THE CALIFORNIA CURRENT OF THE LAST GLACIAL MAXIMUM - RECONSTRUCTION AT 42-DEGREES-N BASED ON MULTIPLE PROXIES

Multiple paleoceanographic proxies in a zonal transect across the Cali fornia Current near 42 degrees N record modem and last glacial maximum (LGM) thermal and nutrient gradients. The offshore thermal gradient, derived from foraminiferal species assemblages and oxygen isotope data , was similar at the LGM to that at present (warmer offshore), but ave rage temperatures were 3.3 degrees +/-1.5 degrees C colder. Observed g radients require that the sites remained under the southward flow of t he California Current, and thus that the polar front remained north of 42 degrees N during the LGM. Carbon isotopic and foraminiferal flux d ata suggests enhanced nutrients and productivity of foraminfera in the northern California Current up to 650 km offshore. In contrast, marin e organic carbon and coastal diatom burial rates decreased during the LGM. These seemingly contradictory results are reconciled by model sim ulations of the LGM wind- field, which suggest that wind stress curl a t 42 degrees N (and thus open-ocean upwelling) increased, while offsho re Ekman transport (and thus coastal upwelling) decreased during the l ast ice age. The ecosystem of the northern California Current during t he LGM approximated that of the modem Gulf of Alaska. Cooling anti pro duction in this legion was thus driven by stronger open-ocean upwellin g and/or southward flow of high-latitude water masses, rather than by coastal upwelling.