Lambert Glacier Amery Ice Shelf System Research Articles

Rapid ice sheet response to deglacial and Holocene paleoenvironmental changes in eastern Prydz Bay, East Antarctica

Prydz Bay lies at the terminus of one of East Antarctica's largest glacial systems and is a key region for understanding the response of the ice sheet to past and future environmental changes. In this study, we explore the dynamics and paleo-geometry of the ice sheet in eastern Prydz Bay, using a combination of bathymetric features on the seafloor to delineate past flow patterns, and cosmogenic nuclide dating of glacial deposits on land to constrain ice sheet terminus chronologies. Large streamlined bedforms on the sea floor record the existence of a primary ice stream in Svenner Channel, collecting ice from multiple tributary ice streams and discharging into the main trunk stream of the Lambert Glacier-Amery Ice Shelf system in Prydz Channel. The location and orientation of the north-eastern tributary to this ice stream also provide evidence for a substantial independent ice dome on the outer shelf at Four Ladies Bank. Exposure of ice-free areas at outer Rauer Group and Vestfold Hills indicates that grounding line retreat across eastern Prydz Bay was largely complete by ∼14 ka BP, and the ice margin had retreated to within ∼1 km of its present position by ∼10 ka BP. Onshore moraines record periods of ice margin retreat during the middle (∼6 ka BP) and very late (∼0.5 ka BP) Holocene coinciding with local warm periods. Subsidence recorded in modern Global Navigation Satellite System (GNSS) observations suggests the regional ice sheet was smaller than at present in the period between the middle and very late Holocene advances. The unusually dynamic ice sheet behaviour in this area is attributed to the smooth, reverse-slope bed characteristics of eastern Prydz Bay, which enabled rapid retreat of the ice sheet margin several hundred kilometres during deglacial events.

Dynamic response of East Antarctic ice sheet to Late Pleistocene glacial–interglacial climatic forcing

Knowledge regarding the response of the East Antarctic Ice Sheet to glacial–interglacial climatic cycles in the late Pleistocene is critical to understanding the global climate system and projections of future sea level rise. Here, we observed notable glacial–interglacial cyclicity in magnetic properties, bulk detrital Sr–Nd isotopes, and Fe/Ti ratios over the previous 530 kyr in three well-dated gravity cores from the continental rise offshore of Prydz Bay (East Antarctica). Our results show that Antarctic continental sources with more Ti-rich magnetite, less radiogenic epsilon neodymium (εNd), and higher Fe/Ti ratios were predominant during glacials in comparison with interglacials. Specifically, the εNd amplitude through MIS 11–5 differs from that in the remainder of the records, which is also expressed in the magnetic coercivity cycles with subdued patterns. Following source identification on the basis of the detrital Sr–Nd distribution, we recognize two main (rock type) sources and infer two types of ice drainage flow pattern (“flank” and “channelized”), which follow different pathways in the Lambert Glacier–Amery Ice Shelf system (LG-AISS). The first follows an eastern path connecting the Ingrid Christensen Coast (flank), while the second follows a central channel via the LG-AISS (channelized) during MIS 11–5. Regular dynamics on glacial–interglacial timescales, manifested by changes in magnetic coercivity, are closely related to the modeled Antarctic ice volume and ice sheet movement, in which the second channelized pathway during MIS 11–5 corresponds to a 340-kyr-long episode with contiguous warmer-than-present Antarctic interglacials (MIS 11, 9, 7, and 5). Our records thus provide the clearest evidence so far of variable patterns of ice sheet dynamics during the late Pleistocene in the Prydz Bay sector of East Antarctica, which coincided with similar variation of ice drainage during the late Miocene–early Pliocene at around 1.13 Ma (ODP188). Similar ice drainage changes in these two periods imply that major ice flow reconfiguration can be triggered repeatedly by abrupt changes from a stable warm period to a cold one. The presented data not only reveal glacial–interglacial cyclicity in ice sheet advance and retreat in the meridional direction, but also implicate latitudinal adjustment (lateral) within a thin elongated drainage basin of the LG-AISS.

