Late Quaternary Cyclic Variations Of Ice Sheet And Oceanography In The Amundsen Sea Sector,Antarctica

For half a century,the ice loss form Amundsen sea ice sheet and ice shelf has attracted broad attention.The bathyal sediments on continental slope and continental rise are less influenced by the erosion of glaciers,so they may be more continuous and comparable than on the shelf.Thus,getting high resolution sedimentary cores on the continental slope and rise plays an essential role on reconstructing the evolution history and mechanisms of Antarctic Ice Sheet,and predicting the climate change in the future.Core AMS01 dredged on the northwestern continental rise of the Amundsen Sea was used to reconstruct the evolution history of paleoceanography and paleoclimate variations since MIS9（about 340ka BP）based on the analyses of AMS¹⁴C dating,color reflectance,grain size and geochemical proxies.The age frame is built by the combination of AMS¹⁴C dating of planktonic foraminifera N.Pachyderma and lithostratigraphy features.The age of the core ranges from MIS9 to MIS2（337¹2 ka BP）.The paleoproductivity proxies such as biogenic silica,biogenic Ba and color b*with high resolution varied constantly and smoothly,corresponding well with the Dome C ice core,reflecting the featue that in areas south of APF,the paleoproductivity declined in glacials and increased in interglacials.Temperature and ice condition of the area are essential to ocean productivity.The synchronous variation of redox-sensitive elements（Mn,Mo et al.）closely coupled with the glacial/interglacial cycle in the late Quaternary.The content of redox-sensitive elements are high in interglacials and low in glacials.The stratification of surface water strengthened,reducing the overturning circulation and deep ocean ventilation in glacial periods,the degradation of organic materials consume the of oxygen,resulting in the oxygen deficit condition of deep water.In interglaciail periods,the southward shift of westerly wind and polar front promote the upwelling of CDW,result in the retreat of ice sheet and sea ice promote the subsiding of oxygen-rich surface water.The grain size and element geochemistry features can indicate the evolutionhistory of West Antarctic Ice Sheet since MIS9.Glacial ages such as MIS8c,MIS8a,MIS6 and MIS2 with coarse sediments have relatively high IRD,high Al₂O₃,K₂O and Zr concentration and low Na₂O/K₂O,K₂O/Al₂O₃ ratio,low W/Cu,U/Ta ratios indicating that the ice sheet expanded to the shelf break.Sediment compositions are controlled by the source area,including coastal rock of Marie Byrd Land and glacial sediment on the continental shelf.The interglacials such as MIS9,MIS7 and MIS5have relatively fine sediments,low IRD contents,high Na₂O/K₂O,K₂O/Al₂O₃ ratio,high W/Cu,U/Ta ratios indicating warm climate,limited sea ice and large-scale retreat of the ice sheet in the Amundsen Sea sector.Erosion of Marie Byrd Land coast andthe West Antarctic hinterland contributes highly to terrigenous detritus elemental composition.The coupled variation of grain size,element geochemistry features,paleoproductivity proxies and redox proxies reflects the response of the ice sheet,sea ice cover,biological pump and ocean circulation to climate change and indicating the results of interaction between ice and ocean in the Amundsen Sea sector.The light brown sediment in MIS8b with characteristics similar to interglacials indicate the high sensitivity of Amundsen sea sector.