Holocene thinning history of David Glacier, Antarctica

<p>The Antarctic Ice Sheet is a significant component of the Earth System, modulating Earth‘s sea level and climate. Present day and projected ice mass losses from Antarctica are of paramount concern to human populations in low-lying communities around the world. Ocean freshening from future ice discharge events also has the potential to destabilise global climate patterns. Over 40 years of satellite observations have tracked changes in ice mass, extent and thickness in Antarctica. However, ice sheets respond on timescales that range from annual to millennial, and a geologic perspective is needed to fully understand ice sheet response on timescales longer than a few decades. This research seeks to provide an improved understanding of Antarcticas future by constraining its past. I focus on one of the largest outlet glaciers in Antarctica, the David Glacier/Drygalski Ice Tongue system which drains the East Antarctic Ice Sheet, dissects the Transantarctic Mountains and discharges into the Ross Sea. I seek to answer two questions; (1) what is the timing and nature of David Glacier thinning since the Last Glacial Maximum approximately 20,000 years ago, and (2) what physical processes were responsible for the observed thinning? I answer these questions by mapping the terrestrial and marine geomorphology along the former margins and seaward extension of David Glacier, and by using surface exposure dating of bedrock and glacial erratics to constrain the timing of glacier thinning. I then use a numerical flowline model to identify the processes that drove glacier thinning and retreat. Surface exposure ages from bedrock and glacial erratics at field sites both upstream and downstream of the modern grounding line reveal that David Glacier thinned for two millennia during the mid-Holocene. Near the coast, this thinning occurred at ∼6.5 kya at a rapid rate of up to 2 m/yr. Upstream from the grounding line, the thinning was more gradual but occurred simultaneously with thinning downstream. The timing of glacial thinning at David Glacier correlates with thinning events at other glaciers in the region and is consistent with offshore marine geological records. To identify the mechanisms responsible for the observed thinning of David Glacier, I conduct numerical model sensitivity experiments along a 1,600 km flowline, extending from the ice sheet interior to the continental shelf edge in the western Ross Sea. Offshore, the glacier flowline follows the Drygalski Trough, where it crosses numerous grounding zone wedges of various sizes. The flowline and prescribed ice shelf width is guided by the orientation and distribution of mega-scale glacial lineations as well as overall sea floor bathymetry. I explore the response of a stable, expanded David Glacier to the effects of increasing sub-ice shelf melt rates, and decreasing lateral buttressing which may have occurred as grounded ice in the Ross Sea migrated southward of the David Glacier. These forcings were also combined to explore potential feedbacks associated with Marine Ice Sheet Instability. This modelling demonstrates that David Glacier likely underwent rapid thinning over a period of ∼500 years as the grounding line retreated to a prominent sill at the mouth of David Fjord. After a period of ∼ 5 ka of stability, a second period of grounding line retreat in the model leads to the glacier reaching its modern configuration. This simulated two-phase grounding line retreat compares well with onshore geologically constrained thinning events at two sites (Mt. Kring and Hughes Bluff), both in terms of timing and rates of past glacier thinning. This retreat pattern can be forced by either increased ice shelf melting or reduced buttressing, but when combined, lower melt rates and less lateral buttressing is required to match onshore geologic constraints. Together, the findings in this thesis provide new data to constrain the past behaviour of a significant portion of the East Antarctic Ice Sheet and critical insights into the mechanisms that control ice sheet thinning and retreat. Incorporation of these constraints and improved understanding of the underlying mechanisms driving glacier thinning and grounding line retreat will ultimately improve continental scale ice sheet models which are used to project the future behaviour of the Antarctic Ice Sheet and its influence on global sea level.</p>

