A High Resolution Study of the Spatial and Temporal Variability of Natural and Anthropogenic Compounds in Offshore Lake Superior Sediments

A HIGH RESOLUTION STUDY OF THE SPATIAL AND TEMPORAL VARIABILITY OF NATURAL AND ANTHROPOGENIC COMPOUNDS IN OFFSHORE LAKE SUPERIOR SEDIMENTS.

A THESIS SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY

JON D. VANALSTINE

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

MAY 2006 Acknowledgements

I would like to acknowledge the Geological Society of America, Sea Grant, UMD

Department of Geological Sciences, and the Large Lakes Observatory for support and funding of this project. Mike King and the crew of the Blue Heron for a great cruise, Tom Johnson and Steve Colman for their insight and help as my advisors, Paul Wilkinson, Dan Engstrom, and Erin Mortenson for prompt 210Pb

Analyses, Kris Rolfhus for MeHg analysis, Joe Werne and Jay Austin for help on issues with my thesis, Nigel Wattrus for many figures and creating visual effects in my presentation, Sarah Grosshuesch and Yvonne Chan for assistance in the lab, and Isla Casteneda, Lindsay Powers, Andy Breckenridge, and Jim Russell for advice and help throughout my two years at LLO. ii Abstract

Nine multi-cores were recovered during the summer of 2005 from an eight square kilometer area that is typical of the deep depositional environments found in the central and western parts of Lake Superior. Core sites were located in the troughs, centers, edges, and ambient regions around ring structures, which are believed to be the surface expression a polygonal fault system generated from the dewatering of underlying glaciolacustrine sediments (Cartwright et al. 2004 ).

One sub-core at each site was extruded at 0.5 cm intervals to 10 or 12 cm depth, and analyzed for 210Pb, biogenic silica (BSi), total organic carbon (TOC), total organic nitrogen (TON), and methyl mercury (MeHg).

The accumulation of bulk sediment, BSi, TOC, and MeHg cumulative inventories display large temporal and spatial variation among core sites throughout the study area. The total inventories of all three parameters vary by nearly a factor of two among the core sites. A comparison of BSi and TOC inventories to bulk sediment inventory reveals a direct relationship between the total compound accumulation at a particular core site and its bulk sedimentation rate. MeHg analyses show that spatial and temporal variability in MeHg appears to be due primarily to proximity to ring structures rather than variable bulk sediment accumulation. Our 8 km 2 study area exhibits a larger range of MeHg values than shown in previous lake-wide studies of MeHg.

Lake Superior is subject to a similar mass balance problem found in the oceans; a previous study determined that up to 80% of the river input of dissolved silica to the lake is not accounted for by either outflow of dissolved

iii silica or by deposition of biogenic silica. However, new estimates based on the mass accumulation of BSi in this study suggests that there is only little imbalance, if any, and that silicate mineral authigenesis is not required to explain the fate of dissolved silica flowing into the lake.

Single core analysis is not valid in regions of complex lake-floor terrain found throughout the central and western basins of Lake Superior. To accurately asses the accumulation of natural and anthropogenic compounds future investigations need to recover cores in the regions around complex lake-floor terrain that have exhibited 'normal' sedimentation, or attain duplicate cores to establish the degree of sediment and compound variability.

iv Table of Contents

Section Pages

Acknowledgments ...... i

Abstract ...... iii-iv

Table of Contents ...... v-vi

List of Figures ...... vii-viii

List of Tables ...... viii

1.0 Introduction ...... 1-2

2.0 Background ...... 3-16 2.1 An Introduction to Lake Superior ...... 3 2.1.1 Geology ...... 3-4 2.1.2 Stratigraphy ...... 4-5 2.1.3 Modern Sediment Sources and Depositional Environments ...... 5-7 2.1.3 Physical Processes Affecting Sediment Accumulation .. 7-12 2.1.4 Contaminant Impacts, Inputs, and Cycling in Lake Superior ...... 13-16

3.0 Methods ...... 17-27 3.1 Field Methods ...... 17-23 3.1.1 Sediment Coring ...... 17-18 3.1.2 Sampling Locations and Dates ...... 19-20 3.1.3 Core Processing on Board the RN Blue Heron ...... 21-23 3.2 Lab Methods ...... 24-27 3.2.1 Water Content and Porosity ...... 24 3.2.2 Analysis for Biogenic Silica ...... 24 3.2.3 Analysis for Total Organic Carbon, Total Organic Nitrogen, and C/N Ratios ...... 25 3.2.4 Stratigraphic Analysis ...... 25 3.2.5 Smear Slides ...... 26 3.2.6 Analysis (HgT and MeHg) ...... 26 3.2.7 21 Pb Analysis ...... 26-27

4.0 Results ...... 28-90 4.1 Core Descriptions ...... 28-31 4.2 Magnetic Susceptibility ...... 32-41 4.3 Water Content ...... 42 4.4 Geochronology ...... 43-66

v 4.4.1 210Pb Background ...... 43-46 4.4.2 210Pb Age Models ...... 46-53 4.4.3 Sediment Focusing and 210Pb Flux to Sediments .... 54-56 4.4.4 Dry Mass Calculations and Inventories of 210Pb ..... 57-60 4.4.5 Bulk Sediment MARs and Cumulative inventories ... 61-66 4.5 Biogenic Silica (BSi) ...... 67-70 4.5.1 Biogenic Silica Concentration ...... 67 4.5.2 Smear Slides ...... 68 4.6 TOC, TON, and C/N Ratios ...... 71-81 4.6.1 Total Organic Carbon ...... 71 4.6.2 Total Organic Nitrogen ...... 72 4.6.3 C/N Ratios ...... 77 4.7 Biogenic Silica and TOC MARs ...... 82-85 4.8 Methyl Mercury (MeHg) ...... 86-88 4.9 Compound Diagenesis ...... 89-90

5.0 Discussion ...... 91-122 5.1 Compound Distributions and Links to Recent Sediment Accumulation ...... 89-119 5.1.1 Inventories of BSi and TOC...... 89-106 5.1.2 A Revised Silica Budget for Lake Superior ...... 107-110 5.1.3 C/BSi Ratios ...... 110-112 5.1.4 Methyl Mercury ...... 112-119 5.2 Compound Variability Relative to Previous Studies ...... 120-121 5.3 Implications for Future Sediment Coring ...... 121 -122

6.0 Conclusions ...... 123-124

7.0 References ...... 125-128

8.0 Appendices ...... 129-144 APPENDIX A: Core locations and depths ...... 129 APPENDIX B: 210Pb data ...... 130-132 APPENDIX C: Water content data ...... 133-135 APPENDIX D: C, N, C/N, BSi, and MeHg data ...... 136-139 APPENDIX F: LRC data ...... 140-144

vi List of Figures ...... vii-viii

Figure 1. Satellite image of sediment resuspension in western Lake Superior. 8 Figure 2. The nine depositional basins of Lake Superior ...... 8 Figure 3. Color bathymetric map of ring structures on the lake floor ...... 11 Figure 4. Distribution of ring structures in western Lake Superior ...... 11 Figure 5. A high resolution seismic reflection profile from the study area .... 12 Figure 6. Contaminant cycling in Lake Superior ...... 14 Figure 7. RN Blue Heron ...... 18 Figure 8. Ocean Instruments multi-corer ...... 18 Figure 9. A high resolution seismic reflection profile ...... 19 Figure 10. Core locations and color bathymetric map of study area ...... 20 Figure 11. Core extruder with threaded rod ...... 23 Figure 12. Core extruders with pins and threaded rod ...... 23 Figure 13. Image and plot of MS for core 2 ...... 33 Figure 14. Image and plot of MS for core 3 ...... 34 Figure 15. Image and plot of MS for core 4 ...... 35 Figure 16. Image and plot of MS for core 5 ...... 36 Figure 17. Image and plot of MS for core 6 ...... 37 Figure 18. Image and plot of MS for core 7 ...... 38 Figure 19. Image and plot of MS for core 8 ...... 39 Figure 20. Image and plot of MS for core 9 ...... 40 Figure 21. Image and plot of MS for core 10 ...... 41 Figure 22. Water content of recovered cores ...... 42 Figure 23. 238U decay series ...... 44 Figure 24. Geochemical cycle of 210Pb ...... 44 Figure 25. Unsupported 210Pb activities ...... 51 Figure 26. CRS age/depth relations ...... 53 Figure 27. Flux of unsupported 210Pb to sediments ...... 56 Figure 28. Focus factors ...... 56 Figure 29. Trend line used to calculate 210Pb inventories ...... 60 Figure 30. Total 210Pb inventories for recovered cores ...... 60 Figure 31. Bulk sediment mass accumulation rates ...... 64 Figure 32. Stacked profiles of bulk sediment mass accumulation rates ...... 65 Figure 33. Bulk sediment inventories ...... 65 Figure 34. %BSi with depth ...... 69 Figure 35. %BSi through time ...... 70 Figure 36. %TOC with depth ...... 73 Figure 37. %TOC through time ...... 74 Figure 38. %TON with depth ...... 75 Figure 39. %TON through time ...... 76 Figure 40. C/N with depth ...... 78 Figure 41. C/N through time ...... 79 Figure 42. Stacked profiles of TOC, TON, C/N, and BSi with depth ...... 80 Figure 43. Stacked profiles of TOC, TON, C/N, and BSi through time ...... 81 Figure 44. BSi mass accumulation rates through time ...... 83

vii Figure 45. TOC mass accumulation rates through time ...... 84 Figure 46. Stacked profiles of TOC and BSi MARs through time ...... 85 Figure 47. MeHg concentrations with depth ...... 87 Figure 48. MeHg concentrations through time ...... 88 Figure 49. One dimensional diagenetic model ...... 90 Figure 50 Bulk sediment inventories from 1942 to the present ...... 92 Figure 51. BSi inventories from 1942 to the present ...... 92 Figure 52. TOC inventories from 1942 to the present ...... 93 Figure 53. Cumulative inventories: bulk sediment vs. BSi ...... 94 Figure 54. Cumulative inventories: bulk sediment vs. TOC ...... 95 Figure 55. BSi inventories from 1942 to the present in map view ...... 98 Figure 56. TOC inventories from 1942 to the present in map view ...... 99 Figure 57. Mean, range, and standard deviations of bulk sediment inventories ...... 101 Figure 58. Bulk sediment coefficients of variation ...... 102 Figure 59. Mean, range, and standard deviations of BSi inventories ...... 103 Figure 60. BSi coefficients of variation ...... 104 Figure 61. Mean, range, and standard deviations of TOC inventories ...... 105 Figure 62. TOC coefficients of variation ...... 106 Figure 63. C/BSi through time ...... 112 Figure 64. Inventory of MeHg from 1940 through the present ...... 116 Figure 65. Surface concentrations of MeHg ...... 116 Figure 66. MeHg inventories from 1942 to the present in map view ...... 117 Figure 67. Mean, range, and standard deviations of MeHg inventories ..... 118 Figure 68. MeHg coefficients of variation ...... 119

List of Tables ...... vii

Table 1. Date, time, depth, and location of core sites...... 19 Table 2. Analyses completed on cores ...... 22 Table 3. Sample containers and sample storage ...... 22 Table 4. Inputs and outputs of dissolved silica in Lake Superior ...... 108

viii 1.0 Introduction

Lake Superior is considered the most pristine of the Laurentian Great

Lakes; however its biota, water column, and sediments contain elevated

concentrations of contaminants (Baker and Eisenreich 1989, Devault et al.

1996). As the regions adjacent to Lake Superior become increasingly developed

and industrialized, many organizations (e.g. Environmental Protection Agency,

MN Pollution Control Agency) have initiated programs dedicated to monitoring

and assessing of contaminant levels and their impact on the lake's ecosystems.

Recent bathymetric surveys have revealed that the floor of Lake Superior

is very complex. Through the use of modern acoustic mapping techniques,

heterogeneous patterns of sediment accumulation have been observed in the

deep depositional zones of Lake Superior, contradicting the assumption of

uniform sediment accumulation on the lake floor. The presence of ubiquitous

sedimentary structures in Lake Superior has been well documented (e.g., (Flood

and Johnson, 1984, Johnson et al. 1984, Flood 1989), however, their detailed

morphology and impacts on sediment accumulation have only recently been

imaged clearly (Cartwright et al. 2004 ).

Given these recently observed heterogeneities in sediment accumulation, studies investigating natural and anthropogenic compounds in Lake Superior sediments may have used inadequate sampling protocols to properly assess the distribution of these compounds, which might have led to a mischaracterization of the degree of contamination in Lake Superior sediments. Routinely, studies have been based on three or four, at most, sediment cores recovered from the entire

1 lake, yielding results that may not have been representative of a lake sub-basin as a whole. These studies have neglected to verify uncertainties in burial rates attained from a single core and to consider the importance of small-scale(< 1 kilometer) heterogeneity in lake-floor morphology or sediment cover (e.g.,

(Eisenreich 1987, Baker and Eisenreich 1989, Rolfhus et al. 2003).

This study examines the variability in sediment composition and accumulation in an eight square kilometer area that is typical of the deep depositional environment found in the central and western parts of Lake

Superior. Specifically, the burial of natural and anthropogenic compounds over the past 150 years is investigated to test the validity of single core analysis in earlier published studies, and to seek relationships between sediment composition and sediment accumulation rates relative to core placement over complex lake floor terrain.

2 2.0 Background

2. 1 An Introduction to Lake Superior

Lake Superior was formed around 11,000 years ago during the retreat of

the Laurentide Ice Sheet (Thomas and Dell 1978). With a surface area of 82,000

square kilometers and a volume of 11,920 cubic kilometers, Lake Superior is the

largest of the Laurentian Great Lakes and represents approximately one-tenth of

the world's liquid surface fresh water. Since the late 1600's, Lake Superior has

seNed as an important avenue for trade and transport throughout the fur, mining,

and forestry eras (Matheson and Munwar 1978). Today, the lake seNes as a

primary source of fresh water for drinking, fishing, tourism and, as a route for

commercial transport of raw material and manufactured goods both within the

continent and to all parts of the world.

2.2.1 Geology

The Lake Superior basin lies between the southern margin of the igneous and metamorphic Precambrian Canadian Shield to the north of the lake and

Lower Paleozoic sedimentary rocks to the south. A lack of limestone in the drainage basin results in waters remarkably low in total dissolved solids

(Matheson and Munwar 1978). The northern and western shoreline of the lake is dominated by the highly resistant gabbros of the Duluth Complex and associated volcanic lavas and inter-flow sediments of the Midcontinent Rift System (Green

1989). The southern shore of Lake Superior is composed of relatively friable

Precambrian feldspathic sandstones of the Oronto Group, Bayfield Group, and

3 equivalents; capped unconformably in most places along the Wisconsin shoreline

by Quaternary glacial and post-glacial deposits (Ojakangas and Morey 1982).

2.2.2 Stratigraphy

Lake Superior sediments can be divided roughly into two major units: a

lower unit of varved or massive glaciolacustrine silty clay deposited as the

southern margin of the Laurentide ice sheet receded from the lake's drainage

basin, and an upper unit of massive, dark gray or brown, non-calcareous clay

deposited during post-glacial times. These sediments are mostly underlain by

glacial till but in some areas directly overlie bedrock (Thomas and Dell 1978).

The lower glaciolacustrine unit is commonly composed of red massive

calcareous clay in lower sections and typically grades upward into red and grey varved calcareous clays (Thomas and Dell 1978). Deposition of the varved clays

is suggested to have begun at 10,550 to 11,000 cal. BP (before 1950) (Fisher and Whitman 1999) and continued to be rapidly deposited until approximately

9,035 cal. BP (Breckenridge et al. 2004 ). Thickness of this unit ranges from 18 m in the northern portions of the lake to zero m where bedrock is exposed, with an average accumulation of approximately one meter. Sedimentation rates determined from varve thicknesses during this time averaged 0.5 cm per year, but on occasion was as fast as 13 cm/yr (Breckenridge et al. 2004 ). Sediment composition of this unit is mostly clay minerals, quartz, feldspars, detrital calcite, and dolomite (Thomas and Dell 1978).

4 Post-glacial sediment accumulations range from 0 - 9 m in thickness, with

greater accumulation in bathymetric depressions throughout northern sub-basins

in Lake Superior. This unit is composed of primarily red-brown or gray-brown

clays in the southern portions of the lake, whereas in the northern areas the clays

are a darker shade of grey. The color of these clays is characteristic of the local watershed geology derived from either the red clay bluffs on the south shore or the grey igneous and metamorphic rocks to the north (Thomas and Dell 1978).

Post-glacial sediments in Lake Superior are non-calcareous because the

lake is undersaturated with respect to calcite and has low sedimentation rates,

allowing complete dissolution of all calcium carbonate that washes into or is formed in the lake. Sediments deposited during the retreat of the ice sheet were deposited at a high enough rate to bury and subsequently preserve calcite and dolomite (Thomas and Dell 1978). Post-glacial sedimentation rates in Lake

Superior are the lowest of the Great Lakes, ranging from 0.1 to 3.2 millimeters per year, and typically averaging about 0.3 mm/yr in the depositional basins

(Evans et al. 1981 ).

2.2.3 Modern Sediment Sources and Depositional Environments

Post-glacial fine-grained sediments in the offshore areas of Lake Superior are primarily derived from shoreline erosion and suspended sediment inputs from tributaries. Secondary sources include taconite tailings, aeolian deposits, autochthonous organic matter, and the products of under-water erosion and transport of previously deposited sediments (Kemp et al. 1978). On a large scale,

5 the southern shore of Lake Superior is significantly more susceptible to erosion than the north shore due to its lithology and exposure to high wave energy during storms with strong northeast winds. The erosion of Quaternary glacial deposits along the north shore of Wisconsin is the major sediment source to Lake

Superior, contributing an estimated 58% of the total external sediment input

(Kemp et al. 1978) (Figure 1 ). The average rates of retreat of the Wisconsin coast are 0.78 and 1.89 meters per year, respectively, for coasts composed of clay and sand or gravel (Johnson and Johnston 1995). These values are 9 - 23 times the average erosion rate of the north shore (.08 meters per year). The second largest source of fine-grained sediment to Lake Superior is river input, which accounts for as much as 30% of the total external sediment flux to the lake. Approximately 40% of the total external sediment load is deposited in the western arm of the lake, due to the location of major sediment sources (Kemp et al. 1978). Sediment accumulation in other depositional areas of the lake depends strongly on proximity to terrestrial sources and to strong currents along the south shore of the lake, which serve to transport external sediment loads to these regions (Kemp et al. 1978).

The floor of Lake Superior can be divided into two regimes: 1) depositional basins, where fine-grained clay and silt-sized sediment is actively accumulating and 2) non-depositional zones, which are underlain by bedrock, till, glaciolacustrine clay, or sand. In non-depositional zones, there may exist a thin, discontinuous layer of recent sediment; however, these localized accumulations of recent sediment accumulation are ephemeral in nature. Sediment

6 accumulation in the deeper depositional zones may account for up to 75% of the total estimated sediment input to Lake Superior (Kemp et al. 1978). The

depositional zones generally lie below 100 m water depth (Johnson 1980) and

have been roughly separated into nine areas that are designated as the Duluth,

Chefswet, Thunder Bay, Isle Royale, Marathon, Caribou, Keweenaw, and lie

Parisienne basins along with an area of north-south trending troughs in the eastern part of the lake termed the Lake Superior Troughs (Figure 1) (Kemp et al. 1978).

2. 2.4 Physical Processes Affecting Sediment Accumulation

Wave energy and deep water currents have historically been the most recognized physical processes that directly affect the accumulation of sediments, nutrients, and pollutants throughout Lake Superior (Thomas and Dell 1978,

Beletsky et al. 1999). Grain-size-distribution studies across bathymetric contours in Lake Superior have shown that in general, coarser sediments occur in the near shore areas, and that sediments become finer offshore into the deep water basins due to the decreased oscillatory currents of wind-stress generated waves with increasing water depth (Thomas and Dell 1978). Other researchers have shown the presence of contourites (Johnson et al. 1980), sand ribbons, scoured troughs, and sediment-covered ring structures (Johnson et al. 1984 ), and reworked relict shore-face attached sand ridges (Wattrus and Rausch 2001) in both the depositional and non-depositional regions of Lake Superior.

7 Figure 1 - Satellite image illustrating sediment input and resuspension during a storm event in the western arm of Lake Superior.

92° 91° 90° 89° 88° 87° 86° 85° I

I I 92° 91° 90° 890 870 86° 85°

Figure 2 - The nine depositional basins of Lake Superior (modified from Breckenridge et al. 2004)

8 These features are created or modified by large storm-induced currents or

persistent deep water currents during spring and fall when the water column is

isothermal (Johnson et al. 1984 ). Some of the currents near the lake floor may

reach velocities in excess of 28 centimeters per second (Flood 1989).

The heterogeneity in the pattern sediment accumulation in depositional

areas in the offshore basins, i.e., the presence of polygonal structures, was first

reported by Berkson and Clay (1973b). Subsequent mapping with side scan

sonar revealed these features to be more ring-like and common in the western

and central parts of Lake Superior (Flood and Johnson, 1984, Johnson et al.

1984, Flood 1989). Recent investigations using seismic reflection profiling and

multi-beam sonar have determined that ring depressions range from 100 to 400

min diameter and 1-7 m deep (Figures 3,4), and are composed of smaller depressions termed pock marks (Cartwright et al. 2004 ). These structures are

hypothesized to be the surface expression of the faulting and/or dewatering of underlying glacial-lacustrine clays, which were rapidly deposited on the lake floor between 9000 and 10,600 cal. BP (Cartwright et al. 2004 ). Pockmarks and rings may have formed during the end of the faulting episode, with post-glacial sediments draping these older structures, or formed at a much later time from fluid flow exploiting the fault network and remobilizing the overlying sediments. It is possible that this fluid flow may be currently active in some areas of the lake, or episodic in nature, contributing to greater variations in sediment accumulation.

Submersible studies (Flood 1989) and high-resolution seismic profiles across ring depressions (Cartwright et al. 2004) show erosional surfaces,

9 slumping, and ripples on the walls and bases of the ring troughs, suggesting that

they are al least partly erosional (Figure 5). These depressions typically formed

in either the post-glacial clays or varved, carbonate-rich clays. Many are coated

by a thin veneer of recent sandy or silty mud across the ring trough. Sediments

recovered from the ring centers are typical of recent sediments in the ambient

regions (i.e. areas of 'normal' sediment accumulation) (Flood 1989). These observations lead us to believe that the distribution of natural and anthropogenic compounds is quite variable spatially and temporally throughout depositional environments typical of the central and western deepwater basins of Lake

Superior.

