Baltic Sea

Potential Temperature ( o C)
8
7
6
5
4
3
2
5.6
6
6.4
6.8
7.2
7.6
8
8.4
8.8
9.2
9.69.6
9.2
8.8
8.4
8
7.6
7.2
6.8
6.4
6
5.6
10
10.4
10.8
10
10.4
10.8
1
7 8 9 10 11 12 13 14
Salinity (g/kg)
Potential Temperature ( o C)
8
7
6
5
4
3
2
5.6
6
6.4
6.8
7.2
7.6
8
8.4
8.8
8.8
8.4
8
7.6
7.2
6.8
6.4
6
5.6
9.29.2
9.69.6
10
10.410.4
10.8
10
10.8
1
7 8 9 10 11 12 13 14
Salinity (g/kg)
Figure 3.2: θ/S plots of hydrographic stations M-7 (grey circles, left panel) and M-8 (grey circles, right
panel) below 60 m. M-7 was conducted between 29 August - 04 September 1997, M-8 between 19 - 24
April 1998. The black line is the 30 yr mean with standard deviations of potential temperature (θ) and
salinity (S) of BMP271. BMP271 and station grid of M-7/M-8 are shown in Fig. 1.2.
9.2) kg/m 3 , the standard deviation increases by about 0.4 ◦ C on the basin-scale.
Dramatic changes in the thermohaline properties were observed especially in the near-bottom
region as a result of the inow (see Fig. 3.2 b). Taking into account that isobaths are closed
up to a depth of approximately 170 m (bold isobath in Fig. 1.2), it becomes evident that the
former cold deep water of the basin was completely replaced by warm water with densities
exceeding σ θ = 9.8 kg/m 3 . It also becomes clear that the former densest water (σ θ =
9.57 kg/m 3 ) was uplifted to reach depths shallower than 170 m. All temperatures that were
measured during the M-8 campaign exceed those of the M-7 survey as well as those of the 30
year climatology measured at BMP271 in layers beneath the halocline ( 60 m). This can also
be seen, for example, by comparing vertical temperature sections crossing the central basin
at 57 ◦ 14.40 ′ N, Fig. 3.5 a, b. Potential temperatures of the deepest layers rose from 5.35 ◦ C
(M-7) to 7.06 ◦ C (M-8) and salinities increased from 12.1 to 12.6 g/kg, respectively. The
spatial variability in θ peaked within the range 8.8 ≤ σ θ ≤ 9.2 kg/m 3 and decreased towards
layers embedded within the pycnocline for σ θ < 7.2 kg/m 3 .
In order to obtain some estimates on changes in the isopycnal distribution of hydrographic
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