Holocene thinning history of David Glacier, Antarctica

<p>The Antarctic Ice Sheet is a significant component of the Earth System, modulating Earth‘s sea level and climate. Present day and projected ice mass losses from Antarctica are of paramount concern to human populations in low-lying communities around the world. Ocean freshening from future ice discharge events also has the potential to destabilise global climate patterns. Over 40 years of satellite observations have tracked changes in ice mass, extent and thickness in Antarctica. However, ice sheets respond on timescales that range from annual to millennial, and a geologic perspective is needed to fully understand ice sheet response on timescales longer than a few decades. This research seeks to provide an improved understanding of Antarcticas future by constraining its past. I focus on one of the largest outlet glaciers in Antarctica, the David Glacier/Drygalski Ice Tongue system which drains the East Antarctic Ice Sheet, dissects the Transantarctic Mountains and discharges into the Ross Sea. I seek to answer two questions; (1) what is the timing and nature of David Glacier thinning since the Last Glacial Maximum approximately 20,000 years ago, and (2) what physical processes were responsible for the observed thinning? I answer these questions by mapping the terrestrial and marine geomorphology along the former margins and seaward extension of David Glacier, and by using surface exposure dating of bedrock and glacial erratics to constrain the timing of glacier thinning. I then use a numerical flowline model to identify the processes that drove glacier thinning and retreat. Surface exposure ages from bedrock and glacial erratics at field sites both upstream and downstream of the modern grounding line reveal that David Glacier thinned for two millennia during the mid-Holocene. Near the coast, this thinning occurred at ∼6.5 kya at a rapid rate of up to 2 m/yr. Upstream from the grounding line, the thinning was more gradual but occurred simultaneously with thinning downstream. The timing of glacial thinning at David Glacier correlates with thinning events at other glaciers in the region and is consistent with offshore marine geological records. To identify the mechanisms responsible for the observed thinning of David Glacier, I conduct numerical model sensitivity experiments along a 1,600 km flowline, extending from the ice sheet interior to the continental shelf edge in the western Ross Sea. Offshore, the glacier flowline follows the Drygalski Trough, where it crosses numerous grounding zone wedges of various sizes. The flowline and prescribed ice shelf width is guided by the orientation and distribution of mega-scale glacial lineations as well as overall sea floor bathymetry. I explore the response of a stable, expanded David Glacier to the effects of increasing sub-ice shelf melt rates, and decreasing lateral buttressing which may have occurred as grounded ice in the Ross Sea migrated southward of the David Glacier. These forcings were also combined to explore potential feedbacks associated with Marine Ice Sheet Instability. This modelling demonstrates that David Glacier likely underwent rapid thinning over a period of ∼500 years as the grounding line retreated to a prominent sill at the mouth of David Fjord. After a period of ∼ 5 ka of stability, a second period of grounding line retreat in the model leads to the glacier reaching its modern configuration. This simulated two-phase grounding line retreat compares well with onshore geologically constrained thinning events at two sites (Mt. Kring and Hughes Bluff), both in terms of timing and rates of past glacier thinning. This retreat pattern can be forced by either increased ice shelf melting or reduced buttressing, but when combined, lower melt rates and less lateral buttressing is required to match onshore geologic constraints. Together, the findings in this thesis provide new data to constrain the past behaviour of a significant portion of the East Antarctic Ice Sheet and critical insights into the mechanisms that control ice sheet thinning and retreat. Incorporation of these constraints and improved understanding of the underlying mechanisms driving glacier thinning and grounding line retreat will ultimately improve continental scale ice sheet models which are used to project the future behaviour of the Antarctic Ice Sheet and its influence on global sea level.</p>

East Antarctic Ice Sheet and Southern Ocean Response to Orbital Forcing from Late Miocene to Early Pliocene, Wilkes Land, East Antarctica

<p>Geological and ice sheet models indicate that marine-based sectors of the East Antarctic Ice Sheet (EAIS) were unstable during periods of moderate climatic warmth in the past. While geological records from the Middle to Late Pliocene indicate a dynamic ice sheet, records of ice sheet variability from the comparatively warmer Late Miocene to Early Pliocene are sparse, and there are few direct records of Antarctic ice sheet variability during this time period. Sediment recovered in Integrated Ocean Drilling Program U1361 drill core from the Wilkes Land margin provides a distal but continuous glacially-influenced record of the behaviour of Antarctic Ice Sheets. This thesis presents marine sedimentological and x-ray fluorescence geochemical datasets in order to assess changes in the dynamic response of the EAIS and Southern Ocean productivity in the Wilkes Land sector during Late Miocene and Early Pliocene to climatic warming and orbital forcing between 6.2 and 4.4 Ma. Two primary lithofacies are identified which can be directly related to glacial–interglacial cycles; enhanced sedimentation during glacials is represented by low-density turbidity flows that occurred in unison with low marine productivity and reduced iceberg rafted debris. Interglacial sediments contain diatomaceous muds with short-lived, large fluxes of iceberg rafted debris preceding a more prolonged phase of enhanced marine productivity. Interglacial sediments coincide with a more mafic source of terrigenous sediment, interfered to be associated with an inland retreat of the ice margin resulting in erosion of lithologies that are currently located beneath the grounded EAIS. Poleward invigoration of the Antarctic Circumpolar Current during glacial–interglacial transitions is proposed to have intensified upwelling, enhancing nutrient availability for marine productivity, and increasing oceanic heat flux at the ice margin acting to erode marine ice sheet grounding lines and triggering retreat. Spectral analysis of the datasets indicated orbital frequencies are present in the iceberg rafted debris mass accumulation rates at all three Milankovitch frequencies, with a dominant 100 kyr eccentricity driven ice discharge. Prolonged intervals of marine productivity correlate to 100 kyr cyclicity occurring at peaks in obliquity. The response of both ice sheet and biological systems to 100 kyr cyclicity may indicate eccentricity-modulated sea ice extent controls the influx of warm water onto the continental shelf.</p>

