06.09.2013 change 06.09.2013

The Baltic Sea emits more CO2 than it can absorb

The Baltic Sea surprised scientists. Contrary to popular belief, every year it emits about 75 million tons of CO2 into the atmosphere, and it absorbs 60 million tons. If other coastal seas behave this way, boundary conditions of climate models will need to be modified.

"Oceanographers share a legitimate and long-standing view that the oceans and seas absorb about one third carbon dioxide (CO2) emitted by human. As many as 20 percent share in the absorption have shelf seas, whose depth does not exceed 200 meters" - told PAP director of the Institute of Oceanology PAS Prof. Janusz Pempkowiak.

According to current knowledge, in such seas as the Baltic CO2 absorption should be particularly intense. Prof. Pempkowiak, together with Dr. Karol Kuliński, decided to verify the popular view and examine how much carbon dioxide the Baltic in fact absorbs from the atmosphere.

"We came to the conclusion that it would pay to determine the role of the Baltic Sea in the absorption of CO2. We believe that such an estimate is important for predicting future climate change" - said Prof. Pempkowiak.

Scientists determined, for example, the amount of carbon-containing chemicals Baltic exchanged with the North Sea, and the flow of carbon compounds from rivers to the Baltic Sea. They took into account 10 other carbon cycle components in the Baltic Sea. It turned out that in the annual settlement the Baltic Sea emits more CO2 to the atmosphere than it absorbs.

"It turned out that the Baltic absorbs about 60 million tons of CO2, mainly in offshore areas. And it emits almost 75 million tons in estuaries and offshore areas" - explained the researcher. As a result, Baltic Sea emits 15 million tonnes of CO2 into the atmosphere every year.

Why does the Baltic itself emit carbon dioxide? Prof. Pempkowiak explained that the river waters transport a lot of organic compounds to the Baltic Sea, that are washed out of the soil and get into the water with sewage. In seawater, they undergo mineralization, resulting in the precipitation of CO2. This excess is emitted into the atmosphere.

The Baltic Sea emits most carbon dioxide in the fall and winter. The situation is reversed between April and October, when the microscopic plants, called phytoplankton, intensively search for carbon dioxide in order to be able to develop dynamically.

"The shelf seas receive nutrients: nitrogen, phosphorus. They allow for the growth of phytoplankton, ie. primary production. In order to increase mass, these tiny plants absorb carbon dioxide. When there is not enough in seawater, carbon dioxide is absorbed from the atmosphere" - said Prof. Pempkowiak.

Not all seas absorb and emit comparable amounts of CO2. Only two big rivers and little pollution enters the Mediterranean Sea, so it absorbs more CO2 than it emits.

According to Prof. Pempkowiak, other seas, which are believed to absorb a lot of CO2, should be re-examined in this respect. "Measurements have been performed in the Yellow Sea, the China Sea, the Black Sea and the North Sea. However, places in the estuaries, where processes of emission and absorption of CO2 occur, are rarely studied by scientists" - said the scientist.

Director of the Institute of Oceanology PAS pointed out that in recent years carbon dioxide attracted particular attention, due to being one of the greenhouse gases. "Climate change is roughly 70 percent due to increased levels of carbon dioxide in the atmosphere" - he explained.

If it turns out that the seas absorbs far less carbon dioxide than previously thought, scientists will also have to lower the estimated CO2 load absorbed by the oceans. "This may cause the revision of predictions about the concentration of CO2 in the atmosphere in 10 or 20 years" - noted the researcher.

This is very important because - as Prof. Pempkowiak explained - CO2 concentration in the atmosphere is a very important factor in the preparation of climate models. These, in turn, allow to predict temperatures in different parts of the globe in the coming years. According to the scholar, the reevaluation of views in the scientific world is inevitable, but it will take a few years before it happens.

The study was conducted in the project BALTEX sponsored by the Ministry of Science and Higher Education, and as part of the "Baltic-C" programme, in various European Union countries participated, such as Sweden, Finland and Germany. The studies continued for about seven years and ended in 2011.

PAP - Science and Scholarship in Poland, Ewelina Krajczyńska

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