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Constraining Circulation Changes Through the Last Deglaciation with Deep-sea Coral Radiocarbon and Sedimentary 231Pa/230Th

Andrea Burke, Ph.D., 2012
Laura Robinson and Olivier Marchal, Advisors

Radioactive isotopes can be used for dating samples and as tracers of ocean processes.  I use radiocarbon and uranium-series isotopes to investigate the ocean’s role in climate change over the last deglaciation. I present a new method for rapid radiocarbon analyses as a means of age-screening deep-sea corals.  From this age survey, I selected forty corals from the Drake Passage and thirteen from Iceland and dated them with uranium-series isotopes, allowing radiocarbon to be used as a tracer.  The Drake Passage radiocarbon records show increased stratification in the Southern Ocean during the last glacial maximum (LGM) that disappeared during Heinrich Stadial 1 (HS1) as atmospheric CO2 began to rise. These records also show evidence for decreased air-sea gas exchange during the Bølling-Allerød coincident with a pause in the deglacial CO2rise. During this time period, the Iceland radiocarbon record shows similar ventilation to that observed today. To further investigate changes in North Atlantic ventilation over the last deglaciation, I used an inverse method to examine sedimentary 231Pa/230Th.  I found that published 231Pa/230Th data from the LGM and HS1 are consistent with the modern circulation, given the uncertainties in both the model and the spatial distribution of these nuclides.