10 N X/'i: 309200 310200 311200 3 12200 313200 3 14200 Meters

52491 00 · 5249100

. 47' 22"

52481OOc _., 220 m

• 23ll

234 5247100- ' 5247 100 + ·H ·2 1·0.

5246 100

't'"20'15"i. g [;; a:. . 3ou:.mo 310'.lUU 3 1 ! :.WU 3 1'..!'..! UU 3 13 :.WU 3 14:.WU

Figure 3 - Color bathymetric map of ring structures on lake floor obtained by seismic profiles. Colors range from blue (deepest) to yellow (shallowest) and clearly show the ring structures. Location is shown in figure 4. Profile from N. Wattrus, LLO.

j 4 ,/

Figure 4 - Distribution of ring structures on the lake floor in western Lake Superior; gray scale refers to number of rings per kilometer along survey line (heavy black line). Light dashed lines are bathymetric contours. Solid dot indicates location of figure 3. Modified from Cartwright et al. (2004).

11 Figure 5 - A typical high-resolution seismic reflection profile from the same detailed survey area. Depth scale on left is in meters below the lake surface. Profile from N. Wattrus, LLO.

12 2.2.5 Contaminant Impacts, Inputs, and Cycling in Lake Superior

Considerable research has been conducted on the introduction, transport, and fate of many contaminants in Lake Superior. Understanding the transport, interactions with sediments, and burial of anthropogenic contaminants in Lake

Superior is important due to the ability of a lake basin to act as a permanent sink, or a source that may reintroduce a contaminant for decades after it is no longer in use. The small ratio of watershed to a lake surface area in Lake Superior, the long residence time of its water, and its long aquatic food chains make the lake very susceptible to atmospherically derived contamination and bioaccumulation

(Eisenreich 1987, Baker and Hites 2000, Rolfhus et al. 2003, Hites 2004). Once introduced to the water column, many contaminants are readily adsorbed onto suspended particles and transported to the lake floor. Most of these contaminants are recycled while settling through the water column, or at the sediment-water interface (Baker et al. 1991 ). Contaminants that are not recycled are deposited on the lake floor where they can be permanently removed from the lake system, enter into the food web through benthic organisms, or be reintroduced into the water column by resuspension mechanisms including sediment re-working by benthic organisms, transport and erosion by currents or slumping, and upward diffusion or advection of pore waters (Figure 6).

13 Atmospheric Deposition

Volatilization -

Reintroduction ••• Recycling at sed/water i terface

Burial in Sediments

Figure 6 - Contaminant cycling in Lake Superior.

14 Studies investigating the level of contaminants in the environment have led to laws prohibiting the manufacture of contaminants such as polychlorinated biphenyls (PCB's), resulting in declines in their input to Lake Superior (Baker and

Eisenreich 1989, Schneider et al. 2001 ). PCB levels have declined in the sediments of the lake since the mid 1970's (Schneider et al. 2001 ); however, the lake has now become a major source of PCB's to the atmosphere by volatilization of dissolved PCB's at the air-water interface (Baker et al. 1991,

Hornbuckle et al. 1994 ). The levels of other contaminants, such as mercury, continue to rise primarily due to atmospheric deposition (Rolfhus et al. 2003).

Newly identified contaminants such as polybrominated diphenyl ethers (PBDE's) are being introduced to the biota, water, and sediments of Lake Superior (Song and Li 2002; Hites 2004 ).

Many of the contaminants found in Lake Superior directly affect the health of people and biota in and around the lake. Mercury is a potent neurotoxin to both humans and wildlife. PCB's are known to cause a variety of adverse health effects in birds, humans, and other mammals (http://www.epa.gov/opptintr/pcb/ effects.html). Recent U.S. research has suggested that PBDE's may not pose a great threat to human health or the environment (http://www.epa.gov/opptintr/ pbde/qanda.html) however, European researchers have found evidence that has linked PBDE exposure to an array of adverse health effects including thyroid hormone disruption, permanent learning and memory impairment, behavioral changes, hearing deficits, fetal malformations and, possibly, cancer (Viberg et al.

2002, Branchi et al. 2002, McDonald 2002). In the U.S., PBDEs are slowly

15 becoming a concern due to their alarming rate of introduction and their identification in the blood, milk, and tissues of humans (http://www.epa.gov

/opptintr/pbde/qanda.html).

As a consequence of the bioaccumulation of many contaminants in the biota of Lake Superior, strict consumption advisories for fish have been implemented, impacting both the sport and commercial fishing industries. The health, lifestyle and economic welfare of people in the Lake Superior region are greatly impacted by elevated concentrations of anthropogenic contaminants in the lake.

16 3.0 Methods

3.1 Field Methods

3. 1. 1 Sediment Coring

Sediment cores BH05-2MC through BH05-10MC were recovered from

nine sites in the study area from the RN Blue Heron (Figure 7) with an Ocean

Instruments multi-corer (Figure 8). SH refers to the Blue Heron, 05 represents

the year of core recovery, and 2-1 OMC stands for the second through the tenth

multi-cores recovered that year. Hereafter, the cores will be designated core 2

through core 10. The multi-corer consists of a four-legged platform that is

lowered to the lake floor and simultaneously collects four duplicate sediment

cores. The corer is monitored acoustically as it is lowered through the water

column , enabling precise determination of the depth, time, and location of contact

with the lake floor. As the multi-corer contacts the lake floor, a triggering

mechanism is activated and four-ten centimeter diameter poly-butyrate tubes are

slowly inserted into the sediments, driven by a hydraulically damped gravity

system. Once the tubes have penetrated fully, mechanical caps and feet seal the tops and bottoms of the tubes to prevent sediment loss as the corer is brought to the surface. In this study, all cores were retrieved with no visible signs of

disturbance and the sediment-water interface intact. Cores from this study

ranged in lengths from 36 to 47 centimeters.

17 ... :.. -:: .. - r..- ---

Figure 7 - RN Blue Heron owned and operated by the Large Lakes Observatory.

Figure 8 - Ocean Instruments Multi-corer on the RN Blue Heron. I I I 18 3.1.2 Sampling Locations and Dates

Nine Sediment cores were recovered during the summer of 2005.

(Table1 ). Core sites were located using both a pos-MV dual satellite GPS

navigation system, relative to lake floor features that were previously mapped by

N. Wattrus with multi-beam sonar and a Knudsen 28 kHz seismic-reflection

profiling system (Figure 9). Within the previously mapped area, multi-cores were

recovered between, on the edges of, and within ring depressions (Figure 10).

Core Date Time Latitude Longitude Water Depth (m) 2MC 6/10/05 2145 47-21.405 89-29.095 202 3MC 6/10/05 2240 47-21.352 89-29.096 199 4MC 6/11/05 0653 47-21 .332 89-28.965 200 SMC 6/11/05 0934 47-21.310 89-28.831 198 6MC 6/11/05 1024 47-21.293 89-28.217 202 ?MC 6/11/05 1111 47-21.328 89-28.231 200 SMC 6/11/05 1857 47-21.446 89-28.152 198 9MC 6/11/05 1937 47-21.271 89-28.146 200 10MC 6/11/05 2027 47-21.072 89-28.446 201

Table 1 - Table showing the date, time, latitude, longitude and depth of core sites.

Ci\R'TO l -T3, 23':l9.49 I

SP: ' ' ' 1 ' ' ' • ' ' 1 ' ' ' • ' ' 1 ' ' ' ' ' ' 1 ' ' ' ' ' ' 1 ' ' ' ' ' ' 1 ' ' ' ' Offset: 0 100 200 300 400 500 600 700 EIOO 900 1000 t 100 1200 1300 MOO

.290

Figure 9 -A high-resolution seismic reflection profile. Y-axis scale is in milliseconds (10 msec = -7.25 meters). Profile from N. Wattrus, LLO.

19 92' 91' !')' 11' 16' IS'

,.,.

Figure 10 - Color bathymetric map of ring structures in the study area showing multi-core locations. Colors range from blue (deepest) to yellow (shallowest) and clearly show the ring structures.

20 3.1.3 Core processing on board the RN Blue Heron

After retrieval of the multi-corer, each of the four sub-cores was removed from the multi-corer frame without disturbing the sediment-water interface. One of the cores at each site had the overlying water extruded and was immediately capped and labeled for stratigraphic analysis at the Limnological Research

Center and archived at the Large Lakes Observatory. The other three cores were extruded at one-half centimeter intervals from 0 to 6 cm, and at one centimeter intervals from 6 to 10 cm in cores 2, 3, and 4, and 6 to 12 cm in the remaining cores for subsequent analyses (Table 2). To extrude the cores, a piston was forced up through the bottom of each core by either turning a nut on a threaded rod to advance the desired length (Figure 11 ), or by removing pins on a carefully machined shaft that allowed the core to drop by the desired sample interval

(Figure 12). Each extruded sample was placed in a small whirl-pak bag or, in the case of samples for organic micro-contaminants, a pre-cleaned amber glass jar

(for PCBs and PBDEs) or a Nalgene bottle (for PCFs). Samples analyzed for mercury content were placed in pre-cleaned clear jars (Table 3). Samples were either frozen or refrigerated at in situ temperatures until analysis on shore.

21 Core BSi, C, Water PBDEs & PCFs Hg N Content PCBs 2 * * * * * * 3 * * * * * * 4 * * * * * * 5 * * * * 6 * * * * 7 * * * * 8 * * * * 9 * * * * 10 * * * 11 * * *

Table 2 - Samples recovered from extruded cores. PBDE: PolyBrominated Diphenyl Ether, PCB: PolyChlorinated Biphenyl, PCF: PolyChlorinated Fluoride, Hg: Mercury.

Sample Amber Nalgene Clear Whirl- Frozen In situ Analysis Jar Bottle Jar pak Temp. PBDEs * * PCBs * * PCFs * * HQ * * BSi * * TOG, TON * * % Water * * * *

Table 3 - Sample containers and storage for analyzed samples.

22 Figure 11 - Core extruder with threaded rod.

Figure 12 - Core extruders with pins and threaded rod.

23 3.2 Lab Methods

3.3.1 Water Content and Porosity

Wet sub-samples of each sample interval were placed in pre-weighed 100

milliliter vials and weighed. Sub-samples ranged from 15 to 30 grams and were

subsequently freeze dried at -40°C for approximately 24 hours. Dried samples

were then re-weighed, for determination of water content and porosity. Finally,

samples were ground with a mortar and pestle in preparation for further

analyses. Dried sub-sample weights ranged from 0.5 to 10 grams per sample.

3.3.2 Analysis for biogenic silica

Biogenic silica (BSi) analyses were completed in the Sedimentology

Laboratory in the Large Lakes Observatory. BSi concentrations in 193 samples

were determined by time-series chemical digestion using the methods of

DeMaster (1979). Approximately 0.3 milligrams of dry sediment was reacted with

40 milliliters of 0.5N NaOH at 85° Celsius. The basic solution was sampled at 5,

15, 30, 60 , 90, 120, and 200 minutes after initial reaction with the sediment, and

analyzed spectro-photometrically for concentration of dissolved silica. One

replicate analysis for every twelve or twenty-four samples was done to determine

analytical reproducibility. All replicates except two are within eight percent the

stated values; the two outliers differ by 11 and 19 percent, but do not show large deviations relative to BSi concentrations throughout the core.

24 3.3.3 Analysis for Total Organic Carbon, Total Organic Nitrogen, and GIN Ratios

Total Organic Carbon (TOC) and Total Organic Nitrogen (TON)

concentrations were measured with a Costech Instruments ECS 4010 CHNS-0

Elemental Combustion System, equipped with a pneumatic auto-sampler, at the

Large Lakes Observatory. A total of 205 samples were analyzed, including

replicates and standards. One replicate analysis for every ten samples was done

to determine analytical reproducibility. For each sample interval, a sub-sample of

approximately twenty milligrams was weighed into a tin capsule. The capsule

was dropped into a 1700° Celsius combustion chamber where it reacted in an

oxygen stream, forming N2 and C02. After flowing through a gas chromatograph

column, these gases were detected by a thermal conductivity detector and

converted to a signal which is proportional to the amount of carbon and nitrogen

in each sample. All carbon data are listed in Appendix D.

3.2.4 Stratigraphic Analysis

As stated previously, one of the four multi-cores from each site was

capped and preserved intact for subsequent stratigraphic analyses. These cores were taken to the Limnological Research Center (LRC), on the Twin Cities

campus of the University of Minnesota, for analysis of magnetic susceptibility

(MS) and wet bulk density on a Geotek multi-sensor scanner. MS was analyzed with an MS point sensor (resolution of 5mm) and wet bulk density was measured

by gamma-ray absorption. The cores were then split length-wise, described

25 visually, and digitally imaged on the Geotek Geoscan-V system using a fixed, polarized light source.

3.2.5 Smear Slides

Each split core was sub-sampled at one-half centimeter inteNals in the top five centimeters for microscopic characterization of the relative abundances of microfossils. Smear slides were prepared following the protocol of the LRC laboratory: a sub-mm3 of sediment was smeared onto a glass microscope slide with deionozed water, allowed to dry, and then mounted in "Opticlear" under a glass cover slip. The smear slides were examined under a petrographic microscope to assess the abundance and preseNation of diatoms and other coarse grained material.

3.2.6 Mercury analysis (HgT and MeHg)

Sub-samples from the first eight (2MC - 9MC) extruded cores were sent to Prof. Kris Rolfhus at the Department of Chemistry and River Research Center,

University of Wisconsin-La Crosse, for analyses of total mercury (HgT) and methyl mercury (MeHg). Methods are outlined in Rolfhus et al. (2003).

3.2. 7 210Pb Analysis

Analyses of 210Pb concentrations for nine of the cores were obtained by contract with Dr. Paul Wilkinson at the Department of Soil Science, University of

Manitoba. I also carried out 210Pb analyses on one core at the St. Croix

Watershed Research Station of the Minnesota Science Museum, under the

26 supervision of Dr. Dan Engstrom. 210Pb was measured at half centimeter depth intervals down to five centimeters and one additional sample from ten centimeters depth was analyzed in each core. For each depth interval, one to three gram samples were analyzed for 210Pb by leaching in 6N HCI in the presence of a 209Po tracer, auto plating Po onto a silver disc (Flynn 1968), and counting decays on the disc in an alpha spectrometer, determining 210Pb via its

210Po daughter. 226Ra was analyzed in only two of the cores by sealing the sample in a 60 x 15 millimeter plastic petri dish, allowing it to age for thirty days, and counting gamma emission from 226Ra on a gamma spectrometer.

27 4.0 Results

4.1 Core Descriptions

Core 2 (Figure 13) is 34 cm long; the top 4 cm consists of a homogenous

dark brown mud with an absence of structures, probably due to bioturbation and

high water content. A layer of gray homogenous clay with a slight tint of brown

coloring lies between 7 and 9.5 cm. At 9.5 cm the sediments become varves

throughout the rest of the core. The varves in Lake Superior are glacialacustrine

in origin, and their top is dated at 9,035 cal. BP (Breckenridge et al. 2004). Each

varve grades from a dark gray on top to a cream or tan towards the bottom. The

transition in coloring is due to the dissolution of carbonate rich clays during the

winter when sedimentation was relatively slower than spring and summer

periods, allowing lake water to dissolve carbonate rich sediments (Thomas and

Dell 1978). The interval from 9.5 to 20 cm contains 7 varves that range from 1 to

2 cm in thickness. Varves are dull gray in color from 20 to 23 cm, and at 23 cm varves turn a more blue-gray color. From 31 cm to the base, the core contains two relatively thick varves that grade in color from gray on the top to a cream color at the base.

Core 3 (Figure 14) is 45 cm long and is composed of dark brown homogenous mud in the top 3 cm. The dark mud grades into medium brown silty clay with no visible structures at 3 cm, and continues to 8.5 cm. From 8.5 to 10 cm lies a black band of Mn hydroxides and oxyhydroxides overlying a red band of Fe hydroxides and oxyhydroxides, representing the boundary between oxic and anoxic sedimentary environments. As reduced Fe and Mn ions, dissolved in

28 porewaters, migrate upward through sediments, they come into contact with oxygen and are subsequently oxidized to form insoluble precipitates, creating the black and red oxide bands (Richardson and Nealson 1989). Gray homogenous clay underlies the iron-rich band for the remainder of the core, with intermittent remnants of both Mn-oxide or Fe-oxide layers and nodules.

Core 4 (Figure 15) is 44 cm long; the top 5.5 cm is composed of homogenous dark brown mud that grades into light brown/tan silty clay to a depth of 8 cm. Black Mn-oxide and red Fe-oxide layers lie between 8 and 8.5 cm depth, below which is a 1.5 cm thick band of tan clay. Below this tan clay is a remnant

Fe-oxide layer 0.5 cm thick. From 10.5 to 11 cm is a layer of gray homogenous clay; below this interval down to 18 cm is a relatively dark band of gray clay with subtle 0.25 cm thick Mn-oxide bands at 13 and 14 cm. From 18 to 20.5 cm is a layer of gray homogenous clay, followed by an interval of gray clay with red staining down to 27.5 cm. Gray homogenous clay with intermittent banding of black Mn-oxides, which range from 0.25 to 0.5 cm in thickness, lie between 27.5 to the end of the core. Most of these bands do not extend across the entire width of the core.

Core 5 (Figure 16) is 43 cm long, the top of the core to 3.5 cm consists of dark brown mud which grades into a light brown mud or clay to 9.5 cm depth.

Mn-oxide and Fe-oxide bands lie between 9.5 and 11 cm; below this interval to the base of the core is gray clay with two darker Mn-oxide bands at 23.5 and 32 cm depth.

29 Core 6 (Figure 17) is 39 cm in length. A layer of dark brown mud lies

between 0 and 4.5 cm, followed by a 3.5 cm interval of light brown mud or clay.

The boundary between these two layers varies in depth with approximately 1.5

cm of relief. Mn-oxide and Fe-oxide bands are contained between 8 and 9 cm;

below these oxide bands lies a thin (-0.5 cm) thick layer of gray clay. Another

Fe-oxide layer lies between 9.5 and 10 cm. At 10 cm the sediments become

gray homogenous clay, which continues to the end of the core. Intermittent

bands of Mn-oxides are present throughout this clay, two of which are thicker

relative to others (-0.15 cm) at 22 and 23 cm.

Core 7 (Figure 18) is 41 cm long, the top 2.5 cm consists of dark brown

mud; the interval from 2.5 to 11 cm contains a layer of light brown mud or clay.

Black Mn-oxide and red Fe-oxide layers lie between 11 and 11.5 cm; below the

oxide layers is brown clay with abundant Fe-oxide staining and two distinct

remnant Fe-oxide layers approximately 0.5 cm thick. The composition switches to gray homogenous clay at 13.25 cm and extends down to 21.5 cm. The clay turns slightly purple in color with an occasional nodule of Fe-oxide between 21.5 and 26.5 cm. Gray homogenous clay lies between 26.5 and 30.5 cm. The core is composed of darker gray homogenous clay below this.

Core 8 (Figure 19) is 41 cm long. The top 3 cm consists of dark brown mud, followed by a 4 cm interval of light brown mud or clay. The core is composed of gray clay with red and brown blotches and linear bands between 7 and 12 cm. An interval of brown tinted gray clay, with abundant Fe-oxide nodules and dark brown blotches, resides between 12 and 16.5 cm. 16.5 to 17.5 cm

30 contains the Fe-oxide band. The core is composed of purple tinted gray clay from

17.5 cm to 31 cm, with bands of black Mn-oxide at 19 and 21.5 cm. The core

contains gray homogenous clay from 31 cm to the base of the core.

Core 9 (Figure 20) is 47 cm long. The core is composed of dark brown

mud from 0 to 4 cm; below this is a 4 cm thick interval of light brown mud or clay.

A faint black band of Mn-oxide lies between 8 and 9 cm; light brown band of mud

or clay resides between 9 and 9.5 cm. Sediment between 9.5 and 10.2 cm is

composed of a thicker more distinct band of black Mn-oxide; below this to 10.5

cm is a red band of Fe-oxide. The rest of the core is composed of homogenous

gray clay composes.

Core 10 (Figure 21) is 43.5 cm long. The top 3.5 cm of the core is

composed of dark brown mud which grades into tan mud at 3.5 cm depth.

Between 5 and 9 cm depth is a layer of tan mud or clay; below this interval to

10.5 cm are the Mn-oxide and Fe-oxide bands. The core is composed of purple tinted gray clay with intermittent blotches and bands of black Mn-oxides from

10.5 to 35 cm. Light gray homogenous clay underlies the purple-gray clay and extends to the base of the core.

Sediment cores exhibit some common characteristics. All cores contain an upper layer of dark brown mud that ranges from 2 to 6 cm in thickness. Below this, with the exception of core 2, cores display an interval of tan mud and clay

(from 2 to 14 cm in thickness) with basal Mn-oxide and Fe-oxide layers. Various shades of grey homogenous clay, with intermittent remnants of Mn-oxide and Fe- oxide bands, lie below these layers in all but one of the cores.

31 4.2 Magnetic Susceptibility Data

Magnetic susceptibility (MS) profiles display down-core changes the concentrations of magnetic minerals. Variations in these concentrations can be due to changing weathering or erosional processes, as well as with various transport and depositional conditions. Variations in these processes result in differences in content and/or composition of the magnetic minerals in recovered sediments (Nowaczyk 2001 ). All MS values reported in this study are in SI units.

Low MS values near the top or base of cores are most likely due to edge effects.

Several cores in this study exhibit similar MS profiles, displaying relatively high MS values in the top 5 to 10 cm, a sharp decrease at the Mn and Fe-oxide boundary, then a step-like or gradual increase in MS values with increasing depth in the core. However, there are subtle differences among these cores, and a few of the cores exhibit vastly different MS profiles (Figures 13-21 ).

One core recovered from the ambient regions in the study area (core 5), cores 3 and 9 from the centers of ring structures, and one core recovered near the edge of the western-most ring structure (core 7) display comparable MS profiles, suggesting that these locations were subject to similar depositional and sediment transport conditions. The remaining five cores each display unique MS profiles, signifying variability in either sediment accumulation or transport processes both between, and across ring structures. Overall, the highest variability is observed in the most recent sediment accumulation and above the

Mn and Fe-oxide layers.

