EASTERN EQUATORIAL PACIFIC GLACIAL-INTERGLACIAL BOTTOM WATER CHEMISTRY CHANGES RECORDED IN FORAMINIFERAL U/CA

During the last glacial-interglacial transition two pulses of increasing atmospheric CO₂ concentrations are recorded in ice cores. These pulses correspond to synchronous decreases in atmospheric Δ¹⁴C recorded in a Bahamian speleothem (Beck et al., 2001) and in surface ocean Δ¹⁴C recorded in corals from offshore Barbados (Fairbanks et al., 2005) and foraminifera from annually layered Cariaco basin sediments (Hughen et al., 2000). Release of a deep ocean ¹⁴C-deplete, respired-carbon reservoir to the surface ocean and atmosphere during the last deglaciation has been cited as a likely mechanism for corresponding increases in atmospheric CO² concentrations (Broecker and Barker, 2007). An increase in glacial deep-water respired carbon storage would result in a shift of DIC speciation towards lower carbonate ion concentrations along with deoxygenation of bottom waters. Trace element analyses of uranium are a valuable tool for constraining past bottom water chemistry. The U/Ca ratio recorded within benthic foraminiferal calcite has been indicated to be negatively correlated to the carbonate saturation state of the waters in which they formed their shells (Raizsch et al., 2011; Keul et al., 2013). Additionally, the U/Ca ratio of the authigenic coating precipitated onto foraminiferal shells reflects the redox state of the sediments with precipitation of uranium occurring during reducing conditions (Boiteau et al., 2012). This study reconstructs changes in past deep-water carbonate ion saturation and redox state in the Eastern Equatorial Pacific over the last 30,000 years through the development of foraminiferal U/Ca and authigenic uranium records.