The sedimentary legacy of a palaeo-ice stream on the shelf of the southern Bellingshausen Sea: Clues to West Antarctic glacial history during the Late Quaternary

Abstract

a b s t r a c tA major trough ("Belgica Trough") eroded by a palaeo-ice stream crosses the continental shelf of the southern Bellingshausen Sea (West Antarctica) and is associated with a trough mouth fan ("Belgica TMF") on the adjacent continental slope. Previous marine geophysical and geological studies investigated the bathymetry and geomorphology of Belgica Trough and Belgica TMF, erosional and depositional processes associated with bedform formation, and the temporal and spatial changes in clay mineral provenance of subglacial and glaciomarine sediments.Here, we present multi-proxy data from sediment cores recovered from the shelf and uppermost slope in the southern Bellingshausen Sea and reconstruct the ice-sheet history since the last glacial maximum (LGM) in this poorly studied area of West Antarctica. We combined new data (physical properties, sedimentary structures, geochemical and grain-size data) with published data (shear strength, clay mineral assemblages) to refine a previous facies classification for the sediments. The multi-proxy approach allowed us to distinguish four main facies types and to assign them to the following depositional settings: 1) subglacial, 2) proximal grounding-line, 3) distal sub-ice shelf/sub-sea ice, and 4) seasonal open-marine. In the seasonal open-marine facies we found evidence for episodic currentinduced winnowing of near-seabed sediments on the middle to outer shelf and at the uppermost slope during the late Holocene.In addition, we obtained data on excess 210 Pb activity at three core sites and 44 AMS 14 C dates from the acid-insoluble fraction of organic matter (AIO) and calcareous (micro-) fossils, respectively, at 12 sites. These chronological data enabled us to reconstruct, for the first time, the timing of the last advance and retreat of the West Antarctic Ice Sheet (WAIS) and the Antarctic Peninsula Ice Sheet (APIS) in the southern Bellingshausen Sea. We used the down-core variability in sediment provenance inferred from clay mineral changes to identify the most reliable AIO 14 C ages for ice-sheet retreat. The palaeo-ice stream advanced through Belgica Trough after w36.0 corrected 14 C ka before present (B.P.). It retreated from the outer shelf at w25.5 ka B.P., the middle shelf at w19.8 ka B.P., the inner shelf in Eltanin Bay at w12.3 ka B.P., and the inner shelf in Ronne Entrance at w6.3 ka B.P. The retreat of the WAIS and APIS occurred slowly and stepwise, and may still be in progress. This dynamical ice-sheet behaviour has to be taken into account for the interpretation of recent and the prediction of future mass-balance changes in the study area. The glacial history of the southern Bellingshausen Sea is unique when compared to other regions in West Antarctica, but some open questions regarding its chronology need to be addressed by future work.

New constraints on the timing of West Antarctic Ice Sheet retreat in the eastern Amundsen Sea since the Last Glacial Maximum

“…From this, three main facies have been identified which are described and interpreted below and illustrated in Figure 2 and supplementary Figure S1. The facies succession broadly follows that documented for sediments recovered in the western ASE Hillenbrand et al, 2010b) and elsewhere on the Antarctic continental shelf (Domack et al, 1999Licht et al, 1999;Evans et al, 2005;Anderson, 2005, 2007;Ó Cofaigh et al, 2005;Hillenbrand et al, 2005Hillenbrand et al, , 2010aHillenbrand et al, ,b, 2013Pudsey et al, 2006;Heroy et al, 2008;McKay et al, 2008) with a muddy diamicton at the base of the sequence, overlain by a transitional muddy sand/sandy-gravel which in turn is capped by a terrigenous to biogenic mud. The primary purpose of our facies approach is to establish the major depositional environments (subglacial, glacier proximal and open marine) to inform and direct our dating strategy.…”

“…In this context, the scarcity of calcareous (micro-)fossils in combination with the large and variable input of reworked fossil organic carbon from the hinterland has hampered efforts to establish a detailed retreat histories, especially when attempting to constrain the subglacial to glacier-proximal transition. Notwithstanding these problems, recent studies from the Bellingshausen Sea and western ASE shelf have demonstrated that with a careful sampling strategy guided by detailed sedimentological information, reliable deglacial chronologies can be produced using the acid insoluble organic (AIO) fraction (Hillenbrand et al 2010a;Smith et al, 2011). This approach requires a local reservoir correction, achieved by dating the surface sediments (usually obtained from box cores) and subtracting this age from down-core ages (cf.…”

“…Postglacial sediments in cores from the mid-outer shelf produced consistently "old" ages whilst those from Cosgrove-Abbott are generally "younger". These "old" 14 C ages, which are particularly apparent in the transitional sediments We also explored the possibility of using bulk organic (C/N,  13 C) and clay mineral parameters to assess the reliability of the down-core age data (e.g., Hillenbrand et al, 2010a) but found no significant correlations (Fig. S2).…”

The role of the cryosphere in source-to-sink systems

“…This is most easily accomplished in modern temperate, meltwater-dominated glacial systems, because sediment production is elevated and thus signal generation is the strongest, resulting in higher mass fluxes that produce the accumulation rates necessary to resolve the recent or short-timescale ice response function Dowdeswell et al, 1998;Dowdeswell and Siegert, 1999;Jaeger and Nittrouer, 1999a;Jaeger, 2002;Andresen et al, 2012;. For modern iceberg-dominated systems, reduced production and flux of sediment to the sink limits our ability to quantify the relationship between ice flux (velocity) and the stratigraphic signal for short (sub-annual to decadal) timescales (Harden et al, 1992;Domack and McClennen, 1996;Lowe and Anderson, 2002;Hillenbrand et al, 2010a;Kirshner et al, 2012;Boldt et al, 2013). Consequently, the greatest advances in linking ice dynamics at modern to Quaternary advance-retreat time scales to sedimentary signal preservation exist for meltwater-dominated systems (Fig.…”

“…Ice extent and dynamics in the Antarctic marine realm are determined from dating subglacial to glacimarine to open-marine lithofacies transitions (see Anderson et al, 2014;Cofaigh et al, 2014;Hillenbrand et al, 2014;Hodgson et al, 2014;Larter et al, 2014;Mackintosh et al, 2014 for cited studies). Because of the scarcity of calcareous fossils in Antarctic shelf sediments, it is particularly challenging to use marine 14 C to develop constraints on the timing of deglaciation and the accompanying sediment flux Andrews et al, 1999;Hall, 2009;Hillenbrand et al, 2010a;Larter et al, 2014;Licht and Andrews, 2002). In light of these dating challenges, the ability to recognize the large-scale regional controls on ice extent (e.g., shelf bathymetry, oceanographic forcing) is easiest when all chronological controls are synoptically summarized Cofaigh et al, 2014;Hillenbrand et al, 2014;Larter et al, 2014).…”