Everything you always wanted to ask about the Lapa do Picareiro Aurignacian and should not be afraid to know: A reply to ‘The early Aurignacian at Lapa do Picareiro really is that old’

Knowledge regarding the response of the East Antarctic Ice Sheet to glacial–interglacial climatic cycles in the late Pleistocene is critical to understanding the global climate system and projections of future sea level rise. Here, we observed notable glacial–interglacial cyclicity in magnetic properties, bulk detrital Sr–Nd isotopes, and Fe/Ti ratios over the previous 530 kyr in three well-dated gravity cores from the continental rise offshore of Prydz Bay (East Antarctica). Our results show that Antarctic continental sources with more Ti-rich magnetite, less radiogenic epsilon neodymium (εNd), and higher Fe/Ti ratios were predominant during glacials in comparison with interglacials. Specifically, the εNd amplitude through MIS 11–5 differs from that in the remainder of the records, which is also expressed in the magnetic coercivity cycles with subdued patterns. Following source identification on the basis of the detrital Sr–Nd distribution, we recognize two main (rock type) sources and infer two types of ice drainage flow pattern (“flank” and “channelized”), which follow different pathways in the Lambert Glacier–Amery Ice Shelf system (LG-AISS). The first follows an eastern path connecting the Ingrid Christensen Coast (flank), while the second follows a central channel via the LG-AISS (channelized) during MIS 11–5. Regular dynamics on glacial–interglacial timescales, manifested by changes in magnetic coercivity, are closely related to the modeled Antarctic ice volume and ice sheet movement, in which the second channelized pathway during MIS 11–5 corresponds to a 340-kyr-long episode with contiguous warmer-than-present Antarctic interglacials (MIS 11, 9, 7, and 5). Our records thus provide the clearest evidence so far of variable patterns of ice sheet dynamics during the late Pleistocene in the Prydz Bay sector of East Antarctica, which coincided with similar variation of ice drainage during the late Miocene–early Pliocene at around 1.13 Ma (ODP188). Similar ice drainage changes in these two periods imply that major ice flow reconfiguration can be triggered repeatedly by abrupt changes from a stable warm period to a cold one. The presented data not only reveal glacial–interglacial cyclicity in ice sheet advance and retreat in the meridional direction, but also implicate latitudinal adjustment (lateral) within a thin elongated drainage basin of the LG-AISS.

Late Quaternary dynamics of the Lambert Glacier-Amery Ice Shelf system, East Antarctica

The Lambert Glacier-Amery Ice Shelf system (LGAISS) is the largest outlet glacier system in East Antarctica but its response to past climate variability is poorly constrained. In this study, we explore its dynamics over the last ∼520 thousand years using new high-resolution sedimentary records retrieved off Prydz Bay. Episodic occurrences of iceberg rafted debris indicate a dynamic ice sheet throughout this interval, while changes in clay mineral compositions provide detailed evidence on the waxing and waning of the LGAISS. Our data indicate that advance and retreat of the LGAISS was sensitive to oceanic forcing, but also responded to local summer insolation when insolation peaks combined with interglacial sea level high stands. Subglacial bed topography may have played an additional role in modulating the LGAISS behaviour, which could explain sectoral differences in the response of the East Antarctic Ice Sheet to climate change. Overall, our records indicate that the LGAISS advanced more extensively during previous late Quaternary glacial periods than during Marine Isotope Stages 2 and 4. Furthermore, the LGAISS retreated more significantly than present during Marine Isotope Stage 13, and only moderately during Marine Isotope Stage 7, which suggests that the duration of warm climatic states could be a key factor affecting the dynamics of the East Antarctic Ice Sheet.

A comparative study of changes in the Lambert Glacier/Amery Ice Shelf system, East Antarctica, during 2004–2008 using gravity and surface elevation observations

ABSTRACTWe present results of a regional comparative study of surface mass changes from 2004 to 2008 based on Gravity Recovery and Climate Experiment (GRACE), The Ice, Cloud and Land Elevation Satellite (ICESat) and CHINARE observations over the Lambert Glacier/Amery Ice Shelf system (LAS). Estimation of the ICESat mass change rates benefitted from the density measurements along the CHINARE traverse and a spatial density adjustment method for reducing the effect of spatial density variations. In the high-elevation inland region, a positive trend was estimated from both ICESat and GRACE data, which is in line with the CHINARE accumulation measurements. In the coastal region, there were areas with high level accumulations in both ICESat and GRACE trend maps. In many high flow-speed glacier areas, negative mass change rates may be caused by dynamic ice flow discharges that have surpassed the snow accumulation. Overall, the mass change rate estimate in the LAS of 2004–2008 from the GRACE, ICESat and CHINARE data is 5.41 ± 4.59 Gt a−1, indicating a balanced to slightly positive mass trend. Along with other published results, this suggests that a longer-term positive mass trend in the LAS may have slowed in recent years.

