Pinning down the sources contributing to the last interglacial (129 – 116 ka) sea-level highstand may be crucial to understanding the vulnerability of modern ice sheets to global warming. Today, ocean warming plays a direct role in sea level rise through thermal expansion and may play an indirect role in future sea level rise through basal melting and subsequent mass loss from the polar ice sheets.
Using the novel proxy of noble gas ratios measured in ice cores, we reconstruct mean ocean temperature (MOT) change during the penultimate deglaciation and last interglacial. We show that peak ocean temperatures were 1.1±0.3°C warmer than today, contributing 0.7±0.3m to thermosteric sea level. This MOT maximum occurred at the end of the termination, coincident with peak Antarctic temperature.
We suggest that most of this enhanced warming was related to a delay in the resumption of the Atlantic Meridional Overturning Circulation (AMOC) and a bipolar seesaw response in global temperature change across the penultimate deglaciation. We also hypothesize that the delayed AMOC recovery and early ocean warming triggered enhanced mass loss from Greenland and Antarctica in the early stages of the last interglacial.