SECT. 3] BASIN SEDIMENTATION AND DIAGENESIS 585 



zone by decomposition of organic matter. As a result, seasonal differences and 

 gradients exist as in the open ocean. In non-stagnant and semi-stagnant basins 

 having deep sills below the euphotic zone, the nutrients have a uniform con- 

 centration corresponding in general to that of the water outside the basin at 

 sill depth. The effects of diagenetic processes in the sediments may be detectable 

 in the bottom water if not masked by the rapid renewal of basin water. 



The neritic basins off southern California, typical of the semi-stagnant type, 

 show little change in nutrient distribution from sill depth to just above the 

 sediment surface. The contents of oxygen and nutrient salts correspond to those 

 of the surrounding ocean water at sill depth. Oxygen may be as low as 0.04 

 ml/1, but does not disappear completely. Hydrogen sulfide is never detected in 

 the water, although the surface sediments of some basins, notably Santa 

 Barbara, have a distinct odor of free sulfide. 



Sulfate, phosphate and silicate may show slight to marked increases in 

 concentration in a thin layer of water just above the sediment; nitrate con- 

 centration varies in both directions depending on the basin, although total fixed 

 nitrogen probably increases in the bottom water of all the southern Cahfornian 

 basins as it does in the Black Sea (Danil'chenko and Chigirin, 1929). The 

 changes at the bottom are due to biodiagenetic processes at the sediment-water 

 interface and within the sediment column resulting in the release of ions to the 

 water. Changes may also be due to ion-exchange processes and it cannot be 

 taken for granted that an increase of ions in the overlying water invariably 

 occurs. Koczy (1953), for instance, showed that in bottom waters of the Atlantic 

 Ocean there is a marked decrease, not only of oxygen, but also of phosphate and 

 silicate, which he explained by base exchange at the mud-water interface. 



Stagnant basins are characterized by the presence of H2S in the bottom 

 waters. A number of such environments have been described, e.g. the Black Sea 

 (Caspers, 1957), some Norwegian fjords (Strom, 1939; Fleming and Revelle, 

 1939), Kaoe Bay (van Riel, 1943; Kuenen, 1943), Cariaco Trench (Richards and 

 Vaccaro, 1956) and Lake Maracaibo (Redfield, 1958). Other areas of the world 

 associated with seasonal upwelling (Callao Bay, Peru, and Walvis Bay, S.W. 

 Africa) will have varying amounts of stagnation depending on the particular 

 circumstances (Brongersma-Sanders, 1948). 



It was shown by Riissian workers (Danil'chenko and Chigirin, 1929; Chigirin, 

 1930) from studies on the Black Sea and by Strom (1939) from Norwegian 

 fjords that the increase of phosphate in waters parallels the increase of hydrogen 

 sulfide. Strom states that a maximum of 700 mg/m^ P2O5 (5 mg A/1. P) was 

 obtained, while Danil'chenko and Chigirin found a maximum of 632 mg/m^ 

 P2O5 (4.5 mg A/1. P). The same relation has been demonstrated by Richards and 

 Vaccaro (1956) in the Cariaco Trench and by Redfield (1958) in Lake Maracaibo. 



The data of Richards and Vaccaro fit the equation (by atoms) 



PO4 = 0.00426(AOU-fSU)- 0.095, 



where AOU is the apparent oxygen utilization and SU is 4 times the sulfide. 

 In other terms, for every 235 atoms of oxygen equivalents consumed, 1 atom of 



