Late-Holocene Expansion of the Greenland Ice Sheet As Recorded by the Vendue Glacier, Graben Land, East Greenland

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Late-Holocene Expansion of the Greenland Ice Sheet as recorded by the Vendue Glacier, Graben Land, East Greenland

Paul Wilcox

B.S. Middle Tennessee State University, 2010

A Thesis

Submitted in Partial Fulfillment

of the Requirements for the Degree of

Master of Science

(In Geology)

The Graduate School

The University of Cincinnati

April 2013

Advisory Committee:

Thomas V. Lowell, Professor of Geology, University of Cincinnati (primary advisor)

Aaron Diefendorf, Assistant Professor of Geology, University of Cincinnati

Brenda Hall, Professor of Earth Sciences and Quaternary and Climate Studies, University of

Maine

Abstract:

The Greenland Ice Sheet, along with the rest of the Arctic, is experiencing dramatic warming resulting in ice loss and sea-level rise. To place this retreat in context, the time when the ice sheet reached its maximum Holocene extent is needed. Here, we present work indicating the most recent activity of an outlet glacier, the Vendue, in the Scoresby Sund region of East

Greenland. We obtained sediment cores from carefully selected glacially fed lakes in order to document ice history. These lakes receive silt only when the glacier margin reaches a critical thickness

Based on the sedimentological properties and the timing of a prominent silt unit at the top of the recovered cores, it is suggested that expansion of the ice sheet was underway by 500 cal yr. BP. Subsequent retreat has not yet been sufficient to stop silt deposition at this site implying that the outlet glacier has not yet thinned to the level occupied ~500 years ago. In addition to the dominant silt layer expressed at ~500 cal yr. BP, other thinner silt layers within the lake indicate the outlet glacier may have been at similar position at 1330, 1700, 2300, and 3500 cal yr. BP.

These lake cores also contain a number of sand layers. Sediment analysis may point to deposition following large slush avalanche events. The most prominent sand units were deposited at 500 and 1330 cal yr. BP coincident with the latest two expansions of the ice sheet.

It may be that such sand layers can track expanded glacier state.

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Table of Contents

Abstract………………………………………………………………………………...... i

Table of Contents……………………………………………………………………………….iii

List of Figures……………………………………………………………………………………v

List of Tables………………………………………………………………………………….....v

Appendix………………………………………………………………………………………..vi

Chapter 1: Introduction…………………………………………………………………………1

Introductory Remarks……………………………………………………………………..1

Current Climate of Greenland…………………………………………………………… 2

Setting……………………………………………………………………………………..3

Methods…………………………………………………………………………………...5

Chapter 2: Silt Recording Glacial Expansions………………………………………………..11

Introduction………………………………………………………………………...... 11

Results………………………………...... 11

Discussion………………………………………………………………………………..14

Silt Source………………………………………………………………………..14

Silt Recording Late Holocene Glacial Expansion……………………………….15

Graben Land Recording Multiple Glacier Episodes…………………………….16

Late Holocene Expansion Recorded at other sites in Greenland………………..17

Conclusion……………………………………………………………………………….19

Chapter 3: Slush Avalanches…………………………………………………………………..23

Introduction……………………………………………………………………………...23

Results…………………………………………………………………………………....23

Discussion……………………………………………………………………………….25

Sand Deposition…………………………………………………………………25

Slush Avalanches Recording Glacial Expansion in Graben Land……………...28

Slush Avalanches in Liverpool Land…………………………………………...29

Conclusion………………………………………………………………………………30

Chapter 4: Summary…………………………………………………………………………..34

References………………………………………………………………………………………36

Appendix………………………………………………………………………………………..40

List of Figures

Figure 1…………………………………………………………………………………………....7

Figure 2…………………………………………………………………………………………....8

Figure 3……………………………………………………………………………………………9

Figure 4…………………………………………………………………………………………..20

Figure 5…………………………………………………………………………………………..21

Figure 6…………………………………………………………………………………………..31

Figure 7…………………………………………………………………………………………..32

Figure 8…………………………………………………………………………………………..33 List of Tables

Table 1…………………………………………………………………………………………...10

Table 2…………………………………………………………………………………………...22

Appendix

Appendix Information………………………………………………………………………….37

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Chapter 1: Introduction

Introductory Remarks:

Over the last century, there has been strong evidence for global warming due to natural as well as anthropogenic inputs (Screen, 2010). This increased warmth has resulted in more surface melt and retreat of the Greenland Ice Sheet and subsequent sea-level rise (Parizek and Alley,

2004). Greenland Ice Sheet’s contribution to sea level more than doubled between 1996 and

2005, from 0.23 mm/yr to 0.57 mm/yr (Rignot and Kanagaratnam, 2006). This retreat has warranted numerous studies focusing on the melting of the Greenland Ice Sheet (eg, Funder,

1972; Abdalati et al., 2001; Krabill et al., 2004; Luthcke et al., 2006; Velicogna and Wahr,

2006); however, less is known about when the ice sheet expanded, especially during the late

Holocene. The aim of this study is to document late Holocene expansions of the ice sheet.

Toward this end we will employ lacustrine sediment studies of lakes adjacent to Vendue Glacier.

The first chapter will interpret glacier expansion from prominent silt units within sediment cores. Sediments cores extracted from “proglacial threshold” lakes can provide continuous high-resolution records of glacier fluctuations. These lakes contain glacial, minerogenic-rich sediments when the ice sheet is expanded and non-glacial, organic-rich sediment during restricted ice (Kaplan et al., 2002; Daigle and Kaufman, 2009).

In Greenland, studies of glacial fluctuations have used lacustrine records to indicate variation in glacier size (Kaplan et al., 2002; Briner et al., 2010; Larson et al., 2011); however, these studies were conducted in West and South Greenland. Relatively little is known about glacier expansions retrieved from lacustrine cores in East Greenland. It is therefore necessary to determine glacial fluctuations in this region in order to fill in this gap.

To identify silt units within the cores, and hence glacial expansions, I will use grain size,

magnetic susceptibility, loss-on-ignition, and mineral identification. Radiocarbon ages from organics will be used to establish periods when glaciers were expanded.

The second chapter will interpret enigmatic sand units recovered in two localities in

Scoresby Sund which are not commonly described from high latitude settings. The process interpreted as responsible for depositing the sands are slush avalanches.

