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Holocene Ice Sheet Dynamics and Detrital Provenance Shifts Along the West Greenland Margin

Holocene Ice Sheet Dynamics and Detrital Provenance Shifts Along the West Greenland Margin
Author: Lina Madaj
Publisher:
Total Pages:
Release: 2021
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ISBN:
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Due to the effect of Arctic Amplification the Arctic is currently warming at least twice as fast as the rest of the planet. Seasonal sea-ice extent has been alarmingly declining in the past decade. Glaciers and ice caps along the Greenland coast and in the Canadian Arctic have been losing mass on an accelerated rate during the past century. As the global climate system is a complex system connecting different regions via atmospheric transport, changes in Arctic climate patterns are affecting the climate and weather conditions in the lower latitudes. The Greenland Ice Sheet as well as glaciers and ice caps in the Canadian Arctic are the largest freshwater storages on the northern hemisphere and expected to be among the highest contributors to global sea level rise. Freshwater input through meltwater discharge is not only affecting sea level rise but further influencing deep water formation in the Labrador Sea and the subpolar North Atlantic and hence global ocean circulation and climate patterns. To be able to sufficiently predict future developments of the Greenland Ice Sheet with respect to mass loss and resulting impacts on the global climate, data from past climate and Greenland Ice Sheet extents are crucially important. The Holocene spanning the last period of the deglaciation after the Last Glacial Maximum culminating in the Holocene Thermal Maximum when atmospheric temperatures were warmer and glacier and ice-sheet extent smaller than today represents the closest analogue to current atmospheric warming and Greenland Ice Sheet mass loss. The wide west Greenland shelf of Baffin Bay and Labrador Sea hosts thick marine sediments archiving around ten thousand years of this past climate and ice-sheet history. Siliciclastic detrital material discharged into Baffin Bay and the Labrador Sea via meltwater and erosion can be separated from those sedimentary archives and traced back to its source region. Radiogenic isotopes (Sr, Nd, Pb) label the source regions of those sediments by fingerprinting the isotopic composition of the prevailing bedrock. Hence, they can be used as reliable provenance tracers. Retreating land-ice masses expose bedrock that before was not subject to erosion, influencing the isotopic signatures delivered into the surrounding ocean. Based on this theory, radiogenic isotopes can record changes in siliciclastic detrital sediment provenance and hence, indirectly trace ice-sheet dynamics. The overall aim of this thesis work is to reconstruct changes in detrital sediment provenance along the west Greenland shelf to gain new insights into Holocene Greenland Ice Sheet dynamics and ocean current-induced sediment transport. Sedimentary archives from three main research areas (eastern Labrador Sea, northeastern Baffin Bay, and Kane Basin, central Nares Strait) record obvious shifts in sediment provenance throughout the Holocene. Those shifts coincide with major regional climatic changes in the research area. Generally, all records reveal the local bedrock as the main source region of detrital material and distal-sourced material transported along the coast via the West Greenland Current as a secondary source. Although the proportion of distal sourced material appears to be small, changes in West Greenland Current strength have been recorded in the isotopic composition. In southwestern Greenland and the Labrador Sea radiogenic isotope records reveal a shift towards a higher proportion of the local Archean Block in the late Holocene caused by Neoglacial ice advance and a reduction in West Greenland Current speed delivering less material from southern most Greenland. Farther north in the Upernavik region, midwest Greenland coast, the isotopic composition marks a change with the transition from early to mid Holocene caused by increased West Greenland Current strength and the opening of Vaigat Strait which enabled erosion and transport of freshly exposed basalts from the Disko Bay area due to ice-sheet retreat. This basalt input is, however, not transported all the way to northernmost Melville Bay (northern Baffin Bay) where the detrital sediment composition is clearly dominated by contribution of the local Committee-Melville Belt without any significant provenance changes throughout the Holocene. Farthest north, the sedimentary record from Kane Basin records provenance shifts that confirm the opening of Nares Strait around 8.3 ka BP. This event is followed by an increased delivery of carbonate-rich detrital sediments from northern Ellesmere Island due to the newly established gateway of Arctic Ocean water transporting sediments from further north to the core location. Additionally determined mineralogical composition of the sedimentary records along the west Greenland coast supports the interpretation drawn from the radiogenic isotopic composition. Furthermore, it points out the additional value of radiogenic isotopes through variations only visible in isotopic composition but not in the mineralogical composition. Further comparison to other studies from the region based on different tracers confirms the reliability and sufficient application of radiogenic isotopes in provenance studies as well as the advantage of multi-proxy approaches in paleoclimatological studies. Overall, this study highlights the advantages and reliability of radiogenic isotopes in provenance studies with regards to reconstructions of ice-sheet dynamics. The combination of the three isotopic systems (Sr, Nd, Pb) enables source region determination with a higher probability compensating for overlapping signatures within individual isotopic systems. The transect of sedimentary records along the west Greenland coast identifies clearly distinguishable isotopic ranges for the different Greenland bedrock terrains, qualifying this approach for further high-resolution investigation in past Greenland Ice Sheet development.