32 0 Magnetic Susceptibility

15 ...... E ._(.) ._Q) 0 () 20 c .c...... n. Q) 0 25

0 5 10 15 20 25 30

Figure 13 - Core 2 image and plot of magnetic susceptibility. MS values start at the top of the core tube, not at the upper-most sediments. All description depths are expressed in centimeters below the top of the sediment, not from the top of the core tube.

33 0 Magnetic Susceptiblity

10 11

15 t wi h ei ...... E ..._.(.) 20 Q) "- 0 0 c ..c...... 0. 25 Q) 0

0 2 4 6 8 10 12 14 16

Figure 14 - Core 3 image and plot of magnetic susceptibility. The top of the core is difficult to see in the image because the top 3 cm has slumped down in the core tube.

34 0 Magnetic Susceptibility

,,...... E 20 u0 c .c 0. 25 Q} 0

0 2 4 6 8 1 0 12 14 16 18 20

Figure 15 - Core 4 image and plot of magnetic susceptibility.

35 0 ..... Magnetic Susceptibility

E -(..) ...... 20 ,_(].) 0 0 c ..c...... a.. 25 (].) 0

0 2 4 6 8 10 12 14 16

Figure 16 - Core 5 image and plot of magnetic susceptibility.

36 0 _____Magnetic..;;....______Susceptibility ____.,. __

15 --E .._,(.) ....(!) 0 u 20 c ..c_. 0. (!) 0 25

40 0 5 10 15 20 25 30 35

Figure 17 - Core 6 image and plot of magnetic susceptibility.

37 15 -E .....Q) 0 () 20 .£ ..c a.Q) 0 25

0 2 4 6 8 10 12 14 16 18

Figure 18 - Core 7 image and plot of magnetic susceptibility.

38 5

15 ,.-... E (.) -....Q) 0 () 20 c .c...... Cl. Q) 0 25

40 0 2

Figure 19 - Core 8 image and plot of magnetic susceptibility.

39 ...... E (.) 20 -,_Q) 0 0 c ..c...... 25 0... Q) 0

0 2 4 6 8 10 12 14

Figure 20 - Core 9 image and plot of magnetic susceptibility.

40 Magnetic Susceptibility

...... E ._....,() Q),_ 20 0 (.) c ..c...... CL Q) 0 25

0 2 4 6 8 10 12 14 16 18

Figure 21 - Core 10 image and plot of magnetic susceptibility.

41 4.3 Water Content

Profiles of water content display porosity differences from the top of the

core to 10 or 12 cm depth. All but one core recovered in this study display

relatively similar profiles of water content with depth, displaying relatively high

water content towards the sediment surface, and an exponential decrease down

core reflecting the increased compaction and loss of porosity with depth (Figure

22). The outlier is Core 2, recovered from the trough of the eastern-most ring

structure, displaying lower percent water than other cores below 4 cm. In this

core, -3.5 cm depth represents the top of the grey glaciolacustrine varves. Due to their relatively older age, these sediments have been subject to greater

compaction and therefore exhibit lower porosity.

% Water

40 50 60 70 80 90 100

-E cu 4 - 2MC c: --- 3MC Cl) --4MC ..!: -Cl) --SMC a. 6 --6MC E ltl a ?MC (/) ..... -o-8MC 0 Cl) 8 - a- 9MC Cl) ltl - a- 10MC cc

Figure 22 -Water content of recovered cores.

42 4.4 Geochronology

4.4. 1 210Pb Background

210Pb has a half life of 22.26 years and has proved to be well suited for dating Great Lakes sediments as much as 150 years old (Robbins and Edgington

1975, Edgington and Robbins 1990). 210Pb is one of the natural radionuclides found in the 238U decay series (Figure 23). As 226Ra decays, a fraction of 222Rn

(an inert gas) escapes from the soils and crust into the atmosphere, subsequently decaying through a number of short lived radionuclides to 210Pb.

Variations in the amount of 222Rn emitted into the atmosphere depend on factors such as soil parent material, grain size, porosity, soil moisture, wind speed, and atmospheric pressure (Krishnaswamy and Lal 1978), but variations are muted by atmospheric mixing.

210Pb is deposited in lake sediments through various mechanisms (Figure

24) (Oldfield and Appleby 1984, Evans, 1980). 226Ra, and other elements higher up in the decay series, can be introduced to a lake as part of the terrigenous input derived from the erosion and transport of material in the drainage area. The

210Pb formed by the in-situ decay of 226Ra in this material is termed the

'supported' portion of 210Pb in the system and is considered to be in equilibrium with co-deposited radium. Additional fluxes of 210Pb, or the 'unsupported' component, from other sources disturb this equilibrium. Excess 210Pb activity is primarily derived from atmospheric fallout; however other mechanisms may also contribute to the total amount of unsupported 210Pb (Figure 24 ).

43 4.5lxl09 y 1602 y 3.82 d 22.26 y 138.4 d 23su -·------... 22c'Ra 222 Rn ---·--·-·--·-... 21opb --·-···--· ... 21op0 --+ 206p b

Figure 23- 238U decay series, showing the principal radionuclides concerned with the production of 210Pb, and their radioactive half-lives (Modified from Appleby, 2001 ).

222Rn 210Pb BOMB PRODUCED? ATMOSPHERIC -----45-60 ATOMS /cm2/mln RESERVOIR ATMOSPHERE

CATCHMENT BASIN 0.4·0.6 ATOMS /cm2/mlo 1.0 -1.5 dpm /cm /yr

ATMOSPHERIC DEPOSITION IN LAKES l.O·l.5 dpm/cm2/yr

210pb RESIDENCE TIME• A FEW \JIEEKS !LAKES, OCEANS)

Figure 24 - Geochemical cycie-of 21 DPb (Modified from Evans 1980).

44 210Pb experiences a short atmospheric residence time (5-10 days), readily attaching to airborne particles and subsequently being introduced to the lake by wet precipitation or dry fallout. In the water column, lead adsorbs onto sediment particles and is transported to the lake floor and deposited. To a lesser extent, lead may also be deposited in the drainage basin and transported to the lake.

Atmospheric lead deposited in the catchment may be either rapidly transported without attaching to terrestrial particles (Benninger et al. 1975) or slowly transported attached to particles to the lake through erosional processes. 222Rn decay within the water column also contributes to the total unsupported lead;

222Rn may be introduced through diffusion from the underlying sediments and the decay of 226Ra in inflowing streams (Krishnaswamy and Lal 1978).

For this study we have assumed that the amount of direct atmospheric fallout 210Pb is much larger than the indirect and/or in situ sources of 210Pb

(Oldfield and Appleby 1984). In cores where 226Ra was measured, excess 210Pb was determined in each sample by subtracting the 226Ra activity from the total

210Pb activity. In cores where 226Ra activity was not measured, we estimated the supported 210Pb from ten centimeters depth in each core and assumed that at this level, all excess 210Pb has decayed to zero. If so; and if the flux of supported

210Pb has not changed with time, the measurement at this depth accurately represents the supported 210Pb at higher levels of the cores. In practice, equilibrium between total 210Pb activity and the supporting 226Ra is achieved after a maximum of approximately six to seven 210Pb half-lives, or 130 to 150 years

(Appleby 2001 ). Using the largest calculated sedimentation rate in this study of

45 0.56 millimeters per year; seven half lives of 210Pb, or 156 years, would be encompassed in the upper 8.7 centimeters of sediment. At this depth the total

210Pb activity would equal the amount of unsupported 210Pb measured in sediments.

4.4.2 210Pb Age Models

Three 210Pb chronology models were tested and compared in this study: the constant flux/constant sedimentation rate model (CFCS), the constant rate of supply model (CRS), and the constant initial concentration model (CIC) (Appleby

2001 ).

The CFCS model assumes a constant flux of unsupported 210Pb to the sediments. When applying the CFCS model, lakes that exhibit constant rates of sediment accumulation will contain equal initial activities of unsupported lead in each layer of sediment. Therefore, sediments of depth m (cumulative dry mass, g

2 cm- ) below the sediment water interface will be of age

t=mlr (1)

2 1 210 where r is the dry mass sedimentation rate (g cm- f ). The unsupported Pb activity will vary with depth according to the following formula

C(m)=C(O)e->-mlr (2)

210 1 where A is the Pb radioactive decay constant (.03114 f ). If the unsupported

210Pb concentration (C) is plotted on a logarithmic scale against m on a linear scale (semi-log plot), the resulting profile will be linear with slope Mr. The

46 sedimentation rate r can be determined graphically from the mean slope of the profile or by a least-squares fit to the data.

The CRS and CIC models were developed for use in lakes where sediment accumulation has varied significantly through time and will therefore exhibit complex variability in unsupported 210Pb profiles (non-linear semi-log profiles). Factors contributing to the non-linearity of 210Pb profiles include dilution of unsupported 210Pb by an increase in sediment accumulation rates, migration of

210Pb through the interstitial waters near the sediment-water interface (Koide et al. , 1973), and sediment focusing and mixing by physical (Nittrouer et al., 1979), or biological (Robbins et al., 1977) processes.

In the CRS model, changes in the sedimentation rate through time will reflect changes in the initial concentration of unsupported 210Pb. In consequence, the concentration of 210Pb in the sediment record will vary inversely in proportion to the sedimentation rate. The procedure for calculating 210Pb dates using the

CRS model is outlined in detail in Appleby and Oldfield (1978). Briefly, if

A=mf°°Cdm= xf"' pCdx (3) is the cumulative unsupported 210Pb at a depth x or cumulative dry mass m

(p=dm/dx is the dry weight/wet volume ratio), then the age t of sediments at depth x satisfies

A=A(O)e-M (4) and is given by:

t= 1/,lJn A(O)/A (5)

47 A(O) is the total unsupported 210Pb in the sediment column. A and A(O) are calculated by numerical integration of the 210Pb profile. The sedimentation rate at a given time is

r=WC (6)

The CIC model assumes that sediments have a constant initial concentration of 210Pb, independent of sediment accumulation rates.

Consequently, the concentration of 210Pb in the sediment record is directly proportional to the sedimentation rate. Therefore, the age of sediments at depth m can be calculated from the equations

1 C(m)=C(O)e-M -7 t= 1,Jn C(O)/C(m) (7) (8)

The CIC model is commonly used in lake systems that exhibit a dominant allochthonous sediment particle input (Oldfield and Appleby 1984) and when non-monotonic variations in the 210Pb concentration versus depth profile exist from hiatuses in sediment accumulation, slumping, or turbidity currents (Appleby

2001 ).

For the cores in this study, the CRS 210Pb model provided the more robust results; as a result the dates derived from the CRS model were applied to the data throughout this study. Dates from the CIC model were not used because extreme variations in the 210Pb versus depth profile from hiatuses, slumping, or turbidity currents were not observed. The CFCS model was applicable to most of the cores; however when a least squares fit trend-line was fitted to 210Pb profiles, significant variations in 210Pb activity above and below the linear trend-line were observed in almost every core.

48 A number of assumptions are associated with the CRS model: 1) a constant flux of unsupported 210Pb from the atmosphere, 2) 210Pb in fresh waters immediately adsorbs to particulate matter in the water column and is rapidly transported to the lake floor so the total unsupported lead in the sediments is due only from atmospheric deposition, and 3) the initial unsupported 210Pb activity in sediments is not re-distributed by post-depositional processes and decays exponentially according to the radioactive decay law.

Biological mixing in the near surface sediments was evident in most of our cores and tends to homogenize the 210Pb concentration within the upper 1.5 cm.

Dates at lower levels in the core are then dependent on when the sediment layer leaves the mixing zone. Many equations and modified 210Pb models have been developed to deal with sediment mixing but have not been applied to the cores used in this study. It is generally accepted that the mixed layer need only be taken into account when the thickness of the mixing zone exceeds approximately

15% of the 210Pb profile (Oldfield and Appleby 1984 ). Based on the obseNed

210Pb profiles in this study, the mixed zone is less than 15% of the 210Pb record and results in minimal error in calculating dates and bulk sedimentation rates.

Semi-log profiles of unsupported 210Pb versus depth in cores 2 - 10 exhibit common characteristics (Figure 25). All cores display a relatively constant

210Pb activity in the upper 1.5 cm of sediment, representing the biologically mixed zone. Below the mixed layer, all but one core shows an exponential decay of

210Pb down to the end of the profile. The exception is core 2, which shows a

49 significant decrease in 210Pb activity below approximately 3.5 cm depth. This decrease in activity represents the top of the varved glaciolacustrine sediments.

50 2MC 3MC 4MC

1 ------E' ..s. Q).... 0 0 u u .5 c ..c 3 ------· ----- 3 ..c 0. 0. Q) Q) 0 0 4 ------4

SMC 6MC 7MC 0------0

-E E' ..s. ..s. 2 ------....Q) 0 0 u u .5 c ..c 3 ------· ------3 ..c Q_ Q_ -Q) -Q) 0 0 4 ------4

SMC 9MC ______10MC .__ 0 0

E' E' ..s. ..s. ....Q) ....Q) 0 0 u u .5 .5 ..c 3 ----- ..c 0. 0. Q) Q) 0 0 ---- ·------4

Figure 25 - Unsupported 21 0Pb activity profiles for analyzed cores

51 The cessation of the grey varve deposition occurred around 9,035 cal. BP

(Breckenridge et al. 2004 ), well beyond the dating capability of 210Pb and should therefore contain essentially no measurable unsupported 210Pb. The curved pattern of decreasing activity in the transition zone from post-glacial to glaciolacustrine sediments is most likely due to diffusion or mixing of the isotope from upper sediment layers which exhibit higher concentrations of 210Pb. Due to its age, core 2 below 3.5 cm will not be discussed further here. Cores 6, 8 and 10 also show slight non-linear deviations on the semi-log plot. Both profiles for cores

6 and 8 suggest increased sedimentation rates at the lower extent of 210Pb analysis (-4-5 centimeters) by exhibiting a steeper slope. The core 10 profile suggests a gradual increase in sedimentation rate throughout the dated portion of the core. This phenomenon is most likely amplified in the upper few centimeters by biological mixing.

CRS age models show near linear age depth relations below 1.5 cm throughout the core (Figure 26). The only non-linear deviations are due to the effects of biological mixing in the upper parts of each core however, the mixing zone does not encompass a significant portion of the core resulting in minimal errors in calculated dates. The age model for core 2 exhibits a linear age depth relationship until reaching the top of the grey varves; dates from the lower portions of this core are not valid for reasons discussed above.

52 2MC 3MC 4MC

E' E' .._Q) ------2 .._Q) 0 0 u u c c 3 ------3 .c .cc.. c..Q) Q) 0 0 4 ------4

SMC 6MC 7MC

2 ------2 0 0 u u .5 .5 3 ------· ------3 .c .cc.. c..Q) Q) 0 0 4 ------4

SMC 9MC 10MC

------·-- 1 E' E' .._Q) 2 ------0 u0 u c .5 .c 3 ------3 .c 0.. c.. -Q) Q) 0 0 4 ------·------4

Figure 26 - CRS age/depth relations.

53 4.4.3 Sediment Focusing and 210Pb Flux to Sediments

The flux of 210Pb is assumed to be constant at any given site when averaged over the course of a year or more (Appleby 2001 ). Variations in a sediment core calculated fluxes are due to either the focusing or erosion of sediments. The flux of 210Pb to the sediments for each core was calculated by equation 9;

P = J\A(O) (9) where Pis the flux of 210Pb to the sediments, A is the decay rate of 210Pb, and

A{O) is the total 210Pb inventory of the core (Figure 27).

The extents of physical post-depositional processes were assessed by calculating a focus factor for each of the core sites. The focus factor is the ratio of the depositional 210Pb flux to the regional atmospheric 210Pb flux (Omelchenko et al. 2003). Focus factors greater than one suggest preferential accumulation of sediments while focus factors less than one suggest a remobilization or erosion of sediments. Regional atmospheric 210Pb flux to the sediments was assumed to be 183 Bq/m2yr (Robbins, J. A. 1982). Focus factors determined for the cores in this study varied from .7 to 1 .3 with a majority of the focus factors proximal to 1, resulting in minimal errors associated with dates and sedimentation rates derived from the CRS 210Pb age model (Figure 28). Calculated 210Pb fluxes and focus factors suggest that most sediment focusing is occurring along the edge and ambient regions of the western-most ring structure while the centers of both rings are subject to the greatest amount of erosion during recent times. Cores

54 recovered from the troughs display essentially no sediment remobilization, at least for the past ca. 150 years.

55 240

220

200 -'->. N E 180 O" ...... --ca x 160 ::::i LL 140

120

"o.,

Figure 27 - Flux of unsupported 210Pb to sediments for each core relative to regional value estimated in Robbins, 1982. A refers to cores taken from 'ambient', or regions adjacent to ring structures, E refers to cores taken on the edge of a ring structure, T refers to cores recovered from the trough of a ring structure, and C refers to cores recovered from the center of a ring structure.

1.2

'- 0 t5 1.0 ro LL (/') ::::i g 0.8 LL

0.6

Figure 28 - Calculated focus factor for each core. See caption for figure 27 for definition of the letters T, C, A, and E.

56 4.4.4 Dry Mass Calculations and Inventories of 210Pb

During the core processing on the RN Blue Heron, cores 2, 3, and 4 were sub-sampled for PBDEs, PCBs, and PCFs and sent to the Minnesota Pollution

Control Agency. We were unable to attain the dry sediment weights sub-sampled for these analyses, so in order to accurately calculate inventories in the sub- sampled cores, equations 10 through 14 were used to calculate the dry sediment weight per sample interval. If

DBD = Mdsed I (Vdsed + Vwater) (10)

3 where DBD is the dry bulk density in (g/cm ), Mdsed is the mass of dry sediment,

Vdsed is the volume of dry sediment, and Vwater is the water volume, and

V dsed = Mdsed I Ds (11) where Ds is the grain-specific gravity, and

V water =Mwater I Dwater (12) where Dwater is the density of water, then

DBD = [1-(PW/100)] I {[1-(PW/100)] IDs+ (PW/100)} (13) where PW is the percent water. The dry sediment weight is:

Wsed =(DBD)(Cs)(Xn -Xn-1) (14) where Wsed is the dry sediment weight per sample interval, Cs is the cross sectional area of the core, and Xn is depth in core. The dry sediment weights calculated from the equation above were subsequently used in all inventory and mass accumulation calculations for cores 2, 3, and 4. Values for grain specific gravity were calculated by equation 15.

Ds =(%0M/100) + [2.0*(%8Si/100)] + (2.65*[(100-%0M-%8Si)/100)]) (15)

57 where %OM is the percent organic matter in sediment (approximated as twice the total organic carbon concentration), 2.0 and 2.65 represent the densities of biogenic silica and bulk sediments respectively, and % BSi is the percent biogenic silica in sediments.

The total inventory of 210Pb reflects the total amount of accumulated unsupported 210Pb throughout the datable portion of the core. Differences in total inventory can be due to variations in the regional 210Pb flux, sedimentation rates, or sediment redistribution from biological or physical processes. Inventories of unsupported 210Pb over the datable portion of the core (top 5 cm) (Figure 30), were calculated by equation 16;

Inventory = 2: Ci mi (16) where Ci is the concentration in a sample interval i and mi is the cumulative mass of sediment in sample interval i. For the inventory of unsupported 210Pb, this method was compared to the trapezium rule, a formula commonly used to calculate the cumulative unsupported 210Pb. (Appleby 2001) (equation 17).

An = An-1 + Y2(Cn + Cn-1HMn - Mn-1) (17)

An is the cumulative unsupported 210Pb inventory above accumulated mass Mn

2 210 (in g/cm ) and Cn is the unsupported Pb concentrations above accumulated mass Mn. Negligible differences in inventories were observed between either method. To attain the inventory of unsupported 210Pb activity below the datable portion of the core (beyond 5 cm depth), an exponential equation was fit to the lower most four or more data points on a plot of accumulated mass versus unsupported 210Pb activity and extrapolated to infinity. The equation was then

58 integrated from the lower most interval of measured accumulated mass (4.5 - 5

cm) to an estimated accumulated mass contained between 0 and 10 cm depth

(Figure 29). Calculated inventories from both above and below 5 cm were added

. to attain a total cumulative inventory of 210Pb for subsequent use in CRS age

models. Inventories ranged from 0.42 to 0.78 Bq/cm2 in recovered cores. The

lowest total inventories were observed in cores recovered from the centers of

ring structures, while other cores exhibited relatively random variations in total

inventory suggesting either differences in sediment accumulation or local

sediment focusing has occurred throughout the study area (Figure 30).

59 3MC CRS y =2.8801 e-4.2035x R2 =0.9959

.E' 0.9 -+--<>------< caC" 0.8 +--->------<

:;:;·:;: 0.7 +-----+------< 0

...... 0 .c a.. "O 0.4 +------'I>------< Cl> 0.3 +------.------< c. 0.2 ::I UJ s:: 0.1 r------....------j ::::>

0.2 0.7 1.2 1.7 2.2 Accumulated Mass (g/cm2)

29 - An exponential trend line fitted to a plot of accumulated mass versus unsupported 10 210 Pb activity in order to calculate the inventory of unsupported Pb below 5 centimeters.

0.8 ------

N -E -52 0- 0.6 >...... 0

cQ) > .E: 0.4 .0 a.. 0

0.2

210 Figure 30 - Total inventory of Pb for recovered cores. See caption for figure 27 for definition of the letters T, C, A, and E.

60 4.4.5 Bulk Sediment Mass Accumulation Rates and Cumulative Inventory

Bulk sediment Mass Accumulation Rates (MARs) and inventories were

obtained from the CRS 210Pb age models for each sample interval to investigate

variability in sediment accumulation through time (Figures 31, 32). Most cores

typically show an increase in sediment accumulation towards the top of the core,

however below the mixed layer profiles show significant variability among the

cores. The MAR profile in 2 displays a relatively low and constant MAR of 58

g/m2 until 1945, then progressively increases to a peak of 141 g/m2 at the top of the core. The large down core decrease in MAR below a date of -1970 is

undoubtedly an artifact of the CRS age model due to the low unsupported 210Pb activities in the much older glaciolacustrine sediments. The presence of the varves at -3.5 cm in clear evidence of an erosional unconformity, thus the MAR

2 below this depth is actually 0 g/m .

