) 1.0 DIC (mg/L) 0.8 POC (μg/L) 313.0 Fe (μg/L) 80.0 PON (μg/L) 32.0 Mn (mg/L) 5.30 TN:TP 43.5 Na (mg/L) 0.27 POC:CHLa 313.0 Ca (mg/L) 0.4 AREA (ha) 2.8 K (mg/L) 0.2 DEPTH (m) 7.5 Mg (mg/L) 0.3 pH 8.0 Li (mg/L) 0.001 SP. COND (μS/cm) 9.8 Sr (mg/L) 0.001 TEMP (ºC) 12.9 Ba (mg/L) 0.002 DIST (km) 265 Al (mg/L) 0.010

DOC = Dissolved Organic Carbon DIC = Dissolved Inorganic Carbon TN = Total Nitrogen (unfiltered) = PON + TKN + nitrite-nitrate (NO3-NO2) TPUF = Total Phosphorus Unfiltered TKN = Total Kjeldahl Nitrogen CHLa = Chlorophyll-a POC = Particulate Organic Carbon PON = Particulate Organic Nitrogen TEMP = surface water temperature DIST = distance from treeline

70

Table 2.2. Radiocarbon dates from Lake TK-2 sediment core. Includes ages calibrated by Seppä et al. (2003) using CALIB 4.3 (Stuiver and Reimer 1993) and INTCAL 98 (Stuiver et al. 1998) calibration data, as well as ages calibrated using CalPal-2007online (Danzeglocke et al. 2007) for comparison. Modified from Seppä et al. (2003). Asterisk (*) indicates date reversal.

Calibrated Laboratory Depth Material 14C date Calibrated 2σ yr BP number (cm) (yr BP) yr BP age range (CalPal- 2007online)

Beta-167871 32-34 bulk sed 2480 ± 40 2540 2710-2400 2575 ± 102 Beta-167872 60-62 bulk sed 3870 ± 40 4290 4410-4160 4311 ± 71 Beta-167873 96-98 bulk sed 5670 ± 40 6440 6540-6360 6458 ± 38 TO-7871 132 twigs 7370 ± 80 8160 8340-8020 8190 ± 107 TO-7870 137* twigs 7190 ± 80 8020 8140-7850 8039 ± 84 TO-7869 142 twigs 7740 ± 90 8500 8720-8360 8537 ± 86 TO-7868 174 twigs 7780 ± 70 8550 8820-8430 8560 ± 78

71 CHAPTER 3

Diatom-inferred Holocene climatic and environmental change in an unusually saline high Arctic nunatak pond on Ellesmere Island (Nunavut, Canada)

C. Alyson Paul

72 ABSTRACT

Stygge Nunatak Pond is a small, shallow, closed-basin pond located on a nunatak

in Jokel Fjord, east-central Ellesmere Island, in the Canadian High Arctic. The ionic

concentration in this pond is unusually high by Arctic standards, with specific conductivity measured at up to 9000 μS/cm. This makes Stygge a very rare example of a

“saline” athalassic (i.e. unimpacted by marine influences) Arctic pond. Small, closed-

basin lakes and ponds are particularly sensitive to changes in the balance between

precipitation and evaporation (P-E, or effective precipitation). For example, even a small

increase in evaporation can cause a substantial reduction in the volume of the pond,

which in turn impacts the water chemistry (including ionic concentration) through

evaporative concentration. These changes to the aquatic environment may consequently

affect the aquatic biota, including diatoms. Because of this relationship, diatoms can be used to reconstruct past changes in P-E balance, ultimately inferring changes in climate.

Two sediment cores (short core: 21.5 cm, taken in 2004; long core: 387 cm, taken in

1984) from Stygge Nunatak Pond were examined in an attempt to reconstruct regional

climate and environmental changes. In addition, modern microhabitat samples were

examined from five different field seasons (1983, 1984, 2001, 2004, 2006) to determine

the modern distribution of diatoms throughout the pond. Based on a basal radiocarbon

date from the long core, the pond has likely existed for more than 10,500 cal. yr BP. The

diatom assemblages from both sediment cores record very similar ecological changes

since approximately 2200 cal. yr BP, with a stable, coldwater assemblage dominated by

Fragilaria construens var. venter, which was later replaced in the early- to mid-20th century (though changes may have begun as early as the 19th century) by dramatic,

73 unprecedented expansions in more complex, periphytic taxa, especially Cymbella descripta, Navicula halophila and Achnanthes minutissima. These assemblage shifts are indicative of recent warming, with a longer open-water period, expanded littoral moss substrates, and increased ionic concentration due to enhanced evaporation relative to precipitation. Between ~10,500 and ~6200 cal. yr BP, the diatom assemblages underwent a shift from a near monoculture of F. construens var. venter to a more complex, epiphytic assemblage, which then reverted back to the former virtual monoculture. These shifts may provide further evidence for an early Holocene thermal maximum in this region of the Arctic, followed by Neoglacial cooling. However, interpretation of assemblages before ~6200 cal. yr BP is complicated by the fact that the sediment beneath 47 cm depth is unconsolidated and embedded within a core of solid ice, a feature that has not been reported in any other Arctic paleolimnological study to date.

Superficial examination of the ice’s contact surfaces, and the fact that radiocarbon dates obtained from entrained sediment are chronologically consistent with those from the solid sediment above, suggest that the ice might be intrasedimental segregation ice, but additional analyses are needed to confirm this hypothesis.

74 INTRODUCTION

Recent climate change in the Arctic

Over recent decades, the issue of climate change has become increasingly

pertinent, as it has become more and more evident that the planet is experiencing a

warming trend of an unprecedented rate and nature (e.g. Jansen et al. 2007). Polar

regions are especially sensitive to such changes (e.g., ACIA 2004; Furgal and Prowse

2008; Hansen et al. 2006; Rouse et al. 1997; Serreze and Francis 2006; Smol 1988), mainly due to positive feedback mechanisms, such as the albedo effect, that exacerbate the effects of warming (ACIA 2004). A growing body of scientific evidence, combining instrumental and observational data with a wide array of paleoclimate proxies, strengthens the consensus that recent (post-industrial) warming across the circumpolar

Arctic is unprecedented over the past several centuries, if not millennia (e.g., Bradley

2000; Douglas et al. 1994; Gajewski and Atkinson 2003; Hinzman et al. 2005; Jansen et al. 2007; Mann et al. 1998; Overpeck et al. 1997; Serreze et al. 2000; Smol et al. 2005).

Paleolimnology and Diatoms

In order to fully comprehend recent climate change, it is important to be able to

elucidate whether it is, indeed, unusual when placed in the context of a longer timeframe,

or whether it is merely part of a natural climate cycle (Smol and Cumming 2000).

Unfortunately, reliable long-term instrumental data simply do not exist, especially in

remote regions like the Arctic, where monitoring stations are geographically sparse and

have only been implemented very recently. Fortunately, however, paleolimnology

provides a powerful tool with which to obtain this crucial missing information.

Paleolimnology infers past environmental conditions using the physical, chemical and

75 biological indicators preserved in the sediments of lakes and ponds (e.g. Smol 2008;

Smol et al. 2001). Of the many biological indicators available, diatoms are the most

extensively used in paleolimnological studies (Douglas et al. 2004; Smol and Cumming

2000). Diatoms (class Bacillariophyceae) are a very diverse and widely distributed

(Stoermer and Smol 1999) group of microscopic, photosynthetic, single-celled algae.

Their siliceous cell walls preserve well in aquatic sediments, and have detailed, taxon- specific patterns that allow identification down to low taxonomic levels (generally species, and often variety). Many diatom taxa have well-defined optima for various environmental variables (Stoermer and Smol 1999). Their fast generation times allow them to respond very quickly to a given environmental perturbation, and because they are autochthonous, they represent the local conditions of the environment in which they originate (Smol 1988; Smol and Cumming 2000). Diatoms are particularly useful in paleolimnological studies in Arctic regions, where lakes and ponds are a ubiquitous feature, and where harsh climatic conditions often preclude the use of other indicators that are commonly implemented in more southerly regions (Douglas et al. 2004; Smol and Cumming 2000), such as tree-rings and pollen.

Saline lakes and climate change in the High Arctic

There are many factors that can affect the ionic concentration of a lake or pond,

including its proximity to the ocean, bedrock composition and weathering, water source and other hydrological variables, and catchment characteristics. An additional factor that has been the focus of several recent studies is climate change, and especially how it can indirectly affect ionic composition through its effects on the precipitation-evaporation (P-

E) balance, or effective precipitation (Fritz et al. 1999; Gasse et al. 1997). Changes in the

76 P-E balance (e.g. from climate warming) can result in large fluctuations in lake volume,

which in turn affects the ionic concentration (and in some cases composition) of the lake

water by either diluting or concentrating it (Gasse et al. 1997; Last and Slezak 1988). For

example, warmer, drier periods result in higher evaporation rates (i.e. a more negative P-

E balance), which increases lake water salinity through evaporative exclusion.

Meanwhile, cooler, wetter periods result in a more positive P-E balance and thus

decreased salinity via dilution (Roberts et al. 2006). This pattern is often observable in

closed-basin lakes over the progression of a single open water season, with increasing

evaporative losses resulting in reduced water levels and correspondingly higher salinity

and specific conductivity (e.g. Veres et al. 1995). Because of this relationship between

climate, P-E balance, and lake water salinity and specific conductivity, changes in these

latter two variables can serve as a useful proxy for climate change (Gasse et al. 1997;

Roberts et al. 2006).

Diatoms are known to be sensitive indicators of salinity and salinity-related

variables such as specific conductivity (e.g. Fritz et al. 1999). As such, they have been

used extensively in paleolimnological studies to reconstruct past changes in salinity, and

to thus make indirect inferences of climate change (e.g. Fritz 1990; Fritz et al. 1991,

1999; Gasse et al. 1997; McGowan et al. 2003; Roberts et al. 2006; Wilson et al. 1994).

However, the vast majority of diatom salinity studies have been carried out in arid

regions at temperate or tropical latitudes, where saline lakes are more common. With the

exception of coastal sites that are, or have been at some point, strongly impacted by

marine influences (e.g. Douglas et al. 2000), high salinity and conductivity systems are very rare in the Arctic (Pienitz et al. 1992, 2000; Veres et al. 1995). Previous studies

77 have examined such lakes in the Yukon Territory (Veres et al. 1995), as well as in West

Greenland (McGowan et al. 2003; Ryves et al. 2002; Willemse et al. 2004).

Stygge Nunatak Pond, a small, shallow pond located on a nunatak on east-central

Ellesmere Island (Figure 3.1), is an extremely rare example of an athalassic (i.e.

uninfluenced by marine processes) high Arctic pond that, by Arctic standards, has

unusually high salinity and conductivity. In fact, its ionic concentration is higher than

that of over 200 lakes and ponds on Ellesmere Island sampled by our labs and associates

(John P. Smol, personal communication). This is likely a result of the pond’s small,

shallow nature, and its unique basin morphometry which, combined with the adjacent

cliffs, forms a natural evaporation dish shape. Furthermore, Stygge is a closed-basin pond, making it particularly sensitive to changes in P-E balance (Fritz et al. 1999;

McGowan et al. 2003; Roberts et al. 2006). All of these characteristics suggest that even slight changes in P-E balance will have a large impact on the volume of water in the pond

(and thus its chemistry). Accordingly, signs of previously higher shorelines are evident

in the form of dark water marks and lines of a white precipitate above current water level.

In addition, there are exposed rocks on the shoreline with lichen growing only on their

upper portions, presumably because water once precluded their growth on the lower

portion. These observations are further indication of a fluctuating water level that has

decreased in the relatively recent past. Therefore, this pond and its sediments may

potentially represent a unique, sensitive archive of Holocene climate change in this

region of the High Arctic.

Early paleolimnological work on climate change in the Canadian High Arctic

began at Cape Herschel (78º37’N, 74º42’W), a peninsula on the east-central coast of

78 Ellesmere Island, not far (i.e. ~80 km) from the location of Stygge Nunatak Pond.

Detailed study of the diatom stratigraphies from the shallow lakes and ponds in the Cape

Herschel region have revealed relatively stable assemblages over most of the Holocene,

with dramatic, unprecedented changes indicative of climate warming occurring in the 19th century (Douglas et al. 1994; 2000). In this chapter, I use fossil diatom records preserved in two sediment cores from Stygge Nunatak Pond in an attempt to reconstruct how climate has changed over the Holocene in this unique system. Comparisons are made between the records from this relatively saline pond and those from previous studies of other Arctic water bodies, especially the nearby, comparatively freshwater Cape Herschel ponds. Additionally, modern microhabitat samples are examined from five different years, spanning a 20-year period, in order to determine how the diatoms are currently distributed throughout the pond, and whether that distribution has changed over time.

METHODS

Site Description

Stygge Nunatak Pond (unofficial name; 78º44.3’N, 78º29.0’W) is located on

Stygge nunatak, which is situated 6 km from the front of Stygge glacier in Jokel Fjord,

east-central Ellesmere Island, Nunavut, Canada (Figure 3.1). The pond is located at 330

m asl and slightly west of the centre of the nunatak, which is composed predominantly of

Archean orthopyroxene granite with a capping of Paleozoic dolomite on one of its two

peaks (Figure 3.2). Stygge is a small, shallow pond with a diameter of approximately

100 m and a maximum depth of 1.2 m. It receives water input in the form of snowmelt,

but has no outlet stream (i.e., it is a closed-basin pond). Its measured pH ranges from 7.4

79 in mid June (1984) to 8.6 in late July (1983, 2004). On the salinity scale, the pond

straddles the boundary between freshwater and subsaline, with measured specific

conductivity starting at around 138 μS/cm (mid-June 1984) and increasing over the

summer season to values measured as high as 9000 μS/cm (late July 2004). These levels

of salinity and conductivity are unusually high for non-coastal high Arctic ponds (Pienitz

et al. 1992, 2000). Signs of previously higher water levels are apparent on the shore,

including lines and other deposits of a white precipitate, as well as dark water marks. In

addition, exposed rocks along the shoreline and well above current water level have

orange jewel lichen (Xanthoria elegans) growing only on their upper halves, with no

lichen occurring on the lower halves where, presumably, water once precluded their development.

Stygge is situated in the High Arctic in a region of continuous permafrost. The present climate in the region is cold and dry, with mean July and January surface air

temperatures of ca. 5ºC and -35ºC, respectively, and annual mean precipitation of ca. 100

mm (Rouse 1993). Evidence that the nunatak has, at some point, been over-ridden with

glacial ice, exists in the form of erratic boulders littering the surface of the dolomite peak

(Weston Blake, Jr., personal communication). The area around the pond is very sparsely

vegetated, supporting mosses and sedges in areas that receive water, as well as some

lichen and dwarf shrubs (mainly Salix), and other flowering plants. The pond itself

supports visible populations of aquatic invertebrates, including Daphnia, fairy shrimp

(Branchinecta paludosa), and tadpole shrimp (Lepidurus arcticus), the last of which is

rare in ponds on Ellesmere Island (John P. Smol, personal communication).

80 Field Methods

Present-day Limnology

Surface water chemistry samples were taken from the pond during five different

field seasons (1983, 1984, 2001, 2004, 2006). In 1984, surface temperature, pH and

specific conductivity were measured twice, once in early June and once near the end of the month. In all years, measurements for pH, specific conductivity and temperature were performed onsite using a handheld Hanna pHEP pH meter, a Yellow Springs

Instrument (YSI) model 33 conductivity meter, and a handheld thermometer, respectively. In addition, water samples for later analysis of a suite of limnological variables were taken and treated in accordance with standard procedures outlined by

Environment Canada (1994). They were then shipped for further analyses to the National

Laboratory for Environmental Testing (NLET) at the Canada Centre for Inland Waters

(CCIW) in Burlington, Ontario, Canada. All samples were kept cold and dark in a cooler until return to the laboratory.

Short Core

In July of 2004, a 21.5 cm sediment core was taken near the centre of Stygge

Nunatak Pond using a 3 inch (i.e. 7.6 cm) diameter Glew gravity corer (Glew 1989). The

core was extruded on site at 0.5 cm intervals using a Glew (1988) extruder.

Long Core

In late May of 1984, when the pond was still completely frozen to the bottom, a

387 cm sediment core was taken by Dr. Weston Blake, Jr. from the best estimation possible (given extensive snow coverage) of the centre of the pond. Because the pond was frozen, the core was taken using a SIPRE corer (Blake, W., Jr. 1982). The core was

81 removed in 21 separate increments, all from the same hole. Each increment was packaged

in a plastic bag. The core consisted of 47 cm of solid lacustrine sediment at the top,

beneath which was approximately 275 cm of solid ice, which was itself underlain by

coarse granitic sand. Though some areas of the ice were apparently sediment-free,

interspersed within it were unconsolidated bits of sediment, in some cases accompanied

by small pebbles. The frozen core was sent to Queen’s University in 1992, where, using a

hacksaw, the solid sediment portion was sectioned into 1 cm intervals, while the icy

portion was sectioned into approximately 2-3 cm intervals.

Microhabitat sampling for diatoms

The modern microhabitats of the pond were sampled over five different field seasons, on the following dates: July 17, 1983; June 10 and 23, 1984; July 7, 2001; July

19, 2004; and July 8, 2006). Microhabitats sampled included surface sediment/sand, rocks, grasses, mosses, and algal net tows, although not all of these were sampled in each of the years listed. Samples were taken following standard protocols used by our lab, as

outlined in Douglas and Smol (1995). In early June 1984, a small (~7x2 m, ~5 cm deep),

semi-attached puddle on a sandy beach at the north end of the pond, largely surrounded

by snow, was also sampled for surface sediment/sand and rock scrapes, and surface

sediment was taken from the open water moat at the southern edge of the pond. Samples

were preserved with Lugol’s solution and kept cool until return to the laboratory.

Laboratory Methods

In an attempt to date the short sediment core, radioisotopic analysis of 210Pb activity was undertaken at MyCore Scientific, Deep River, Ontario. 210Pb activity was

measured using alpha spectroscopy, and dates were determined using the constant rate of

82 supply (CRS) model (Appleby, 2001). In addition to the 210Pb dating, accelerator mass spectrometry (AMS) radiocarbon (14C) dating was performed by the stable isotope lab at

INSTAAR (Institute of Arctic and Alpine Research), University of Colorado, Boulder,

Colorado, on two intervals of the short core (8.5-9.0 and 19.0-19.5 cm) using the humic

acid fraction from bulk sediment. INSTAAR also dated three intervals from the long core: one from the bottom of the solid sediment section of the core (44-45 cm), and two taken from the icy section (~107-111 and 298-301 cm). In addition, fragments of washed-in terrestrial mosses (predominantly Bryum pseudotriquetrum and Campylium stellatum, identified by J.A. Janssens), found at a depth of 43.5-45.0 cm in the long core, were analyzed for radiocarbon activity using AMS at IsoTrace Radiocarbon Laboratory,

Toronto, Ontario. Radiocarbon dates were calibrated using the online Cologne

Radiocarbon Calibration & Palaeoclimate Research Package (CalPal-2007online;

Danzeglocke et al. 2007).

Sediment samples for diatom enumeration were processed in accordance with the

standard procedures for diatoms, as outlined by Battarbee et al. (2001). For the short core, 43 half-cm intervals were processed, constituting the full core. For the sediment portion of the long core, every other 1 cm interval up to 20 cm was processed, and every fourth one after that, making 16 samples from this part of the core. In the icy section, subsampling intervals were unavoidably less regular, as the ice was less consistently subsectioned, mainly split into chunks approximately 2-3 cm long. A total of 26 intervals, each incorporating 2-3 cm of the core, and separated by approximately 6 cm, were processed from this portion of the core, from 47-322 cm depth, giving a total of 42 diatom samples from the long core. For both cores, each sample was placed in a glass

83 scintillation vial, to which was added 15 mL of a 1:1 solution of concentrated nitric acid

(HNO3) to concentrated sulphuric (H2SO4) acid. The vials were placed in a hot water

bath for several hours in order to digest any organic matter in the samples. The

remaining material was rinsed with deionized water and allowed to settle overnight. The

supernatant was removed, and the samples were rinsed again. This procedure was

repeated until a neutral pH was attained (about 6 rinses). A small amount of the resulting

slurries was spread over glass coverslips and left to evaporate at room temperature on

slide warmers. The coverslips were then mounted onto glass microscope slides using

Naphrax® mounting medium, which has a refractive index of 1.74.

Because of their often very high organic content, microhabitat samples were

digested using CEM Corporation’s Microwave Accelerated Reaction System for

Extraction (MARSX). This process is faster than conventional techniques when dealing

with a small number of samples (Parr et al. 2004), and is much more efficient at digesting

samples with large organic components, such as peat and moss samples. The MARSX

uses 10 mL of nitric acid per sample. Once the microwave digestion was complete,

samples were rinsed and slides were made in a manner identical to that described above

for the two sediment cores.

For each sediment interval and microhabitat sample, a minimum of 400 diatom

valves (where possible) was identified and enumerated along random transects of the

coverslip. This was done using a Leica DMR microscope at 1000x magnification, with differential interference contrast (DIC) and a 100x oil immersion objective and oil immersion condenser lens. Diatoms were identified to the lowest taxonomic level possible (at least species, and often variety) using multiple sources, including Camburn et

84 al. (1984-1986), Krammer and Lange-Bertalot (1986, 1988, 1991a, 1991b), Krammer

(1992), Camburn and Charles (2000), Fallu et al. (2000). Chrysophycean stomatocysts were also enumerated, but not identified, and expressed relative to the number of diatom

valves counted (Smol 1985). To aid in diatom identification, and for comparative

purposes to ensure taxonomic consistency, photomicrographs of various diatom taxa

were taken using the Leica microscope and a Retiga 1300 camera. Raw diatom counts for each sediment interval were converted to percent relative abundances, and these data were then used to create stratigraphic profiles for the short and long core, as well as for the microhabitat samples. This was done using the computer program C2, version 1.3

(Juggins 2003).

RESULTS

The values for the various water chemistry and other limnological measurements

taken during the five different field seasons are listed in Table 3.1, with a more extensive

list in Appendix C. As mentioned above, Stygge Nunatak Pond has an unusually high

ionic concentration for an athalassic lake in the Arctic, with specific conductivity

measured as high as 9000 μS/cm. Accordingly, the pond has notably high levels of

- 2- + 2+ 2+ 2+ + 2+ numerous ions (e.g. Cl , SO4 , Na , Ca , Mg , Sr , K , Ba ) as well as DIC (dissolved

inorganic carbon) relative to other lakes and ponds in the central Canadian Arctic tundra

(e.g. see Douglas and Smol 1994 and Rühland et al. 2003). DOC (dissolved organic

carbon), POC (particulate organic carbon), and TKN (total Kjeldahl nitrogen) also reach

relatively high levels with respect to most Arctic tundra lakes, likely due to evaporative

concentration.

85 Radioisotopic dating

Unsupported 210Pb activity levels for the 12 samples analyzed from the short core

are shown in Table 3.2, and a plot of 210Pb activity versus depth for the same core is

shown in Figure 3.3. Calendar dates are also calculated from the CRS model. The curve

shows an exponential decline in 210Pb activity from the top of the core to the bottom.

This pattern is typical of an undisturbed sediment profile, and is thus a good indication

that no significant sediment mixing has occurred. All unsupported 210Pb appears to be

contained within the upper approximately 3.5 cm of sediment, which dates back to

approximately 1938 A.D. Such a low sedimentation rate is characteristic of high Arctic freshwater environments (Wolfe et al. 2004).

Radiocarbon dating results for both the short and long cores are listed in Table

3.3, and displayed graphically in Figure 3.4. A radiocarbon date taken from the humic

acid fraction of bulk sediment from 19.0-19.5 cm, near the bottom of the short core, reveals that this core dates back to over 2246 ± 59 cal yr BP (2225 ± 15 14C yr BP).

Another age obtained in this way (2270 ± 60 cal yr BP, 2255 ± 15 14C yr BP), taken from

8.5-9.0 cm, was not chronologically consistent, overlapping with the much deeper age mentioned above (19.0-19.5 cm). Because of this inconsistency, a sample from 9.0-9.5 cm, the interval just beneath the one with the anomalous age, was later sent for 14C

analysis, with a resultant age determination of 2234 ± 60 cal. yr BP (2200 ± 60 14C yr

BP). This is virtually identical to the original 8.5-9.0 cm dating result, and similarly incongruous chronologically. However, through correspondence with INSTAAR, we

received confirmation that there was a “larger than typical amount of carbonate material present in the sample” from 9.0-9.5 cm. Combined with the anomalously old age

86 determinations from this part of the core, this suggests that these intervals are potentially

influenced by the ‘old-carbon’ or ‘reservoir’ effect. Furthermore, the deeper age from

19.0-19.5 cm is chronologically and sedimentologically congruent with ages determined

from the long core (discussed below), and given that there is no evidence of sediment mixing from either the diatom or 210Pb profiles, we have chosen to discard the

anomalously old ages from the 8.5-9.5 cm level for the purposes of the diatom analysis

and interpretation.

Humic acid radiocarbon ages were also obtained from three levels in the long

core. The deepest of these ages, at 298-301 cm, indicates that Stygge Nunatak Pond has

existed since at least 10,558 ± 25 cal yr BP (9345 ± 20 14C yr BP), and thus the long

sediment core documents approximately the entire Holocene. The other two humic acid

dates were taken from 44-45 cm (6303 ± 6 cal yr BP, 5510 ± 15 14C yr BP) and 107-111 cm (7380 ± 35 cal yr BP, 6450 ± 35 14C yr BP). The two deepest ages (107-111 cm and

298-301 cm) were determined from sediment embedded within the ice section of the

core. Given the unknown origins of this ice, these ages should be interpreted with

caution; however, they are nonetheless chronologically congruent with the rest of the

dates from the core. An additional radiocarbon age was obtained from fragments of

washed-in terrestrial mosses extracted from the core at 43.5-45 cm. The result (6210 ±

94 cal yr BP, 5440 ± 80 14C yr BP) corroborates the humic acid age taken from the same

level in the core. Furthermore, the terrestrial origin of the mosses decreases potential

complications from ‘old carbon’, thus increasing the reliability of the age determination.

All radioisotopic ages for the Stygge cores are plotted against depth in Figure 3.4, where

87 210Pb dates are shown in blue and calibrated 14C ages in red (with the anomalously old results, discussed above, in green).

Diatoms

A total of 96 diatom taxa was recorded throughout Stygge Nunatak Pond’s sediment cores and modern microhabitats (Appendices D through F). A list of the most common taxa, their authorities, and their modern synonyms is included in Appendix B.

The assemblages were overwhelmingly dominated by benthic taxa, with planktonic taxa mainly absent or, where present, barely at trace levels. The diatoms were generally well preserved, with some large taxa (e.g. Navicula vulpina) exhibiting some mechanical damage, though this was not sufficient to interfere with identification and enumeration.

Short core

The top ~1 cm of the short (21.5 cm) core was light brown in colour, followed by a darker, anoxic layer from ~2-2.5 cm. After this depth it became a mottled light grey, and, due to a sulfurous odour, we suspected it was also anoxic. At about 6.5-7 cm, the sediment became stiffer in consistency, and at 8-8.5 cm it became lighter grey in colour.

Percent relative abundances of the most common taxa in the short core are shown in Figure 3.5. Horizontal lines divide the stratigraphy into three “zones” based on visual approximation of the areas where important changes occur in the assemblage. In the earliest part of the core (Zone 1), the assemblage is dominated by the small, benthic

Fragilaria construens var. venter (from 30-60%) and, to a lesser extent, Denticula kuetzingii (15-25%) and Navicula halophila (15-30%). The assemblage remains relatively stable until around 8.5-9.0 cm (i.e. the start of Zone 2), where F. construens var. venter begins a notable decline, remaining below 20-25 % relative abundance for the

88 rest of the core. Also in this zone there is a relatively small but notable increase in D.

kuetzingii, with smaller increases in N. halophila and C. descripta. Furthermore,

Achnanthes minutissima and Cymbella angustata begin to increase in relative abundance here. However, the most dramatic change in the diatom assemblage occurs after approximately 3.0-3.5 cm (Zone 3), where C. descripta begins a dramatic expansion from

consistently below 10% relative abundance to dominant values reaching greater than 50%

at the top of the core. Slight further increases in A. minutissima and C. angustata also

occur in these most recent intervals, along with a steep decline in D. kuetzingii. N. halophila remains a dominant part of the assemblage, while small decreases in Nitzschia

cf. frustulum and Navicula vulpina are apparent.