Holocene Reconstruction of the West Greenland Current and the Greenland Ice Sheet Margin Near Disko Bay Using Foraminiferal Assemblages

Holocene Reconstruction of the West Greenland Current and the Greenland Ice Sheet Margin Near Disko Bay Using Foraminiferal Assemblages
Author: Mariah E. Walton
Publisher:
Total Pages: 114
Release: 2010
Genre: Foraminifera
ISBN:
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Recent Greenland Ice Sheet retreat has been shown to be caused at least in part by ocean subsurface warming. Foraminiferal assemblages and IRD counts from four marine sediment cores in the region of Disko Bay (West Greenland) are presented here to help explore the relationship between oceans and ice sheets. Faunal shifts indicate that Atlantic Waters via the West Greenland Current (WGC) were first felt in the bay sometime between 9 and 8.5 cal. kyr BP. A dramatic rise in calcareous fauna from 6.2 - 3.5 cal. kyr BP in all cores indicates a significant shift in the strength of the WGC, with Atlantic associated fauna peaking at 4.5 cal. kyr BP. This coincides with the believed retreat of Jakobshavn Isbrae behind its present margin, suggesting that subsurface warming may have played a part in the ice stream's retreat in the past.

Holocene Sea-ice and Ice-sheet Variability on the Northeast Greenland Continental Shelf

Holocene Sea-ice and Ice-sheet Variability on the Northeast Greenland Continental Shelf
Author: Nicole Syring
Publisher:
Total Pages:
Release: 2020
Genre:
ISBN:
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Sea ice; Biomarker; Holocene; Northeast Greenland. - When will all the Arctic sea ice in summer be gone? The rapid decline in average sea-ice extent by more than one-third during the last 3 to 4 decades leaves a sad note in terms of climate model projections. Dramatic Arctic sea-ice loss generally appears faster than climate models have forecasted. Nowadays, rapidly changing environmental conditions in the Fram Strait, the passage between Greenland and Spitsbergen, are of particular concern. Sea-ice loss here is rising and the Northeast Greenland Ice Sheet is thinning. During past decades, the amount of drift ice export has increased through Fram Strait, contributing with a significant number to the freshwater budget of the Nordic seas and global ocean circulation. Here our analysis of the Northeast Greenland continental shelf located in the western Fram Strait, uniquely records past climate changes in a highly versatile environmental system of the Arctic Ocean. Multivariate analysis of molecular highly branched isoprenoids (HBIs), specific sterols, foraminifers and organic/inorganic bulk parameters were carried out on selected downcore records and surface samples from the Northeast Greenland continental shelf. These proxies allow reconstructions of past changes in sea-ice cover, primary production, terrigenous input as well as ice-sheet extent. The first manuscript provides insights into past sea-ice variability on the outer Northeast Greenland continental shelf and the seasonal formation of the Northeast Water Polynya since the onset of the Holocene to present-day. This outer shelf regime is highly influenced by drift ice and cold water from the central Arctic Ocean and annually occurring local sea-ice formation. Interactive sea-ice and ocean dynamics regulate the regional climate and biology on the marginal shelf. Continuous seasonal sea-ice presence throughout the Holocene within three prominent stages mark relatively abrupt shifts at ~9 ka and ~1 ka. A reduced to variable sea-ice cover with an overall high primary productivity most likely driven by maximum solar insolation was observed during the early Holocene. Sea-ice melt and the intensified inflow of warmer recirculating Atlantic Water favored intensive planktic blooms and fluxes of both marine and terrigenous organic matter. Environmental conditions changed towards seasonal sea-ice conditions and a stronger drift ice signal rather than local one, evidenced by terrigenous biomarkers and IRD content during the mid Holocene. Finally, a stable seasonal sea-ice margin within a fully developed polynya environment occurred during the late Holocene and highlights the last 1 ka. To understand ocean - sea ice - ice sheet interactions, a second study focuses on the inner Northeast Greenland continental shelf where marine terminating outlet glaciers of the Northeast Greenland Ice Stream are bounded by a near permanent lastfast ice barrier named Norske Øer. A downcore record that fronts the 79°Glacier embayment and includes sedimentological, micropaleontological and organic-geochemical data sets, provides fundamental insights into the detailed initial late Weichselian deglacial to Holocene sea-ice and ice sheet history. In contrast to the outer shelf, drift ice is rather trivial while the local ice barrier plays a fundamental role by preventing glaciers from calving due to the buttressing effect. A reconstruction of the waxing/waning 79°Glacier and changes in the Norske Øer ice barrier during this specific interval was generated, showing the timing of 79°Glacier retreat and disintegration, accompanied by the intensification in sea-ice conditions. Distinct lithofacies types represent the transition from deglacial conditions with a grounded 79°Glacier through a proximal to a distal glaciomarine environment displaying the onset of the 79°Glacier retreat and total disintegration of the ice shelf at 7.9 ka. Our biomarker and foraminiferal proxy records reflect local sea-ice conditions that changed from a stable sea-ice margin and high productivity system during the early Holocene Thermal Maximum (~10.6 to 9.6 ka) to prolonged seasonal sea-ice conditions in the late early Holocene (9.6 to 7.9 ka) and near perennial sea-ice conditions in the mid to late Holocene (7.9 ka to present). These changes are strongly triggered by Atlantic Water inflow decreasing from early to late Holocene times. The intrusion of warmer Atlantic Water towards the Northeast Greenland continental shelf and changes in the solar insolation supposed to be the main climate drivers. A third study addresses ways of possible diagenetic alteration on organic bulk parameters and biomarkers in recent and sub-recent samples from the Northeast Greenland continental shelf in comparison with other Arctic records. Multicorer records may be altered by near-surface degradation processes, suggested from the extremely high concentration values in the surface sediments sharply decreasing to minimum values within the uppermost about ~5 cm. Downcore records, however, predominately still reflect a primary signal. In summary ...

