The West Antarctic Ice Sheet retreat in Pine Island Bay, Amndsen Sea, Antarctica, as documented by clay mineral assemblages
Final Report Abstract
The Amundsen Sea Embayment is a probable site for the initiation of a future collapse of the West Antarctic Ice Sheet. This study contributes to a better understanding of the transport pathways of subglacial sediments into the embayment at present and during the last glacial period. It presents the clay mineral composition of sediment samples taken from the seafloor surface (ca. 50 samples) and from some 40 marine cores (ca. 900 samples) in order to decipher spatial and temporal changes in the sediment provenance. The most striking feature in the present-day clay mineral distribution is the high concentration of kaolinite, which is mainly supplied by the Thwaites glacier system and indicates the presence of hitherto unknown kaolinite-bearing sedimentary strata in the hinterland, probably in the Byrd Subglacial Basin. The presence of a sedimentary substrate, in turn, is an important factor affecting the dynamics of fast-flowing glaciers and ice-streams. In contrast, the Bentley Subglacial Trench, which is drained by Pine Island Glacier, hosts the main modern source for illite. Smectite originates from the erosion of volcanic rocks in Ellsworth Land and western Marie Byrd Land. The clay mineral assemblages in diamictons deposited during the last glacial period are distinctly different from those in corresponding surface sediments. In general, they are enriched in kaolinite. The changes in sediment composition indicate that glacial sediment sources were different from modern ones, which could reflect changes in the catchment areas of the glaciers and ice streams. This probably indicates a migration of the ice divides. Our interpretation has major implications for the long-term stability of the West Antarctic Ice Shelf, because it points towards a dynamically evolving drainage system in the past, similar to that observed today. Furthermore it highlights that one has to proceed with caution when reconstructing palaeo-drainage patterns based on modern sediment sources in this area. The clay mineral assemblages in the sediment cores proved to be an important tool for selecting samples for AMS 14C-dating in order to reconstruct the retreat history of the West Antarctic Ice Sheet. Our results indicate that deglaciation was probably underway as early as 22351 cal yr BP, reaching the mid-shelf by 13837 cal yr BP and the inner shelf to within c.10-12 km of the present ice shelf front between 12618 and 10072 cal yr BP. MDR television reported about our Antarctic research activities within the programme “Lexi-TV Antarktis” on 14. December 2011.
Publications
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(2011): Deglacial history of the West Antarctic Ice Sheet in the western Amundsen Sea Embayment. - Quaternary Science Reviews, 30: 488-505
Smith, J.A., Hillenbrand, C.-D., Kuhn, G., Larter, R.D., Graham, A.G.C., Ehrmann, W., Moreton, S.G. & Forwick, G.
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(2011): Provenance changes between recent and glacial-time sediments in the Amundsen Sea Embayment, West Antarctica: clay mineral assemblage evidence. - Antarctic Science, 23(5): 471-486
Ehrmann, W., Hillenbrand, C.-D., Smith, J.A., Graham, A.G.C., Kuhn, G. & Larter, R.D.
