Sea surface temperature changes in the southern California borderlands during the last glacial‐Interglacial cycle

A variety of evidence suggests that average sea surface temperatures (SSTs) during the last glacial maximum in the California Borderlands region were significantly colder than during the Holocene. Planktonic foraminiferal δ 18 O evidence and average SST estimates derived by the modern analog technique indicate that temperatures were 6°–10°C cooler during the last glacial relative to the present. The glacial plankton assemblage is dominated by the planktonic foraminifer Neogloboquadrina pachyderma (sinistral coiling) and the coccolith Coccolithus pelagicus , both of which are currently restricted to subpolar regions of the North Pacific. The glacial‐interglacial average SST change determined in this study is considerably larger than the 2°C change estimated by Climate: Long‐Range Investigation, Mapping, and Prediction (CLIMAP) [1981]. We propose that a strengthened California Current flow was associated with the advance of subpolar surface waters into the Borderlands region during the last glacial.