Holocene Ice Margin Fluctuations of the Greenland Ice Sheet in the Disko Bugt Region, West Greenland

Holocene Ice Margin Fluctuations of the Greenland Ice Sheet in the Disko Bugt Region, West Greenland
Author:
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Total Pages: 173
Release: 2014
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ISBN:
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The current response of the Greenland Ice Sheet (GrIS) margin to climate change is spatially and temporally variable. Understanding the mechanisms that control this variability is crucial for accurate predictions of how the GrIS will change in the future. One factor that appears to play a role in driving the varying response exhibited along the margin of the GrIS is the ice margin setting (marine-terminating or land-terminating). Recent research has demonstrated that basal melting of marine-terminating glaciers may increase their vulnerability to climatic perturbations, while their land-terminating counterparts may lag in their reaction similar climatic changes. While these trends are illustrated in historic and modern records, longer temporal records are needed to place these observations in context. Here, I present a chronology of GrIS fluctuations within the Disko Bugt region of West Greenland. This record spans the Holocene, and is constrained by 10Be and radiocarbon ages. Through building this chronology, I reconstruct the pattern and timing of Holocene ice margin fluctuations and evaluate the response of differing ice margin types (marine-based or land-based) to regional climate forcing. From my chronology it is apparent that, on millennial timescales early Holocene ice margin retreat rates were synchronous within Disko Bugt. This pattern extends along the western margin of the GrIS, with all the sections of the ice margin examined displaying similar retreat rates despite dissimilar marginal settings. This is strikingly different than modern trends, where marine-based outlet glaciers exhibit significantly higher retreat rates than their land-based counterparts. The record of ice margin reaction to recent warming demonstrates a distinct pattern of asynchrony. In my late Holocene records, marine-based glaciers initiate retreat much sooner than land-based sectors of the ice margin. I believe this feature demonstrates a relationship between ice margin type and response time. I propose that in West Greenland faster glaciers maintain a closer equilibrium with changing climate than slower flowing glaciers. In total, the historic pattern of relative stability of land-based sectors of the GrIS is in contrast with the longer records of Holocene ice margin fluctuation. Additionally, a relationship between ice margin type and response time suggests that land-based sectors of the ice margin lag in their reaction to climate forcing on decadal scales. This indicates that historically stable sectors of the ice margin may be expected to undergo significant future retreat, as a larger percentage of the GrIS margin begins to react to 20th century warming.