Long core – Sediment (~ 0-47 cm)

The long core from Stygge, taken in 1984, consists of approximately 47 cm of

sediment overlying 275 cm of an ice matrix with sediment inclusions. The top ~19-20

cm (Zone S2, Figure 3.6) of the sediment portion is approximately equivalent to the short

core (although the latter has 20 additional years of sedimentation at the top). The long

core was counted at a much coarser resolution than the short core. When comparing the

diatom assemblage from the short core to that from the corresponding portion of the long core (Zone S2), it is evident that the major trends are very similar. For example, the lower part of the long core sediment is dominated by F. construens var. venter with smaller, though important, contributions from D. kuetzingii and N. halophila. The small, benthic Fragilaria taxa decrease substantially towards the top of the core, as does D. kuetzingii. Furthermore, the top-most sediment intervals record the same dramatic increase in C. descripta, and similar increases in A. minutissima and C. angustata, as are

89 recorded in the short core. However, a large difference from the short core diatom profile

is apparent in the magnitude of the increase in these latter two species, which is much

more pronounced in the long core. Furthermore, there is a very dramatic increase in N. halophila in the long core that is not evident in the short core stratigraphy.

In Zone S1, which lies directly beneath the zone corresponding to the short core

(Zone S2), the diatom assemblage is composed of virtually 100% F. construens var.

venter until the appearance of D. kuetzingii, N. halophila and C. descripta at

approximately 31-32 cm (Figure 3.6).

Long core – Ice portion (~47-322 cm)

In the earliest layers of sediment embedded in the unusual ice portion of the long

core (Zone I, Figure 3.6), the diatom assemblages are effectively monocultures of F.

construens var. venter. A change occurs between about 245-248 cm and 61-64 cm,

where other species such as Navicula vulpina, D. kuetzingii and C. angustata reach

relative abundances greater than anywhere else in the entire core. In addition, smaller yet

notable increases occur in taxa such as A. minutissima, Nitzschia cf. frustulum, and

Navicula viridis, while species that are not evident in the sediment portion of the core

(nor in the short core), such as Denticula subtilis and Cymbella cf. designata, make an

appearance here in the middle of the ice section. Extremely low abundances (too low to

warrant inclusion in the stratigraphy) of planktonic taxa, such as Cyclotella

pseudostelligera and a few Aulacoseira species, were present near the bottom (in various intervals below 167-170 cm) of the ice section.

90 Microhabitats

The diatom counts from the various microhabitat samples taken in 1983, 1984,

2001, 2004 and 2006 are presented in two different forms here: one figure groups the

samples by sampling year (Figure 3.7), while the other groups them according to

microhabitat type (i.e. surface sediment/sand, rock scrape, grass, moss-type substrate, and

algal sand; Figure 3.8). Plankton net tows are not included, as no diatoms were recorded

in these samples. In both figures it is clear that the modern samples from all years are

dominated by Achnanthes minutissima and Cymbella descripta. F. construens var. venter

reaches high relative abundances in three samples from 1984 (Figure 3.7), all of which

were collected from surface sediment or sand habitats (Figure 3.8). Although many of

the species are present in every year, a few taxa appear in notable abundances only in the

most recent sampling year (2006), namely Denticula subtilis, Nitzschia cf. sublinearis, N. cf. alpina and N. commutata (Figure 3.7). All three of these Nitzschia species are also found almost exclusively in the moss-like microhabitats (Figure 3.8).

DISCUSSION

The diatom assemblages of Stygge Nunatak Pond were overwhelmingly

dominated by benthic taxa, with planktonic species generally absent, or, where present,

only at trace levels. This is characteristic of the majority of high Arctic ponds (including

those at Cape Herschel; Douglas and Smol 1993), which are generally shallow and ice

covered for most of the year (Smol 1988; Smol and Cumming 2000), limiting the

development of planktonic organisms (Smol 1983). Stygge’s most common and most

abundant taxa, which are presented in the diatom stratigraphies and microhabitat graphs

91 (Figures 3.5, 3.6, 3.7 and 3.8), belong to the benthic genera Achnanthes, Navicula,

Cymbella, Fragilaria, Denticula and Nitzschia. This type of assemblage composition is consistent with other studies from various regions across the Canadian Arctic

Archipelago (e.g. Antoniades et al. 2004, 2005a; Bouchard et al. 2004; Douglas and Smol

1995; Lim et al. 2001a,b, 2007; Michelutti et al. 2003a, 2006; Van de Vijver et al. 2003).

Short core

The continued presence of Navicula halophila throughout the short core (Figure

3.5) suggests that Stygge has been relatively saline throughout the period represented by the core (i.e. since before about 2200 cal yr BP), as this aptly named species is generally found on the higher end of salinity and conductivity gradients (e.g. Pienitz et al. 1992;

McGowan et al. 2003; Ryves et al. 2002). In the early part of the core (Zone 1), the diatom assemblage is dominated by Fragilaria construens var. venter. Small, benthic, alkaliphilous diatoms (including some Fragilaria species) are a characteristic feature of cold, oligotrophic, alkaline waters. They are commonly observed in sediment cores as the initial colonizers of early post-glacial Holocene lakes and ponds, as they are highly competitive in these typically cold, physically disturbed, high alkalinity environments

(Lotter and Bigler 2000; Smith 2002; Smol 1983, 1988). Modern conditions that provide a likely analogue to these post-glacial environments exist in Proteus Lake, an exposed, high altitude site on Pim Island, near Cape Herschel (Smol 1983). Until very recent years, this lake had remained permanently ice covered throughout most or all of the year, with only a narrow peripheral moat melting in the summer. As such, the modern diatom assemblage consists of over 90% small Fragilaria taxa (predominantly F. construens var.

venter; Smol 1983). The dominance of this taxon in the bottom half of the Stygge short

92 core therefore suggests that conditions in the pond were relatively alkaline and cold,

likely with extensive ice cover.

The diatom assemblages in the Stygge short core remain relatively stable for the

first half of the core (Zone 1), until approximately 8.5-9.0 cm, where the once-dominant

F. construens var. venter begins a notable decline, remaining at much lower relative abundances for the rest of the core. Similar marked declines in these small, benthic

Fragilaria taxa have been recorded in other Arctic sediment cores (e.g. Antoniades et al.

2005b; Douglas et al. 1994; Douglas and Smol 2000; Keatley et al. 2006; Smol 1983), and have been interpreted as a likely indication of amelioration to warmer, less alkaline,

and less oligotrophic conditions (Antoniades et al. 2005b; Douglas et al. 1994; Keatley et

al. 2006; Smol 1988).

The most dramatic change in the core, and perhaps the most ecologically

significant, occurs in the top 3.5-4 cm (approximately 1938 or slightly before), with the

dramatic and unprecedented expansion of Cymbella descripta from abundances below

10-15%, to dominance at nearly 55% in the uppermost sediment intervals (Figure 3.5).

To my knowledge, no other Arctic diatom study has reported this species at such high relative abundances in either modern or down-core samples, as it is generally only a minor component of assemblages in other studies (e.g. Antoniades et al. 2004, 2005a;

Bigler and Hall 2002; Douglas and Smol 1995; Michelutti et al. 2003a; Robinson and

Kawecka 2005; Weckström et al. 1997). C. descripta is a tube-dweller (Dermot

Antoniades, personal communication); that is, it lives within an autogenously formed

mucilaginous sheath. Like other Cymbella species (Pienitz et al. 1995; Antoniades et al.

2005a), it is also epiphytic, mostly living attached via a stalk to macrophytes. These

93 characteristics constitute a relatively complex life strategy, and, as such, this taxon requires a longer ice-free period (and thus a longer growing season) than simpler, adnate forms in order to develop (Douglas and Smol 1999). Douglas and Smol (1993) observed this pattern in the present-day ponds they sampled at Cape Herschel, where the pond with the longest growing season attained a more complex diatom assemblage (corresponding to a later stage of succession) than did the pond that, due to its position at a higher elevation, had the shortest growing season. Thus, this dramatic increase in C. descripta in the most recent sediments of Stygge is possibly an indication of recent regional climate warming, which would provide the increased ice-free period and longer growing season that would allow this more complex diatom to flourish. Similarly unprecedented changes occur in the sediment cores from ponds at Cape Herschel, where the assemblages show relative stability and low diversity for the past few millennia, interrupted at the tops of the cores by abrupt shifts to assemblages with higher diversity and/or higher complexity

(Douglas 1993; Douglas et al. 1994).

Whereas in Stygge the dramatic recent shift in the diatom assemblages seems to

have begun around the early to mid 20th century, the striking changes in the Cape

Herschel ponds appear to have started in the 19th century. Although the challenges inherent in obtaining accurate dates in Arctic lakes and ponds, as well as differences in

sampling resolution, make direct comparisons between various records difficult, this

discrepancy in timing could potentially be related to differences in lake size, as Stygge is

larger than most of the ponds on Cape Herschel (John P. Smol, personal communication),

and larger lakes and ponds tend to be less sensitive to environmental change than smaller

ones (Douglas et al. 1994; Douglas and Smol 1999). For example, in their study of three

94 cores from ponds on Ellef Ringnes and Ellesmere islands (Canadian High Arctic),

Antoniades et al. (2005b) found similar recent dramatic ecological shifts in the diatom

assemblages in all three ponds, but the onset of these changes was earlier in the two

ponds from Ellef Ringnes Island (mid 19th century) than in the substantially larger one on

Ellesmere Island (mid-20th century, consistent with the timing of dramatic changes in

Stygge). Though the disparity in pond size was, in this case, considerably larger than that

between Stygge and the Cape Herschel ponds, it is possible that the latter difference may

be enough to give Stygge a relatively larger thermal intertia, thus delaying the effects of

climate warming. Furthermore, other diatom studies from the Canadian High Arctic have

recorded evidence for unprecedented 20th-century warming (e.g. Keatley et al. 2006,

Melville Island; Michelutti et al. 2003b, Cornwallis Island; Perren et al. 2003, Ellesmere

Island), and non-biological evidence for warming after ~1865, but especially after ~1908, was put forth by Smith et al. (2004) in their varved sediment records from a lake on

Ellesmere Island.

Notable increases in Achnanthes minutissima and Cymbella angustata occur

around the same time as the dramatic increase in C. descripta discussed above. Other

diatom studies from the Canadian High Arctic have recorded increases in A. minutissima

in the most recent sediments (e.g. Antoniades et al. 2005b; Douglas et al. 1994, Keatley

et al. 2006; Lim et al. 2008), and have implicated climate warming as the most likely

cause of this and other assemblage shifts. In fact, in their record from Self Pond at Alert

(Ellesmere Island), Antoniades et al. (2005b) show an excellent correlation between the

A. minutissima relative abundance profile and the measured air temperature records from the Alert Meteorological Station. As both A. minutissima and C. angustata are associated

95 with mosses and other macrophyte substrates (e.g. Douglas and Smol 1993, 1995; Lim et

al. 2001a), an increase in these taxa is consistent with a climate warming scenario, in

which an increased duration of the ice-free period and growing season would allow

increased growth and potential diversification of littoral macrophytes, thus providing

more substrates on which these diatom species can grow and thrive (Douglas et al. 1994;

Smol 1988). Consistent with this hypothesis, Elison Lake at Cape Herschel experienced

a dramatic and unprecedented expansion of Pinnularia balfouriana, an epiphytic diatom

that is strongly associated with mosses, in its most recent sediment (Douglas et al. 1994).

Concurrent with the dramatic increase in C. descripta, Denticula kuetzingii

undergoes a steep decline in the top-most sediment intervals of Stygge. A similar trend

for this species was observed at Cape Herschel (Camp Pond, Douglas et al. 1994). D.

kuetzingii is associated with sediment and especially moss habitats in the High Arctic

(Douglas and Smol 1993, 1995; Lim et al. 2001a, 2007, 2008); therefore, its decrease

towards the top of the core could be interpreted as a decrease in moss substrates, and thus

a shorter ice-free period, from cooler climatic conditions. This would be in direct

opposition to the interpretation of the trends in other species, presented above.

Furthermore, D. kuetzingii is associated with somewhat higher nutrient (TN) and DOC

sites on Banks and Bathurst islands (Lim 2007, 2001a respectively), and was found in

warmer sites on Bathurst Island, likely because of elevated nutrient concentrations due to

heightened evaporative concentration at these sites (Lim et al. 2001a). One would

therefore expect this taxon to increase with a warming climate, which would provide

warmer water and higher levels of nutrients. Accordingly, in a downcore study of two

shallow ponds on Banks Island, in which D. kuetzingii constituted an important

96 component of the diatom assemblages, Lim et al. (2008) found a marked post-1850

increase in this taxon (which they attributed to climate warming) in one pond.

Interestingly, though, in the other pond, whose sediment record began around 1940, D.

kuetzingii experienced a steady decline from dominance at the bottom of the core (~95%

relative abundance) to ~25% in the most recent sediment. Perhaps the recent decrease in

this species in Stygge Nunatak Pond, as well as in the Banks Island pond, could be the

result of a threshold being crossed in its tolerance to some other temperature-related

variable, such as salinity, the detrimental effects of which would override any advantages

that might be provided from increasing levels of nutrients and its preferred substrate (i.e.

mosses).

Besides the most recent and dramatic species shifts, other, more subtle changes

are also apparent in the diatom assemblages, beginning at around 8.5-9.0 cm. All of

these changes are congruent with the early beginnings of a warming trend. For example,

a notable increase in the moss epiphyte D. kuetzingii could be in response to the commencement of increased moss growth and proliferation around the edges of the pond

as the summer ice-free season became longer (or the melted moat of water at the edge

became larger, if the pond did not yet become completely ice-free in summer). This also

would account for A. minutissima and C. angustata beginning to increase here, as well as slight increases in N. halophila and the structurally complex C. descripta. Furthermore,

these changes occur concurrently with the substantial decrease in the cold-water,

alkaliphilous Fragilaria construens var. venter (mentioned above), lending even further

support to the establishment of a warmer climate at this time. Because there is currently

no reliable date available for this level in the core, it is impossible to conclusively

97 determine the timing of these early changes. However, given the distribution of the 210Pb dates in the top few cm of the core, it is reasonable to speculate that this lower depth may correspond to sometime in the 1800s. This timing would be consistent with some other paleolimnological studies from the circumpolar Arctic, many of which track the onset of recent warming trends to around the mid-1800s (summarized by Smol et al. 2005). Thus, the early shifts in the diatom assemblages of the Stygge short core may be recording the onset of a warming trend, potentially beginning in the 19th century, with more intense warming evident in the dramatic diatom shifts occurring in the early- to mid-20th century.

Long core – Sediment

The approximately 47 cm of sediment at the top of the long core is divided in

Figure 3.6 into a zone that approximately corresponds with the short core (Zone S2), and the zone lying directly beneath this section (Zone S1). From Zone S1 it is apparent that the diatom assemblage in Stygge was once almost entirely a monoculture of Fragilaria construens var. venter, from 47 cm (which dates to before 6210 ± 94 cal. yr BP, 5440 ±

80 14C yr BP) until approximately 31-32 cm. As mentioned above, this monoculture of the small Fragilaria species is typical of early post-glacial Holocene lakes and ponds.

Above approximately 31-32 cm, the assemblage becomes much more diverse, with the addition of taxa from the genera Achnanthes, Cymbella, Navicula, Denticula and

Nitzschia (Zone S2). This includes the appearance of N. halophila, which may indicate the initiation of increased salinization of the pond, perhaps marking the point in time at which the water level sank below the outlet stream, creating a closed basin.

It is evident from Zone 2 (the portion of the long core that corresponds to the short core) that the main trends in the diatom assemblage changes are very similar to

98 those in the short core, and can be interpreted in the same way. There is, however, an

interesting difference in the long core stratigraphy, in that the recent increases in A.

minutissima and C. angustata are much more pronounced than in the short core. In addition, N. halophila undergoes a striking increase in the top few centimetres of the long

core that is not at all evident in the short core. This discrepancy between the two cores is not surprising, as it is clear from field notes and photographs taken in the 1984 field

season that the long core was taken from a location closer to shore than the short core,

which was extracted from the centre of the pond. Although it is common practice to take

cores from the centre of a lake or pond, the long core was taken at an earlier time of year

(late May), when the pond was still completely frozen, with a cover of snow over it and

its surrounding catchment. This would have made it much more difficult to judge the true centre of the pond, compared to when the short core was taken (early July), when the pond was completely ice-free. At present, the bottom of Stygge is quite heterogeneous,

with moss banks becoming much more abundant closer to shore than in the central area, where there is mostly bare sediment. Thus, it is not unexpected that a core taken closer to shore, where there is a much greater diversity and higher abundance of littoral habitats, would be more sensitive to increases in the relative abundances of the diatom taxa that inhabit these substrates (e.g. Wolfe 1996). This is supported by the fact that, as mentioned earlier, the taxa with more pronounced increases at the top of the long core are all epiphytic.

Despite the discrepancies in species percentages between the two cores, it is

important to note that the two diatom profiles are both displaying the same overall

ecological trend, with a relatively stable assemblage dominated by small, benthic,

99 coldwater diatoms succeeded by unprecedented increases in more complex and epiphytic

taxa. The most likely interpretation of this trend is the recent proliferation of moss

substrates in response to a lengthening of the ice-free period (and the ensuing physical

and chemical changes to the limnological environment), which likely results ultimately

from a warming climate. In fact, the drastic increase in N. halophila in the long core

presents an even stronger case for warming, which would cause increased evaporation

and thus increased evapoconcentration of the pond’s water, raising salinity levels and

providing more ideal conditions for this halophilic diatom. A similar trend in this species

was observed in a pond on western Greenland (McGowan et al. 2003).

Long core – Ice portion

Beneath the 47 cm of sediment in the long core was an approximately 275 cm long section of solid ice matrix with inclusions of sediment and pebbles interspersed throughout it, and within that sediment, well-preserved diatoms (Zone I, Figure 3.6).

Ground ice is a common feature of periglacial regions; however, to the extent of my knowledge, no previous paleolimnological study in the Arctic has reported the occurrence of a sediment core matching this description. Interpretation of the diatom profile from this section of the core poses a problem, given that the origins of the ice are as yet unknown. Three possible origins include: 1) buried glacial ice; 2) buried lake ice (either surface or anchor ice); or 3) intrasedimental segregation ice (Robert Gilbert, personal communication).

The first two options, buried glacial or buried lake ice, are the least plausible of

the three. The incorporation into the ice of sediment that is apparently lacustrine in

nature, containing diatoms that are important components of the pond’s modern and

100 down-core assemblages, and producing radiocarbon ages that make chronological sense with ages from the overlying pond sediment, does not corroborate with what would be expected in either glacial or lake ice when one considers their structure and the processes

behind their formation.

Intrasedimental segregation (or segregated) ice is the most plausible of the three

possibilities. This type of ground ice forms in frozen sediment (e.g. permafrost), when

water migrates towards the freezing (0ºC) plane in response to temperature and pressure

gradients established by the freezing process itself (French 1996; Williams and Smith

1989). In Stygge’s case, this could have occurred as the pond froze to the bottom and

into the sediment, with the freezing plane migrating ~47 cm down (i.e. to the depth at

which the ice is found in the core). An ice lens then begins to form at the freezing plane,

effectively removing water from the sediment directly below it; this creates a water

pressure differential, inducing more water to be drawn upwards by capillary action to

replace the water that has been frozen (Williams and Smith 1989). The ice lens grows

slowly downward as the new water freezes, with growth continuing in this way as long as

there is an ample supply of water (French 1996). Ice formed in this manner is stratified,

and generally contains fragments of the soil or sediment in which it develops (French

1996). This would account for the bits of sediment entrapped in Stygge’s ice, as well as the preservation of the radioisotopic age chronology.

If ice segregation is, in fact, the mechanism behind the formation of Stygge’s ice,

and the sediment incorporated into the ice once formed a continuous profile with the

undisturbed sediment above it, it would mean that the sediment record in the long core

likely captures the pond’s entire post-glacial history, dating back to approximately 10,558

101 ± 25 cal. yr BP. As mentioned earlier, the near monoculture of F. construens var. venter

at the bottom of the core is consistent with an early post-glacial diatom assemblage.

What is somewhat interesting, however, is the diversification of the assemblage in the

middle of the ice section of the core (Figure 3.6), with C. angustata, D. kuetzingii, and

especially N. vulpina becoming important contributors, often achieving relative

abundances greater than in the overlying sediment (discussed above), and A. minutissima,

N. halophila, N. cf. viridula, Nitzschia cf. frustulum, Cymbella cf. designata, and

Denticula subtilis appearing in smaller abundances. Radiocarbon dates from the entrained sediment constrain this change to between approximately 10,500 and 6,200 cal. yr BP. Towards the top of the ice section, these taxa are again replaced by a near monoculture of F. construens var. venter, which continues into the sediment layers above. These shifts early on in the history of the pond are not consistent with the majority of diatom profiles from other high Arctic ponds, which, as mentioned previously, generally exhibit low diversity and stable assemblages throughout most of the core’s length, until more recent intervals, where dramatic diversification and ecological shifts occur (e.g. Douglas et al. 1994).

Bradley (1990) summarized the general trends in paleoclimate over the Holocene

on Ellesmere Island based on evidence from a variety of climate proxies, and Kaufman et

al. (2004) and Kaplan and Wolfe (2006) provide similar summaries for various regions of

the Arctic (including the Canadian High Arctic). Strong evidence points to an early

Holocene Thermal Maximum (HTM) occurring between ~10,000-7000 cal yr BP, with

warm conditions equivalent to, or perhaps even warmer than present, persisting between

~10,000-4,000 cal yr BP. Substantial Neoglacial cooling is believed to have occurred

102 after 3500 cal yr BP (but potentially starting as early as 5500 cal yr BP), with possibly the

coldest temperatures of the entire Holocene being reached between around 400-100 yr BP

(i.e. 1550-1900). Finally, the better part of the past century has been exceptionally warm

relative to the rest of the late Holocene, apparently with the highest inferred temperatures

for over 1000 years (Bradley 1990). The early Holocene shifts in the Stygge long core,

with the decline in coldwater Fragilaria species and compensatory increases in more

complex, epiphytic forms, are consistent with a warming trend. The timing of this

apparent warming overlaps with the proposed early- to mid-Holocene warm period. If the relative abundance of F. construens var. venter is any indication, this would potentially place the HTM somewhere before 7400 cal. yr BP, at the inflection point of this taxon’s relative abundance profile (between 152-128 cm). It would follow, then, that the subsequent recovery of this cold-water, alkaline taxon to nearly 100% relative abundance could represent Neoglacial cooling, suggesting an onset at around 71 cm, sometime before approximately 6200 cal. yr BP).

If the diatom shifts in the ice section of the core do, indeed, represent a Holocene

thermal maxiumum (and subsequent Neoglacial cooling), with temperatures reaching

levels comparable to those of today (or higher), then one might expect to find a similar

increase in Navicula halophila here as is occurring at the top of the cores. Why is this

not the case? Wolfe (2000) suggests that, in contrast to the warm and relatively arid

conditions of the more recent warming, the early-to-mid Holocene warming may have

been warm and wet. Thus, perhaps any increase in evaporation from warming in the

early-to-mid Holocene would have been largely counteracted by increased precipitation,

precluding the evapoconcentration and resultant heightened salinity and conductivity that

103 presumably prompted the expansion of this halophilic taxon at the top of the core.

Furthermore, wetter conditions could also account for the trace observations of

planktonic taxa (Aulacoseira and Cyclotella spp.) in this section of the core that were not

noted anywhere else in the core, as warmth combined with more precipitation could have

provided a longer ice-free period and a pelagic zone deep enough for some planktonic

taxa to develop. Higher precipitation could perhaps also help explain the unparalleled

importance of Navicula vulpina in the middle of the icy section, as this taxon has been

closely associated with high nutrients and high levels of DOC (Antoniades et al. 2005a;

Lim et al. 2001a), both of which could have been heightened in the pond with increased precipitation and therefore increased runoff.

Although the segregation ice hypothesis is, at present, the most fitting explanation

for this anomalous ice, any interpretation of the ice’s origins, and thus the diatom changes

within the ice, are speculative at this point. Ascertaining the origin of massive ground ice

is often quite complicated (French and Harry 1990; Williams and Smith 1989), and more

information is required to begin to draw any conclusions on the subject. Closer

examination of the structure of the ice through crystallography may help reveal the mode of formation and the conditions under which it developed (French 1996). For example, the size of the individual ice crystals is an indication of the rate at which they formed, with larger crystals taking more time than smaller ones (French 1996). Glacier ice, therefore, has very large crystals compared to lake ice or segregation ice. The orientation of ice crystals is another important diagnostic feature. The crystals in segregated ice, for example, would be oriented perpendicular to the sediment surface (i.e., vertically), whereas mature glacial ice crystals would be horizontally aligned (Williams and Smith

104 1989). However, the reliability of these characteristics in identifying ice origins can

commonly be compromised over long periods of time by the altering effects of

recrystallization (Williams and Smith 1989). Further information can be gleaned from

analyzing the isotopic composition of the ice, which can be used to estimate the source of

the water and the approximate temperature under which the ice formed (French 1996).

Finally, the nature of the point of contact between the ice and the overlying and underlying sediments is also a distinguishing feature (French 1996, Ingólfsson and

Lokrantz 2003). Glacial ice (and other buried ice) tends to have sharp, unconformable

contact surfaces, whereas segregated ice generally grades into the sediment and can have

vertical strands of bubbles at the soil-ice interface. Stygge’s contact surfaces are both

gradational, further suggesting that the ice is segregated in nature. However, further analyses are warranted in order to confirm this hypothesis.

Microhabitats

The two graphs showing the diatom percent relative abundances for the modern

microhabitat samples (Figures 3.7 and 3.8) provide information on how the diatom taxa

are currently distributed throughout the pond. The dominant taxa in all five years, and

throughout all microhabitat types, are A. minutissima and C. descripta. A. minutissima is

a cosmopolitan taxon found in high abundances in other high latitude or high altitude

sites, spanning wide ranges of environmental conditions (e.g. Bigler and Hall 2002; Lim

et al. 2001a, 2007, 2008; Michelutti et al. 2006; Pienitz et al. 1995; Van de Vijver et al.

2003). Furthermore, the dominance of these two species is consistent with the downcore

stratigraphies (discussed above), because both taxa have increased substantially in recent

sediments. To a much lesser extent, C. angustata, N. halophila, and A. flexella are also

105 important throughout the pond in all years, which is also consistent with the downcore

profiles. D. kuetzingii shows a marked decrease towards the top of the sediment cores,

and is accordingly not an important component of the modern microhabitat samples.

F. construens var. venter is dominant in three samples taken in 1984 (samples 4-

84, 5-84 and 8-84, Figure 3.7). This is likely not a function of the sampling year, but

rather is related to the specific microhabitats sampled, in combination with the conditions

under which they were taken. As is evident from Figure 3.7, all three of these samples

were collected from surface sediment or sand, the preferred substrate for this taxon

(Douglas and Smol 1993). In addition, all three samples were taken under particularly cold conditions. For example, samples 4-84 and 5-84 were taken through a hole in the ice when the pond was still ice-covered, and 8-84 was taken from a puddle that was situated directly adjacent to a snow bank at the time of sampling, which was feeding cold snowmelt into the puddle. This was the only field season in which the pond was sampled early enough in the year to have captured the expansion of this coldwater diatom under these ideal conditions. The rest of the surface sediment/sand samples were taken from open water, either later in the season or from the melted moat around the edge of the pond, and thus under much warmer conditions. These findings lend further support to the hypothesis that the large decline in F. construens var. venter in the sediment cores represents warming conditions in the pond.

In the graph separating the samples by sampling year (Figure 3.7), a few species

stand out as occurring in notable relative abundances only in the most recent year (2006).

These include Denticula subtilis, Nitzschia cf. sublinearis, N. cf. alpina and N.

commutata. Furthermore, all excepting D. subtilis are also found almost exclusively in

106 the moss-like microhabitats of the pond (Figure 3.8). Interestingly, these three Nitzschia species were not important in the sediment cores. This, combined with the fact that they are present only in microhabitat samples from 2006 (two years after the short core and 22 years after the long core was taken), and only in moss samples, may indicate that these moss epiphytes have increased to appreciable abundances only within the past two years.

The stimulus for these increases could perhaps have been an increase in moss substrates, or some other favourable change to the aquatic environment. However, because 2006 was the only year in which mosses were sampled, this apparently recent increase in these taxa could, in fact, be a misleading sampling artifact, and must therefore be viewed with caution.