Slush Avalanches have rarely, if ever, been described as the transportation mechanism for sand in a sediment core collected from a proglacial lake. They are typically seen as water- saturated snow, flowing like a mudflow along stream channels due to intense spring thaw

(Goldthwait, 1958). Determining if these sand units are indeed deposited by slush avalanches can be used to infer past glacial expansions. This, in turn, could be used to support glacial expansions in other arctic localities where sand is found in sediment cores.

Here, we aim to illustrate that these sand units are deposited by slush avalanches. We will also speculate if they can be related to the extent of the Vendue or other glaciers.

Current Climate of Greenland:

East Greenland climate is largely dominated by the East Greenland Current (Pickart and

Sutherland, 2008). The current exits the Arctic Ocean through the Fram Strait and brings cold, dry conditions to East Greenland. The low salinity water masses that accompanies the cold waters masses of the East Greenland Current transports sea ice southward along the East

Greenland coast and creates an almost perennial sea-ice cover off East Greenland (Pickart and

Sutherland, 2008). This causes a temperature inversion and frequent fog formation especially along the low coastal regions (Funder, 1978). This, in turn, hampers insolation which leads to a strong temperature decline from the interior to the outer coastal regions of East Greenland

(Wagner et al., 2000).

Setting:

This study was conducted in the Scoresby Sund region located in Central East Greenland

(Fig. 1). The Greenland Sea is to the East and the Greenland Ice Sheet is to the West. The specific field site of Graben Land is located in the western portion of Scoresby Sund and is adjacent to the Greenland Ice Sheet.

Scoresby Sund

The Greenland Ice Sheet drains, via large fjords, into Scoresby Sund of East Greenland in the form of outlet glaciers (Fig. 1). These fjords extend inland to a distance of 300 km and constitute the largest fjords in the Northern Hemisphere. The fjords have steep slopes and form plateaus that reach 1500 – 2500 m in elevation. The plateaus contain small ice caps in the more interior region (Funder, 1989). The outlet glaciers that terminate in the fjords, being part of the

Greenland Ice Sheet, track the behavior of the Greenland Ice Sheet and are therefore sensitive indicators of past glacial expansions.

The bedrock that constitutes the region consists of a succession of older Lower and

Middle Proterozoic metamorphic/plutonic rocks in the west and Devonian, Carboniferous and

Permian sedimentary rocks towards younger Tertiary igneous rocks to the east (Stendal and Frei,

2008). Ice free areas expose glacially eroded bedrock with thin quaternary sediments draped over them.

Graben Land

Graben Land (71° N and 28°E, Fig. 1) is composed of rugged, mostly granitic terrain that shows past evidence of glacial activity. The Vendue Glacier makes a right angle bend and thus flows past both ends of a major graben. This geometry forms an ice-contact lake (Tsunami

Lake) on the western side of the graben that discharges into the graben before flowing through

seven lakes and eventually coming into contact with the glacier at the eastern side of the graben.

Elevation is approximately 1000 m on the floor of the graben with mountains situated to the north and the south reaching elevation just over 1800 meters. The mountains to the south contained a large ice cap extending to the valley floor while the mountains to the north have only a small ice cap which could not be seen from the valley floor. There was no evidence of stream flow into the lakes from the two ice caps. The westernmost two glacially fed proglacial lakes, informally named here Black Hole and Ice Fall, were selected for coring.

Black Hole Lake

Black Hole Lake (948 m a.s.l, 15,800 m2, Table 1) is a proglacial lake located approximately 1.5 km east of the Vendue Glacier margin (Fig. 2). The lake is fed by a fast- flowing stream originating in an ice-contact lake over mostly granitic rock and, to a lesser extent, by a small stream originating from a high-elevation lake to the north. Rock flour was visible as suspended sediment in the stream. There is no delta at the inlet. The lake is elongated west to east. The bathymetry indicates a “top hat” shaped appearance with steep sloping sides and a basin situated at approximately 14 m depth (Fig. 3). A unique feature of the lake is a small deep spot in the middle of the basin that extends to a depth of approximately 22 m. The lake drains to the east via a wide and shallow outlet. Large boulder concentration from slopes processes are found on the north of the lake.

Ice Fall Lake

Ice Fall Lake (942 m a.s.l, 8,400 m2, Table 1) lies approximately 300 m to the east and downstream of Black Hole Lake and is connected by a wide and shallow channel (Fig. 2). The channel is composed of large granitic rocks approximately 1 m in diameter. The stream contains visible rock flour. The bathymetry is relatively simple with a single “kettle shaped” basin with

steep sloping sides that gradually levels out to a single basin of approximately 9 m depth (Fig. 3).

Similar to Black Hole Lake, large boulder concentration from slopes processes are found on the north of the lake.

Methods:

Fieldwork

Identification of specific sites to core within Black Hole and Ice Fall Lake was done by developing bathymetric maps using the Hummingbird Matrix 47 3D Depth sonar device. The lakes were transected 15 times in Black Hole Lake and 9 times in Ice Fall Lake in long, narrow oscillating patterns. Sites were selected in the deep, flat parts of the lake to gain the highest resolution and most extensive sediment record.

Five cores were collected from Black Hole Lake using a combination of a rod-driven

Livingstone piston corer and a percussion corer modified after Nesje (1992) to adapt to a range of lake depths and sediment thicknesses. Four cores were collected in Ice Fall Lake using a percussion corer (Table 1). Both corers were employed from a rigid-floor inflatable raft

(Achilles LEXI-96). For use with the piston corer, a collapsible aluminum frame with pulleys to insert and extract the rod was used. Cores were collected in 1-1.5 meter segments from these two lakes.

Laboratory Analysis

Initial core descriptions were undertaken at the Limnological Research Center in

Minneapolis. Using the facilities, physical and textural description, high-resolution imaging, high resolution magnetic susceptibility (MS), high resolution density measurements, and smear slide identification were done according to the laboratory operational procedures

(http://lrc.geo.umn.edu/laccore/procedures.html). Magnetic susceptibility is expressed in

volume-normalized susceptibility values, with units of 10-5 SI.

Additional analysis at the University of Cincinnati included: Loss-on-ignition (LOI), grain size analysis, smear slide identification, and XRD analysis. LOI was done by taking sediment sample every 2 cm and heating the samples at 550° C (Bengtsson and Enell, 1986).

