An Overview of the Physical Oceanography of the Gulf of California

Abstract

The Gulf of California (GC) presents several oceanographic features that make it unique among semienclosed seas of similar latitude and dimensions, the most important being strong tidal mixing, some of it close to deep stratification. Three-dimensional numerical model results suggest that tidal mixing may be more important than the thermohaline circulation in causing the long-term residual circulation, which consists of outflow in the upper 200 m and inflow below, plus a seasonally-reversing surface layer. The GC is an evaporative basin, but in the mean it gains heat through the surface. Lacking a sill at the point of connection with the Pacific Ocean (PO), the GC is constantly shaken by a wide spectrum of signals coming from the PO, including tides, subinertial trapped waves of various frequencies and El Nino. The seasonal dynamics and thermodynamics of the GC are dominated by the PO, not by local wind or buoyancy flux. Local processes are important at shorter time scales and in altering the thermohaline characteristics of the upper-layer waters. Tidal currents generate internal tides, packets of solitons, and sea surface temperature fronts from which jets may form. Coastal upwelling also seems to generate jets that separate from capes, especially on the mainland coast. The mesoscale off-shore circulation in the GC consists of a series of basin-wide geostrophic gyres that reach below 1000 m; their effect on the mean and seasonal circulation and thermodynamics of the GC remains to be studied. During summer, the currents in the mainland continental shelf are due to coastal trapped waves, while during winter they are wind-driven. The most important interannual anomalies in the GC are due to El Nino.