46 



of the Gulf of California. According to Roden, the circulation in the Gulf 

 is somewhat complicated and not completely known. In the winter months, 

 the outflow of water is thought to occur at the surface, and inflow at greater 

 depths. In the summer, this situation is reversed. 



During the winter months (December — March), the high salinity waters 

 in the northern Gulf are cooled, filling the northern basins and moving 

 southward along the coast of Baja California. This movement of water, 

 plus strong tidal currents through the narrows between the large central 

 islands attains speeds of several knots. This situation causes the turbulence 

 which, in turn, is responsible for the abnormally high bottom oxygen and 

 temperature values described previously for this region. According to 

 U.S. Hydrographic Office charts (1947), coastal surface currents move 

 south along the Baja California side of the Gulf in the winter months. In 

 July, water moves into the Gulf at the surface along the east side and 

 center of the Gulf, with some water moving in a southward direction close 

 to the southern portion of the Baja California peninsula. According to 

 Roden (1958), the monthly average speed of these currents in the southern 

 and central portions of the Gulf is between 5 cm. and 20 cm sec. 



Except for the anomalous situation in the tidal channels between the 

 large islands in the Gulf, these surface currents probably have little effect 

 upon the adult sub-littoral benthic animals. They are important, however, 

 in influencing the planktonic larval transport of many benthic animals. 

 The fact that the currents moving into the Gulf from the south seem to 

 terminate in the vicinity of Tiburon Island, may account for the fact that 

 few truly Panamic species with planktonic larvae are found in the northern 

 Gulf above Tiburon Island. Although water does flow north through 

 Ballenas Channel, the colder surface water temperatures, due to turbulent 

 upwelling, may restrict the movement of Panamic species into the northern 

 Gulf on the west side. The fact that many moUusk and crustacean species 

 taken on the east side of the Gulf do not appear on the west side, and vice 

 versa, might also be explained by the fact that the currents on opposite 

 sides of the Gulf flow in opposite directions. The longshore currents on the 

 east side, with a prevailing movement to the north, also influence the 

 distribution of the fine sediments, so that clayey bottoms are generally 

 found to the north of the few permanent river mouths. Indirectly, then, 

 the currents influence the distribution of clay bottom dwellers in providing 

 their special niche in specific areas. 



