The Swedish national marine monitoring programme of the pelagic, the water column, includes monthly measurements of hydrography, nutrient concentration and phytoplankton for the seas around Sweden; the Skagerrak, the Kattegat, the Sound, the Baltic Proper and the Gulf of Bothnia. Data is collected, analysed and reported on behalf of SwAM (Swedish Agency for Marine and Water Management).
This annual report describes interesting observations from the monitoring and summarizes the main results of 2019. At the end of the report and in the Appendix time series from 1960 to 2019 are also presented.
2019 was the 10th warmest year since reporting started in 1860 and the precipitation was also higher than normal, despite this; groundwater levels were low, especially in southern Sweden. Two stronger storms passed Sweden during the beginning of the year, Alfrida (January 1-2) and Jan (January 10- 11). This year's winter was very mild and the maximum ice spread was only 88,000 km2 which is less than normal, the ice season ended in mid-May. There were no autumn storms in 2019 and the autumn was slightly colder than normal in the north but warmer in the south.
During the year, only a few minor inflows of water from the Kattegat to the Baltic Sea occurred through the Sound. Three inflows were large enough to improve the oxygen situation in the southern Baltic Proper. The largest occurred in late November to mid-December. The effects of this inflow will be observable in spring 2020. A small change was observed in the oxygen concentration in the Eastern Gotland Basin at the beginning of the year, as a result of an inflow during the fall of 2018.
The spring bloom started in February in the Kattegat and sometime between March and April in the Skagerrak. In April, a small bloom of the fish toxic genus Pseudochattonella was observed at stations Anholt E and N14 Falkenberg. The nontoxic coccolitophoride Emiliania huxleyi was found in the Kattegat and Skagerrak from May to November in varying quantities. The potentially toxic diatom genus Pseudo-nitzschia was present in high cell numbers in October and November. In the Baltic Proper, the spring bloom was observed from March to April with high cell numbers of diatoms and a dinoflagellate typical for the spring, Peridiniella catenata. Cyanobacteria were observed in elevated quantities as early as May and increased in late June to culminate at the end of July when they had also spread into the Bothnian Sea. The amount of filamentous cyanobacteria decreased in August, and colony forming pico cyanobacteria increased.
Nutrient concentrations in the surface water were mainly within normal levels except in the Skagerrak and the Kattegat at the start of the year when slightly lower levels of phosphate, silicate and dissolved inorganic nitrogen were measured. Even in Skagerrak's and Kattegat's deep waters, the levels of dissolved inorganic nitrogen were lower than normal during parts of the first half of the year, and in the Kattegat and the Sound phosphate levels were also low. The levels of dissolved inorganic nitrogen were also low during the beginning of the year in the Baltic Proper, while phosphate levels were more normal. In the Baltic Proper, elevated silicates and phosphate levels were observed in deep water with little or no oxygen.