East Antarctic Ice Sheet and Southern Ocean Response to Orbital Forcing from Late Miocene to Early Pliocene, Wilkes Land, East Antarctica

<p>Geological and ice sheet models indicate that marine-based sectors of the East Antarctic Ice Sheet (EAIS) were unstable during periods of moderate climatic warmth in the past. While geological records from the Middle to Late Pliocene indicate a dynamic ice sheet, records of ice sheet variability from the comparatively warmer Late Miocene to Early Pliocene are sparse, and there are few direct records of Antarctic ice sheet variability during this time period. Sediment recovered in Integrated Ocean Drilling Program U1361 drill core from the Wilkes Land margin provides a distal but continuous glacially-influenced record of the behaviour of Antarctic Ice Sheets. This thesis presents marine sedimentological and x-ray fluorescence geochemical datasets in order to assess changes in the dynamic response of the EAIS and Southern Ocean productivity in the Wilkes Land sector during Late Miocene and Early Pliocene to climatic warming and orbital forcing between 6.2 and 4.4 Ma. Two primary lithofacies are identified which can be directly related to glacial–interglacial cycles; enhanced sedimentation during glacials is represented by low-density turbidity flows that occurred in unison with low marine productivity and reduced iceberg rafted debris. Interglacial sediments contain diatomaceous muds with short-lived, large fluxes of iceberg rafted debris preceding a more prolonged phase of enhanced marine productivity. Interglacial sediments coincide with a more mafic source of terrigenous sediment, interfered to be associated with an inland retreat of the ice margin resulting in erosion of lithologies that are currently located beneath the grounded EAIS. Poleward invigoration of the Antarctic Circumpolar Current during glacial–interglacial transitions is proposed to have intensified upwelling, enhancing nutrient availability for marine productivity, and increasing oceanic heat flux at the ice margin acting to erode marine ice sheet grounding lines and triggering retreat. Spectral analysis of the datasets indicated orbital frequencies are present in the iceberg rafted debris mass accumulation rates at all three Milankovitch frequencies, with a dominant 100 kyr eccentricity driven ice discharge. Prolonged intervals of marine productivity correlate to 100 kyr cyclicity occurring at peaks in obliquity. The response of both ice sheet and biological systems to 100 kyr cyclicity may indicate eccentricity-modulated sea ice extent controls the influx of warm water onto the continental shelf.</p>

Sequence Stratigraphy, Chronostratigraphy and Zircon Geochronology of the CIROS-1 Drill Core, Ross Sea, Antarctica: Implications for Cenozoic Glacial and Tectonic Evolution

