Fourth Study Conference on BALTEX Scala Cinema Gudhjem

2. Winter inflow 2003
After the very strong inflow of North Sea waters into the
Baltic Sea in winter 1975/76, only moderate such events
have been observed from then on, and with even strongly
decreased frequency, compared to the century before.
The latest of these now rare events happened in 1977 and
1993. After that, the lasting stagnation period caused
strong oxygen deficiency and increasing hydrogen
sulphide concentrations in depth levels below 70 m (Fig.
3).
Figure 3. Near-bottom distribution of oxygen and
hydrogen sulphide in autumn 2002
Recently, they have been followed by one of comparable
importance in January 2003. After the classification
scheme of Franck et al. (1987), the current inflow with
intensity Q = 12 ranks only in the range of the weak ones,
but it has been recognised with general attention
especially due to the extreme anoxic situation observed in
the Baltic deep waters during the last years (Nausch et al.,
2003).
The cold, oxygen-rich inflow from the Kattegat into the
western Baltic in January 2003 was first occasionally
noticed by the Swedish r/v “Argos” but could be
confirmed by Darss Sill mast data a few days later when
the highly saline waters were recorded there for several
consecutive days. Motivated by that, the Baltic Research
Institute Warnemünde (IOW) carried out a short ad-hoc
expedition with r/v “Prof. A. Penck”.
At the Arkona Basin buoy, the inflow waters arrived with
a further delay of some days and reached the Bornholm
Basin already by the end of January. The successive
penetration into deeper basins could be tracked by regular
Baltic monitoring cruises in February, March, May,
August and October 2003. By inspection of additional
CTD profiles, a more detailed insight could be gained
into the spatial and temporal structures along the
- 62 -
propagation path. At the end of April, the inflow signal
could be detected by a mooring in the Gotland Deep by a
dramatic decrease of temperatures. In May, the central
Gotland Basin station reached oxygen concentrations
near the bottom which belong to the highest ever
recorded there. The oxygen depletion during spring and
summer 2003 could not turn back the central Baltic
basins to anoxic conditions (Fig. 4), on the opposite, the
renewal waters have propagated further north and
reached the Farö Deep in winter 2003/2004.
Figure 4. Near-bottom distribution of oxygen and
hydrogen sulphide in autumn 2003
References
R. Feistel, G. Nausch, V. Mohrholz, E. Lysiak-Pastuszak,
T. Seifert, W. Matthäus, S. Krüger, J. Sehested
Hansen,
Warm Waters of Summer 2002 in the Deep Baltic Proper,
Oceanologia, 45, pp. 571-592, 2003a
R. Feistel, G. Nausch, W. Matthäus, E. Hagen, Temporal
and Spatial Evolution of the Baltic Deep Water
Renewal in Spring 2003, Oceanologia 45, pp. 623-
642, 2003b
H. Franck, W. Matthäus, R. Sammler, Major inflows of
saline water into the Baltic Sea during the present
century. Gerlands Beiträge zur Geophysik 96, pp.
517-531, 1987
G. Nausch, R. Feistel, H. U. Lass, K. Nagel, H. Siegel,
Hydrographisch-chemische Zustandseinschätzung der
Ostsee 2002. - Meereswissenschaftliche Berichte 55,
pp.1-71, 2003