| Summary: | Despite a year of pandemic, the environmental monitoring in the pelagic could be done largely as planned in 2020. It was the warmest year on land since national statistics started in 1860. This was also shown in the sea where especially the surface temperature in winter was higher than usual. In the Baltic Sea, the lowest winter temperature was two degrees above normal and the maximum distribution of sea ice was the lowest ever measured. The autumn was also warm and in November the surface water in the Baltic Sea was about 1 degree warmer than normal.In the Kattegat, there were signs of the spring bloom in February with high chlorophyll levels and high species diversity. In March, the nutrients were largely depleted in the surface water and the spring bloom of diatoms was over for this time. At one occasion, in April, toxins were reported in mussels along the West Coast that exceeded the warning limit. In the Skagerrak, the spring bloom started a little later than in the Kattegat, and in the Baltic Sea even later. In April, the spring bloom was observed in the Western Gotland Basin with high chlorophyll concentrations and typical dinoflagellates species for the season. In the Gulf of Bothnia, there was an early spring bloom of diatoms in April. This early bloom may have been an effect of the mild winter. The bloom of cyanobacteria in the Baltic Sea started already in May when cyanobacteria were observed at several stations. In August, cyanobacteria were also observed along the West Coast. These had probably been transported out with water from the Baltic Sea. A late bloom of the microzooplankton Noctiluca scintillans was observed at several sites along the West Coast in December. N. scintillans turns the water red during blooms and when it is dark, its fluorescence causes beautiful bioluminescence.Throughout the year high levels of silicate were observed in the Baltic Sea and low levels of DIN in the surface waters of the Gulf of Bothnia. Otherwise, the levels of nutrients did not deviate much from normal.In the ...
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