Mega-scale glacial lineations and grounding-zone wedges in Prydz Channel, East Antarctica

The Prydz Bay continental shelf was sculpted by the Lambert Glacier–Amery Ice Shelf system, a large outlet glacier that drains 16% of the East Antarctic Ice Sheet (Allison 1979; Fig. 1a). Prydz Channel (71–73° E; Fig. 1b) is a NW-trending cross-shelf trough (500–700 m deep) in western Prydz Bay that formed in the Pliocene, when the Lambert-Amery system first developed a fast-flowing ice stream (Fig. 1b; Cooper & O'Brien 2004). In Prydz Channel mega-scale glacial lineations (MSGLs) delineate the direction and orientation of past ice flow, and large grounding-zone wedges (GZWs; Batchelor & Dowdeswell 2015) in the inner channel mark the limit of the Last Glacial Maximum (LGM) ice advance about 250 km from the shelf edge (Fig. 1c, d, e). Fig. 1. Multibeam swath bathymetry and seismic-reflection profile of Prydz Channel, East Antarctica. ( a ) Location of study area (red box; map from IBCSO v. 1.0). ( b ) General bathymetry of Prydz Channel, delineated by the 500 m contour, and other relevant regional features. ( c ) Multibeam swath bathymetry of mega-scale glacial lineations (MSGLs) in Prydz Channel and grounding-zone …

Modelling the response of the Lambert Glacier–Amery Ice Shelf system, East Antarctica, to uncertain climate forcing over the 21st and 22nd centuries

Abstract. The interaction between the climate system and the large polar ice sheet regions is a key process in global environmental change. We carried out dynamic ice simulations of one of the largest drainage systems in East Antarctica: the Lambert Glacier–Amery Ice Shelf system, with an adaptive mesh ice sheet model. The ice sheet model is driven by surface accumulation and basal melt rates computed by the FESOM (Finite-Element Sea-Ice Ocean Model) ocean model and the RACMO2 (Regional Atmospheric Climate Model) and LMDZ4 (Laboratoire de Météorologie Dynamique Zoom) atmosphere models. The change of ice thickness and velocity in the ice shelf is mainly influenced by the basal melt distribution, but, although the ice shelf thins in most of the simulations, there is little grounding line retreat. We find that the Lambert Glacier grounding line can retreat as much as 40 km if there is sufficient thinning of the ice shelf south of Clemence Massif, but the ocean model does not provide sufficiently high melt rates in that region. Overall, the increased accumulation computed by the atmosphere models outweighs ice stream acceleration so that the net contribution to sea level rise is negative.

Ice thickness over the southern limit of the Amery Ice Shelf, East Antarctica, and reassessment of the mass balance of the central portion of the Lambert Glacier-Amery Ice Shelf system

AbstractWe combine radio-echo sounding ice thickness data from the BEDMAP Project database and the PCMEGA (Prince Charles Mountains Expedition of Germany and Australia) dataset to generate a new ice thickness grid for the southern limit region of the Amery Ice Shelf, East Antarctica. We then reassess the mass balance of the central portion of the Lambert-Amery system, incorporating flow information derived from synthetic aperture radar interferometry (InSAR) and a modeled surface mass-balance dataset based on regional atmospheric modeling. Our analysis reveals that Mellor and Fisher Glaciers are approximately in balance to the level of our measurement uncertainty, while Lambert Glacier has a positive imbalance of 4.2 ±2.3 Gta1. The mass budget for the whole Lambert Glacier basin is approximately in balance, and the average basal melt rate in the downstream section of the ice shelf is 5.1 ± 3.0 m a-1. Our results differ substantially from other recent estimates using hydrostatically derived ice thickness data.

