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Reconstructing Deglacial Ocean Ventilation Using Radiocarbon: Data and Inverse Modeling

Ning Zhao, Ph.D., 2017
Lloyd Keigwin, Advisor

Significant changes occurred during the last deglaciation (roughly 10-20 thousand years before present) throughout the climate system. The ocean is a large reservoir of carbon and heat, however, its role during the deglaciation is still not well understood. In this thesis, I rely on radiocarbon measurements on fossil biogenic carbonates from seafloor samples to constrain deglacial ocean ventilation rates. First, new marine 14C records from sites in the eastern tropical Pacific and the western North Atlantic show that the deglacial ocean ventilation was not very different than today. Then I produce an extensive compilation of deep water 14C data, and combine these data with a box model in order to test their consistency with modern rates of basin-scale ocean ventilation. Overall, this thesis suggests that, although deep ocean ventilation may have varied at some locations during the last deglaciation, the occurrence of basin-scale ventilation changes are much more difficult to be put on a firm footing. An imbalance between cosmogenic production and radioactive decay appears as the most natural explanation for the deglacial 14C activity decline observed in both the atmosphere and the deep ocean.