Unlike these Nitzschia species, Denticula subtilis shows no preference for any one microhabitat in Stygge (Figure 3.8), and so its appearance in only the 2006 sampling year can be more reliably interpreted as a very recent increase in this taxon’s relative abundance. This is an interesting observation, as D. subtilis has been recognized as an indicator of high specific conductivity in ponds elsewhere in the High Arctic (e.g.

Antoniades et al. 2004; 2005a; Michelutti et al. 2006). Its recent increase is therefore likely an indication of increased specific conductivity, resulting from higher rates of evaporation due to climate warming. In addition, its absence from the sediment cores

(aside from a few small appearances in the anomalous icy section of the long core) may be an indication that a threshold has now been crossed, with perhaps unprecedented levels of salinity and specific conductivity being reached in this pond.

107 Summary and Conclusions

A small, shallow, closed-basin pond such as Stygge Nunatak Pond, which is

unusually high in ionic concentration and shows clear evidence for past water level

fluctuations, is expected to be especially sensitive to changes in climate. The diatom

assemblages of both the short and long sediment cores from this pond record the same

overall ecological trends over the time since approximately 2200 cal. yr BP: simple,

stable, coldwater early assemblages consisting largely of the dominant Fragilaria

construens v. venter and subdominants Navicula halophila and Denticula kuetzingii, with

relatively recent (early- to mid-20th century) and unprecedented marked increases in more complex and epiphytic diatoms indicative of a longer ice-free period, resulting ultimately from a warmer climate. A longer ice-free period would allow for the development of more complex diatom forms, and an expanded littoral zone with increased macrophytes

(i.e. mosses), providing more abundant and more diverse substrate for epiphytic diatoms.

Moreover, the dramatic recent expansion of the halophilic N. halophila recorded in the

long core lends further support for a recent warming, which would cause an increase in

ionic concentration likely due to enhanced evaporative concentration.

Interpretation of the long core diatom assemblages below ~47 cm was

complicated by the unexpected finding of the long section of solid ice interspersed with

bits of sediment. If the ice is segregated in origin, then the diatom record preserved in the

embedded sediment may provide potential evidence for an early- to mid-Holocene warm

period and subsequent Neoglacial cooling in the region of Stygge Nunatak. If this is the

case, it is unlike most down-core diatom records from the High Arctic, which generally record a stable, cold-water assemblage over most of the Holocene, with recent dramatic

108 and unprecedented changes indicative of warming. However, until the origins of the ice can be conclusively ascertained, any interpretation of the diatoms entrained within it must remain speculative.

The diatom assemblages from modern microhabitat samples taken during five different field seasons (1983, 1984, 2001, 2004, 2006) are consistent with the assemblages in the most recent intervals at the top of the sediment cores, with dominance of A. minutissima and C. descripta in all microhabitat types, and smaller but important

contributions from C. angustata, N. halophila, and A. flexella. The appearance of D. subtilis, a species known to prefer high conductivity environments, in the microhabitats

from only the most recent sampling year (2006), combined with its virtual absence from

the sediment cores (taken in 1984 and 2004), suggests that salinity and conductivity may

have reached unprecedented levels in the pond in 2006, providing potential further

evidence that the current climate warming in this region of the Canadian High Arctic is

unprecedented.

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117 FIGURE CAPTIONS

Figure 3.1. Map showing the location of Stygge Nunatak, upon which lies Stygge Nunatak Pond, in Jokel Fjord on Ellesmere Island, Nunavut, High Arctic Canada.

Figure 3.2. a) Satellite image of Jokel Fjord, with arrow pointing at Stygge Nunatak. b) Photograph of Stygge Nunatak, surrounded by Stygge glacier, with arrow pointing at Stygge Nunatak Pond. The nunatak is composed of Archean orthopyroxene granite, with a dolomite cap on one of its peaks (visible at right). c) Closer view of Stygge Nunatak Pond (arrow), with dolomite cap and Stygge glacier in background. d) Stygge Nunatak Pond, with white precipitate and jewel lichen-encrusted rocks visible in foreground at right, and Stygge glacier in background. Satellite image from Google Earth (2008); photographs courtesy of Marianne S.V. Douglas (b,c; July 2004) and Alyson Paul (d; July 2006).

Figure 3.3. Profile of 210Pb activity (Bq/g) plotted against depth (cm) in the short sediment core from Stygge Nunatak Pond, Ellesmere Island, High Arctic Canada. Also included are 210Pb dates determined using the constant rate of supply (CRS) model.

Figure 3.4. A graph of all radioisotopic dates from both the short and long cores of Stygge Nunatak Pond, plotted against depth (cm). 210Pb dates are shown in blue, and calibrated 14C dates in red. The green points represent two calibrated 14C dates that are anomalously old for their position in the core.

Figure 3.5. A stratigraphic profile of the percent relative abundances of the most important diatom taxa in the short sediment core taken from Stygge Nunatak Pond, Ellesmere Island, Canada, in 2004. Horizontal dashed lines demarcate three “zones” based on visual identification of the areas where important changes occur in the assemblages. 210Pb dates, as well as one calibrated 14C date determined from humic acids in the sediment, are included.

Figure 3.6. A stratigraphic profile of the percent relative abundances of the most important diatom taxa in the long sediment core taken from Stygge Nunatak Pond, Ellesmere Island, Canada, in 1984. Horizontal dashed lines demarcate three “zones” (Zones I, S1 and S2) based on visual identification of the areas where important changes occur in the assemblages. Zones S1 and S2 represent the sediment portion of the long core, with S2 being approximately equivalent to the entire short core. Zone I represents the icy portion of the long core, which had bits of sediment interspersed throughout it.

Figure 3.7. Percent relative abundances of the most important diatom taxa from various microhabitat samples from Stygge Nunatak Pond, Ellesmere Island, Canada. Samples are separated by horizontal lines into groups based on the year in which they were taken (1983, 1984, 2001, 2004, 2006).

118

Figure 3.8. Percent relative abundances of the most important diatom taxa from various microhabitat samples from Stygge Nunatak Pond, Ellesmere Island, Canada. Samples are separated by horizontal lines into groups based on the specific microhabitat type from which they were taken (surface sediment/sand, rock scrape, grass, moss-type substrate, or algal sand).

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tulum tulum tulum tulum

a a a a

s s s s 1983 1984 2001 2004 2006

il il il il

u u u u

g g g g

fr fr fr fr

f. f. f. f.

Fra Fra Fra Fra

c c c c

a a a a

i i i i

h h h h

c c c c

s s s

s 0 20 40 60 80 100

z z z z

phila phila phila phila

t t t t

i i i i

o o o o

N N N N

icula kuetzingii kuetzingii kuetzingii kuetzingii icula icula icula icula

t t t

t 010

Den Den Den Den

cula hal hal hal hal cula cula cula cula i i i i 010

Nav Nav Nav Nav

010

a a a a

Relative(%) Abundance

pt pt pt pt i i i i

r r r r

c c c c

es es es es

a d d d d a a a a l l l l

el el el el

b b b b

ngustata ngustata ngustata ngustata

ym ym ym ym

a a a a

C C C C a a a a

0 20406080

Cymbell Cymbell Cymbell Cymbell

010

minutissima minutissima minutissima minutissima

thes thes thes thes

n n n n

Achna Achna Achna Achna

020406080

e type & code code code code & & & & type type type type e e e e l l l l

Samp Samp Samp Samp rock (9-01) (9-01) rock rock (9-01) (9-01) rock rock (43-06) rock (43-06) rock (11-84) rock (146-84) rock (242-04) rock rock (242-04) rock rock (369-83) rock sand (335-84) grass (243-04) grass (243-04) grass (368-83) surf. sed.(8-01) surf. surf. sed.(8-01) surf. surf. sed. (4-84) sed. surf. surf. sed. (42-06) sed. surf. surf. sed. (42-06) sed. surf. wet moss (45-06) moss wet wet moss (45-06) moss wet sub. moss (44-06) sub. moss sub. moss (44-06) sub. moss surf. sed. (241-04) sed. surf. surf. sed. (241-04) sed. surf. surf. sed. (145-84) sed. surf. algal(15-01) sand algal(15-01) sand sub. grass (10-01)sub. grass sub. grass (10-01)sub. grass emerg. grassemerg. (47-06) emerg. grassemerg. (47-06) rock (PUDDLE)(9-84) rock (PUDDLE)(9-84) coarse sand (370-83) sub. saxifrage (46-06) sub. saxifrage (46-06) sand (PUDDLE)(8-84) surf. sedsurf. (moat)(12-84) gr. algae at (48-06) shore gr. algae at (48-06) shore surf. sed. (2nd hole)(5-84)(2nd sed. surf. Gr. algaeGr. (367-83) on sand Figure 3.7

126

ommutata ommutata ommutata

na na

na

c c c li li li

ap ap ap

. .

. f f f

c c c

tzschia tzschia tzschia tzschia

ia ia ia i i

i h h h

N N N

sublinearis sublinearis sublinearis sublinearis

010 . . . . sc sc sc

cf cf cf cf lis lis lis lis

i i i i itz itz

itz

N N N

ia ia ia ia ia

bt bt bt

bt 010 h h h h

u u u

u

a s s s s a a a a l l l l

Nitzsc Nitzsc Nitzsc

Nitzsc

ta ta ta ta exilis/cryptocephala exilis/cryptocephala exilis/cryptocephala exilis/cryptocephala 01020

is is is is

er er er er a a a a a

l l l l

s s s s

c c c c

Denticu Denticu Denticu

Denticu

in in in in en en en

en 010 icu icu icu icu

r r r r

v v v v

la la la la

l l l

l

Na Na Na Na

010

soeh soeh soeh soeh

a a a a

flexe flexe flexe flexe

ul ul ul ul

Cymbella Cymbella Cymbella Cymbella Cymbella s s s s

010 ic ic ic ic

he he he he

t t t t

a a a a

av av av

av

N N N N

010

nan nan nan nan

h h h

h

vulpin vulpin vulpin vulpin

Ac Ac Ac Ac a a a

a 010

cul cul cul cul i i i i

av av av av

N N N N

020

s s s s s

n n n

n

rue rue rue rue t t t

t venter venter venter venter

m m m m . . . .

lu lu lu lu ar ar ar ar

u u u u v v v

v

st st st st grass

i i i i

ru ru ru ru

f f f

f

gi gi gi

gi rock scrapes ragilaria cons cons cons cons ragilaria ragilaria ragilaria ragilaria

n n n n

cf. cf. cf. cf. sand on algae F F F F

tzi tzi tzi

tzi moss-type substrate

Surface sed./sand ia ia ia ia

ia e e e e

h h h h la la la la

ku ku ku ku

sc sc sc sc hi hi hi

hi 0 20 40 60 80 100

a a a a

p p p

p

itz itz itz itz

ul ul ul ul

lo lo lo lo

N N N N

ic ic ic

ic 010 ha ha ha

ha a a a a a

ul ul ul ul Dent Dent Dent Dent

010

vic vic vic vic

a a a a

N N N N

010

Relative Abundance (%) Abundance Relative a a a a

ipt ipt ipt

ipt r r r r

sc sc sc sc

e e e

e

a d d d d a a a a l l l

l

ngustata ngustata ngustata ngustata

a a a a

ymbel ymbel ymbel

ymbel C C C C

020406080

Cymbella Cymbella Cymbella Cymbella Cymbella

010

e e e

e od od od od

Achnanthes minutissima minutissima minutissima minutissima Achnanthes Achnanthes Achnanthes Achnanthes c c c c

020406080 & & &

&

type type type

type

le le le le

p p p

p

am am am am

S S S S (9-01) rock rock (11-84) rock rock (43-06) rock rock (369-83) rock (242-04) rock (146-84) rock sand (335-84) sand grass (368-83) grass (243-04) grass surf. sed.(8-01) sed.(8-01) surf. surf. sed.(4-84) surf. sed. (42-06) sed. surf. wet moss (45-06) moss wet sub. moss (44-06) moss sub. algal sand (15-01) algal sand sub. grass (10-01) grass sub. surf. sed. (241-04) sed. surf. (145-84) sed. surf. emerg. grass (47-06) grass emerg. rock (PUDDLE)(9-84) (PUDDLE)(9-84) rock coarse sand (370-83) sand coarse sub. saxifrage (46-06) saxifrage sub. sand (PUDDLE)(8-84) sand sedsurf. (moat)(12-84) gr. algae at shore (48-06) shore at algae gr. surf. sed. (2nd hole)(5-84) (2nd sed. surf. (367-83) algae on sand Gr. Figure 3.8

127

Table 3.1. A list of the major surface water chemistry measurements from Stygge Nunatak Pond, taken during 5 different field seasons (2006, 2004, 2001, 1984, 1983). 2006 2004 2001 1984 1983 (July 8) (July 19) (July 7) (June 23) (July 17)

Cl (mg/L) 35.4 101 143 99.3 100.3

SO4 (mg/L) 82.7 309 510 158.9 163.4

SiO2 (mg/L) 0.6 1.31 1.21 3.81 5.55 DOC (mg/L) 13.8 27.4 33.4 ------DIC (mg/L) 17.2 30.1 31.0 ------Fe (mg/L) 0.199 0.144 0.312 ------Mn (mg/L) 0.012 0.003 0.005 ------Na (mg/L) 26.0 84.5 110.0 75.5 75.4 Ca (mg/L) 22.9 64.4 87.4 30.0 34.4 K (mg/L) 5.28 16.9 21.1 13.62 14.7 Mg (mg/L) 21.7 66.6 94.4 50.9 52.1 Li (mg/L) 0.008 0.002 0.035 ------Sr (mg/L) 0.086 0.236 0.347 ------Ba (mg/L) 0.003 0.006 0.009 ------Al (mg/L) 0.048 0.023 0.060 ------TN-F (mg/L) 0.92 1.87 2.48 ------TP-UF (mg/L) 0.016 0.010 0.011 0.012 0.015 TKN (mg/L) 0.936 1.77 2.66 ------CHLa (μg/L) 2.1 0.5 1.6 ------POC (mg/L) 1.22 0.747 0.865 ------PON (mg/L) 0.08 0.051 0.053 ------POC:CHLa 580.95 1494 540.63 ------pH 8.32 8.58 8.4 June 10: 7.4 8.64 June 23: 7.66 SP. COND 432 9000 1090 June 10: 138 800 (μS/cm) June 23: 425 TEMP (ºC) 12 12 8 June 10: 0.1 12 June 23: 4

DOC = Dissolved Organic Carbon; DIC = Dissolved Inorganic Carbon; TN-F = Total Nitrogen (filtered); TP-UF = Total Phosphorus Unfiltered; TKN = Total Kjeldahl Nitrogen; CHLa = Chlorophyll-a; POC = Particulate Organic Carbon; PON = Particulate Organic Nitrogen; SP. COND. = specific conductivity; TEMP = surface water temperature

128

Table 3.2. Unsupported 210Pb activi ty for 12 inte rvals from th e short sediment c ore taken from Stygge Nunatak Po nd, Ellesme re Island, High Arctic C anada. Also inclu ded are 210Pb dates determined using the constant rate of supply (CRS) model.

Depth in Core Unsupported 210Pb Activity CRS model 210Pb Dates (cm) (Bq/g) 0.0-0.5 0.0 51 2004.5 0.5-1.0 0. 056 1999 1.0-1.5 0. 044 1992 1.5-2.0 0. 035 1982 2.0-2.5 0. 021 1964 2.5-3.0 0.0 15 1944 3.0-3.5 0.0 19 1938 3.5-4.0 0.0 14 background 4.0-4.5 0.0 16 4.5-5.0 0.0 14 10.5-11.0 0.0 11 20.5-21.0 0.012

129

Table 3.3. AMS radiocarbon dates from both the short and long cores from Stygge Nunatak Pond, Ellesmere Island, High Arctic Canada.The majority of dates were taken from the humic acid fraction of bulk sediment samples (INSTAAR), with one done on washed-in fragments of terrestrial mosses (Bryum pseudotriquetrum and Campylium stellatum) (IsoTrace Radiocarbon Laboratory). Calibrated ages and the 68% confidence intervals (1σ) were calculated using CalPal-2007online.

Age Calibrated 1σ Lab # Core Depth Material δ13C (14C yr Age confidence (cm) dated (‰) BP) (cal yr BP) interval

Short Core CURL-9357 8.5-9.0 humic acids -21.2 2255 ± 15 2270 ± 60 2209-2330 CURL-9655 9.0-9.5 humic acids -22.1 2200 ± 20 2234 ± 60 2173-2294 CURL-9356 19.0-19.5 humic acids -19.9 2225 ± 15 2246 ± 59 2187-2305

Long Core TO-3429 43.5-45.0 terrestrial -25.0 5440 ± 80 6210 ± 94 6115 - 6304 moss fragments CURL-9370 44.0-45.0 humic acids -27.4 5510 ± 15 6303 ± 6 6297-6309 CURL-9368 107.0-111.0 humic acids -21.2 6450 ± 15 7380 ± 35 7344-7415

CURL-9362 298.0-301.0 humic acids -23.2 9345 ± 20 10,558 ± 25 10532-10583

130 CHAPTER 4

General Discussion and Conclusions

The global climate is warming at an alarming rate (IPCC 2007). Polar regions,

such as those in the Canadian Arctic, are known to be especially sensitive to climate

warming, and are already being impacted substantially, as is evidenced from numerous

scientific records as well as indigenous human observation (e.g. ACIA 2004; Hinzman et

al. 2005; IPCC 2007). The effects of climate change appear to be influencing Arctic

lakes in diverse ways (Schindler and Smol 2006), with many sites showing marked and

unprecedented changes in their physical, chemical, and biological characteristics. For

example, after millennia of relatively stable diatom assemblages, shallow ponds at Cape

Herschel, Ellesmere Island, recorded striking recent (post-industrial) community changes

consistent with climate warming (Douglas et al. 1994). Furthermore, Smol and Douglas

(2007) have recently noted that some ponds from the same area have begun to desiccate

entirely during the short summer season (likely due to increased evaporation), a

phenomenon that has likely not occurred in thousands of years. Clearly, ecological

thresholds are already being crossed. Meanwhile, global climate models predict that

warming and its effects, even under the most conservative estimates of future greenhouse

gas emissions, will continue and intensify further. It is therefore important to obtain a

better understanding of how the Arctic’s sensitive freshwater ecosystems have responded

to past climate fluctuations, so that we might predict their responses to future change.

Despite the fact that paleoclimate studies in the Canadian Arctic have increased in

recent years (Pienitz et al. 2004), there is still much to be learned about past environmental changes in this large and diverse region. The objective of this thesis was

131 to examine how diatom assemblages in two separate freshwater bodies, located in different regions of the central Canadian Arctic, have changed in response to climatic and environmental change over the Holocene. Both of these study sites possess certain characteristics that have rarely been addressed in the paleolimnological literature from this region. The first, Lake TK-2 (Chapter 2), is located in an under-studied geographical area in the continental Arctic, near the southern boundary of the high Arctic Archipelago.

The second study site, Stygge Nunatak Pond (Chapter 3), is a rare example of an athalassic high Arctic pond with unusually high ionic concentrations.

Marked changes throughout the diatom profiles from both of these sites suggest that Holocene climate has been dynamic in both regions. In Lake TK-2, an early

Holocene assemblage unlike most other post-glacial assemblages from the central

Canadian Arctic may indicate a transient period of relative warmth (~9000-8550 cal yr

BP), possibly as a result of anticyclonic air circulation patterns around the retreating

Laurentide Ice Sheet (Glen MacDonald, personal communication). This could have temporarily drawn warmer air from more southern latitudes northward, a hypothesis that is supported by a small peak in arboreal pollen grains in the pollen profile from the same core (Seppä et al. 2003). This was replaced by an assemblage more typical of lakes on recently deglaciated landscapes, which, similar to Stygge’s earliest assemblages, is indicative of probably cooler, alkaline conditions.

Both sites record compelling evidence for an early- to mid-Holocene warm period, occurring earlier in Stygge (between approximately 10,500 and 7300 cal yr BP) than in TK-2 (between approximately 7000 to 3500 cal yr BP). These disparate timings are consistent with those recognized for the Holocene Thermal Maximum (HTM) in their

132 respective regions (e.g. Kaufman et al. 2004). Subsequent diatom shifts in both lakes indicate a Neoglacial cooling trend.

Interestingly, the diatoms from the TK-2 sediment core may record exciting new evidence for the abrupt and dramatic 8.2k cooling anomaly. This supports the observations of Seppä et al. (2003), who found that the only marked change in the pollen profile from this same core was indicative of a sudden cooling, potentially correlative

with the 8.2k event. To my knowledge, evidence for this well-known, potentially world-

wide climate anomaly has yet to be reported from any other paleolimnological study from

the Canadian Arctic. Its absence from other records may simply be because some of the

previously studied sediment cores do not extend far back enough in time to capture this

relatively early point in the Holocene. Additionally, they may not be sampled at a

sufficiently high resolution to detect this probably very brief (on the order of decades)

event. This underscores the value of high resolution Arctic sediment records that

encompass most or all of the Holocene.

In addition to the above changes, the diatom assemblages from both Lake TK-2

and Stygge Nunatak Pond add to the growing body of paleolimnological evidence for

recent (19th-20th century) climate warming across much of the circumpolar Arctic. This

evidence is manifest in marked and unprecedented ecological shifts occurring in the top-

most sediment layers from both lakes. In TK-2, a dramatic expansion of small,

planktonic Cyclotella species, coinciding with an equally dramatic decline in the once-

dominant, heavily-silicified Aulacoseira lirata complex, is consistent with similar trends

that have been recorded in lower latitude regions (e.g. proximal to treeline) across the circumpolar Arctic (Rühland et al. 2008; Smol et al. 2005). The shift is suggestive of

133 increased open water and/or enhanced thermal stability in the water column, as well as

related limnological changes.

In contrast, in the much shallower but high Arctic Stygge Nunatak Pond, the

observed shifts were among the benthic assemblages, with a dramatic increase in more complex and epiphytic diatom taxa (e.g. Cymbella descripta) indicative of a longer growing season and enhanced littoral moss cover. Furthermore, marked expansion of

Navicula halophila in the most recent sediments suggests that ionic concentration in the

pond has increased, likely in response to increased evaporation. Moreover, Denticula

subtilis, a taxon associated with particularly high levels of conductivity (e.g. Antoniades

et al. 2004, 2005; Michelutti et al. 2006), appears in only the most recent (2006) modern

microhabitat samples, suggesting that increasing rates of evaporation may be accelerating

in very recent years.

Thus, the recent community shifts in these two freshwater bodies, which are

located in very different regions of the Canadian Arctic, lend further support to the

growing realization that recent warming is a widespread rather than regional

phenomenon. Although the nature of the specific changes are different in the two lakes,

both ultimately indicate the same environmental changes – namely, an increase in the

duration of the ice-free period resulting from a warming climate.

Future Directions

Based on the results of this thesis, a promising direction for future paleolimnogical work in the central Canadian Low Arctic might be to follow up on the potential detection of the 8.2k anomaly in the TK-2 core. It would be interesting to further explore this phenomenon by examining detailed, high-resolution, down-core

134 diatom assemblage changes in other lakes in the region near Lake TK-2, and elsewhere.

This may help to elucidate whether paleolimnological evidence for this dramatic cooling event is detected more extensively than current limited records might suggest.

The substantial portion of ice included within the long core from Stygge Nunatak

Pond, combined with the fact that permafrost in many regions of the Arctic is thawing,

suggests that continued climate warming may eventually disrupt the chronological

sediment profile that is currently preserved in this unique pond. The window of opportunity for studying this rare system may therefore be limited. It would be useful to examine the diatom assemblages from modern microhabitat samples taken during future field seasons, in order to monitor how the modern assemblages are changing.

Specifically, it would be interesting to determine whether Denticula subtilis, which is associated with especially high specific conductivity and appears for the first time in the

2006 samples, continues to increase in importance, as rates of evapoconcentration will presumably accelerate with continued warming.

Overall, the results summarized in this thesis begin to bridge some of the gaps

that exist in the paleolimnogical literature for the Canadian Arctic. Continuing

examinations of the diatom histories of lakes and ponds with varying physical, chemical,

hydrological, and geological characteristics, and in regions where long-term

paleolimnological studies are lacking, will help to further our understanding of Holocene

climate dynamics across this vast, widely varying region.

135 REFERENCES

ACIA (Arctic Climate Impact Assessment). 2004. Impacts of a warming Arctic. Cambridge University Press, Cambridge, UK. Available online: http://amap.no/acia/

Antoniades, D., M.S.V. Douglas and J.P. Smol. 2004. Diatom species-environment relationships and inference models from Isachsen, Ellef-Ringnes Island, Canadian High Arctic. Hydrobiologia 529: 1-18.

Antoniades, D., M.S.V. Douglas and J.P. Smol. 2005. Benthic diatom autecology and inference model development from the Canadian High Arctic Archipelago. Journal of Phycology 41: 30-45.

Douglas, M.S.V., J.P. Smol, and W. Blake Jr. 1994. Marked post-18th century environmental change in High-Arctic ecosystems. Science 266: 416-419.

Hinzman, L.D., N.D. Bettez, W.R. Bolton, F.S. Chapin, M.B. Dyurgerov, C.L. Fastie, B. Griffith, R.D. Hollister, A. Hope, H.P. Huntington, A.M. Jensen, G.J. Jia, T. Jorgenson, D.L. Kane, D.R. Kane, G. Kofinas, A.H. Lynch, A.H. Lloyd, A.D. McGuire, F.E. Nelson, W.C. Oechel, T.E. Osterkamp, C.H. Racine, V.E. Romanovsky, R.S. Stone, D.A. Stow, M. Sturm, C.E. Tweedie, G.L. Vourlitis, M.D. Walker, D.A. Walker, P.J. Webber, J.M. Welker, K.S. Winker and K. Yoshikawa. 2005. Evidence and implications of recent climate change in northern Alaska and other Arctic regions. Climate Change 72: 251-298.

IPCC. 2007. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Michelutti, N., J.P. Smol and M.S.V. Douglas. 2006. Ecological characteristics of modern diatom assemblages from Axel Heiberg Island (High Arctic Canada) and their application to paleolimnological inference models. Canadian Journal of Botany 84: 1695- 1713.

Pienitz, R., M.S.V. Douglas and J.P. Smol (eds.). 2004. Long-term Environmental Change in Arctic and Antarctic Lakes. Springer, Dordrecht, Netherlands, 562 pp.

Rühland, K., A.M. Patterson and J.P. Smol. 2008. Hemispheric-scale patterns of climate- related shifts in planktonic diatoms from North American and European lakes. Global Change Biology 14: 1-15.

Schindler, D.W. and J.P. Smol. 2006. Cumulative effects of climate warming and other human activities on freshwaters of Arctic and Subarctic North America. AMBIO 35: 160- 168.

136 Seppä, H., L.C. Cwynar and G.M. MacDonald. 2003. Post-glacial vegetation reconstruction and a possible 8200 cal. yr BP event from the low arctic of continental Nunavut, Canada. Journal of Quaternary Science 18: 621-629.

Smol, J.P. and M.S.V. Douglas. 2007. From controversy to consensus: making the case for recent climate change in the Arctic using lake sediments. Frontiers in Ecology and the Environment 5: 466-474.

Smol, J.P., A.P. Wolfe, H.J.B. Birks, M.S.V. Douglas, V.J. Jones, A. Korhola, R. Pienitz, K. Rühland, S. Sorvari, D. Antoniades, S.J. Brooks, M.A. Fallu, M. Hughes, B.E. Keatley, T.E. Laing, N. Michelutti, L. Nazarova, M. Nyman, A.M. Paterson, B. Perren, R. Quinlan, M. Rautio, E. Saulnier-Talbot, S. Siitonen, N. Solovieva, and J. Weckström. 2005. Climate-driven regime shifts in the biological communities of arctic lakes. Proceedings of the National Academy of Science 102: 4397-4402.

