102
P.J. Millero
Fig. 4.11. Profile of salinity,
Salinity
temperature, and sigma-T (aT)
12
14
16
18
20
22
24
in the Framvaren Fjord (Yao
0
and Millero 1995h)
20
40
0
60
0
Temp.
0
g 80
0
oS:
0
a
~ 100
0
Salinity 0
120
0
0
140
0
0
160
0
B
180
6
8
10
12
14
16
18
20
Temperature (OC) and Sigrna-T
In 1993 we made some chemical studies of the Framvaren Fjord (Yao and Millero
1995b). The large salinity gradient (Fig. 4.11) accounts for the large density gradient
(pycnocline) that separates the surface and deep water. The surface waters have a salinity of 12, while the deep waters have salinities as high as 24. The salinity gradient
prevents vertical mixing and the formation of H2S below a depth of about 18 m. The
temperatures of the surface waters (Fig. 4.11) fluctuate from 0 °C in the winter to 19°C
in the summer. The deep waters have a uniform temperature of 7-8 °C. The water
masses can be divided into four major layers:
1. the low salinity surface layer (0-2 m) above the sill depth
2. the intermediate oxygenated layer down to -18 m
3. the deep water where steep gradients in the chemistry occur (18-90 m)
4. the bottom water below 90 m, where changes in salinity and chemistry are small
The deep basin has been anoxic for about 8000 years. The sill was dredged in 1850,
resulting in the formation of a new layer of H2S. A vertical section of O2 and H2S in
the central basin is shown in Fig. 4.12. A surface maximum is observed in O2 due to
the photosynthesis of phytoplankton. The O 2 goes to zero at about 18 m and the H2S
increases to concentrations as high as 6 mM or 6000 flM. These values are the highest levels of H 2 S found in any anoxic basin. The dissolved oxygen in the surface water
was 283 flM, which is close to the saturated value (285 flM) . The maximum value 292 flM
in the subsurface (6 m) is due to photosynthesis. The oxygen concentration decreased