Physical, Chemical, and Biological Oceanography 

 of the Entrance to the Gulf of California , 

 Spring of 1960 



By 



RAYMOND C. GRIFFITHS, Assistant Specialist^ 



Institute of Marine Resources, Scripps Institution of Oceanography 



University of California, San Diego 



La Jolla, Gal. 92037 



ABSTRACT 



The whole area at the entrance to the Gulf of California and off southwestern 

 Lower California in the spring of 1960 was underlain by Intermediate Water (marked 

 by a salinity minimum of about 34.5 p.p.t. at about 800 m.) and, above that, by Sub- 

 tropical Subsurface Water (marked by a salinity maximum of 34.80 p.p.t. at about 

 200 nn.). Above these waters were: to the northwest, California Current Surface 

 Water (marked by a shallow salinity minimum of about 34.10 p.p.t. at about 100 m.); 

 to the northeast, Gulf Surface Water (markedby high surface salinities that obscure 

 the maximum of the Subtropical Subsurface Water); and, to the south. Subtropical 

 Surface Water (nnarked by intermediate salinities and high temperatures). 



The most innportant oceanographic feature of the area was a strong front 

 between California Current and Gulf Surface Waters. At Cape San Lucas this front 

 was roughly vertical, but to the south and west it became more sinuous and much 

 weaker and was formed more and more by California and Subtropical Surface 

 Waters. At the Cape the stronger flow of the California Current Water seemed to 

 hold back the Gulf outflow at the surface, and to the south of the Cape it penetrated 

 Gulf Surface Water at depths between 50 and 100 m., spreading horizontally or 

 affecting in some way the entire Gulf entrance, often in a complicated manner. The 

 vertical front at Cape San Lucas thus became a horizontal one offshore at depth. 

 The frontal system was very clearly shown in the distributions of temperature and 

 salinity in the upper 100 m., but only between 50 and 100 m. in the oxygen distribu- 

 tion. 



The Subtropical Subsurface Water was in the extensive oxygen mininnum of the 

 eastern Pacific, and the oxygen content of the surface waters was affected by up- 

 welling and probably by phytoplankton activity. 



The second important feature of the area was upwelling. Distributions of tem- 

 perature, salinity, and oxygen showed it to be strong off western Lower California 

 and weaker off Cape Corrientes and other parts of the eastern side of the Gulf 

 entrance. The water upwelled off Lower California was initially low in oxygen con- 

 tent, but this content increased as the water moved south. The distributions of tem- 

 perature and, particularly, salinity showed this transport. The standing crop of 

 zooplankton was generally highest in the areas in which upwelled water occurred. 



INTRODUCTION 



This paper describes the oceanography of 

 the entrance to the Gulf of California and adja- 

 cent waters off western Lower California, 

 observed in the spring of 1960. It is based 

 on all the data of the May 1960 cruise (TO- 

 60-1) of the STOR (Scripps Tuna Oceanography 



•^ Present address: United Nations Special Fund Fish- 

 eries Research and Development Project, Apartado2578, 

 Caracas, Venezuela. 



Research) Program, and some data of the 

 April 1960 cruise (6004-B) of CalCOFI (Cali- 

 fornia Cooperative Oceanic Fisheries Inves- 

 tigations). Data reports of these cruises, 

 including particulars of methods, have been 

 published by the Scripps Institution of Oceanog- 

 raphy (1961, 1967). 



Our interest in this area arises from the 

 fact that tuna are known to migrate seasonally 

 across it (Schaefer, Chatwin, and Broadhead, 

 1961). The purpose of the paper is to present 

 and interpret observations about ocean 



