Holocene Interaction Between Ocean Circulation and the West Greenland Ice Sheet
Author: Kerstin Perner
Publisher:
Published: 2012
Total Pages: 0
ISBN-13:
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Late Quaternary Ice-ocean Interactions in Central West Greenland
Author: David John McCarthy
Publisher:
Published: 2011
Total Pages:
ISBN-13:
DOWNLOAD EBOOKA 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.
Ice Drift, Ocean Circulation and Climate Change
Author: Jens Bischof
Publisher: Springer Science & Business Media
Published: 2000-11
Total Pages: 254
ISBN-13: 9781852336486
DOWNLOAD EBOOKThe issue of global warming and climate change is of continuous concern. Since the 1970s, it bas been shown that the pack-ice around the Arctic Ocean is thinning, the margin of permafrost is moving north and the vegetation in the high northern parts of the world is changing (the 'greening' of the Arctic). But are these changes the result of human activity or simply regular variations of the Earth's climate system? Over thousands of years, a continuous archive of iceberg and sea ice drift bas formed in the deep-sea sediments, revealing the place of the ice's origin and allowing a reconstruction of the surface currents and the climate of the past. However, the drift of floating ice from one place to another is not just a passive record of past ocean circulation. It actively influences and changes the surface ocean circulation, thus having a profound effect on climate change. Ice Drift, Ocean Circulation and Climate Change is the first book to focus on the interactions between ice, the ocean and the atmosphere and to describe how these three components of the climate system influence each other. It makes clear the positive contribution of paleoclimatology and paleoceanography and should be read by anyone concerned with global warming and climate change.
Holocene Ice Sheet Dynamics and Detrital Provenance Shifts Along the West Greenland Margin
Author: Lina Madaj
Publisher:
Published: 2021
Total Pages:
ISBN-13:
DOWNLOAD EBOOKDue 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.
The Marine and Continental Cryosphere in NW Greenland
Author: Eleanor Georgiadis
Publisher:
Published: 2020
Total Pages: 196
ISBN-13:
DOWNLOAD EBOOKNares Strait is one of three channels of the Canadian Arctic Archipelago (CAA) which connect the Arctic Ocean to Baffin Bay. The CAA throughflow is a major component of ocean circulation in western Baffin Bay. Nares Strait borders the CAA to the east, separating Ellesmere Island from Greenland, and is 80% covered in sea ice 11 months of the year. The heavy sea ice cover is constituted of (1) Arctic (multi-year) sea-ice having entered the strait by the north, and (2) locally formed first year sea ice, which consolidates the ice cover. The hydrological history of the area is intimately linked to the formation of land-fast sea ice in the strait, constituting ice arches. The seaice cover in Nares Strait regulates freshwater (liquid and solid) export towards Baffin Bay, and is integral to the formation of an area of open water in northernmost Baffin Bay: The North Water polynya. Nares Strait has been at the heart of major geomorphological changes over the past 10,000 years. Its deglacial and post-glacial history is marked by (1) rapid retreat of the Greenland and Innuitian ice-sheets which coalesced along Nares Strait during the Last Glacial Maximum, (2) post-glacial shoaling associated to isostatic rebound, and (3) variable multi-year and seasonal sea ice conditions. Little is known about the evolution of these three environmental components of the Nares Strait history, and they are poorly constrained in terms of chronology and synchronism with other regional changes. Nares Strait and its eventful Holocene history provide a unique case study of the response of the marine and continental cryosphere to rapid climate change, such as that affecting Arctic regions in modern times. The marine sediment archives that were retrieved during the ANR GreenEdge and ArcticNet (2014 and 2016) cruises of CCGS Amundsen offer a unique opportunity to investigate the Deglacial to Late Holocene history of Nares Strait. Our reconstructions are based on a multi-proxy study of these cores, including sedimentologic (grain size and lithofacies), geochemical (XRF), mineralogical (q-XRD), micropaleontological (planktic and benthic foraminiferal assemblages), and biogeochemical (sea ice biomarkers IP25 and HBI III). Our results include an age for the Deglacial opening of Nares Strait between 9.0 and 8.3 cal. ka BP, with the event likely occurring closer to the later bracket of the timeframe (i.e., ca 8.5-8.3 cal. ka BP). This event established the throughflow from the Arctic Ocean towards northernmost Baffin Bay. Environmental conditions were highly unstable in the Early Holocene, and marine primary productivity was limited. A period of minimum sea-ice cover occurred from ca 8.1 to 7.5 cal. ka BP, during the Holocene Thermal Maximum, when atmospheric temperatures were higher than today in Nares Strait. Sea-ice cover became more stably established as a seasonal feature around 7.5 cal. ka BP and primary productivity related to ice edge blooms increased. Eventually, the duration of the ice arches increased and they were present in spring and into the summer from 5.5 to 3.7 cal. ka BP, which allowed the inception of the North Water polynya. The North Water reached its maximal potential between 4.5 and 3.7 cal. ka BP, when warmer Atlantic-sourced water upwelled in the polynya, providing nutrients for primary productivity. The establishment of a near-perennial ice arch in northern Nares Strait prevented export of multi-year sea ice into Nares Strait and hindered the formation of the southern ice arch, ultimately resulting in a less productive polynya over the past ca 3.0 cal. ka BP.
Holocene Sea-ice and Ice-sheet Variability on the Northeast Greenland Continental Shelf
Author: Nicole Syring
Publisher:
Published: 2020
Total Pages:
ISBN-13:
DOWNLOAD EBOOKSea 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 Reconstruction of the West Greenland Current and the Greenland Ice Sheet Margin Near Disko Bay Using Foraminiferal Assemblages
Author: Mariah E. Walton
Publisher:
Published: 2010
Total Pages: 114
ISBN-13:
DOWNLOAD EBOOKRecent 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.
