Increase in Deglacial Ocean Heat Content Linked to Contrasts in Extratropical Warming

Proxy-based reconstructions suggest that equilibrium changes in global mean sea surface temperature (ΔGMSST) are nearly equivalent to changes in mean ocean temperature (ΔMOT) on glacial-interglacial timescales over the past 900,000 years. However, the underlying mechanisms responsible for this relationship remain poorly understood. Here we use simulations from Paleoclimate Modeling Intercomparison Project Phase 3 and 4 (PMIP3/4) to investigate equilibrium ΔMOT and its linkage to sea surface temperature changes between the Last Glacial Maximum (LGM, ∼21,000 years ago) and pre-Industrial. Results show that PMIP3/4 simulations generally underestimate proxy-based ΔMOT. Regression analysis reveals that LGM MOT is strongly modulated by mid-latitude SST cooling, with the Southern Ocean having a greater influence compared to other oceanic regions, thus helping explain why models with similar ΔGMSSTs exhibit significantly different ΔMOTs. Additionally, we find a strong relationship between simulated Antarctic sea-ice coverage and Southern Ocean SST changes, with implications for constraining sea-ice reconstructions.