Cores 3 and 9 were both recovered from the centers of ring structures and display relatively similar MAR histories. Core 3 shows a continual decrease from

112 g/m2 at the base of the dated interval to 84 g/m2 in 1977, and an increase to

105 g/m2 at the top of the core. Core 9 also exhibits a decrease in MARs throughout most of the dated interval; with a low of 88 g/m2 in 1981 and an increase to 101 g/m2 in 1998, but from 1998 to the present MARs decreased to

2 93 g/m .

With the exception of core 10, the other cores were recovered from the edges of ring structures and ambient regions; many of which exhibit somewhat similar MAR characteristics through time. Core 4 has the highest overall

61 accumulation rates, beginning with a MAR of 151 g/m2 in 1957, decreasing to

126 g/m2 in 1998, then increasing and peaking at 160 g/m2 at the top of the core.

Core 5 shows a more complex history of MARs, starting with 161 g/m2 in 1944,

decreasing to 114 g/m2 in 1968, and then generally increasing to 143 g/m2 at

recent times. Core 6 begins with a MAR of 148 g/m2 in 1930, increases and

peaks at 152 g/m2 in 1938, decreases to a low of 94 g/m2 in 1971, and then continually increases through the next 34 years to a MAR of 128 g/m2 at the top of the core. Core 8 has a similar trend to core 6, but with an initial MAR of 127 g/m2 in 1935, an increase and peak to 154 g/m2 in 1954, a decrease to 101 g/m2

in 1987, and a gradual increase to 119 g/m2 to the top of the core. Cores 7 and

10 also show similar trends to one another, both showing arcuate profiles with the highest MARs and the base and top of the dated interval. Core 7 begins with a MAR of 113 g/m2 in 1897, decreases to a low of 78 g/m2 in 1959, and gradually increasing to a peak of 120 g/m2 at the top. Core 10 starts with a MAR of 139 g/m2 in 1924, decreases to a low of 109 g/m2 in 1971, and continually increases and peaks at a value of 14 7 g/m2 in recent years.

Bulk sediment inventories reveal the total amount of accumulated sediment in a given core. The graph of bulk sediment inventory from year 1942 illustrates the highly variable sediment accumulation between core sites in this study (Figure 33). In general, cores recovered throughout the ambient regions exhibit higher bulk sediment inventories while cores recovered in the troughs and in the centers of ring structures display relatively lower inventories. The observation of large differences in bulk sediment inventory between cores

62 recovered on the edges of ring structures and cores from the troughs is suggestive of very different depositional regimes across ring structures.

63 2MC 3MC 4MC 2000 ------2000 1990 ------1990 1980 ------1980 ------1970 1000 ------1960 ------1950 1940 1940 1930 1930 1920 1920 1910 1910 1900 1900

1 8 9 0 -'-r-----.--,.----.--.--.---,-----.--,.----.--r--' '-r--.----,-,---.---+-.--.----,-,--..--' 1890 60 80 100 120 140 160 60 80 100 120 140 160 60 80 100 120 140 160 SMC 6MC 7MC 2000 ------2000 1990 1990 1980 1980 1970 1970 1960 1960 1950 1950 1940 1940 1930 1930 1920 1920 1910 1910 1900 1900 1 8 9 0 60 80 100 120 140 160 60 80 100 120 140 160 60 80 100 120 140 160 BMC 9MC 10MC 2000 ------2000 1990 ------1990 1980 ------1980 1970 ------1970 1960 ------1960 1950 ------1950 1940 ------1940 1930 ------1930 1920 ------1920 1910 ------1910 1900 ------1900 1890 1890 60 80 100 120 140 160 60 80 100 120 140 160 60 80 100 120 140 160 (g/m2 yr)

Figure 31 - Bulk sediment mass accumulation rates.

64 2000

1990

1980

1970

1960 -- 2MC 3MC -- 4MC 1950 -- SMC -- 6MC o 7MC 1940 - o- BMC -- 9MC 1930 - 0- 10MC

1920

1910

1900

1890

40 60 80 100 120 140 160 180 g/m2

Figure 32 - Stacked plot of bulk sediment mass accumulation rates through time.

Bulk Sediment

8000 ------

7000 ------

N -..§ 6000 9

5000

4000

Figure 33 -Inventory of bulk sediment from 1942 to the present. See caption for figure 27 for definition of the letters T, C, A, and E.

65 In conjunction with variable inventories, there is not a consistent history of sediment mass accumulation reflected in profiles of mass accumulation. For example, during the 1960's cores 5, 6, 7, and 10 exhibited some of the lowest sediment accumulation rates throughout their depositional history. Paradoxically, cores 4 and 8 display relatively high MARs during this period suggesting lateral shifts in sediment accumulation among core sites through time. The variability in inventories and MARs observed among cores recovered from the edges or troughs of different ring structures leads us to the conclusion that sedimentation not only varies between ambient regions and within the ring structures, but between individual ring structures as well, suggesting that sediment accumulation in this offshore depositional environment is indeed quite complex.

However, nearly all of the cores do display a consistent rise in bulk sediment

MAR in the last decade or so.

66 4.5 Biogenic Silica (BSi)

4. 5. 1 Biogenic Silica Concentration

Diatoms are one of two algal groups that compose the majority of the

phytoplankton biomass in Lake Superior (Munawar and Munawar 1978) and their frustules are commonly preserved in the lake floor sediments. The concentration of these diatom remains in sediments is expressed as weight percent biogenic silica (%BSi). When used in conjunction with total organic carbon, %BSi is considered a good estimate of "export production," or the rain of algal detritus out of the photic zone. Often, studies (e.g. Wollin et al. 1988) use %BSi to reconstruct and assess ecological changes in a system, which are frequently interpreted as reflecting anthropogenic perturbations to a system.

%BSi profiles generally display similar trends with a decrease in concentration with depth and age (Figures 34 and 35). Superimposed on the general trends are slight deviations observed in cores 3, 4, 5, 7, and 9. These cores exhibit higher BSi concentrations in the late 1980's or 1990's rather than at the top of the core. In addition to this, some cores also show sharp decreases in

BSi concentrations that stray from the general trend.

67 4.5.2 Smear Slides

The abundance and integrity of diatom tests decreased considerably down core. Smear slides from 0.0 to 0.5 cm were dominated by complete tests and relatively larger broken diatom fragments displaying angular edges. Some fragments exhibited dissolution based on the roundedness of test edges. Midway through the dated portion of the cores (-2.5 cm) whole diatom tests became less abundant and smear slides became dominated by test fragments. Most fragments and whole tests showed signs of dissolution by displaying rounded edges and became increasingly faded, appearing as if they were becoming thin.

At 4.5 to 5.0 cm the number of fragments and whole tests became noticeably smaller. Intact tests became relatively rare in most of the cores, and were dominated by test fragments with rounded edges. Core 2 exhibited no diatom tests below 4.0 cm.

68 0 2MC

2 2 3 3 E -E ,s 4 4 ,s Q) .....Q) 5 5 ..... 0 0 () 6 6 () c c ..r:::. 7 7 ..r:::. 0. 0. Q) 8 8 Q) 0 0 9 9 10 10 11 ------11 12 0 2 8 10 0 2 4 6 8 10 2 4 6 8 10 SMC .---....----..---..----.--.-7MC 0 ------· 1 2 2 -3 3 E' Q4 4 ,s s 5 e0 () 6 6 () c c ·- 7 7 ..r:::. ..r:::. 0. 0. 8 8 Q) Q) 0 0 9 ------9 10 ------10 11 ------11

1 2 -!---.---.-0-r--r---r--..--r---r--l 2 4 6 8 10 2 4 6 8 10 2 10 0 8MC 9MC

2 2 E'3 3E' ,s 4 4 ,s Q) 0 5 s e0 () 6 6 () c ..r:::. 7 7 ..r:::. 0. Q) 8 8 g- 0 o 9 9 10 10 11 11 12 12 2 4 6 8 10 2 4 6 8 10 2 4 6 8 10 % BioSi

Figure 34 - Percent biogenic silica plotted against the base of each depth interval.

69 2MC 2000 2000 1990 1990 1980 1980 1970 1970 1960 1960 1950 ------1950 1940 1940 1930 1930 1920 ------1920 1910 ------1910 1900 ------1900 1890 ------1890

2 3 4 5 6 7 8 9 3 4 5 6 7 8 9 3 4 5 6 7 8 9 5MC 6MC 7MC 2000 2000 1990 1990 1980 ------· 1980 1970 ------· 1970 1960 ------· ------1960 1950 ------· ------·------1950 1940 1940 1930 1930 1920 1920 1910 1910 1900 1900

3 4 5 6 7 8 9 3 4 7 8 9 3 4 5 6 7 8 9 8MC 10MC 2000 ------2000 1990 ------1990 1980 1980 1970 ------1970 1960 1960 1950 1950 1940 1940 1930 ------1930 1920 ------1920 1910 ------1910 1900 ------· ------1900

3 4 5 6 7 8 9 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 % BioSi

Figure 35 - Percent biogenic silica plotted against age.

70 4.6 Concentrations of Total Organic C, Total Organic N, and C/N Ratios

4. 6. 1 Total Organic Carbon (TOG)

The concentration of TOC represents the total amount of organic carbon

that has escaped decomposition in the water column or sediments. TOC

concentration is expressed as a weight percentage of organic carbon in

accumulated sediments (% TOC). This parameter has been routinely used in

studies to investigate environmental changes or anthropogenic impacts within a drainage basin.

All but two of the cores exhibit relatively simple profiles displaying a steady

increase in % TOC from the base of the dated interval to the top of the core, with subtle decreases over some age intervals (Figures 36 and 37). The two exceptions to this general observation are core 5 and 9. The concentration in

1983 in core 5 exhibits an unusually high TOC concentration of 5.4%, and core 9 has atypically high concentrations between -1940 and 1965. These relatively large spikes in % TOC give rise to the question of analytical error. The spike in core 5 may be due to analytical error because it is a single data point unsupported by time or depth synchronous increases in % TOC from other cores in the study area. The spike observed in core 9 is most likely not due to analytical error. Although profiles of the other cores suggests that there are no time or depth synchronous events to support this increase in % TOC, data points directly adjacent to this interval show an increase in % TOC as well.

71 4.6.2 Total Organic Nitrogen (TON)

All profiles of% TON display a progressive increase in nitrogen from the

base of the dated interval to the top of the core (Figures 38 and 39). The only deviations from this trend are observed in cores 2, 4, and 8; these cores exhibit very small decreases in %TON in the upper-most sediment interval.

72 3MC 4MC 0

2 2 3 E 3E' 4

2 ------2 3 3 E E 4 5 5 .....

Figure 36 - Percent total organic carbon plotted against base of depth interval.

73 3MC 2000 2000 1990 1990 1980 ------1980 1970 1970 1960 1960 1950 1950 1940 ------1MO 1930 ------1930 1920 ------1920 1910 ------1910 1900 ------1900 1890 ------1890

0 2 3 4 5 2 3 4 5 2 3 5 SMC 6MC 2000 ------2000 1990 ------1990 1980 ------1980 1970 ------1960 ------1960 1950 ------1950 1940 ------1940 1930 ------1930 1920 ------1920 1910 ------· ------1910 1900 ------· ------1900

2 3 4 5 2 3 4 5 2 3 4 5 SMC 9MC 10MC 2000 ------2000 1990 ------1990 1980 ------1980 1970 ------1970 1960 ------1950 ------1950 1940 ------1940 1930 1930 1920 1920 1910 1910 1900 1900

2 3 4 5 2 3 4 5 2 3 4 5 Wt.% Carbon

Figure 37 - Percent total organic carbon plotted against age.

74 4MC 0

2 2 -3 3- E 2- 4 4 § 5 5 -.....Q) 0 0 () 6 - 6 () c c 7 ------7 _c·- 0.. 8 ------8 0. Q) -Q) 0 9 ------9 0 10 ------10 11 ------11

12 -+--.----,--,--,--,--,--,---..--< t--r-r-r-r-r-r-r-r-i t--r-r-r-r-r-ir-r-ic-+- 12 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.8 0.0 0.2 0.4 0.6 0.8 SMC 7MC 0 1 1 2 2 3 -3 "E _Q_ 4 4 (.) 5 5 -.....Q) 0 0 () 6 6 () .£ 7 .£ _c 7 _c 0.. 8 8 0. Q) -Q) 0 9 9 0 10 10 11 11 12-t---.---....-0---r---r---r---r---r--,--l >--r-.--C)----,..--..--..--..----1 12 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 SMC 9MC 10MC 0 0 1 2 2 -3 3- E _Q_ 4 4 (.) 5 5 -.....Q) 0 0 () 6 6 () c c 7 7 _c 0.. 0..Q) 8 8 Q) 0 9 9 0 10 10 11 ------11 12 12 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 Wt. % Nitrogen

Figure 38 - Percent total organic nitrogen plotted against base of depth interval.

75 2000 2000 1990 1990 1980 1980 1970 1970 1960 1960 1950 1950 1940 ------1940 1930 ------1930 1920 ------1920 1910 ------1910 1900 ------1900

0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 SMC GMC 7MC 2000 2000 1990 1990 1980 ------1980 1970 1970 1960 1960 1950 1950 1940 ------1940 1930 ------·------1930 1920 ------1920 1910 ------1910 1900 ------1900

0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 8MC 9MC 10MC 2000 ------2000 1990 ------1990 1980 1980 1970 1970 1960 1960 1950 1950 1940 ------1WO 1930 ------1930 1920 ------1910 ------1910 1900 1900

0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 Wt. % Nitrogen

Figure 39 - Percent total organic nitrogen plotted against age.

76 4. 6.3 GIN Ratios

The majority of organic matter deposited in Lake Superior sediments is derived from phytoplankton (Kemp and Johnston 1979), however, there are terrestrial and anthropogenic contributions as well, particularly in areas that receive relatively high fluxes of river discharge (Maier and Swain 1977).

The C/N ratio provides information on the relative contributions of aquatic and terrestrial sources to the organic matter (Meyers and lshiwitari 1995). Higher C/N values {>20) suggest a dominance of terrestrial organic matter, while lower values (<15) indicate organic matter from an aquatic origin (phytoplankton).

C/N ratios from all cores indicate a dominant aquatic origin for organic matter preseNed in sediments (Figures 40 and 41 ). Overall, profiles of C/N progressively decrease towards the top of the core but only slightly; however occasional peaks in the C/N ratio up to values of 12 or 13 suggest some periods of higher input of terrestrially derived material, for example from 1930 to 1970 in core 7 and from 1930 to 1960 in core 9. The timing of these greater inputs of terrestrial organic matter, however, is not consistent among all of the cores.

77 0

2 2 ...... -..3 3 E E 4 .....Q.) 5 5 0 0 () () 6 - 6 c c 7 7 .ca. a. 8 8 Q.) Q.) 0 0 9 9 10 10 11 ------11 12 4 6 8 10 12 4 6 8 10 12 4 6 8 10 12 o--r----..---r-----,SMC .---..----..----..----..----6MC _ 7MC___, _ 1 2 2 ...... 3 3.-.. E E 4 Q.)..... 5 5 0 0 () 6 6 () c c .c 7 7 8 a.Q.) 8 a.Q.) 0 9 9 0 10 10 11 ------11 1--.--..--.--...--..--.---..--.--+-12 4 6 10 12 4 6 10 12 4 6 iMc10 12 0 -.---.---.,---,....--.------, ,---,....--,....--,....--,....---, ..--.---..---r---r-----r-1 0

2 ------2 ...... 3 3 ...... E E 4 .....Q.) 5 5 0 0 () 6 6 () c 7 7 .c .c a. 8 Q.) 8 -fil- 0 9 9 0 10 10 11 11 12 -+--.--.--.-..-...--..--.--.------i 1--r--r--r----r--r--r--.------i 1--..--,....-,....-....-,...._,....-,....-,_....+. 12 4 6 8 10 12 4 6 8 10 12 4 6 8 10 12 C/N Ratio

Figure 40 - C/N ratios plotted against base of depth interval.

78 2MC 3MC 4MC 2000 ------2000 1990 ------1990 1980 ------1980 1970 1970 1960 1960 1950 ------1950 1940 ------1940 1930 ------1930 1920 1920 1910 1910 1900 1900

8 9 10 11 8 9 10 11 8 9 10 11 SMC 6MC 7MC 2000 2000 1990 1980 1980 1970 1970 1960 1960 1950 ------·------1950 1940 ------· 1940 1930 ------1930 1920 ------· 1920 1910 ------· ------· 1910 1900 ------· 1900

8 9 10 11 12 13 8 9 10 11 8 9 10 11 SMC 9MC 10MC 2000 2000 1990 1990 1980 1980 1970 1970 1960 1960 1950 ------1950 1940 ------1940 1930 ------· ------1930 1920 ------1920 1910 ------1910 1900 ------1900

8 9 10 11 8 9 10 11 12 8 9 10 11 C/N Ratio

Figure 41 - C/N ratios plotted against age.

79 All Cores % C vs Depth All Cores % N vs Depth

2 2

3 3

4 4

5 E E' u 6 .ca. a.Cl,) Cl,) 0 7 7 0

8 8

9 9

10 10

11 11 12 ----- 0 2 3 4 5 0.0 0.1 0.2 0.3 0.4 0.5 0.6 --+- 2MC All Cores C/N vs Depth All Cores % BioSi vs Depth - 3MC 0 ---- 4MC ---- 5MC ---- 6MC o ?MC 2 2 --<>- 8MC -o- 9MC -o- 10MC 3 3

4 4

5 5 E' E' I ------.c 6 6 a..c a.Cl,) Cl,) 0 7 ------7 0 8 t 8 9 9

10 ------10

11 ------11

4 6 8 10 12 0 2 4 6 8 10

Figure 42 - Stacked plots of TOC, TON, C/N, and BSi versus base of depth interval.

80 % TOC versus Age % TON versus Age

2000 2000

1990 1990

1980 1980

1970 1970

1960 1960

1950 1950

1940 1940

1930 1930

1920 1920

1910 1910

1900 1900 -o- 2MC 1890 1890 - o- 3MC -- 4MC 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 -- 5MC -- 6MC %BioSi versus Age C/N versus Age o ?MC - o- BMC 2000 2000 -o- 9MC -o- 10MC 1990 1990

1980 1980

1970 1970

1960 1960

1950 1950

1940 1940

1930 1930

1920 1920

1910 1910

1900 1900

1890 1890

7 8 9 10 11 12 13 2 3 4 5 6 7 8 9 10

Figure 43 - Stacked plots of TOC, TON, C/N, and BSi versus age.

81 4.7 Biogenic Silica and Total Organic Carbon Mass Accumulation Rates

BSi and carbon MARs were derived by multiplying the percent composition of BSi or carbon by the bulk sediment mass accumulation rates in each sample interval. All MARs are expressed in units of g/m2/yr. The MAR of organic carbon and BSi is typically a more accurate representation of the amount of these compounds preserved in sediments than solely%TOC or %BSi; variations in sedimentation rates throughout the depositional history of a core can lead to a dilution or concentration of organic carbon or BSi and skewing the data.

Profiles of both BSi (Figure 44) and TOC (Figure 45) display a general trend of MARs starting to increase around 1960 and continuing to increase to the present. During earlier years, the MARs are relatively constant. Some notable deviations do exist however, for example MARs in cores 6 and 10 do not reach a steady value at their bases; MARs increase from -1925 to -1960. Other profiles

(cores 5 and 8) display relatively smaller deviations from the general trend.

82 4MC 2000 2000 1990 1990 1980 ------1980 1970 ------1970 1960 1960 1950 1950 1940 1940 1930 ------1930 1920 1920 1910 1910 1900 1900 1890 1890 2 4 6 8 10 12 14 2 4 6 8 10 12 14 2 4 6 8 10 12 14 SMC 6MC 7MC 2000 ------2000 1990 1990 1980 1980 1970 1970 1960 1960 1950 1950 1940 1940 1930 1930 1920 1920 1910 1910 1900 1900 18 9 0 2 4 6 8 10 12 14 2 4 6 8 10 12 14 2 4 6 8 10 12 14 8MC 9MC 10MC 2000 ------2000 1990 1990 1980 1980 1970 1970 1960 1960 1950 1950 1940 1940 1930 ------· 1930 1920 ------1920 1910 ------1910 1900 ------· 1900 1 8 9 0 1890 2 4 6 8 10 12 14 2 4 6 8 10 12 14 2 4 6 8 10 12 14 BSi MAR (g/m2 yr)

Figure 44 - Biogenic silica mass accumulation rates through time.

83 2MC 3MC 2000 ------2000 1990 1990 1980 1980 1970 ------1970 1960 ------1960 1950 ------1950 1940 ------1940 1930 ------1930 1920 ------1920 1910 ------1910 1900 ------1900

0 1 2 3 4 5 6 7 2 3 4 5 6 7 2 3 4 5 6 7 SMC 6MC 7MC 2000 2000 1990 1990 1980 1980 1970 ------1970 1960 ------1960 1950 ------1950 1940 ------1940 1930 ------1930 1920 ------1920 1910 ------1910 1900 1900 1890 2 3 4 5 6 7 2 3 4 5 6 7 2 3 4 5 6 7 SMC 9MC 10MC 2000 ------2000 1990 ------·------1990 1980 ------1980 1970 ------1970 1960 ------1960 1950 ------1950 1940 1940 1930 1930 1920 1920 1910 1910 1900 1900 1890 1890 2 3 4 5 6 7 2 3 4 5 6 7 2 3 4 5 6 7 TOC MAR (g/m2 yr)

Figure 45 - Total organic carbon mass accumulation rates through time.

84 2000

1990

1980

1970

1960

1950

1940

1930

1920

1910

1900

1890 -- 2MC - o- 3MC 0 2 4 6 8 10 12 14 16 -- 4MC 2 BSi MAR (g/m /yr) -- 5MC -- 6MC o 7MC 2000 - o- BMC --o- 9MC 1990 - o- 10MC 1980

1970

1960 1950

1940 1930

1920 1910

1900

1890

0 2 3 4 5 6 7 2 TOC MAR (g/m /yr)

Figure 46 - Stacked plots of TOC and BSi MARs against age.

