Abstract. In the Baltic Sea, salinity and its large variability, both horizontal and vertical, are key physical factors in determining the overall stratification conditions. In addition to that, salinity and its changes also have large effects on various ecosystem processes. Several factors determine the observed two-layer vertical structure of salinity. Due to the excess of river runoff to the sea, there is a continuous outflow of water masses in the surface layer with a compensating inflow to the Baltic in the lower layer. Also, the net precipitation plays a role in the water balance and consequently in the salinity dynamics. The salinity conditions in the sea are also coupled with changes in the meteorological conditions. The ecosystem is adapted to the current salinity level: a change in the salinity balance would lead to ecological stress for flora and fauna, as well as related negative effects on possibilities to carry on sustainable development of the ecosystem. The Baltic Sea salinity regime has been studied for more than 100 years. In spite of that, there are still gaps in our knowledge of the changes in salinity in space and time. An important part of our understanding of salinity is its long-term changes. However, the available scenarios for the future development of salinity are still uncertain. We still need more studies on various factors related to the salinity dynamics. Among others, more knowledge is needed, e.g., from meteorological patterns at various space scales and timescales as well as mesoscale variability in precipitation. Also, updated information on river runoff and inflows of saline water is needed to close the water budget. We still do not understand the water mass exchange accurately enough between North Sea and Baltic Sea and within its sub-basins. Scientific investigations of the complicated vertical mixing processes are additionally required. This paper is a continuation and update of the BACC (Baltic Assessment of Climate Change for the Baltic Sea Region) II book, which was published in 2015, including information from articles issued until 2012. After that, there have been many new publications on the salinity dynamics, not least because of the major Baltic inflow (MBI) which took place in December 2014. Several key topics have been investigated, including the coupling of long-term variations of climate with the observed salinity changes. Here the focus is on observing and indicating the role of climate change for salinity dynamics. New results on MBI dynamics and related water mass interchange between the Baltic Sea and the North Sea have been published. Those studies also included results from the MBI-related meteorological conditions, variability in salinity, and exchange of water masses between various scales. All these processes are in turn coupled with changes in the Baltic Sea circulation dynamics.

Abstract. In the Baltic Sea, salinity and its large variability, both horizontal and vertical, are key physical factors in determining the overall stratification conditions. In addition to that, salinity and its changes also have large effects on various ecosystem processes. Several factors determine the observed two-layer vertical structure of salinity. Due to the excess of river runoff to the sea, there is a continuous outflow of water masses in the surface layer with a compensating inflow to the Baltic in the lower layer. Also, the net precipitation plays a role in the water balance and consequently in the salinity dynamics. The salinity conditions in the sea are also coupled with the changes in the meteorological conditions. The ecosystem is adapted to the current salinity level: a change in the salinity balance would lead to ecological stress of flora and fauna, and related negative effects on possibilities to carry on sustainable development of the ecosystem. The Baltic Sea salinity regime has been studied for more than 100 years. In spite of that, there are still gaps in our knowledge of the changes of salinity in space and time. An important part of our understanding of salinity are its long-term changes. However, the available scenarios for the future development of salinity are still inaccurate. We still need more studies on various factors related to salinity dynamics. Among others more knowledge is needed, e.g. from meteorological patterns in various space and time scales and mesoscale variability in precipitation. Also, updated information on river runoff and inflows of saline water is needed to close the water budget. We still do not understand accurately enough the water mass exchange between North Sea and Baltic Sea and within its sub-basins. Scientific investigations of the complicated vertical mixing processes are additionally required. This paper is a continuation and update of the BACC II book which was published in 2015, including information from articles issued until 2012. After that, there have been many new publications on the salinity dynamics, not least because of the Major Baltic Inflow which took place in December 2014. Several key topics have been investigated, including the coupling of long-term variations of climate with the observed salinity changes. Here the focus is on observing and indicating the role of climate change for salinity dynamics. New results of MBI-dynamics and related water mass interchange between the Baltic Sea and the North Sea have been published. Those studies also included results from the MBI-related meteorological conditions, variability in salinity and exchange of water masses between various scales. All these processes are in turn coupled with changes in the Baltic Sea circulation dynamics.

No abstract

The Russian part of the Southeastern Baltic Sea has a specific ice regime, which is determined by geographical location and climate conditions. Satellite data are widely used to study the propagation of sea ice. The advantages of radar images (RLI) from satellites equipped with synthetic aperture radar (SAR) are a large area coverage and independence from daylight and cloud-cover conditions. There were 840 SAR images of the Southeastern Baltic Sea analyzed for the period from December 1 to March 31, 2004–2019. It is shown that in modern conditions ice phenomena in the southeast Baltic do not occur every year. It is shown that in recent conditions ice phenomena do not occur every year in the Southeastern Baltic Sea. The revealed spatial and temporal variations in the ice regime are determined by the consequences of climate changes in the Southeastern part of the Baltic Sea. The intensity of ice formation depend on temperature conditions. Ice formation begins mainly in the second half of January-early February. The average duration of sea ice period is 22 days per season. The probability of observing sea ice from a satellite is maximum in February. Stable ice fields occur when the daily average air temperatures drop below –5 °C during 5 or more days. The maximum duration of ice period and maximum ice extent are observed in February.

Исследования в прибрежной зоне российского сектора юго-восточной части Балтийского моря, выполненные ежемесячно с апреля 2008 по апрель 2009 г., позво-лили описать закономерности сезонного распределения концентрации хлорофилла (Хл) «а» и первичной продукции (ПП) фитопланктона в столбе воды под влиянием условий среды. Показано, что вертикальное распределение Хл «а» определяется его концентрацией в поверхностном слое и гидрофизическими условиями, а распределе-ние ПП по вертикали является убывающей функцией глубины и света. В конце вес-ны–начале лета, при лимитировании роста фитопланктона биогенными элементами, может наблюдаться образование подповерхностного максимума Хл «а», вследствие чего возрастает вклад этого слоя в интегральную ПП. Рассчитаны показатели про-дуктивности фитопланктона в прибрежной зоне в зависимости от трофического со-стояния вод (олиготрофное, мезотрофное, эвтрофное). Показана значительная вариация величин Хл «а» (1,2–19,8 мг·м-3) и ПП фитопланктона (40–2153 мгC·м-2·сут-1) от олиготрофного уровня зимой (декабрь–март) до эвтрофного – весной (апрель) и ле-том в периоды максимального развития фитопланктона. Проведен анализ предлагае-мых для Балтийского моря алгоритмов расчета ПП, включающих известные уравне-ния для описания зависимости фотосинтеза от света, предложенные Дж. Стиллом, Т. Платтом и А. Яссби–Т. Платтом. Уравнения Т. Платта и А. Яссби–Т. Платта обес-печивали лучшее соответствие вычисленных для разных глубин значений ПП с дан-ными ее натурных измерений на выбранных горизонтах, а уравнение Дж. Стилла точнее воспроизводило интегральные величины ПП.