137 Appendix A. Raw diatom count data for the sediment core from Lake TK-2.

198-199 196-197 192-193 186-187 180-181 174-175 Taxon cm cm cm cm cm cm Achnanthes 2-dot 2 Achnanthes acares 2 17 Achnanthes acares (blurry) Achnanthes bicapitata Achnanthes bicapitata (small) 97 121 23 4 19 6 Achnanthes biasolettiana v. subatomus 0 0 3 3 2 2 Achnanthes c.f. difficilima Achnanthes c.f. minutissima Achnanthes c.f. rossii 1 2 12 Achnanthes c.f. stolida 40 1 3 Achnanthes carissima 1 27 7 Achnanthes carissima (tall) 2 1 Achnanthes chlidanos 3 2 1 Achnanthes curtissima 46 7 7 9 Achnanthes daoensis 2 Achnanthes depressa 1 Achnanthes didyma 3 Achnanthes flexella 1 Achnanthes girdle1 Achnanthes girdle2 Achnanthes girdle3 Achnanthes helvetica 2 Achnanthes imperfecta 1 Achnanthes impexiformis (MAF) 1 Achnanthes kuelbsii Achnanthes kriegeri 1 1 Achnanthes lacus-vulcani 1 1 Achnanthes laevis 2 Achnanthes laterostrata Achnanthes laterostrata (straighter) Achnanthes levanderi 1 Achnanthes marginulata 1 Achnanthes minutissima 5 13 7 11 8 3 Achnanthes minutissima (small) 3 12 105 29 16 Achnanthes nitidiformis 88 103 6 1 1 Achnanthes oblongella Achnanthes petersenii 1 Achnanthes pusilla 1 3 Achnanthes saccula Achnanthes scotica 7 6 1 4 10 6 Achnanthes sp.1 (AADW) Achnanthes sp.2(MAFp.150) Achnanthes sp.(lemon) Achnanthes suchlandtii 1 Achnanthes subatomoides (aff) Achnanthes subatomoides 1 2 2 Achnanthes thermalis

138 Appendix A (continued)

198-199 196-197 192-193 186-187 180-181 174-175 Taxon cm cm cm cm cm cm Achnanthes ventralis 1 2 9 Actinella punctata Amphora ovalis Amphora small 2-dot valve Aulacoseira c.f. ambigua Aulacoseira c.f. subarctica (MAF) Aulacoseira distans (girdle) Aulacoseira distans (valve) Aulacoseira distans var. nivalis (girdle) Aulacoseira distans var. nivalis (valve) Aulacoseira lirata (girdle) Aulacoseira lirata (valve) Aulacoseira lirata var. biseriata (girdle) Aulacoseira lirata var. biseriata (valve) Aulacoseira perglabra (girdle) Aulacoseira perglabra (valve) Aulacoseira perglabra var. florinae (girdle) Aulacoseira perglabra var. florinae (valve) 1 Aulacoseira sp. (super fine punctae) Brachysira brebissonii Brachysira brebissonii (girdle) Brachysira brebissonii var. zellensis Brachysira sp1 (long) Brachysira styriaca Brachysira vitrea Caloneis c.f. lauta 6 2 5 8 1 5 Caloneis c.f. silicila Caloneis c.f. tenuis Caloneis c.f. tenuis FORM B Caloneis molaris 1 4 c.f. Cymbella big girdle Cyclotella bodanica v. lemanica 2 3 Cyclotella pseudostelligera 37 28 1 Cyclotella stelligera 3 4 Cyclotella ocellata 4 1 Cyclotella rossii Cymbella cesatii 1 Cymbella c.f. angustata Cymbella c.f. cuspidata Cymbella c.f. descripta 2 Cymbella c.f. ehrenbergii Cymbella c.f. norvegica Cymbella c.f. tynnii Cymbella gaeumannii 4 6 20 1 1 5 Cymbella gracilis Cymbella hebredica 2 Cymbellla lapponica 3 1

139 Appendix A (continued)

198-199 196-197 192-193 186-187 180-181 174-175 Taxon cm cm cm cm cm cm Cymbella lapponica (affinity) Cymbella mesiana Cymbella microcephala Cymbella naviculiformis 1 1 Cymbella silesiaca 9 4 20 1 2 Cymbella sinuata Cymbella sp1 4 Diploneis c.f. elliptica Diploneis finnica Diploneis marginestriata 12 13 19 10 Diploneis parma (KLB) 21 2 Diploneis smithii var. dilatata Eunotia arculus Eunotia arcus Eunotia bidentula Eunotia bilunaris Eunotia bilunaris var. mucophila Eunotia c.f. pectinalis v. undulata Eunotia circumborealis Eunota denticulata Eunotia diodon Eunotia exigua Eunotia girdle1 Eunotia girdeHUGE Eunotia faba Eunotia flexuosa Eunotia incisa Eunotia meisteri Eunotia monodon Eunotia nymanniana Eunotia praerupta Eunotia rhynchocephala Eunotia rhynchocephala var. satelles Eunotia serra Eunotia soleirolii/minor Fragilaria brevistriata Fragilaria brevistriata var. papillosa 5 Fragilaria capucina 1 2 Fragilaria c.f. capucina c. mesolepta Fragilaria c.f. parasitica (but bigger) Fragilaria c.f. pinnata Fragilaria construens 1 Fragilaria construens var. binodia Fragilaria construens var. pumila Fragilaria construens var. venter 1 2 22 Fragilaria construens var. venter (diam.) Fragilaria pinnata

140 Appendix A (continued)

198-199 196-197 192-193 186-187 180-181 174-175 Taxon cm cm cm cm cm cm Fragilaria pseudoconstruens Fragilaria virescens var. exigua 2 4 5 Frustulia rhomb. c.f. v. amphipleuroides Frustulia rhomboides var. crassinervia 1 Frustulia rhomboides var. rhomboides 3 2 1 1 Frustulia rhomboides var. saxonica Gomphonema c.f. truncatum Gomphonema gracile Gomphonema parvulum 1 2 4 Gomphonema parvulum (small) Navicula aff. Achnanthes rossii 10 Navicula aff. Disjuncta 1 Navicula aff. humerosa Navicula barbell-like 1 Navicula bryophila 5 2 3 1 4 Navicula c.f. agrestis Navicula c.f. bahusiensis 1 Navicula c.f. cincta Navicula c.f. exilis 4 1 16 7 1 Navicula c.f. explanata Navicula c.f. halophila 1 Navicula c.f. medioconvexa Navicula c.f. minima Navicula c.f. pupula 4 1 3 9 3 Navicula c.f. submolesta (MAF) 1 Navicula c.f. subrotundra Navicula cocconeiformis Navicula crytocephala 2 8 Navicula cryptotenella 2 Navicula digitulus 13 4 4 2 Navicula digitulus (longer) 13 7 Navicula duerrenbergiana Navicula girdle 1 (small) Navicula pseudoscutiformis 2 0 2 6 3 12 Navicula girdle 3 Navicula girdle 4 Navicula girdle 5 (big) Navicula schmassmannii 2 0 53 213 138 85 Navicula jaagii 1 Navicula jaernefeltii 38 44 6 6 13 9 Navicula kuelbsii 1 87 10 Navicula laticeps 2 2 Navicula laevissima 1 1 1 Navicula leptostriata 10 2 11 Navicula mediocris 2 Navicula micropunctata Navicula minima 1

141 Appendix A (continued)

198-199 196-197 192-193 186-187 180-181 174-175 Taxon cm cm cm cm cm cm Navicula pseudoscutiformis 2 2 6 3 12 Navicula pupula 3 5 4 15 Navicula radiosa 3 18 8 10 22 37 Navicula "rectangle" 1 Navicula seminulum 2 9 20 Navicula soehrensis v. hassiaca Navicula sp.1 Navicula sp.1 Navicula sublitissima 2 1 1 Navicula submuralis 7 Navicula submuralis (girdle) Navicula tridentula 2 Navicula variostriata 2 Navicula variostriata (small) 20 16 29 8 10 20 Navicula variostriata (sm. pointier) 4 Navicula ventralis Navicula vitiosa Navicula/Caloneis sp. Neidium affine Neidium ampliatum 1 Neidium bisulcatum Nitszchia c.f. radicula Nitzschia bryophila 2 5 2 Nitzschia fonticola 5 5 2 1 2 Nitzschia gracilis Nitzschia inconspicua Nitzschia perminuta 7 7 18 12 3 2 Nitzschia sp. (BIG) Peronia fibula Pinnularia balfouriana 1 Pinnularia barbell shaped Pinnularia c.f. borealis Pinnularia c.f. pulchra 1 1 Pinnularia c.f. rupestris Pinnularia c.f. viridis Pinnularia divergentissima 2 1 Pinnularia divergentissima v. martinii 1 Pinnularia gibba Pinnularia interrupta 2 3 10 Pinnularia maior 2 Pinnularia microstauron 2 3 Pinnularia microstauron (HUGE) Pinnularia nobilis 1 Pinnularia nodosa Pinnularia subgibba Pinnularia viridis Stauroneis anceps (bald/blank) 1 2 4

142 Appendix A (continued)

198-199 196-197 192-193 186-187 180-181 174-175 Taxon cm cm cm cm cm cm Stauroneis anceps (striated) Stauroneis phoenicenteron 1 1 Stauroneis tiny spp 1 Stenopterobia anceps Stenopterobia curvula Stenopterobia delicatissima Surirella c.f. linearis Surirella HUGE (length of scale bar) Surirella robusta Tabellaria flocculosa strain IV 1 1 1 1 Tetracyclus glans Total Diatoms 407 439 474 467 415 419 Chrysophyte Cysts 22 27 61 27 31 57 Protozoan plates 0 1 4 1 1 1 Phytoliths 0 0 0 0 0 0 Cyst:Diatom ratio 0.098 0.110 0.205 0.104 0.130 0.214

143 Appendix A (continued)

166-167 160-161 154-155 148-149 142-143 136-137 Taxon cm cm cm cm cm cm Achnanthes 2-dot Achnanthes acares 5 2 4 Achnanthes acares (blurry) Achnanthes bicapitata 11 15 Achnanthes bicapitata (small) 2 18 Achnanthes biasolettiana v. subatomus 0 0 0 0 0 0 Achnanthes c.f. difficilima Achnanthes c.f. minutissima Achnanthes c.f. rossii 4 Achnanthes c.f. stolida Achnanthes carissima Achnanthes carissima (tall) Achnanthes chlidanos 4 1 Achnanthes curtissima 6 1 1 Achnanthes daoensis Achnanthes depressa Achnanthes didyma Achnanthes flexella Achnanthes girdle1 Achnanthes girdle2 Achnanthes girdle3 Achnanthes helvetica Achnanthes imperfecta 1 Achnanthes impexiformis (MAF) Achnanthes kuelbsii Achnanthes kriegeri Achnanthes lacus-vulcani Achnanthes laevis Achnanthes laterostrata 19 28 Achnanthes laterostrata (straighter) 2 Achnanthes levanderi Achnanthes marginulata 2 1 Achnanthes minutissima 1 1 Achnanthes minutissima (small) Achnanthes nitidiformis 4 16 Achnanthes oblongella Achnanthes petersenii 4 Achnanthes pusilla Achnanthes saccula Achnanthes scotica 3 1 Achnanthes sp.1 (AADW) Achnanthes sp.2(MAFp.150) Achnanthes sp.(lemon) Achnanthes suchlandtii 3 17 Achnanthes subatomoides (aff) Achnanthes subatomoides 1 Achnanthes thermalis

144 Appendix A (continued)

166-167 160-161 154-155 148-149 142-143 136-137 Taxon cm cm cm cm cm cm Achnanthes ventralis Actinella punctata Amphora ovalis 1 Amphora small 2-dot valve Aulacoseira c.f. ambigua Aulacoseira c.f. subarctica (MAF) Aulacoseira distans (girdle) 3 Aulacoseira distans (valve) Aulacoseira distans var. nivalis (girdle) Aulacoseira distans var. nivalis (valve) Aulacoseira lirata (girdle) 2 1 2 3 11 46 Aulacoseira lirata (valve) 12 17 50 19 3 17 Aulacoseira lirata var. biseriata (girdle) Aulacoseira lirata var. biseriata (valve) 2 Aulacoseira perglabra (girdle) Aulacoseira perglabra (valve) Aulacoseira perglabra var. florinae (girdle) Aulacoseira perglabra var. florinae (valve) 2 Aulacoseira sp. (super fine punctae) 1 Brachysira brebissonii Brachysira brebissonii (girdle) Brachysira brebissonii var. zellensis Brachysira sp1 (long) Brachysira styriaca 1 Brachysira vitrea Caloneis c.f. lauta 1 1 Caloneis c.f. silicila Caloneis c.f. tenuis Caloneis c.f. tenuis FORM B Caloneis molaris c.f. Cymbella big girdle Cyclotella bodanica v. lemanica 3 Cyclotella pseudostelligera Cyclotella stelligera Cyclotella ocellata 1 Cyclotella rossii Cymbella cesatii Cymbella c.f. angustata Cymbella c.f. cuspidata Cymbella c.f. descripta Cymbella c.f. ehrenbergii Cymbella c.f. norvegica Cymbella c.f. tynnii Cymbella gaeumannii 2 Cymbella gracilis Cymbella hebredica 2 Cymbellla lapponica 1

145 Appendix A (continued)

166-167 160-161 154-155 148-149 142-143 136-137 Taxon cm cm cm cm cm cm Cymbella lapponica (affinity) Cymbella mesiana Cymbella microcephala Cymbella naviculiformis Cymbella silesiaca 1 2 2 Cymbella sinuata 2 Cymbella sp1 Diploneis c.f. elliptica Diploneis finnica 1 Diploneis marginestriata 1 Diploneis parma (KLB) Diploneis smithii var. dilatata 4 4 18 11 Eunotia arculus Eunotia arcus Eunotia bidentula Eunotia bilunaris 1 Eunotia bilunaris var. mucophila Eunotia c.f. pectinalis v. undulata 1 Eunotia circumborealis Eunota denticulata Eunotia diodon Eunotia exigua Eunotia girdle1 Eunotia girdeHUGE Eunotia faba Eunotia flexuosa Eunotia incisa Eunotia meisteri Eunotia monodon Eunotia nymanniana Eunotia praerupta Eunotia rhynchocephala Eunotia rhynchocephala var. satelles Eunotia serra Eunotia soleirolii/minor Fragilaria brevistriata 24 15 12 16 Fragilaria brevistriata var. papillosa 6 8 Fragilaria capucina Fragilaria c.f. capucina c. mesolepta Fragilaria c.f. parasitica (but bigger) 8 Fragilaria c.f. pinnata Fragilaria construens 5 Fragilaria construens var. binodia Fragilaria construens var. pumila 17 Fragilaria construens var. venter 32 2 8 5 13 Fragilaria construens var. venter (diam.) 5 4 40 Fragilaria pinnata 4 2 18 9 50

146 Appendix A (continued)

166-167 160-161 154-155 148-149 142-143 136-137 Taxon cm cm cm cm cm cm Fragilaria pseudoconstruens 11 10 Fragilaria virescens var. exigua 4 1 Frustulia rhomb. c.f. v. amphipleuroides Frustulia rhomboides var. crassinervia Frustulia rhomboides var. rhomboides 1 Frustulia rhomboides var. saxonica Gomphonema c.f. truncatum Gomphonema gracile 2 Gomphonema parvulum Gomphonema parvulum (small) Navicula aff. Achnanthes rossii Navicula aff. Disjuncta Navicula aff. humerosa Navicula barbell-like Navicula bryophila 1 Navicula c.f. agrestis Navicula c.f. bahusiensis Navicula c.f. cincta 1 Navicula c.f. exilis 1 Navicula c.f. explanata Navicula c.f. halophila Navicula c.f. medioconvexa Navicula c.f. minima Navicula c.f. pupula 2 Navicula c.f. submolesta (MAF) Navicula c.f. subrotundra Navicula cocconeiformis Navicula crytocephala Navicula cryptotenella Navicula digitulus 1 Navicula digitulus (longer) Navicula duerrenbergiana Navicula girdle 1 (small) Navicula pseudoscutiformis 0 0 0 0 8 4 Navicula girdle 3 Navicula girdle 4 Navicula girdle 5 (big) Navicula schmassmannii 4 0 0 0 5 6 Navicula jaagii Navicula jaernefeltii 2 1 4 Navicula kuelbsii 2 2 7 Navicula laticeps Navicula laevissima Navicula leptostriata Navicula mediocris Navicula micropunctata Navicula minima

147 Appendix A (continued)

166-167 160-161 154-155 148-149 142-143 136-137 Taxon cm cm cm cm cm cm Navicula pseudoscutiformis 8 4 Navicula pupula 1 2 2 5 Navicula radiosa 3 7 9 Navicula "rectangle" Navicula seminulum 7 1 Navicula soehrensis var. hassiaca Navicula sp.1 Navicula sp.1 Navicula sublitissima 1 Navicula submuralis 2 Navicula submuralis (girdle) Navicula tridentula Navicula variostriata Navicula variostriata (small) 2 0 0 1 6 4 Navicula variostriata (small pointier) Navicula ventralis Navicula vitiosa 2 1 4 5 Navicula/Caloneis sp. Neidium affine Neidium ampliatum 2 Neidium bisulcatum Nitszchia c.f. radicula Nitzschia bryophila 1 Nitzschia fonticola 3 Nitzschia gracilis Nitzschia inconspicua Nitzschia perminuta 2 2 7 7 Nitzschia sp. (BIG) 1 Peronia fibula Pinnularia balfouriana 1 3 3 Pinnularia barbell shaped 1 Pinnularia c.f. borealis 2 1 Pinnularia c.f. pulchra 1 Pinnularia c.f. rupestris Pinnularia c.f. viridis Pinnularia divergentissima 1 Pinnularia divergentissima v. martinii 4 Pinnularia gibba Pinnularia interrupta 1 3 3 Pinnularia maior Pinnularia microstauron 1 Pinnularia microstauron (HUGE) Pinnularia nobilis Pinnularia nodosa Pinnularia subgibba 1 2 Pinnularia viridis Stauroneis anceps (bald/blank)

148 Appendix A (continued)

166-167 160-161 154-155 148-149 142-143 136-137 Taxon cm cm cm cm cm cm Stauroneis anceps (striated) Stauroneis phoenicenteron Stauroneis tiny spp Stenopterobia anceps Stenopterobia curvula Stenopterobia delicatissima Surirella c.f. linearis Surirella HUGE (length of scale bar) Surirella robusta Tabellaria flocculosa strain IV 1 1 Tetracyclus glans Total Diatoms 144 25 54 102 207 413 Chrysophyte Cysts 11 2 0 16 49 27 Protozoan plates 0 0 0 0 6 0 Phytoliths 0 0 0 0 0 0 Cyst:Diatom ratio 0.133 0.138 0.000 0.239 0.321 0.116

149 Appendix A (continued)

130-131 122-123 116-117 110-111 104-105 102-103 Taxon cm cm cm cm cm cm Achnanthes 2-dot Achnanthes acares 10 7 11 15 3 10 Achnanthes acares (blurry) 4 Achnanthes bicapitata 2 2 1 4 Achnanthes bicapitata (small) Achnanthes biasolettiana v. subatomus 0 0 0 0 0 0 Achnanthes c.f. difficilima 1 Achnanthes c.f. minutissima Achnanthes c.f. rossii Achnanthes c.f. stolida 1 5 Achnanthes carissima 3 Achnanthes carissima (tall) 1 Achnanthes chlidanos Achnanthes curtissima 1 6 5 17 11 Achnanthes daoensis Achnanthes depressa Achnanthes didyma Achnanthes flexella 1 Achnanthes girdle1 Achnanthes girdle2 Achnanthes girdle3 Achnanthes helvetica Achnanthes imperfecta Achnanthes impexiformis (MAF) Achnanthes kuelbsii 1 Achnanthes kriegeri 1 1 Achnanthes lacus-vulcani 3 4 4 Achnanthes laevis Achnanthes laterostrata 1 Achnanthes laterostrata (straighter) Achnanthes levanderi Achnanthes marginulata 1 3 1 Achnanthes minutissima 3 3 9 2 Achnanthes minutissima (small) Achnanthes nitidiformis 1 2 Achnanthes oblongella 2 Achnanthes petersenii 2 4 Achnanthes pusilla 1 Achnanthes saccula Achnanthes scotica 2 3 12 8 Achnanthes sp.1 (AADW) Achnanthes sp.2(MAFp.150) 3 Achnanthes sp.(lemon) 1 Achnanthes suchlandtii 12 18 16 Achnanthes subatomoides (aff) 3 Achnanthes subatomoides Achnanthes thermalis

150 Appendix A (continued)

130-131 122-123 116-117 110-111 104-105 102-103 Taxon cm cm cm cm cm cm Achnanthes ventralis 1 Actinella punctata Amphora ovalis 1 3 Amphora small 2-dot valve Aulacoseira c.f. ambigua Aulacoseira c.f. subarctica (MAF) Aulacoseira distans (girdle) Aulacoseira distans (valve) Aulacoseira distans var. nivalis (girdle) Aulacoseira distans var. nivalis (valve) Aulacoseira lirata (girdle) 24 41 15 54 56 68 Aulacoseira lirata (valve) 34 35 12 6 7 Aulacoseira lirata var. biseriata (girdle) 11 3 2 Aulacoseira lirata var. biseriata (valve) 3 1 3 Aulacoseira perglabra (girdle) 9 10 Aulacoseira perglabra (valve) 4 34 28 Aulacoseira perglabra var. florinae (girdle) 2 Aulacoseira perglabra var. florinae (valve) 3 3 Aulacoseira sp. (super fine punctae) Brachysira brebissonii 1 Brachysira brebissonii (girdle) Brachysira brebissonii var. zellensis Brachysira sp1 (long) Brachysira styriaca Brachysira vitrea Caloneis c.f. lauta 2 2 2 2 5 Caloneis c.f. silicila 2 2 Caloneis c.f. tenuis Caloneis c.f. tenuis FORM B Caloneis molaris c.f. Cymbella big girdle Cyclotella bodanica v. lemanica 1 Cyclotella pseudostelligera 1 2 1 2 3 Cyclotella stelligera 3 1 Cyclotella ocellata 11 2 7 4 Cyclotella rossii 1 Cymbella cesatii Cymbella c.f. angustata Cymbella c.f. cuspidata Cymbella c.f. descripta Cymbella c.f. ehrenbergii 1 Cymbella c.f. norvegica Cymbella c.f. tynnii Cymbella gaeumannii 2 1 4 4 10 10 Cymbella gracilis 1 Cymbella hebredica 1 2 3 1 4 Cymbellla lapponica 3

151 Appendix A (continued)

130-131 122-123 116-117 110-111 104-105 102-103 Taxon cm cm cm cm cm cm Cymbella lapponica (affinity) Cymbella mesiana Cymbella microcephala Cymbella naviculiformis 1 1 Cymbella silesiaca 2 2 2 1 4 7 Cymbella sinuata Cymbella sp1 Diploneis c.f. elliptica Diploneis finnica Diploneis marginestriata 1 3 2 1 Diploneis parma (KLB) Diploneis smithii var. dilatata 4 4 1 Eunotia arculus Eunotia arcus Eunotia bidentula Eunotia bilunaris Eunotia bilunaris var. mucophila Eunotia c.f. pectinalis v. undulata Eunotia circumborealis Eunota denticulata Eunotia diodon Eunotia exigua Eunotia girdle1 Eunotia girdeHUGE Eunotia faba Eunotia flexuosa Eunotia incisa 1 2 Eunotia meisteri Eunotia monodon Eunotia nymanniana Eunotia praerupta 2 Eunotia rhynchocephala 1 Eunotia rhynchocephala var. satelles Eunotia serra 1 Eunotia soleirolii/minor 3 Fragilaria brevistriata 24 53 56 19 Fragilaria brevistriata var. papillosa 27 15 33 22 Fragilaria capucina Fragilaria c.f. capucina c. mesolepta Fragilaria c.f. parasitica (but bigger) Fragilaria c.f. pinnata Fragilaria construens 5 14 8 6 Fragilaria construens var. binodia 1 Fragilaria construens var. pumila Fragilaria construens var. venter 63 58 39 13 8 Fragilaria construens var. venter (diam.) 49 90 Fragilaria pinnata 49 72 73 46 7

152 Appendix A (continued)

130-131 122-123 116-117 110-111 104-105 102-103 Taxon cm cm cm cm cm cm Fragilaria pseudoconstruens 6 5 3 Fragilaria virescens var. exigua 18 11 21 84 73 Frustulia rhomb. c.f. v. amphipleuroides Frustulia rhomboides var. crassinervia 1 1 Frustulia rhomboides var. rhomboides 2 5 5 Frustulia rhomboides var. saxonica 2 Gomphonema c.f. truncatum 1 Gomphonema gracile Gomphonema parvulum 1 4 Gomphonema parvulum (small) Navicula aff. Achnanthes rossii Navicula aff. Disjuncta Navicula aff. humerosa Navicula barbell-like Navicula bryophila 2 2 4 4 Navicula c.f. agrestis Navicula c.f. bahusiensis Navicula c.f. cincta Navicula c.f. exilis 1 3 1 Navicula c.f. explanata Navicula c.f. halophila Navicula c.f. medioconvexa 1 Navicula c.f. minima Navicula c.f. pupula Navicula c.f. submolesta (MAF) Navicula c.f. subrotundra Navicula cocconeiformis 1 5 2 1 Navicula crytocephala Navicula cryptotenella Navicula digitulus 6 Navicula digitulus (longer) Navicula duerrenbergiana Navicula girdle 1 (small) Navicula pseudoscutiformis 4 8 6 6 1 4 Navicula girdle 3 Navicula girdle 4 Navicula girdle 5 (big) Navicula schmassmannii 8 16 21 67 76 61 Navicula jaagii Navicula jaernefeltii 3 13 7 4 3 Navicula kuelbsii 1 17 8 Navicula laticeps Navicula laevissima 1 1 Navicula leptostriata 1 Navicula mediocris 4 Navicula micropunctata Navicula minima 4 1

153 Appendix A (continued)

130-131 122-123 116-117 110-111 104-105 102-103 Taxon cm cm cm cm cm cm Navicula pseudoscutiformis 4 8 6 6 1 4 Navicula pupula 1 2 2 1 Navicula radiosa 2 3 3 3 Navicula "rectangle" Navicula seminulum 9 15 2 3 25 25 Navicula soehrensis var. hassiaca Navicula sp.1 2 Navicula sp.1 Navicula sublitissima 2 1 Navicula submuralis 2 3 4 2 Navicula submuralis (girdle) Navicula tridentula Navicula variostriata Navicula variostriata (small) 6 3 0 9 8 7 Navicula variostriata (small pointier) Navicula ventralis Navicula vitiosa 13 10 11 22 3 Navicula/Caloneis sp. Neidium affine Neidium ampliatum 1 1 2 Neidium bisulcatum Nitszchia c.f. radicula 2 Nitzschia bryophila Nitzschia fonticola 6 6 Nitzschia gracilis Nitzschia inconspicua Nitzschia perminuta 9 1 12 11 11 Nitzschia sp. (BIG) Peronia fibula Pinnularia balfouriana 5 11 18 Pinnularia barbell shaped Pinnularia c.f. borealis Pinnularia c.f. pulchra Pinnularia c.f. rupestris Pinnularia c.f. viridis 2 3 Pinnularia divergentissima Pinnularia divergentissima v. martinii 1 Pinnularia gibba 1 1 Pinnularia interrupta 1 1 2 5 7 Pinnularia maior Pinnularia microstauron 2 3 5 Pinnularia microstauron (HUGE) Pinnularia nobilis Pinnularia nodosa 1 Pinnularia subgibba Pinnularia viridis 3 Stauroneis anceps (bald/blank) 5 3

154 Appendix A (continued)

130-131 122-123 116-117 110-111 104-105 102-103 Taxon cm cm cm cm cm cm Stauroneis anceps (striated) Stauroneis phoenicenteron 1 Stauroneis tiny spp Stenopterobia anceps Stenopterobia curvula Stenopterobia delicatissima Surirella c.f. linearis Surirella HUGE (length of scale bar) Surirella robusta Tabellaria flocculosa strain IV 2 4 5 2 Tetracyclus glans Total Diatoms 445 530 410 452 441 443 Chrysophyte Cysts 20 19 38 32 25 21 Protozoan plates 0 1 2 2 7 3 Phytoliths 0 0 1 0 0 0 Cyst:Diatom ratio 0.082 0.067 0.156 0.124 0.102 0.087