Cenozoic landscape and ice drainage evolution in the Lambert Glacier–Amery Ice Shelf system

AbstractLandforms and sediments in the Prince Charles Mountains record the timing and magnitude of Cenozoic palaeotopographic changes in the Lambert Glacier–Amery Ice Shelf system. A review of geomorphic and sedimentological evidence indicates that considerable (>1–2 km) glacial incision into a pre-glacial palaeosurface occurred along the major outlet glaciers during the Cenozoic. This erosion was in turn the likely driver for uplift that averaged c. 50 m/Ma along the flank of the Amery Ice Shelf since at least the mid-Miocene Epoch. The volume of eroded material is an order of magnitude greater than the quantity of sediment presently preserved in Prydz Bay, suggesting considerable export of Cenozoic sediment off the continental shelf. The magnitude of erosion recorded in the Prince Charles Mountains is sufficient to have focussed Cenozoic ice-drainage patterns, but was too slow to have driven Quaternary changes in ice volume.

Late Eocene Glaciofluvial to Glaciomarine transition in the Lambert Graben: constraints from lithofacies and mineralogy of ODP Site 1166 sediments, Prydz Bay, Antarctica

AbstractThe transition from a glaciofluvial to a glacial sedimentary environment contains critical information for evaluating the onset of glaciation and early glacial dynamics in Antarctica. This study presents investigations of a sediment core from Ocean Drilling Program Leg 188, Site 1166, on the continental shelf in Prydz Bay, in order to provide evidence for the first occurrence of late Eocene glaciers in the Lambert Graben, East Antarctica. The Lambert Graben is a large fault-bounded structure, at least 700 km long and 100 km wide, and presently hosts the Lambert Glacier–Amery Ice Shelf system. The core consists of middle Eocene glacially influenced alluvial plain sediments, c. 110 m in total thickness that are overlain by a c. 20 m-thick early Oligocene glaciomarine succession. The upper contact is a major unconformity. Grain-surface microtextures, such as fractured plates and a relatively high content of ilmenite in alluvial outwash-plain sediments, indicate mixed northern and southern Prince Charles Mountains provenance and initiation of glaciers as early as middle Eocene time. Distribution of the major heavy minerals indicates a change to garnet-rich granulite terrain in sediment-supply during later ice-sheet evolution, when a lack of detritus from the southern Prince Charles Mountains becomes apparent. Glacier advance was no longer restricted to the Lambert Graben and the drainage area became wider. Good preservation of these low-stand glaciofluvial outwash-plain deposits was related to regional subsidence that progressed to a marine transgression and glaciomarine deposition when ice was able to advance to the continental shelf edge.

Linkages between East Antarctic Ice Sheet extent and Southern Ocean temperatures based on a Pliocene high‐resolution record of ice‐rafted debris off Prydz Bay, East Antarctica

Ice‐rafted debris mass accumulation rates (IRD MAR) at a drill site on the Antarctic continental margin are investigated to evaluate the linkages between East Antarctic Ice Sheet extent and Southern Ocean temperatures in the early to mid‐Pliocene. ODP Site 1165 is within 400 km of the Antarctic coastline and in the direct pathway of icebergs released by the Amery Ice Shelf. The Amery Ice Shelf is the largest ice shelf in East Antarctica and it buttresses the Lambert Glacier drainage system, which accounts for 14% of the outflow from the East Antarctic Ice Sheet. IRD MAR were low during peak Southern Ocean warming in the early Pliocene. After a brief precursor, a tenfold increase in IRD MAR at 3.3 Ma marks the termination of the early Pliocene ice sheet minimum, coincident with the M2 glacial. For the mid‐Pliocene, a strong correlation exists between the high‐amplitude signal in the LR04 benthic stack and IRD MAR, suggesting linkages between East Antarctic ice extent, global ice volume and deep‐water temperatures. The IRD record at Site 1165 provides evidence of greater sensitivity of the Lambert Glacier‐Amery Ice Shelf system to Southern Ocean warming than is currently predicted by ice sheet models, which may relate to uncertainties in the understanding of ocean heat uptake, poleward heat transport and ice sheet‐ocean interactions.