Grain size, at 2 cm vertical spacing, was measured with an automated Beckman Coulter LS230.

Grain sizes were sampled at 0.5 cm or 1 cm spacing in select sand units. Ninety-six smear slides were made at depths of interest in Black Hole Lake. A smear slide was made for each unit in order to examine similarities or differences in mineralogy throughout the cores. Identification of minerals was done using The Colour Atlas of Rocks and Minerals in Thin Section (Mackenzie and Adams, 1994) and the Tool for Microscopic Identification (TMI) provided by the

Limnolgoical Research Institute (https://tmi.laccore.umn.edu/). Further mineralogic analysis was done using X-Ray Diffraction (XRD). XRD analysis was done by drying the samples in an oven at 400° C. The samples were then ground up into a powder and placed in Seiments D-500

Powder X-Ray Defractometer. Samples were run from 2- 65° at 0.05 step size at a 1 second count. Results were analyzed according to the Table of Key Lines in X-Ray Powder Diffraction

Patterns of Mineral in Clays and Associated Rocks (Chen, 1977).

Chronology was established with radiocarbon dates within the sediment cores. All samples were rinsed with deionized water before drying, weighing and storing in glass containers. Samples were then labeled and sent to the National Ocean Science Accelerator Mass

Spectrometry Facility (NOSAMS) for radiocarbon analysis. Ages were calibrated using the

Calib 6.0 for years cal BP with a 2-sigma range.

Figure 1: A: Greenland; black box denotes location of Scoresby Sund. B: Scoresby Sund; black box denotes location of Graben Land. C: Aerial photo of Graben Land.

Figure 2: Map of field site. A: Tsunami Lake; ice-contact lake, no cores were retrieved. B: Black

Hole Lake coring site. C: Ice Fall Lake coring site. Individual coring sites indicated by red dots.

Figure 3: Bathymetric maps of Black Hole Lake (B) and Ice Fall Lake (C) with core locations.

Two cores in Black Hole Lake (BHL11-1A-1 and BHL11-2A-1) were situated on the perimeter of the lake while three cores (BHL11-3A-1, BHL11-3B-1 and BHL11-3B-2) were situated in the central part of the lake.

Chapter 2: Silts Recording Glacial Expansions

Introduction:

Silts are commonly found in proglacial lakes in arctic localities (eg, Karlén, 1976, 1981;

Nesje et al., 2001; Briner et al., 2010). Silts contained within glacially fed lakes are derived from the glacier and originates from erosion of bedrock beneath glaciers (Karlén, 1976). The silts are subsequently transported to proglacial lakes where they will form distinct silt units within sediment cores.

Sediments cores extracted from “proglacial threshold” lakes can provide continuous high- resolution records of glacier fluctuations. These lakes constrain the timing of glacial expansions when glacial meltwater is received and glacial retractions when no glacial meltwater is received.

In this way, proglacial lakes contain glacial, minerogenic-rich sediments when the ice sheet is expanded and non-glacial, organic-rich sediment during restricted ice (Kaplan et al., 2002;

Daigle and Kaufman, 2009). The significance of lakes in this respect was first recognized in the mid-1970’s (Karlén, 1976) and has been applied to numerous studies on alpine glaciers (eg,

Karlén, 1981; Leonard, 1985; Nesje et al., 1991, 1992, 1994; Leemann and Niessen, 1994) and ice sheets (eg, Kaplan et al., 2002; Briner et al., 2010; Wagner 2011, Larson et al., 2011).

In Greenland, early studies documenting glacial fluctuations primarily used in situ plants on moraines (Funder, 1972, 1978; Hjort, 1979); however, moraines are often destroyed by earlier, larger glacial advances and thus don’t record smaller fluctuations (Karlén, 1976).

Because of this, studies of glacial fluctuations in Greenland have used lacustrine records to indicate variation in glacier size in more detail (Kaplan et al., 2002; Briner et al., 2010; Larson et al., 2011); however, these studies were conducted in West and South Greenland. Relatively little is known about glacier expansions retrieved from lacustrine cores in East Greenland. It is

therefore necessary to determine glacial fluctuations in this region in order to fill in this gap.

Here, expansions of the Greenland ice sheet in the Scoresby Sund region, recorded from silts in proglacial lake sediment cores, will be discussed. To identify silt units within the cores, and hence glacial expansions, I will use grain size, magnetic susceptibility, loss-on-ignition, and mineral identification. Radiocarbon ages from organics will be used to establish periods when glaciers were expanded.

Results:

Black Hole Lake General Results

Black Hole Lake contains six distinct bluish grey silt units (Appendix A1) located throughout the core. They are seen as small (<1 cm thick) units near the base of the cores to 10- cm-thick units at the top of the cores. Silt units showed distinct low grain sizes between 20 and

70 μm (Appendix C). The silts have high MS values at approximately 20 SI and low LOI between 0 and 4%. From smear slide analysis, silts typically contain 50-75% quartz and 10-

50% mica. To support this, there were five XRD samples taken in BHL11-1A-1 at depths of 17,

40.5, 60, 90, and 101 cm (Appendix D1). Different counts were seen for certain minerals. The counts of representative mica and quartz were most intense at 8.8 and 20.9 theta, respectively.

When comparing mica and quartz at 2 theta 8.8 and 2 theta 20.9, respectively, the silt units within Black Hole Lake were similar in mineralogy with a 3:2 ratio of quartz to mica (Appendix

D1).

Ten 14C radiocarbon ages were obtained from Black Hole Lake (Table 2). Five samples were taken from the central part of the lake and five were taken from cores near the perimeter of the lake. The plant material sampled was Warnstorfia exannulata (aquatic moss). The oldest sample was dated at 4742 ± 60 cal yr. BP and the youngest sample was dated at 388 ± 30 cal yr.

BP. Two small (<1 cm) silt units were found between 4742 ± 60 and 1347 ± 60 cal yr. BP. Two silt units approximately 3 cm thick were found between 1347 ± 60 and 1319 ± 40 cal yr. BP.

One 3 cm thick silt unit was found directly below a sample dated at 388 ± 30 cal yr. BP. One large (10 cm) thick silt was found immediately above 388±30 cal yr. BP.