155 Appendix A (continued)

98-99 96-97 92-93 86-87 80-81 74-75 68-69 62-63 Taxon cm cm cm cm cm cm cm cm Achnanthes 2-dot Achnanthes acares 4 2 3 4 6 5 Achnanthes acares (blurry) Achnanthes bicapitata 3 7 1 6 5 1 1 1 Achnanthes bicapitata (small) Achnanthes biasolettiana v. subatomus 0 0 0 0 0 0 0 0 Achnanthes c.f. difficilima Achnanthes c.f. minutissima Achnanthes c.f. rossii 1 Achnanthes c.f. stolida 3 4 3 2 8 3 1 Achnanthes carissima 4 1 2 5 5 Achnanthes carissima (tall) 1 Achnanthes chlidanos Achnanthes curtissima 2 2 6 9 10 14 16 16 Achnanthes daoensis Achnanthes depressa Achnanthes didyma 1 Achnanthes flexella 1 2 Achnanthes girdle1 Achnanthes girdle2 Achnanthes girdle3 Achnanthes helvetica Achnanthes imperfecta Achnanthes impexiformis (MAF) Achnanthes kuelbsii 1 2 Achnanthes kriegeri 2 1 4 Achnanthes lacus-vulcani 1 2 5 5 4 Achnanthes laevis Achnanthes laterostrata Achnanthes laterostrata (straighter) Achnanthes levanderi 1 Achnanthes marginulata 1 5 6 6 3 1 Achnanthes minutissima 1 1 2 Achnanthes minutissima (small) Achnanthes nitidiformis Achnanthes oblongella Achnanthes petersenii Achnanthes pusilla 1 1 Achnanthes saccula 1 1 2 Achnanthes scotica 2 3 9 20 4 15 16 14 Achnanthes sp.1 (AADW) Achnanthes sp.2(MAFp.150) Achnanthes sp.(lemon) Achnanthes suchlandtii Achnanthes subatomoides (aff) Achnanthes subatomoides Achnanthes thermalis

156 Appendix A (continued)

98-99 96-97 92-93 86-87 80-81 74-75 68-69 62-63 Taxon cm cm cm cm cm cm cm cm Achnanthes ventralis 2 Actinella punctata Amphora ovalis 6 1 1 Amphora small 2-dot valve Aulacoseira c.f. ambigua 1 Aulacoseira c.f. subarctica (MAF) Aulacoseira distans (girdle) 1 1 Aulacoseira distans (valve) 5 1 2 1 Aulacoseira distans var. nivalis (girdle) 2 7 2 3 4 9 Aulacoseira distans var. nivalis (valve) 3 12 2 2 5 2 Aulacoseira lirata (girdle) 25 23 42 17 30 4 6 3 Aulacoseira lirata (valve) 36 55 38 20 42 20 17 22 Aulacoseira lirata var. biseriata (girdle) 9 35 42 47 51 40 28 115 Aulacoseira lirata var. biseriata (valve) 4 25 9 9 13 10 7 4 Aulacoseira perglabra (girdle) 2 4 8 7 13 2 Aulacoseira perglabra (valve) 59 40 26 13 21 34 16 13 Aulacoseira perglabra var. florinae (girdle) Aulacoseira perglabra var. florinae (valve) 1 1 4 3 6 3 2 9 Aulacoseira sp. (super fine punctae) Brachysira brebissonii 2 5 3 2 2 Brachysira brebissonii (girdle) Brachysira brebissonii var. zellensis Brachysira sp1 (long) Brachysira styriaca Brachysira vitrea Caloneis c.f. lauta Caloneis c.f. silicila Caloneis c.f. tenuis Caloneis c.f. tenuis FORM B Caloneis molaris c.f. Cymbella big girdle Cyclotella bodanica v. lemanica Cyclotella pseudostelligera 2 2 5 2 Cyclotella stelligera 1 1 2 Cyclotella ocellata 1 Cyclotella rossii Cymbella cesatii Cymbella c.f. angustata 1 1 Cymbella c.f. cuspidata 1 Cymbella c.f. descripta Cymbella c.f. ehrenbergii Cymbella c.f. norvegica Cymbella c.f. tynnii Cymbella gaeumannii 5 6 16 17 12 19 14 12 Cymbella gracilis 2 1 2 3 Cymbella hebredica 5 4 3 2 2 4 Cymbellla lapponica 2 1 1

157 Appendix A (continued)

98-99 96-97 92-93 86-87 80-81 74-75 68-69 62-63 Taxon cm cm cm cm cm cm cm cm Cymbella lapponica (affinity) Cymbella mesiana Cymbella microcephala Cymbella naviculiformis Cymbella silesiaca 8 2 2 3 5 6 1 4 Cymbella sinuata Cymbella sp1 Diploneis c.f. elliptica 1 Diploneis finnica Diploneis marginestriata 1 5 2 3 1 3 1 Diploneis parma (KLB) Diploneis smithii var. dilatata Eunotia arculus Eunotia arcus 0.5 Eunotia bidentula Eunotia bilunaris 0.5 Eunotia bilunaris var. mucophila Eunotia c.f. pectinalis v. undulata Eunotia circumborealis Eunota denticulata Eunotia diodon 3 1 3 1 Eunotia exigua Eunotia girdle1 Eunotia girdeHUGE Eunotia faba 1 Eunotia flexuosa 0.5 0.5 Eunotia incisa 0.5 1 Eunotia meisteri Eunotia monodon 0.5 1 Eunotia nymanniana Eunotia praerupta 1.5 Eunotia rhynchocephala 1 2 1 Eunotia rhynchocephala var. satelles 2 1 1 Eunotia serra 2 1 Eunotia soleirolii/minor 2.5 1 3 6 Fragilaria brevistriata 2 Fragilaria brevistriata var. papillosa Fragilaria capucina 3 1 1 Fragilaria c.f. capucina c. mesolepta Fragilaria c.f. parasitica (but bigger) Fragilaria c.f. pinnata Fragilaria construens Fragilaria construens var. binodia Fragilaria construens var. pumila Fragilaria construens var. venter 10 7 1 Fragilaria construens var. venter (diamond) Fragilaria pinnata 1 5 1

158 Appendix A (continued)

98-99 96-97 92-93 86-87 80-81 74-75 68-69 62-63 Taxon cm cm cm cm cm cm cm cm Fragilaria pseudoconstruens Fragilaria virescens var. exigua 137 109 76 64 104 93 95 60 Frustulia rhomboides c.f. v. amphipleuroides Frustulia rhomboides var. crassinervia 2 2 1 6 Frustulia rhomboides var. rhomboides 4 7 3 12 3 4 6 Frustulia rhomboides var. saxonica Gomphonema c.f. truncatum Gomphonema gracile Gomphonema parvulum 5 2 3 4 Gomphonema parvulum (small) Navicula aff. Achnanthes rossii Navicula aff. Disjuncta Navicula aff. humerosa Navicula barbell-like Navicula bryophila 6 1 1 3 2 3 3 Navicula c.f. agrestis Navicula c.f. bahusiensis Navicula c.f. cincta Navicula c.f. exilis 2 1 2 1 1 Navicula c.f. explanata Navicula c.f. halophila Navicula c.f. medioconvexa Navicula c.f. minima Navicula c.f. pupula Navicula c.f. submolesta (MAF) Navicula c.f. subrotundra 1 Navicula cocconeiformis 4 3 1 Navicula crytocephala Navicula cryptotenella Navicula digitulus 1 7 Navicula digitulus (longer) Navicula duerrenbergiana Navicula girdle 1 (small) Navicula pseudoscutiformis 1 1 0 1 2 2 4 0 Navicula girdle 3 Navicula girdle 4 Navicula girdle 5 (big) Navicula schmassmannii 12 10 26 21 20 28 44 28 Navicula jaagii Navicula jaernefeltii 3 1 3 1 1 2 Navicula kuelbsii Navicula laticeps Navicula laevissima 1 Navicula leptostriata Navicula mediocris 2 Navicula micropunctata Navicula minima

159 Appendix A (continued)

98-99 96-97 92-93 86-87 80-81 74-75 68-69 62-63 Taxon cm cm cm cm cm cm cm cm Navicula pseudoscutiformis 1 1 1 2 2 4 Navicula pupula 1 4 7 1 1 Navicula radiosa 1 2 Navicula "rectangle" Navicula seminulum 8 4 17 25 6 26 44 40 Navicula soehrensis var. hassiaca Navicula sp.1 Navicula sp.1 2 Navicula sublitissima 1 1 1 2 Navicula submuralis 4 7 4 12 5 Navicula submuralis (girdle) Navicula tridentula 1 1 1 Navicula variostriata 1 1 Navicula variostriata (small) 11 4 9 11 6 7 7 5 Navicula variostriata (small pointier) Navicula ventralis Navicula vitiosa 3 10 4 11 Navicula/Caloneis sp. Neidium affine Neidium ampliatum 2 3 1 3 1 2 1 1 Neidium bisulcatum Nitszchia c.f. radicula Nitzschia bryophila Nitzschia fonticola 2 1 2 Nitzschia gracilis Nitzschia inconspicua Nitzschia perminuta 9 6 1 10 4 14 3 Nitzschia sp. (BIG) Peronia fibula 0.5 1 2 Pinnularia balfouriana 1 1 1 Pinnularia barbell shaped Pinnularia c.f. borealis Pinnularia c.f. pulchra Pinnularia c.f. rupestris 1 1 Pinnularia c.f. viridis 1 5 4 17 15 1 1 6 Pinnularia divergentissima Pinnularia divergentissima var. martinii 1 Pinnularia gibba 1 1 Pinnularia interrupta 4 3 12 19 4 5 6 5 Pinnularia maior Pinnularia microstauron 2 3 Pinnularia microstauron (HUGE) Pinnularia nobilis Pinnularia nodosa Pinnularia subgibba Pinnularia viridis 1 3 1 3 1 Stauroneis anceps (bald/blank) 1 2 2 4 2 4 3

160 Appendix A (continued)

98-99 96-97 92-93 86-87 80-81 74-75 68-69 62-63 Taxon cm cm cm cm cm cm cm cm Stauroneis anceps (striated) Stauroneis phoenicenteron 2 2 Stauroneis tiny spp Stenopterobia anceps 0.5 Stenopterobia curvula Stenopterobia delicatissima Surirella c.f. linearis Surirella HUGE (length of scale bar) Surirella robusta Tabellaria flocculosa strain IV 6 7 5 5 5 5 3 3 Tetracyclus glans Total Diatoms 416.5 419.5 432 449.5 421 436.5 442 431 Chrysophyte Cysts 72 69 30 33 47 24 24 8 Protozoan plates 7 1 6 3 4 6 2 1 Phytoliths 0 0 0 0 0 0 0 0 Cyst:Diatom ratio 0.257 0.248 0.122 0.128 0.183 0.099 0.098 0.036

161 Appendix A (continued)

56-57 50-51 44-45 38-39 32-33 31-32 30-31 29-30 Taxon cm cm cm cm cm cm cm cm Achnanthes 2-dot Achnanthes acares 3 1 3 2 1 5 Achnanthes acares (blurry) Achnanthes bicapitata 2 3 4 3 2 1 11 Achnanthes bicapitata (small) Achnanthes biasolettiana v. subatomus 0 0 0 2 0 0 0 0 Achnanthes c.f. difficilima Achnanthes c.f. minutissima 2 2 5 Achnanthes c.f. rossii Achnanthes c.f. stolida 3 2 1 2 2 2 Achnanthes carissima 17 4 3 9 1 Achnanthes carissima (tall) 1 2 6 Achnanthes chlidanos Achnanthes curtissima 18 6 9 25 14 10 32 19 Achnanthes daoensis Achnanthes depressa 2 Achnanthes didyma Achnanthes flexella 1 2 2 1 Achnanthes girdle1 Achnanthes girdle2 Achnanthes girdle3 Achnanthes helvetica Achnanthes imperfecta Achnanthes impexiformis (MAF) Achnanthes kuelbsii 1 Achnanthes kriegeri 1 4 Achnanthes lacus-vulcani 2 2 2 5 2 1 7 9 Achnanthes laevis Achnanthes laterostrata Achnanthes laterostrata (straighter) Achnanthes levanderi 1 Achnanthes marginulata 4 1 5 1 2 2 4 Achnanthes minutissima 3 4 Achnanthes minutissima (small) Achnanthes nitidiformis Achnanthes oblongella Achnanthes petersenii 1 Achnanthes pusilla 1 1 Achnanthes saccula 2 1 Achnanthes scotica 26 3 5 14 7 11 25 16 Achnanthes sp.1 (AADW) Achnanthes sp.2(MAFp.150) Achnanthes sp.(lemon) Achnanthes suchlandtii Achnanthes subatomoides (aff) Achnanthes subatomoides Achnanthes thermalis

162 Appendix A (continued)

56-57 50-51 44-45 38-39 32-33 31-32 30-31 29-30 Taxon cm cm cm cm cm cm cm cm Achnanthes ventralis Actinella punctata Amphora ovalis 1 1 3 2 Amphora small 2-dot valve Aulacoseira c.f. ambigua Aulacoseira c.f. subarctica (MAF) 1 Aulacoseira distans (girdle) 1 1 1 4 Aulacoseira distans (valve) 1 1 Aulacoseira distans var. nivalis (girdle) 9 8 5 10 6 2 11 9 Aulacoseira distans var. nivalis (valve) 2 2 3 2 2 4 Aulacoseira lirata (girdle) 5 10 22 28 104 79 87 86 Aulacoseira lirata (valve) 9 47 40 26 32 38 20 26 Aulacoseira lirata var. biseriata (girdle) 87 104 87 65 17 4 6 Aulacoseira lirata var. biseriata (valve) 5 2 7 3 3 4 3 5 Aulacoseira perglabra (girdle) 7 9 21 6 10 21 16 24 Aulacoseira perglabra (valve) 8 34 15 9 18 25 10 10 Aulacoseira perglabra var. florinae (girdle) 1 Aulacoseira perglabra var. florinae (valve) 12 9 4 4 9 4 3 6 Aulacoseira sp. (super fine punctae) Brachysira brebissonii 3 6 6 2 2 1 Brachysira brebissonii (girdle) Brachysira brebissonii var. zellensis Brachysira sp1 (long) 1 4 Brachysira styriaca 1 2 Brachysira vitrea Caloneis c.f. lauta 2 2 1 Caloneis c.f. silicila Caloneis c.f. tenuis Caloneis c.f. tenuis FORM B Caloneis molaris c.f. Cymbella big girdle Cyclotella bodanica v. lemanica Cyclotella pseudostelligera 7 4 3 6 6 2 1 Cyclotella stelligera 2 1 1 Cyclotella ocellata 1 Cyclotella rossii Cymbella cesatii 1 Cymbella c.f. angustata 2 Cymbella c.f. cuspidata Cymbella c.f. descripta Cymbella c.f. ehrenbergii 1 Cymbella c.f. norvegica Cymbella c.f. tynnii Cymbella gaeumannii 18 11 18 7 11 21 23 Cymbella gracilis 1 1 Cymbella hebredica 4 5 2 5 1 2 7 Cymbellla lapponica 1 2

163 Appendix A (continued)

56-57 50-51 44-45 38-39 32-33 31-32 30-31 29-30 Taxon cm cm cm cm cm cm cm cm Cymbella lapponica (affinity) Cymbella mesiana 2 1 Cymbella microcephala 2 2 Cymbella naviculiformis Cymbella silesiaca 4 3 6 4 7 10 7 6 Cymbella sinuata Cymbella sp1 1 1 2 Diploneis c.f. elliptica Diploneis finnica Diploneis marginestriata 2 2 2 Diploneis parma (KLB) Diploneis smithii var. dilatata Eunotia arculus 2 Eunotia arcus 0.5 1 Eunotia bidentula Eunotia bilunaris 1 Eunotia bilunaris var. mucophila Eunotia c.f. pectinalis v. undulata Eunotia circumborealis 1 Eunota denticulata Eunotia diodon 2 0.5 Eunotia exigua Eunotia girdle1 Eunotia girdeHUGE Eunotia faba 2.5 0.5 2 Eunotia flexuosa 0.5 Eunotia incisa 1 1 1 1 Eunotia meisteri Eunotia monodon Eunotia nymanniana 0.5 Eunotia praerupta Eunotia rhynchocephala 1 2 1 Eunotia rhynchocephala var. satelles Eunotia serra Eunotia soleirolii/minor 1 Fragilaria brevistriata Fragilaria brevistriata var. papillosa Fragilaria capucina Fragilaria c.f. capucina c. mesolepta Fragilaria c.f. parasitica (but bigger) Fragilaria c.f. pinnata Fragilaria construens Fragilaria construens var. binodia Fragilaria construens var. pumila 3 Fragilaria construens var. venter 3 2 Fragilaria construens var. venter (diamond) Fragilaria pinnata

164 Appendix A (continued)

56-57 50-51 44-45 38-39 32-33 31-32 30-31 29-30 Taxon cm cm cm cm cm cm cm cm Fragilaria pseudoconstruens Fragilaria virescens var. exigua 52 66 50 66 91 102 65 94 Frustulia rhomboides c.f. v. amphipleuroides Frustulia rhomboides var. crassinervia 1 1 5 4 6 6 Frustulia rhomboides var. rhomboides 12 2 4 9 3 3 5 Frustulia rhomboides var. saxonica 2 Gomphonema c.f. truncatum Gomphonema gracile 2 Gomphonema parvulum 2 1 2 4 Gomphonema parvulum (small) Navicula aff. Achnanthes rossii Navicula aff. Disjuncta Navicula aff. humerosa Navicula barbell-like Navicula bryophila 8 4 1 4 6 Navicula c.f. agrestis Navicula c.f. bahusiensis Navicula c.f. cincta Navicula c.f. exilis 2 1 1 1 Navicula c.f. explanata 1 Navicula c.f. halophila Navicula c.f. medioconvexa Navicula c.f. minima Navicula c.f. pupula 1 Navicula c.f. submolesta (MAF) Navicula c.f. subrotundra Navicula cocconeiformis 2 2 2 Navicula crytocephala Navicula cryptotenella Navicula digitulus Navicula digitulus (longer) Navicula duerrenbergiana Navicula girdle 1 (small) Navicula pseudoscutiformis 1 2 0 0 0 1 2 2 Navicula girdle 3 Navicula girdle 4 Navicula girdle 5 (big) 2 Navicula schmassmannii 29 31 31 53 40 31 37 45 Navicula jaagii Navicula jaernefeltii 3 2 1 2 Navicula kuelbsii Navicula laticeps Navicula laevissima 1 Navicula leptostriata 1 2 Navicula mediocris 2 3 2 4 2 Navicula micropunctata Navicula minima

165 Appendix A (continued)

56-57 50-51 44-45 38-39 32-33 31-32 30-31 29-30 Taxon cm cm cm cm cm cm cm cm Navicula pseudoscutiformis 1 2 1 2 2 Navicula pupula 3 1 3 1 2 2 3 Navicula radiosa 3 2 Navicula "rectangle" Navicula seminulum 26 3 22 22 13 8 24 21 Navicula soehrensis var. hassiaca 1 Navicula sp.1 Navicula sp.1 Navicula sublitissima 3 2 5 4 1 Navicula submuralis 1 2 2 6 2 Navicula submuralis (girdle) Navicula tridentula 2 Navicula variostriata 3 2 Navicula variostriata (small) 17 5 16 16 11 6 10 12 Navicula variostriata (small pointier) Navicula ventralis 2 Navicula vitiosa 5 3 10 16 Navicula/Caloneis sp. Neidium affine Neidium ampliatum 2 3 Neidium bisulcatum Nitszchia c.f. radicula Nitzschia bryophila 1 Nitzschia fonticola 2 2 1 2 Nitzschia gracilis Nitzschia inconspicua Nitzschia perminuta 7 3 3 14 7 5 11 3 Nitzschia sp. (BIG) Peronia fibula 2 1 Pinnularia balfouriana 2 1 Pinnularia barbell shaped Pinnularia c.f. borealis Pinnularia c.f. pulchra 1 2 Pinnularia c.f. rupestris Pinnularia c.f. viridis 1 10 4 1 1 3 4 1 Pinnularia divergentissima Pinnularia divergentissima var. martinii 1 Pinnularia gibba 2 Pinnularia interrupta 5 5 4 3 5 4 15 8 Pinnularia maior 1 4 Pinnularia microstauron 1 4 3 Pinnularia microstauron (HUGE) Pinnularia nobilis Pinnularia nodosa Pinnularia subgibba Pinnularia viridis 1 2 1 Stauroneis anceps (bald/blank) 6 3 2 5 4 4 4 5

166 Appendix A (continued)

56-57 50-51 44-45 38-39 32-33 31-32 30-31 29-30 Taxon cm cm cm cm cm cm cm cm Stauroneis anceps (striated) Stauroneis phoenicenteron 1 1 2 1 Stauroneis tiny spp Stenopterobia anceps Stenopterobia curvula Stenopterobia delicatissima Surirella c.f. linearis 2 Surirella HUGE (length of scale bar) Surirella robusta Tabellaria flocculosa strain IV 4 2 3 4 2 3 4 Tetracyclus glans Total Diatoms 452.5 407 426.5 471.5 492 442 528.5 541 Chrysophyte Cysts 19 27 24 21 18 17 14 20 Protozoan plates 3 1 1 8 6 1 2 7 Phytoliths 0 0 1 0 0 0 0 0 Cyst:Diatom ratio 0.077 0.117 0.101 0.082 0.068 0.071 0.050 0.069

167 Appendix A (continued)

28-29 27-28 26-27 25-26 24-25 23-24 22-23 21-22 Taxon cm cm cm cm cm cm cm cm Achnanthes 2-dot Achnanthes acares 7 2 1 4 1 7 2 4 Achnanthes acares (blurry) Achnanthes bicapitata 4 2 2 10 1 2 4 4 Achnanthes bicapitata (small) Achnanthes biasolettiana v. subatomus 0 0 0 0 0 1 0 0 Achnanthes c.f. difficilima Achnanthes c.f. minutissima 2 Achnanthes c.f. rossii Achnanthes c.f. stolida 4 8 9 10 4 10 14 7 Achnanthes carissima 7 3 2 1 16 21 10 Achnanthes carissima (tall) 1 5 8 7 Achnanthes chlidanos 1 Achnanthes curtissima 31 20 12 23 13 35 28 13 Achnanthes daoensis Achnanthes depressa 1 Achnanthes didyma Achnanthes flexella 1 Achnanthes girdle1 Achnanthes girdle2 Achnanthes girdle3 Achnanthes helvetica Achnanthes imperfecta Achnanthes impexiformis (MAF) Achnanthes kuelbsii 2 2 Achnanthes kriegeri 4 3 2 1 2 Achnanthes lacus-vulcani 1 1 8 9 4 3 4 6 Achnanthes laevis Achnanthes laterostrata Achnanthes laterostrata (straighter) Achnanthes levanderi 4 4 Achnanthes marginulata 3 5 4 1 4 4 4 Achnanthes minutissima 2 3 2 4 Achnanthes minutissima (small) Achnanthes nitidiformis Achnanthes oblongella Achnanthes petersenii Achnanthes pusilla 1 2 1 Achnanthes saccula 1 2 Achnanthes scotica 22 18 11 10 11 20 22 20 Achnanthes sp.1 (AADW) Achnanthes sp.2(MAFp.150) Achnanthes sp.(lemon) Achnanthes suchlandtii Achnanthes subatomoides (aff) Achnanthes subatomoides Achnanthes thermalis 1

168 Appendix A (continued)

28-29 27-28 26-27 25-26 24-25 23-24 22-23 21-22 Taxon cm cm cm cm cm cm cm cm Achnanthes ventralis 1 2 Actinella punctata Amphora ovalis 1 2 1 1 2 Amphora small 2-dot valve Aulacoseira c.f. ambigua Aulacoseira c.f. subarctica (MAF) 2 Aulacoseira distans (girdle) 1 Aulacoseira distans (valve) 2 Aulacoseira distans var. nivalis (girdle) 5 4 7 11 10 6 6 9 Aulacoseira distans var. nivalis (valve) 2 4 1 1 6 6 4 5 Aulacoseira lirata (girdle) 68 105 75 59 80 50 42 66 Aulacoseira lirata (valve) 17 17 22 12 39 13 14 8 Aulacoseira lirata var. biseriata (girdle) 2 5 4 9 7 1 6 3 Aulacoseira lirata var. biseriata (valve) 1 6 2 7 1 1 4 2 Aulacoseira perglabra (girdle) 12 13 9 14 8 3 23 7 Aulacoseira perglabra (valve) 15 19 16 10 24 9 12 15 Aulacoseira perglabra var. florinae (girdle) Aulacoseira perglabra var. florinae (valve) 4 8 6 5 9 10 4 10 Aulacoseira sp. (super fine punctae) Brachysira brebissonii 4 1 2 1 1 1 Brachysira brebissonii (girdle) Brachysira brebissonii var. zellensis Brachysira sp1 (long) 2 Brachysira styriaca Brachysira vitrea 1 Caloneis c.f. lauta 2 2 4 Caloneis c.f. silicila Caloneis c.f. tenuis Caloneis c.f. tenuis FORM B Caloneis molaris c.f. Cymbella big girdle Cyclotella bodanica v. lemanica Cyclotella pseudostelligera 1 2 3 2 10 1 Cyclotella stelligera 3 1 2 Cyclotella ocellata Cyclotella rossii Cymbella cesatii Cymbella c.f. angustata Cymbella c.f. cuspidata Cymbella c.f. descripta Cymbella c.f. ehrenbergii 1 1 Cymbella c.f. norvegica Cymbella c.f. tynnii 2 Cymbella gaeumannii 7 12 15 11 11 8 14 18 Cymbella gracilis 1 Cymbella hebredica 2 11 2 3 2 5 1 3 Cymbellla lapponica 2 4 3 2 4

169 Appendix A (continued)

28-29 27-28 26-27 25-26 24-25 23-24 22-23 21-22 Taxon cm cm cm cm cm cm cm cm Cymbella lapponica (affinity) Cymbella mesiana Cymbella microcephala Cymbella naviculiformis 1 Cymbella silesiaca 7 11 1 5 4 9 5 3 Cymbella sinuata Cymbella sp1 Diploneis c.f. elliptica Diploneis finnica Diploneis marginestriata 2 2 2 1 4 1 Diploneis parma (KLB) Diploneis smithii var. dilatata Eunotia arculus 1 0.5 1 Eunotia arcus Eunotia bidentula 1 Eunotia bilunaris 0.5 0.5 1 Eunotia bilunaris var. mucophila Eunotia c.f. pectinalis v. undulata Eunotia circumborealis Eunota denticulata Eunotia diodon Eunotia exigua 1 Eunotia girdle1 2 Eunotia girdeHUGE 2 Eunotia faba 1.5 Eunotia flexuosa Eunotia incisa 1 1 0.5 0.5 0.5 2 Eunotia meisteri Eunotia monodon 0.5 Eunotia nymanniana 1 Eunotia praerupta Eunotia rhynchocephala 1 2 Eunotia rhynchocephala var. satelles 2 Eunotia serra 1 Eunotia soleirolii/minor 1 4 2 Fragilaria brevistriata Fragilaria brevistriata var. papillosa Fragilaria capucina 2 4 Fragilaria c.f. capucina c. mesolepta 2 Fragilaria c.f. parasitica (but bigger) Fragilaria c.f. pinnata Fragilaria construens Fragilaria construens var. binodia Fragilaria construens var. pumila 1 1 Fragilaria construens var. venter 1 1 Fragilaria construens var. venter (diamond) Fragilaria pinnata

170 Appendix A (continued)

28-29 27-28 26-27 25-26 24-25 23-24 22-23 21-22 Taxon cm cm cm cm cm cm cm cm Fragilaria pseudoconstruens Fragilaria virescens var. exigua 76 71 75 85 100 71 52 138 Frustulia rhomboides c.f. v. amphipleuroides 1 Frustulia rhomboides var. crassinervia 4 5 2 6 3 2 3 Frustulia rhomboides var. rhomboides 10 5 5 8 5 5 2 7 Frustulia rhomboides var. saxonica Gomphonema c.f. truncatum Gomphonema gracile 2 Gomphonema parvulum 2 5 2 2 1 Gomphonema parvulum (small) 4 1 1 Navicula aff. Achnanthes rossii Navicula aff. Disjuncta Navicula aff. humerosa 1 Navicula barbell-like 2 Navicula bryophila 1 1 2 1 1 1 Navicula c.f. agrestis Navicula c.f. bahusiensis Navicula c.f. cincta Navicula c.f. exilis 1 3 Navicula c.f. explanata Navicula c.f. halophila Navicula c.f. medioconvexa Navicula c.f. minima Navicula c.f. pupula 1 1 Navicula c.f. submolesta (MAF) Navicula c.f. subrotundra Navicula cocconeiformis 1 2 1 1 Navicula crytocephala Navicula cryptotenella Navicula digitulus 2 1 Navicula digitulus (longer) Navicula duerrenbergiana 1 Navicula girdle 1 (small) Navicula pseudoscutiformis 0 2 0 1 1 0 0 0 Navicula girdle 3 Navicula girdle 4 Navicula girdle 5 (big) Navicula schmassmannii 61 43 46 27 33 61 35 42 Navicula jaagii Navicula jaernefeltii 2 1 5 Navicula kuelbsii Navicula laticeps Navicula laevissima 2 Navicula leptostriata 2 4 1 Navicula mediocris 1 2 Navicula micropunctata Navicula minima

