The Mid-Pleistocene Transition (MPT) marks a critical shift in Earth's climate system, and its underlying causes remain a topic of ongoing research. Existing evidence suggests that decreasing glacial atmospheric pCO₂ played a role in driving the MPT. Although such CO₂ is often considered to be sequestered in the deep ocean, there is no quantitative estimate of deep-ocean carbon storage on a global scale, primarily due to a lack of constraint from the Indian and Southern Ocean. Here, we analyze the B/Ca ratios of the benthic foraminifera Cibicidoides wuellerstorfi for estimating paleo-deep-water Δ[CO₃²⁻] in the Indian Ocean. Using samples from IODP Site U1482/1483 that correspond to glacial and interglacial peaks, we present the first DIC record in the Indian Ocean across the MPT. The implications for the evolution of the global ocean carbonate system across the MPT as well as the whole-ocean-atmosphere-lithosphere carbon budget will also be discussed.

DIC,Indian Ocean,MPT