Ice Fall Lake General Results

Ice Fall Lake revealed fewer and smaller silt units than Black Hole Lake; however, grain size, MS values, LOI values and XRD values of the silts were similar to those of Black Hole

Lake. Three small (<1 cm) thick silt units were identified. (Appendix A2). The uppermost silt unit at 12 cm in IFL11-1A-1 showed a grain size of approximately 50 μm while the grain sizes of silt bands at 68 cm in IFL11-A-1 and 7 cm in IFL11-1C-1 had grain sizes of approximately 100

μm. While processing the cores, mica flakes from the mica sand unit were likely transported to silt units owing to the increased grain size with respect to Black Hole Lake. The silt units had high MS values between 15 and 30 SI and low LOI percentages between 2 and 7%. From XRD analysis, a sample taken from IFL11-1A-1 at 12 cm had high amounts of quartz to mica (3:2 ratio, Appendix D2).

Seven 14C Radiocarbon dates were taken from Ice Fall Lake (Table 2). The oldest sample was from terrestrial debris and dated at 4035 ± 50 cal yr. BP and the youngest sample was from terrestrial debris and dated at 464 ± 40 cal yr. BP. One silt unit was immediately above a sample of Warnstorfia exannulata dated at 1702 ± 40 cal yr. BP and one silt unit was sampled from terrestrial debris in a silt unit at 464 ± 40 cal yr. BP.

Discussion:

Glacial expansions will be described using silt as a proxy. The silt source will be discussed first followed by a discussion of multiple meltwater episodes recorded by silt and conclude with a discussion of glacial expansions at other localities in Greenland.

Silt Source

The source of the silt is derived from Vendue Glacier and is subsequently deposited into

Black Hole and Ice Fall Lakes. Silt could be deposited in two ways. First, silt could come from the Vendue Glacier when it was advanced completely across Tsunami Lake in which it would deposit silt directly into the outlet stream; however, this is unlikely because the Vendue Glacier has only retreated approximately 10 m in the study area since its Little Ice Age glacial maximum (Briner et al., 2010, Lowell et al., 2010). It is therefore unlikely that Vendue Glacier extended 850 m to the east side of the lake and deposited silt directly into the outlet. The most likely scenario is silt being transported as suspended material across Tsunami Lake and out of the outlet stream.

By observing the distinct contact between silt and organic remains, a threshold is apparent in the study area at which the suspended silt is either prevented from being deposited in the proglacial lakes or allowed to be deposited in the proglacial lakes. The threshold is a bedrock outlet of Tsunami Lake (Fig. 4). In order for silt to be received in Black Hole and Ice Fall Lake,

Tsunami Lake must exist and be high enough to release water out of the catchment through the bedrock threshold. The glacier and the outlet stream limit the height of Tsunami Lake. Vendue

Glacier has to be at an expanded state to raise Tsunami Lake in order to reach the bedrock threshold at which silt laden water can escape through the outlet stream. In Graben Land, the presence of a threshold means that downstream lakes are quite sensitive to changes in the level of

Tsunami Lake as reflected by the presence or absence of silt in the sediments. Organic remains in Black Hole and Ice Fall Lakes occur at times when Vendue Glacier is in a retracted state and hence Tsunami Lake is absent or too low to allow silt laden meltwater release to the downstream lakes (Deline et al., 2004). Once the bedrock threshold is reached again, the silt laden water will be deposited and prevent organic growth. The simplest way to interpret the sedimentary sequence is as a binary signal whereby it is either meltwater (silts) or no meltwater (organics). In the study area, this binary signal was observed throughout the past 4,700 and is therefore useful in determining glacial expansions. During our field study in August of 2011, Tsunami Lake was high enough to allow water to pass through the outlet stream. Silt from the glacier was clearly visible indicating that the glacier was at an expanded state enough to raise Tsunami Lake to a height at which silt laden meltwater could flow over the bedrock threshold and into Black Hole and Ice Fall Lakes.

Silt Recording Late Holocene Glacial Expansion

Six silt bands were noticed in Black Hole Lake (BHL). The most extensive of these silt bands were deposited at the top of the cores. There are two ways in which one could determine age of uppermost silt deposition. First, one could take a mean pooled age of samples collected near the base of the uppermost silt unit. This yielded an age of 542 cal yr. BP. This represents the oldest age in which silt could be deposited. Second, one could use the calibration curves to assign an age of the uppermost silt unit found in both BHL and Ice Fall Lake (IFL). Because the uppermost silt units in both lakes had similar 14C ages and were the largest silt units deposited in each respective lake, I am interpreting them as being from the same event. Because the calibration curves gave a binary peak of ages, calibrated ages were altered from their original 14C ages (Table 2). The calibration curves of a sample collected in BHL with an age of 388 ± 30 cal

yr. BP and a sample collected in IFL with an age of 464 ± 40 cal yr. BP were used because they represent the tightest stratigraphic range. The age of 388 ± 30 cal yr. BP had a binary peak with a 50% probability of being between 318-393 cal yr. BP and 425-481 cal yr. BP while the age of

464 ± 40 cal yr. BP had a binary peak with a 24% probability of being between 329-359 cal yr.

BP and a 76% probability of being between 429-503 cal yr. BP. Here, we suggest that the minimum age is closer to 470 cal yr. BP due to the 76% probability of the date of 464 ± 40 in

IFL being correct. Therefore, the silt was deposited between 470 and 540 cal yr. BP. Here, we take the age of 500 cal yr. BP as being the age of silt deposition.

The silt deposited at 500 cal yr. BP was the thickest silt unit in the cores (10 cm) and therefore represents the longest timespan at which the Vendue Glacier was expanded far enough to allow meltwater release downstream. Silt is continuing to be deposited today indicated that the Vendue Glacier has not yet thinned to the level occupied ~500 years ago.

Graben Land Recording Multiple Meltwater Episodes

Based on evidence described earlier in the discussion that silt is representative of meltwater input, it is suggested that other silt bands within the cores also represent periods when meltwater was being actively deposited into the proglacial lakes.

There are four prominent silt bands found in Black Hole Lake. Two of the silt bands are interrupted by sand at 500 cal yr. BP and at 1330 cal yr. BP. The silt deposited at 1330 cal yr.

