Abstract
A decrease in atmospheric CO2 partial pressure(pCO2)is considered an important prerequisite for the onset and intensification of Northern Hemisphere Glaciation(NHG).However,how the ocean sequestered missing CO2 during the NHG is still uncertain.Changes in surface productivity and deep ventilation in the Southern Ocean(SO)have been proposed to explain the variations in atmospheric pCO2 over the last eight glacial cycles,but it is unclear whether these mechanisms contributed to the decrease in atmospheric pCO2 during the NHG.Using titanium-normalized contents and mass accumu-lation rates of biogenic opal and total organic carbon from the International Ocean Discovery Program(IODP)Expedition 374 Site U1524A,we reconstruct the productivity in the Ross Sea,Antarctica,from 3.3 Ma to 2.4 Ma.The productivity records exhibit a long-term decreasing trend and several distinct phased evolutionary features.Specifically,the local productivity fluctuated dramatically during 3.3-3.0 Ma,decreased gradually during 3.0-2.6 Ma,and remained relatively constant during 2.6-2.4 Ma.By comparing productivity with its potential influences,we infer that the phased and long-term evolutions of productivity were mainly controlled by changes in deep ocean ventilation.Sea ice expansion might have decreased productivity during 3.3-3.0 Ma by light attenuation.Changes in eolian dust input have little effect on productivity.Further analysis revealed no coupling linkage between productivity and atmospheric pCO2,indicating that the productivity in the SO Antarctic Zone(AZ)was not the main factor controlling the atmospheric CO2 decrease during the NHG.To improve our understanding of the role of SO processes in the NHG,further studies should focus on the potential influences of deep ocean ventilation on atmospheric pCO2 in the AZ,and similar studies should also be extended to the sea area in the Subantarctic Zone.
基金项目
National Natural Science Foundation of China(42076232 &42006075)
Impact and Response of Antarctic Seas to Climate Change Program(IRASCC2020-2022-01-03-02)
Taishan Scholars Projects Funding(TS20190963 & TSQN202211265)
万方数据