A numerical simulation of water mass formation in the northern Gulf of California during winter

A numerical simulation was performed using realistic bathymetry, winter hydrography and forcing (wind, surface heat flux and evaporation) in the northern Gulf of California. As a result of cooling and evaporation, water in the shallow regions increases its density and sinks. At depth, the surface water spreads horizontally in a cyclonic sense (shallow water to its right) around the basin. Most of the sinking takes place toward the end of a strong wind, cooling, and evaporation event. In the northern Gulf of California salinity decreases with depth, under normal hydrographic conditions. Therefore, the surface water formed is recognized at depth by its saline and warm signature, relative to the original waters at that depth. The water that sinks reaches depths at which its density is almost equal to the surrounding water, but its salinity and temperature are higher. Sinking to intermediate depths of 75 m occurs mainly along the relatively broader northeastern shelf. This water travels toward the head of the gulf (toward the northwest), where it sinks farther due to the increased bottom slopes in the region. The densest water, arriving at the head of the gulf, sinks to depths of 115 m during weak forcing about 25 days after the strong forcing events have ceased. This water now travels toward the southeast at a speed of about 8 cm s−1 along the southwestern slope. Along this path, water mixes, lowering its salinity and density. High salinity surface water can be traced to depths of 230 m and all the way to the open boundary of the domain. The final state presents strong bottom temperature and salinity fronts, which are in qualitative agreement with the limited available observations. Although the effect of increased salinity on density is about 25% of the increase resulting from temperature, the effect of evaporation is significant in producing saltier, denser waters that reach greater depths.