欧洲南极冰芯的记录显示，过去80万年以来，冰期时期大气CO2浓度的最小值保持稳定，然而自42.5万年以来间冰期CO2浓度却明显增高，但是导致间冰期大气CO2浓度升高的原因目前尚不清楚。由于北大西洋的底层水碳酸根离子浓度与大气CO2的浓度变化密切相关，我们假设间冰期大气中二氧化碳浓度的峰值主要受冰消期深海释放的CO2量影响。为了验证我们的假设，拟选择T5（42.5万年）和T7（62.5万年）两个冰消期进行研究。T5和T7两个冰消期氧同位素都发生了大幅度变化，但是T7期大气二氧化碳浓度增加量显著偏低。本研究将利用北大西洋深层水获取的多个IODP/ODP岩芯为材料，通过底栖有孔虫B/Ca和Cd/Ca来重建T5和T7期北大西洋底层水碳酸根离子和营养盐的变化历史。本项目将有助于进一步了解深海在调控大气CO2浓度变化中的作用和意义。

A fundamental change in the atmospheric pCO2 concentration is observed at ~425 ka in the European Project for Ice Coring in Antarctica (EPICA) Dome C (EDC) ice core. The glacial pCO2 minima have remained almost identical for the last 800 ka; however, the interglacial pCO2 values have been markedly higher since 425 ka. What caused this shift in interglacial pCO2 levels is not yet clearly understood..It is here we hypothesize that the bottom water carbonate ion concentration of the North Atlantic varied in concert with the changes in atmospheric pCO2 and that peak concentration of atmospheric pCO2 during interglacials is determined by degassing of the oceans during glacial terminations. To test this hypothesis, a comparison will be made between changes in bottom water carbonate ion concentration associated with glacial terminations 5 (T5) and 7 (T7). Both terminations are characterized by large amplitude shifts in oxygen isotopes; however, T7 is accompanied by a much smaller increase in atmospheric pCO2. In the proposed study, we will address several specific hypotheses:.（1）During the cold glacial periods preceding T5 and T7, enhanced Antarctic Bottom Water /southern component water flow displaced the North Atlantic Deep Water, and thus lowered the bottom water [CO32-] and increased nutrient concentrations; this process reversed following glacial terminations to a warmer climate..（2）Changes in the North Atlantic bottom water carbonate ion concentrations during T5 and T7 were synchronous with pCO2, methane and temperature changes documented in the EDC ice core..（3）T5 was characterized by greater upwelling and hence greater CO2 release from the oceans than during T7, which was characterized by less CO2 ventilation from the deep ocean..This project will also extend the existing boron/calcium calibration database in benthic foraminifers to explore whether regions of the global deep ocean with low carbonate ion concentration, including the Southern Ocean, can be incorporated into the calibration equation. Existing deep-sea sediment samples from four North Atlantic sites bathed by either North Atlantic Deep Water or Antarctic Bottom Water will be used for the study.