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.

Automated summary

Changes in ocean carbon inventory are likely the main factor causing the decline in glacial atmospheric pCO2. By studying the western tropical Pacific, it was found that the size-normalized weight of planktonic foraminifera can be used to estimate the paleo-deep-water CO32- concentration. It was discovered that the deep-water CO32- concentration in this region has changed since approximately 1.4 million years ago, possibly due to a weakening of North Atlantic Deep Water. The glacial and interglacial deep-water CO32- concentrations showed a gradual decline, indicating an increase in DIC content in the deep Pacific.