Montes, J.M.; Lavín, M.F., and Parés-Sierra, A.F., 2016. Seasonal heat and salt balance in the Upper Gulf of California.

The salinity and heat balance, as well as the seasonal variation of the average absolute salinity (⟨S_A⟩) and conservative temperature (⟨Θ⟩), were described by using data from 24 cruises within four domains in the Upper Gulf of California (UGC). Monthly values of S_A and Θ, and surface fluxes obtained from ERA-Interim reanalysis data sets were fitted to a seasonal signal, and the horizontal fluxes of salinity and heat content were calculated by using balance equations. The UGC exports salt and heat to the Northern Gulf of California (NGC) almost all year, with an annual mean of 1.6 g/kg per year for the salinity flux and 0.16 terawatts (TW) for the heat flux. The results suggest that the net excess of evaporation (∼0.8 m/y) and heat gain by the surface (∼70 W/m²) are the main factors controlling the exchange of salinity and heat between the UGC and the NGC. To help identify the relevant dynamic factor involved in the heat and salinity balances, a high-resolution numerical model, the regional ocean modeling system (ROMS), was implemented for the region. The main feature of the UGC circulation consists of a cyclonic surface flow that extends downward as a laterally sheared flow pattern, with inflow at the Sonora coast side and outflow at the Baja California coast side. Although the cyclonic circulation pattern remains most of the year, the maximum velocities (∼0.20 m/s) are reached in June. The results indicate that the major exchange between the UGC and the NGC occurs in June and July when the net volume transport (∼0.9 Sverdrups) is dominated by the horizontal overturning transport.