A brief note on Supercooled Glacial Deep Waters

According to hydrographic profiles, about 2-5% of the present deep Southern Ocean waters have temperatures 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 shows the presence of substantial volumes of supercooled glacial intermediate/deep waters primarily in the equatorial to northern Pacific. Our study explores the formation mechanisms of these waters in the subarctic North Pacific and their importance in creating deep ocean stratification with potential impacts on ocean carbon storage. We also address several modeling caveats in representing only surface sea ice in the present generation of climate models (not allowing for subsurface freezing) and in ensuring tracer conversation in longterm transient climate model simulations.