Collaborative Research: Determining climate related changes in water mass structure, paleoventilation, and paleocirculation in the Southeast Indian and Southern Oceans

现代海洋的二氧化碳含量大约是大气的50倍，但科学家认为，在冰川时期，海洋的二氧化碳含量可能更高，导致大气中二氧化碳含量大幅减少。冰河时期大气中二氧化碳浓度的降低可能导致全球气温下降。大气-海洋的大部分二氧化碳交换发生在南大洋，并与海洋和大气环流过程有关。通过研究水团结构和化学特征，科学家们希望确定二氧化碳交换的关键控制因素，即水团从表面上升和下沉的位置，以及它们在更深的海洋中移动的途径。这项研究将建立年龄模型，并允许在以前从印度洋收集的一组独特的沉积物岩心之间建立详细的相关性。这些岩心跨越了一系列的深度和位置，将支持一个国际研究小组的相关努力，利用地球从最后一个冰川时代过渡到现代气候时沉积的沉积物中发现的各种化学示踪剂，研究和跟踪该地区重要的水团。这项工作为本科生提供研究机会，并支持博士后科学家的早期职业生涯。南印度洋中深度（~500 ~ 1400 m）水团的环流和通风是大气-海洋CO2分配的核心。在冰期，温盐环流和由风驱动的南大洋通风的变化被认为在隔绝大气CO2方面发挥了重要作用。要详细了解温盐翻转环流和风驱动通风的物理机制之间的相互作用，需要精确定义整个消冰过程中水团边界和性质的变化。利用沉积物岩心材料的垂直和水平样带是确定过去海洋结构变化的基础。已公布的冰川南大西洋古代用物样带与西南太平洋的差异很大，这导致了东南印度洋的过程对冰川CO2交换有重大影响的观点。因此，这项拟议的工作将在2018年CROCCA-2S巡航中获得的精选六套岩心中提供基础地层学（岩心重建两海海洋环流和二氧化碳）。这6个岩心被选中在澳大利亚西部和南部地区的东南印度洋亚南极和亚热带水域下创建深度和纬度横断面。临时多传感器岩心记录器和CaCO3数据表明，这些岩心地点之间存在连贯的冰川-间冰期地层。将主要通过浮游生物和底栖生物的δ18O分析，努力扩大这一初始地层。相关的努力将限制随着大气环流变化而变化的地表锋面位置，以及随着海洋环流模式而变化的深水团边界和性质。最终的科学目标是确定代用物（如13c、18O、Nd同位素）水平和垂直分布的时间演变，这些代用物将重建南大洋这一关键区域的水源和通气历史。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The modern oceans hold about fifty times more CO2 than the atmosphere, but scientists think this may have been even greater during glacial periods causing a significant reduction in the amount found in the atmosphere. Reduced atmospheric CO2 concentration during ice ages likely contributed to colder global temperatures. Much of the atmospheric-oceanic CO2 exchange takes place in the Southern Ocean and is associated with processes of oceanic and atmospheric circulation. By studying the water mass structure and chemical characteristics, scientists hope to define key controls over the exchange of CO2, namely where water masses rise and sink from the surface and the pathways they travel in the deeper ocean. This study will establish age models and allow detailed correlations between a unique set of sediment cores previously collected from the Indian Ocean. These cores span a range of depths and locations that will support associated efforts of an international team of researchers to study and track important water masses in the area using a variety of chemical tracers found in the sediments deposited as the Earth transitioned out of the last glacial ice age into the modern climate. This work provides undergraduate student research opportunities and supports an early career post-doctoral scientist.The circulation and ventilation of water masses at intermediate depths (~500-1400 m) in the Southern Indian Ocean are central to atmosphere-ocean CO2 partitioning. During glaciations, changes in both thermohaline circulation and wind-driven Southern Ocean ventilation are believed to have played an important role in sequestering atmospheric CO2. A detailed understanding of the interaction between the physical mechanisms of thermohaline overturning circulation and wind-driven ventilation requires precise definition of changes in water mass boundaries and properties across the deglaciation. The use of vertical and horizontal transects of sediment core material has been fundamental in identifying past variations in the structure of the ocean. Published transects of paleo-proxies in the glacial South Atlantic differ substantially from the Southwest Pacific, leading to the idea that processes in the Southeast Indian Ocean had a significant influence on glacial CO2 exchange. Consequently, this proposed work will provide foundational stratigraphy in a selected suite of six cores obtained on the CROCCA-2S cruise in 2018 (Coring to Reconstruct Ocean Circulation and Carbon-dioxide Across 2 Seas). These 6 cores have been selected to create depth and latitudinal transects underlying both subantarctic and subtropical waters in the Southeast Indian Ocean from a region west and south of Australia. Provisional multi-sensor core logger and CaCO3 data suggest coherent glacial-interglacial stratigraphies between these core sites. Efforts will concentrate on expanding this initial stratigraphy, principally via planktonic and benthic δ18O analyses. Associated efforts will constrain surface frontal locations that shift in response to changes in atmospheric circulation, as well as deep water mass boundaries and properties that vary with ocean circulation patterns. The ultimate scientific objective is to determine the temporal evolution of the horizontal and vertical distribution of proxies (e.g.13C, 18O, Nd isotopes) that will reconstruct the water source and ventilation history of this critical region of the Southern Ocean.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.