Baltic Sea

4. The Deep Circulation in the EGB (Inter-basin
communication of deep Baltic basins and their eects
for the deep circulation)
4.1 Hydrography of the Eastern Gotland Basin
During the RAGO eld campaign in September 2006 two diagonal cross-sections were conducted
to monitor the current hydrographic situation of the EGB. The rst transect was
conducted on the 26 September 2006 starting in the northeast corner of the basin travelling
to the southwest corner. The transect contained 13 CTD proles measuring potential temperature,
salinity, oxygen and pressure (see Fig. 4.1). The second transect conducted a day later
covered the area from the northwest to the southeast corner (Fig. 4.2). The location of both
transects is marked in Fig. 1.1. Both transects revealed a cold, oxygen- rich inow just below
the halocline in 90 − 150 m with core temperatures of 5.6 ◦ C and an oxygen concentration of 1
ml/l. The inowing waters are easy to distinguish from the surrounding water, which contains
somewhat higher temperatures (6 ◦ C) and is anoxic (0 ml/l). The inowing water masses slope
from east to west across the basin. In the East they were located directly below the halocline in
depths between 90 − 150m, whereas in the west they appeared in depths between 110-175 m.
Since the two transects in September 2006 only provided a snapshot of the hydrographic
situation in the EGB, further investigations were made to unravel the development of the
timescale of the inow. A reliable source is the central monitoring station (BMP271, see
Fig. 1.2) of the EGB, where depth proles of temperature, salinity and oxygen conducted
in January/February, May, July, September and November 2006 revealed a high variability in
temperatures and oxygen between 100 − 150 m depth (Fig. 4.3 A, B and E). Even in the rather
stable salinity proles (Fig. 4.3 C) small uctuations were made out in those depths. Below
150 m temperatures clearly divide between warmer (January to July) and colder temperatures
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