09:30 〜 09:45
[MIS08-03] West Antarctic Ice Sheet dynamics in the glacial–interglacial cycles during the Mid Pliocene: Results from Amundsen Sea sediment cores
キーワード：西南極氷床、中期鮮新世、アムンゼン海、ストロンチウム・ネオジム・鉛同位体
The ice draining into the Amundsen Sea Embayment in West Antarctica is currently being lost at an accelerated pace, compared to other drainage sectors of Antarctica (e.g., Rignot et al., 2019). Ice loss in the Amundsen Sea sector is a precursor for major West Antarctic Ice Sheet (WAIS) retreat or even WAIS collapse that take place in the future, similar to the major WAIS deglaciation that occurred during Pliocene (5.3–2.6 Ma) (DeConto and Pollard, 2016). If vast amounts of meltwater released during WAIS retreat were advected by the westward coastal current to the Wilkes Land margin of East Antarctica, the formation of dense shelf water there would have been weakened, and instead relatively warm Circumpolar Deep Water would have been directed far onto the shelf, triggering additional melting in the Wilkes Land drainage sector of the East Antarctic Ice Sheet.
In this study, to evaluate ice loss of WAIS deglaciation during Pliocene based on geochemical evidences, we have analyzed detrital Sr, Nd and Pb isotopes on deep-sea sediments (IODP Expedition 379 Site U1532; Gohl et al., 2021). Sr-Nd-Pb isotopes were measured on the < 63µm grain size fraction (i.e., clay and silt) of U1532 sediments and of core-top sediments along the western Antarctic margin, and also on bulk rocks collected in western Antarctica (provided by the OSU Polar rock repository, https://prr.osu.edu). These multi-isotope signatures can be used as robust geochemical tracers of sediment provenance. The extent of the WAIS (i.e., WAIS ice loss) during the Pliocene can be inferred by creating an isotopic map of the detrital source areas and using that map to identify the source areas of the detrital deposits.
Site U1532 was drilled at a water depth of ~4000 m on Resolution Drift offshore from the eastern Amundsen Sea Embayment. Their sedimentary record spans the time period back to ~6 Ma. We observed repeated biogenic bearing and partly bioturbated ice-rafted debris (IRD) layers in the Pliocene intervals, and these IRD units are also characterized by a predominance of open water diatoms (Fragilariopsis barronii, Dactyliozolen antarcticus, etc), suggesting that the IRD units reflect relatively warm periods (i.e., interglacial periods) when at least the marine-terminating Amundsen Sea drainage sector of the WAIS retreat.
We measured Sr-Nd-Pb isotopic compositions of some of these Pliocene IRD units corresponding to interglacial periods, and found that all these IRD layers exhibited different Sr-Nd-Pb isotope values from those of the glacial non-IRD sediments, indicating changes in sediment provenances during Pliocene glacial–interglacial cycles. Comparison with isotopic maps created from the core-top and Antarctic rock samples’ isotope data clearly identified the potential sediment source regions during the interglacial to glacial periods. In the presentation, we will argue potential extent of the glacial–interglacial ice loss of WAIS during the Mid Pliocene.
In this study, to evaluate ice loss of WAIS deglaciation during Pliocene based on geochemical evidences, we have analyzed detrital Sr, Nd and Pb isotopes on deep-sea sediments (IODP Expedition 379 Site U1532; Gohl et al., 2021). Sr-Nd-Pb isotopes were measured on the < 63µm grain size fraction (i.e., clay and silt) of U1532 sediments and of core-top sediments along the western Antarctic margin, and also on bulk rocks collected in western Antarctica (provided by the OSU Polar rock repository, https://prr.osu.edu). These multi-isotope signatures can be used as robust geochemical tracers of sediment provenance. The extent of the WAIS (i.e., WAIS ice loss) during the Pliocene can be inferred by creating an isotopic map of the detrital source areas and using that map to identify the source areas of the detrital deposits.
Site U1532 was drilled at a water depth of ~4000 m on Resolution Drift offshore from the eastern Amundsen Sea Embayment. Their sedimentary record spans the time period back to ~6 Ma. We observed repeated biogenic bearing and partly bioturbated ice-rafted debris (IRD) layers in the Pliocene intervals, and these IRD units are also characterized by a predominance of open water diatoms (Fragilariopsis barronii, Dactyliozolen antarcticus, etc), suggesting that the IRD units reflect relatively warm periods (i.e., interglacial periods) when at least the marine-terminating Amundsen Sea drainage sector of the WAIS retreat.
We measured Sr-Nd-Pb isotopic compositions of some of these Pliocene IRD units corresponding to interglacial periods, and found that all these IRD layers exhibited different Sr-Nd-Pb isotope values from those of the glacial non-IRD sediments, indicating changes in sediment provenances during Pliocene glacial–interglacial cycles. Comparison with isotopic maps created from the core-top and Antarctic rock samples’ isotope data clearly identified the potential sediment source regions during the interglacial to glacial periods. In the presentation, we will argue potential extent of the glacial–interglacial ice loss of WAIS during the Mid Pliocene.