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Warmer than present Antarctic and Southern Ocean temperatures during the last interglacial, approximately 128,000 years ago, have been attributed to changes in north-south ocean heat transport, causing opposing hemispheric temperature anomalies. We investigate the magnitude of Antarctic warming and Antarctic ice core isotopic enrichment in response to Northern Hemisphere meltwater input during the early last interglacial. A 1,600-year HadCM3 simulation driven by 0.25 Sv of meltwater input reproduces 50-60% of the peak Southern Ocean summer sea surface temperature anomaly, sea ice retreat, and ice core isotope enrichment. We also find a robust increase in the proportion of cold season precipitation during the last interglacial, leading to lower isotopic values at the Antarctic ice core sites. These results suggest that a HadCM3 simulation including 0.25 Sv for 3,000-4,000 years would reconcile the last interglacial observations, providing a potential solution for the last interglacial missing heat problem.

Plain Language Summary The Antarctic isotope and temperature maximum, which occurred approximately 128,000 years Before Present (yBP) during the warmer than present last interglacial period, is hypothesized to have resulted from a slowdown in northward ocean heat transport due to ice sheet melting into the North Atlantic-a mechanism known as the bipolar seesaw. We test this hypothesis by running and analyzing long, fully coupled, isotope-enabled climate model simulations, which include meltwater entering the North Atlantic, for this critical period 128,000 yBP. Results are evaluated against ocean and ice core data. After 1,600 years, we simulate 55% of the peak Southern Ocean summer sea surface temperature anomaly, 50% of the estimated winter sea ice retreat, and 60% of the ice core isotope enrichment reconstructed during the early last interglacial Antarctic climate optimum.