471
Processes in the Oceans
concentration of 178 μM thiosulfate was found in the pore waters of the sediments in the
Cariaco Trench, but this may be the result of oxidation of the sediments during collection.
The formation of thiosulfate in the sediments could result from the reaction of MnO 2 and
FeOOH minerals with H 2 S or possibly from the reduction of sulfate.
The pH measurements made during the cruise are shown in Figure  10.60. The maximum value of pH (8.26 to 8.30) occurred between 5 and 30 m depth in both basins. The pH
[H 2 S] (µM)
0
20
40
60
Depth (m)
0
200
400
600
800
1000
1200
1400
[O 2 ] (µM)
0
50
100
150
200
250
Oxygen
Sulfide
Figure 10.57
Profiles of oxygen and hydrogen sulfide in the eastern (closed symbols) and western (open symbols) basins of
the Cariaco Trench.
Table 10.9
Depth of the Oxic–Anoxic Interface in the Cariaco Trench
Date
Depth (m)
[H 2 S], μM
Author a
1955
375
30
Richards and Vacacaro
1957
340
24
Richards and Benson
1958
320
22
Richards
1965
300
26
Richards
1968
297
28
Fanning and Pilson
1970
300
30
Richards
1971
270
32
Spencer and Brewer
1973
250
35
Bacon et al.
1982
300
47
Hastings and Emerson
1986
270
63–71
Casso et al.
1990
330
58
Zhang and Millero
a References to earlier work were given by Zhang, J.-Z., and
Millero, F.J., Deep Sea Res., 40, 1023, 1993.