Collaborative Research: Coring in the Southeast Indian and Southern Oceans to examine climate driven changes in watermass paleoventilation, sources, and structure

海洋中的二氧化碳是大气中二氧化碳的50倍。二氧化碳与大气的交换和二氧化碳在海洋中的储存是控制大气浓度的重要因素。在最近的冰河时期，大气中的二氧化碳浓度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。今天，南大洋的风驱动的海-气交换是这两个水库之间二氧化碳交换的主要机制之一。在最后一次冰期期间，海洋环流变化和由此引起的海洋化学变化导致的南大洋交换减少，被认为在封存海洋中的更多二氧化碳方面发挥了重要作用；然而，关于南大洋冰川海洋和大气环流的具体状态仍在争论中。目前的研究因缺乏来自关键地点的合适沉积岩芯而受到阻碍；现有的岩心集中在南大西洋和西南太平洋。这两个区域之间的水团的化学和环流明显发生了变化，但从南印度洋的关键区域获得的信息很少，目前大部分二氧化碳交换都发生在那里。在过去30年的研究中，该地区确实存在的为数不多的岩芯已经耗尽。在这项研究中，研究人员将在前往东南印度洋水域的邮轮上收集岩芯，并进行初步的岸基地层和环境分析。与澳大利亚科学家的合作将是这项工作不可或缺的一部分，这些核心将成为世界各地科学家的重要资源。该项目支持对研究生和博士后研究人员的培训。南印度洋中等深度(~500-1400米)水团的循环和通风是大气-海洋二氧化碳分配的核心。在冰川期间，温盐环流的变化和南大洋风力驱动的通风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和西南太平洋的古替代断面有很大不同，这导致了东南印度洋的过程对冰川二氧化碳交换产生了重大影响的想法。因此，这项工作将限制随着大气环流变化而变化的表面锋面位置，以及随海洋环流模式变化的深水团边界和特性。邮轮的目标是获得30-50个岩芯，以在澳大利亚以西和南部地区的东南印度洋亚南极和亚热带水域下面建立深度和纬度横断面。科学目标是确定将重建南大洋这一关键区域的水源和通风历史的替代物(如13C、18O、Nd同位素)的水平和垂直分布的时间演变。科学成果将产生：1)上一次冰川循环期间南大洋印度洋部分水团的第一个深度断面，以及2)地表水和深水属性的纬向断面。

Fifty times more CO2 resides in the ocean than the atmosphere. Exchange of CO2 with the atmosphere and the storage of CO2 in the ocean is an important control on atmospheric concentrations. During recent ice ages, atmospheric CO2 concentrations were naturally 30% lower than pre industrial levels. Extensive evidence indicates this reduction was caused by greater storage of CO2 in the ocean. Today, wind-driven air-sea exchange in the Southern Ocean is one of the primary mechanisms for CO2 exchange between these two reservoirs. During the last glacial interval, reduced exchange in the Southern Ocean driven by changes in ocean circulation and the resulting changes in ocean chemistry is believed to have played an important role in sequestering more CO2 in the ocean; however, there is ongoing debate about the specific state of glacial oceanic and atmospheric circulation in the Southern Ocean. Current studies are hampered by a lack of suitable sediment cores from key locations; existing cores are 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 is little information available from the critical region of the Southern Indian Ocean where much of the CO2 exchange occurs today. The few cores from this area that do exist have been exhausted over the past 30 years of research. In this study, researchers will collect cores on a cruise to Southeast Indian Ocean waters and conduct the initial shore-based stratigraphic and environmental analyses. Collaborations with Australian scientists will be an integral part of this work and these cores will be an important resource for scientists around the world. The project supports the training of both a graduate student and a postdoctoral researcher.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 work 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 cruise objective is to obtain 30-50 cores 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. The 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. The scientific outcomes will be to produce: 1) the first depth transect of water mass proxies in the Indian Ocean sector of the Southern Ocean over the last glacial cycle, and 2) a latitudinal transect of surface and deep water properties.