Biomarker temperature estimates for modern and last glacial surface waters of the California Current System between 33° and 42°N

Abstract

Sea surface temperature (SST) estimates were made using data for C37‐39 alkenones analyzed in modern and glacial‐age intervals of sediment cores collected along an east‐west (∼42°N from 125° to 132°W) and a north‐south (41°–33°N) transect of the California Current system (CCS). The prymnesiophyte biomarker results suggest that surface waters warmed significantly throughout this region since the last glacial maximum (LGM) but the magnitude of warming varied spatially. Stratigraphic profiles from four sediment cores along the north‐south transect indicate the warming period was confined to the glacial/interglacial transition (15‐10 ka), with SST reaching a maximum value at ∼10 ka and maintaining a uniformly high value throughout the Holocene. Comparison of estimates derived from analysis of modern and LGM sediment intervals indicates the magnitude of the SST change was minimal for locations south of about 36°N (≤1°–2°C) and increased significantly (3°–5°C) north of this latitude. Using a simple heat balance model, we calculate from the latitudinal gradient in SST that southward flow in the California Current system during the LGM was about 60% of that measured today at 36°N. Our findings support the conclusion of others based on pollen data that coastal upwelling in the region of the northeast Pacific off northern California was significantly reduced or even completely shutdown during the LGM.