No abstract

Increasing evidence for an elaborate subglacial drainage network underneath modern Antarctic ice sheets suggests that basal meltwater has an important influence on ice stream flow. Swath bathymetry surveys from previously glaciated continental margins display morphological features indicative of subglacial meltwater flow in inner shelf areas of some paleo ice stream troughs. Over the last few years several expeditions to the Eastern Amundsen Sea embayment (West Antarctica) have investigated the paleo ice streams that extended from the Pine Island and Thwaites glaciers. A compilation of high-resolution swath bathymetry data from inner Pine Island Bay reveals details of a rough seabed topography including several deep channels that connect a series of basins. This complex basin and channel network is indicative of meltwater flow beneath the paleo-Pine Island and Thwaites ice streams, along with substantial subglacial water inflow from the east. This meltwater could have enhanced ice flow over the rough bedrock topography. Meltwater features diminish with the onset of linear features north of the basins. Similar features have previously been observed in several other areas, including the Dotson-Getz Trough (Western Amundsen Sea embayment) and Marguerite Bay (SW Antarctic Peninsula), suggesting that these features may be widespread around the Antarctic margin and that subglacial meltwater drainage played a major role in past ice-sheet dynamics

An understanding of the glacial history of Pine Island Bay (PIB) is essential for refining models of the future stability of the West Antarctic Ice Sheet (WAIS). New multichannel seismic reflection data from inner PIB are interpreted in context of previously published reconstructions for the retreat history in this area since the Last Glacial Maximum. Differences in the behavior of the ice sheet during deglaciation are shown to exist for the western and eastern parts of PIB. While we can identify only a thin veneer of sedimentary deposits in western PIB, eastern PIB shows sedimentary layers ≤ 400 msTWT. This is interpreted as a result of differences in ice retreat: a fast ice retreat in western PIB accompanied by rapid basal melting led to production of large meltwater streams, a slower ice retreat in eastern PIB is most probably the result of smaller drainage basins resulting in less meltwater production.

Subglacial meltwater drainage can enhance localized melting along grounding zones and beneath the ice shelves of marine-terminating glaciers. Efforts to constrain the evolution of subglacial hydrology and the resulting influence on ice stability in space and on decadal to millennial timescales are lacking. Here, we apply sedimentological, geochemical, and statistical methods to analyze sediment cores recovered offshore Thwaites Glacier, West Antarctica to reconstruct meltwater drainage activity through the pre-satellite era. We find evidence for a long-lived subglacial hydrologic system beneath Thwaites Glacier and indications that meltwater plumes are the primary mechanism of sedimentation seaward of the glacier today. Detailed core stratigraphy revealed through computed tomography scanning captures variability in drainage styles and suggests greater magnitudes of sediment-laden meltwater have been delivered to the ocean in recent centuries compared to the past several thousand years. Fundamental similarities between meltwater plume deposits offshore Thwaites Glacier and those described in association with other Antarctic glacial systems imply widespread and similar subglacial hydrologic processes that occur independently of subglacial geology. In the context of Holocene changes to the Thwaites Glacier margin, it is likely that subglacial drainage enhanced submarine melt along the grounding zone and amplified ice-shelf melt driven by oceanic processes, consistent with observations of other West Antarctic glaciers today. This study highlights the necessity of accounting for the influence of subglacial hydrology on grounding-zone and ice-shelf melt in projections of future behavior of the Thwaites Glacier ice margin and marine-based glaciers around the Antarctic continent.

