A Brief Note on Supercooled Glacial Deep Waters

Abstract According to hydrographic profiles, approximately 2%–5% of the present‐day deep Southern Ocean contains supercooled waters that are below the freezing point. Which role these supercooled waters may have played under glacial conditions is an open question. To elucidate the variations and mechanisms of deep ocean supercooling in the past, we analyze a recently conducted quasi‐transient Earth system model simulation (CESM1.2), which covers the climate history of the past 3 million years. After the mid‐Pleistocene Transition (MPT, ∼1.2–0.75 million years ago, Ma), the simulation reveals the presence of substantial volumes of supercooled glacial intermediate and deep waters, primarily in the equatorial to northern Pacific. Our study examines the formation mechanisms of these waters in the subarctic North Pacific and their significance in shaping deep ocean stratification, with potential implications for glacial ocean carbon storage. We also address several modeling caveats, including the representation of surface sea ice only and the conservation of tracers in long‐term transient climate model simulations.