BP was 5 cm thick and therefore represent a shorter temporal duration than the 10 cm thick silt deposited at 500 cal yr. BP. The sand layers found with these two silt events are interpreted as instantaneous (Chap. 2), thus where the sand is bounded by silt layers, both silt layers are considered to be part of the same unit. Thinner (<1 cm) bluish grey silt bands, similar to the uppermost silt band, likely representing shorter temporal durations, have provisional ages

assignments of 1700 and 3300 cal yr. BP (Appendix F). These two silt units were found in- between Warnstorfia exannulata samples dated at 1347 ± 60 and 4742 ± 60 cal yr. BP. The age of the silt at 1700 cal yr. BP was determined from a similar silt unit observed in Ice Fall Lake which was dated at 1702 ± 40 cal yr. BP. The age of the silt at 3300 cal yr. BP was determined using a time depth plot (Appendix F). We therefore have four silts in the lakes at 500, 1330,

1700 and 3300 cal yr. BP.

We suggest that the Graben Land proglacial lakes, due to their ideal placement downstream of a bedrock threshold that makes the cored lakes sensitive to the presence or absence of silt in the sediments, records four periods when the glacier was at a position to allow meltwater to flow into the proglacial lakes. This means the glacier was at an expanded position at these four periods. Despite recent thinning, Vendue Glacier has been at an expanded position which allows meltwater to reach the study lakes since 500 cal yr. BP.

Late Holocene Glacial Expansions Recorded at other sites in Greenland

The age of this silt unit at 500 cal yr. BP is consistent with glacial expansions elsewhere in Greenland (Fig. 5). Based on material dated on an outer moraine system, studies on the

Qassimiut lobe in southern Greenland concluded that the date of the historical maximum advance varies between 400 cal yr. BP and present (Weidick et al., 2004). From lacustrine studies in West Greenland, Briner et al. (2011) suggests advance of Jakabshavn glacier between

350 and 400 cal yr. BP. Lacustrine studies in South Greenland by Larson et al. (2011) reported the latest ice advance in South Greenland occurred at 500 cal yr. BP. The silt at the uppermost part of the cores therefore correlates with glacial expansion during the late Holocene. It also represents the longest duration when silt laden meltwater was being deposited into the proglacial lakes during the last 4,500 years. This agrees with other studies in East Greenland which report

that largest glacial expansions in the Holocene are occurring during this time period (Hall et al.,

2008; Kelly et al., 2008, Lowell et al., 2013); as well as other parts of Greenland (Kaplan et al.,

2002; Weidick et al., 2004; Briner et al., 2011; Larson et al., 2011).

This work contrasts work from Liverpool Land, East Greenland in which glacial expansion were reported to begin at 850 cal yr. BP (Lowell et al., 2013). The study was conducted on a local ice cap (Istorvet Ice Cap), approximately 200 km to the east near the coast.

The expansion on the Istorvet Ice Cap occurred approximately 350 years before the expansion begun on the Vendue Glacier in Graben Land. We hypothesize the inverse gradient climate that exists between the coast and interior regions of Greenland could account for the difference in age. Perennial sea ice creates foggy conditions that will reduce temperature and prevent ablation of local ice caps, such as Istorvet, near the coast. The coast is also much wetter which increases accumulation. This, in turn, causes the glaciation limit to be much lower on the coast than inland

(Funder, 1978). I hypothesis that the lower temperatures that accompany the fog modulate the elevation line altitude and cause glaciers on the coast to advance at an earlier time than glaciers inland. By observing records from the Danish Meteorological Society, Ittoqqortoormiut, a coastal village near Istorvet Ice Cap, has more than double the amount of days with fog than any other record in Greenland (Appendix H). It is also shown in Appendix H that fog will lower the air temperature quite rapidly. This supports the notion of fog being a viable mechanism for earlier glacial expansions on the coast than inland.

Similar to the glacial expansion at 500 cal yr. BP, the date of 1330 cal yr. BP is consistent with other reports of glacial expansion in Greenland. In southern Greenland, Bennike and

Sparrenbom (2007) provided a minimum age of the Narssarssuaq stade between 1100 and 1300 cal yr. BP. More recently, Larson et al. (2011) noted that a few glaciers in Southern Greenland

made a significant advance during the Narssarssuaq stages slightly before 1200 cal yr. BP.

Conclusion:

Fluctuations of the Vendue Glacier, an outlet of the Greenland Ice Sheet were identified using cores from lake sediments. These lakes constrain the timing of glacial expansions when glacial meltwater is received and glacial retractions when no glacial meltwater is received. In this way, proglacial lakes contain glacial, minerogenic-rich sediments when the ice sheet is expanded and non-glacial, organic-rich sediment during restricted ice. Only when the Vendue

Glacier is advanced does it raise the lake level high enough to allow minerogenic-rich sediments to escape Tsunami Lake and become transported downstream to the proglacial lakes.

In East Greenland, relatively little is known about glacier expansions retrieved from lacustrine cores. It is therefore necessary to determine glacial fluctuations in this region in order to fill in this gap.

Our results indicated that there is an extensive period in which silt laden meltwater was being delivered into the proglacial lakes from 500 cal yr. BP until present. In addition to this prominent silt layer at ~500 years ago, other thinner silt bands indicating that the Vendue Glacier many have been at similar positions at 1330, 1700 and 3300 cal yr. BP. The age of 500 cal yr.

BP agrees with the timing of glacier expansions in South Greenland (Weidick et al., 2004;

Larson et al., 2011), and West Greenland (Briner et al., 2011). We hypothesis that the difference in timing of the glaciation in the Scoresby Sund region 200 km to the east in Liverpool Land at

850 cal yr. BP is due to perennial sea which causes frequent fog on the coast. The lower temperatures that accompany the fog will modulate the elevation line altitude and cause glaciers on the coast to advance at an earlier time than glaciers inland.

Figure 4: Conceptual model of glacier positioning and lake level response. Absence of Tsunami

Lake and lower Tsunami Lake water levels traps sediments and accommodates organic production in Black Hole and Ice Fall Lake (Green). Higher Tsunami Lake water levels transports more sediment and prevents organic production (Gray). Tsunami Lake receives continuous sediment supply. Scale is relative to depth of Black Hole and Ice Fall Lakes.

Figure 5: Timing of late Holocene expansion from studies conducted on the Greenland Ice Sheet.

Chapter 3: Slush Avalanches

Introduction:

The lakes cored in Graben Land contain a number of large (20 cm thick) sand units.

