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

Abstract

AbstractChanges in ocean carbon inventory are considered the likely primary driver of declining glacial atmospheric pCO2 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 Δ[CO32−]. Then, we apply this approach to reconstruct deep‐water Δ[CO32−] in the western tropical Pacific since ∼1.4 Ma. At ∼1.0–0.9 Ma, a rapid weakening of North Atlantic Deep Water (NADW) resulted in a transient increase of ∼10 μmol kg−1 in deep‐water Δ[CO32−], after which deep‐water Δ[CO32−] declined at ∼0.9–0.7 Ma. Glacial and interglacial deep‐water Δ[CO32−] reveals stepwise declines of about 7 and 10 μmol 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.