85 4.8 Methyl Mercury (MeHg)

All cores in this study show the typical diagenetic MeHg profiles that have been observed in other studies (Figures 47 and 48) (e.g. Rolphus et al. 2003) which have recovered cores from the deep depositional areas in Lake Superior.

Profiles exhibit lower concentrations of MeHg in deeper sediments with concentrations increasing, at times exponentially, towards the top of the core. No time or depth synchronous MeHg depositional events are observed in any of the profiles.

86 0 0 1 2 2 3 3 E E .s- 4 4 .s- ,_Q) 5 5 ,_Q) 0 0 (.) 6 6 (.) c .£; £ 7 7 £ Ci. Ci. Q) 8 8 Q) 0 9 9 0 10 10 11 ------11 12 12 0.0 0.2 0.4 0 .6 0.8 0.0 0.2 0.4 0 .6 0 .8 0 .0 0.2 0.4 0 .6 0 .8 SMC 6MC 0 7MC 0 1 1 2 2 3 3 -E E .s 4 4 -.s Q) ,_ 5 5 ,_Q) 0 0 (.) 6 6 (.) .£; .£; £ 7 7 £ Ci. Ci. Q) 8 8 Q) 0 9 9 0 10 10 11 11 12 12 0.0 0 .2 0.4 0 .6 0.8 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0 .8 0 SMC 9MC 0 ------1 2 2 3 3 E -E - 4 4 .s .s Q) ,_Q) ,_ 5 5 0 0 (.) (.) 6 6 c c £ 7 7 £ 0. Ci. Q) Q) 8 8 - 0 0 9 9 10 ------10 11 ------11 12 12 0.0 0.2 0.4 0 .6 0.8 0.0 0.2 0.4 0.6 0.8 Me Hg (ng/g)

Figure 47 - Methyl mercury plotted against base of sample interval.

87 2MC 2000 2000 1990 1990 1980 1980 1970 1970 1960 1960 1950 ------1950 1940 ------1940 1930 ------1930 1920 ------1920 1910 ------1910 1900 ------1900 1890 ------1890

0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 SMC 6MC 7MC 2000 ----- 2000 1990 1990 1980 1980 1970 ------1970 1960 ------1960 1950 1950 1940 1940 1930 1930 1920 1920 1910 1910 1900 1900 1890 1890 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 BMC 9MC 2000 2000 1990 1990 1980 1980 1970 1970 1960 1960 1950 1950 1940 1940 1930 ------1930 1920 1920 1910 ------1910 1900 ------1900

0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 MeHg (ng/g)

Figure 48 - Methyl mercury plotted against age.

88 4.9 Compound Diagenesis

The concentrations of BSi, TOC, TON, C/N, and MeHg are undoubtedly affected by diagenesis, and therefore down-core profiles of these compounds display both changes in the concentrations of compounds and the effects of diagenetic reactions. Smear slides clearly indicate greater dissolution of diatom tests with increasing depth in each core, resulting in %8Si profiles that may amplify trends towards lower concentrations with depth. The oxidation of organic matter augments decreases in %TOC with depth and in turn, most likely impacts the shape of MeHg and TON profiles, and C/N ratios as well. An augmented decrease in TOC is illustrated in figure 49. Total organic carbon concentrations in sediments are plotted along with a regression line, which represents a one- dimensional model for microbial decomposition of TOC, assuming steady-state diagenesis (Berner, 1980). The regression line illustrates a 'typical' down-core diagenetic trend that is often obseNed in lacustrine and marine sediments.

89 TOTAL ORGANIC CARBON {mmol per gm

E 20 .,g- )( 30 ! 40

Figure 49 - Early diagenesis in sediments of Lake Greifensee, Switzerland. Regression line is an empirical diagenetic model for the decay of TOG. Modified from Berner (1980).

90 5.0 Discussion

5.1 Compound Distributions and Links to Recent Sediment Accumulation.

5. 1. 1 Inventories of BSi and TOG

Data from this study provides strong evidence supporting our hypothesis that the distribution of natural and anthropogenic compounds is quite variable spatially and temporally over the last 150 years at scales of 1 - 10 km 2 in depositional environments typical of the central and western deepwater basins of

Lake Superior.

Plots of bulk sediment, BSi, and TOC cumulative inventories since 1942 display considerable variation among core sites throughout the study area

(Figures 49-51 ). The total inventories of all three parameters vary by nearly a factor of two among the core sites. A comparison of BSi and TOC inventories to bulk sediment inventory reveals a direct relationship between the sediment accumulation rate at a particular core site and the accumulated amount of each compound (Figures 52-53).

2 BSi inventories range from about 300 to 590 g/m , while TOC inventories range from 190 to 290 g/m2 in the study area. In general, inventories are higher in the ambient regions and near the edges of ring structures relative to inventories from cores recovered from the centers and troughs, however there are a few exceptions to this. Core 4 was recovered from the edge of a ring structure but exhibits the highest inventory of both BSi and TOC; similarly core

10 was recovered from a trough but displays inventories similar to cores recovered from ambient regions and ring edges.

91 Bulk Sediment

8000 ------

7000

...... N E 6000 9

5000

4000

Figure 50 -Inventory of bulk sediment from 1942 through the present. A refers to cores taken from 'ambient', or regions in between ring structures, E refers to cores taken on the edge of a ring structure, T refers to cores recovered from the trough of a ring structure, and C refers to cores recovered from the center of a ring structure.

Biogenic Silica

600 ------

500

N' E 9 400

300

Figure 51 -Inventory of BSi from 1942 through the present. See caption to Figure 49 for definition of the letters T, C, A, and E.

92 Total Organic Carbon

300 ------

250 N' E 9 200

150 --

Figure 52 - Inventory of TOC from 1942 through the present. See caption to Figure 1 for definition of the letters T, C, A, and E.

93 Bulk Sediment and BSi Cumulative Inventories (1942 - 2005)

120 •

100 • 2MC • • • 3MC • • ,, • 4MC -N 80 • 5MC ._E • C'l • • • • • 6MC -(/) • •• • • ?MC 60 • • co • 8MC • • 9MC 10MC 40 •• •• • • 20 •

0 200 400 600 800 1000 1200 1400 1600 Bulk Sed (g/m2)

Figure 53 - Cumulative inventories, from 1942 to the present, for bulk sediment and BSi plotted against each other illustrating the linear relationship between sediment accumulation rates and the concentration of BSi in sediments among cores.

94 Bulk Sediment and TOC Cumulative Inventories (1942 -2005)

• 2MC 50 • 3MC • • 4MC •• • 5MC N' 40 • • 6MC E • I!! -C'l 7MC -(.) • BMC 30 .....0 • 9MC • 10MC 20 • • •• 10

0 200 400 600 800 1000 1200 1400 1600 Bulk Sed (g/m2)

Figure 54 - Cumulative inventories, from 1942 to the present, for bulk sediment and TOC plotted against each other illustrating the linear relationship between sediment accumulation rates and the concentration of TOC in sediments among cores.

95 Less variability is observed between cores recovered from either ambient regions or the centers of ring structures than from within, or on the edges of troughs (Figures 49-51, 54-55) The difference in inventories among cores recovered from ring edges is undoubtedly due to the inconsistent nature in which sediment accumulates over the ring troughs. Seismic profiles that extend from ambient regions to ring troughs display a diverse array of features that range from erosional surfaces and slumps to sloping edges that show only a gradual thinning of post-glacial sediments (Cartwright et al. 2004) (Figures 5, 9). In contrast to core 7, core 4 was recovered from a trough edge where the sediment accumulation pattern is similar to what is observed in ambient regions. The comparatively high inventory, and a focus factor greater than one, suggests this core site is an area of localized sediment focusing. Relative to 2, the high inventories observed in core 10 suggest that sedimentation in this trough site has been comparable to that in the ambient regions, at least for the past -100 years.

However there is a strikingly different gray clay below 35 cm depth in core 10 that is not observed in either of the cores from the ambient sites (5 and 8), revealing that sedimentation at site 10 has been 'normal' for the time represented by 35 cm of sediment (roughly the past 1000 - 1500 years).

Regardless of location, all core sites contain a sediment accumulation record of at least the last 50 to 60 years which suggests that active erosion by bottom currents facilitated by dewatering, or other mechanisms responsible for the formation of ring structures, has not been a common occurrence in the study area during recent times. Sediment erosion from deep water currents has been

96 previously documented in the eastern basins of Lake Superior with the use of submersibles (Val Klump et al. 1989). Johnson et al. (1984) have also shown side-scan images of ring structures that have been partially filled with sediment, most likely from sediment redistribution caused by the Keweenaw Current.

Although all cores in our study area retain relatively complete recent sediment accumulation records, the substantial variability in inventories indicates that deep water currents cause some sediment focusing in and around the ring structures.

Due to its location, our study area is not likely to be strongly affected by the Keweenaw Current, which runs eastward along the north shore of the

Keweenaw Peninsula, and other high velocity currents that have been observed, mainly in constricted settings where currents are focused elsewhere in Lake

Superior. However, this area could possibly be affected to a lesser extent by bottom currents associated with storm seiches, thus allowing a majority of the sediment to blanket ring structures in the study area. An open source model of

Lake Superior suggests the potential for deep-water currents reaching 10 cm/second in the study area (J. Austin personal communication). Currents driven by wind stress, particularly when the lake is isothermal, or by density driven currents from surface heat fluxes may create currents strong enough to redistribute sediment as well (Beletsky et al. 1999). The morphometry of rings could modify currents just above the lake floor by creating current breaks or localized increases in current velocity resulting in the observed complex sediment and compound distributions throughout the troughs, centers, and ambient regions of the study area.

97 +

Figure 55 - The inventories in g/m2 of biogenic silica from 1942 to the present. Actual inventory is listed beside the core number. Large-circle rad ii correspond to higher inventories.

98 +

Figure 56 - The inventories in g/m2 of organic carbon from 1942 to the present. Actual inventory is listed beside the core number. Large-circle radii correspond to higher inventories.

99 Figures 56 through 61 use the range, standard deviation, and coefficient of variation per decade to illustrate that variability is not only observed in the spatial distribution of total cumulative inventories of bulk sediment, BSi, and

TOC, but in their temporal distribution as well. Each of these statistical parameters is designed to measure of the range of variation from an average of a group of measurements. The standard deviation is defined as the positive square root of the variance; 68% of all measurements fall within one standard deviation of the average. The coefficient of variation is a measure of the ability to repeatedly obtain the same value for a single sample or method (i.e.; duplicate or replicate analyses). It is defined as the ratio of the standard deviation to the mean value multiplied by 100.

The ranges in decadal inventories (plotted as error bars) can be as large as the value of the mean inventory itself, and standard deviations reach almost

50% of the mean when all cores are considered (Figures 56, 58, 60). Decadal coefficients of variation range from 0 to over 90% (57, 59, 61 ). These observations suggest that ring structures, and other lake floor features, have undoubtedly impacted the bulk sediment and natural compound accumulations through time to a significant degree throughout the central and western basins of

Lake Superior.

100 Bulk Sediment

Troughs (Range) Centers (Range)

1300 1300 1200 1200 1'1100 1'1100 :91000 :91000 c 900 c 900 g; 800 ======r ======g; 800 c ---- -1 - --1 - ·--.--1--t- -I---- 700 700 ----- __ __! __ ------:,ii 600 :,ii 600 ::;; ::;; 500 ------==f ==l=== 500 400 400

r::,<::.r::, q,'?>r::, "q,'Or::, q,'\r::, "q,'<>r::, q,":>r::, q,'>-r::, q,">r::, q,"vr::, q,'-r::, q,r::.<::. Ricy !¢cy" '°cy" .,_cy" r:F" a,'Y" -.C:J" "v\S "v\S ""' ""' -.C?> ""' " -.C?> -.C?> "q, Ambient (Range)

1300

'E 1100 -----1------1------1'1100 ------·---1------:g1000 ------1-----I------:91000 ------.9 900 900 c ------c g; 800 ------g; 800 700 700 :,ii 600 :,ii 600 ::;; ::;; ---!------500 500 400 400

All Cores (Range) All Cores (Standard Deviation)

1300 ------1300 ------1200 1200 ------i------1'1100 ----{--f------1'1100 31000 ------______I ______:91000 900 ------900 c c ======g; 800 g; 800 ----L-r---r------c c 700 700 Q) 600 :,ii 600 ::;;"' ------::;; 500 ------500 400 ------400

Figure 57 - The mean values of decadal bulk sediment inventories plotted with error bars representing the range or standard deviation of the inventory values. Most recent time interval is only 5 years, resulting in relatively lower inventories. Plot titles indicate whether error bars represent either range or standard deviation.

101 Bulk Sediment Coefficients of Variation

Troughs Centers

70 ------70

60 60

c: g 50 co

0 40

cQ) "(3 30 !E Q) 0 (.) 20

10 10

Edges Ambient Regions

ro ------ro

M ------M

Figure 58 - Decadal and whole core coefficients of variation for bulk sediment inventories among cores grouped by location of recovery.

102 Biogenic Silica

Troughs (Range) Centers (Range) 120 120 110 110 100 100 190 r-----l ______190 s 80 s 80 70 r------70 .9 60 c: 60 Ql 50 > 50 r ---- E E ====f -1-=i ======- 1-- :r- - 1------1-- c: 40 c: 40 ------===f ======r==t ==-=====f--i -- ! Ql "' 30 ------} -- ;:!;"' 30 20 10 ------10 r------

130 120 120 110 110 100 ------N'100 N' 90 E -§, 90 s 80 80 <:- 70 .9 70 0 c: c: 60 Ql 60 Ql > > 50 E 50 E c: :::::: {:=::::::::::::::: ==1==- :::::::::::: __ :::::::::::: c: 40 40 ------Ql "'Ql 30 ;:!;"' 30 ------;:!; ------· 20 20 10 ------10 0

All Cores (Range) All Cores (Standard Deviation) 120 110 100 ------· 190 ----1------s 80 <:- 70 .9 c: 60 Ql > E 50 c: 40 Ql ;:!;"' 30 20 10 ------0

Figure 59 - The mean values of decadal biogenic silica inventories plotted with error bars representing the range or standard deviation of the inventory values. Most recent time interval is only 5 years, resulting in relatively lower inventories. Plot titles indicate whether error bars represent either range or standard deviation.

103 BSi Coefficients of Variation

Troughs Centers

90 90

80 80

70 c 70 c 0 .Q 60 60

0 50 50 0 c c 40 40

gi 30 () 30 8 20 20

10 10

Edges Ambient Regions

00 ------00

M ------M

c 70 70 c .Q .Q 60 60

0 50 5o 0 c c 40 40

Q) gi 30 () 30 8 20

Figure 60 - Decadal and whole core coefficients of variation for biogenic silica inventories among cores grouped by location of recovery.

104 Total Organic Carbon

Troughs (Range) Centers (Range)

------

• I • - - 1------

------N' E i • 940 ------I · --i ______2':' 0 c:30 Q) > .!: ai20 ai20 Q) Q) ::;E ::;E 10 ------10

All Cores (Range) All Cores (Standard Deviation)

------1::

I·10

Figure 61 - The mean values of decadal total organic carbon inventories plotted with error bars representing the range or standard deviation of the inventory values. Most recent time interval is only 5 years, resulting in relatively lower inventories. Plot titles indicate whether error bars represent either range or standard deviation.

105 Carbon Coefficients of Variation

Troughs Centers

70 ------70

60 ------M

c 50 ,g ro

40 0

cQ) 30 J1 Q) 0 20 ()

10 10

Edges Ambient Regions

70 ------70

M ------M

Figure 62 - Decadal and whole core coefficients of variation for total organic carbon inventories among cores grouped by location of recovery.

106 5. 1.2 A Revised Silica Budget for Lake Superior

The silica budget of Lake Superior was studied by Johnson and

Eisenreich (1979), who suggested that 80% of the river input of dissolved Si02 to the lake is not accounted for by either outflow of dissolved silica or by deposition of biogenic silica. A similar mass balance problem of silica had been observed in the oceans. The authors provided estimates for the major sources and sinks of

8 silica to Lake Superior resulting in an excess of 3.0 to 3.8 x 10 kg Si02/yr determined by subtracting the total inputs of silica from the total outputs. Johnson and Eisenreich were able to show that excess silica could not be accounted for solely through diatom burial by demonstrating that sediments would need to comprise up to 20% BSi, and would have to contain 5 to 20 x 107 diatoms/g of sediment based on the assumption that the mean weight of a diatom test is 10-9 g. Lake Superior sediments do not contain, on average, this number of diatom tests in sediments. In order to balance the silica budget of Lake Superior, the authors claimed that a majority of the silica input to Lake Superior was used in the authigenic formation of new silicate minerals. However, new calculations based on the mass accumulation of BSi in this study suggests that biogenic silica burial does in fact account for most of the silica input to Lake Superior.

107 Inputs I Source Amount (1 ois kg SiO.:/yr) Tributaries 4.2 Atmosphere 0.26 Shoreline Erosion 0.07 Bottom Sediments .21-.78 Total Inputs 4.5-5.3

Outputs I Source Amount (1 ois kg River Outflow 1.4-1. 7 Adsorption to Particulates 0.1 Diatom Burial 3.1 Silicate Authigenisis 0-0.4

Table 4 - A summary of the inputs and outputs for dissolved silica in Lake Superior. The sources for previously established inputs and outputs are referenced in Johnson and Eisenreich, 1979. Values for diatom burial and silicate authigenesis are new here.

108 Table 4 summarizes the previously established inputs and outputs of silica to Lake Superior, as well as the newly established values for diatom burial and silicate authigenesis. Rather than using the mean weight of a diatom test to determine the amount of BSi burial Lake Superior, the average of BSi MARs below a depth of 3 cm from all cores (excluding core 2) was used. Core 2 was neglected because of the unconformity at approximately 3.5 cm depth, resulting in MARs of zero. BSi MAR profiles display the highest MARs in the upper 2 to 3 cm of sediment, or the most recent 3 to 5 decades, then reach a constant value below this depth to the end of the datable portion of the core. This asymptotic

MAR value was used to calculate the total burial of BSi through the last 100 to

150 years. The increase in MARs above this depth is most likely due to the dissolution of diatom tests, rather than an increase in BSi flux to the sediments over the last century. Lake Superior's trophic status has remained relatively unaffected by human development, for this reason it is unlikely that any processes have upset the steady-state silica budget in the lake. Silica has an estimated residence time in the lake of approximately 50 years (Johnson and

Eisenreich 1979); therefore, the sinks of silica are assumed to be in equilibrium with silica fluxes to the lake. Likewise, diatom burial observed in our cores is assumed to be in equilibrium with current diatom productivity.

The average MAR of BSi was estimated at 6,905 kg/km2yr in our study area. Assuming that only areas deeper than 110 meters depth exhibit a net accumulation of sediments (Johnson 1980), then approximately 55%, or an area

2 of 45,000 km , of Lake Superior is subject to net sediment accumulation

109 (Johnson and Eisenreich 1979). Multiplying this value by the mean BSi MAR gives a total burial of 3.1 x 108 kg/yr in the sediments of Lake Superior, falling within the range of excess silica calculated by Johnson and Eisenreich.

8 Assuming their maximum input of silica to the lake (-5.3 x 10 kg Si02/yr), there

8 exists a maximum unaccounted input of only 0.4 x 10 kg Si02/yr to the lake. If there is in fact an excess cf silica, it is most likely sequestered in the formation of new authigenic silicate minerals, as suggested by Johnson and Eisenreich.

However, the new estimate of biogenic silica burial in this study suggests that there is only little imbalance, if any, and that silicate mineral authigenesis is not required to explain the fate of dissolved silica flowing into the lake.

5.1.3 C/BSi Ratios

TOC and BSi are commonly used as measures of past algal productivity in large lakes. The C/BSi ratio shows the relative influence of diatoms on the concentration of total organic carbon. The C/BSi ratio for the cores used in this study is not constant with depth, but does vary within a relatively small range of

0.5 to 0.8 (Figure 62). All cores show a consistent increase in C/BSi trend with age. The data initially suggests the study area has received a lesser influence of diatoms towards recent times. However this is most likely not the case, trends are most likely due to differences in diagenetic rates of carbon and silica. If BSi dissolves faster than organic carbon oxidizes, a down core increase will be observed in the C/BSi ratio. Decay rates were calculated for both BSi and TOC

110 from values averaged over all cores. Calculated half lives for BSi and TOC were

65 and 85 years, respectively, resulting in the obseNed down core trends.

111 2000

1990

1980

1970 -o- 2MC 1960 - o--- 3MC -- 4MC 1950 -- 5MC -- 6MC 1940 0 ?MC - o--- 8MC -o- 9MC 1930 --e- 10MC 1920

1910

1900

1890

0.4 0.5 0.6 0.7 0.8 0.9 1.0 C/BSi

Figure 63 - C/BSi ratio through time.

112 5. 1.4 Methyl Mercury

The cumulative inventories of MeHg from 1940 to the present and the

range of surface MeHg concentrations among core sites are highly variable

throughout the study area (Figures 63 - 67). Cores recovered from ambient

2 regions display significantly higher inventories of MeHg (up to 1355 g/m ) than do

2 cores taken from the troughs and centers of ring structures (as low as 749 g/m ).

Core sites located on the edges exhibit inventories that range from values typical

of the ambient regions to less than what is observed in the troughs or centers of

rings. This range of values is most likely due to reasons discussed in previous

sections.

Compared to TOC and BSi, the inventory of MeHg does not appear to

correlate as closely to bulk sediment accumulation. For example, core 4 has the

highest bulk sediment accumulation of all recovered cores; however it also

exhibits one of the lowest MeHg inventories. Similarly, core 7 has the lowest overall bulk sediment inventory but displays a relatively high MeHg inventory.

MeHg also does not seem to exhibit any strong correlation with BSi or TOC accumulation or concentration. Cores with relatively high inventories of TOC or

BSi do not necessarily exhibit high inventories of MeHg.

The spatial variability in MeHg appears to be due primarily to proximity to ring structures (Figures 63-65). Cores recovered within ring troughs, or ring centers, exhibit significantly lower MeHg inventories and concentrations in the upper-most sediments than cores from ambient [intra-ring] regions. As discussed above, the remobilization and redistribution caused by deep water currents may

113 be a mechanism for this pattern of MeHg deposition, but if so, one might expect

J .! the inventory of MeHg to co-vary with inventories of bulk sediment, TOC, and

BSi, which they do not. Other factors that may contribute to the obseNed pattern

in MeHg accumulation consist of differences in the microbial community

composition, the presence of sulfate, and the nature of particle decomposition

across ring structures (Rolphus et al. 2003 and references therein). We have no

data on the distribution of microbial communities, which might be expected to

vary relatively independently of the physical effects of bottom currents. While the

primary mechanism that causes the obseNed spatial variability of MeHg in the

study area is not known, there is undoubtedly a link between the variability of

both surficial MeHg concentrations and inventories, and the presence of these

lake floor features.

