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

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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.