Cosmogenic nuclide evidence for enhanced sensitivity of an East Antarctic ice stream to change during the last deglaciation

Glacial sediments from the Prince Charles Mountains, East Antarctica, record late Pleistocene ice thickness variability in the Lambert Glacier–Amery Ice Shelf system, one of the world9s largest ice drainages. A former glacial limit, demarcated by minimally weathered deposits, follows a concave longitudinal profile, indicating a zone of strong ice streaming through the northernmost 500 km of the Lambert Graben. In situ 10 Be and 26 Al exposure ages from these relatively unweathered deposits indicate that the most recent phase of ice lowering occurred between ca. 18 and 8 ka, preceding by as many as 6 k.y. the deglaciation of adjacent coastal regions. Earlier onset of deglaciation in an area of strong ice streaming suggests a heightened sensitivity of the East Antarctic Ice Sheet to climate and sea-level changes following the Last Glacial Maximum than previously recognized.

Analysis of velocity field, mass balance, and basal melt of the Lambert Glacier–Amery Ice Shelf system by incorporating Radarsat SAR interferometry and ICESat laser altimetry measurements

By incorporating recently available remote sensing data, we investigated the mass balance for all individual tributary glacial basins of the Lambert Glacier–Amery Ice Shelf system, East Antarctica. On the basis of the ice flow information derived from SAR interferometry and ICESat laser altimetry, we have determined the spatial configuration of eight tributary drainage basins of the Lambert‐Amery glacial system. By combining the coherence information from SAR interferometry and the texture information from SAR and MODIS images, we have interpreted and refined the grounding line position. We calculated ice volume flux of each tributary glacial basin based on the ice velocity field derived from Radarsat three‐pass interferometry together with ice thickness data interpolated from Australian and Russian airborne radio echo sounding (RES) surveys and inferred from ICESat laser altimetry data. Our analysis reveals that three tributary basins have a significant net positive imbalance, while five other subbasins are slightly positive or close to zero balance. Overall, in contrast to previous studies, we find that the grounded ice in Lambert Glacier–Amery Ice Shelf system has a positive mass imbalance of 22.9 ± 4.4 Gt a−1. The net basal melting for the entire Amery Ice Shelf is estimated to be 27.0 ± 7.0 Gt a−1. The melting rate decreases rapidly from the grounding zone to the ice shelf front. Significant basal refreezing is detected in the downstream section of the ice shelf. The mass balance estimates for both the grounded ice sheet and the ice shelf mass differ substantially from other recent estimates.

Mass budget of the grounded ice in the Lambert Glacier–Amery Ice Shelf system

AbstractWe used remote-sensing and in situ measurements of surface accumulation rate, ice surface velocity, thickness and elevation to evaluate the mass budgets of grounded ice-flow regimes that form the Lambert Glacier–Amery Ice Shelf system. Three distinct drainage regimes are considered: the western and eastern margins of the ice shelf, and the southern grounding line at the major outlet glacier confluence, which can be identified with drainage zones 9, 11 and 10 respectively of Giovinetto and Zwally (2000). Our findings show the entire grounded portion of the basin is approximately in balance, with a mass budget of –4.2±9.8 Gt a–1. Drainages 9, 10 and 11 are within balance to the level of our measurement uncertainty, with mass budgets of –2.5±2.8 Gt a–1, –2.6±7.8 Gt a–1 and 0.9±2.3 Gt a–1, respectively. The region upstream of the Australian Lambert Glacier basin (LGB) traverse has a net mass budget of 4.4±6.3 Gt a–1, while the downstream region has –8.9±9.9 Gt a–1. These results indicate that glacier drainages 9, 10 and 11, upstream and downstream of the Australian LGB traverse, are in balance to within our measurement error.

Cenozoic landscape evolution of an East Antarctic oasis (Radok Lake area, northern Prince Charles Mountains), and its implications for the glacial and climatic history of Antarctica

