MURSYS - Baltic Sea





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MURSYS - Baltic Sea

   
 
 

STATE OF THE BALTIC SEA IN 2003

  Helsinki Commission (HELCOM)

(http://www.helcom.fi/environment.html)

On the 6th meeting of HELCOM MONAS (Monitoring and Assessment Group) in Gdynia, Poland in October 2003 the state of the Baltic was summarised as follows:

The key message for the Baltic Sea in 2003 is the January inflow.

The deep waters of the Baltic Proper were significantly stripped of oxygen in a so-called "stagnation state" since the last major inflow in 1993. The stagnation period was terminated by the intrusion of about 200 kmł of cold, salty (>17 psu) and well oxygenated of Kattegat water in January 2003.

The effect of the January inflow was enhanced by preceding smaller inflows in autumn 2002 and an exceptional water movement in late summer 2002. Unusual weather conditions in late summer 2002 caused the transport of extremely warm waters into layers at and below the permanent pycnocline. The warm waters, though carrying small amounts of oxygen, were capable to remove completely hydrogen sulphide from the Gdańsk Basin by November 2002 and considerably reduced its concentrations even up to the Gotland Basin.

The propagation of the January inflow through the deep Baltic basins was meticulously followed during the year. The inflow reached the western part of the Bornholm Basin at the end of January and by mid-February the whole Bornholm Baisn and the Hanö Bight were well oxygenated. Its first signs in the Gdańsk Deep have been detected in April and in May the central station of the Gotland Deep area has shown remarkable amounts of oxygen between 200 m and the bottom, up to 4 ml/L. The initial effects of the January inflow have been amplified in the western regions of the Baltic Proper, up to the Gdańsk Deep, by weaker inflows in March and May 2003. In August the propagation of the main water body of the January inflow was continuing into the central Gotland Basin and the ventilation of the water layers below the halocline was in dynamical progress. However, anoxic regions have still been observed in the western sectors of the eastern Gotland Basin. The western Gotland Basin was not influenced by the inflow up to the last decade of September and the deep water layers of the Färo Deep were still completely anoxic but with reduced hydrogen sulphide levels.

Another inflow event was observed in the Sound by r/v "Argos" during the monitoring expedition on 23rd of September.

The spring bloom in 2003 was most intense, as estimated by the intensity index, in all areas of the Baltic Sea since 1992. In all areas the intensity index was higher than in the previous year (the remarkable 2002) and the long time average. The bloom started in very early March in Arkona Basin and the Gulf of Finland and in mid-March in the northern Baltic Proper, though the NERI monitoring Cruise Report from 10 - 19 February reported of a very early bloom in the Belt Sea with the chlorophyll a maximum of 17 µg/L. The intensity of the bloom increased from west to east, as did the length of the bloom which lasted ca. 37 days in the Arkona Basin, 56 days in the northern Baltic Proper and 73 days in the Gulf of Finland.

In summer, particularly in the very warm August, strong cyanobacteria blooms occurred in the whole western and eastern Gotland Sea and also in the Gdańsk Basin, especially in the Gulf of Gdańsk as well as in the northern Bornholm Sea, Arkona Sea and Mecklemburg Bight. The cyanobacteria formed yellow-brownish patches on the water surface.

In the second half of August, in the Kattegat, the Sound and the Belt Sea with associated estuaries, but excluding the Arkona Basin, the area of oxygen deficiency (<4 mg/L) and severe oxygen deficiency (<2 mg/L), according to Danish standards, was only 1/5 of the extent at the same time last year.
Also in the Polish coastal zone: in the inner Gulf of Gdańsk and in the Szczecin Lagoon, incidents of severe oxygen deficiency have occurred in August 2003 in the near bottom waters.

The assessment was based on:

  • Polish monitoring data collected within the HELCOM COMBINE programme; Cruise Reports of r/v "Baltica"; http://baltyk.imgw.gdynia.pl
  • Indicator Reports: Water exchange between the Baltic Sea and the North Sea and conditions in the deep basins; Rainer Feistel and Günther Nausch (eds.), IOW; http://www.helcom.fi/environment/indicators2003/inflow.html
  • Indicator Reports: Phytoplankton spring bloom biomass in the Gulf of Finland, Northern Baltic Proper and Arkona Basin in 2003; Vivi Fleming and Seppo Kaitala (eds.), FIMR; http://www.helcom.fi/environment/indicators2003/springbloom.html
  • Baltic Sea Research Institute Warnemünde, Cruise Report, r/v "Alexander v. Humboldt"
  • Cruise Reports of from r/v "Argos", SMHI-Oceanographical Laboratory
  • Monitoring Cruise Reports, Ministry of Environment, NERI, Denmark.

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