Western equatorial Pacific deep water carbonate chemistry during the Last Glacial Maximum and deglaciation: Using planktic foraminiferal Mg/Ca to reconstruct sea surface temperature and seafloor dissolution

We present a reconstruction of deep‐water carbonate saturation state (ΔCO 3 2− ) in the western equatorial Pacific for the Last Glacial Maximum (LGM) and deglaciation based on changes in the Mg/Ca ratio of planktic foraminifers with increased water depth. Our data suggest there have been changes in bottom water ΔCO 3 2− over the past 25,000 years at water depths as shallow as 1.6 km. The ΔCO 3 2− reconstruction for the LGM suggests ΔCO 3 2− was similar or slightly higher than modern values between 1.6 and 2.0 km, shifting sharply to lower values (an average ∼30 μ mol/kg lower) below 2.5 km. The shift in chemistry between 2.0 and 2.5 km supports a hypothesis that Pacific overturning circulation occurred deeper during the LGM with a slightly more ventilated water mass above 2.0 km. The data are not consistent with enhanced preservation in this region of the deep Pacific at depths greater than 2.5 km, suggesting that the long‐held view of better preservation throughout the glacial deep Pacific must be reevaluated. For the deglaciation, we have evidence of a ΔCO 3 2− maximum that suggests enhanced deglacial preservation between 1.6 and 4.0 km in comparison to the Holocene and the LGM. The deglacial ΔCO 3 2− was as much as 28 μ mol/kg higher than modern between 1.6 and 4.0 km. Results suggest carbonate burial rates were 1.5 times greater during the deglacial than the over the past 5 kyr.