<p>Antarctica plays a central role in the global climate system. Understanding the continent's past climate interactions is key to predicting its future response to, and influence on, global climate change. In recent decades, sediment cores drilled on the Antarctic continental margin have provided direct evidence of past climatic and tectonic events. Drilled in 1986 from sea ice in western McMurdo Sound, the pioneering 702 m-long CIROS-1 core extended back to the Late Eocene and provided some of the first evidence of the antiquity and history of the Antarctic ice sheets. The CIROS-1 drill core recovered a depositional history of the western margin of the Victoria Land Basin adjacent to the Trans-Antarctic Mountains. It was located directly offshore from where the Ferrar Glacier, which drains the East Antarctic Ice Sheet, discharges into the Ross Sea. Consequently CIROS-1 contains a record of both the glacial and tectonic Cenozoic evolution of the Antarctic margin. This thesis provides a timely re-evaluation of the CIROS-1 core with new analysis techniques that enable further insights into the glacial and tectonic history of the western Ross Sea region, and includes three key objectives: (1) Re-examine CIROS-1 sedimentology and stratigraphy and provide a new facies and sequence stratigraphic analysis using modern methods developed from recent drilling projects (e.g. CRP, ANDRILL). (2) Develop a new integrated chronostratigraphic model through an assessment and compilation of previous studies, which provides a context for the interpretation of detrital zircon data, climate and tectonic history. (3) Undertake a detailed examination of the provenance of CIROS-1 sediments using cutting edge in situ analysis techniques of detrital zircons (U-Pb and trace element analysis using LA-ICP-MS). Glaciomarine sequence stratigraphic analysis identifies 14 unconformity-bound sequences occurring in two distinctive stratigraphic motifs. The four sequences located beneath the 342 mbsf unconformity contain relatively complete vertical facies succession. They were deposited in shallow marine, fluvio-deltaic conditions with distal glaciers terminating on land, and possibly calving into the ocean in adjacent valleys as evidenced by occasional ice-rafted debris. The ten sequences located above ~342 mbsf have a fundamentally different architecture. They are incomplete (top-truncated), contain subglacial and ice proximal facies grading upsequence into distal glaciomarine and shelf conditions. Top truncation of these sequences represents overriding of the CIROS-1 site by the paleo-Ferrar Glacier during glacial phases. A revised age model for CIROS-1 is presented that utilises new calibrations for Antarctic diatom zones and compiles three previously published age models for different sections of the core (Roberts et al., 2003; Wilson et al., 1998; Hannah et al., 1997). The new age model allows correlation of Late Oligocene cycles with coeval cycles in CRP-2/2A, 80 km to the north. A fundamental orbital control on the dynamics of these East Antarctic Ice Sheet outlet glaciers is evident from this comparison. Both glacier systems respond in-phase to longer-period orbital components (e.g. eccentricity 100 kyr and 400 kyr), but differ in their sensitivity to precession (20 kyr). It appears that during the Late Oligocene the Ferrar catchment responded to 20 kyr precession cycles, whilst the larger MacKay Glacier, which is more directly connected to the East Antarctic Ice Sheet, responded to longer duration 125 kyr (eccentricity) forcing. CIROS-1 zircons group into four distinct geochemical suites. Zircons formed in felsic igneous environments dominate the CIROS-1 population, with 89 % of zircons analysed showing geochemical characteristics inherent to granitic/rhyolitic zircons. Approximately 7 % of CIROS-1 zircons have a highly trace element enriched igneous provenance and were most probably sourced from enriched enclaves in granitic/rhyolitic units or from pegmatites. Approximately 3 % of CIROS-1 zircons show a metamorphic geochemical signature, and ~1 % formed in trace element depleted igneous environments. The zircons were sourced from the local basement (Koettlitz, Granite Harbour Groups), the Beacon Supergroup, and potentially, lithologies of the East Antarctic Craton located under the ice, or components of the Trans-Antarctic Mountains located under the current baseline of geologic exposure. Large-scale, systematic temporal trends in zircon characteristics have been divided into three distinct climatic periods: Zone 1 (702-366 mbsf, Late Eocene), Zone 2 (366-250 mbsf, Late Oligocene) and Zone 3 (< 250 mbsf, Late Oligocene and Early Miocene). Zircons deposited during these periods show unique properties. During Zone 1, Antarctica experienced a relatively warm temperate climate and alpine style glaciers flowed eastwards through the Trans-Antarctic Mountains. Zircons in this zone contain a subtle record of unroofing of geochemically zoned Granite Harbour and Koettlitz units located in the Ferrar Valley. During Zone 2 deposition, glaciers flowed though the Trans-Antarctic Mountains draining a large and ephemeral EAIS, which oscillated on orbital time scales. Zircons in this interval show variable properties, high numbers and were most probably deposited as the paleo-Ferrar Glacier deeply incised the Ferrar Fiord. In contrast, Zone 3 is characterised by a flux of McMurdo Volcanic Complex derived sediments, together with systematic changes in zircon characteristics. These patterns indicate a Late Oligocene shift in ice flow to the site (above ~250 mbsf). Due to a cooling that culminated in the Mi-1 glaciation, ice flow to the site changed from an eastward to a northward flow, in response to an increased ice volume in the Ross embayment.</p>