Similar sand units were also observed in Liverpool Land 200 km to the east (Lowell et al., 2013); however, sand deposits do not appear to be commonly described from high latitude settings. The process interpreted as responsible for depositing the sands are called slush avalanches.

Slush Avalanches have rarely, if ever, been described as the transportation mechanism for sand in a sediment core collected in a glacially fed lake. They are typically seen as water- saturated snow, flowing like a mudflow along stream channels due to intense spring thaw

(Goldthwait, 1958). They are observed in many Arctic localities such as Greenland (Washburn and Goldthwait, 1958), Sweden (Gude and Scherer, 1995), and Iceland (Dacaulne and

Sæmundsson, 2006). Determining if these sand units are indeed deposited by slush avalanches can be used to infer past glacial expansions. This, in turn, could be used to support glacial expansions in other arctic localities where sand is found in sediment cores.

Here, we aim to illustrate that these sand units are deposited by slush avalanches. We will also speculate if they can be related to the extent of the Vendue or other glaciers.

Results:

Black Hole Lake General Results

Black Hole Lake has two large (20 cm) sand units with several graded beds (Appendix

C). The sand units were bounded by silt units. There were four graded beds in the upper sand unit and two graded beds in the lower sand unit. Grain size ranged between 60 and 250 μm. The low average grain size of 60 μm accounts for the silt that was often intermixed with the sand units. Cores BHL11-3A-1, BHL11-3B-1, and BHL11-3B-2 in the central part of the lake had

higher grain sizes than cores BHL11-1A-1 and BHL11-2A-1 on the perimeter of the lake. The central cores had sand ranging between 60 and 250 μm while the perimeter cores had grain sizes between 80 and 140 μm. The two large sand units contained silt units both below and above the sand units which formed distinct low grain size values between 20 and 70 μm. Sand had high

MS values between 18 and 33 which was noticeably higher than the organics and silt at approximately 10 and 20 SI, respectively. LOI was inverse of MS. The sand had low LOI percentages at less than 2% while the organics had high LOI percentages between 7% and 11%.

The grey silt had similar LOI values as the sand between 2 and 4%. From smear slide analysis, quartz and mica were most common in the sand units with quartz typically being more abundant

(> ~60%), with minor (<~10%) of other minerals. To support this, there were eleven XRD samples taken at levels indicated in (Appendix D1). Representative mica and quartz were most intense at 8.8 and 20.9 theta, respectively, showing different counts for certain minerals. Even though the counts varied between each sample by upwards of 40%, the representative peaks of mica and quartz were consistent. When comparing the most representative intensities of mica and quartz at 2 theta 8.8 and 2 theta 20.9, respectively, there were higher amounts of quartz than mica (3:2 ratio) (Appendix D1).

Ice Fall Lake General Results

Ice Fall Lake contained numerous massive sand units (Appendix A2), several of which could not be correlated with Black Hole Lake. Only two of the sand units could be correlated to

Black Hole Lake (Fig. 7). Grain size was variable with a large range of high grain sizes between

100 and 375 μm. The uppermost unit of sand is 150 μm, as in Black Hole Lake. From visual inspection, the high abundance of mica most likely resulted in increased and variable grain sizes found in Ice Fall Lake. Sand units between 20 and 30 SI interrupted organic units of low MS

values of approximately 10 SI. Sand units at the uppermost part of the core had similar MS values as Black Hole Lake of approximately 20 SI. The sand unit had high LOI percentages between 7% and 12% Macro organic material could clearly be seen within these units. From smear slide analysis, quartz and mica were most common in the mica sand units with mica being more abundant (~>80%). To support this, there were nine XRD samples were taken at the levels indicated in (Appendix B). When comparing the most representative intensities of mica and quartz at 2 theta 8.8 and 2 theta 20.9, respectively, there were higher amounts of mica than quartz (6:1 ratio) (Appendix D2).

Discussion:

Enigmatic sand units were found in Graben Land and could hint at possible glacial expansions. The process responsible for the sand deposition will be discussed first followed by a discussion of how the sand could be used to infer glacial expansions and conclude with a discussion of similar sand units found in Liverpool Land.

Sand Deposition

Several processes could account for the sand units deposited in Graben Land. These processes include glacial proximity, landslides, glacier lake outburst floods (GLOFs) or slush avalanches; however, three of these processes are unlikely in the study area and will be discussed below.

The Vendue Glacier being at a position to deposit sand directly into Black Hole and Ice

Fall Lakes are unlikely because the Vendue Glacier has only retreated approximately 10 m in the study area since its Little Ice Age glacial maximum (Briner et al., 2010, Lowell et al., 2010).

It is therefore unlikely that Vendue Glacier extended 850 m to the east side of Tsunami Lake and deposited sand directly into the Black Hole and Ice Fall Lakes.

From sediment analysis, the sand in Graben Land was deposited quickly during landslides, GLOFs or slush avalanches. Furthermore, two dates sampled below and above one of the sand units at approximately 1330 cal yr. BP were very similar and had a difference in age could not be distinguished.

Landslides were unlikely to deposit the sand in the field area given the large boulders present on the slopes and no sand visible. The sand layers are therefore most likely deposited from GLOFs or slush avalanches. In the first case, an ice dam would break and release large amounts of sediment laden water downstream (Maizels, 1997); in the second case, seasonal melt water would remain in the snow pack until released as large slush avalanches (Gude and Scherer,

1999).

It is unlikely that GLOFs from ice dam collapse was responsible for the numerous sand units deposited in the glacially fed lakes due to the difficulty of GLOFs from ice dam collapse to produce multiple floods (Maizels, 1997). Furthermore, Tsunami Lake would act as an excellent sediment trap for any debris that was released from an ice dam failure. GLOFs from moraine failure are also doubtful because Tsunami Lake is bounded by bedrock. Also, there is no evidence of an incised channel. The lack of correlation among sand units rule out GLOFs as a source of the sand; therefore, slush avalanches are the most likely explanation of sand deposition in the given study areas and will be described in detail.