171 Appendix A (continued)

28-29 27-28 26-27 25-26 24-25 23-24 22-23 21-22 Taxon cm cm cm cm cm cm cm cm Navicula pseudoscutiformis 2 1 1 Navicula pupula 1 2 2 1 1 2 Navicula radiosa 4 1 2 Navicula "rectangle" Navicula seminulum 19 13 30 13 11 31 24 24 Navicula soehrensis var. hassiaca Navicula sp.1 Navicula sp.1 Navicula sublitissima 2 1 1 2 4 2 2 Navicula submuralis 5 2 4 6 5 Navicula submuralis (girdle) Navicula tridentula 1 1 Navicula variostriata 2 2 2 Navicula variostriata (small) 13 20 10 15 18 18 15 20 Navicula variostriata (small pointier) Navicula ventralis 2 1 1 Navicula vitiosa 3 4 Navicula/Caloneis sp. Neidium affine Neidium ampliatum 1 2 1 3 2 Neidium bisulcatum Nitszchia c.f. radicula Nitzschia bryophila 2 Nitzschia fonticola 2 2 5 2 Nitzschia gracilis Nitzschia inconspicua 2 Nitzschia perminuta 5 4 6 6 6 2 8 8 Nitzschia sp. (BIG) Peronia fibula 0.5 Pinnularia balfouriana 2 2 Pinnularia barbell shaped Pinnularia c.f. borealis Pinnularia c.f. pulchra Pinnularia c.f. rupestris 1 Pinnularia c.f. viridis 3 6 4 3 2 1 Pinnularia divergentissima Pinnularia divergentissima var. martinii 3 1 2 Pinnularia gibba Pinnularia interrupta 4 10 3 7 4 9 7 13 Pinnularia maior Pinnularia microstauron 1 3 1 3 Pinnularia microstauron (HUGE) Pinnularia nobilis Pinnularia nodosa Pinnularia subgibba Pinnularia viridis 1 Stauroneis anceps (bald/blank) 6 1 2 2 4 7 4

172 Appendix A (continued)

28-29 27-28 26-27 25-26 24-25 23-24 22-23 21-22 Taxon cm cm cm cm cm cm cm cm Stauroneis anceps (striated) Stauroneis phoenicenteron 1 2 3 1 2 Stauroneis tiny spp Stenopterobia anceps 0.5 0.5 4 Stenopterobia curvula Stenopterobia delicatissima Surirella c.f. linearis 1 Surirella HUGE (length of scale bar) 1 1 Surirella robusta 4 Tabellaria flocculosa strain IV 2 1 2 2 4 4 2 2 Tetracyclus glans 1 Total Diatoms 476 486 417.5 445.5 475 480.5 449 557 Chrysophyte Cysts 21 13 22 13 14 18 24 23 Protozoan plates 8 8 6 7 8 9 3 8 Phytoliths 0 0 0 0 0 0 0 0 Cyst:Diatom ratio 0.081 0.051 0.095 0.055 0.056 0.070 0.097 0.076

173 Appendix A (continued)

20-21 19-20 18-19 17-18 16-17 15-16 14-15 13-14 Taxon cm cm cm cm cm cm cm cm Achnanthes 2-dot Achnanthes acares 5 5 1 2 Achnanthes acares (blurry) Achnanthes bicapitata 1 8 4 5 2 2 3 1 Achnanthes bicapitata (small) Achnanthes biasolettiana v. subatomus 1 0 0 2 2 0 0 2 Achnanthes c.f. difficilima Achnanthes c.f. minutissima Achnanthes c.f. rossii Achnanthes c.f. stolida 17 9 11 3 8 2 9 6 Achnanthes carissima 14 5 5 5 4 7 Achnanthes carissima (tall) 3 1 4 1 Achnanthes chlidanos 1 1 1 Achnanthes curtissima 31 19 25 20 14 5 5 8 Achnanthes daoensis Achnanthes depressa Achnanthes didyma Achnanthes flexella 1 1 1 Achnanthes girdle1 Achnanthes girdle2 Achnanthes girdle3 Achnanthes helvetica Achnanthes imperfecta Achnanthes impexiformis (MAF) Achnanthes kuelbsii 2 1 3 Achnanthes kriegeri 1 2 3 1 1 Achnanthes lacus-vulcani 7 9 3 6 2 1 9 Achnanthes laevis Achnanthes laterostrata Achnanthes laterostrata (straighter) Achnanthes levanderi Achnanthes marginulata 5 2 8 2 5 2 4 Achnanthes minutissima 1 1 2 1 Achnanthes minutissima (small) Achnanthes nitidiformis Achnanthes oblongella Achnanthes petersenii Achnanthes pusilla Achnanthes saccula Achnanthes scotica 24 13 21 18 17 3 12 10 Achnanthes sp.1 (AADW) Achnanthes sp.2(MAFp.150) Achnanthes sp.(lemon) Achnanthes suchlandtii Achnanthes subatomoides (aff) Achnanthes subatomoides Achnanthes thermalis

174 Appendix A (continued)

20-21 19-20 18-19 17-18 16-17 15-16 14-15 13-14 Taxon cm cm cm cm cm cm cm cm Achnanthes ventralis Actinella punctata Amphora ovalis 4 3 1 Amphora small 2-dot valve Aulacoseira c.f. ambigua Aulacoseira c.f. subarctica (MAF) Aulacoseira distans (girdle) 1 Aulacoseira distans (valve) 2 1 1 Aulacoseira distans var. nivalis (girdle) 4 14 10 9 9 6 15 10 Aulacoseira distans var. nivalis (valve) 3 5 3 7 5 8 4 2 Aulacoseira lirata (girdle) 35 42 48 80 81 130 53 59 Aulacoseira lirata (valve) 7 20 10 9 10 9 9 14 Aulacoseira lirata var. biseriata (girdle) 4 6 2 3 6 7 8 14 Aulacoseira lirata var. biseriata (valve) 2 1 4 2 2 7 2 3 Aulacoseira perglabra (girdle) 10 14 13 15 14 29 6 11 Aulacoseira perglabra (valve) 11 13 8 19 19 33 24 25 Aulacoseira perglabra var. florinae (girdle) 2 Aulacoseira perglabra var. florinae (valve) 7 8 20 20 17 19 24 12 Aulacoseira sp. (super fine punctae) Brachysira brebissonii 1 2 2 1 1 2 Brachysira brebissonii (girdle) Brachysira brebissonii var. zellensis Brachysira sp1 (long) 3 1 1 1 1 1 Brachysira styriaca Brachysira vitrea 1 Caloneis c.f. lauta 1 3 Caloneis c.f. silicila Caloneis c.f. tenuis Caloneis c.f. tenuis FORM B Caloneis molaris c.f. Cymbella big girdle Cyclotella bodanica v. lemanica Cyclotella pseudostelligera 9 1 1 2 Cyclotella stelligera 2 1 Cyclotella ocellata Cyclotella rossii Cymbella cesatii Cymbella c.f. angustata Cymbella c.f. cuspidata Cymbella c.f. descripta Cymbella c.f. ehrenbergii 1 1 Cymbella c.f. norvegica 1 Cymbella c.f. tynnii Cymbella gaeumannii 24 29 24 14 7 4 13 7 Cymbella gracilis 1 Cymbella hebredica 4 2 2 2 1 3 9 Cymbellla lapponica

175 Appendix A (continued)

20-21 19-20 18-19 17-18 16-17 15-16 14-15 13-14 Taxon cm cm cm cm cm cm cm cm Cymbella lapponica (affinity) Cymbella mesiana 2 1 Cymbella microcephala Cymbella naviculiformis 1 1 Cymbella silesiaca 4 5 8 3 7 3 8 Cymbella sinuata Cymbella sp1 2 2 Diploneis c.f. elliptica Diploneis finnica Diploneis marginestriata 1 2 2 2 4 1 Diploneis parma (KLB) Diploneis smithii var. dilatata Eunotia arculus 2.5 1 Eunotia arcus 1 Eunotia bidentula Eunotia bilunaris 0.5 0.5 1 Eunotia bilunaris var. mucophila Eunotia c.f. pectinalis v. undulata Eunotia circumborealis Eunota denticulata Eunotia diodon 1 Eunotia exigua Eunotia girdle1 Eunotia girdeHUGE Eunotia faba 1 1 0.5 Eunotia flexuosa Eunotia incisa 1 1 1 0.5 Eunotia meisteri 1 Eunotia monodon 0.5 Eunotia nymanniana 2 Eunotia praerupta Eunotia rhynchocephala 1 2 1 Eunotia rhynchocephala var. satelles 2 1 Eunotia serra 1 1 1 Eunotia soleirolii/minor Fragilaria brevistriata 2 Fragilaria brevistriata var. papillosa Fragilaria capucina Fragilaria c.f. capucina c. mesolepta Fragilaria c.f. parasitica (but bigger) Fragilaria c.f. pinnata Fragilaria construens Fragilaria construens var. binodia Fragilaria construens var. pumila 2 Fragilaria construens var. venter 7 1 3 8 Fragilaria construens var. venter (diamond) Fragilaria pinnata 1

176 Appendix A (continued)

20-21 19-20 18-19 17-18 16-17 15-16 14-15 13-14 Taxon cm cm cm cm cm cm cm cm Fragilaria pseudoconstruens Fragilaria virescens var. exigua 129 95 70 113 104 103 106 119 Frustulia rhomboides c.f. v. amphipleuroides Frustulia rhomboides var. crassinervia 7 3 8 3 3 5 1 8 Frustulia rhomboides var. rhomboides 9 3 5 2 3 8 8 16 Frustulia rhomboides var. saxonica Gomphonema c.f. truncatum Gomphonema gracile 1 2 Gomphonema parvulum 2 2 2 2 2 2 Gomphonema parvulum (small) 2 Navicula aff. Achnanthes rossii Navicula aff. Disjuncta Navicula aff. humerosa Navicula barbell-like Navicula bryophila 2 1 3 Navicula c.f. agrestis Navicula c.f. bahusiensis Navicula c.f. cincta Navicula c.f. exilis 3 Navicula c.f. explanata 1 Navicula c.f. halophila Navicula c.f. medioconvexa Navicula c.f. minima Navicula c.f. pupula Navicula c.f. submolesta (MAF) Navicula c.f. subrotundra Navicula cocconeiformis 4 2 1 3 1 2 6 Navicula crytocephala Navicula cryptotenella Navicula digitulus Navicula digitulus (longer) Navicula duerrenbergiana Navicula girdle 1 (small) Navicula pseudoscutiformis 9 0 2 2 1 10 3 3 Navicula girdle 3 Navicula girdle 4 Navicula girdle 5 (big) Navicula schmassmannii 57 11 19 29 33 12 11 19 Navicula jaagii Navicula jaernefeltii 3 3 3 1 3 2 1 Navicula kuelbsii Navicula laticeps Navicula laevissima 1 2 Navicula leptostriata 1 1 1 1 Navicula mediocris 7 3 1 2 1 Navicula micropunctata Navicula minima

177 Appendix A (continued)

20-21 19-20 18-19 17-18 16-17 15-16 14-15 13-14 Taxon cm cm cm cm cm cm cm cm Navicula pseudoscutiformis 9 2 2 1 10 3 3 Navicula pupula 2 3 2 2 4 1 Navicula radiosa 2 1 1 2 1 1 Navicula "rectangle" Navicula seminulum 25 28 24 14 19 4 16 6 Navicula soehrensis var. hassiaca Navicula sp.1 Navicula sp.1 Navicula sublitissima 6 2 2 1 1 Navicula submuralis 10 2 5 1 Navicula submuralis (girdle) Navicula tridentula 1 2 Navicula variostriata 1 1 2 3 4 2 Navicula variostriata (small) 10 18 23 21 10 23 13 10 Navicula variostriata (small pointier) Navicula ventralis 1 2 1 Navicula vitiosa 3 Navicula/Caloneis sp. Neidium affine Neidium ampliatum 2 4 2 1 Neidium bisulcatum 1 Nitszchia c.f. radicula Nitzschia bryophila 2 1 Nitzschia fonticola 1 3 4 Nitzschia gracilis Nitzschia inconspicua Nitzschia perminuta 6 6 1 2 1 5 8 Nitzschia sp. (BIG) Peronia fibula 1 0.5 1 Pinnularia balfouriana 1 2 Pinnularia barbell shaped Pinnularia c.f. borealis Pinnularia c.f. pulchra 1 Pinnularia c.f. rupestris Pinnularia c.f. viridis 3 1 7 4 1 13 Pinnularia divergentissima Pinnularia divergentissima var. martinii 1 1 1 Pinnularia gibba 2 2 1 1 Pinnularia interrupta 8 15 13 6 4 7 6 8 Pinnularia maior 1 Pinnularia microstauron 3 3 1 2 1 Pinnularia microstauron (HUGE) 2 Pinnularia nobilis Pinnularia nodosa Pinnularia subgibba 1 1 Pinnularia viridis 1 Stauroneis anceps (bald/blank) 3 5 3 3 1 2 3 6

178 Appendix A (continued)

20-21 19-20 18-19 17-18 16-17 15-16 14-15 13-14 Taxon cm cm cm cm cm cm cm cm Stauroneis anceps (striated) 1 Stauroneis phoenicenteron 1 Stauroneis tiny spp Stenopterobia anceps 0.5 Stenopterobia curvula 0.5 Stenopterobia delicatissima 1 Surirella c.f. linearis 1 1 Surirella HUGE (length of scale bar) 1 1 Surirella robusta Tabellaria flocculosa strain IV 3 2 3 2 2 1 2 1 Tetracyclus glans Total Diatoms 571 479 429.5 485.5 450.5 493.5 428.5 465 Chrysophyte Cysts 11 21 26 17 28 27 18 13 Protozoan plates 7 2 6 3 7 4 4 6 Phytoliths 0 0 0 0 0 0 0 0 Cyst:Diatom ratio 0.037 0.081 0.108 0.065 0.111 0.099 0.078 0.053

179 Appendix A (continued)

12-13 11-12 10-11 9-10 8-9 7-8 5-6 4-5 Taxon cm cm cm cm cm cm cm cm Achnanthes 2-dot 1 Achnanthes acares 1 5 7 6 7 1 6 1 Achnanthes acares (blurry) Achnanthes bicapitata 4 4 5 2 5 4 3 3 Achnanthes bicapitata (small) Achnanthes biasolettiana v. subatomus 24 31 48 63 43 12 29 18 Achnanthes c.f. difficilima Achnanthes c.f. minutissima Achnanthes c.f. rossii Achnanthes c.f. stolida 27 11 17 16 11 10 10 14 Achnanthes carissima 13 4 15 18 11 7 8 14 Achnanthes carissima (tall) 2 3 2 5 1 8 3 Achnanthes chlidanos 1 Achnanthes curtissima 20 30 42 32 33 17 30 16 Achnanthes daoensis Achnanthes depressa Achnanthes didyma Achnanthes flexella 1 1 Achnanthes girdle1 Achnanthes girdle2 Achnanthes girdle3 Achnanthes helvetica Achnanthes imperfecta Achnanthes impexiformis (MAF) Achnanthes kuelbsii 1 2 1 1 Achnanthes kriegeri 1 1 1 1 1 Achnanthes lacus-vulcani 2 2 11 5 4 2 4 5 Achnanthes laevis Achnanthes laterostrata Achnanthes laterostrata (straighter) Achnanthes levanderi Achnanthes marginulata 4 3 4 8 11 9 6 6 Achnanthes minutissima 3 2 1 2 1 5 Achnanthes minutissima (small) Achnanthes nitidiformis Achnanthes oblongella Achnanthes petersenii Achnanthes pusilla 1 Achnanthes saccula 6 4 Achnanthes scotica 23 28 34 34 27 17 26 12 Achnanthes sp.1 (AADW) Achnanthes sp.2(MAFp.150) Achnanthes sp.(lemon) Achnanthes suchlandtii Achnanthes subatomoides (aff) Achnanthes subatomoides 1 Achnanthes thermalis

180 Appendix A (continued)

12-13 11-12 10-11 9-10 8-9 7-8 5-6 4-5 Taxon cm cm cm cm cm cm cm cm Achnanthes ventralis 2 Actinella punctata 0.5 2 Amphora ovalis 1 Amphora small 2-dot valve Aulacoseira c.f. ambigua Aulacoseira c.f. subarctica (MAF) Aulacoseira distans (girdle) 1 1 Aulacoseira distans (valve) 1 1 1 1 Aulacoseira distans var. nivalis (girdle) 20 9 18 19 18 17 12 6 Aulacoseira distans var. nivalis (valve) 3 4 2 3 6 2 13 2 Aulacoseira lirata (girdle) 64 62 44 34 32 60 18 34 Aulacoseira lirata (valve) 22 25 5 6 4 27 4 25 Aulacoseira lirata var. biseriata (girdle) 4 10 2 12 15 8 8 Aulacoseira lirata var. biseriata (valve) 4 2 1 3 2 2 Aulacoseira perglabra (girdle) 4 11 14 2 4 15 2 22 Aulacoseira perglabra (valve) 14 17 5 7 15 15 10 16 Aulacoseira perglabra var. florinae (girdle) 6 13 5 1 Aulacoseira perglabra var. florinae (valve) 18 11 15 10 19 18 26 12 Aulacoseira sp. (super fine punctae) Brachysira brebissonii 1 1 1 1 2 3 Brachysira brebissonii (girdle) 2 Brachysira brebissonii var. zellensis 1 Brachysira sp1 (long) 1 2 1 Brachysira styriaca Brachysira vitrea 1 1 Caloneis c.f. lauta 2 Caloneis c.f. silicila Caloneis c.f. tenuis 2 Caloneis c.f. tenuis FORM B 2 Caloneis molaris c.f. Cymbella big girdle Cyclotella bodanica v. lemanica Cyclotella pseudostelligera 2 1 2 2 3 2 8 Cyclotella stelligera 1 1 2 Cyclotella ocellata Cyclotella rossii Cymbella cesatii Cymbella c.f. angustata Cymbella c.f. cuspidata Cymbella c.f. descripta Cymbella c.f. ehrenbergii 1 Cymbella c.f. norvegica Cymbella c.f. tynnii Cymbella gaeumannii 10 16 17 6 25 14 15 13 Cymbella gracilis Cymbella hebredica 3 6 2 1 3 7 4 4 Cymbellla lapponica 1 2

181 Appendix A (continued)

12-13 11-12 10-11 9-10 8-9 7-8 5-6 4-5 Taxon cm cm cm cm cm cm cm cm Cymbella lapponica (affinity) 2 Cymbella mesiana Cymbella microcephala Cymbella naviculiformis 2 3 Cymbella silesiaca 2 11 5 6 5 6 14 3 Cymbella sinuata Cymbella sp1 2 Diploneis c.f. elliptica Diploneis finnica Diploneis marginestriata 1 3 2 3 Diploneis parma (KLB) Diploneis smithii var. dilatata Eunotia arculus Eunotia arcus 0.5 2 Eunotia bidentula Eunotia bilunaris 0.5 Eunotia bilunaris var. mucophila Eunotia c.f. pectinalis v. undulata Eunotia circumborealis Eunota denticulata 1 Eunotia diodon Eunotia exigua 2.5 Eunotia girdle1 Eunotia girdeHUGE Eunotia faba 1.5 1 Eunotia flexuosa Eunotia incisa 2 1 Eunotia meisteri 2 Eunotia monodon Eunotia nymanniana Eunotia praerupta 2 2 1 Eunotia rhynchocephala 2 1 1 Eunotia rhynchocephala var. satelles Eunotia serra Eunotia soleirolii/minor 1 Fragilaria brevistriata Fragilaria brevistriata var. papillosa Fragilaria capucina Fragilaria c.f. capucina c. mesolepta Fragilaria c.f. parasitica (but bigger) Fragilaria c.f. pinnata Fragilaria construens Fragilaria construens var. binodia Fragilaria construens var. pumila 2 Fragilaria construens var. venter 1 1 1 3 Fragilaria construens var. venter (diamond) Fragilaria pinnata

182 Appendix A (continued)

12-13 11-12 10-11 9-10 8-9 7-8 5-6 4-5 Taxon cm cm cm cm cm cm cm cm Fragilaria pseudoconstruens Fragilaria virescens var. exigua 68 43 78 60 64 85 84 100 Frustulia rhomboides c.f. v. amphipleuroides Frustulia rhomboides var. crassinervia 2 5 4 3 4 8 9 Frustulia rhomboides var. rhomboides 2 7 7 3 5 2 7 6 Frustulia rhomboides var. saxonica Gomphonema c.f. truncatum Gomphonema gracile 1 Gomphonema parvulum 1 1 2 Gomphonema parvulum (small) 2 Navicula aff. Achnanthes rossii Navicula aff. Disjuncta Navicula aff. humerosa 1 Navicula barbell-like 1 Navicula bryophila 4 5 5 5 4 Navicula c.f. agrestis 2 Navicula c.f. bahusiensis Navicula c.f. cincta Navicula c.f. exilis 1 1 3 4 1 2 1 Navicula c.f. explanata Navicula c.f. halophila Navicula c.f. medioconvexa Navicula c.f. minima 4 Navicula c.f. pupula Navicula c.f. submolesta (MAF) Navicula c.f. subrotundra Navicula cocconeiformis 1 1 3 2 Navicula crytocephala Navicula cryptotenella Navicula digitulus 1 1 1 3 Navicula digitulus (longer) Navicula duerrenbergiana Navicula girdle 1 (small) 2 4 Navicula pseudoscutiformis 18 18 14 6 6 7 6 5 Navicula girdle 3 9 4 Navicula girdle 4 2 2 Navicula girdle 5 (big) Navicula schmassmannii 30 22 29 12 9 9 0 17 Navicula jaagii Navicula jaernefeltii 1 1 Navicula kuelbsii Navicula laticeps Navicula laevissima 2 3 2 1 Navicula leptostriata 1 1 1 1 1 Navicula mediocris 4 Navicula micropunctata Navicula minima 2

183 Appendix A (continued)

12-13 11-12 10-11 9-10 8-9 7-8 5-6 4-5 Taxon cm cm cm cm cm cm cm cm Navicula pseudoscutiformis 18 18 14 6 4 3 6 5 Navicula pupula 2 2 2 3 1 1 1 Navicula radiosa 1 1 1 1 Navicula "rectangle" Navicula seminulum 20 19 10 37 19 10 8 13 Navicula soehrensis var. hassiaca Navicula sp.1 Navicula sp.1 Navicula sublitissima 3 4 6 3 6 4 1 Navicula submuralis 5 6 4 2 1 Navicula submuralis (girdle) 2 Navicula tridentula Navicula variostriata 1 1 4 9 2 2 5 Navicula variostriata (small) 11 10 12 0 12 5 8 0 Navicula variostriata (small pointier) Navicula ventralis 2 Navicula vitiosa Navicula/Caloneis sp. Neidium affine 2 Neidium ampliatum 1 2 1 2 2 Neidium bisulcatum 1 Nitszchia c.f. radicula Nitzschia bryophila 2 Nitzschia fonticola 2 1 Nitzschia gracilis Nitzschia inconspicua Nitzschia perminuta 3 3 2 2 3 5 4 Nitzschia sp. (BIG) Peronia fibula Pinnularia balfouriana Pinnularia barbell shaped Pinnularia c.f. borealis Pinnularia c.f. pulchra 1 1 2 1 1 Pinnularia c.f. rupestris Pinnularia c.f. viridis 13 9 1 10 2 Pinnularia divergentissima 1 Pinnularia divergentissima var. martinii 2 1 2 2 Pinnularia gibba 1 Pinnularia interrupta 6 7 6 6 10 13 8 6 Pinnularia maior Pinnularia microstauron 3 6 1 4 1 Pinnularia microstauron (HUGE) Pinnularia nobilis Pinnularia nodosa Pinnularia subgibba Pinnularia viridis Stauroneis anceps (bald/blank) 10 6 7 4 3 12 7 5

184 Appendix A (continued)

12-13 11-12 10-11 9-10 8-9 7-8 5-6 4-5 Taxon cm cm cm cm cm cm cm cm Stauroneis anceps (striated) Stauroneis phoenicenteron 1 2 2 1 Stauroneis tiny spp Stenopterobia anceps 1 2.5 1.5 Stenopterobia curvula Stenopterobia delicatissima Surirella c.f. linearis 1 1 2 1 1 Surirella HUGE (length of scale bar) 1 Surirella robusta Tabellaria flocculosa strain IV 3 2 2 1 3 3 Tetracyclus glans Total Diatoms 510 521 543 468.5 516 486 454 452 Chrysophyte Cysts 28 33 25 22 26 22 15 28 Protozoan plates 7 3 2 5 1 1 7 2 Phytoliths 0 0 0 0 0 0 0 0 Cyst:Diatom ratio 0.099 0.112 0.084 0.086 0.092 0.083 0.062 0.110

185 Appendix A (continued)

3-4 2-3 1-2 0-1 Taxon cm cm cm cm Achnanthes 2-dot Achnanthes acares 2 4 2 7 Achnanthes acares (blurry) Achnanthes bicapitata 5 Achnanthes bicapitata (small) Achnanthes biasolettiana v. subatomus 23 15 24 30 Achnanthes c.f. difficilima Achnanthes c.f. minutissima 2 Achnanthes c.f. rossii Achnanthes c.f. stolida 10 1 5 20 Achnanthes carissima 14 3 1 Achnanthes carissima (tall) Achnanthes chlidanos Achnanthes curtissima 25 16 32 46 Achnanthes daoensis Achnanthes depressa Achnanthes didyma Achnanthes flexella 1 1 Achnanthes girdle1 2 Achnanthes girdle2 4 Achnanthes girdle3 4 Achnanthes helvetica Achnanthes imperfecta Achnanthes impexiformis (MAF) Achnanthes kuelbsii 4 2 3 6 Achnanthes kriegeri 2 Achnanthes lacus-vulcani 5 15 6 11 Achnanthes laevis Achnanthes laterostrata Achnanthes laterostrata (straighter) Achnanthes levanderi Achnanthes marginulata 9 3 12 16 Achnanthes minutissima 2 3 3 Achnanthes minutissima (small) Achnanthes nitidiformis Achnanthes oblongella Achnanthes petersenii Achnanthes pusilla 2 4 Achnanthes saccula Achnanthes scotica 18 11 13 17 Achnanthes sp.1 (AADW) 1 2 Achnanthes sp.2(MAFp.150) Achnanthes sp.(lemon) Achnanthes suchlandtii Achnanthes subatomoides (aff) Achnanthes subatomoides 1 2 Achnanthes thermalis

186 Appendix A (continued)

3-4 2-3 1-2 0-1 Taxon cm cm cm cm Achnanthes ventralis 2 2 2 Actinella punctata 1 1.5 0.5 Amphora ovalis 1 Amphora small 2-dot valve 2 Aulacoseira c.f. ambigua Aulacoseira c.f. subarctica (MAF) Aulacoseira distans (girdle) 5 2 1 Aulacoseira distans (valve) 1 1 1 Aulacoseira distans var. nivalis (girdle) 10 20 18 Aulacoseira distans var. nivalis (valve) 13 8 9 Aulacoseira lirata (girdle) 37 23 14 8 Aulacoseira lirata (valve) 3 5 5 6 Aulacoseira lirata var. biseriata (girdle) 15 5 6 Aulacoseira lirata var. biseriata (valve) 4 5 1 Aulacoseira perglabra (girdle) 15 25 10 29 Aulacoseira perglabra (valve) 20 14 16 12 Aulacoseira perglabra var. florinae (girdle) 3 2 Aulacoseira perglabra var. florinae (valve) 11 11 9 7 Aulacoseira sp. (super fine punctae) Brachysira brebissonii 4 1 2 Brachysira brebissonii (girdle) Brachysira brebissonii var. zellensis Brachysira sp1 (long) Brachysira styriaca Brachysira vitrea Caloneis c.f. lauta Caloneis c.f. silicila Caloneis c.f. tenuis Caloneis c.f. tenuis FORM B Caloneis molaris c.f. Cymbella big girdle 2 Cyclotella bodanica v. lemanica Cyclotella pseudostelligera 10 23 52 48 Cyclotella stelligera 2 2 4 7 Cyclotella ocellata Cyclotella rossii Cymbella cesatii Cymbella c.f. angustata Cymbella c.f. cuspidata Cymbella c.f. descripta Cymbella c.f. ehrenbergii 1 Cymbella c.f. norvegica Cymbella c.f. tynnii Cymbella gaeumannii 19 23 8 15 Cymbella gracilis Cymbella hebredica 3 1 3 Cymbellla lapponica

