Long‐term forecast of oceanic conditions off California and their biological implications

Abstract

The impact of global warming due to an increased content of atmospheric CO 2 is studied by forcing a numerical eddy‐resolving ocean model with wind stresses, heat fluxes, and open boundary conditions obtained from a state‐of‐the‐art coupled model. Specifically, we have compared the 1986–1996 and 2040–2050 decades to describe and analyze the changes attained by several oceanographic variables in the California Current System. A richer atmosphere in CO 2 leads to increased sea surface and near‐surface temperatures in the model domain and to an increased stratification along the coast that, however, is not strong enough to overcome the effect of increased upwelling favorable winds. A mild oceanic cooling is forecast below the 70‐m depth, in agreement with recent studies of global warming trends. Near‐surface vertical velocities increase by about 30% in April, but our simulations also forecast anomalous offshore transports in most of the coastal areas. The eddy kinetic energy decreases, on an annual mean, along the California Current main path with maximum negative anomalies in winter. The upward displacement of the 26.5 isopycnal surface, especially in the northern half of our study area, leads to an increase in the concentration of nutrients in the subsurface. The agreement between some results of this forecasting study and recent published findings would suggest that the current global warming trend would persist in the study area with similar changes to those observed over the last half century.