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

今天，海洋中的二氧化碳是大气中二氧化碳的50倍。因此，海洋和大气之间的二氧化碳交换是控制大气浓度的重要因素。在最近的冰河时期，大气中的二氧化碳自然比工业化前的水平低30%。大量证据表明，这种减少是由于海洋中二氧化碳的储存增加所致。人们普遍认为，在上一次冰川期间，海洋环流的变化以及由此产生的海洋化学变化，在海洋中储存更多二氧化碳方面发挥了重要作用。然而，关于南大洋冰川环流的具体状况仍在争论中。此前的研究主要集中在南大西洋和西南太平洋。这两个区域之间的水团化学和环流明显发生了变化，但南印度洋关键区域的信息仍然很少。这就是今天大部分二氧化碳交换发生的地方。该项目的工作将集中在最近一次前往东南印度洋水域的邮轮上收集的岩芯。这些岩心提供了来自关键地点和海洋深度的新材料，这些材料是填补这一知识空白所需的。这些样品将被分析碳、氧和钕的同位素，以确定水团和通风历史。该研究小组最近完成的初步分析构成了这项工作的基础，这项工作旨在确定深海环流和二氧化碳封存的变化。与澳大利亚和英国科学家的合作是这项工作不可或缺的一部分，因为这些核心预计将成为世界各地科学家的重要资源。这项工作还将支持本科生和研究生，以及博士后研究人员。南印度洋中等深度(~500-1400米)水团的环流和通风是大气和海洋之间二氧化碳分配的核心。在冰川期间，温盐环流和南大洋风驱动的通风的变化被认为在隔离大气二氧化碳方面发挥了重要作用。要详细了解温盐翻转环流的物理机制和风力驱动的通风之间的相互作用，就需要准确地定义整个消冰期的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横断面是确定海洋结构过去变化的基本方法。已公布的冰川南大西洋与西南太平洋的古替代断面有很大不同，表明东南印度洋的过程对冰川二氧化碳交换产生了重大影响。因此，这项拟议的工作将侧重于在2018年CROCCA-2S巡航中获得的一套选定的六个岩芯(用于重建两大洋的海洋环流和二氧化碳的岩心)。这6个岩芯被选为在澳大利亚以西和南部的东南印度洋亚南极和亚热带水域下面创建深度和纬度横断面。我们的18O地层学表明，这些核心地点之间存在持续的沉积和连贯的冰川-间冰期信号。工作将集中于限制随着大气环流变化而变化的表面锋面位置，以及随经向翻转环流模式变化而变化的深水团边界和性质。最终的科学目标是确定将用于重建南大洋这一关键区域的水源(例如18O和ND同位素)和通风历史(例如13C)的替代物的水平和垂直分布的时间演变。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。

Today fifty times more CO2 resides in the ocean than the atmosphere. Consequently, exchange of CO2 between the ocean and atmosphere is an important control on atmospheric concentrations. During recent ice ages, atmospheric CO2 was naturally 30% lower than pre-industrial levels. Extensive evidence indicates this reduction was caused by greater storage of CO2 in the ocean. During the last glacial interval, changes in ocean circulation, and the resulting changes in ocean chemistry, are widely believed to have played an important role in storing more CO2 in the ocean. However, there is ongoing debate about the specific state of glacial circulation in the Southern Ocean. Previous studies have largely concentrated in the South Atlantic and Southwestern Pacific. There are clearly changes in the chemistry and circulation of water masses between these two regions, but there remains little information from the critical region of the Southern Indian Ocean. This is where much of the CO2 exchange occurs today. Work for this project will focus on cores collected during a recent cruise to Southeast Indian Ocean waters. These cores provide new material from key locations and ocean depths that are needed to fill this knowledge gap. The samples will be analyzed for isotopes of carbon, oxygen, and neodymium to determine water mass and ventilation histories. Initial analyses recently completed by this research group form the foundation for this work that seeks to determine changes in deep ocean circulation and CO2 sequestration. Collaborations with Australian and British scientists is an integral part of this work as these cores are expected to be an important resource for scientists around the world. This work will also support undergraduate and graduate students, and postdoctoral researchers.The circulation and ventilation of water masses at intermediate depths (~500-1400 m) in the Southern Indian Ocean are central to CO2 partitioning between the atmosphere and ocean. During glaciations, changes in both thermohaline circulation and wind-driven Southern Ocean ventilation are believed to have played important roles 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, suggesting that processes in the Southeast Indian Ocean had a significant influence on glacial CO2 exchange. Consequently, this proposed work will focus on 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. Our 18O stratigraphies suggest continuous sedimentation and coherent glacial-interglacial signals between these core sites. Efforts will concentrate on constraining surface frontal locations that shift in response to changes in atmospheric circulation, as well as deep water mass boundaries and properties that vary with changes in meridional overturning circulation patterns. The ultimate scientific objective is to determine the temporal evolution of the horizontal and vertical distribution of proxies that will be used to reconstruct water sources (e.g. 18O and Nd isotopes) and the ventilation history (e.g.13C) in 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.