187 Appendix A (continued)

3-4 2-3 1-2 0-1 Taxon cm cm cm cm Cymbella lapponica (affinity) Cymbella mesiana 1 Cymbella microcephala Cymbella naviculiformis 1 3 Cymbella silesiaca 4 10 4 4 Cymbella sinuata Cymbella sp1 Diploneis c.f. elliptica Diploneis finnica Diploneis marginestriata 1 Diploneis parma (KLB) Diploneis smithii var. dilatata Eunotia arculus 1 Eunotia arcus 0.5 Eunotia bidentula Eunotia bilunaris 0.5 0.5 Eunotia bilunaris var. mucophila 0.5 Eunotia c.f. pectinalis v. undulata Eunotia circumborealis Eunota denticulata Eunotia diodon Eunotia exigua 1 Eunotia girdle1 Eunotia girdeHUGE Eunotia faba Eunotia flexuosa 0.5 Eunotia incisa 1 1 Eunotia meisteri Eunotia monodon Eunotia nymanniana 1 Eunotia praerupta 2 2 4 Eunotia rhynchocephala 1 3 6 Eunotia rhynchocephala var. satelles 1 Eunotia serra 2 2 Eunotia soleirolii/minor Fragilaria brevistriata Fragilaria brevistriata var. papillosa Fragilaria capucina 2 Fragilaria c.f. capucina c. mesolepta Fragilaria c.f. parasitica (but bigger) Fragilaria c.f. pinnata 5 Fragilaria construens Fragilaria construens var. binodia Fragilaria construens var. pumila Fragilaria construens var. venter 13 Fragilaria construens var. venter (diamond) Fragilaria pinnata 6

188 Appendix A (continued)

3-4 2-3 1-2 0-1 Taxon cm cm cm cm Fragilaria pseudoconstruens Fragilaria virescens var. exigua 102 131 98 86 Frustulia rhomboides c.f. v. amphipleuroides Frustulia rhomboides var. crassinervia 5 Frustulia rhomboides var. rhomboides 2 5 2 Frustulia rhomboides var. saxonica 1 1 Gomphonema c.f. truncatum Gomphonema gracile 2 Gomphonema parvulum 2 3 4 Gomphonema parvulum (small) 3 Navicula aff. Achnanthes rossii Navicula aff. Disjuncta Navicula aff. humerosa Navicula barbell-like Navicula bryophila 3 1 1 2 Navicula c.f. agrestis Navicula c.f. bahusiensis Navicula c.f. cincta Navicula c.f. exilis 3 2 3 Navicula c.f. explanata Navicula c.f. halophila Navicula c.f. medioconvexa Navicula c.f. minima 4 4 Navicula c.f. pupula Navicula c.f. submolesta (MAF) Navicula c.f. subrotundra Navicula cocconeiformis 1 1 Navicula crytocephala Navicula cryptotenella 2 Navicula digitulus 2 1 Navicula digitulus (longer) Navicula duerrenbergiana Navicula girdle 1 (small) 2 7 4 Navicula pseudoscutiformis 2 9 1 6 Navicula girdle 3 2 2 Navicula girdle 4 4 Navicula girdle 5 (big) 2 4 Navicula schmassmannii 11 20 8 11 Navicula jaagii Navicula jaernefeltii 11 6 12 Navicula kuelbsii Navicula laticeps Navicula laevissima 2 Navicula leptostriata Navicula mediocris 2 3 Navicula micropunctata 2 Navicula minima

189 Appendix A (continued)

3-4 2-3 1-2 0-1 Taxon cm cm cm cm Navicula pseudoscutiformis 2 7 1 Navicula pupula 1 1 Navicula radiosa 2 3 1 Navicula "rectangle" Navicula seminulum 10 8 5 10 Navicula soehrensis var. hassiaca Navicula sp.1 Navicula sp.1 Navicula sublitissima 1 1 Navicula submuralis 1 1 Navicula submuralis (girdle) Navicula tridentula Navicula variostriata 2 4 5 Navicula variostriata (small) 0 0 0 0 Navicula variostriata (small pointier) Navicula ventralis Navicula vitiosa Navicula/Caloneis sp. 1 Neidium affine Neidium ampliatum 3 3 1 2 Neidium bisulcatum Nitszchia c.f. radicula Nitzschia bryophila Nitzschia fonticola 2 2 2 5 Nitzschia gracilis 1.5 2 Nitzschia inconspicua Nitzschia perminuta 8 9 24 23 Nitzschia sp. (BIG) Peronia fibula 0.5 Pinnularia balfouriana 1 Pinnularia barbell shaped Pinnularia c.f. borealis Pinnularia c.f. pulchra Pinnularia c.f. rupestris Pinnularia c.f. viridis Pinnularia divergentissima Pinnularia divergentissima var. martinii Pinnularia gibba Pinnularia interrupta 11 11 3 6 Pinnularia maior Pinnularia microstauron 2 1 2 2 Pinnularia microstauron (HUGE) Pinnularia nobilis Pinnularia nodosa Pinnularia subgibba Pinnularia viridis Stauroneis anceps (bald/blank) 8 2 3

190 Appendix A (continued)

3-4 2-3 1-2 0-1 Taxon cm cm cm cm Stauroneis anceps (striated) 3 Stauroneis phoenicenteron 1 1 1 Stauroneis tiny spp Stenopterobia anceps Stenopterobia curvula Stenopterobia delicatissima Surirella c.f. linearis 1 1 2 Surirella HUGE (length of scale bar) Surirella robusta Tabellaria flocculosa strain IV 2 6 6 2 Tetracyclus glans Total Diatoms 518 524 471.5 522 Chrysophyte Cysts 26 21 57 56 Protozoan plates 5 11 5 3 Phytoliths 0 0 0 0 Cyst:Diatom ratio 0.091 0.074 0.195 0.177

191 Appendix B. Most common diatom taxa, including their taxonomic authorities and modern synonyms, from the Lake TK-2 and Stygge Nunatak Pond sediment cores, as well as from modern microhabitat samples taken over five different field seasons from Stygge Nunatak Pond.

Taxon Authority Synonym Achnanthes Achnanthes biasolettiana var. Lange-Bertalot Achnanthidium biasolettiana subatomus var. subatomus A. carissima Lange-Bertalot --- A. curtissima Carter --- A. flexella (Kützing) P.T.Cleve Eucocconeis flexella A. impexa Lange-Bertalot A. laterostrata (Hustedt) Round & Bukhtiyarova Karayevia laterostrata A. lacus-vulcani Lange-Bertalot & Krammer A. marginulata (Grunow) Bukhtiyarova & Round Psammothidium marginulatum A. minutissima (Kützing) Czarnecki Achnanthidium minutissimum A. nitidiformis Lange-Bertalot A. scotica Psammothidium scoticum A. stolida (Krass.) Krass. A. suchlandtii Hustedt Aulacoseira A. distans (Ehrenberg) Simonsen --- A. distans var. nivalis (W. Smith) Haworth --- A. lirata (Ehrenberg) Ross --- A. lirata var. biseriata (Grunow) Haworth --- A. perglabra (Østrup) Haworth --- A. perglabra var. floriniae (Camburn) Haworth --- Cyclotella C. pseudostelligera Hustedt --- C. stelligera Cleve & Grunow in Cleve --- Cymbella C. angustata (W. Smith) Cleve C. cesatii Krammer Encyonopsis cesatii C. descripta (Hustedt) Krammer & Lange- Bertalot C. cf. designata C. cf. ehrenbergii Kützing C. gaeumannii (Meister) Krammer Encyonema gaeumannii C. gracilis (W.Smith in Gregory) Van Heurck Cymbella lunata; Encyonema lunatum C. hebridica (Gregory) Grunow ex Cleve E. hebridicum C. incerta (Grunow) Cleve C. lapponica C. mesiana C. microcephala Grunow in Van Heurck Encyonopsis microcephala C. naviculiformis (Auerswald) Krammer Cymbopleura naviculiformis C. cf. norvegica C. silesiaca (Bleisch) Mann in Round et al. Encyonema silesiacum C. sinuata Gregory Reimeria sinuata C. cf. tynnii

192 Appendix B (continued)

Taxon Authority Synonym Denticula D. kuetzingii Grunow D. subtilis Grunow Diploneis D. marginestriata Hustedt D. parma Cleve D. smithii var. dilatata (M. Perag.) Boyer Eunotia E. arcus Ehrenberg E. arculus (Grunow) Lange-Bertalot & Nörpel E. bidentula W.Smith E. bilunaris (Ehrenberg) Mills E. bilunaris var. mucophila Lange-Bertalot & Nörpel E. circumborealis E. denticulata (Brébisson) Rabenhorst E. diodon Ehrenberg E. exigua (Brébisson ex Kützing) Rabenhorst E. faba Ehrenberg --- E. flexuosa (Brébisson) Kützing E. incisa Gregory --- E. meisteri Hustedt E. minor (Kützing) Grunow in Van Heurck E. monodon Ehrenberg E. nymanniana Grunow E. pectinalis var. undulata (Ralfs) Rabh. E. praerupta Ehrenberg E. rhynchocephala Hustedt E. rhynchocephala var. Nörpel & Lange-Bertalot satelles E. serra Ehrenberg Fragilaria F. brevistriata Grunow in Van Heurck Pseudostaurosira brevistriata Williams & Round F. brevistriata var. papillosa (Cleve-Euler) comb. nov. Pseudostaurosira brevistriata var. papillosa F. construens Ehrenberg Staurosira construens F. construens var. binoda (Ehrenberg) Grunow Stauyrosira construens var. binoda F. construens var. pumila Grunow F. construens var. venter (Ehrenberg) Grunow in Van Staurosira construens var. Heurck venter F. cf. parasitica (W.Smith) Morales Pseudostaurosira. parasitica F. pinnata Ehrenberg Staurosirella pinnata F. pseudoconstruens Marciniak Pseudostaurosira pseudoconstruens F. virescens var. exigua (Grunow) Krammer & Lange- --- Bertalot

193 Appendix B (continued)

Taxon Authority Synonym Frustulia F. rhomboides (Ehrenberg) De Toni --- F. rhomboides var. Lange-Bertalot & Krammer F. crassinervia crassinervia F. rhomboides var. saxonica (Rabenhorst) De Toni F. saxonica Navicula N. digitulus Hustedt Naviculadicta digitulus N. exilis/cryptocephala N. halophila (Grunow ex Van Heurck) Mann Craticula halophila in Round et al. N. jaernefeltii Hustedt Cavinula jaernefeltii N. kuelbsii Lange-Bertalot Microstatus kuelbsii N. radiosa Kützing N. schmassmannii Hustedt --- N. seminulum (Grunow) Mann Sellaphora seminulum N. soehrensis (Krasske) Lange-Bertalot & Chamaepinnularia soehrensis Krammer N. cf. viridula (Kützing) Ehrenberg N. vulpina Kützing Nitzschia N. cf. alpina N. commutata Grunow N. cf. frustulum (Kützing) Grunow in Cleve & Grunow N. perminuta (Grunow) Peragallo --- N. cf. sublinearis Hustedt Pinnularia P. balfouriana P. cf. viridis (Nitzsch) Ehrenberg Stauroneis S. anceps Ehrenberg

194 Appendix C. Complete list of surface water chemistry measurements taken from Stygge Nunatak Pond over five different field seasons.

2006 2004 2001 1984 1983 Variable Units July 8 July 19 July 7 June 23 July 17 pH 8.32 8.58 8.40 June 10: 7.40 8.64 June 23: 7.66 COND μS/cm 432 9000 1090 June 10: 138 800 June 23: 425 Temp. ºC 12 12 8 June 10: 0.1 12 June 23: 4.0 NO3NO2-F mg/L < 0.005 < 0.005 0.013 NH3-N-F mg/L 0.065 0.128 0.064 CHLA μg/L 2.1 0.5 1.6 CHLA-COR μg/L Sus Int < 0.1 1.3 CL mg/L 35.4 101 143 99.3 100.3 SO4 mg/L 82.7 309 510 158.9 163.4 DOC mg/L 13.8 27.4 33.4 DIC mg/L 17.2 30.1 31.0 CA mg/L 22.9 64.4 87.4 30 34.4 MG mg/L 21.7 66.6 94.4 50.9 52.1 K mg/L 5.28 16.9 21.1 13.62 14.7 NA mg/L 26 84.5 110 75.5 75.4 NO2-N-F mg/L 0.001 0.003 0.003 POC mg/L 1.220 0.747 0.865

PON mg/L 0.080 0.051 0.053 SIO2 mg/L 0.60 1.31 1.21 3.81 5.55 SRP-P-F mg/L 0.0009 0.0026 0.0026 TKN-N-F mg/L 0.936 1.77 2.66 AG/E-MS μg/L 0.010 0.003 <0.001 AL/E-MS μg/L 48.1 22.5 60.0 AS/E-MS μg/L 0.30 0.72

195 Appendix C (continued)

2006 2004 2001 1984 1983 Variable Units July 8 July 19 July 7 June 23 July 17 B/E-MS μg/L 20.5 36.8 BA/E-MS μg/L 2.78 6.07 8.90 BE/E-MS μg/L 0.008 0.007 <.0002 BI/E-MS μg/L < 0.001 < 0.001 CD/E-MS μg/L 0.018 0.015 <.001 CO/E-MS μg/L 0.206 0.250 <.001 CR/E-MS μg/L 0.401 0.593 <.001 CU/E-MS μg/L 4.37 7.34 13.00 FE/E-MS μg/L 199 144 312 GA/E-MS μg/L 0.017 0.018 LA/E-MS μg/L 0.058 0.040 LI/E-MS μg/L 7.80 23.70 35.00 MN/E-MS μg/L 12.20 2.64 4.80 MO/E-MS μg/L 2.39 6.85 11.00 NI/E-MS μg/L 2.67 5.45 7.00 PB/E-MS μg/L 0.081 0.236 <0.005 RB/E-MS μg/L 0.75 2.03 SB/E-MS μg/L 0.011 < 0.001 SE/E-MS μg/L 0.08 0.16 SR/E-MS μg/L 85.9 236 347 TL/E-MS μg/L 0.002 0.006 U/E-MS μg/L 1.15 2.35 V/E-MS μg/L 0.500 0.496 <0.001 ZN/E-MS μg/L 0.69 1.12 1.00 TN-N-F mg/L 0.92 1.87 2.48 TP-P-F mg/L 0.0055 0.0096 0.0177 TP-P-UF mg/L 0.0161 0.0101 0.0105 0.0117 0.0149

196 Appendix D. Raw diatom count data from the short sediment core from Stygge Nunatak Pond.

0.0-0.5 0.5-1.0 1.0-1.5 1.5-2.0 2.0-2.5 2.5-3.0 3.0-3.5 3.5-4.0 Taxon cm cm cm cm cm cm cm cm Achnanthes minutissima 25 41 19 24 28 26 29 18 Achnanthes flexella 5 3 4 3 5 4 3 Achnanthes c.f. oestrupii Amphora c.f. acutiuscula 2 7 Amphora copulata 1 2 2 Amphora veneta 2 2 2 3 Cymbella angustata 12 7 9 9 20 38 24 17 Cymbella descripta 249 221 225 190 157 113 50 78 Cymbella c.f. gracilis Cymbella c.f. silesiaca Cymbella/Amphora smooth/blank 2 1 1 2 4 3 Cymbella sp1 Cymbella sp2 (curvy raphe) Cyclotella antiqua Cyclotella ocellata Fragilaria c.f. construens f. subsalina 6 2 Fragilaria c.f. lapponica (shorter) 9 2 Fragilaria construens v. venter 29 42 43 107 93 26 60 33 Navicula halophila 136 91 116 101 143 122 132 135 Navicula soehrensis 2 Navicula vulpina 2 5 2 2 5 7 7 11 Navicula c.f. viridula Navicula c.f. lapponica Navicula pupula Navicula tiny diamond Navicula sp1 2 Navicula sp2 (BIG) 2 Navicula sp raphe ends far apart Navicula girdles 1 2 Denticula kuetzingii 2 7 7 15 34 65 101 98 Neidium sp Nitzschia frustulum 4 4 5 8 14 12 Nitzschia c.f. inconspicua 6 6 6 2 2 5 Nitzschia BIG sp Pinnularia c.f. microstauron 2 1 Stauroneis phoenicenteron 1 1 Eunotia praerupta (HUGE) Total Diatoms 464 426 439 454 500 425 439 430 Chrysophyte Cysts 3 7 7 5 11 26 20 20

197 Appendix D (continued)

4.0-4.5 4.5-5.0 5.0-5.5 5.5-6.0 6.0-6.5 6.5-7.0 7.0-7.5 7.5-8.0 Taxon cm cm cm cm cm cm cm cm Achnanthes minutissima 14 23 12 14 4 11 7 11 Achnanthes flexella 1 4 1 5 3 2 Achnanthes c.f. oestrupii Amphora c.f. acutiuscula 1 5 2 2 2 Amphora copulata 4 2 3 2 Amphora veneta 2 5 2 1 Cymbella angustata 13 17 11 8 3 2 5 7 Cymbella descripta 45 45 48 44 35 40 30 33 Cymbella c.f. gracilis 2 Cymbella c.f. silesiaca Cymbella/Amphora smooth/blank 11 9 5 9 7 4 4 7 Cymbella sp1 1 Cymbella sp2 (curvy raphe) 1 1 Cyclotella antiqua Cyclotella ocellata 2 2 Fragilaria c.f. construens f. subsalina 2 2 1 4 6 6 9 1 Fragilaria c.f. lapponica (shorter) 8 8 1 10 5 4 Fragilaria construens v. venter 47 32 19 55 96 52 135 85 Navicula halophila 126 107 158 148 153 139 117 145 Navicula soehrensis 3 1 2 Navicula vulpina 13 15 6 6 7 9 10 16 Navicula c.f. viridula Navicula c.f. lapponica Navicula pupula 1 1 Navicula tiny diamond Navicula sp1 Navicula sp2 (BIG) 2 1 Navicula sp raphe ends far apart Navicula girdles 1 Denticula kuetzingii 126 143 141 129 122 124 135 123 Neidium sp 1 Nitzschia frustulum 18 14 18 15 19 28 23 16 Nitzschia c.f. inconspicua 4 2 2 Nitzschia BIG sp Pinnularia c.f. microstauron 1 1 1 4 1 Stauroneis phoenicenteron Eunotia praerupta (HUGE) Total Diatoms 421 438 437 440 458 431 496 460 Chrysophyte Cysts 17 29 24 22 18 25 19 21

198 Appendix D (continued)

8-8.5 8.5-9 9-9.5 9.5-10 10-10.5 10.5-11 11-11.5 Taxon cm cm cm cm cm cm cm Achnanthes minutissima 4 3 3 5 0 5 9 Achnanthes flexella 5 2 2 1 3 1 4 Achnanthes c.f. oestrupii Amphora c.f. acutiuscula 1 1 2 1 Amphora copulata 1 1 1 2 3 Amphora veneta 3 1 1 Cymbella angustata 1 3 2 3 2 Cymbella descripta 35 37 19 20 24 15 28 Cymbella c.f. gracilis Cymbella c.f. silesiaca Cymbella/Amphora smooth/blank 7 3 8 10 2 2 7 Cymbella sp1 Cymbella sp2 (curvy raphe) Cyclotella antiqua 1 Cyclotella ocellata 2 1 Fragilaria c.f. construens f. subsalina 3 4 3 Fragilaria c.f. lapponica (shorter) 2 4 1 1 1 Fragilaria construens v. venter 99 144 184 203 154 238 166 Navicula halophila 157 140 88 120 112 86 115 Navicula soehrensis 5 5 2 Navicula vulpina 6 16 14 13 20 11 16 Navicula c.f. viridula 1 6 2 6 1 Navicula c.f. lapponica 2 Navicula pupula 1 1 Navicula tiny diamond 2 Navicula sp1 Navicula sp2 (BIG) Navicula sp raphe ends far apart 1 Navicula girdles 1 Denticula kuetzingii 96 89 51 90 74 53 94 Neidium sp 2 Nitzschia frustulum 20 23 14 13 24 20 11 Nitzschia c.f. inconspicua 1 2 2 Nitzschia BIG sp Pinnularia c.f. microstauron 2 2 1 1 Stauroneis phoenicenteron Eunotia praerupta (HUGE) Total Diatoms 437 470 402 492 431 441 465 Chrysophyte Cysts 10 22 13 19 15 15 12

199 Appendix D (continued)

11.5-12 12-12.5 12.5-13 13-13.5 13.5-14 14-14.5 Taxon cm cm cm cm cm cm Achnanthes minutissima 4 8 1 0 5 4 Achnanthes flexella 3 4 4 2 1 Achnanthes c.f. oestrupii Amphora c.f. acutiuscula 2 3 Amphora copulata 2 1 Amphora veneta 1 1 3 1 3 Cymbella angustata 1 2 1 1 Cymbella descripta 20 24 15 25 36 25 Cymbella c.f. gracilis Cymbella c.f. silesiaca Cymbella/Amphora smooth/blank 3 3 5 3 9 3 Cymbella sp1 Cymbella sp2 (curvy raphe) Cyclotella antiqua 2 1 Cyclotella ocellata Fragilaria c.f. construens f. subsalina 1 2 4 3 Fragilaria c.f. lapponica (shorter) 1 2 3 1 Fragilaria construens v. venter 243 228 238 224 142 254 Navicula halophila 70 80 71 77 130 62 Navicula soehrensis 2 Navicula vulpina 5 7 7 13 11 6 Navicula c.f. viridula 2 3 3 6 3 Navicula c.f. lapponica Navicula pupula 1 Navicula tiny diamond Navicula sp1 Navicula sp2 (BIG) Navicula sp raphe ends far apart Navicula girdles 1 Denticula kuetzingii 72 93 79 85 99 68 Neidium sp 1 Nitzschia frustulum 5 15 21 10 20 17 Nitzschia c.f. inconspicua Nitzschia BIG sp Pinnularia c.f. microstauron 2 3 2 1 Stauroneis phoenicenteron 1 Eunotia praerupta (HUGE) Total Diatoms 434 473 450 459 466 449 Chrysophyte Cysts 6 9 8 16 13 8

200 Appendix D (continued)

14.5-15 15-15.5 15.5-16 16.0-16.5 16.5-17.0 17.0-17.5 Taxon cm cm cm cm cm cm Achnanthes minutissima 1 4 5 7 0 9 Achnanthes flexella 2 5 5 9 5 Achnanthes c.f. oestrupii Amphora c.f. acutiuscula 1 3 2 Amphora copulata 4 1 1 1 1 3 Amphora veneta 3 1 1 3 1 2 Cymbella angustata 1 3 2 4 2 Cymbella descripta 31 24 34 25 18 19 Cymbella c.f. gracilis Cymbella c.f. silesiaca 1 Cymbella/Amphora smooth/blank 1 1 6 4 4 1 Cymbella sp1 Cymbella sp2 (curvy raphe) Cyclotella antiqua 1 Cyclotella ocellata Fragilaria c.f. construens f. subsalina 1 9 Fragilaria c.f. lapponica (shorter) 4 2 4 3 Fragilaria construens v. venter 181 165 180 215 256 163 Navicula halophila 102 86 121 99 85 138 Navicula soehrensis 2 4 2 2 Navicula vulpina 8 10 13 13 13 17 Navicula c.f. viridula 5 4 3 6 6 3 Navicula c.f. lapponica Navicula pupula Navicula tiny diamond Navicula sp1 Navicula sp2 (BIG) Navicula sp raphe ends far apart Navicula girdles 1 Denticula kuetzingii 99 82 87 111 83 100 Neidium sp Nitzschia frustulum 3 20 31 20 6 22 Nitzschia c.f. inconspicua Nitzschia BIG sp Pinnularia c.f. microstauron 1 Stauroneis phoenicenteron 1 Eunotia praerupta (HUGE) 2 Total Diatoms 448 419 497 523 482 486 Chrysophyte Cysts 12 17 12 13 11 11

201 Appendix D (continued)

17.5-18.0 18.0-18.5 18.5-19.0 19.0-19.5 Taxon cm cm cm cm Achnanthes minutissima 6 6 7 5 Achnanthes flexella 5 5 2 Achnanthes c.f. oestrupii 1 Amphora c.f. acutiuscula 1 3 Amphora copulata 1 2 4 Amphora veneta 2 Cymbella angustata 2 5 2 3 Cymbella descripta 10 27 22 17 Cymbella c.f. gracilis Cymbella c.f. silesiaca Cymbella/Amphora smooth/blank 3 1 2 4 Cymbella sp1 Cymbella sp2 (curvy raphe) 1 4 Cyclotella antiqua 2 Cyclotella ocellata Fragilaria c.f. construens f. subsalina 19 4 2 Fragilaria c.f. lapponica (shorter) 2 1 8 2 Fragilaria construens v. venter 257 170 153 175 Navicula halophila 88 131 144 107 Navicula soehrensis 1 Navicula vulpina 4 14 8 13 Navicula c.f. viridula 2 3 4 6 Navicula c.f. lapponica Navicula pupula Navicula tiny diamond Navicula sp1 Navicula sp2 (BIG) Navicula sp raphe ends far apart Navicula girdles 1 Denticula kuetzingii 65 71 95 109 Neidium sp Nitzschia frustulum 18 18 18 9 Nitzschia c.f. inconspicua 2 2 Nitzschia BIG sp Pinnularia c.f. microstauron Stauroneis phoenicenteron 1 Eunotia praerupta (HUGE) Total Diatoms 483 450 484 464 Chrysophyte Cysts 17 11 18 15

202 Appendix D (continued)

19.5-20.0 20.0-20.5 20.5-21.0 21.0-21.5 Taxon cm cm cm cm Achnanthes minutissima 1 8 2 8 Achnanthes flexella 8 1 5 2 Achnanthes c.f. oestrupii Amphora c.f. acutiuscula 2 2 Amphora copulata 3 1 3 Amphora veneta 3 3 1 Cymbella angustata 2 2 1 4 Cymbella descripta 37 24 36 20 Cymbella c.f. gracilis Cymbella c.f. silesiaca 1 Cymbella/Amphora smooth/blank 5 2 Cymbella sp1 Cymbella sp2 (curvy raphe) Cyclotella antiqua Cyclotella ocellata Fragilaria c.f. construens f. subsalina 1 4 3 Fragilaria c.f. lapponica (shorter) 2 Fragilaria construens v. venter 154 228 181 259 Navicula halophila 95 58 75 60 Navicula soehrensis 2 4 6 Navicula vulpina 16 15 13 17 Navicula c.f. viridula 6 6 11 5 Navicula c.f. lapponica Navicula pupula Navicula tiny diamond Navicula sp1 2 Navicula sp2 (BIG) Navicula sp raphe ends far apart Navicula girdles 1 Denticula kuetzingii 79 51 85 59 Neidium sp Nitzschia frustulum 22 19 23 4 Nitzschia c.f. inconspicua Nitzschia BIG sp 1 Pinnularia c.f. microstauron Stauroneis phoenicenteron 1 Eunotia praerupta (HUGE) Total Diatoms 439 421 445 449 Chrysophyte Cysts 9 9 6 5

203 Appendix E. Raw diatom count data for the long sediment core from Stygge Nunatak Pond.

0-1 2-3 4-5 6-7 8-9 11-12 13-14 15-16 Taxon cm cm cm cm cm cm cm cm Achnanthes minutissima 76 83 22 11 10 1 11 Achnanthes flexella 13 7 2 2 3 3 13 2 Achnanthes c.f. oestrupii Achnanthes c.f. chlidanos Achnanthes c.f. marginulata Achnanthes subatomoides Amphora c.f. acutiuscula 2 1 1 Amphora sp1(big) Amphora sp2 3 1 1 Brachysira c.f. vitrea/neoexilis Brachysira c.f. serians Cymbella c.f. descripta 125 71 17 10 11 9 31 3 Cymbella c.f. angustata 15 13 5 1 1 4 1 Cymbella mystery Cymbella c.f. gracilis Cymbella c.f. hebredica Cymbella c.f. silesiaca Cymbella/Amphora smooth/blank 1 1 1 Cymbella sp1 Cymbella sp2 (curvy raphe) Cyclotella antiqua 3 Cyclotella bodanica var. lemanica Cyclotella ocellata Cyclotella cf. rossii Cyclotella stelligera Cyclotella pseudostelligera Fragilaria c.f. construens f. subsalina 1 3 Fragilaria c.f. lapponica (shorter) Fragilaria pinnata Fragilaria capucina Fragilaria brevistriata v.papillosa Fragilaria construens v. venter 6 9 296 321 330 352 237 404 Navicula halophila 174 145 27 19 22 9 29 14 Navicula soehrensis 9 7 2 2 11 3 Navicula vulpina 1 6 6 8 7 2 15 6 Navicula c.f. viridula 2 4 1 2 1 3 Navicula c.f. viridula var. rosellata p.515) Navicula c.f. digitulus Navicula c.f. lapponica Navicula c.f. leptostriata Navicula c.f. micropunctata Navicula pupula Navicula tiny diamond

