474
Chemical Oceanography, 4th Edition
a much larger increase at shallower depths. Temperature data available from other Cariaco
Trench expeditions together with our data are plotted in Figure 10.63. Between 1955 and
1982, an average increase of 0.006°C per year occurred, while a much faster rate of increase,
0.028°C per year, occurred in the past 8 years. At 300 m, a much larger increase in the rate
of change of temperature was found. Richards (Zhang and Millero, 1993a) found values of
17.08°C in 1965, and Scranton et al. (1987) found values of 17.55°C in 1982 compared with our
values of 17.79°C in the western basin and 17.89°C in the eastern basin in 1990. Further measurements are needed to verify the recent increase in temperature of the deep basin. Since
the temperatures we reported were made with reversing thermometers rather than a CTD
(conductivity temperature depth) system, our results may be too high because of errors in
the calibration of the thermometers.
The concentrations of hydrogen sulfide in deep waters of the Cariaco Trench have
increased with time as suggested by Richards (1965) and Scranton et al. (1987). The increase
(Figure 10.65) in the concentration at 1300 m between 1982 and 1990 (1.58 μM yr –1 ) is consistent with the increases observed between 1965 and 1982 (1.42 μM yr –1 ). The average
rate of increase over a 40-year span from the 1950s to the 1990s is 1.11 μM yr –1 . The sulfide
enrichment of the deep waters in the eastern basin relative to the western basin reported
by Richards in 1975 was also observable in our data (at 1300 m, 58 μM in the eastern basin
and 55 μM in the western basin).
Salinity variations in the deep portion of the Cariaco Trench are harder to trace than the
temperature variations. Scranton et al. (1987) found that the salinity increased by 0.008
TCO 2 (mmol kg
–1 )
2.0
2.1
2.2
2.3
2.4
2.5
Depth (m)
0
200
400
600
800
1000
1200
1400
pH
7.8
8.0
8.2
8.4
TA (mmol kg
–1 )
2.3
2.4
2.5
2.6
2.7
2.8
pH
TA
TCO 2
Figure 10.60
Profiles of the pH, TCO 2 , and TA in the Cariaco Trench (1982–1990).
Chemical Oceanography, 4th Edition
a much larger increase at shallower depths. Temperature data available from other Cariaco
Trench expeditions together with our data are plotted in Figure 10.63. Between 1955 and
1982, an average increase of 0.006°C per year occurred, while a much faster rate of increase,
0.028°C per year, occurred in the past 8 years. At 300 m, a much larger increase in the rate
of change of temperature was found. Richards (Zhang and Millero, 1993a) found values of
17.08°C in 1965, and Scranton et al. (1987) found values of 17.55°C in 1982 compared with our
values of 17.79°C in the western basin and 17.89°C in the eastern basin in 1990. Further measurements are needed to verify the recent increase in temperature of the deep basin. Since
the temperatures we reported were made with reversing thermometers rather than a CTD
(conductivity temperature depth) system, our results may be too high because of errors in
the calibration of the thermometers.
The concentrations of hydrogen sulfide in deep waters of the Cariaco Trench have
increased with time as suggested by Richards (1965) and Scranton et al. (1987). The increase
(Figure 10.65) in the concentration at 1300 m between 1982 and 1990 (1.58 μM yr –1 ) is consistent with the increases observed between 1965 and 1982 (1.42 μM yr –1 ). The average
rate of increase over a 40-year span from the 1950s to the 1990s is 1.11 μM yr –1 . The sulfide
enrichment of the deep waters in the eastern basin relative to the western basin reported
by Richards in 1975 was also observable in our data (at 1300 m, 58 μM in the eastern basin
and 55 μM in the western basin).
Salinity variations in the deep portion of the Cariaco Trench are harder to trace than the
temperature variations. Scranton et al. (1987) found that the salinity increased by 0.008
TCO 2 (mmol kg
–1 )
2.0
2.1
2.2
2.3
2.4
2.5
Depth (m)
0
200
400
600
800
1000
1200
1400
pH
7.8
8.0
8.2
8.4
TA (mmol kg
–1 )
2.3
2.4
2.5
2.6
2.7
2.8
pH
TA
TCO 2
Figure 10.60
Profiles of the pH, TCO 2 , and TA in the Cariaco Trench (1982–1990).