Evolution And Mechanisms Of Productivity And Subsurface Hydrology In The Weddell Sea,Antarctica Since MIS 5

The Southern Ocean is of great significance to regulating global climate change,and the Antarctic Zone is the key place to modulate global thermohaline circulation and atmospheric carbon dioxide（p CO₂）.It is of great significance to uncover the mechanism about glacial-interglacial cycles of p CO₂ and the rules of hydrological evolution in Antarctic Zone.In this study,the core D5-12,which located in the northwestern Weddell Sea in the Antarctic Zone,was studied.The productivity of Weddell Sea（Antarctic Zone）since MIS 5 was reconstructed based on the biogenic opal content,and the subsurface water temperature and salinity were reconstructed through Mg/Ca ratio andδ¹⁸O measurement on planktic foraminifera subsurface species Neogloboquadrina.Pachyderma（sinistral）.Combing relevant paleoenvironment and paleoclimate records,the control mechanism and influence factors of the evolution of the subsurface water temperature and salinity and the productivity in Weddell Sea is analysed.And we further explored the relationship between productivity and atmospheric p CO₂,and the relationship between subsurface water evolution,ice sheet and ocean current evolution.The productivity evolution in the Weddell Sea since MIS 5 was reconstructed based on the biogenic opal content from sediment cores.The results indicated that the productivity in the Weddell Sea showed glacial-interglacial variations,with high productivity during warm periods（MIS 5 and 3）and low productivity during cold periods（MIS 4 and 2）,and a long-term decreasing trend was also observed.By combining our productivity records and those collected from other areas in the Southern Ocean,the mirror-image model of productivity evolution in the Antarctic and Subantarctic zones was confirmed.Furthermore,the comparison between the productivity records and potential environmental influence factors indicated that the meridional movement of Westerlies as well as the expansion and retreat of sea ice controlled the nutrient availability from deep water into surface,by influencing deep ventilation,and ultimately drove glacial-interglacial and long-term variations of productivity in the Weddell Sea since MIS 5.The sequestration and release of CO₂ due to variation of deep ventilation in the Weddell Sea probably contributed to the long-term trend and glacial-interglacial cycles of p CO_2-atm since MIS 5.Reconstruction of the subsurface hydrologic evolution of the Weddell Sea shows that the subsurface water temperature and salinity of the Weddell Sea are characterized by cycles of low values in ice age（MIS 4 and 2）and high values in interglacial age（MIS 3）.There is a strong consistency between the evolution of temperature and salinity,specifically manifested as an increase in salinity as the temperature increases and vice versa.Combined with other sea surface temperature（SST）records in the Southern Ocean,it is found that the subsurface water temperature of the Weddell Sea has a larger fluctuation than that of other SST records in glacial and interglacial cycles.By comparing subsurface water temperature and salinity of the with other potential environmental factors,it is found that the hydrological characteristics of the water mass are mainly controlled by the upwelling of the Circumpolar Current.The influence of subsurface water evolution on the record of deep water upwelling around the Antarctic zone and on the stability of the Antarctic ice sheet is further discussed.Our study confirms rationality of above hypothesis on the mechanism of atmospheric p CO₂ glacial-interglacial cycles in the Southern Ocean,and clarifies the influence of the subsurface water hydrological evolution of the Weddell Sea on the stability of Antarctic Ice Sheet,indicating that the Southern Ocean plays an important role in the global climate evolution.