Deglacial and palaeoenvironmental history of Anvers-Hugo Trough, western Antarctic Peninsula

Abstract

The Antarctic Peninsula Ice Sheet (APIS) is currently experiencing significant mass loss, contributing to global sea level rise. Increasing mass loss is primarily a response to reductions in the thickness and extent of ice shelves, triggering retreat, acceleration and drawdown of marine terminating glaciers. These changes have occurred in tandem with atmospheric and oceanic warming, which have had additional impacts on sea ice, the properties of water masses and marine productivity. A full assessment of these recent changes, together with the relative importance of key drivers for initiating grounding line and ice shelf retreat, is limited by the timescales over which we have recorded contemporaneous measurements of ice sheet change(s) and climate observations. Consequently, there remains a need to understand the behaviour of the APIS over a range of timescales so that we can fully understand future ice sheet change. This study utilises marine geological and geophysical data from Anvers-Hugo Trough (AHT), to improve our understanding of the glacial and environmental history of the western Antarctic Peninsula following the Last Glacial Maximum (25-19 kyr BP).

Detailed multi-proxy analysis of sediment cores allows identification of sedimentary units deposited over the last deglaciation of AHT. Particular focus is paid investigating the variability in sediments deposited in the transitional (grounding line proximal to distal) environment in order to identify key depositional processes active in this setting and infer grounding line behaviour over deglaciation. Transitional sedimentary units are found to be deposited systematically; varying with marine processes, grounding line retreat rate, the presence/absence of an ice shelf, bathymetric position and across trough position. Quantitative assessment of absolute diatom abundance and species assemblages, aid reconstruction of the palaeoenvironmental conditions in AHT during and after deglaciation and allow the link between deglaciation and primary productivity to be assessed. These data indicate that the AHT experienced a period of enhanced diatom productivity following the last deglaciation of the trough, associated with meltwater discharge and nutrient input from sea and glacial ice melt. This led to deposition of laminated diatomaceous oozes, with their spatial distribution and accumulation influenced by seafloor bathymetry. This indicates that the distribution of laminated oozes does not necessarily reflect the spatial extent of surface productivity. The timing of deglaciation and post-glacial environmental change is inferred from 27 new radiocarbon dates. The grounding line had retreated from the mid-shelf as early as 15.84 cal. kyr BP, reaching Palmer Deep on the inner shelf shortly before ~12.85 cal. kyr BP. Peak, postglacial primary productivity on the mid to inner shelf followed grounding line retreat by ~4.6 kyr, indicating that deglaciation alone did not create this highly productive environment within AHT. Additional drivers of glacial and/or sea-ice melt, including high atmospheric and sea surface temperatures, were required to trigger this period of peak diatom productivity.

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