The Atlantic's role in ice age inception and termination: Assessing carbon storage and release with new Brazil Margin profiles from MIS 2 to MIS 6

冰期-间冰期二氧化碳(CO2)循环的驱动因素仍然是古气候学领域中最重要的悬而未决的问题之一。大气中较低的二氧化碳水平对应着冰盖的扩张，而二氧化碳水平的上升是冰盖消退的主要驱动力。尽管长期以来，人们一直认为海洋-大气交换是二氧化碳水平的中介，但其根本机制仍然难以捉摸。在最后一次冰川盛期(LGM；约20,000年前)，大西洋深处的分层程度比今天更高，这可能加强了深渊的碳储存。如果早期冰期的特征是类似的模式，这将表明层化是深海碳储存的基础，因此也是冰川的基础。最近的研究还表明，在最后一次冰川消融期间，大西洋深层环流放缓，这可能导致表层海洋和大气中的碳积累。如果这一机制是冰盖消退的关键驱动力，那么在过去14万年的每一次冰川消融期间，都应该存在大西洋深层环流减弱的证据。该项目的主要目标是利用西南大西洋多个岩心的数据来评估上一次完整冰川周期期间海洋环流和碳储存的变化。利用大约1500米至4000米水深的沉积物岩心，这项研究将评估：1)大西洋经向翻转环流(AMOC)的强度，2)南大西洋水柱分层，3)它们与海洋碳储量的关系。通过分析底栖有孔虫贝壳中的碳和氧同位素比率，将重建AOC强度和水柱分层。碳储量将通过分析过去14万年关键冰期和间冰期期间底栖有孔虫中的硼与钙的比率(B/Ca)来评估。每个岩芯都将使用氧同位素地层学来确定年代，氧同位素地层学是古气候学领域的一种著名工具。拟议中的工作可能会改变我们对气候系统的理解，因为它将创建第一张跨越上一个完整冰川周期的大西洋深层环流和碳储存的综合图片。因此，这些结果将为理解长时间尺度上大气二氧化碳变异性的来源提供一个独特的框架。这些结果还应有助于更广泛的古气候界，因为它提供了内部一致的岩心深度横断面，可以使用超出当前项目范围的分析进行研究。这项拟议工作的教育影响包括康涅狄格大学的一名研究生和两名本科生参与。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The driver of glacial-interglacial carbon dioxide (CO2) cycles remains one of the most important unresolved questions in the field of paleoclimatology. Lower atmospheric CO2 levels correspond to ice sheet expansion, while rising CO2 levels are a primary driver of ice sheet retreat. Although it has long been assumed that ocean-atmosphere exchange mediates CO2 levels, the underlying mechanisms have remained elusive. During the Last Glacial Maximum (LGM; ~20,000 years ago), the deep Atlantic was more stratified than today, which likely enhanced carbon storage in the abyss. If earlier glacial intervals were characterized by a similar pattern, it would suggest that stratification is fundamental to deep ocean carbon storage and therefore glaciations. Recent studies also suggest the deep Atlantic circulation slowed during the last deglaciation, which may result in carbon accumulation in the surface ocean and atmosphere. If this mechanism is a key driver of ice sheet retreat, then evidence for a weaker deep Atlantic circulation should exist during each deglaciation of the last 140,000 years. The primary goal of this project is to use data from multiple cores in the Southwest Atlantic to assess changes in ocean circulation and carbon storage during the last full glacial cycle. Using sediment cores from approximately 1500 m to 4000 m water depth, the research will assess: 1) the strength of the Atlantic's meridional overturning circulation (AMOC), 2) water column stratification in the South Atlantic, and 3) their relation to oceanic carbon storage. AMOC strength and water column stratification will be reconstructed by analyzing carbon and oxygen isotopic ratios in the shells of benthic (bottom dwelling) foraminifera. Carbon storage will be assessed by analyzing the boron to calcium ratio (B/Ca) in benthic foraminifera during key glacial and interglacial intervals of the last 140,000 years. Each core will be dated using oxygen isotope stratigraphy, a well-known tool in the field of paleoclimatology.The proposed work could transform our understanding of the climate system by creating the first integrated picture of deep Atlantic circulation and carbon storage spanning the last full glacial cycle. The results will therefore provide a unique framework for understanding the source of atmospheric CO2 variability over long timescales. The results should also be useful to the broader paleoclimate community by providing an internally consistent depth transect of cores that can be studied using analyses beyond the scope of the current project. The educational impact of the proposed work includes the participation of a graduate student and two undergraduate students at the University of Connecticut.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.