Salinity dynamics of the Baltic Sea

Abstract

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.

Climate Change in the Baltic Sea Region: A Summary

“…In summary, we conclude that the processes that control the variability of salinity in the Baltic Sea and its entire water and energy cycles are still not fully understood (Lehmann et al, 2021). The time-dependence of the haline stratification and its links to climate change are in special need of further study.…”

“…Therefore, gaps were statistically filled using a GAMM model (general 4211 additive mixed models) taking the seasonality into account. Tables Table 1: Variables of this assessment and further reference (1: Lehmann et al, 2021;2: Kuliński et al, 2021;3: 4315 Rutgersson et al, 2021;4: Weisse et al, 2021;5: Reckermann et al, 2021;6: Gröger et al, 2021a;7: Christensen 4316 et al, 2021;8: Meier et al, 2021a;9: Viitasalo, 2021 (Leppäranta and Myrberg, 2009;4322 Sündermann and Pohlmann, 2011;www.ospar.org;British Oceanographic Data Centre). Greater North Sea -4323 being the neighbouring sea area to the Baltic Sea -is shown as a sub-region of the NE-Atlantic, but other European 4324 sub-regions are not listed (from Myrberg et al, 2019 and southern (<60°N) Baltic Sea basin (1878−2020 is selected for comparison with (Rutgersson et al, 2014), with 4328 an equally long time period).…”

“…1. Salinity dynamics of the Baltic Sea (Lehmann et al, 2021): water and energy cycles with focus on Baltic Sea salinity during past climate variability, meteorological patterns at various space and time scales and mesoscale variability in precipitation, variations in river runoff and various types of inflows of saline water, exchange of water masses between various sub-basins and vertical mixing processes. The paper also includes the observed trends of salinity during the last >100 years.…”

“…Knowledge gaps and research needs have been intensively discussed within the grand challenge working groups of Baltic Earth and are summarized by the BEARs (Lehmann et al, 2021;Kuliński et al, 2021;Rutgersson et al, 2021;Weisse et al, 2021;Christensen et al, 2021;Gröger et al, 2021a;Meier et al, 2021a;Viitasalo, 2021;Reckermann et al, 2021).…”

Reply on RC2

“…mm year -1 (North), 1.37 mm year -1 (South), significant on 99% using the phase-scrambling method . Tables Table 1: Variables of this assessment and further reference (1: Lehmann et al, 2021;2: Kuliński et al, 2021;3: Rutgersson et al, 2021;4: Weisse et al, 2021;5: Reckermann et al, 2021;6: Gröger et al, 2021a;7: Christensen et al, 2021;8: Meier et al, 2021a;9: Viitasalo, (Leppäranta and Myrberg, 2009;4322 Sündermann and Pohlmann, 2011;www.ospar.org;British Oceanographic Data Centre). Greater North Sea -4323 being the neighbouring sea area to the Baltic Sea -is shown as a sub-region of the NE-Atlantic, but other European 4324 sub-regions are not listed (from Myrberg et al, 2019) and southern (<60°N) Baltic Sea basin (1878−2020 is selected for comparison with (Rutgersson et al, 2014), with 4328 an equally long time period).…”