Lambert Glacier Amery Ice Shelf 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.

The ice flux to the Lambert Glacier and Amery Ice Shelf along the Chinese inland traverse and implications for mass balance of the drainage basins, East Antarctica

Study of the mass balance of the Antarctic Ice Sheet is critical to estimate its potential contribution to global sea-level rise in the future. As the largest drainage system, the Lambert Glacier–Amery Ice Shelf drainage system plays an important role in the mass balance of the Antarctic Ice Sheet. In this study, the ice thickness measured by airborne ice-penetrating radar with high spatial resolution and accuracy and accurate ice velocity measured by in situ GPS stations along the route of the Chinese National Antarctic Research Expedition inland traverse were used to calculate the ice flux with unprecedented accuracy. This transverse is from Zhongshan Station to Dome A, passing through the east side of the Lambert Glacier and the smaller coastal glacier in the C-Cp basin. The results show that the ice flux across the entire traverse is 24.7 ± 2.8 Gt a−1, along which the section in drainage basin B–C (Lambert Glacier) has an ice flux of 20.9 ± 1.9 Gt a−1 and the section in drainage basin C–Cp (basin adjacent to Lambert Glacier) contributed 3.8 ± 0.4 Gt a−1. The ice flux values in both regions are coincident with the mass balance calculated from the Ice, Cloud, and Land Elevation Satellite, Earth Observing System. Meanwhile, the C–Cp basin shows an ice flux value of 6.6 ± 0.8 Gt a−1 across the grounding line.

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.

Paleomagnetism and biostratigraphy of sediments from Southern Ocean ODP Site 744 (southern Kerguelen Plateau): Implications for early-to-middle Miocene climate in Antarctica

New paleomagnetic results from lower-to-middle Miocene samples from Ocean Drilling Program (ODP) Holes 744A and 744B, cored during ODP Leg 119 on the southern Kerguelen Plateau (Indian Ocean sector; Southern Ocean), provide a chronostratigraphic framework for an existing and under-utilized paleoclimate archive during a key period of Antarctic climate and ice sheet evolution. Site 744 is strategically positioned for high-latitude paleoceanographic and paleoclimatic studies because it lies within the southern domain of the Antarctic Circumpolar Current (ACC) and in proximity to the large and active Lambert Glacier-Amery Ice Shelf drainage system of the East Antarctic Ice Sheet. Magnetostratigraphic results were reported previously for this site, but technical difficulties and limited sampling prevented confident correlation of the magnetic polarity record with the geomagnetic polarity timescale. Our results, which are constrained by new semi-quantitative analyses of diatom assemblages and radiolarian first and last appearance events that are evaluated within a regional Southern Ocean biostratigraphic dataset through Constrained Optimization (CONOP) model runs, permit significant refinement of previous age models for the lower-to-middle Miocene sequence recovered at Site 744 (spanning the interval from ~21 to 13.7Ma). An extended record of sediment accumulation, with average sedimentation rates of ~0.7–0.9cm/kyr, is interrupted by a series of hiatuses in the middle Miocene. These disruptions in sediment supply, or erosional events, could mark a local response of north–south fluctuations in the location and/or strength of the Antarctic Circumpolar Current during transient glacial events within the Mid-Miocene Climate Optimum (MMCO; ~17 to 14.45Ma). With the enhanced age control provided by this study, combined with a refined chronostratigraphy for the underlying upper Eocene to Oligocene strata, Site 744 becomes a good candidate for future high-resolution stable isotope and microfossil paleoecological work, which will further elucidate the late Paleogene and early Neogene paleoenvironmental history of the Southern Ocean.

Inferring ice-flow directions from single ice-sheet surface images using the Radon transform

AbstractWe present a new method for extracting the direction of surface flow for ice sheets, based on the detection of flow-induced features that are visible in satellite imagery. The orientation of linear features is determined using a Radon transform and only requires a single image. The technique is demonstrated by applying it to the RADARSAT mosaic of Antarctica, over the Lambert Glacier–Amery Ice Shelf region of East Antarctica. Comparisons with both existing flow-direction fields and traced streamlines over the same area provide an evaluation of the method. We also illustrate its application to Landsat 7 imagery.

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

Abstract Landforms 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

Abstract The 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.

