Abstract
The Mid‐Pleistocene Transition (MPT) is characterized by global cooling, an increase in ice volume, and a glacial‐interglacial cycle shift from 41 to 100 kyr without any significant change in insolation. Although the role of the Southern Ocean in driving the MPT has been proposed, only a few studies have been conducted in the Ross Sea sector of the Southern Ocean that span the MPT. In particular, our understanding of CaCO₃ variation in the Southern Ocean is limited due to its general absence in Antarctic sediments. We analyzed biogenic opal, CaCO₃, bulk δ15N, and grain size from two cores collected from the Ross Sea continental rise to reconstruct the paleoceanographic record during the Pleistocene including the MPT. We found a shift from diatom‐to CaCO3‐dominant deposition with stepwise increases in bulk δ15N values during the MPT. The pre‐MPT interval was characterized by high diatom productivity with no evidence of CaCO₃ preservation under nutrient‐enriched conditions. During the MPT diatom production decreased leading to improved CaCO₃ preservation due to enhanced stratification, as supported by increased bulk δ15N values and higher coccolith abundances. Further increases in bulk δ15N values indicate that stratification became even more enhanced after the MPT. Based on the foraminiferal fragmentation ratio, we infer that carbonate preservation in the Ross Sea sector of the Southern Ocean improved after the MPT, and that during the late Pleistocene, enhanced preservation extended to deeper water depths. Key Points The Pleistocene paleoceanographic history in the Ross Sea sector of the Southern Ocean was revealed A shift from diatom‐to CaCO₃‐dominant deposition occurred during the Mid‐Pleistocene Transition Carbonate preservation expanded to greater water depths in the Ross Sea sector during the late Pleistocene