Di Lorenzo, E., A. J. Miller, N. Schneider and J. C. McWilliams, 2005:

The warming of the California Current: Dynamics and ecosystem implications.

Journal of Physical Oceanography,35, 336-362.

Abstract. The long-term changes in the observed temperature and salinity along the Southern California coast are studied using a four dimensional space-time analysis of the 52 year (1949-2000) California Cooperative Oceanic Fisheries Investigations (CalCOFI) hydrography combined with a sensitivity analysis of an eddy permitting primitive equation ocean model under various forcing scenarios. A warming trend in temperature and a deepening trend in the depth of the mean thermocline between 1950 and 1998 are found to be primarily forced by large-scale decadal fluctuations in surface heat fluxes combined with horizontal advection by the mean currents. After 1998 the surface heat fluxes suggest the beginning of a period of cooling, which is consistent with colder observed ocean temperatures. Salinity changes are decoupled from temperature and are primarily controlled by horizontal advection by anomalous currents. A cooling trend in SST is driven in the ocean model by the 50 year NCEP wind reanalysis, which contains a positive trend in upwelling favorable winds along the Southern California Coast. The magnitude of this cooling (0.2 degrees Celsius), however, is small compared to the observed warming trend (1 degree Celsius) and is not detectable in the CalCOFI hydrography. The signature of the increased winds also is evident in both model and observations as an intensification of the mean currents of the Southern California Current System (SCCS). Model mesoscale eddy variance significantly increases in recent decades in response to both the stronger upwelling winds and the deepened isopycnals, suggesting that the stability properties of the SCCS have also changed. Within 50 to 100 km of the coast, the ocean model simulations show strong evidence that the isopycnal deepening reduces the nutrient flux to the ocean surface, counteracting any effects of the increased upwelling winds. The long-term trend of the model proxy for surface nutrients is consistent with the observed decline in zooplankton concentration.

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