Sedimentary Records Of Productivity And Deep-Sea Ventilation Since MIS 3 In The Ross Sea,Antarctic

The Southern Ocean,also known as the Antarctic Ocean,is an enormous body of water.It plays an important role in the global carbon cycle and climate change because it stores more heat and carbon dioxide(CO₂)and is more sensitive to global climate changes.The Ross Sea is the second largest marginal sea of the Southern Ocean and one source of global ocean deep water.The study of the paleoceanography and carbon cycle of this area,therefore is more effective to predict the future change of the atmospheric CO₂concentration and global climate.The subjects of this study include three box cores(BC008,BC010 and BC006)and one gravity core(GC16)which were collected from the continental slope and basin of the Ross Sea.These cores were selected to analyze the sedimentary dynamic environment,paleoproductivity,deep water ventilation and redox stability of the Ross Sea since MIS 3 and to verify it's influence on atmospheric CO₂ and the response to global climate change based on the dataset of sediment analyses,including AMS¹⁴C dating,oxygen and carbon isotope ratios of foraminifera,grain size,ice-rafted debris(IRD),TOC,TN and their isotopes(?¹³C_org,?¹⁵N_org),biogenic silica content and the XRF geochemical scanning data,and so on.The results show that the bottom current and sea ice activities are relatively active in the offshore of Ross Sea shelf since MIS 3,especially at about 29 ka BP and since14.0 ka BP.The source of organic matter is highly affected by terrigenous input which can be related to variations of ice-shelf activity and local temperature.The contribution of marine organic matter is slightly higher from 22.3 ka BP to deglaciation.Along with the rise of global temperature,ice shelf disintegration,and sea ice activity increasing,the organic matter is mainly terrestrial source.The characteristics of paleoproductivity changes are as follows:the biogenic components are well preserved and the productivity was high due to the relatively weak sedimentary dynamics during MIS 3 period.Since the Holocene,however,the productivity has been reduced due to strong sea ice cover and bottom current.In addition,during the deglaciation period,the deep-sea ventilation in the study area is steadiy enhanced and shows most severe at about 16 ka BP which probably contribute to the rise of atmospheric CO₂.The main trigger for this mechanism may be Pola seesaw effect,which leads to the uneven heat distribution between the north and south poles,and then result in the change of the intensity of the Atlantic Meridional Overturning Circulation(AMOC)and the position and intensity of the Southern Hemisphere Westerly Winds belt(SWW),and then drives the upwelling of the deep water in the Southern Ocean.The oxygen content of the bottom water in the Ross Sea is relatively low during the LGM period because the storage of remineralized carbon in the deep water is increasing.The oxidized bottom water condition are improved due to the strengthening of deep water ventilation during MIS 3,Heinrich-Stadial 1(HS 1)and Younger Dryas(YD).