The temporal distribution of MeHg reveals a complex history of

accumulation throughout the study area (Figures 66, 67). The upper-most

sediments hold the highest inventories of MeHg, due to relatively high

concentrations, but also display some of the highest variability in values between

core sites. With all cores combined (Figure 64), standard deviations range from

30 to 50% of the mean in sediments near the top of the core, then gradually

increase to over 70% of the mean, illustrating the high variability in MeHg

accumulation through time among cores. This variability is also shown in figure

67; coefficients of variation are relatively high in most decades between cores

recovered in the centers or edges compared to cores taken from the ambient

114 regions around ring structures, displaying very different temporal MeHg accumulation histories between regions within and adjacent to ring structures.

115 I I I I I Methyl Mercury

1300 ------·------

1200

1100

1000 i::' .8 c:: Q) 900 >c:: Ol soo I Q) ::2! 700

600

500

2MC 4MC 6MC ?MC 3MC 9MC 5MC SMC

Figure 64 - Inventory of MeHg that have accumulated since year 1940. See caption to Figure 49 for definition of the letters T, C, A, and E.

Methyl Mercury 1.0

O.S -

.§ 0.6 ------"§

cQ) (.) c:: 0 () 0.4 ------Ol I Q) ::2! 0.2

2MC 4MC 6MC ?MC 3MC 9MC 5MC SMC

Figure 65 -Surface concentrations of MeHg. See caption to Figure 49 for definition of the letters T, C, A, and E.

116 +

Figure 66 - The inventories in ng/m2 of MeHg from 1940 to the present. Actual inventory is listed beside the core number. Large-circle radii correspond to higher inventories.

117 Methyl Mercury I Troughs (Mean Only) Centers (Range) I 400 400 ------360 I 1320 .9280 c:

E150 c ------0

0 0 80 ------

r:::,'::f> R>"' !Or;:, b"' i.."' r:::/'C/J ,;:/'q, cy.._o:, .._o:, .._C!J "vr:::,C:S "vr:::,C:S .._q,03 .._q,'O .._q,"i .._q,'O'° .... '°

Edges (Range) 440 ------, 400 ------·

N E320 r------

r------c c -;::: 160 ==

M ------L------

R>"' !Or;:, b"' i.."' .... "vc:s '°.._03 '°.._Cfi '°.._Ci>

All Cores (Range) All Cores (Standard Deviation)

400

N E320

9240

Figure 67 - The mean values of decadal methyl mercury inventories plotted with error bars representing the range or standard deviation of the inventory values. Most recent time interval is only 5 years, resulting in relatively lower inventories. Plot titles indicate whether error bars represent either range or standard deviation.

118 MeHg Coefficients of Variation

Centers

80 80

70 70 c c .Q 60 60 ,g ro ro "?a 50 50 > 0 40 40 ·0 ·u !E 30 30 (.) gi () 20 20

Edges Ambient Regions

00 ------00

70 ------70 c c ,g 60 60 ,g ro ro > 50 50> 0 0 40 40 ·u ·u :E gi 30 - 0 () () 20 - 20

10 10

Figure 68 - Decadal and whole core coefficients of variation for methyl mercury inventories among cores grouped by location of recovery. Coefficients could not be calculated for troughs because only one core recovered from the trough of a ring structure was analyzed for MeHg.

119 I I I 5.2 Compound Variability Relative to Previous Studies I Few studies have investigated the spatial and temporal distribution of I j MeHg in the sediments of Lake Superior. Although total Hg (HgT) analyses in

I offshore waters indicate levels are relatively low compared to other freshwater I systems (Clecker 1995), the presence of MeHg in fish and the implementation of

fish consumption advisories indicates that MeHg is being formed and is

consequently bioaccumulating in the food chain of Lake Superior.

Typically, previous investigations of HgT and MeHg in Lake Superior

sediments have been based on single cores taken from different depositional

sub-basins to establish variability and to construct lake-wide assessments of

contamination levels (e.g. Rolfhus et al. 2003, Rossman 1999) under the

assumption that MeHg concentrations in one core would be representative of the

entire sub-basin. One of the most recent studies investigating the level of MeHg

in Lake Superior sediment cores using "clean techniques" for analysis was

Rolfhus et al. (2003). The lake wide assessment of Rolfhus et al. (2003)

displayed MeHg concentrations ranging from 0.13 to 0.47 ng/g in the upper

centimeter of sediment in box cores. Rolfhus et al. also showed an exponential

decrease in MeHg down to background levels within the top 10 cm in each core;

similar trends were observed in our cores. We observed a larger range of MeHg

values across our relatively small study area than the Rolfhus et al. (2003) study

reported for the entire lake. MeHg concentrations in this study range from 0.18 to

0.64 ng/g in the top centimeter of sediment.

120 This study not only illustrates the need to account for complex lake floor

features in contaminant assessment studies, but the need for high resolution

sub-sampling of sediment cores. Up to three-fold increases in MeHg

concentrations are observed at 0.0 - 0.5 cm depth relative to 0.5 - 1.0 cm depth.

Given the low sedimentation rates and low organic matter content in offshore

Lake Superior sediments, a thick sampling resolution(> 0.5 cm) resolution may

lead to miscalculations in the flux of MeHg, and other contaminants, to the

sediments.

5.3 Implications for Future Coring

The results of this study provide conclusive evidence that sediment accumulation rates and composition vary significantly in and around the ring structures that are common throughout the central and western depositional basins of Lake Superior. Concentrations of BSi, TOC, and MeHg vary by about a factor of two and are relatively low within or near ring structures. The large heterogeneity across these features needs to be taken into account in order to properly assess the accumulation of natural compounds or level of contamination in Lake Superior sediments. Ambient regions between rings exhibit the lowest variability in sedimentary parameters (Figures 65, 66). Although the centers of ring structures also exhibit very low coefficients of variation, ambient regions compose a much larger area of the lake floor relative to ring centers and are therefore, much easier to locate. In order to recover cores that exhibit 'normal' sediment accumulation, an investigator should attempt to record depths on an

121 echo sounder in order to establish the 'ambient' depth (depths between or outside of ring depressions) in a region of interest and try to recover cores away from ring structures. In an area that exhibits a high density of ring structures an investigator should consider taking cores at 2 to 3 sites knowing that if MARs in one core are substantially different from the other, the lower MARs are most likely due to cores recovered within, or very near a ring structure.

122 6.0 Conclusions

This is the first study to document small scale heterogeneity in the burial

of natural and anthropogenic compounds over the past 150 years across

complex lake floor terrain. Multi cores were recovered from the centers, troughs,

edges, and ambient regions near ring structures that are commonly found

throughout the deep depositional environments located in the central and

western parts of Lake Superior.

210Pb, TOC, TON, and BSi analyses of sediment cores revealed that

inventories of these compounds displays large temporal and spatial variability

across ring structures and strongly co-vary with bulk sediment accumulation.

MeHg analyses show that spatial and temporal variability in MeHg appears to be

due primarily to proximity to ring structures rather than variable bulk sediment

accumulation. Other factors that were not investigated in this study may

contribute to the observed pattern in MeHg accumulation.

Johnson et al. (1980) investigated the silica budget of Lake Superior and

suggested that 80% of the river input of dissolved Si02 to the lake is not

accounted for by either outflow of dissolved silica or by deposition of biogenic

silica; a similar mass balance problem found in the oceans. However, new

estimates based on the mass accumulation of BSi suggests that there is only

little imbalance, if any, and that silicate mineral authigenesis is not required to explain the fate of dissolved silica flowing into the lake.

Regardless of core location, all core sites contain a sediment accumulation record of at least the last 50 to 60 years, which, suggests active

123 erosion or redistribution by bottom currents, facilitated by dewatering or other mechanisms responsible for the formation of ring structures, has not been a major influence on overall sedimentation in the study area during recent times.

However, the observed bulk sediment and compound distributions suggest some modification has occurred during recent times, possibly by weak bottom currents associated with storm seiches. While the primary mechanism that causes the variability of bulk sediment and compounds in the study area is not known, there is undoubtedly a link between the variability of these parameters and the presence of complex lake floor morphology.

The large heterogeneity across these features needs to be considered in order to properly assess the accumulation of natural compounds or levels of contamination in Lake Superior sediments. Ambient regions consistently displayed the lowest ranges, standard deviations, and coefficients of variation of bulk sediment and compound inventories among cores, and compose the largest area of the lake floor relative to ring centers and troughs. For these reasons, we suggest that an investigator should attempt to record depths on an echo sounder in order to establish the 'ambient' depth (depths between or outside of ring depressions) in a region of interest and try to recover cores away from ring structures, or consider taking cores at multiple sites to assess the variability.

124 7 .0 References

Appleby, P. G. 2001. Chronostratigraphic techniques in recent sediments. Pages 171-203 in W. M. Last and J.P. Smol, editors. Tracking Environmental Change Using Lake Sediments Vol. 1: Basin Analysis, Coring, and Chronological Techniques. Kluwer Academic Press, Dordrecht. Appleby. P.G. and Oldfield, T., 1978. The calculation of lead-210 dates assuming a constant rate of supply of unsupported 210Pb to the sediment. Catena. 5:1-8. Baker, J. E., and S. J. Eisenreich. 1989. PCBs and PAHs as tracers of particulate dynamics in large lakes. Journal of Great Lakes Research 15:84-103. Baker, J. E., S. J. Eisenreich, and B. J. Eadie. 1991. Sediment trap fluxes and benthic recycling of organic carbon, polycyclic aromatic hydrocarbons, and polychlorobiphenyl congeners in Lake Superior. Environmental Science and Technology 25:500-509. Baker, J. I., and R. A. Hites. 2000. Siskiwit Lake revisited: Time trends of polychlorinated dibenzo-p-dioxin and dibenzofuran deposition at Isle Royale, Michigan. Environmental Science and Technology 34:2887-2891. Beletsky, D., Saylor, J.H., and Schwab, D.J. 1999. Mean Circulation in the Great Lakes. Journal of Great Lakes Research. 25(1 ):78-93. Benninger, L.K., Lewis, D.M. and Turekian, K.K., 1975. The use of natural 210Pb as a heavy metal tracer in the river-estuarine system. In: Marine Chemistry in the Coastal Environment, ed. T.M. Church, Symp. Ser. Am. Chem. Soc. 18:202-210. Berkson, J.M. and Clay, C.S. 1973b. Possible syneresis origin of valleys on the floor of Lake Superior. Nature, 245:89-91 . Berner, R. A. 1980. Early diagenesis: A theoretical approach. Princeton University Press. Princeton, N.J. Branchi, I.; Alleva, E.; Costa, L.G. 2002. Effects of perinatal exposure to a polybrominated diphenyl ether (PBDE99) on mouse neurobehavioural development. Neuro Toxicity. 23:375-384. Breckenridge, A., Johnson, T.C., Beske-Diehl, S., and Mothersill, J.S. 2004. The timing of regional Lateglacial events and post-glacial sedimentation rates from Lake Superior. Quaternary Science Reviews. 23:2355-2367. Cartwright, J. A., N. J. Wattrus, D. E. Rausch, and A. Bolton. 2004. Recognition of an early Holocene polygonal fault system in Lake Superior: Implications for the compaction of fine-grained sediments. Geology 32:253-256. Clecker, L.B. Ph.D. Dissertation, University of Michigan, Ann Arbor, Ml, 1995. 32 DeMaster, D. J. 1979. The marine budgets of silica and Si . Ph.D. Dissertation. Yale University, New Haven. Devault, D.S., Clark, J., and Lahvis, F. 1988. Contaminants and trends in fall run coho salmon. J. Great Lakes Res. 14:23-33.

125 Edgington, D. N., and J. A. Robbins. 1990. Time scales of sediment focusing in large lakes as revealed by measurement of fallout Cs-137. Pages 210-223 in M. Tilzer and S. Serruya, editors. Large Lakes: Ecological Structure and Function. Brock/Springer Series in Contemporary Bioscience, Springer Verlag, Berlin. Eisenreich, S. J. 1987. The chemical limnology of polar organic contaminants: PCB's in Lake Superior. Pages 393-469 in R. A. Hites and S. J. Eisenreich, editors. Sources and Fates of Aquatic Pollutants. American Chemical Society, Washington, D. C. Evans, J.E., 1980. 210Pb Geochronology in Lake Superior Sediments: Sedimentation Rates, Organic Carbon Deposition, Sedimentary Environments, and Post-Depositional Processed. M.S. Thesis, Univ. Minnesota, Dept. of Geology and Geophysics, Minneapolis, MN. p. 16-22. Fisher, T.G. , Whitman, R.L. 1999. Deglacial and Lake Level fluctuation history recorded in cores, Beaver Lake, Upper Peninsula, Michigan. Journal of Great Lakes Research. 25:263-27 4. Flood, R. D. 1989. Submersible studies of current-modified bottom topography in Lake Superior. Journal of Great Lakes Research 15:3-14. Flood, R. D., and T. C. Johnson. 1984. Side-scan targets in Lake Superior - evidence for bedforms and sediment transport. Sedimentology 31 :311 - 333. Flynn, W.W. 1968. the determination of low levels of 210Po in environmental materials. Anal. Chim. Acta. 43:221-227. Green, J. C. 1989. Physical volcanology and mid-Proterozoic lava plateau lavas: the Keweenawan North Shore Volcanic Group, Minnesota. Bull. Geol. Soc. Am. 101 :486-500. Hites, R. A. 2004. Polybrominated diphenyl ethers in the environment and in people: a meta-analysis of concentrations. Environmental Science and Technology 38:945-956. Hornbuckle, K. C., J. D. Jeremiason, C. W. Sweet, and S. J. Eisenreich. 1994. Seasonal variations in air-water exchange of polychlorinated biphenyls in Lake Superior. Environmental Science and Technology 28:1491-1501. Johnson, T. C., and S. J. Eisenreich. 1979. Silica in Lake Superior: mass balance considerations and a model for dynamic response to eutrophication. Geochimica Cosmochimica Acta 43:77-91. Johnson, T.C. 1980. Late-glacial and post glacial sedimentation in Lake Superior based on seismic-reflection profiles. Quaternary Research. 13:380-391. Johnson, T.C., Carlson, T.W., and Evans, J.E. 1980. Contourites in Lake Superior. Geology. 8:437-441. Johnson, T. C., J. D. Halfman, W. H. Busch, and R. D. Flood. 1984. Effects of bottom currents and fish on sedimentation in a deep-water, lacustrine environment. Geological Society of America Bulletin 95:1425-1436. Johnson, B. L. and Johnston, C. A. 1995. Relationship of lithology and geomorphology to erosion of the Western Lake Superior Coast. Journal of Great Lakes Research. 21 (1 ):3-16.

126 Kemp, A. L. W., Dell, C. I., and Harper, N. S. 1978. Sedimentation rates and a sediment budget for Lake Superior. Journal of Great Lakes Research. 4(3- 4):276-287. Koide, M., Bruland, K.W., and Goldberg, E.D., 1973. Th-288ffh-232 and Pb-210 geochronologies in marine and lake sediments. Geochem. Cosmochim. Acta 37. p. 1178-1187. Krishnaswamy, S., and Lal, D. 1978. Radionuclide limnochronology. In Lakes, Chemistry, Geology and Physics. ed. A. Lerman, p. 153-177 (New York). Matheson, D. H. and Munawar, M. 1978. Lake Superior basin and its development. Journal of Great Lakes Research. 4(3-4 ):249-263. McDonald, T. 2002. A perspective in the potential health risks of PBDEs. Chemosphere. (46):745-755. Munawar, M., and I. F. Munawar. 1978. Phytoplankton of Lake Superior 1973. Journal of Great Lakes Research 4:415-442. Nittrouer, C.A., Sternberg, R.W., Carpenter, r., and Bennett, F.T., 1979. The use of Pb-210 Geochronology as a Sedimentological Tool: Application to the Washington Continental Shelf. Marine Geology. 31 :297-316. Nowaczyk, N.R. 2001. Logging of Magnetic Susceptibility. Pages 155-170 in W. M. Last and J. P. Smol, editors. Tracking Environmental Change Using Lake Sediments Vol. 1: Basin Analysis, Coring, and Chronological Techniques. Kluwer Academic Press, Dordrecht. Ojakangas, R. W. and Morey, G. B. 1982. Keweenawan sedimentary rocks of the Lake Superior region: A summary. In: Wold, R. J. Hinze, W. J. (Eds), Geology and Tectonics of the Lake Superior Basin. Geol. Soc. Am. Mem. 156:157-164. Oldfield, F. and Appleby, P.G. 1984. Empirical testing of 210Pb-dating models for lake sediments. In Lake Sediments and Environmental History. eds. Haworth, E.Y. and Lund, J.W.G. University of Minnesota Press, Minneapolis, MN. 405pp. Omelchenko, A., Lockhart, W. L., and Wilkinson, P. 2003. Depositional characteristics of lake sediments in Canada as determined by Pb-210 and Cs-137. Nata Science Series: IV: Earth and Environmental Sciences, Vol. 48. 2005, XVI, 334 p. Richardson, L.L. and Nealson, K.H. 1989. Distributions of manganese, iron, and manganese-oxidizing bacteria in Lake Superior sediments of different organic carbon content. Journal of Great Lakes Research. 15(1 ):123-132. Robbins, J.A., Krezoski, J.R., and Mozley, S.C., 1977. Radioactivity in Sediments of the Great Lakes: Post-Depositional Redistribution by Deposit-Feeding Organisms. Earth and Planetary Science Letters. 36:325-333. Robbins, J. A., and D. N. Edgington. 1975. Determination of recent sedimentation rates in Lake Michigan using 21 OPb and 137Cs. Geochimica Cosmochimica Acta 39:285-304. Robbins, J. A. 1982. Stratigraphic and dynamic effects of sediment reworking by Great Lakes zoobenthos. Hydrobiologia. 92:611-622.

127 Rolfhus, K. R., H. E. Sakamoto, L. B. Cleckner, R. W. Stoor, C. L. Babiarz, R. C. Back, H. Manolopoulos, and J. P. Hurley. 2003. Distribution and fluxes of total and methylmercury in Lake Superior. Environmental Science and Technology 37:865-872. Rossman, R. 1999. Horizontal and vertical distributions of mercury in 1983 Lake Superior sediments with estimated of storage and mass flux. Journal of Great Lakes Research. 25(4):683-696. Schneider, A.R., Stapleton, H.M., Cornwell, J., and Baker, J.E. 2001 Recent Declines in PAH, PCB, and Toxaphene Levels in the Northern Great Lakes As Determined from High Resolution Sediment Cores. Env. Science and Technology. 35(19): 3809-3815. Song, W., and A. Li. 2002. Temporal and spatial distribution of PBDEs and PCBs in sediments of Lake Superior. Thomas, R. L. and Dell, C. I. 1978. Sediments of Lake Superior. Journal of Great Lakes Research. 4(3-4 ): 264-275. Val Klump, J., Paddock, R., Remsen, C.C., Fitzgerald, S., Boraas, M., and Anderson, P. 1989. Variations in sediment accumulation rates and the flux of labile organic matter in eastern Lake Superior basins. Journal of Great Lakes Research. 15(1):104-122. Viberg, H.; Fredriksson, A.; Eriksson, P. 2002. Neonatal exposure to the brominated flame retardant 2,2',4,4',5-pentabromodiphenyl ether causes altered susceptibility in the cholinergic transmitter system in the adult mouse. Toxicol. Sci. 67(1):104-7. Wattrus, N.J. and Rausch, D.E. 2001. A preliminary survey of relict shoreface- attached sand ridges in Western Lake Superior. Mar. Geol. 179: 163-177. Wollin, J.A., Stoermer, E.F., and Schelske, C.L. 1991. Recent changes in Lake Ontario 1981-1987: Microfossil evidence of phosphorus reduction. Journal of Great Lakes Research. 17:229-240.

128 8.0 Appendices

Appendix A - Core Locations and Depths

Core Date Time Latitude Longitude Water Depth (m) 1MC 6/10/05 0905 46-48.623 91-51.912 44.6 2MC 6/10/05 2145 47-21.405 89-29.095 202 3MC 6/10/05 2240 47-21.352 89-29.096 199 4MC 6/11/05 0653 47-21.332 89-28.965 200 5MC 6/11/05 0934 47-21.310 89-28.831 198 6MC 6/11/05 1024 47-21.293 89-28.217 202 7MC 6/11/05 1111 47-21.328 89-28.231 200 BMC 6/11/05 1857 47-21.446 89-28.152 198 9MC 6/11/05 1937 47-21.271 89-28.146 200 10MC 6/11/05 2027 47-21.072 89-28.446 201 11MC* 6/11/05 2100 47-21.016 89-28.976 199.5

* Core 11 MC data was added at a later date, and is not included in figures throughout the text.