Interplay of deep‐water sedimentary processes is responsible for building a myriad of features and deposits across mixed turbidite–contourite systems, from <5 cm beds to >200 km long sedimentary drifts. Investigations of the spatial and temporal variability of their sedimentary facies and facies associations is crucial to reveal the dynamics between along‐slope bottom currents and down‐slope turbidity currents, as well as their impact on drift construction and channel erosion. This study focuses on extensive modern mixed (turbidite–contourite) systems, developed across the continental rise of the Pacific margin of the Antarctic Peninsula. Nine sediment cores were sampled and analysed, through grain size and geochemical methods, to study the sedimentary facies at high‐resolution (ca 1 to 20 cm). Three main facies associations have been identified across distinct morphological features (i.e. mounded drifts and trunk channels), comprising intercalations of hemipelagites, bottom current reworked sands (which include fine to coarse‐grained contourites) and gravitational facies (turbidites and mass‐transport deposits). These facies associations reflect fluctuations of the background sedimentation, oscillations of the bottom‐current velocity and of the frequency of gravity‐driven currents. The sedimentary record features cyclic alternations during the Late Quaternary (>99 kyr), suggesting that variations between along‐slope bottom currents and down‐slope turbidity currents are strongly linked to glacial–interglacial cycles during Marine Isotope Stages 1 to 6. Sedimentary records affected by bottom currents on polar margins, such as those of the Antarctic Peninsula, are essential to decipher the facies and facies sequences of bottom‐current deposits, as the low degree of bioturbation throughout most of the sediments allows us to observe the original sedimentary structures, which are poorly preserved in similar deposits from other continental margins.

The southern Bellingshausen Sea (SBS) is a rapidly-changing part of West Antarctica, where oceanic and atmospheric warming has led to the recent basal melting and break-up of the Wilkins ice shelf, the dynamic thinning of fringing glaciers, and sea-ice reduction. Accurate sea-floor morphology is vital for understanding the continued effects of each process upon changes within Antarctica's ice sheets. Here we present a new bathymetric grid for the SBS compiled from shipborne echo-sounder, spot-sounding and sub-ice measurements. The 1-km grid is the most detailed compilation for the SBS to-date, revealing large cross-shelf troughs, shallow banks, and deep inner-shelf basins that continue inland of coastal ice shelves. The troughs now serve as pathways which allow warm deep water to access the ice fronts in the SBS. Our dataset highlights areas still lacking bathymetric constraint, as well as regions for further investigation, including the likely routes of palaeo-ice streams. The new compilation is a major improvement upon previous grids and will be a key dataset for incorporating into simulations of ocean circulation, ice-sheet change and history. It will also serve forecasts of ice stability and future sea-level contributions from ice loss in West Antarctica, required for the next IPCC assessment report in 2013

Trough mouth fans (TMFs) are sediment depocentres that form along high-latitude continental margins at the mouths of some cross-shelf troughs. They reflect the dynamics of past ice sheets over multiple glacial cycles and processes operating on (formerly) glaciated continental shelves and slopes, such as erosion, reworking, transport and deposition. The similarities and differences in TMF morphology and formation processes in the Arctic and Antarctic regions remain poorly constrained. We analyse the dimensions and geometries of 15 TMFs from Arctic and Antarctic margins and the grain size distribution of 82 sediment cores centred on them. We compare the grain size composition of sub- and proglacial diamictons deposited on the shelves and glacigenic debris flows deposited on the adjacent TMFs and find a significant difference between Arctic and Antarctic margins. Antarctic margins show a coarser grain size composition for both glacigenic debris flows and shelf diamictons. This significant difference provides insight into high-latitude sediment input, transportation and glacial–interglacial regimes. We suggest that surface runoff and river discharge are responsible for enhanced fine-grained sediment input in the Arctic compared with the Antarctic.

The Amundsen Sea embayment of West Antarctica is in a prominent location for a series of tectonic and magmatic events from Paleozoic to Cenozoic times. Seismic, magnetic and gravity data from the embayment and Pine Island Bay (PIB) reveal the crustal thickness and some tectonic features. The Moho is 24-22 km deep on the shelf. NE-SW trending magnetic and gravity anomalies and the thin crust indicate a former rift zone that was active during or in the run-up to breakup between Chatham Rise and West Antarctica before or at 90 Ma. NW-SE trending gravity and magnetic anomalies, following a prolongation of Peacock Sound, indicate the extensional southern boundary to the Bellingshausen Plate which was active between 79 and 61 Ma.