Sea-surface temperature estimates in the Southeast Pacific based on planktonic foraminiferal species; modern calibration and Last Glacial Maximum

Estimates of sea-surface temperatures based on foraminiferal faunal species suggest that the Eastern Equatorial Pacific Ocean was 3–5°C cooler during the Last Glacial Maximum (LGM) than at present. Analysis of new cores from the Southeast Pacific reveals a likely source of ice-age cooling in variations of the Peru Current. Off southern Peru, LGM ocean temperatures were 6–8°C cooler than at present, consistent with substantial cooling on land inferred from regional glacier advances and ice-core data. In the Southeast Pacific, ice-age foraminiferal assemblages have good modern analogs, and transfer functions that define assemblages based on ancient samples yield results similar to those based on coretop samples. During the LGM, subpolar species dominate the Eastern Boundary Current off Peru and extend to the equator. In contrast, the range of the equatorial upwelling species remains roughly constant. We infer from these data and a heat budget model that equatorward advection of cool water, more than equatorial upwelling, drove LGM cooling of the Eastern Tropical Pacific Ocean.