This report presents the main results of the Swedish national marine monitoring programme of the pelagic during 2018. The monitoring data of hydrography, nutrients and phytoplankton are analysed for the seas surrounding Sweden: the Skagerrak, the Kattegat, the Sound, the Baltic Proper, the Bothnian Sea and the Bothnian Bay
The national environmental monitoring of the pelagic is carried out by SMHI (Swedish Meteorological and Hydrological Institute), Stockholm University and UMF (Umeå Marine Sciences Centre). Data is collected, analysed and reported with support from Swedish environmental monitoring and on behalf of by SwAM (Swedish Agency for Marine and Water Management). The SMHI monitoring is made in cooperation between the national environmental monitoring of the pelagic and the SMHI oceanographic sampling programme for the seas surrounding Sweden and is cofinanced by SwAM and SMHI. This annual summary of the national monitoring is made by SMHI and is financed by the contract between SwAM and SMHI.
The weather in 2018 was characterized by high air temperatures and a few storms that implied consequences for the state in the sea. The spring arrived quickly and the sea surface temperature increased rapidly from April toMay. In August and September two storms, named Johanne and Knud,passed the region and the surface layer was well-mixed at several stations. At the East coast upwelling events were noted in both the Baltic Proper and the Bothnian Sea.
During the year there were two small deep water inflows to the Baltic Proper that temporarily improved the oxygen condition in the southern parts. No improvements of the oxygen condition were seen in the Eastern and Western Gotland Basins, instead the amount of hydrogen sulphide increased in these basins during the year.
The spring bloom had arrived in the Skagerrak and the Kattegat in March and concentrations of dissolved inorganic phosphorus (DIP) and dissolved inorganic nitrogen (DIN) were close to or at the detection limit from April to September. In the Skagerrak and the Kattegat the spring bloom was dominated by the diatom Skeletonema marinoi. In the Baltic Proper the spring bloom was observed a month later, in April. The extensive cyanobacteria bloom in the Baltic Proper started already in May and during the late September cruise cyanobacteria were still abundant. The dinoflagellate Prorocentrum compressum was found in high cell numbers during the autumn at all stations on the West coast. This flagellate has rarely been observed previously and although it is not harmful it is interesting when species suddenly occur and stay for a longer period. The potentially harmful diatom genus Pseudo-nitzschia bloomed in the beginning of December.
Surface concentrations of DIP and DIN were mainly normal except from in the Skagerrak and the Kattegat where concentrations were lower than usual in December. Concentrations of silicate were above normal levels before the spring bloom at most of the stations and in the Baltic Proper silicate was also high in the autumn.
In 2018 there were some difficulties with available research vessels for the planned cruises and some cruises needed to be cancelled with short notice. Many planned observations were therefore missed, in particular during the summer period.