Antarctic Intermediate Water Ventilation Through the Last Deglaciation Off Chile

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OCE-0751643One of the most important and unexplained observations of the climate transition from the Last Glacial Maximum into the Holocene is the abrupt rise in atmospheric CO2 content and coincident decrease in the atmosphere's radiocarbon (14C) content that began about 16,000 years ago. It has been hypothesized that these changes reflect a sudden change in deep ocean circulation because the ocean is a much larger reservoir of carbon than the atmosphere. The strongest evidence for a deep ocean-atmosphere connection comes from a study by Marchitto et al., (2007) that showed the radiocarbon content of fossil benthic foraminifera from Baja California decreased dramatically starting 16,000 years ago. They hypothesized these data reflect the transit of 'old' carbon from the deep Southern Ocean to the north Pacific. In this project, the PI will confirm these published results and test the hypothesis that the increase in deglacial atmospheric CO2 was due to outgasing of the deep Southern Ocean via Antarctic Intermediate Water by studying the radiocarbon content of fossil benthic and planktic foraminifera in a suite of sediment cores along a depth transect from the Chilean margin. Because this region is very close to the presumed Southern Ocean source of the old deep water, and the cores span a range of intermediate ocean water depths, they are ideal for testing the Baja California observations and hypotheses. The PI will develop oxygen isotope stratigraphies and chronologies for the Chilean core suite to identify the deglacial interval, and will measure radiocarbon in benthic foraminifera from the cores to define the depth range and the extent of the radiocarbon ventilation changes during the deglaciation. The results of this research will test an important component of the evolving theory to explain how the land, the sea and the atmosphere interacted during the deglaciation to alter global climate. Broader impacts will include fundamental research to help explain the mechanisms of past climate change, K-12 outreach and international mentoring of a Chilean postdoctoral fellow, Dr. Ricardo dePol Holz.