In order for slush avalanche to form, certain meteorological conditions must exist. This includes high snowpack and enhanced melting (Nyberg, 1985; Decauline and Sæmundsson,

2006; Echerstorfer and Christiansen, 2012; Gude and Scherer, 1995, 1999). Meltwater from the snowpack percolates towards the snow base as snow conditions reach the 0 °C isotherm. When the liquid water forms a saturated layer above an impermeable layer, meltwater follows the

hydraulic gradient, accumulating in area of horizontal meltwater convergence and generates slush flow event often in multiple pulses (Gude and Scherer, 1999). For a water table to form in the snowpack, the release zone must have an inclination below 20° and are most often situated adjacent to steeper slopes, providing meltwater (Echerstorfer and Christiansen, 2012). Following the suggestion by Nyberg 1985, we define slush avalanches as major events that travel up to 2 km. Sediment mobilized during slush avalanches can range from fine grain silt to boulders 2 m in diameter.

Slush avalanches in Graben Land would be transported over frozen lakes and sediment would settle to the lake-bottom during spring thaw (Fig. 6). The lakes are frozen at least 10 months out of the year. This would explain how sand would be transported past Tsunami Lake.

It also explains the lack of correlation between lakes as slush avalanches will often bypass or leave little sediment in certain lakes as they are quickly transported down valley over the frozen topography. Correlation was found between two of the slush avalanches in both Black Hole and

Ice Fall Lakes at the tops of the cores indicating that the slush avalanches are indeed flowing downstream over the lakes, however there are several sand units that are found below the two uppermost sand units in Ice Fall Lake that could not be correlated to Black Hole Lake (Fig. 7).

Graded sand could also be seen in two sand units from Black Hole Lake and are consistent with reports of multiple pulses of suspended material that are released from slush avalanches (Gude and Scherer, 1999). These pulses are only faintly visible in Ice Fall Lake. It is difficult to explain how the graded bedded was preserved if they are indeed from different pulses of a slush avalanche. I hypothesis that the pulses released by the slush avalanche was greatly disturbed with a variety of grain sizes over Black Hole Lake. Upon settlement, the different sized grains reorganized into graded bedding. Once the slush avalanche had reached Ice Fall Lake and the

larger grains had settled over Black Hole Lake, the grains were much more homogenous and accounts for the more massive structures. In addition, Graben Land has adequate topography to release slush avalanches. The steep mountain slopes to the north and south with a gently sloping stream catchment of less than 20° are reported suitable for slush avalanche release (Gude and

Scherer, 1995). Furthermore, the front of the glacier is approximately 1.5 km from the lakes in which the cores were extracted which has been reported as reasonable distances slush avalanches can travel (Nyberg, 1985). The lakes are 15 m below the elevation of Tsunami Lake. Together, this evidence indicates that slush avalanches are responsible for depositing sand in Black Hole and Ice Fall Lakes.

Slush Avalanches Recording Glacial Expansion in Graben Land

Although the exact conditions for large slush avalanches are numerous, a hint comes because several sand units were deposited at times of expanded glaciers as recorded by silt units both below and above two of the prominent sand units from Black Hole Lake (Appendix C).

The silts represent only those times when the glacier was expanded. Black Hole Lake, being a

“proglacial threshold” lake, constrains the timing of glacial advance and retreat by having its drainage basin partially occupied by advancing ice. In this way, it can transition from being non- glacial lake to glacially fed lake (Kaplan et al., 2002; Daigle and Kaufman, 2009). The existence of Tsunami Lake controls the binary glacier/non-glacial signal in Black Hole Lake. Only when

Tsunami Lake exists and the glacier is at an expanded state does silt laden meltwater flow into

Black Hole Lake. In this view, the two slush avalanches in Black Hole Lake were deposited during periods when the glacier was at an expanded state and actively delivering silt laden meltwater into Black Hole Lake.

By observing the ages of the sand units, it is apparent that there are two periods in Graben

in which sand is most frequently deposited (Fig. 8). Sand units were estimated using a time depth chart (Appendix F). In Graben Land, the first period occurs at 1330 cal yr. BP. This time also marks an abrupt increase in sedimentation in Graben Land as presented in Appendix F as a result of the sand being instantaneously deposited relative to the other units, most likely within hours (Gude and Scherer, 1995). The second period occurs at 500 cal yr. BP. Again, as with the slush avalanches at approximately 1330 cal yr. BP, this time frame of approximately 500 cal yr.

BP marks an increase in sedimentation in Graben Land as presented in Appendix F. Sand layers also occurred at 2100, 2700 and 3300 cal yr. BP (Fig. 8).

Slush Avalanches in Liverpool Land

Similar to Graben Land, slush avalanches most likely deposited the sands units in

Liverpool Land. The large, abrupt sand units with evidence of graded bedding as well as lack of correlation among sediment cores correlate with the sand units in Graben Land. In addition, the setting of the proglacial lakes is similar. The proglacial lake where sediment was retrieved (Half and Half Lake) is approximately 2 km from the glacier front similar to Black Hole and Ice Fall

Lakes. Furthermore, the steep mountain slopes and gently sloping stream catchments of less than 20° in Liverpool Land is adequate for slush avalanche formation.

The sand in Liverpool Land was deposited at approximately 1200 cal yr. BP based on five radiocarbon dates sampled above and within the sand units. This correlates to a sharp increase in sedimentation in Half and Half Lake at 1200 cal yr. BP (Appendix F). It was curious to note that the event at 1200 cal. yr. BP roughly correlates with a sharp sediment increase with

Black Hole Lake in Graben Land (Appendix F). It would be interesting to see if this pattern exists in other lakes.

Conclusion:

The mechanism responsible for depositing sand into glacial fed lakes was examined in order to determine if the sand could be used to infer past glacial expansions. This, in turn, could be used to support glacial expansions in other arctic localities where sand is found in sediment cores. The sands are interpreted to be deposited from slush avalanches and released when there is an adequate snowbase and melting to allow hydraulic pressure build-up and release of the slush avalanche. Due to the specific meteorological conditions, the regional extent of the sand units at two sites, and the timing of one of the slush avalanches during known glacial intervals in the late Holocene, slush avalanches could hint at possible periods of glacial expansion. Two

Prominent slush avalanches occurred at 500 and 1300 cal yr. BP with smaller deposits at 2100,

2700 and 3300 cal yr. BP.

Evidence of slush avalanches were also found in Liverpool Land, Greenland. They were deposited at approximately 1200 cal yr. BP which roughly correlates with the timing of the slush avalanche event at 1300 cal yr. BP in Graben Land.

Figure 6: Conceptual model of slush avalanche being transported across frozen lakes.