Ice-free areas Antarctica reveal a multi-million year history of landscape evolution, but most attention up to now has focused on the Transantarctic Mountains. The Amery Oasis in the northern Prince Charles Mountains borders the Lambert Glacier—Amery Ice Shelf System that drains 1 million km 2 of the East Antarctic Ice Sheet, and therefore provides a record of fluctuations of both local and regional ice since the ice sheet first formed in early Oligocene time. This glacial record has been deciphered by (i) geomorphological mapping from aerial photographs and on the ground, (ii) documenting the relationship between thick well-dated, uplifted glaciomarine strata and the underlying palaeolandscape, (iii) examining surficial sediment facies, and (iv) surface-exposure dating using 10Be and 26Al. The SE Amery Oasis records at least 10 million years of landscape evolution beginning with a pre-late Miocene phase of glacial erosion, followed by deposition of glaciomarine strata of the Battye Glacier Formation (Pagodroma Group) in late Miocene time. A wet-based ice sheet next expanded over the SE Amery Oasis, following which deposition of the glaciomarine Pliocene Bardin Bluffs Formation (Pagodroma Group) took place. Both formations were uplifted; by at least 500 and 200 m, respectively. Their tops are characterised by geomorphological surfaces upon which intensive periglacial activity took place. Higher-level bedrock areas were subjected to deep weathering and tor-formation. Early Pleistocene time was characterised by expansion of a cold-based ice sheet across the whole area, but it left little more than patches of sandy gravel and erratic blocks. Late Pleistocene expansion of local ice (the Battye Glacier) saw deposition of moraine-mound complexes on low ground around Radok Lake and ice-dammed lake phenomena. Subglacial drainage of the lake escaped to the east exhuming the sediment-filled gorges. Holocene landscape modification has been relatively superficial. Overall, the landscape of the Amery Oasis evolved primarily under the influence of wet-based (probably polythermal) glaciers in Miocene and Pliocene times, whereas the Quaternary Period was characterised mainly by cold-based glaciers that had comparatively little impact on the landscape.

Accumulation variability and mass budgets of the Lambert Glacier-Amery Ice Shelf system, East Antarctica, at high elevations

AbstractThe temporal and spatial variability of the annual accumulation rate and the mass budgets of five sub-basins of the Lambert Glacier-Amery Ice Shelf system (LAS), East Antarctica, at high elevations are assessed using a variety of datasets derived from field measurements and modeling. The annual temporal variations of the accumulation rate for four cores from the west and east sides of the LAS are around ±34%. Decadal fluctuation of the accumulation from the DT001 firn core drops to ±10%, and the 30 year fluctuation to ±5%, which is assumed to contain the information about the regional and long-term trend in accumulation. The 15-point running mean of the annual accumulation rate derived from stake measurements can remove most of the high-frequency spatial variation so as to better represent the local accumulation. Model simulations show that the spatial variability of erosion/ deposition of snow by the wind has a noticeable impact on the surface mass balance at the higher parts of the LAS. Mass-budget estimates at high-elevation sub-basins of the LAS suggest drainage 9 has a negative imbalance of −0.7 ± 0.4 Gta-1, Lambert and Mellor Glaciers have a positive imbalance of 3.9 ± 2.1 and 2.1 ±2.4 Gta-1 respectively, and Fisher Glacier and drainage 11 are approximately in balance. The higher-elevation region as a whole has a positive mass imbalance of 4.4 ± 6.3 Gta-1, which is consistent with the most recent radar altimetry assessment that shows an overall thickening over this region.

The Pleistocene evolution of the East Antarctic Ice Sheet in the Prydz bay region: stable isotopic evidence from ODP Site 1167

Ocean Drilling Program Leg 188, Prydz Bay, East Antarctica is part of a larger initiative to explore the Cenozoic history of the Antarctic Ice Sheet through direct drilling and sampling of the continental margins. In this paper, we present stable isotopic results from Ocean Drilling Program (ODP) Site 1167 located on the Prydz Channel Trough Mouth Fan (TMF), the first Antarctic TMF to be drilled. The foraminifer-based δ 18O record is interpreted along with sedimentary and downhole logging evidence to reconstruct the Quaternary glacial history of Prydz Bay and the adjacent Lambert Glacier Amery Ice Shelf System (LGAISS). We report an electron spin resonance age date of 36.9±3.3 ka at 0.45 m below sea floor and correlate suspected glacial–interglacial cycles with the global isotopic stratigraphy to improve the chronology for Site 1167. The δ 18O record based on planktonic ( Neogloboquadrina pachyderma (s.)) and limited benthic results ( Globocassidulina crassa), indicates a trend of ice sheet expansion that was interrupted by a period of reduced ice volume and possibly warmer conditions during the early–mid-Pleistocene (0.9–1.38 Ma). An increase in δ 18O values after ∼900 ka appears to coincide with the mid-Pleistocene climate transition and the expansion of the northern hemisphere ice sheet. The δ 18O record in the upper 50 m of the stratigraphic section indicates as few as three glacial–interglacial cycles, tentatively assigned as marine isotopic stages (MIS) 16–21, are preserved since the Brunhes/Matuyama paleomagnetic reversal (780 ka). This suggests that there is a large unconformity near the top of the section and/or that there may have been few extreme advances of the ice sheet since the mid-Pleistocene climate transition resulting in lowered sedimentation rates on the Prydz Channel TMF. The stable isotopic record from Site 1167 is one of the few available from the area south of the Antarctic Polar Front that has been linked with the global isotopic stratigraphy. Our results suggest the potential for the recovery of useful stable isotopic records in other TMFs.