Late Neogene ice drainage changes in Prydz Bay, East Antarctica and the interaction of Antarctic ice sheet evolution and climate

During the late Neogene, the Lambert Glacier–Amery Ice Shelf drainage system flowed across Prydz Bay and showed several changes in flow pattern. In the Early Pliocene, the Lambert Glacier ice stream reached the shelf edge and built a trough mouth fan on the upper continental slope. This was associated with an increase in ice discharge from the Princess Elizabeth Land coast into Prydz Bay. The trough mouth fan consists mostly of debris flow deposits derived from the melting out of subglacial debris at the grounding line at the continental shelf edge. The composition of debris changes at around 1.1 Ma BP from material derived from erosion of the Lambert Graben and Prydz Bay Basin to mostly basement derived material. This probably results from a reduction in the depth of erosion and hence the volume of ice in the system. In the trough mouth fan, debris flow intervals are separated by thin mudstone horizons deposited when the ice had retreated from the shelf edge. Age control in an Ocean Drilling Program hole indicates that most of the trough mouth fan was deposited prior to the Brunhes–Matuyama Boundary (780 ka BP). This stratigraphy indicates that extreme ice advances in Prydz Bay were rare after the mid Pleistocene, and that ice discharge from Princess Elizabeth Land became more dominant than the Lambert Glacier ice in shelf grounding episodes, since the mid Pleistocene. Mechanisms that might have produced this change are extreme inner shelf erosion and/or decreasing ice accumulation in the interior of East Antarctica. We interpret this pattern as reflecting the increasing elevation of coastal ice through time and the increasing continentality of the interior of the East Antarctic Ice Sheet. The mid Pleistocene change to 100 ka climatic and sea level cycles may also have affected the critical relationship between ice dynamics and the symmetry or asymmetry of the interglacial/glacial climate cycle duration.

Pleistocene deglaciation chronology of the Amery Oasis and Radok Lake, northern Prince Charles Mountains, Antarctica

Abstract The East Antarctic Ice Sheet is the largest ice mass on Earth with a capacity to raise global sea level by up to 65 m. As the Lambert Glacier–Amery Ice Shelf drainage system is the largest to reach the coast of Antarctica, quantifying its evolution over the Quaternary is a vital component in developing an understanding of the Antarctic response to future climate change. Here we present a deglaciation chronology based on 10 Be and 26 Al in situ cosmogenic exposure ages of the northern Prince Charles Mountains, which flank the Lambert Glacier–Amery system, and that records the progressive emergence of McLeod Massif and Radok Lake basin from beneath the Mac.Robertson Land lobe of the East Antarctic Ice Sheet. The exposure ages monotonically decrease with both decreasing altitude and increasing proximity to the Amery Ice Shelf at the Antarctic coast. Exposure ages from the crests of McLeod Massif near the edge the Amery Ice Shelf and from Fisher Massif, 75 km further inland, each at ∼1200 m above sea level, are 2.2 ± 0.3 and 1.9 ± 0.2 Ma, respectively, suggesting their continuous exposure above the ice sheet at least since close to the Plio–Pleistocene boundary. An extensive plateau at ∼800 m altitude on McLeod Massif above Battye Glacier records the massif's increased emergence above the ice sheet surface at about between 880 and 930 ka ago indicating 400 m of ice volume reduction in the mid Pleistocene. Correcting these apparent ages for a reasonable choice in erosion rate would extend this event to ∼1.15 Ma — a period identified from Prydz Bay ODP core-1167 when sedimentation composition alters and rates decrease 10-fold. Exposure ages from boulder-mantled erosional surfaces above and beyond the northern end of Radok Lake at 220 m, range from 28 to 121 ka. Independent of choice of model interpretation to explain this age spread, the most recent major reoccupation of Radok Lake by Battye Glacier ice occurred during the last glacial cycle. Moraine ridges at the lower altitude of 70–125 m were deposited during the final withdrawal of Battye Glacier ice from the lake basin between 11 and 20 ka ago. This new chronology indicates that the highest Amery Oasis peaks have not been overridden by the Mac.Robertson Land lobe of the East Antarctic Ice Sheet for at least the past 2 Ma. Since this time we document 3 major periods of regional reduction in ice sheet volume at ∼1.1 Ma, during the last glacial cycle (120 to 30 ka) and through the Last Glacial Maximum (20 to 10 ka) that resulted in an overall 1000 m of ice lowering in the Battye Glacier–Radok Lake region.

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.