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The last interglacial (LIG; Marine Isotope Substage 5e, similar to 127-117 ka) experienced globally warmer than modern temperatures; however, profound differences in regional climate occurred that are relevant to the assessment of future climate change scenarios. Tropical Atlantic sea surface temperature (SST) and hydrology are intrinsic to the spatiotemporal evolution of past and future climate. We present eight monthly resolved coral Sr/Ca and delta O-18 records (130-118 ka) to reconstruct mean western tropical Atlantic SST and seawater delta O-18 changes during the LIG. Cooler and fresher than modern surface waters are indicated for the middle of the LIG at similar to 126 ka. This was followed by a rapid transition to modern-like SSTs and salinities that characterized the remaining part of the LIG. Our results, which account for differences found among corals, proxies, and SST calibration uncertainties, agree with western tropical Atlantic sediment records. Together, they suggest that an oceanic regime existed that differed from today.

Plain Language Summary The last interglacial is a period of time that occurred approximately similar to 127 to 117 thousand years ago and experienced globally warmer than modern temperatures, similar to those predicted by computer simulations of future climate change. However, little is known about the temperature and hydrology of the tropical oceans at this time. We analyzed fossil Caribbean corals that lived between 130 and 118 thousand years ago and record within their structures the properties of the seawater they inhabited. From these we reconstructed snapshots of past mean sea surface temperatures and the changing influences of regional ocean currents. Surprisingly, we found cooler and fresher than modern surface waters occurred within the tropical Atlantic at similar to 126 thousand years ago, a time usually associated with peak global warming. These anomalous conditions were followed by a rapid transition to modern-like sea surface temperatures and salinities that went on to define the remaining part of the LIG until similar to 118 ka. Our results agree with other reconstructions of last interglacial climate derived from tropical Atlantic sediment records. Together, they suggest changes in ocean currents that transport waters into the Caribbean and we highlight the complementary use of widely different marine archives to assess past climate change.