Late Quaternary Ice-ocean Interactions in Central West Greenland

Late Quaternary Ice-ocean Interactions in Central West Greenland
Author: David John McCarthy
Publisher:
Total Pages:
Release: 2011
Genre: Climatic changes
ISBN:
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A greater knowledge of the interactions between the Greenland Ice Sheet and climate is critical to understanding the possible impacts of future global warming, including ice sheet contribution to global sea-level rise and perturbations to ocean circulation. Recent acceleration, thinning and retreat of major tidewater glaciers in Greenland and Antarctica during the past two decades demonstrate the potential for ice sheets to respond to climate change much faster than previously assumed. One approach to understanding the role of atmospheric and oceanic warming to ice sheet dynamics is to investigate how ice sheets responded to past periods of climate change. This thesis uses benthic foraminifera as a proxy to reconstruct past changes in the temperature of the relatively warm West Greenland Current, to investigate the possible influence of ocean warming on ice sheet dynamics during the initial marine-based deglaciation phase, and throughout the Holocene, when the ice was positioned close to the present margin. This thesis finds that the marine-based ice sheet in central West Greenland collapsed rapidly due to a combination of high relative sea-level and ice sheet thinning due to climatic warming. Foraminiferal evidence does not support a major influence of ocean forcing on initial deglaciation. However, Holocene changes in the relative temperature of the West Greenland Current may have had a more significant influence on ice stream dynamics following the marine-based ice retreat, when outlet glaciers were positioned within coastal fjords. Changes in the relative temperature of the West Greenland Current are determined?upstream? by wider scale changes in the North Atlantic region.

Late Glacial and Holocene Fluctuations of Local Glaciers and the Greenland Ice Sheet, Eastern and Western Greenland

Late Glacial and Holocene Fluctuations of Local Glaciers and the Greenland Ice Sheet, Eastern and Western Greenland
Author: Laura B. Levy
Publisher:
Total Pages: 408
Release: 2014
Genre:
ISBN:
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"The Greenland Ice Sheet (GrIS) is responding sensitively to climate change and its meltwater has the potential to influence global sea level. Recently, large changes in the GrIS have occurred including increased velocities of outlet glaciers and melt over ~97% of the ice sheet. One means to understand modern and help predict future changes in the GrIS is to examine how it responded to past climate conditions. In this dissertation I provide a longer-term perspective of changes in the GrIS as well as in smaller, independent glaciers near the ice sheet margins (i.e., "local" glaciers). My research documents the past extents of the GrIS in central East and southern West Greenland during the Holocene Epoch (11,600 yrs ago-present) and provides evidence for climate conditions along the ice sheet margin during late glacial time (~17,500-11,600 yrs ago) and the Holocene Epoch. I use geomorphic mapping, surface exposure dating and lake sediment analyses to demonstrate that the GrIS and local glaciers in central East Greenland were receding during the Younger Dryas cold event (~12,900-11,600 yrs ago) and deposited the Milne Land stade moraines at the end of the Younger Dryas. I hypothesize that these ice marginal fluctuations were primarily influenced by air or ocean surface temperatures. I document the Holocene fluctuations of a local glacier that completely disappeared indicating peak warm conditions between ~9.3 and 6.0 cal kyr BP. The formation of this glacier at 2.6 cal kyr BP and its persistence from ~1.9 cal kyr BP-present suggests cold conditions during late Holocene time. I also use geomorphic mapping and surface exposure dating to document the extents of the GrIS in southern West Greenland, near Kangerlussuaq. I show that the Keglen, Ørkendalen and Historical moraines were deposited at 7.3 ka, 6.3 ka, and by ~AD 1950, respectively. These data indicate that the GrIS was as small as or smaller than at present during much of middle to late Holocene time. Finally, I synthesize my results and discuss possible causes of GrIS marginal changes in central East and southern West Greenland including changes in air and ocean temperatures and changes in sea level."

