Cold winter takes toll on Baltic Sea

Oxygen depletion releases nutrients from bottom

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A layer of salty water with little oxygen is forming at the bottom of the Baltic Sea. As a result, oxygen-free areas could appear in the deepest parts of the sea, releasing nutrients into the water.
      These observations were made on the annual winter voyage of the marine research vessel Aranda in the northern part of the Baltic Sea. The findings from the voyage were released on Tuesday, on the eve of the Baltic Sea Action Summit, which opened in Helsinki today.
      “In several years the situation in the Gulf of Finland has been good because the layers have been mixed up. The bottom has mostly had oxygen and then the sediment is able to bind phosphorous well”, says special researcher Juha Flinkman of the Finnish Environment Institute, who was also the head of the voyage.
      When phosphorous enters the sea water, it spurs the growth of algae.
     
Salty water has flowed into the Gulf of Finland, because a high pressure system, which has prevailed since late December, and northerly and easterly winds, have pushed surface water toward the southern part of the Baltic.
      “In winters when there is little ice, wind energy can be all that is needed to mix up the layers of water in the Gulf of Finland. Now the ice cover has been solid in a very wide area, which can influence the situation”, Flinkman says.
      None of the feared Mnemiopsis leidyi comb jellies, which have been seen as a threat to fish stocks in the Baltic, were to be found in the northern part of the Baltic. However, there were plenty of Mertensia ovum, their harmless relatives.
     
Measurements taken on the Aranda indicate that the phosphate levels in the water at the surface of the Gulf of Finland is higher than they were last winter. The nutrient situation in the Gulf of Bothnia is about the same as it was a year earlier. Further north, in the Bay of Bothnia, the nitrate content had grown somewhat.
      Flinkman says that the amount of phosphates in the surface layer correlates to a degree with the blue-green algae situation in the coming summer.
     “Many other factors also affect it, but the keys are there for a situation that is worse than last year”, Flinkman says.
      In none of the measurements did the nitrogen content of the northern Baltic Sea fall below the target set by the Commission for the Protection of the Baltic Sea Environment (HELCOM).
     
The Baltic Sea Action Summit takes place in Helsinki today, Wednesday. Juha Flinkman says that he hopes that there would be “at least something more than just talk”.
      Juha-Markkuk Leppänen, head of research at the Finnish Environment Institute, lists reducing eutrophication, cutting back on toxic substances, and improved safety of maritime transport - particularly that of oil - as important goals for the summit.
      “All commitments made in that direction are very welcome”, Leppänen says.

More on this subject:
 COMMENTARY: Baltic Sea can be destroyed in many ways

Previously in HS International Edition:
  Baltic Sea commitments contain something old, something new, and something borrowed (9.2.2010)
  Poor oxygen situation threatens Gulf of Finland - once again (26.3.2009)
  Feared comb jellies found in Baltic turn out to be harmless species (10.2.2009)

Links:
  Baltic Sea Action Summit

Helsingin Sanomat