Seasonal variability of temperature, salinity, velocity, vorticity and sea level in the central Gulf of California, as inferred from historical data

Historical data from 17 cruises into the Guaymas basin, central part of the Gulf of California, are globally analysed. Temperature, across‐gulf integrated velocity, sea level, and salinity have a significant seasonal cycle. The last variable has an important semi‐annual component, presenting four extremes per year. The others are mainly annual, reaching their maximum values in summer and their minima in winter. By interaction with the atmosphere, the central gulf is gaining heat and losing fresh water during the whole year, on a monthly‐mean time scale (the only exception is an unimportant gain of fresh water in August). This implies net heat and salinity fluxes into the open ocean, through the gulf's mouth. Temperature and salinity vertical gradients at the surface are well correlated with atmospheric forcing, through turbulent diffusion of heat and salt. Average velocity correlates with the along‐gulf wind stress with zero lag, as if frictionally dragged in a surface layer, with a short relaxation time. Seasonal sea‐level changes are mainly caused by the thermal expansion of the water column. Horizontal processes (advection and diffusion) are as important as, or more important than, vertical diffusion for both heat and salt balances in the upper layers. Vorticity, the across‐gulf derivative of the velocity field, does not show a seasonal cycle. Its contribution to the instantaneous geostrophic velocity and surface elevation near each coast is larger than that due to the across‐gulf average velocity.