Late Glacial and Holocene History of the Greenland Ice Sheet Margin in Nunatarssuaq, Northwestern Greenland

Late Glacial and Holocene History of the Greenland Ice Sheet Margin in Nunatarssuaq, Northwestern Greenland
Author: Lauren Brett Farnsworth
Publisher:
Total Pages: 136
Release: 2016
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ISBN:
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It is uncertain as to how the Greenland Ice Sheet (GrIS) will respond to future climate changes. One means of assessing the sensitivity of the GrIS to projected climate conditions is to determine its response to past conditions. I reconstructed late glacial and Holocene (~15 ka-present) GrIS extents in the Nunatarssuaq, northwestern Greenland. I applied geomorphic mapping, 10Be surface exposure dating and 14C dating of subfossil plants to determine a chronology of past GrIS extents. I also analyzed sediment cores from a glacially fed lake. 10Be ages of boulders and bedrock exposed during deglaciation from the Last Glacial Maximum (LGM; ~26-19.5 ka) are apparently old due to 10Be inherited from prior periods of exposure. The youngest 10Be age (~15 ka) may also contain inherited 10Be but approximates the time of deglaciation. Subfossil plants transported to the GrIS margin on shear planes date to ~4.6 cal ka BP and indicate a less extensive GrIS during middle Holocene time. Geomorphic mapping documents higher levels of Nordsø, a glacial lake dammed by a more extensive GrIS margin. I constrain the age of this GrIS extent to ~3-2 ka using 14C ages of in situ subfossil plants on nunataks and 10Be ages of boulders on the drift deposited during the advance. A fresh drift occurs ~30-50 m beyond the present GrIS margin. 10Be ages of this fresh drift range from 2.2 to 0.5 ka. I interpret the youngest 10Be age (~0.5 ka) as the time the drift was exposed. 14C ages of in situ subfossil plants indicate that the GrIS was at or behind its present margin at AD ~1662-1897. I compare my record of GrIS extents to other glacial fluctuations and climate records. I find that the GrIS margin in Nunatarssuaq fluctuated at similar times as local ice masses and other GrIS margins. The middle Holocene GrIS recession occurred during relatively warm conditions registered by regional climate records and the late Holocene GrIS advances occurred during cooler conditions. I also document asynchronous GrIS margin fluctuations in Nunatarssuaq. These require further investigation to determine whether they were influenced by climate conditions or ice dynamics.

Reconstructing Ice Sheet and Alpine Glacier Margins During the Early Holocene on Nuussuaq in Central West Greenland

Reconstructing Ice Sheet and Alpine Glacier Margins During the Early Holocene on Nuussuaq in Central West Greenland
Author: Sandra L. Cronauer
Publisher:
Total Pages: 99
Release: 2014
Genre:
ISBN:
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Comparison of past ice sheet margin and alpine glacier reconstructions to paleoclimate records can offer insight into the dominant forcing mechanisms that determine glacial response to changes in climate. Previous research on a major ice stream in central West Greenland reveals that the Greenland Ice Sheet (GrIS) responded to abrupt centennial-scale cold periods at ~9. 3 and ~8. 2 ka. The aim of this thesis is to determine whether or not alpine glaciers and a land-terminating ice sheet margin on the peninsula of Nuussuaq in central West Greenland also responded to abrupt climate changes in the early Holocene. To this end, I reconstructed ice sheet and alpine glacier histories on Nuussuaq using cosmogenic 10Be surface exposure dating (herein 10Be dating) and lake sediment analysis. Neither the ice margin nor alpine glacier chronologies indicate a response to abrupt climate change at 9. 3 ka or 8. 2 ka. I found that the Drygalski Moraines are early Holocene in age, with mean moraine ages of 8. 6 ℗ł 0. 4 ka (n=2), 8. 5 ℗ł 0. 2 ka (n=3), and 7. 6 ℗ł 0. 1 ka (n=2) from outer to inner. The moraine chronology, combined with radiocarbon dated lake sediment stratigraphy from an adjacent proglacial lake, reveal that the ice margin remained within about one kilometer of its present position from ~9. 9 to 5. 4 ka. This evidence for ice sheet stability during the first half of the Holocene, followed by minimum ice extent between ~5. 4 and 0. 6 ka, contrasts with many records of early Holocene warmth during the Holocene maximum of Northern Hemisphere summer insolation. This period of ice margin stability may relate to adjacent ocean temperatures, which did not increase until the middle Holocene. A 10Be chronology of moraines deposited by a nearby alpine glacier reveals glacier stability at 10. 5 ℗ł 0. 3 ka, during the Preboreal period. Moraine deposition at this time is potentially due to increased moisture availability as the GrIS retreated and sea ice declined. The alpine glacier chronology also fits well within an emerging pattern of alpine glacier advance during the Preboreal period on East and West Greenland. The results presented in this thesis suggest that GrIS and alpine glacier margin response to changes in climate is complex, and that detailed chronologies from moraines on Greenland can shed light on the intricate processes that link glaciers and climate.