The California Current of the Last Glacial Maximum at 42oN: Reconstruction based on multiple proxies

Multiple paleoceanographic proxies in a zonal transect across the California Current near 42øN record modern and last glacial maximum (LGM) thermal and nutrient gradients. The offshore thermal gradient, derived from foraminiferal slx•ies assemblages and oxygen isotope data, was similar at the LGM to that at present (warmer offshore), but average temperatures were 3.3 ø +1.5øC colder. Observed gradients require that the sites remained under the southward flow of the California Current, and thus that the polar front remained north of 42øN during the LGM. Carbon isotopic and foraminiferal flux data suggests enhanced nutrients and productivity of foraminfera in the northern California Current up to 650 km offshore. In contrast, marine organic carbon and coastal diatom burial rates decreased uring the LGM. These seemingly contradictory esults are reconciled by model simulations of the LGM windfield, which suggest that wind stress curl at 42øN (and thus open-ocean upwelling) increased, while offshore Ekman transport (and thus coastal upwelling) decmasexl during the last ice age. The ecosystem of the northern California Current during the LGMapproximated that of the modern Gulf of Alaska. Cooling and production in this region was thus driven by stronger open-ocean upwelling and/or southward flow of high-latitude water masses, rather than by coastal upwelling.