Baltic Sea needs fast corrective actions

Salty and oxygen-depleted water reaching as far as the Eastern Gulf of Finland could spell difficult cyanobacterial bloom conditions next year as well, according to the findings of the latest monitoring cruise by the research vessel Aranda.

Research results also clearly show that fast actions are needed to improve the state of the Baltic Sea.

The Aranda completed its first monitoring cruise after its renovation successfully, despite challenging weather conditions, according a press release issued by the Finnish Environment Institute (SYKE).

“The challenging circumstances were a good test for the performance of the vessel, the laboratories and our sampling equipment. We were able to collect samples in the Gulf of Finland, the Northern Baltic Sea and the Southern Bothnian Sea essential for the assessment of the status of the sea,” said SYKE Leading Researcher Maiju Lehtiniemi.

Lehtiniemi and Senior Researcher Pekka Kotilainen from SYKE were the chief scientists of the latest monitoring cruise which began on 11 September.

“The renovated Aranda proved functional, and the modifications allow us to make even more efficient use of the vessel. Aranda is now fit for unrestricted international voyages, and it can be used in all kinds of weather conditions in the Baltic Sea,” said SYKE Director-General Lea Kauppi.

“Both the results of Aranda’s voyage and other monitoring data clearly show that fast actions are still needed to improve the state of the Baltic Sea,” said Lea Kauppi.

Old, salty, oxygen-depleted and phosphorus-rich water from the deeps of the Baltic Proper, which became displaced as a result of the major Baltic inflows of 2014-2016, has been flowing into the Gulf of Finland since the autumn of 2016. As is typical in persistent high-pressure conditions, surface water from the Gulf of Finland flowed into the Baltic Proper over the summer and was replaced by salty and oxygen-depleted deep water as far as the easternmost parts of the Gulf of Finland.

The entire Gulf of Finland is highly stratified at the moment. The halocline and thermocline are located at the depths of 20-30 metres. Beneath, there are considerable volumes of salty water with elevated phosphate levels.

How much of the phosphorus will end up in the surface layer, depends on wind conditions during the rest of the autumn and ice conditions over the coming winter. This, in turn, is of crucial importance from the perspective of next summer’s cyanobacteria blooms.

Salty water has also been pushed into the Southern Bothnian Sea through the Sea of Åland. However, there has been no decrease in benthic oxygen levels and there are no signs of elevated phosphate levels compared to the situation two years ago.

The cyanobacterial blooms of the summer of 2018 were the heaviest this decade. Almost the entire Gulf of Finland was covered in algae at times.

“The situation was not due to phosphorus emissions in the Gulf of Finland’s own catchment area. Water quality in offshore areas and also in the archipelago was affected by the anoxic and phosphate-rich deep water flowing in from the Baltic Proper. Emissions during the current millennium have decreased more in the drainage basin of the Gulf of Finland than anywhere else in the Baltic Sea Region,” explained Senior Research Scientist Seppo Knuuttila.