Sequence Stratigraphy, Chronostratigraphy and Zircon Geochronology of the CIROS-1 Drill Core, Ross Sea, Antarctica: Implications for Cenozoic Glacial and Tectonic Evolution

<p>Antarctica plays a central role in the global climate system. Understanding the continent's past climate interactions is key to predicting its future response to, and influence on, global climate change. In recent decades, sediment cores drilled on the Antarctic continental margin have provided direct evidence of past climatic and tectonic events. Drilled in 1986 from sea ice in western McMurdo Sound, the pioneering 702 m-long CIROS-1 core extended back to the Late Eocene and provided some of the first evidence of the antiquity and history of the Antarctic ice sheets. The CIROS-1 drill core recovered a depositional history of the western margin of the Victoria Land Basin adjacent to the Trans-Antarctic Mountains. It was located directly offshore from where the Ferrar Glacier, which drains the East Antarctic Ice Sheet, discharges into the Ross Sea. Consequently CIROS-1 contains a record of both the glacial and tectonic Cenozoic evolution of the Antarctic margin. This thesis provides a timely re-evaluation of the CIROS-1 core with new analysis techniques that enable further insights into the glacial and tectonic history of the western Ross Sea region, and includes three key objectives: (1) Re-examine CIROS-1 sedimentology and stratigraphy and provide a new facies and sequence stratigraphic analysis using modern methods developed from recent drilling projects (e.g. CRP, ANDRILL). (2) Develop a new integrated chronostratigraphic model through an assessment and compilation of previous studies, which provides a context for the interpretation of detrital zircon data, climate and tectonic history. (3) Undertake a detailed examination of the provenance of CIROS-1 sediments using cutting edge in situ analysis techniques of detrital zircons (U-Pb and trace element analysis using LA-ICP-MS). Glaciomarine sequence stratigraphic analysis identifies 14 unconformity-bound sequences occurring in two distinctive stratigraphic motifs. The four sequences located beneath the 342 mbsf unconformity contain relatively complete vertical facies succession. They were deposited in shallow marine, fluvio-deltaic conditions with distal glaciers terminating on land, and possibly calving into the ocean in adjacent valleys as evidenced by occasional ice-rafted debris. The ten sequences located above ~342 mbsf have a fundamentally different architecture. They are incomplete (top-truncated), contain subglacial and ice proximal facies grading upsequence into distal glaciomarine and shelf conditions. Top truncation of these sequences represents overriding of the CIROS-1 site by the paleo-Ferrar Glacier during glacial phases. A revised age model for CIROS-1 is presented that utilises new calibrations for Antarctic diatom zones and compiles three previously published age models for different sections of the core (Roberts et al., 2003; Wilson et al., 1998; Hannah et al., 1997). The new age model allows correlation of Late Oligocene cycles with coeval cycles in CRP-2/2A, 80 km to the north. A fundamental orbital control on the dynamics of these East Antarctic Ice Sheet outlet glaciers is evident from this comparison. Both glacier systems respond in-phase to longer-period orbital components (e.g. eccentricity 100 kyr and 400 kyr), but differ in their sensitivity to precession (20 kyr). It appears that during the Late Oligocene the Ferrar catchment responded to 20 kyr precession cycles, whilst the larger MacKay Glacier, which is more directly connected to the East Antarctic Ice Sheet, responded to longer duration 125 kyr (eccentricity) forcing. CIROS-1 zircons group into four distinct geochemical suites. Zircons formed in felsic igneous environments dominate the CIROS-1 population, with 89 % of zircons analysed showing geochemical characteristics inherent to granitic/rhyolitic zircons. Approximately 7 % of CIROS-1 zircons have a highly trace element enriched igneous provenance and were most probably sourced from enriched enclaves in granitic/rhyolitic units or from pegmatites. Approximately 3 % of CIROS-1 zircons show a metamorphic geochemical signature, and ~1 % formed in trace element depleted igneous environments. The zircons were sourced from the local basement (Koettlitz, Granite Harbour Groups), the Beacon Supergroup, and potentially, lithologies of the East Antarctic Craton located under the ice, or components of the Trans-Antarctic Mountains located under the current baseline of geologic exposure. Large-scale, systematic temporal trends in zircon characteristics have been divided into three distinct climatic periods: Zone 1 (702-366 mbsf, Late Eocene), Zone 2 (366-250 mbsf, Late Oligocene) and Zone 3 (< 250 mbsf, Late Oligocene and Early Miocene). Zircons deposited during these periods show unique properties. During Zone 1, Antarctica experienced a relatively warm temperate climate and alpine style glaciers flowed eastwards through the Trans-Antarctic Mountains. Zircons in this zone contain a subtle record of unroofing of geochemically zoned Granite Harbour and Koettlitz units located in the Ferrar Valley. During Zone 2 deposition, glaciers flowed though the Trans-Antarctic Mountains draining a large and ephemeral EAIS, which oscillated on orbital time scales. Zircons in this interval show variable properties, high numbers and were most probably deposited as the paleo-Ferrar Glacier deeply incised the Ferrar Fiord. In contrast, Zone 3 is characterised by a flux of McMurdo Volcanic Complex derived sediments, together with systematic changes in zircon characteristics. These patterns indicate a Late Oligocene shift in ice flow to the site (above ~250 mbsf). Due to a cooling that culminated in the Mi-1 glaciation, ice flow to the site changed from an eastward to a northward flow, in response to an increased ice volume in the Ross embayment.</p>

