Collecting Deep-sea Corals from off of Tasmania to Measure the History of Southern Ocean Radiocarbon Concentrations

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In the Southern Ocean, Antarctic Intermediate Water (AAIW) and sub-Antarctic Mode Water (SAMW) set the properties of the base of the tropical thermocline, and therefore play an important role in the tropics' ability to alter global climate. Antarctic Bottom Water (AABW) fills much of the global abyssal depths, and is therefore the most important reservoir in measuring the ocean's ability to store and release CO2. For these reasons, the rate at which these water masses ventilate the intermediate and deep ocean is a key parameter in many theories of glacial-interglacial climate change, and rapid climate shifts. This proposal will constrain the Southern Ocean's history by collecting fossil deep-sea corals from south of Tasmania to then measure the past profiles of Delta14C, at ice core resolution. Radiocarbon is the crucial tracer because its inherent time information lets us constrain deep circulation rates. The waters south of Tasmania are known to contain abundant modern and fossil corals and the bathymetry of the region is well suited to find samples between 500 and 3,000 meters deep. In this project, I plan to conduct a a two-cruise sampling program; cruise 1 will map and survey the area with the CSIRO vessel Southern Surveyor and the Autonomous Benthic Explorer (ABE) from WHOI, cruise 2 will collect and characterize corals from the key locations identified in cruise 1 with a UNOLS vessel and the ROV Jason. The PI will archive all samples and make them available to all researchers who wish to work on them. A web-basedprogram of daily updates and background information geared towards middle school science students is planned for the cruises.