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 CO₂ rise. 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.