180 



123W 



20 



The California Current is part of a permanent, ocean- 

 wide gyre in the surface waters of the North Pacific. It 

 38 N forms the east part of this gyre, which is defined in 

 the west by the Kuroshio Current (Pacific Gulf Stream), 

 in the north by the North Pacific Current, and in the 

 south by the North Equatorial Current. In the Gulf of 

 the Farallones, currents over the Continental Slope are 

 quite distinct from the southeastward-flowing water 

 of the California Current farther offshore. These slope 

 currents are confined to a relatively narrow band sea- 

 ward of the Continental Shelf and flow northwest- 

 ward, parallel to the topography, as the California 

 Undercurrent. In the gulf, the undercurrent is generally 

 found over the slope in water depths less than 2,600 

 feet. Bathymetry in meters (1 m = 3.281 ft). 



WATER MOVEMENTS AND WINDS OFF THE NORTHERN CALIFORNIA COAST 



In spring and summer, strong winds blowing 

 toward the equator, together with the Corio- 

 lis effect (the tendency of winds and currents 

 to veer to the right in the Northern Hemi- 

 sphere and to the left in the Southern Hemi- 

 sphere), push surface water away from the 

 California coast. To fill its place, nutrient- 

 rich colder water rises to the surface in 





\ 



Typical spring and 

 summer conditions, 

 intensified during Las Ninas 



the yearly upwelling that makes the ocean 

 off northern California so cold in spring and 

 summer and the Gulf of the Farallones so 

 biologically productive. When El Nino atmo- 

 spheric phenomena occur, they disrupt this 

 pattern and cause downwelling, which pre- 

 vents the replenishment of nutrients to sur- 

 face waters and can have a major impact on 

 sea life. For example, in 1997-98, thousands 

 of seals and sea lions starved to death when 



downwelling warm water drove away many of 

 the fish and squid on which they normally fed. 

 Young animals, such as the sea lion pup shown 

 here, were particularly vulnerable. Areas of 



cold, upwelled water (blue) along the central 

 California coast are shown in the satellite 

 image below (NOAA AVHRR satellite data, pro- 

 cessed at Naval Postgraduate School). 





Strongly reversed 

 conditions, common 

 during El Nifios 



124W 



- 37N 



Current Patterns Over the Continental Shelf and Slope 21 



