THE BENTHIC FAUNA OF THE DEEP BASINS 

 OFF SOUTHERN CALIFORNIA 



By Olga Hartman and J. Laurens Barnard 



INTRODUCTION 



The large oval-shaped offshore area of southern California from 

 Point Conception to south of the Mexican border, lying between the 

 shoreline and the continental escarpment, is rugged and covered with 

 water varying in depth to about 2107 meters (Chart 1). West of the 

 escarpment the sea floor drops rather sharply to around 3700 meters. 

 About two-thirds of this vast area, known as a borderland (Shepard and 

 Emery, 1941), comprises the eight offshore islands, the shallow sub- 

 merged shelf, the various slopes, submarine canyons and shallower banks 

 and ridges. The other one-third consists of submerged enclosed basins 

 ranging in depth from 627 to 2107 meters. The basins are separated 

 from one another by islands and submerged ridges which vary in depth 

 from 475 to 1902 meters. Thirteen basins have been named (Shepard 

 and Emery, 1941, and Emery, 1954). The three along shore, called the 

 San Pedro, Santa Monica and Santa Barbara Basins, are the shallowest, 

 and those farther seaward are deeper. In shape most of the basins are 

 elongate oval in a northwest-southeast direction. The lowest places on 

 the ridges surrounding the basins are called sills. They largely deter- 

 mine the kind and amount of subsill water supplied to the basins, in- 

 cluding the salinity, amount of dissolved oxygen, and the temperature. 

 Most of the flow or replacement is from south to north (Emery, 1954). 

 The temperature of the bottom water varies from 6.26 to 2.52° C. In 

 each basin it is approximately the same as that of the water at sill depth 

 and varies according to the sill depth of each basin. 



The physical characteristics of the basin floors have slight, though 

 measurable, differences. When grossly examined, the sediments appear 

 uniformly fine in texture, dark green to bluish in color, and sticky clayey 

 to silty in consistency. The amounts of chlorophyll derivatives found in 

 the dried sediments vary from one basin to the next, and in general show 

 a decrease from near shore to outer basins. Organic matter is highest in 

 basins of intermediate depth (Orr and Grady, 1957). The amounts of 

 dissolved oxygen vary, so that oxidizing conditions prevail in the surface 

 sediments of Santa Catalina Basin, and reducing conditions in San Pedro, 



[1] 



