465 
HYPERSALINE BASINS 
Description of the Basins 
Anoxic hypersaline basins exist on the outer continental shelf and the up- 
per continental slope of the northern Gulf of Mexico and elsewhere. A par- 
ticularly large one was discovered in 1975 (Shokes et al., 1977) about 150 
n miles due south of Morgan City, Louisiana (Figure 8, inset). The basin 
is about one-third full of brine that is 8.6 times as salty (3109/1) as the 
1800m of normal seawater (369/1) overlying the basin (Figure 9). This 
brine layer is 180m thick and occupies a J-shaped area measuring 15 by 2 n 
miles (Figure 8). The brine has originated from the seawater dissolution 
of a salt dome that is exposed somewhere on the basin wall. It is thought 
that this process began about 10,000 years ago and that at least 30,000 
years will be required to completely fill the basin with brine. 
Suitability of Brine Basins as Polluted Material Dumpsites 
These brine basins are nearly devoid of life. Only simple bacterial life 
can exist in them. The bacteria are utilizing organic matter that descends 
from above and are producing methane (CHq)» ammonia (NH3), and hydrogen 
sulfide (H)S). These actions keep the dissolved oxygen content eof the 
brine at zero (Figure 10). The following factors indicate that the basins 
would be excellent places into which to deposit very polluted dredged ma- 
terial: 
(a) the basin will retain its present configuration for at least 
20,000 years 
(b) nearby abiotic 
(c) anoxic 
(d) great stability of brine layer that would not be disturbed 
by passage of storm waves, including those generated by hur- 
ricanes. 
