Dynamics of the southern California current system

The dynamics of seasonal to long-term variability of the Southern California Current System (SCCS) is 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.; The dynamics of the seasonal cycle in the SCCS can be summarized as follows. In spring upwelling favorable winds force an upward tilt of the isopycnals along the coast (equatorward flow). Quasi-linear Rossby waves are excited by the ocean adjustment to the isopycnal displacement. In summer as these waves propagate offshore poleward flow develops at the coast and the Southern California Eddy (SCE) reaches its seasonal maxima. Positive wind stress curl in the Southern California Bight is important in maintaining poleward flow and locally reinforcing the SCE with an additional upward displacement of isopycnals through Ekman pumping. At the end of summer and throughout the fall instability processes within the SCE are a generating mechanism for mesoscale eddies, which fully develop in the offshore waters during winter.; On decadal timescales a warming trend in temperature (1 C) and a deepening trend in the depth of the mean thermocline (20 m) 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. The temporal and spatial distribution of the warming is coherent over the entire northeast Pacific Ocean. Salinity changes are decoupled from temperature and uncorrelated with indices of large-scale oceanic variability. Temporal modulation of southward horizontal advection by the California Current is the primary mechanism controlling local salinity changes in the SCCS.; 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. The long-term trend of the model proxy for surface nutrients is consistent with the observed decline in zooplankton concentration.