Diagnosing the origin of isotopically light carbon in the South Atlantic during the last deglaciation: An oceanic or geologic source?

在最近的地质历史中，大气二氧化碳的最大增幅发生在最后一次冰川消融期间(从20000年前到10000年前)。随着北半球大冰盖的融化，大气中的二氧化碳水平上升了约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完全解释。最近的冰芯结果表明，二氧化碳的上升与碳同位素的负漂移相吻合。在多个大洋盆地的表层和中层深度也出现了类似的碳同位素异常，但规模更大，表明这是一个海洋来源。记录到的最大变化发生在大西洋约1至2公里处，这表明该盆地中深处的过程在二氧化碳上升中发挥了关键作用。确定碳同位素信号的来源对于解开在最近地质历史中驱动大气二氧化碳变化的机制至关重要。该项目的主要目标是利用西南大西洋的数据来诊断冰川消融期间碳同位素异常的来源。研究小组将使用来自巴西边缘的高分辨率沉积物岩心的深度横断面来评估表层和深水信号的相对时间。该团队还将使用放射性碳和其他微化石的化学分析来推断碳同位素异常的来源。工作将集中在测试两个相互竞争的假说上，一个假说要求碳来自深海，另一个假说要求碳来自地质储藏库。这一结果可能会改变我们对气候系统的理解，因为它限制了碳同位素最低值的来源，从而限制了大气二氧化碳在冰川-间冰期时间尺度上变化的驱动因素。拟议工作对教育的更广泛影响包括一名研究生和两名本科生的参与，他们将从事独立研究项目，以补充该项目的总体目标。

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 the large Northern Hemisphere ice sheets 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 coincided with a negative carbon isotopic excursion. Similar although larger carbon isotope anomalies occurred at surface and intermediate depths in multiple ocean basins, pointing to an oceanic source. The largest documented changes occurred from ~1 to 2 km in the Atlantic, suggesting that processes at mid-depth in this basin played a key role in the CO2 rise. Identifying the origin of the carbon isotope signal is essential to unraveling the mechanisms that drove atmospheric CO2 variability in the recent geologic past. The primary goal of this project is to use data from the Southwest Atlantic to diagnose the source of the carbon isotope anomalies during the deglaciation. The researcher team will use a depth transect of high resolution sediment cores from the Brazil Margin to evaluate the relative timing of surface and deep water signals. The team will also use radiocarbon and other chemical analyses of microfossils to infer the origin of the carbon isotope anomaly. Work will focus on testing two competing hypotheses, one that calls for carbon originating from the abyssal ocean and the other that invokes carbon from a geological reservoir. The results could transform our understanding of the climate system by constraining the source of carbon isotopic minima and therefore the driver of atmospheric CO2 variability on glacial-interglacial timescales. The educational broader impacts of the proposed work include the participation of a graduate student and two undergraduates who will pursue independent research projects that complement the overall goals of the project.