110 



Water 



Figure 97. Oxygen-depth curves for open sea and for 

 waters below basin sills. Arrows indicate sill depths. 

 From Rittenberg, Emery, and Orr (1955, Fig. 2). 



from the northwest because the adjacent 

 Santa Cruz Basin contains no water that 

 cold. Clearly, the water had to come from 

 San Clemente Basin, adjacent to the south- 

 east, where water at the approximate depth 

 of the sill of San Nicolas Basin is of the cor- 

 rect temperature (Fig. 98). Colder and 

 denser water at greater depth was blocked 

 off by the sill. By making similar compari- 

 sons for all basins, the route of the basin 

 water can easily be traced. Comparisons of 

 the less definite salinity, oxygen, and silica 

 concentrations provide confirming evidence 

 of the direction of flow. The exact depth in 

 the San Clemente Basin having water of the 

 same temperature as that at the bottom of 

 the San Nicolas Basin is a measure of the ef- 

 fective sill depth of the San Nicolas Basin. 

 For basins having charted, or sounded, sills 

 shallower than 1000 meters, the efi'ective sill 

 depth is less than 50 meters shallower than 

 the charted sill depth; for basins having 



deeper sills, the effective sill depth is as 

 much as 200 meters deeper than the charted 

 one. 



Water present in most of the basins in the 

 area of Chart I funneled northwestward 

 through an unnamed and unexplored basin 

 east of Velero Basin (Fig. 99). Since the sill 

 of each basin along the path of the water is 

 shallower than that of the basin immediately 

 to the south, each sill acts as a submerged 

 dam preventing the northward flow of suc- 

 cessively shallower layers of bottom water. 

 Dividing, and in some places rejoining, the 

 bottom water flows northwestward from 

 basin to basin. It is confined to definite 

 paths by high basin slopes except for the 

 San Pedro and Santa Catalina Basins, whose 

 sills are so shallow compared to surrounding 

 topography that water can enter these basins 

 from a variety of directions. All the water 

 in the Santa Barbara Basin and some of it 

 in the Tanner, West Cortes, and Long Basins 

 enters from the open sea to the west because 

 these basins have their lowest or low sills 

 facing in that direction. In view of the di- 

 rections of flow and the temperature-salinity 

 relationships (T-S curves) of the basin waters, 

 it is evident that most of the basins con- 

 tain a high percentage of Southern Water. 



The fact that there is a slight mixing 

 gradient just below the basin sills suggests 

 a slow loss and replenishment of the basin 

 water. This is verified by the fact that the 

 basin water is not stagnant and devoid of 

 oxygen. In fact, Rittenberg, Emery, and Orr 

 (1955) showed that about 3.0 ml of oxygen is 

 required annually for oxidation of organic 

 matter in the top 30 cm of a 1 sq cm column 

 of sediment at the bottom of Santa Cata- 

 hna Basin and about 1.5 ml is needed for 

 that of the Santa Barbara Basin. At these 

 rates of use, all the oxygen in the basin 

 waters would be used in only about 2 years; 

 thus, there must be complete replenishment 

 in less than 2 years to account for the - 

 absence of appreciable depletion of oxygen 

 in the basin waters as compared with those 

 of the open sea at the same depths as the 

 basin sills. Confirmation for this rapid rate 

 of replacement of the water was found in the 

 fact that ammonia regenerated from the sedi- 