129 Appendix B - 210Pb Data

Core Sample Dry Wt. Excess Pb-210 Pb-210 Bq/g +/- 1SD Activity Bq/g+/- !SD BH05 lnteNal (cm (qm./sq.cm. (Bq/g) (Bq/g) +/- Error Ra-226 Error 2MC 0-0.5 0.0458 1.47E+OO 1.51 E+OO +!- 2.28E-02 0.5-1.0 0.0839 1.41E+OO 1.45E+OO +/- 2.05E-02 1.0-1 .5 0.1479 1.39E+OO 1.43E+OO +/- 2.36E-02 1.5-2.0 0.1967 1.29E+OO 1.33E+OO +/- 2.33E-02 2.0-2.5 0.2842 1.24E+OO 1.28E+OO +/- 1.78E-02 2.5-3.0 0.3787 1.08E+OO 1.12E+OO +!- 1.75E-02 3.0-3.5 0.4827 8.31E-01 8.71E-01 +!- 1.19E-02 3.5-4.0 0.6027 5.54E-01 5.94E-01 +!- 9.13E-03 4.0-4.5 0.7421 2.01E-01 2.41 E-01 +/- 4.50E-03 4.5-5.0 1.1058 1.73E-02 5.73E-02 +/- 2.04E-03 9.5-10.0 3.93E-02 +/- !.78E-03 4.06E-02 6.40E-03 3MC 0-0.5 0.045 l.47E+OO l.50E+OO +/- 2.43E-02 0.5-1.0 0.106 l.41E+OO l.44E+OO +/- 2.35E-02 1.0-1 .5 0.180 l.25E+OO l.28E+OO +/- l.87E-02 1.5-2.0 0.267 9.49E-OI 9.79E-01 +/- l.79E-02 2.0-2.5 0.366 6.05E-OI 6.35E-OI +/- 9. I 7E-03 2.5-3.0 0.477 3.70E-OI 4.00E-01 +/- 7.20E-03 3.0-3.5 0.595 2.48E-OI 2.78E-OI +/- 5. I 7E-03 3.5-4.0 0.721 l.53E-OI l.83E-OI +/- 3.87E-03 4.0-4.5 0.846 7.33E-02 l.03E-OI +/- 3.74E-03 4.5-5.0 0.976 4.88E-02 7.88E-02 +/- 2.71E-03 9.5-10.0 3.33E-02 +/- l.38E-03 3.77E-02 6.00E-03 4MC 0-0.5 0.0306 1.51E+OO 1.54E+OO +/- 2.09E-02 0.5-1 .0 0.0546 1.48E+OO 1.52E+OO +/- 2.08E-02 1.0-1.5 0.1140 1.48E+OO 1.52E+OO +/- 2.19E-02 1.5-2.0 0.1811 1.41E+OO 1.44E+OO +!- 2.13E-02 2.0-2.5 0.2608 1.27E+OO 1.30E+OO +/- 1.60E-02 2.5-3.0 0.3482 1.00E+OO 1.04E+OO +!- 1.33E-02 3.0-3.5 0.4440 7.46E-01 7.80E-01 +/- 1.03E-02 3.5-4.0 0.5551 5.64E-01 5.98E-01 +/- 8.88E-03 4.0-4.5 0.6640 4.22E-01 4.56E-01 +/- 6.64E-03 4.5-5.0 0.7899 3.09E-01 3.43E-01 +/- 6.21E-03 9.5-10.0 3.30E-02 6.70E-02 +/- 2.84E-03 3.49E-02 6.00E-03 5MC 0-0.5 0.0391 l.47E+OO l.50E+OO +/- 2.16E-02 0.5-1.0 0.0897 l.38E+OO l.41E+OO +/- l .88E-02 1.0-1.5 0.1467 !.32E+OO l .36E+OO +/- 1.72E-02 1.5-2.0 0.2190 l.13E+OO 1.17E+OO +/- l.60E-02 2.0-2.5 0.3070 9.06E-OI 9.40E-OI +/- l .20E-02 2.5-3.0 0.3901 7.92E-OI 8.26E-OI +/- l .30E-02 3.0-3.5 0.4755 6.81E-OI 7.15E-OI +/- l .21E-02 3.5-4.0 0.5540 5.22E-OI 5.56E-OI +/- 9.55E-03 4.0-4.5 0.6564 3.41E-OI 3.75E-OI +/- 6.97E-03 4.5-5.0 0.7636 2.27E-OI 2.61E-OI +/- 6.08E-03 9.5-10.0 3.77E-02 +/- l.63E-03

130 6MC 0-0.5 0.0240 l.46E+OO l.49E+OO +/- 1.60E-02 0.5-1 .0 0.0757 l.40E+OO l .44E+OO +/- 1.61E-02 1.0-1 .5 0.1364 l .34E+OO l.37E+OO +/- l.51E-02 1.5-2.0 0.2059 l.20E+OO l.24E+OO +!- 1.41E-02 2.0-2.5 0.2846 l.OIE+OO l.05E+OO +!- l .22E-02 2.5-3.0 0.3791 8.42E-01 8.76E-01 +/- l.07E-02 3.0-3.5 0.4698 5.76E-01 6.!0E-01 +/- 6.53E-03 3.5-4.0 0.5928 2.99E-Ol 3.33E-01 +/- 4.92E-03 4.0-4.5 0.7050 l.82E-Ol 2.16E-Ol +/- 3. 00E-03 4.5-5.0 0.8232 l.44E-Ol l.78E-Ol +/- 3.43E-03 9.5-10.0 8.24E-03 4.22E-02 +/- 1.78E-03 3.69E-02 7.00E-03 ?MC 0-0.5 0.0422 1.40E+OO 1.44E+OO +/- 1.79E-02 4.29E-01 1.50E-02 0.5-1.0 0.0974 1.42E+OO 1.45E+OO +/- 1.84E-02 1.0-1.5 0.1571 1.38E+OO 1.41E+OO +/- 1.71E-02 4.15E-01 7.13E-03 1.5-2.0 0.2250 1.23E+OO 1.26E+OO +/- 1.52E-02 4.31E-01 1.54E-02 2.0-2.5 0.3106 9.44E-01 9.80E-01 +/- 1.13E-02 4.63E-01 1.15E-02 2.5-3.0 0.4028 6.53E-01 6.89E-01 +/- 9.33E-03 3.53E-01 1.19E-02 3.0-3.5 0.5046 3.61E-01 3.97E-01 +/- 4.89E-03 1.36E-01 8.03E-03 3.5-4.0 0.6208 2.39E-01 2.76E-01 +/- 4.11E-03 4.0-4.5 0.7443 1.40E-01 1.??E-01 +/- 3.63E-03 1.16E-02 2.82E-03 4.5-5.0 0.8665 6.61 E-02 1.03E-01 +/- 2.63E-03 SMC 0-0.5 0.0267 1.46E+OO 1.50E+OO +/- 2.39E-02 3.95E-01 2.22E-02 0.5-1.0 0.0818 1.40E+OO 1.44E+OO +/- 1.85E-02 3.81 E-01 1.76E-02 1.0-1 .5 0.1426 1.30E+OO 1.33E+OO +/- 1.61E-02 4.24E-01 8.36E-03 1.5-2.0 0.2149 1.13E+OO 1.17E+OO +/- 1.36E-02 4.52E-01 1.50E-02 2.0-2.5 0.3054 7.90E-01 8.27E-01 +/- 1.15E-02 4.03E-01 1.23E-02 2.5-3.0 0.4006 4.??E-01 5.14E-01 +/- 6.60E-03 3.0-3.5 0.5095 3.74E-01 4.11E-01 +/- 5.75E-03 2.34E-01 1.00E-02 3.5-4.0 0.6196 2.68E-01 3.05E-01 +/- 4.58E-03 4.0-4.5 0.7430 2.20E-01 2.57E-01 +/- 4.27E-03 8.24E-02 8.02E-03 4.5-5.0 0.8552 1.88E-01 2.25E-01 +/- 4.08E-03 9.5-10.0 3.68E-02 +/- 1.38E-03 0.00E+OO O.OOE+OO 9MC 0-0.5 0.0311 1.37E+OO 1.41E+OO +/- 2.15E-02 4.68E-01 2.61 E-02 0.5-1.0 0.0971 1.15E+OO 1.19E+OO +/- 1.58E-02 4.83E-01 1.81 E-02 1.0-1.5 0.1677 9.93E-01 1.03E+OO +/- 1.41E-02 4.60E-01 1.44E-02 1.5-2.0 0.2299 8.44E-01 8.84E-01 +/- 1.34E-02 4.65E-01 1.57E-02 2.0-2.5 0.3218 5.99E-01 6.39E-01 +/- 9.55E-03 4.14E-01 1.23E-02 2.5-3.0 0.4335 3.88E-01 4.28E-01 +/- 7.86E-03 3.0-3.5 0.5415 2.52E-01 2.92E-01 +/- 5.31 E-03 1.65E-01 1.11 E-02 3.5-4.0 0.6617 1.57E-01 1.97E-01 +/- 4.83E-03 4.0-4.5 0.7862 9.84E-02 1.38E-01 +/- 3.86E-03 O.OOE+OO O.OOE+OO 4.5-5.0 0.9174 5.44E-02 9.44E-02 +/- 2.93E-03 9.5-10.0 8.94E-04 4.09E-02 +/- 1.96E-03 10MC 0-0.5 0.0379 1.37E+OO 1.42E+OO +/- 1.57E-02 0.5-1.0 0.0945 1.41E+OO 1.45E+OO +/- 1.74E-02 1.0-1.5 0.1454 1.33E+OO 1.38E+OO +/- 1.52E-02 1.5-2.0 0.2207 1.18E+OO 1.23E+OO +/- 1.30E-02 2.0-2.5 0.3123 1.03E+OO 1.08E+OO +/- 1.25E-02 2.5-3.0 0.4119 7.73E-01 8.19E-01 +/- 1.0?E-02 3.0-3.5 0.5109 5.53E-01 5.99E-01 +/- 8.41E-03 3.5-4.0 0.6325 4.19E-01 4.65E-01 +/- 7.1?E-03 4.0-4.5 0.7446 2.59E-01 3.05E-01 +/- 5.18E-03 4.5-5.0 0.8731 1.41E-01 1.87E-01 +/- 3.?0E-03 9.5-10.0 6.03E-02 1.00E-02

131 11MC 0-0.5 0.0369 l.45E+OO l.45E+OO +/- 0.5-1 .0 0.09735 1.47E+OO 1.47E+OO +/- 1.0-1.5 0.16625 l.47E+OO 1.47E+OO +/- 1.5-2.0 0.2373 l .34E+OO 1.34E+OO +/- 2.0-2.5 0.31665 l.31E+OO 1.31E+OO +/- 2.5-3.0 0.407 1.17E+OO 1.1 7E+OO +!- 3.0-3.5 0.5063 8.99E-01 8.99E-01 +/- 3.5-4.0 0.614 6.33E-Ol 6.33E-01 +!- 4.0-4.5 0.73015 4.16E-Ol 4.16E-01 +/- 4.5-5.0 0.8514 3.20E-Ol 3.20E-01 +/- 9.5-10.0 4.02E-02 4.02E-02 +/-

132 Appendix C - Water Content Data

Core Sample Interval Vial Wt. Wet Sample Wet sample Water wt. DrvWt. % Water dried sed. Cl> BH05 (cml (q) +Vial Wt. (q) Wt. lol (q) and Vial lo (g) 2MC 0.0-0.5 5.6737 17.3712 11.6975 10.6449 6.7263 91.0015 1.0526 0.963361 0.5-1 .0 5.6235 17.8882 12.2647 11.3366 6.5516 92.43275 0.9281 0.969474 1.0-1 .5 5.6814 14.3052 8.6238 7.5612 6.744 87.67829 1.0626 0.94872 1.5-2.0 5.8592 20.502 14.6428 13.2431 7.2589 90.44104 1.3997 0.960937 2.0-2.5 5.811 14.4924 8.6814 7.2597 7.2327 83.62361 1.4217 0.929955 2.5-3.0 5.8138 12.501 6.6872 5.514 6.987 82.45604 1.1732 0.924357 3.0-3.5 5.7682 18.047 12.2788 9.9326 8.1144 80.89227 2.3462 0.916716 3.5-4.0 5.7977 20.0096 14.2119 11 .1339 8.8757 78.34209 3.078 0.903891 4.0-4.5 5.6851 21 .564 15.8789 11 .97 9.594 75.38306 3.9089 0.888416 4.5-5.0 5.7087 15.2786 9.5699 4.6273 10.6513 48.35265 4.9426 0.708806 5.0-5.5 5.8238 13.7498 7.926 5.1961 8.5537 65.55766 2.7299 0.8319 5.5-6.0 5.7336 16.4806 10.747 7.0898 9.3908 65.97004 3.6572 0.834446 6.0-7.0 5.6185 30.7443 25.1 258 16.0651 14.6792 63.93866 9.0607 0.821745 7.0-8.0 5.7277 21.5978 15.8701 9.9622 11.6356 62.77339 5.9079 0.81 4273 8.0-9.0 5.6204 32.0172 26.3968 16.5824 15.4348 62.81974 9.8144 0.814573 9.0-10.0 5.6698 31.0896 25.4198 15.4549 15.6347 60.79867 9.9649 0.801289 7.0-8.0 Duolicate 5.8174 21 .0845 15.2671 9.6348 11.4497 63.10825 5.6323 0.816434 3MC 0.0-0.5 5.7316 25.6428 19.9112 18.1567 7.4861 91 .18838 1.7545 0.964166 0.5-1 .0 5.7299 16.4166 10.6867 9.4152 7.0014 88.10203 1.2715 0.950623 1.0-1 .5 5.6732 16.0686 10.3954 8.9249 7.1437 85.85432 1.4705 0.940406 1.5-2.0 5.7607 19.133 13.3723 11.1841 7.9489 83.63632 2.1882 0.930015 2.0-2.5 5.636 16.1 415 10.5055 8.5761 7.5654 81 .63438 1.9294 0.920362 2.5-3.0 5.717 21 .0599 15.3429 12.2117 8.8482 79.59186 3.1312 0.910234 3.0-3.5 5.6842 19.8101 14.1259 11.1173 8.6928 78.70153 3.0086 0.905727 3.5-4.0 5.7928 22.2 16.4072 12.6751 9.5249 77.25328 3.7321 0.898273 4.0-4.5 5.7104 19.6522 13.9418 10.8105 8.8417 77.5402 3.1313 0.899762 4.5-5.0 5.771 22.752 16.981 13.0043 9.7477 76.58147 3.9767 0.894763 5.0-5.5 5.7306 20.3684 14.6378 11.0855 9.2829 75.73201 3.5523 0.890275 5.5-6.0 5.8227 25.7511 19.9284 15.0475 10.7036 75.50782 4.8809 0.889082 6.0-7.0 5.7581 27.5676 21.8095 16.2789 11 .2887 74.64133 5.5306 0.884432 7.0-8.0 5.7504 21 .6951 15.9447 11 .6541 10.041 73.09074 4.2906 0.875963 8.0-9.0 5.7167 28.5982 22.8815 16.1162 12.482 70.43332 6.7653 0.860989 9.0-10.0 5.8454 31 .2019 25.3565 17.3625 13.8394 68.47357 7.994 0.849557 10.0-11.0 na na na na na na na na 11.0-12.0 na na na na na na na na 7.0-8.0 Duplicate 5.622 22.7526 17.1306 12.5018 10.2508 72.97935 4.6288 0.875347 4MC 0.0-0.5 5.807 15.3003 9.4933 8.9049 6.3954 93.80194 0.5884 0.975216 0.5-1 .0 5.6513 19.497 13.8457 13.1698 6.3272 95.11834 0.6759 0.980643 1.0-1.5 5.7285 15.7678 10.0393 8.8734 6.8944 88.38664 1.1659 0.951895 1.5-2.0 5.795 13.576 7.781 6.7716 6.8044 87.02737 1.0094 0.945777 2.0-2.5 5.7695 15.4864 9.7169 8.2399 7.2465 84.79968 1.477 0.935504 2.5-3.0 5.65 14.4716 8.8216 7.3648 7.1068 83.48599 1.4568 0.9293 3.0-3.5 5.683 20.5014 14.8184 12.1637 8.3377 82.08511 2.6547 0.922559 3.5-4.0 5.7245 18.6664 12.9419 10.2984 8.368 79.5741 2.6435 0.910144 4.0-4.5 5.7523 20.9956 15.2433 12.1829 8.8127 79.92298 3.0604 0.91 1895 4.5-5.0 5.7979 19.6021 13.8042 10.6609 8.9412 77.22939 3.1433 0.898149 5.0-5.5 5.6728 19.6995 14.0267 10.9281 8.7714 77.90927 3.0986 0.901668 5.5-6.0 5.6485 16.5628 10.9143 8.4954 8.0674 77.83733 2.4189 0.901297 6.0-7.0 5.7965 27.2888 21.4923 16.4984 10.7904 76.76424 4.9939 0.895721 7.0-8.0 5.8036 25.9139 20.1103 15.4119 10.502 76.63685 4.6984 0.895053 8.0-9.0 5.6752 27.4704 21 .7952 16.4985 10.9719 75.69786 5.2967 0.890094 9.0-10.0 5.7258 20.78 15.0542 11 .5663 9.2137 76.83105 3.4879 0.896071 10.0-11 .0 na na na na na na na na 11.0-12.0 na na na na na na na na 9.0-10.0 Duplicat 5.7171 20.6182 14.9011 11.425 9.1932 76.67219 3.4761 0.895239

133 SMC 0.0-0.5 5.6917 29.8038 24.1121 22.2873 7.5165 92.43202 1.8248 0.969471 0.5-1 .0 5.6403 28.9236 23.2833 20.7173 8.2063 88.97923 2.566 0.954529 1.0-1 .5 5.8684 27.5712 21 .7028 18.8049 8.7663 86.64735 2.8979 0.944046 1.5-2.0 5.7609 29.1703 23.4094 19.9471 9.2232 85.20979 3.4623 0.937419 2.0-2.5 5.7212 27.8785 22.1573 18.2499 9.6286 82.36518 3.9074 0.923917 2.5-3.0 5.8163 25.8018 19.9855 16.3394 9.4624 81 .75627 3.6461 0.920958 3.0-3.5 5.689 25.1147 19.4257 15.8059 9.3088 81 .36592 3.6198 0.919048 3.5-4.0 5.8052 25.5923 19.7871 15.8194 9.7729 79.94805 3.9677 0.912021 4.0-4.5 5.6198 26.7591 21 .1393 16.7053 10.0538 79.02485 4.434 0.90737 4.5-5.0 5.7544 26.6354 20.881 16.3033 10.3321 78.0772 4.5777 0.902532 5.0-5.5 5.719 27.8072 22.0882 16.8925 10.9147 76.47749 5.1957 0.894216 5.5-6.0 5.81 27.6063 21 .7963 16.496 11.1103 75.68257 5.3003 0.890012 6.0-7.0 5.7638 29.4326 23.6688 17.8315 11 .6011 75.33758 5.8373 0.888173 7.0-8.0 5.8584 27.828 21 .9696 16.4472 11.3808 74.86345 5.5224 0.885629 8.0-9.0 5.6721 28.583 22.9109 16.5696 12.0134 72.32191 6.3413 0.871691 9.0-10.0 5.6785 29.7697 24.0912 17.2085 12.5612 71.43065 6.8827 0.866678 10.0-11 .0 5.7556 29.0572 23.3016 15.7514 13.3058 67.59793 7.5502 0.844338 11 .0-12.0 5.7908 25.1329 19.3421 13.2041 11 .9288 68.26611 6.138 0.848327 6.0-7.0 Duolicate 5.671 29.6828 24.0118 18.0944 11 .5884 75.35628 5.9174 0.888273 6MC 0.0-0.5 5.7318 28.9712 23.2394 21 .674 7.2972 93.26403 1.5654 0.972972 0.5-1.0 5.7172 30.8059 25.0887 22.3226 8.4833 88.97472 2.7661 0.954509 1.0-1 .5 5.6832 28.3707 22.6875 19.6443 8.7264 86.58645 3.0432 0.943768 1.5-2.0 5.8199 29.4809 23.661 20.1409 9.34 85.12278 3.5201 0.937013 2.0-2.5 5.6701 27.1245 21.4544 17.8433 9.2812 83.16849 3.6111 0.927783 2.5-3.0 5.7626 26.8746 21.112 17.3032 9.5714 81.95908 3.8088 0.921946 3.0-3.5 5.7602 28.2384 22.4782 18.0637 10.1747 80.36097 4.4145 0.914082 3.5-4.0 5.6711 27.6535 21 .9824 17.3008 10.3527 78.70296 4.6816 0.905734 4.0-4.5 5.6918 27.9717 22.2799 17.4816 10.4901 78.46355 4.7983 0.904512 4.5-5.0 5.7979 27.6574 21.8595 17.141 10.5164 78.41442 4.7185 0.904261 5.0-5.5 5.732 28.5944 22.8624 17.7808 10.8136 77.77311 5.0816 0.900966 5.5-6.0 5.8126 29.4807 23.6681 18.267 11.2137 77.17983 5.4011 0.897891 6.0-7.0 5.6739 27.2025 21 .5286 16.485 10.7175 76.57256 5.0436 0.894716 7.0-8.0 5.6774 29.239 23.5616 17.8231 11 .4159 75.64469 5.7385 0.889811 8.0-9.0 5.7957 31 .836 26.0403 18.915 12.921 72.63741 7.1253 0.87345 9.0-10.0 5.7213 27.4311 21.7098 16.2079 11 .2232 74.65707 5.5019 0.884517 10.0-11 .0 5.6132 28.8639 23.2507 17.2331 11.6308 74.11863 6.0176 0.881598 11 .0-12.0 5.8155 30.2613 24.4458 18.2429 12.0184 74.62591 6.2029 0.884349 6.0-7.0 Duplicate 5.7336 25.9179 20.1843 15.5174 10.4005 76.87856 4.6669 0.896319 9.0-10.0 Duplicat 5.6767 27.5925 21 .9158 16.3576 11.2349 74.63839 5.5582 0.884416 7MC 0.0-0.5 5.5959 29.8688 24.2729 22.2344 7.6344 91 .60175 2.0385 0.965939 0.5-1 .0 5.5913 31 .3045 25.7132 22.7781 8.5264 88.58524 2.9351 0.95278 1.0-1 .5 5.7609 30.0832 24.3223 21.3249 8.7583 87.67633 2.9974 0.948712 1.5-2.0 5.8297 30.4288 24.5991 21.1359 9.2929 85.92144 3.4632 0.940715 2.0-2.5 5.6082 29.2495 23.6413 19.9486 9.3009 84.3803 3.6927 0.933536 2.5-3.0 5.7858 28.1493 22.3635 18.2953 9.854 81 .80875 4.0682 0.921214 3.0-3.5 5.731 27.3459 21 .6149 17.3638 9.9821 80.33255 4.2511 0.91394 3.5-4.0 5.8261 28.1329 22.3068 17.5384 10.5945 78.62356 4.7684 0.905329 4.0-4.5 5.6305 28.636 23.0055 17.8207 10.8153 77.46278 5.1848 0.899361 4.5-5.0 5.7254 28.3418 22.6164 17.5687 10.7731 77.68124 5.0477 0.900492 5.0-5.5 5.8629 28.9134 23.0505 17.5504 11 .363 76.13891 5.5001 0.892432 5.5-6.0 5.7183 30.4637 24.7454 18.7699 11 .6938 75.85208 5.9755 0.890913 6.0-7.0 5.8212 28.1424 22.3212 16.8003 11.3421 75.26611 5.5209 0.88779 7.0-8.0 5.7927 29.0052 23.2125 17.1973 11 .8079 74.08638 6.0152 0.881423 8.0-9.0 5.6009 30.9619 25.361 18.689 12.2729 73.69189 6.672 0.879269 9.0-10.0 5.6695 30.0301 24.3606 17.5815 12.4486 72.17187 6.7791 0.870852 10.0-11.0 5.708 30.3846 24.6766 17.5625 12.8221 71 .17066 7.1141 0.865204 11 .0-12.0 5.7932 30.4832 24.69 17.322 13.1612 70.15796 7.368 0.859403 6.0-7.0 Duolicate 5.6062 28.6885 23.0823 17.3692 11 .3193 75.249 5.7131 0.887699 BMC 0.0-0.5 5.7176 24.245 18.5274 16.8291 7.4159 90.83358 1.6983 0.962637 0.5-1 .0 5.8603 30.1248 24.2645 21 .4916 8.6332 88.57219 2.7729 0.952722 1.0-1.5 5.8634 28 .2156 22.3522 19.4511 8.7645 87.02096 2.9011 0.945747 1.5-2.0 5.8598 29.6518 23.792 20.2928 9.359 85.29254 3.4992 0.937804 2.0-2.5 5.7589 29.7647 24.0058 19.9438 9.8209 83.07909 4.062 0.927355 2.5-3.0 5.8617 28.2042 22.3425 18.1614 10.0428 81 .28634 4.1811 0.918657 3.0-3.5 5.8567 30.0443 24.1876 19.2714 10.7729 79.67471 4.9162 0.91065 3.5-4.0 5.5992 29.6067 24.0075 18.8461 10.7606 78.50089 5.1614 0.904703 4.0-4.5 5.7647 30.2343 24.4696 19.0333 11 .201 77.78345 5.4363 0.901019 4.5-5.0 5.7845 30.3288 24.5443 18.998 11.3308 77.4029 5.5463 0.89905 5.0-5.5 5.6061 30.1513 24.5452 18.7647 11 .3866 76.44957 5.7805 0.894069 5.5-6.0 5.7069 31 .2738 25.5669 19.4958 11 .778 76.25406 6.0711 0.893039 6.0-7.0 5.8624 31 .5111 25.6487 19.1605 12.3506 74.70359 6.4882 0.884768 7.0-8.0 5.7518 31 .0473 25.2955 18.1539 12.8934 71 .76731 7.1416 0.86858 8.0-9.0 5.6709 30.987 25.3161 17.6799 13.3071 69.83659 7.6362 0.857544 9.0-10.0 5.7192 31 .1145 25.3953 17.5927 13.5218 69.27542 7.8026 0.854276 10.0-11 .0 5.8618 32.4378 26.576 18.28 14.1578 68.78387 8.296 0.85139

