Glacial-Interglacial Carbon Reorganization and Carbonate Compensation in the Pacific Ocean (PI: T. Marchitto)
Past variations in the dissolution and preservation of seafloor calcium carbonate (CaCO3) offer fundamental insights into the workings of the global carbon cycle and the controls on atmospheric carbon dioxide (CO2) levels. According to the 'CaCO3 compensation' hypothesis, there was a net shift of CO2 from the upper ocean into the deep ocean during the last glacial period, resulting in seafloor dissolution of CaCO3 and an increase in whole-ocean pH that compounded the glacial atmospheric CO2 drop. This project will quantitatively test several aspects of the CaCO3 compensation hypothesis, building upon preliminary foraminiferal trace metal and shell weight work in the deep eastern equatorial Pacific (EEP). The project will be divided into the testing of four main hypotheses: (1) carbonate chemistry in the EEP was tightly coupled to atmospheric CO2 over the last glacial-interglacial cycle, with transient carbonate ion [CO3] minima during CO2 drops and [CO3] maxima during CO2 rises; (2) the magnitudes of the Termination I and II (deglacial) [CO3] spikes were roughly equivalent at ~30 umol/kg; (3) [CO3] rises during glacial terminations were associated with the release of CO2 from the deep ocean into the upper ocean, recorded by the carbon isotopic composition (d13C) of benthic and planktonic foraminifera; and (4) regrowth of forests following deglaciation produced secondary [CO3] spikes after Terminations I and II. This work promises to contribute significantly to the understanding of the ocean's role in atmospheric CO2 cycles. Society may ultimately benefit from such knowledge if the oceans hold any hope for sequestration of anthropogenic CO2; or if future increases in CO2 uptake by the oceans impact deep sea carbonate chemistry, resulting in feedbacks on atmospheric CO2. This project will provide extensive learning and training experiences for a new PhD student, a geology undergraduate student, and a professional research assistant.
