Sustained Deep Pacific Carbon Storage After the Mid‐Pleistocene Transition Linked to Enhanced Southern Ocean Stratification

Changes in ocean carbon inventory are considered the likely primary driver of declining glacial atmospheric pCO(2) through the Mid-Pleistocene Transition (MPT). Here, we present global core-top calibrations of the "size-normalized weight" (SNW) of planktonic foraminifera for estimating paleo-deep-water Delta[CO32-]. Then, we apply this approach to reconstruct deep-water Delta[CO32-] in the western tropical Pacific since similar to 1.4 Ma. At similar to 1.0-0.9 Ma, a rapid weakening of North Atlantic Deep Water (NADW) resulted in a transient increase of similar to 10 mu mol kg(-1) in deep-water Delta[CO32-], after which deep-water Delta[CO32-] declined at similar to 0.9-0.7 Ma. Glacial and interglacial deep-water Delta[CO32-] reveals stepwise declines of about 7 and 10 mu mol kg(-1), respectively, after MIS 20 (0.79-0.81 Ma) and MIS 19 (0.76-0.79 Ma), reflecting increased DIC content in the deep Pacific. We infer that a sustained increase in deep Pacific carbon storage following the MPT was linked to enhanced oceanic stratification and greater influence of CO2-rich Southern Ocean-sourced waters.