Millennial-scale atmospheric CO2 variability during the last deglaciation: Testing the biological pump hypothesis using upper ocean carbon isotope records

在最近的地质历史中，大气中二氧化碳的最大增加发生在最后一次冰川消融期间（从2万年前到1万年前）。随着北半球冰盖的融化，大气中的二氧化碳含量上升了约30%。尽管进行了广泛的研究，但二氧化碳变化的根本原因尚未得到充分解释。最近的冰芯结果表明，CO2的上升可以追溯到同位素轻碳源（即低13C/12C比的碳）。一个可能的原因是海洋光合作用减少，这将导致海洋表面和大气中轻碳的积累。更少的光合作用也会减少低13C/12C碳的数量，这些碳以有机物的形式从海洋表面落到中等深度。因此，降低的海洋生物生产力应该在表层和中间深度产生相反的碳同位素信号，表层海洋变得同位素较轻（低13C/12C），而中间深度变得较重（高13C/12C）。这项工作的结果可以通过限制碳同位素信号的来源，从而改变我们对气候系统的理解，从而改变上次冰川消融期间大气二氧化碳变化的驱动因素。提议的工作的更广泛的教育影响包括研究生和康涅狄格大学的本科生的参与。该项目的主要目标是利用来自多个地点的数据来评估最后一次冰川消融期间海洋光合作用的变化。研究小组将使用来自五个不同地点的高分辨率沉积物岩心，包括西南大西洋、东南大西洋、南大洋、西南太平洋和东部热带太平洋。每个岩心都是从中间（~1000 m）深度提取的，这应该对通过水柱的有机物量很敏感。研究小组将通过分析底栖生物（海底生物）和浮游生物（海洋表层生物）化石中的碳同位素比例来评估光合作用的变化。研究小组还将分析底栖生物化石中硼与钙的比例，以推断中等水深下碳浓度的总体变化。

The largest increase in atmospheric CO2 in the recent geologic past occurred during the last deglaciation (from 20,000 to 10,000 years ago). As ice sheets in the Northern Hemisphere melted, atmospheric CO2 levels rose by ~30%. Despite extensive research, the underlying cause of the CO2 change has yet to be fully explained. Recent ice core results show that the CO2 rise can be traced to an isotopically light carbon source (i.e. carbon with a low 13C/12C ratio). One possible cause is reduced marine photosynthesis, which would result in the accumulation of light carbon in the surface ocean and atmosphere. Less photosynthesis would also reduce the amount of low 13C/12C carbon that falls from the surface ocean to intermediate depths in the form of organic matter. Thus, reduced marine biological productivity should yield opposing carbon isotopic signals at surface and intermediate depths, with the surface ocean becoming isotopically lighter (lower 13C/12C) and intermediate depths becoming heavier (higher 13C/12C). The results of this work could transform our understanding of the climate system by constraining the source of carbon isotopic signals and therefore the driver of atmospheric CO2 variability during the last deglaciation. The broader educational impact of the proposed work includes the participation of a graduate student and an undergraduate at the University of Connecticut.The primary goal of this project is to use data from multiple locations to assess changes in marine photosynthesis during the last deglaciation. The research team will use high resolution sediment cores from five different locations, including the Southwest Atlantic, the Southeast Atlantic, the Southern Ocean, and Southwest Pacific, and the eastern tropical Pacific. Each core was retrieved from intermediate (~1000 m) depths that should be sensitive to the amount of organic matter falling through the water column. The team will assess variations in photosynthesis by analyzing the carbon isotopic ratio in the fossils of benthic (sea floor dwelling) and planktonic (surface ocean dwelling) organisms. The team will also analyze the ratio of boron to calcium in the benthic fossils to infer overall changes in carbon concentration at intermediate water depths.