134 10MC 0.0-0.5 5.6431 31 .1439 25.5008 23.4244 7.7195 91.85751 2.0764 0.967031 0.5-1 .0 5.6646 29.8595 24.1949 21.4467 8.4128 88.64141 2.7482 0.95303 1.0-1.5 5.8042 29.3691 23.5649 20.97791 8.39119 89.02185 2.58699 0.954717 1.5-2.0 5.7883 29.646 23.8577 20.2475 9.3985 84.86778 3.6102 0.935823 2.0-2.5 5.7853 28.5191 22.7338 18.9896 9.5295 83.53025 3.7442 0.929511 2.5-3.0 5.6419 30.4139 24.772 20.1766 10.2373 81 .44922 4.5954 0.919456 3.0-3.5 5.5998 27.7941 22.1943 17.9451 9.849 80.85454 4.2492 0.916529 3.5-4.0 5.6755 28.413 22.7375 18.0119 10.4011 79.21671 4.7256 0.908341 4.0-4.5 5.7513 29.0119 23.2606 18.191 10.8209 78.20521 5.0696 0.903189 4.5-5.0 5.7996 30.5368 24.7372 19.1608 11 .376 77.45743 5.5764 0.899333 5.0-5.5 5.7844 31 .8076 26.0232 19.8063 12.0013 76.11016 6.2169 0.89228 5.5-6.0 5.6811 28.7012 23.0201 17.6558 11.0454 76.69732 5.3643 0.89537 6.0-7.0 5.8159 29.3083 23.4924 17.8026 11.5057 75.78025 5.6898 0.890531 7.0-8.0 5.6701 29.4064 23.7363 17.842 11 .5644 75.16757 5.8943 0.887263 8.0-9.0 5.8427 30.9982 25.1555 18.9146 12.0836 75.19071 6.2409 0.887387 9.0-10.0 5.6694 32.0587 26.3893 19.5074 12.5513 73.92163 6.8819 0.880525 10.0-11.0 5.6019 30.096 24.4941 18.2374 11 .8586 74.4563 6.2567 0.883431 11 .0-12.0 5.6107 31 .497 25.8863 19.1788 12.3182 74.08861 6.7075 0.881435 6.0-7.0 Duolicate 5.7928 29.9627 24.1699 18.3827 11 .58 76.05617 5.7872 0.891994 11MC 0.0-0.5 5.8190 26.5583 20.7393 19.2723 7.2860 92.9265 1.4670 0.9716 0.5-1.0 5.7906 28.7930 23.0024 20.4042 8.3888 88.7047 2.5982 0.9533 1.0-1 .5 5.8580 28.4524 22.5944 19.7118 8.7406 87.2420 2.8826 0.9467 1.5-2.0 5.7276 28.9840 23.2564 20.2050 8.7790 86.8793 3.0514 0.9451 2.0-2.5 5.8619 29.8232 23.9613 20.4802 9.3430 85.4720 3.4811 0.9386 2.5-3.0 5.7264 26.9084 21 .1820 17.7201 9.1883 83.6564 3.4619 0.9301 3.0-3.5 5.8162 22.8419 17.0257 13.9955 8.8464 82.2022 3.0302 0.9231 3.5-4.0 5.7237 29.3328 23.6091 19.0917 10.2411 80.8659 4.5174 0.9166 4.0-4.5 5.8165 29.1512 23.3347 18.5609 10.5903 79.5421 4.7738 0.9100 4.5-5.0 5.5498 29.5549 24.0051 18.9052 10.6497 78.7549 5.0999 0.9060 5.0-5.5 5.6322 30.0639 24.4317 18.8752 11.1887 77.2570 5.5565 0.8983 5.5-6.0 5.7182 26.7412 21 .0230 16.0332 10.7080 76.2650 4.9898 0.8931 6.0-7.0 5.6056 30.1540 24.5484 18.7795 11 .3745 76.4999 5.7689 0.8943 7.0-8.0 5.6348 30.6796 25.0448 18.7723 11 .9073 74.9549 6.2725 0.8861 8.0-9.0 5.7278 31 .2278 25.5000 18.7700 12.4578 73.6078 6.7300 0.8788 9.0-10.0 5.7559 29.3046 23.5487 17.1341 12.1705 72.7603 6.4146 0.8741 10.0-11 .0 5.8644 30.0445 24.1801 17.1862 12.8583 71 .0758 6.9939 0.8647 11.0-12.0 5.8674 33.1330 27.2656 19.1591 13.9739 70.2684 8.1065 0.8600 1.5-2.0 Duolicate 5.7164 13.3829 7.6665 6.4731 6.9098 84.4336 1.1934 0.9338 2.5-3.0 Duplicate 5.7638 18.8521 13.0883 10.9234 7.9287 83.4593 2.1649 0.9292 3.0-3.5 Duolicate 5.7171 21 .8419 16.1248 13.3185 8.5234 82.5964 2.8063 0.9250 5.5-6.0 Duplicate 5.7253 20.5088 14.7835 11.2202 9.2886 75.8968 3.5633 0.8911 11 .0-12.1O Duolic 5.7112 31.8267 26.1155 18.3629 13.4638 70.3142 7.7526 0.8603

135

_\ Appendix D - C, N, C/N, BSi, and MeHg Data

Core Base of Wt.% Wt.% C/N BioSi Me Hg Sample Interval Carbon Nitrogen Ratio (%) (ng/g) 2MC 0.5 4.296 0.471 9.121 6.56 0.18543 1 4.306 0.481 8.952 6.59 0.17778 1.5 4.208 0.444 9.477 7.21 0.23479 2 4.073 0.434 9.385 7.77 0.18496 2.5 3.86 0.406 9.507 7.40 0.16007 3 3.748 0.397 9.441 7.32 0.16552 3.5 3.637 0.391 9.302 6.32 0.18613 4 3.454 0.36 9.594 3.93 0.08987 4.5 2.268 0.223 10.170 2.55 0.08892 5 0.642 0.074 8.676 3.34 0.01926 5.5 0.488 0.101 4.832 4.62 0.01247 6 0.461 0.097 4.753 3.52 0.01285 7 0.439 0.098 4.480 4.50 0.02158 8 0.466 0.103 4.524 4.70 0.03705 9 0.433 0.081 5.346 5.17 0.03642 10 0.973 0.089 10.933 2.52 0.03791 3MC 0.5 4.254 0.51 8.341 7.85 0.3479 1 4.178 0.478 8.741 8.07 0.28255 1.5 3.988 0.463 8.613 8.84 0.14794 2 3.891 0.435 8.945 7.50 0.27342 2.5 3.673 0.404 9.092 6.74 0.15194 3 3.646 0.385 9.470 6.68 0.12515 3.5 4.07 0.384 10.599 5.45 0.19667 4 3.136 0.349 8.986 6.01 0.12208 4.5 2.869 0.355 8.082 5.77 0.08482 5 2.704 0.329 8.219 5.23 0.05457 5.5 2.669 0.328 8.137 4.83 0.05839 6 2.659 0.329 8.082 4.77 0.06036 7 2.607 0.327 7.972 3.74 0.0723 8 2.433 0.306 7.951 4.58 0.03862 9 2.152 0.276 7.797 3.33 0.02907 10 2.299 0.246 9.346 0.84 0.05004

136 4MC 0.5 4.231 0.481 8.796 9.12 0.24986 1 4.194 0.511 8.207 7.93 0.21807 1.5 4.1 0.497 8.249 9.34 0.14426 2 3.974 0.475 8.366 9.27 0.10936 2.5 4.071 0.473 8.607 8.04 0.15441 3 3.697 0.435 8.499 7.06 0.13432 3.5 3.677 0.418 8.797 6.27 0.10087 4 3.59 0.401 8.953 6.79 0.1022 4.5 3.512 0.387 9.075 7.21 0.0952 5 3.365 0.361 9.321 6.83 0.06959 5.5 3.419 0.368 9.291 6.54 0.06528 6 3.441 0.353 9.748 5.72 0.04599 7 3.103 0.346 8.968 6.22 0.03011 8 2.872 0.33 8.703 6.41 0.01721 9 2.579 0.313 8.240 5.49 0.04529 10 2.609 0.312 8.362 4.00 0.00319 SMC 0.5 4.199 0.516 8.138 8.58 0.39862 1 4.126 0.495 8.335 8.80 0.25615 1.5 3.926 0.466 8.425 8.48 0.23746 2 3.82 0.438 8.721 5.66 0.23785 2.5 5.372 0.427 12.581 7.01 0.15331 3 3.638 0.417 8.724 6.67 0.12403 3.5 4.151 0.414 10.027 6.44 0.12658 4 3.65 0.392 9.311 5.78 0.24293 4.5 3.539 0.37 9.565 5.54 0.17951 5 3.221 0.353 9.125 5.18 0.03874 5.5 2.874 0.321 8.953 4.87 0.04703 6 2.631 0.309 8.515 3.91 0.02985 7 2.385 0.291 8.196 3.70 0.02587 8 2.289 0.283 8.088 2.52 0.03133 9 2.18 0.279 7.814 2.80 0.02478 10 2.039 0.259 7.873 3.18 0.03879 11 1.813 0.236 7.682 3.36 0.02662 12 1.936 0.239 8.100 3.36 0.01444 6MC 0.5 4.145 0.494 8.391 8.43 0.38949 1 4.178 0.492 8.492 8.34 0.1313 1.5 4.088 0.467 8.754 8.41 0.05344 2 3.826 0.442 8.656 7.98 0.12581 2.5 3.854 0.425 9.068 6.88 0.10561 3 3.794 0.401 9.461 6.58 0.07197 3.5 3.625 0.375 9.667 6.46 0.1044 4 3.326 0.364 9.137 6.62 0.1284 4.5 3.5 0.351 9.972 6.39 0.03261 5 3.942 0.361 10.920 6.11 0.02373 5.5 3.099 0.351 8.829 6.10 0.0457 6 3.093 0.345 8.965 5.66 0.03271 7 2.684 0.325 8.258 4.98 0.01599 8 2.539 0.311 8.164 3.64 0.02438 9 2.504 0.298 8.403 3.02 0.01746 10 2.507 0.308 8.140 3.94 0.0771 11 2.391 0.301 7.944 3.57 0.10807 12 2.346 0.293 8.007 3.23 0.08058

137 ?MC 0.5 4.189 0.495 8.463 7.99 0.91125 1 4.148 0.489 8.483 7.46 0.37489 1.5 4.032 0.482 8.365 8.43 0.43062 2 3.975 0.458 8.679 8.50 0.17609 2.5 3.706 0.431 8.599 7.40 0.13833 3 4.067 0.413 9.847 5.74 0.16131 3.5 3.944 0.368 10.717 5.43 0.07216 4 3.269 0.347 9.421 5.55 0.13145 4.5 2.733 0.327 8.358 5.46 0.16117 5 3.001 0.336 8.932 3.58 0.11155 5.5 2.554 0.319 8.006 3.32 0.11501 6 2.514 0.314 8.006 3.77 0.01597 7 2.482 0.303 8.191 3.61 0.02328 8 2.372 0.299 7.933 3.36 0.01347 9 2.291 0.289 7.927 2.80 0.0106 10 2.064 0.267 7.730 3.09 0.00653 11 2.009 0.26 7.727 2.53 0.00655 12 1.983 0.254 7.807 2.64 0.01059 8MC 0.5 4.26 0.482 8.838 7.60 0.49784 1 4.176 0.508 8.220 7.47 0.39119 1.5 4.153 0.473 8.780 7.35 0.26234 2 3.909 0.439 8.904 7.33 0.20208 2.5 3.631 0.415 8.749 5.65 0.20539 3 3.513 0.394 8.916 5.14 0.21544 3.5 3.465 0.388 8.930 5.40 0.12446 4 3.364 0.368 9.141 5.31 0.09782 4.5 3.504 0.369 9.496 5.10 0.06587 5 3.47 0.361 9.612 5.12 0.04592 5.5 3.245 0.367 8.842 4.88 0.09435 6 3.141 0.316 9.940 3.97 0.03519 7 3.274 0.353 9.275 4.00 0.02976 8 2.2 0.251 8.765 2.90 0.01355 9 1.71 0.21 8.143 2.35 0.02187 10 1.793 0.219 8.187 2.26 0.0145 11 1.816 0.217 8.369 2.81 0.03435 12 1.868 0.227 8.229 2.70 9MC 0.5 4.149 0.481 8.626 7.43 0.13221 1 3.909 0.459 8.516 7.76 0.2548 1.5 3.703 0.426 8.692 4.43 0.2489 2 3.643 0.4 9.108 6.77 0.08596 2.5 3.492 0.391 8.931 5.72 0.1649 3 3.878 0.391 9.918 5.71 0.07329 3.5 4.861 0.401 12.122 5.29 0.10739 4 3.088 0.359 8.602 5.20 0.05831 4.5 2.924 0.324 9.025 5.18 0.03036 5 2.478 0.284 8.725 4.48 0.01825 5.5 2.642 0.307 8.606 3.93 0.02889 6 2.488 0.322 7.727 4.38 0.02573 7 2.647 0.302 8.765 3.55 0.02687 8 2.427 0.321 7.561 3.99 0.02139 9 2.077 0.244 8.512 3.46 0.0525 10 2.108 0.281 7.502 3.48 0.03097 11 2.096 0.237 8.844 2.49 0.01435 12 2.214 0.271 8.170 2.66 0.03553

138 10MC 0.5 4.19 0.508 8.248 8.66 1 4.183 0.507 8.250 8.43 1.5 4.174 0.485 8.606 7.66 2 3.906 0.437 8.938 7.38 2.5 3.638 0.419 8.683 6.45 3 3.74 0.434 8.618 6.26 3.5 3.673 0.4 9.183 5.65 4 3.645 0.394 9.251 5.43 4.5 3.573 0.377 9.477 6.21 5 3.462 0.369 9.382 5.66 5.5 3.038 0.349 8.705 5.27 6 2.829 0.354 7.992 5.54 7 2.673 0.335 7.979 4.90 8 2.564 0.325 7.889 4.37 9 2.57 0.326 7.883 4.52 10 2.421 0.309 7.835 4.71 11 2.458 0.294 8.361 4.09 12 2.341 0.265 8.834 3.68 11MC 0.5 4.284 0.535 8.007 8.50 1 4.516 0.542 8.332 7.81 1.5 4.079 0.505 8.077 8.63 2 4.025 0.474 8.492 8.81 2.5 4.053 0.453 8.947 7.58 3 3.978 0.455 8.743 7.19 3.5 3.794 0.413 9.186 6.41 4 3.654 0.419 8.721 3.87 4.5 3.52 0.393 8.957 5.29 5 3.518 0.376 9.356 5.66 5.5 3.288 0.374 8.791 4.89 6 3.568 0.349 10.223 4.94 7 2.627 0.341 7.704 3.07 8 2.56 0.329 7.781 4.51 9 2.36 0.301 7.841 3.86 10 2.179 0.285 7.646 3.38 11 2.114 0.268 7.888 3.57 12 2.018 0.261 7.732 3.84

139 Appendix F - LRC Data

2MC

3 1 3 P-wave Velocity (m/s) Density (g/cm3) IMP (10 kgs- m- ) Frac. Porosity Resistance (Ohms) 0.0 0

5.0

10.0 ------10

"E 15.0 ------15 "E .!2. .!2.

0 0 () 20.0 ------20 () .5 .5 .c .c 0. 0. Q) 25.0 0 ------25

30.0 ------

35.0

40.0 40 0 0 0 ": ""! "'0 0 0 0 0 0"' .... co O> OIO 0 0 0 0 ..,. .... 0 . ·o 0 0 0 0 ..,. ..,. ..,. 0 g ci 0 0 0 "' :: :: N "' "' "' "' "' "' "' "' "'"

3MC

Frac. Porosity Resistance (Ohms) 0

5.0

10.0 ------10

15.0 ------15 E .!2. 20.0 20 0 0 () () .5 c .c 25.0 25 0. 0. Q) Q) 0 30.0 30 °

35.0 ------35

0 0 0 0 0 0 0 co Cl co ..,. .... 0 0 0 0 ..,. ..,. .... O> 0 0 0 "'

140 4MC

P-wave Velocity (m/s) Density (g/cm3) Frac. Porosity Resistance (Ohms) 0.0 0

5.0 5

10.0 10

15.0 15 E

20.0 20 f!! 0 0 (.) (.) .s: c: .<:: 25.0 25 0. 0. <1l <1l 0 30.0 ------30 °

35.0 ------35

40.0 40

45.0 45 0 a> 0 0 0 0 ..,. N N ..,. ..,. ..,. ci "' "' "' "'

SMC

P-wave Velocity (mis) Density (g/cm3) Frac. Porosity 0.0

5.0 ------5

10.0 10

15.0 15 E E

f!! 20.0 ------20 f!! 0 0 (.) (.) .s: c: .<:: 25.0 25 0. 0. <1l <1l 0 30.0 ------30 °

35.0 ------35

40.0 40

45.0 0 0 co a> 0 0 0 0 0 0 ,._ "'0..,. 0 ("') I.() ..,. 0 . co ci ci C\I

141 6MC

P-wave Velocity (m/s) Density (g/cm3) Frac. Porosity 0.0

5.0

10.0 ------10

E 15.0 ------15 I

0 0 u 20.0 ------20 u .!:: .!:: .r:: .r::

c.Q) c. 0 25.0 ------25

30.0 ------

35.0 ------

0 cnoooooooo 0 ci C\IV

7MC

5.0 ------

10.0 10

E 15.0 ------15 E'

0 0 u 20.0 ------20 u .!:: .!:: .r:: .r:: c. 0. Q) 25.0 25 Q) 0 0

30.0 ------30

35.0 ------

40.0

0 0 0 0 0 0 0 M V LO «> I'- "'

142 SMC

Frac . Porosity 0

5.0

10.0 ------10

E' 15.o 15 E' ..s. ..s.

0 8 20.0 u .s .s .i:::: .i:::: 25.o 25 c. aQ) Q) 0 0

30.0 ------

35.0 ------

40.0 ------40

0 0 0 0 0 0 O(!)CX)OC'\1""1"<.0a:>OC\1-.:t"a:>cocncncncn..- N NM M-.;:--.;:- ..,. ..,. I'- "' "' "' N cicicicicicicicicicici

9MC

P-wave Velocity (m/s) Density (g/cm3) Frac. Porosity Resistance (Ohms) 0.0 0

5.0 5

10.0 ------10

15.0 15 E' E' ..s. ..s. 20.0 ------20 0 0 u u .s 25.0 -- 25 .s .i:::: ------c. .i:::: Q) c.Q) 0 30.0 ------30 0

35.0 ------35

40.0 ------40

45.0 45

0 0 0 0 ..,. I'- 0 0 "' ..,. "' "' "'

143 10MC

P-wave Velocity (m/s) Density (g/cm3) Frac. Porosity Resistance (Ohms) 0.0

5.0

10.0

15.o

0 20.0 () .5 .5 .c a 25.0 25 c. Q) Q) Cl Cl

30.0 ------30

35.0

40.0

0 0 0 .... ,._ 0 ...... "'

11MC

Frac. Porosity P-wave Velocity (mis) Density (g/cm3) Resistance (Ohms)

5.a

1a.a

'E 15.a 15 'E

0 20.a () 20 8 .!: .c t 25.a 25 Q) c.Q) Cl Cl

30.a 30

35.a

0 0 0 0 0 Ov 0 0 0 0 0 0 IX) v ...... 0 M , NM V U"J

144