Pliocene–Pleistocene glaciomarine sedimentation in eastern Prydz Bay and development of the Prydz trough-mouth fan, ODP Sites 1166 and 1167, East Antarctica

Lithostratigraphy, grain sizes and down-hole logs of Site 1166 on the continental shelf, and Site 1167 on the upper slope, are analyzed to reconstruct glacial processes in eastern Prydz Bay and the development of the Prydz trough-mouth fan. In eastern Prydz Bay upper Pliocene–lower Pleistocene glaciomarine sediments occur interbedded with open-marine muds and grade upward into waterlaid tills and subglacial tills. Lower Pleistocene sediments of the trough-mouth fan consist of coarse-grained debrites interbedded with bottom-current deposits and hemipelagic muds, indicating repeated advances and retreats of the Lambert Glacier–Amery Ice Shelf system with respect to the shelf break. Systematic fluctuations in lithofacies and down-hole logs characterize the upper Pliocene–lower Pleistocene transition at Sites 1166 and 1167 and indicate that an ice stream advanced and retreated within the Prydz Channel until the mid Pleistocene. The record from Site 1167 shows that the grounding line of the Lambert Glacier did not extend to the shelf break after 0.78 Ma. Published ice-rafted debris records in the Southern Ocean show peak abundances in the Pliocene and the early Pleistocene, suggesting a link between the nature of the glacial drainage system as recorded by the trough-mouth fans and increased delivery of ice-rafted debris to the Southern Ocean.

Digital elevation models for the Lambert Glacier–Amery Ice Shelf system, East Antarctica, from ERS-1 satellite radar altimetry

AbstractThe Lambert Glacier–Amery Ice Shelf system is a major component of the East Antarctic ice sheet. This paper presents two digital elevation models (DEMs) that have been generated for the Lambert–Amery system from validated European Remote-sensing Satellite (ERS-1) radar altimeter waveform data. The first DEM covers the Amery Ice Shelf only, and was produced using kriging on a 1 km grid. The second is a coarser (5 km) DEM of the entire Lambert–Amery system, generated via simple averaging procedures. The DEMs provide unprecedented surface elevation information for the Lambert–Amery system and allow new insight into the glaciology of the region.

Mass balance of the Lambert Glacier–Amery Ice Shelf system, East Antarctica: a comparison of computed balance fluxes and measured fluxes

AbstractWe combine European Remote-sensing Satellite (ERS-1) radar altimeter surface elevations (Fricker and others, 2000) with six different accumulation distributions to compute balance fluxes for the Lambert Glacier–Amery Ice Shelf drainage system. These interpolated balance fluxes are compared with fluxes derived from in situ measurements of ice thickness and velocity at 73 stations of the Lambert Glacier basin traverse and at 11 stations further downstream, to assess the system’s state of balance. For the upstream line we obtain a range of imbalance estimates, from −23.8% to +19.9% of the observed flux, reflecting the sensitivity to the accumulation distributions. For some of the accumulation distributions the imbalance estimates vary significantly between different parts of the line. Imbalance estimates for the downstream line range from −17.7% to +70.2%, with four of the estimates exceeding +30%, again reflecting the sensitivity of the result to input accumulation, and strongly suggesting that the mass balance of the region between the two lines is positive. Our results confirm the importance of accurate estimates of accumulation in ice-sheet mass-balance studies. Furthermore, they suggest that it is not possible to accurately determine the state of balance of large Antarctic drainage basins on the basis of currently available accumulation distributions.