Figure 7: Correlation between composite Black Hole Lake (BHL) core and Ice Fall Lake (IFL) core. Red arrows are depths where radiocarbon was sampled. Yellow lines show correlating units between cores. Ages are in Calibrated years BP.

Figure 8: Age distribution of sand layers in Liverpool Land and Graben Land. Green bars are from Graben Land and yellow bar is from Liverpool Land.

Chapter 3: Summary

Due to current warming and retreat of the Greenland Ice Sheet (eg, Funder, 1972;

Abdalati et al., 2001; Krabill et al., 2004; Luthcke et al., 2006; Velicogna and Wahr, 2006), it is necessary to place the current retreat into context by observing past glacial expansions. In East

Greenland, relatively little is known about past glacial expansions. To fill this gap, lacustrine sediments were used to provide a continuous record of glacial expansions over the past 4,700 years in Graben Land, East Greenland. Silt and sand contained in the cores were used as proxies for glacial expansions.

In Chapter 1, fluctuations of the Vendue Glacier, an outlet of the Greenland Ice Sheet were identified using silt from proglacial lake cores. These lakes constrain the timing of glacial expansions when glacial meltwater is received and glacial retractions when no glacial meltwater is received. In this way, proglacial lakes contain glacial, minerogenic-rich sediments when the ice sheet is expanded and non-glacial, organic-rich sediment during restricted ice. Only when the Vendue Glacier is advanced does it raise the lake level high enough to allow minerogenic- rich sediments to escape Tsunami Lake and become transported downstream to the proglacial lakes.

BP agrees with the timing of glacier expansions in South Greenland (Weidick et al., 2004;

Larson et al., 2011), and West Greenland (Briner et al., 2011). I hypothesis that the difference in timing of the glaciation in the Scoresby Sund region 200 km to the east in Liverpool Land at 850

cal yr. BP is due to perennial sea which causes frequent fog on the coast. The lower temperatures that accompany the fog will modulate the elevation line altitude and cause glaciers on the coast to advance at an earlier time than glaciers inland.

In chapter 2, the mechanism responsible for depositing sand into proglacial lakes was examined in order to determine if the sand could be used to infer past glacial expansions. This, in turn, could be used to support glacial expansions in other arctic localities where sand is found in sediment cores.

Based on the results, the sands are interpreted to be deposited from slush avalanches and released when there is an adequate snowbase and melting to allow hydraulic pressure build-up and release of the slush avalanche. Due to the specific meteorological conditions, the regional extent of the sand units at two sites, and the timing of one of the slush avalanches during known glacial intervals in the late Holocene, slush avalanches could hint at possible periods of glacial expansion. Two Prominent slush avalanches occurred at 500 and 1300 cal yr. BP with smaller deposits at 2100, 2700 and 3300 cal yr. BP.

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Appendix

This section contains supplemental material provided for Chapters 1, 2 and 3. The supplemental material will be provided in this order:

A. Stratigraphy and data from cores

1. Black Hole Lake………………………………………………………………41

2. Ice Fall Lake…………………………………………………………………..42

B. Stratigraphy column legend…………………………………………………………..43

C. Grain size……………………………………………………………………………..44

D. Smear slide and XRD data

1. Black Hole Lake………………………………………………………………45

2. Ice Fall Lake…………………………………………………………………..46

E. Sample XRD chart……………………………………………………………………47

F. Time-Depth…………………………………………………………………………...48

G. Weather………………………………………………………………………………49

H. Fog……………………………………………………………………………………50

I. General core descriptions……………………………………………………………...51

Cores are located at positions shown. The height of BHL11-1A-1, BHL11-3B-1 and BHL11-2A1 had to be adjusted to be shown at the sediment water interface (Table 2). Note vertical scale changes between water and sediment cores

Cores are located at positions shown. The height of IFL11-1A-1 had to be adjusted to be shown at the sediment water interface (Table

2). Note vertical scale changes between water and sediment cores.

Unit descriptions of stratigraphic units in Black Hole and Ice Fall Lakes. 43

Grain size from Black Hole Lake; core BHL11-1A-1. Collected 10.3 m below lake surface.

Smear slide and XRD results of Black Hole Lake. XRD analysis only includes mica and quartz.

Smear slide and XRD results of Ice Fall Lake. XRD analysis only includes mica and quartz.

Three XRD graphs of silt, sand and mica sand with representative counts of mica and quartz indicated by red and green arrows, respectively.

Depth age curve with sand units removed due to their instantaneous deposition. Cores HH-2C- 1N, HH-2B-1L, HH-1A-1L, HH-1A-4N and HH-1A-5L were used for the composite core of Half and Half Lake. Core BHL11-1A-1 was used for Black Hole Lake. Cores IFL11-1A-1, IFL11-1A-2, IFL11-1B-1 and IFL11-1C-1 were used for the composite core of Ice Fall Lake.

Weather at three sites in East Greenland was monitored to provide a glimpse of the different climate patterns in a continental setting. One station was located in Graben Land and two stations were located in Renland. The weather at these sites will be compared to weather at Scorsby Sund. Site 1 (Graben Land) at N71.17 and W28.97 at elevation of 998 meters, site 2 (Renland) at N71.17 and W27.31 at elevation of 1053 meters, site 3 (Renland) at N71.03 and W27.41 at elevation of 820 meters. Davis Vantage Vue Wireless Weather Station model #06250 was used to monitor the weather at three sites. At sites 1 and 2, the station was placed on a hill above camp. At site 3, the station was placed in below the surrounding relief. Site 1 recorded weather from August 18-24; site 2 from August 24-28; site 3 from August 28-September 1. Weather was compared to hourly weather data collected during the same time period at Nerlerit Inaat (CNP). Dashed lines denote times when weather station was being transported to a new site. This only applies to Graben Land/Renland temperature data.

Chart shows the standard normal of the number of days of fog per year at 11 sites in Greenland recorded from 1961-1990. Red Box indicates site in East Greenland near Istorvet Ice Cap.

Graph shows the abrupt temperature drop that accompanies fog.

Appendix I:

Contains initial descriptions of sediment cores and is organized by core site and the core

Id. Each page contains a description of each major stratigraphic unit, picture of core and whole core magnetic susceptibility. Black Hole Lake is shown first followed by Ice Fall Lake.