An Interdisciplinary Approach Towards Understanding Late Pleistocene Ice Sheet Change
Author: Joshua Cuzzone
Publisher:
Published: 2014
Total Pages: 128
ISBN-13:
DOWNLOAD EBOOKThe results presented in this dissertation address a number of questions regarding late Pleistocene and Holocene ice-sheet and climate interactions, spanning disciplines involving paleoclimatology and atmospheric science. These studies use various techniques in geochemistry, climate modeling, and ice-sheet modeling to address ice- sheet response to climate and the attendant interactions between the atmosphere and ice- sheets. An important question in paleoclimatology involves the response of past ice sheets to a warming climate, with the end goal of providing context for understanding the response of future ice sheets to anthropogenic warming. A longstanding question regards the timing and rate of retreat for the Scandinavian Ice Sheet (SIS) during the Holocene. Much work has been done to constrain the retreat of the SIS from the last glacial maximum to the well-defined Younger Dryas moraines, however, little is known regarding the SIS Holocene retreat. Presented is a compilation of 87 10Be surface exposure ages from Sweden and Norway. These ages provide a high-resolution reconstruction of the SIS deglaciation during the Holocene, and allow for close comparison with proxies of temperature and insolation. The results suggest an asymmetric deglaciation of the SIS, with retreat forced by both a warming climate and and ice-sheet dynamics depending on time and location. The record also provides a means for evaluating the SIS contribution to Holocene sea-level rise. Combining this with estimates from the Laurentide Ice Sheet and the Greenland Ice Sheet, our results suggest that ~23 m of residual sea-level rise exists at the start of the Holocene. We suggest an Antarctic source, which has implications for understanding the sensitivity of the Antarctic Ice Sheet to Holocene climate change. Ice-sheets exert a large presence on the overlying atmosphere, with these interactions influencing the general circulation and ultimately the surface mass balance of the ice sheet. Prior work has indicated striking differences in the atmospheric circulation between the LGM and present day. Using a fully coupled climate simulation of the last deglaciation, the atmospheric circulation is studied, with respect to the stationary waves and storm tracks. For this study, we focus on the LIS. Our results show an enhanced stationary wave, forced mechanically by the topography of the LIS along western North America, which provides moisture, driven by enhanced ridging. This mechanism provides a positive feedback, whereby a larger ice sheet drives a more positive wintertime mass balance. Eventually, as the ice sheet melts, this stationary wave weakens, and the moisture flux decreases. Over the eastern LIS, coupled atmosphere and ice-sheet dynamics conspire to weaken the storm track at the LGM. As the ice melts, however, the storm track becomes broader and strengthens. The storm track becomes an efficient means for moisture delivery to the eastern LIS, with this relationship strengthening through the deglaciation. We suggest that enhanced wintertime accumulation from the strengthening storm track may have played a strong role in offsetting summertime ablation along the eastern LIS, and thus may be a reason why the LIS terminated over eastern North America. Another longstanding question in paleoclimatology involves the role of CO2 and insolation on driving the deglaciation of the great Northern hemisphere ice sheets. To investigate this question we one way coupled the 3-dimensional thermomechanical ice- sheet model, Glimmer to climate simulations of the last deglaciation using GENMOM. We first built up a realistic LIS, constrained by the best available reconstructions of the area and volume, by perturbing parameters to obtain the best fit. Once a suitable spun-up LGM LIS was created, we forced the deglaciation of the LIS using climate simulations of the last deglaciation using either varying insolation only, and varying CO2 only. Our results show similar trends in the deglaciation of the LIS relative to simulations of the deglaciation forced with all forcings (CO2 and insolation). Upon further inspection, our results prove that the one way coupling scheme is unable to capture the influence of the separate forcings. Instead, the topography boundary condition used to drive the climate simulations dictates the distribution of heat and moisture, and thus the deglaciation. Our results show that in order to properly simulate the response of the LIS to CO2 and insolation only forcings, an asynchronous coupling scheme or coupled climate-ice-sheet models should be used.
Late Glacial and Holocene Fluctuations of Local Glaciers and the Greenland Ice Sheet, Eastern and Western Greenland
Author: Laura B. Levy
Publisher:
Published: 2014
Total Pages: 408
ISBN-13:
DOWNLOAD EBOOK"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."
Past Interaction of Ocean Circulation and West Antarctic Ice Sheet Dynamics in the Amundsen Sea Sector
Author: Johanna Gille-Petzoldt
Publisher:
Published: 2023
Total Pages: 0
ISBN-13:
DOWNLOAD EBOOKThe West Antarctic Ice Sheet is highly sensitive to ocean forcing and is currently experiencing grounding line retreat and ice shelf thinning. Since the response of the ice sheet to a warming world is unknown, it is important to analyze past warmer-than-present periods, e.g. the Pliocene, for comparison with possible future changes. Two drill sites, Site U1532 and Site U1533 of IODP Expedition 379, were linked to a large network of 2D high-resolution seismic reflection data to analyze changes of the West Antarctic Ice Sheet from the latest Miocene to the Pleistocene. During the Pliocene, between 4.2 to 3.2 Ma, a warm period was recognized with a highly dynamic West Antarctic Ice Sheet, correlating with reduced ocean bottom current activity. This period can be described as an overarching warm period with several advance and retreat phases of the West Antarctic Ice Sheet in the Amundsen Sea Sector.