Calibrating Antarctic ice sheet mass loss due to millennial-scale ocean thermal forcing

Throughout the Late Pleistocene, millennial-scale cycles in the rate of poleward heat transport resulted in repeated heating and cooling of the Southern Ocean1. Ice sheet models2 suggest that this variation in Southern Ocean temperature can force fluctuations in the mass of the Antarctic ice sheet that transiently impact sea level by up to 15 meters. However, current geologic evidence for Antarctic ice response to this ocean thermal forcing is unable to calibrate these models, leaving large uncertainty in how Antarctica contributes to sea level on millennial timescales. Here we present a >100kyr archive of East Antarctic Ice Sheet response to Late Pleistocene millennial-scale climate cycles recorded by transitions from opal to calcite in subglacial precipitates. 234U-230Th dates for two precipitates define a time series for 32 mineralogic transitions that match Antarctic climate fluctuations, with precipitation of opal during cold periods and calcite during warm periods. Geochemical evidence indicates opal precipitation via cryoconcentration of silica in subglacial water and calcite precipitation from the admixture of meltwater flushed from the ice sheet interior. These freeze-flush cycles represent changes in subglacial hydrologic-connectivity driven by ice sheet thickness response to Southern Ocean temperature oscillations around the Ross Embayment. Changes in Ross Embayment ice mass require high ocean-ice heat exchange2, and would occur only after retreat of the West Antarctic Ice Sheet3 and large portions of the East Antarctic Ice sheet margin4. These results point to high Antarctic ice sheet sensitivity to millennial-scale ocean thermal forcing throughout the Late Pleistocene, and when combined with modeling results2, predict that an Antarctic ice volume of at least 2–5 meters sea level equivalent is vulnerable to millennial-scale climate forcing.

Unveiling lithosphere heterogeneity beneath the East Antarctic Ice Sheet in the Wilkes Subglacial Basin

