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

海洋中的二氧化碳含量是大气中的50倍。二氧化碳与大气的交换以及二氧化碳在海洋中的储存是对大气浓度的重要控制。在最近的冰期，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储存增加造成的。今天，在南大洋，风驱动的海气交换是这两个储存库之间二氧化碳交换的主要机制之一。在末次冰期，由于海洋环流的变化以及由此引起的海洋化学变化，南大洋的交换减少被认为对在海洋中吸收更多的二氧化碳起了重要作用；然而，关于南大洋冰川海洋和大气环流的具体状态一直存在争论。目前的研究受到关键地点缺乏合适沉积物岩心的阻碍；现有的地核集中在南大西洋和西南太平洋。在这两个区域之间，水团的化学成分和循环明显发生了变化，但从南印度洋的关键区域获得的信息却很少，而今天大部分的二氧化碳交换都发生在那里。在过去30年的研究中，该地区少数几个确实存在的岩心已经耗尽。在这项研究中，研究人员将在前往东南印度洋水域的游轮上收集岩芯，并进行初步的岸基地层学和环境分析。与澳大利亚科学家的合作将是这项工作的一个组成部分，这些核心将成为世界各地科学家的重要资源。该项目支持培养一名研究生和一名博士后。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，这项工作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质量边界和性质。巡航的目标是获得30-50个核心，从澳大利亚西部和南部地区获得东南印度洋亚南极和亚热带水域的深度和纬度横断面。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。科学成果将产生：1)最后一个冰期旋回期间南大洋印度洋部分水团代用物的第一个深度样带，以及2)地表和深水性质的纬度样带。

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.