204 Appendix E continued

0-1 2-3 4-5 6-7 8-9 11-12 13-14 15-16 Taxon cm cm cm cm cm cm cm cm Navicula sp1 Navicula sp2 (BIG) Navicula sp raphe ends far apart Navicula girdles 1 Navicula c.f. seminuloides 1 Denticula kuetzingii 6 56 64 29 39 34 46 20 Denticula subtilis Neidium sp Nitzschia frustulum 28 19 18 21 15 14 10 Nitzschia c.f. inconspicua Nitzschia c.f. gracilis Nitzschia c.f. commutata Pinnularia interrupta Pinnularia c.f. microstauron 2 Pinnularia c.f. intermedia Pinnularia c.f. borealis Pinnularia subgibba Stauroneis phoenicenteron Stenopterobia c.f. delicatissima Caloneis sp. Asterionella ralfsii Aulacoseira c.f. perglabra Aulacoseira c.f. perglabra v. florinae Aulacoseira c.f. subarctica Aulacoseira sp. Eunotia praerupta (HUGE) Eunotia c.f. exigua Eunotia c.f. arculus Eunotia triodon Eunotia musicola v. tridentula Frustulia rhomboides Tabellaria flocculosa strain 3p Tabellaria flocculosa strain 4 Total Diatoms 430 439 460 420 447 434 415 464 Chrysophyte Cysts 6 18 17 5 5 7 8 9

205 Appendix E (continued)

17-18 19-20 23-24 27-28 31-32 35-36 Taxon cm cm cm cm cm cm Achnanthes minutissima 3 2 2 1 Achnanthes flexella 7 3 2 2 1 Achnanthes c.f. oestrupii Achnanthes c.f. chlidanos Achnanthes c.f. marginulata Achnanthes subatomoides Amphora c.f. acutiuscula 2 Amphora sp1(big) Amphora sp2 1 1 1 2 Brachysira c.f. vitrea/neoexilis Brachysira c.f. serians Cymbella c.f. descripta 9 12 10 3 1 Cymbella c.f. angustata 1 2 Cymbella mystery Cymbella c.f. gracilis Cymbella c.f. hebredica Cymbella c.f. silesiaca Cymbella/Amphora smooth/blank 1 3 2 1 Cymbella sp1 Cymbella sp2 (curvy raphe) 2 Cyclotella antiqua 1 Cyclotella bodanica var. lemanica Cyclotella ocellata Cyclotella cf. rossii Cyclotella stelligera Cyclotella pseudostelligera Fragilaria c.f. construens f. subsalina 2 1 2 1 Fragilaria c.f. lapponica (shorter) Fragilaria pinnata Fragilaria capucina Fragilaria brevistriata v.papillosa Fragilaria construens v. venter 358 406 390 447 425 453 Navicula halophila 24 11 27 12 10 Navicula soehrensis 1 2 Navicula vulpina 7 8 6 4 7 4 Navicula c.f. viridula 1 1 1 Navicula c.f. viridula var. rosellata Navicula c.f. digitulus Navicula c.f. lapponica Navicula c.f. leptostriata Navicula c.f. micropunctata Navicula pupula Navicula tiny diamond

206 Appendix E (continued)

17-18 19-20 23-24 27-28 31-32 35-36 Taxon cm cm cm cm cm cm Navicula sp1(?) Navicula sp2 (BIG) Navicula sp raphe ends far apart Navicula girdles 1 Navicula c.f. seminuloides Denticula kuetzingii 16 16 35 10 3 Denticula subtilis Neidium sp Nitzschia frustulum 7 10 2 2 Nitzschia c.f. inconspicua Nitzschia c.f. gracilis Nitzschia c.f. commutata Pinnularia interrupta Pinnularia c.f. microstauron Pinnularia c.f. intermedia Pinnularia c.f. borealis Pinnularia subgibba Stauroneis phoenicenteron 1 Stenopterobia c.f. delicatissima Caloneis sp. Asterionella ralfsii Aulacoseira c.f. perglabra Aulacoseira c.f. perglabra v. florinae Aulacoseira c.f. subarctica Aulacoseira sp. Eunotia praerupta (HUGE) Eunotia c.f. exigua Eunotia c.f. arculus Eunotia triodon Eunotia musicola v. tridentula Frustulia rhomboides Tabellaria flocculosa strain 3p Tabellaria flocculosa strain 4 Total Diatoms 438 473 480 479 463 458 Chrysophyte Cysts 5 5 3 1 8 1

207 Appendix E (continued)

40-42 42-43 47-50 56-58.5 61-64 69-71 Taxon cm cm cm cm cm cm Achnanthes minutissima 1 Achnanthes flexella 2 Achnanthes c.f. oestrupii Achnanthes c.f. chlidanos Achnanthes c.f. marginulata Achnanthes subatomoides Amphora c.f. acutiuscula Amphora sp1(big) 1 Amphora sp2 Brachysira c.f. vitrea/neoexilis Brachysira c.f. serians Cymbella c.f. descripta 1 Cymbella c.f. angustata Cymbella mystery Cymbella c.f. gracilis Cymbella c.f. hebredica Cymbella c.f. silesiaca Cymbella/Amphora smooth/blank Cymbella sp1 Cymbella sp2 (curvy raphe) 1 Cyclotella antiqua Cyclotella bodanica var. lemanica Cyclotella ocellata Cyclotella cf. rossii 1 Cyclotella stelligera Cyclotella pseudostelligera Fragilaria c.f. construens f. subsalina 2 Fragilaria c.f. lapponica (shorter) 1 Fragilaria pinnata Fragilaria capucina Fragilaria brevistriata v.papillosa Fragilaria construens v. venter 600 680 656 630 452 376 Navicula halophila 2 Navicula soehrensis Navicula vulpina 1 2 19 36 Navicula c.f. viridula 1 1 Navicula c.f. viridula var. rosellata Navicula c.f. digitulus Navicula c.f. lapponica Navicula c.f. leptostriata Navicula c.f. micropunctata Navicula pupula Navicula tiny diamond

208 Appendix E (continued)

40-42 42-43 47-50 56-58.5 61-64 69-71 Taxon cm cm cm cm cm cm Navicula sp1(?) Navicula sp2 (BIG) Navicula sp raphe ends far apart Navicula girdles 1 Navicula c.f. seminuloides Denticula kuetzingii 1 2 34 54 Denticula subtilis Neidium sp Nitzschia frustulum 2 4 4 Nitzschia c.f. inconspicua Nitzschia c.f. gracilis Nitzschia c.f. commutata Pinnularia interrupta Pinnularia c.f. microstauron Pinnularia c.f. intermedia Pinnularia c.f. borealis Pinnularia subgibba Stauroneis phoenicenteron Stenopterobia c.f. delicatissima Caloneis sp. Asterionella ralfsii Aulacoseira c.f. perglabra Aulacoseira c.f. perglabra v. florinae Aulacoseira c.f. subarctica Aulacoseira sp. Eunotia praerupta (HUGE) Eunotia c.f. exigua 1 Eunotia c.f. arculus Eunotia triodon Eunotia musicola v. tridentula Frustulia rhomboides Tabellaria flocculosa strain 3p Tabellaria flocculosa strain 4 Total Diatoms 602 682 657 635 513 479 Chrysophyte Cysts 0 0 0 3 7 5

209 Appendix E (continued)

86-89 92-95 104-107 116-119 119-122 128-131 Taxon cm cm cm cm cm cm Achnanthes minutissima 1 1 1 Achnanthes flexella 1 Achnanthes c.f. oestrupii Achnanthes c.f. chlidanos Achnanthes c.f. marginulata Achnanthes subatomoides Amphora c.f. acutiuscula 4 Amphora sp1(big) Amphora sp2 Brachysira c.f. vitrea/neoexilis 1 1 Brachysira c.f. serians Cymbella c.f. descripta Cymbella c.f. angustata 19 23 22 18 21 25 Cymbella mystery 2 2 3 5 4 Cymbella c.f. gracilis Cymbella c.f. hebredica Cymbella c.f. silesiaca Cymbella/Amphora smooth/blank Cymbella sp1 Cymbella sp2 (curvy raphe) Cyclotella antiqua Cyclotella bodanica var. lemanica Cyclotella ocellata Cyclotella cf. rossii Cyclotella stelligera 1 1 Cyclotella pseudostelligera Fragilaria c.f. construens f. subsalina Fragilaria c.f. lapponica (shorter) Fragilaria pinnata Fragilaria capucina Fragilaria brevistriata v.papillosa Fragilaria construens v. venter 304 280 304 314 300 143 Navicula halophila 1 4 0 3 Navicula soehrensis Navicula vulpina 51 46 44 58 62 82 Navicula c.f. viridula 1 3 1 3 4 3 Navicula c.f. viridula var. rosellata Navicula c.f. digitulus Navicula c.f. lapponica Navicula c.f. leptostriata Navicula c.f. micropunctata 1 Navicula pupula Navicula tiny diamond

210 Appendix E (continued)

86-89 92-95 104-107 116-119 119-122 128-131 Taxon cm cm cm cm cm cm Navicula sp1(?) Navicula sp2 (BIG) Navicula sp raphe ends far apart Navicula girdles 1 Navicula c.f. seminuloides Denticula kuetzingii 65 53 38 15 21 38 Denticula subtilis 2 1 Neidium sp Nitzschia frustulum 9 2 3 Nitzschia c.f. inconspicua Nitzschia c.f. gracilis Nitzschia c.f. commutata Pinnularia interrupta Pinnularia c.f. microstauron Pinnularia c.f. intermedia Pinnularia c.f. borealis Pinnularia subgibba Stauroneis phoenicenteron 1 Stenopterobia c.f. delicatissima 0.5 Caloneis sp. Asterionella ralfsii Aulacoseira c.f. perglabra Aulacoseira c.f. perglabra v. florinae Aulacoseira c.f. subarctica Aulacoseira sp. Eunotia praerupta (HUGE) Eunotia c.f. exigua Eunotia c.f. arculus 1 Eunotia triodon 1 Eunotia musicola v. tridentula Frustulia rhomboides 1 Tabellaria flocculosa strain 3p Tabellaria flocculosa strain 4 Total Diatoms 443.5 409 421 418 422 306 Chrysophyte Cysts 0 5 4 3 3 5

211 Appendix E (continued)

142-145 149-152 160-163 167-170 195-198 204-207 Taxon cm cm cm cm cm cm Achnanthes minutissima 2 7 4 Achnanthes flexella Achnanthes c.f. oestrupii Achnanthes c.f. chlidanos Achnanthes c.f. marginulata 2 1 Achnanthes subatomoides Amphora c.f. acutiuscula 1 4 1 2 Amphora sp1(big) 1 Amphora sp2 Brachysira c.f. vitrea/neoexilis 1 1 Brachysira c.f. serians 1 Cymbella c.f. descripta Cymbella c.f. angustata 1 20 16 17 7 Cymbella mystery 10 6 6 2 Cymbella c.f. gracilis Cymbella c.f. hebredica Cymbella c.f. silesiaca Cymbella/Amphora smooth/blank Cymbella sp1 Cymbella sp2 (curvy raphe) Cyclotella antiqua 1 Cyclotella bodanica var. lemanica Cyclotella ocellata Cyclotella cf. rossii Cyclotella stelligera 1 Cyclotella pseudostelligera Fragilaria c.f. construens f. subsalina 1 2 3 1 Fragilaria c.f. lapponica (shorter) 1 2 Fragilaria pinnata 2 Fragilaria capucina Fragilaria brevistriata v.papillosa 1 Fragilaria construens v. venter 348 238 203 206 182 204 Navicula halophila 2 2 Navicula soehrensis 1 Navicula vulpina 52 94 107 60 100 74 Navicula c.f. viridula 2 10 5 7 10 4 Navicula c.f. viridula var. rosellata 1 Navicula c.f. digitulus Navicula c.f. lapponica Navicula c.f. leptostriata Navicula c.f. micropunctata Navicula pupula Navicula tiny diamond

212 Appendix E (continued)

142-145 149-152 160-163 167-170 195-198 204-207 Taxon cm cm cm cm cm cm Navicula sp1(?) Navicula sp2 (BIG) Navicula sp raphe ends far apart Navicula girdles 1 Navicula c.f. seminuloides Denticula kuetzingii 9 15 19 27 9 7 Denticula subtilis 1 2 7 1 3 Neidium sp Nitzschia frustulum 3 11 6 5 4 2 Nitzschia c.f. inconspicua Nitzschia c.f. gracilis Nitzschia c.f. commutata 1 2 2.5 Pinnularia interrupta 1 1 Pinnularia c.f. microstauron Pinnularia c.f. intermedia 3 Pinnularia c.f. borealis Pinnularia subgibba Stauroneis phoenicenteron 1 Stenopterobia c.f. delicatissima Caloneis sp. 1 2 2 Asterionella ralfsii Aulacoseira c.f. perglabra Aulacoseira c.f. perglabra v. florinae 1 Aulacoseira c.f. subarctica Aulacoseira sp. Eunotia praerupta (HUGE) Eunotia c.f. exigua Eunotia c.f. arculus Eunotia triodon Eunotia musicola v. tridentula 1 Frustulia rhomboides Tabellaria flocculosa strain 3p 1 Tabellaria flocculosa strain 4 1 Total Diatoms 422 409 370 353 335 302.5 Chrysophyte Cysts 6 4 4 12 2 1

213 Appendix E (continued)

214-217 223-226 234-236 245-248 254-256.67 Taxon cm cm cm cm cm Achnanthes minutissima Achnanthes flexella Achnanthes c.f. oestrupii Achnanthes c.f. chlidanos 1 Achnanthes c.f. marginulata Achnanthes subatomoides 2 Amphora c.f. acutiuscula Amphora sp1(big) Amphora sp2 Brachysira c.f. vitrea/neoexilis 1 Brachysira c.f. serians Cymbella c.f. descripta Cymbella c.f. angustata 1 Cymbella mystery Cymbella c.f. gracilis Cymbella c.f. hebredica 1 Cymbella c.f. silesiaca 1 Cymbella/Amphora smooth/blank Cymbella sp1 Cymbella sp2 (curvy raphe) Cyclotella antiqua 1 Cyclotella bodanica var. lemanica 1 Cyclotella ocellata Cyclotella cf. rossii Cyclotella stelligera 1 Cyclotella pseudostelligera 2 Fragilaria c.f. construens f. subsalina 2 3 Fragilaria c.f. lapponica (shorter) 1 Fragilaria pinnata Fragilaria capucina 1 Fragilaria brevistriata v.papillosa Fragilaria construens v. venter 232 169 163 24 172 Navicula halophila 1 1 1 Navicula soehrensis Navicula vulpina 37 27 24 4 3 Navicula c.f. viridula 5 3 3 Navicula c.f. viridula var. rosellata Navicula c.f. digitulus 1 Navicula c.f. lapponica Navicula c.f. leptostriata 1 Navicula c.f. micropunctata Navicula pupula Navicula tiny diamond

214 Appendix E (continued)

214-217 223-226 234-236 245-248 254-256.67 Taxon cm cm cm cm cm Navicula sp1(?) Navicula sp2 (BIG) Navicula sp raphe ends far apart Navicula girdles 1 Navicula c.f. seminuloides Denticula kuetzingii 7 2 4 Denticula subtilis 1 Neidium sp 2 Nitzschia frustulum 5 2 Nitzschia c.f. inconspicua Nitzschia c.f. gracilis 2 Nitzschia c.f. commutata 0.5 1.5 Pinnularia interrupta Pinnularia c.f. microstauron Pinnularia c.f. intermedia Pinnularia c.f. borealis Pinnularia subgibba Stauroneis phoenicenteron Stenopterobia c.f. delicatissima Caloneis sp. Asterionella ralfsii 1 1 Aulacoseira c.f. perglabra 1 Aulacoseira c.f. perglabra v. florinae Aulacoseira c.f. subarctica 1 Aulacoseira sp. Eunotia praerupta (HUGE) Eunotia c.f. exigua Eunotia c.f. arculus Eunotia triodon Eunotia musicola v. tridentula Frustulia rhomboides Tabellaria flocculosa strain 3p Tabellaria flocculosa strain 4 Total Diatoms 303.5 201 206.5 29 181 Chrysophyte Cysts 5 2 3 0 1

215 Appendix E (continued)

276-279 288-291 311.33- 315-317 317-322 Taxon cm cm 315 cm cm cm Achnanthes minutissima 2 Achnanthes flexella Achnanthes c.f. oestrupii Achnanthes c.f. chlidanos Achnanthes c.f. marginulata Achnanthes subatomoides 1 Amphora c.f. acutiuscula Amphora sp1(big) Amphora sp2 Brachysira c.f. vitrea/neoexilis Brachysira c.f. serians Cymbella c.f. descripta 2 Cymbella c.f. angustata Cymbella mystery Cymbella c.f. gracilis Cymbella c.f. hebredica Cymbella c.f. silesiaca Cymbella/Amphora smooth/blank Cymbella sp1 Cymbella sp2 (curvy raphe) Cyclotella antiqua Cyclotella bodanica var. lemanica Cyclotella ocellata Cyclotella cf. rossii Cyclotella stelligera 1 1 Cyclotella pseudostelligera 2 Fragilaria c.f. construens f. subsalina 2 Fragilaria c.f. lapponica (shorter) Fragilaria pinnata Fragilaria capucina Fragilaria brevistriata v.papillosa Fragilaria construens v. venter 191 198 199 203 196 Navicula halophila 1 Navicula soehrensis Navicula vulpina 5 2 2 2 Navicula c.f. viridula 3 Navicula c.f. viridula var. rosellata Navicula c.f. digitulus Navicula c.f. lapponica Navicula c.f. leptostriata Navicula c.f. micropunctata Navicula pupula Navicula tiny diamond

216 Appendix E (continued)

276-279 288-291 311.33-315 315-317 317-322 Taxon cm cm cm cm cm Navicula sp1(?) Navicula sp2 (BIG) Navicula sp raphe ends far apart Navicula girdles 1 Navicula c.f. seminuloides Denticula kuetzingii 2 1 Denticula subtilis 2 Neidium sp Nitzschia frustulum Nitzschia c.f. inconspicua Nitzschia c.f. gracilis Nitzschia c.f. commutata Pinnularia interrupta Pinnularia c.f. microstauron Pinnularia c.f. intermedia Pinnularia c.f. borealis 1 Pinnularia subgibba 1 Stauroneis phoenicenteron Stenopterobia c.f. delicatissima Caloneis sp. Asterionella ralfsii Aulacoseira c.f. perglabra Aulacoseira c.f. perglabra v. florinae Aulacoseira c.f. subarctica 1 1 Aulacoseira sp. 1 Eunotia praerupta (HUGE) Eunotia c.f. exigua Eunotia c.f. arculus Eunotia triodon Eunotia musicola v. tridentula Frustulia rhomboides Tabellaria flocculosa strain 3p Tabellaria flocculosa strain 4 Total Diatoms 205 205 203 206 204 Chrysophyte Cysts 2 1 2 3 7

217 Appendix F. Raw diatom count data from the modern microhabitat samples from Stygge Nunatak Pond, taken over five different field seasons. Taxon 367-83 368-83 369-83 370-83 4-84 5-84 12-84 145-84 Achnanthes minutissima 347 204 290 443 6 6 233 315 Achnanthes flexella 1 9 7 54 2 8 30 Achnanthes cf. kryophila Achnanthes cf. marginulata Achnanthes cf. ziegleri Amphora species 1 4 1 2 18 11 2 Amphora species 1 (longer) Amphora species 2 2 2 1 6 Amphora cf. acutiuscula 1 6 Amphora smooth/blank 1 Cymbella descripta 53 210 132 43 1 10 192 138 Cymbella angustata 2 6 5 4 9 8 Cymbella cf. incerta 6 30 12 13 Cymbella cf. silesiaca Cymbella cf. naviculiformis Cyclotella pseudostelligera 2 Fragilaria construens Fragilaria cf. crotonensis Fragilaria brevistriata Fragilaria cf. lapponica Fragilaria construens var. venter 4 5 4 2 485 344 0 4 Navicula c.f. halophila 2 10 5 6 0 7 17 11 Navicula c.f. halophilioides Navicula vulpina 11 4 2 Navicula soehrensis 2 6 2 2 4 16 Navicula cf. bryophila Navicula cf. exilis/cryptocephala 3 3 2 9 8 Navicula cf. salinarum 2 5 Navicula cf. sublitissima 1 Navicula sp. Denticula kuetzingii 4 9 Denticula subtilis Denticula cf. valida 3 Nitzschia frustulum 1 15 Nitzschia frustulum (long) Nitzschia frustulum (long, coarse) striae) Nitzschia (BIG sp) 1 Caloneis cf. silicula 5 6 2 10 0 0 7 18 Caloneis sp. Cocconeis cf. placentula Cocconeis sp. (girdles) Neidium sp. (ampliatum?) 1 Pinnularia sp. Pinnularia sp. Chunky girdles Pinnularia interrupta 1 Stauroneis anceps Stauroneis phoenicenteron 1 Aulacoseira cf. distans Aulacoseira small sp Aulacoseira cf. italica Total Diatoms 417 454 467 634 498 408 507 570 Chrysophyte Cysts 0 1 1 2 0 3 8 4

218 Appendix F (continued)

Taxon 11-84 146-84 335-4 338-84 143-84 8-84 9-84 149-84 Achnanthes minutissima 254 300 319 335 5 350 319 119 Achnanthes flexella 16 20 29 23 61 9 42 Achnanthes cf. kryophila 1 Achnanthes cf. marginulata 1 Achnanthes cf. ziegleri 2 Amphora species 1 5 4 9 4 6 10 Amphora species 1 (longer) 3 1 2 Amphora species 2 1 3 2 1 2 Amphora cf. acutiuscula 1 10 3 Amphora smooth/blank 2 Cymbella descripta 197 184 24 101 4 31 147 77 Cymbella angustata 3 4 4 2 74 Cymbella cf. incerta 1 2 4 4 12 2 29 Cymbella cf. silesiaca 1 Cymbella cf. naviculiformis 1 Cyclotella pseudostelligera 1 Fragilaria construens 7 Fragilaria cf. crotonensis 1 Fragilaria brevistriata 2 Fragilaria cf. lapponica Fragilaria construens var. venter 3 0 5 2 36 0 6 0 Navicula c.f. halophila 9 11 2 6 1 0 1 5 Navicula c.f. halophilioides 2 Navicula vulpina 2 3 15 3 Navicula soehrensis 13 4 8 12 5 12 Navicula cf. bryophila Navicula cf. exilis/cryptocephala 6 11 5 10 7 2 Navicula cf. salinarum 3 Navicula cf. sublitissima Navicula sp. 1 Denticula kuetzingii 3 2 Denticula subtilis Denticula cf. valida Nitzschia frustulum 2 11 Nitzschia frustulum (long) Nitzschia frustulum (long, coarse) Nitzschia (BIG sp) 0.5 1.5 Caloneis cf. silicula 4 2 4 0 2 10 3 33 Caloneis sp. 1 Cocconeis cf. placentula 19 Cocconeis sp. (girdles) Neidium sp. (ampliatum?) 1 Pinnularia sp. 10 Pinnularia sp. Chunky girdles Pinnularia interrupta Stauroneis anceps 1 Stauroneis phoenicenteron Aulacoseira cf. distans 1 Aulacoseira small sp 1 Aulacoseira cf. italica 1 Total Diatoms 503.5 547 412 500 113 508.5 500 433 Chrysophyte Cysts 9 7 0 1 6 4 2 12

219 Appendix F (continued)

Taxon 334-84 8-01 9-01 10-01 15-01 241-04 242-04 243-04 Achnanthes minutissima 263 283 165 36 237 153 65 125 Achnanthes flexella 19 20 18 1 26 34 3 Achnanthes cf. kryophila Achnanthes cf. marginulata Achnanthes cf. ziegleri Amphora species 1 2 1 2 10 Amphora species 1 (longer) Amphora species 2 2 3 2 Amphora cf. acutiuscula 1 3 3 1 3 Amphora smooth/blank Cymbella descripta 153 107 221 365 105 145 360 382 Cymbella angustata 5 31 8 9 11 7 2 Cymbella cf. incerta 5 3 6 Cymbella cf. silesiaca Cymbella cf. naviculiformis Cyclotella pseudostelligera Fragilaria construens 2 Fragilaria cf. crotonensis Fragilaria brevistriata Fragilaria cf. lapponica 2 2 Fragilaria construens var. venter 0 2 0 0 24 7 2 0 Navicula c.f. halophila 9 13 15 17 37 20 9 1 Navicula c.f. halophilioides Navicula vulpina 1 12 4 Navicula soehrensis 12 20 4 Navicula cf. bryophila 1 Navicula cf. exilis/cryptocephala 1 1 Navicula cf. salinarum 1 2 2 2 Navicula cf. sublitissima Navicula sp. Denticula kuetzingii 2 3 1 Denticula subtilis 1 Denticula cf. valida Nitzschia frustulum 2 1 Nitzschia frustulum (long) Nitzschia frustulum (long, coarse) Nitzschia (BIG sp) Caloneis cf. silicula 4 0 2 0 2 0 2 0 Caloneis sp. Cocconeis cf. placentula Cocconeis sp. (girdles) Neidium sp. (ampliatum?) 1 Pinnularia sp. 2 Pinnularia sp. Chunky girdles Pinnularia interrupta Stauroneis anceps Stauroneis phoenicenteron Aulacoseira cf. distans Aulacoseira small sp Aulacoseira cf. italica Total Diatoms 472 436 465 427 462 418 459 515 Chrysophyte Cysts 10 1 7 9 7 9 9 52

220 Appendix F (continued)

Taxon 42-06 43-06 44-06 45-06 46-06 47-06 48-06 Achnanthes minutissima 149 139 64 104 173 296 163 Achnanthes flexella 17 9 1 2 6 4 Achnanthes cf. kryophila Achnanthes cf. marginulata Achnanthes cf. ziegleri Amphora species 1 3 3 2 Amphora species 1 (longer) Amphora species 2 16 2 2 6 Amphora cf. acutiuscula 8 3 1 2 3 2 Amphora smooth/blank 3 Cymbella descripta 119 291 254 168 310 171 214 Cymbella angustata 11 6 15 12 3 7 Cymbella cf. incerta 3 2 Cymbella cf. silesiaca Cymbella cf. naviculiformis Cyclotella pseudostelligera Fragilaria construens Fragilaria cf. crotonensis Fragilaria brevistriata Fragilaria cf. lapponica Fragilaria construens var. venter 1 0 6 11 0 0 0 Navicula c.f. halophila 14 5 11 17 12 3 35 Navicula c.f. halophilioides Navicula vulpina 5 5 Navicula soehrensis 20 2 9 2 6 18 Navicula cf. bryophila Navicula cf. exilis/cryptocephala Navicula cf. salinarum 5 6 Navicula cf. sublitissima Navicula sp. Denticula kuetzingii 1 4 3 2 Denticula subtilis 38 10 14 10 7 4 Denticula cf. valida Nitzschia frustulum 4 1 4 3 Nitzschia frustulum (long) 29 57 5 2 Nitzschia frustulum (long, coarse) 18 17 8 Nitzschia (BIG sp) 2 9 18 1 Caloneis cf. silicula 1 2 12 2 2 0 0 Caloneis sp. Cocconeis cf. placentula Cocconeis sp. (girdles) 2 Neidium sp. (ampliatum?) Pinnularia sp. Pinnularia sp. Chunky girdles 5 2 6 Pinnularia interrupta Stauroneis anceps Stauroneis phoenicenteron Aulacoseira cf. distans Aulacoseira small sp Aulacoseira cf. italica Total Diatoms 417 470 469 433 545 474 459 Chrysophyte Cysts 14 4 30 20 15 9 1

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