Cool surface waters of the subtropical North Pacific Ocean during the last glacial

One of the most controversial results of the CLIMAP12 project's reconstruction of past sea surface temperature (SST) is that large areas of the subtropical Pacific Ocean were warmer during the last glacial period than they are today. This finding has important implications because SST patterns at low to subtropical latitudes strongly influence climate, and SST changes are closely linked with climate fluctuations3,4,5. Until now, a lack of well-preserved, high-resolution marine sediment cores from the region has hindered efforts to confirm these unexpectedly high ice-age SST estimates. Here we use both the oxygen-isotope compositions and species assemblages of planktonic foraminifera in a shallow-water core with high deposition rates near Hawaii to estimate glacial SST of the subtropical North Pacific Ocean. Contrary to the CLIMAP results2, our data indicate that the annual average SST in this region was ∼2 °C cooler during the last glaciation than it is today. These results help to reconcile the marine SST record with inferences drawn from snowline depressions on Hawaii during the last glacial3,6, and should ultimately yield improved estimates of global climate sensitivity by providing important new constraints on climate model simulations of ice-age cycles.