Collapse of the California Current during glacial maxima linked to climatechange on land

Time series of alkenone unsaturation indices gathered along the California margin reveal Large (4 degrees to 8 degreesC) glacial-interglacial changes in sea surface temperature (SST) over the past 550,000 years. Interglacial times with SSTs equal to or exceeding that of the Holocene contain peak abu ndances in the pollen of redwood, the distinctive component of the temperat e rainforest of the northwest coast of California. In the region now domina ted by the California Current, SSTs warmed 10,000 to 15,000 years in advanc e of deglaciation at each of the past five glacial maxima. SSTs did not ris e in advance of deglaciation south of the modern California Current front. Glacial warming along the California margin therefore is a regional signal of the weakening of the California Current during times when large ice shee ts reorganized wind systems over the North Pacific. Both the timing and mag nitude of the SST estimates suggest that the Devils Hole (Nevada) calcite r ecord represents regional but not global paleotemperatures, and hence does not pose a fundamental challenge to the orbital ("Milankovitch") theory of the Ice Ages.