&lt;p&gt;The Wilkes Subglacial Basin in East Antarctica hosts one of the largest marine-based and hence potentially more unstable sectors of the East Antarctic Ice Sheet (EAIS). Predicting the past, present and future behaviour of this key sector of the EAIS requires that we also improve our understanding of the lithospheric cradle on which it flows. This is particularly important in order to quantify geothermal heat flux heterogeneity in the region. &amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;The WSB stretches for almost 1600 km from the Southern Ocean towards South Pole. Like many intracratonic basins, it is a long-lived geological feature, which originated and evolved in different tectonic settings. A wide basin formed in the WSB in a distal back arc basin setting, likely in response to a retreating West Antarctic Paleo-Pacific active margin from Permo-Triassic times. Jurassic extension then led to the emplacement of part of a huge flood basalt province that extends from South Africa to Australia.&amp;#160; The region was then affected by relatively minor upper crustal Mesozoic to Cenozoic(?) extension and transtension, producing narrow graben-like features that were glacially overdeepened, and presently steer enhanced glacial flow of the Matusevich, Cook and Ninnis glaciers.&lt;/p&gt;&lt;p&gt;Here we present the results of our enhanced geophysical imaging and modelling in the WSB region performed within the 4D Antarctica project of ESA, which aims to help quantify the spatial variability in subglacial Antarctic geothermal heat flux (GHF), one of the least well constrained parameters of the entire continent.&lt;/p&gt;&lt;p&gt;We exploit a combination of airborne radar and aeromagnetic data compilations and crustal and lithosphere thickness estimates from both satellite and airborne gravity and independent passive seismic constraints to develop new geophysical models for the region. To help constrain the starting models, including depth to basement beneath the Permian to Jurassic cover rocks, we applied a variety of depth to magnetic and gravity source estimation approaches from both line and gridded datasets. Given the huge differences between recent satellite gravity estimates of crustal thickness (Pappa et al., 2019, JGR) and sparse seismological constraints, we examine different scenarios for isostatic compensation of Rock Equivalent Topography and intracrustal loads, as a function of variable effective elastic thickness (Te) across the WSB and its flanks. &amp;#160;&lt;/p&gt;&lt;p&gt;Our models reveal a major lithospheric-scale boundary along the northeastern margin of the WSB, separating the Ross Orogen from a cryptic and composite Precambrian Wilkes Terrane. At the onset of enhanced flow for the central Cook ice stream, we image a Precambrian basement high with a felsic bulk composition. We suggest based on the similarity in potential field signatures that it represents late Paleoproterozoic to Mesoproterozoic igneous basement as exposed in South Australia, where it also associated with high GHF (80-120 mW/m&lt;sup&gt;2&lt;/sup&gt;), primarily caused by anomalously radiogenic granitoids.&lt;/p&gt;&lt;p&gt;We hypothesise that the differences in basement depth and metasediment/sediment thickness, coupled with differences in intracrustal heat production give rise to significantly greater heterogeneity in GHF beneath different sectors of the WSB than previously recognised. To help quantify such heterogeneity we develop a suite of new probabilistic thermal models for the study region.&lt;/p&gt;

The unique behavior of stable water isotopes profiles during interglacial periods at Talos Dome, Antarctica

&lt;p&gt;The growth and decay of marine ice sheets act as important controls on regional and global climate, in particular, the behavior of the ice sheets is a key uncertainty in predicting sea-level rise during and beyond this century. The East Antarctic Ice Sheet (EAIS), which contains deep subglacial basins with reverse-sloping, is considered to be susceptible to ice loss caused by marine ice sheet instability. Sediment core offshore Wilkes Subglacial Basin reveals oscillations in the provenance of detrital sediment that have been interpreted to reflect an erosion of Wilkes Basin during interglacial periods MIS 5, MIS 7, and MIS 9 greater than Holocene period (Wilson et al., 2018). The aim of our study is to investigate past climate and environmental changes in the coastal area of the East Antarctic Ice Sheet during MIS 7.5 and 9.3 with the help of a new high-resolution water isotopes record of the TALDICE ice core.&lt;/p&gt;&lt;p&gt;Here we present new &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;D high resolution (5 cm) records covering the oldest portion of the TALDICE ice core. MIS 7.5 and 9.3 isotopic signal reveals a unique feature, already observed for MIS 5.5, that has not been spotted in other Antarctic ice cores (Masson-Delmotte et al., 2011). Interglacial periods at TALDICE are characterized by a first peak, observed in correspondence to the culmination of the deglaciation event as for all Antarctic cores, followed by a less pronounced isotopic peak (for MIS 5.5 and 9.3) or a plateau (for MIS 7.5) prior to the glacial inception. Several factors might drive this peculiar behavior of the water stable isotopes record, as an increase in temperatures due to a drop in surface elevation or changes in moisture sources.&lt;/p&gt;&lt;p&gt;The new &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;D high-resolution records for the TALDICE ice core reveal a unique pattern that characterizes interglacial periods at Talos Dome. Taking into account the coastal position of the core and its vicinity to the Wilkes Subglacial Basin we intend to investigate the possible decrease in surface elevation, through the application of the GRISLI ice sheet model (Quiquet et al., 2018), and changes in moisture sources, traceable from the d-excess record.&lt;/p&gt;