Baltic Sea

example, accepting the geostrophic adjustment within such eddy-like features, the shape of
the isopycnals suggests dierently rotating features in and below the main halocline, Fig. 3.6 b.
Here, the feature with an anticyclonic rotation occurred at 19.65 ◦ E in the halocline (70 - 90
m), while the cyclonic one was placed directly beneath it in 90 - 120 m. Their generation
mechanisms are considered to be outside the scope of this study, but were examined in more
detail by Reiÿmann (2002), Reiÿmann (2005) and Zhurbas and Paka (1997).
Looking for associated mixing conditions, all estimated values of Tu suggest that there was
a predominance of the diusive convective regime in the whole deep domain (Fig. 3.6 b). All
Tu values between −90 ◦ < Tu< −60 ◦ (or 0.25 < R ρ < 1), indicated a large tendency
for diusive convection, were generally found on top of the warm intrusions. This is nicely
illustrated for the particularly strong intrusion in Fig. 3.6 b (between 19.99 ◦ E and 20.15 ◦ E).
This intrusion was topped at around 161 m depth by a single cell with a peak value of Tu =
−83.9 ◦ (or R ρ = 0.81). The lateral extension of this patch stretched over the distance of
10 km (19.99 − 20.15) ◦ E.
3.2.3 Vertical and temporal variability
The temporal evolution of temperature and salinity between the two basin-scale eld campaigns
M7 and M8 discussed above is illustrated by a series of CTD proles taken at or near
the central monitoring station BMP271 (see Fig. 3.7). The initial three proles measured in
August and November 1997 show very little vertical and temporal variabilities, and comparatively
low bottom temperatures. No signs of inow activity could be identied at this early
stage. However, the proles taken on 17-18 February 1998, more than 3 months later, exhibit
a dramatically dierent picture. The potential temperature had strongly increased below 60 m,
and peak values near the bottom increased from 5.3 ◦ C (31 August 1997) to 7.2 ◦ C (18 February).
The near-bottom potential densities rose from σ θ = 9.55 kg/m 3 to σ θ = 9.85 kg/m 3 ,
and water denser than the pre-inow maximum were then found in the entire depth range
below 165 m (not shown).
The inowing water masses are seen to occur as intrusions, causing high vertical and temporal
variability in the temperature proles. Note that only very little vertical/ temporal variability
was observed below approximately 210 m depth. This suggests that the renewal of the nearbottom
waters was already completed on the 18 February 1998. Above this level, however,
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