Late Holocene Sea temperatures along the central California coast

Mussel shells from central California coastal archaeological sites record c hanges in sea surface temperatures in the past 2000 years. Water temperatur es, inferred from oxygen isotopes in the shells, were about 1 degrees C coo ler than present and stable between 2000 and 700 yr ago. Between about 700 and 500 yr ago, seasonal variation was greater than present, with extremes above and below historic levels. Water temperatures were 2-3 degrees C cool er than today 500-300 yr ago. The interval of variable sea temperatures 700 -500 yr ago partially coincided with an interval of drought throughout cent ral California. A coincident disruption in human settlement along the coast suggests movements of people related to declining water sources. Quantitie s of fish bone in central coast middens dating to this same period are high relative to other periods, and the remains of northern anchovies, a specie s sensitive to changing oceanographic conditions, are also abundant. The co ntinued use of local fisheries suggests that changes in settlement and diet were influenced more by drought than by a decrease in marine productivity, as fish provided a staple during an interval of low terrestrial productivi ty. (C) 1999 University of Washington.