Preprints
https://doi.org/10.5194/esd-2021-15
https://doi.org/10.5194/esd-2021-15

  04 Jun 2021

04 Jun 2021

Review status: this preprint is currently under review for the journal ESD.

Salinity dynamics of the Baltic Sea

Andreas Lehmann1, Kai Myrberg2,3, Piia Post4, Irina Chubarenko5, Inga Dailidiene6, Hans-Harald Hinrichsen1, Karin Hüssy7, Taavi Liblik8, Urmas Lips8, H. E. Markus Meier9, and Tatiana Bukanova5 Andreas Lehmann et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany
  • 2Finnish Environment Institute/Marine Research Centre Helsinki, Finland
  • 3Marine Research Institute, Klaipeda University, Klaipeda, Lithuania
  • 4Institute of Physics, University of Tartu, Estonia
  • 5Laboratory of Marine Physics, P.P.Shirshov Institute of Oceanology RAS, Kaliningrad, Russia
  • 6Faculty of Marine Technology and Natural Sciences, Klaipeda University, Klaipeda, Lithuania
  • 7National Institute of Aquatic Resources, Technical University of Denmark, Charlottenlund, Denmark
  • 8Marine Systems Institute at Tallinn University of Technology, Tallinn, Estonia
  • 9Leibniz Institute for Baltic Sea Research, Warnemünde, Rostock, Germany

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.

Andreas Lehmann et al.

Status: open (until 20 Aug 2021)

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Andreas Lehmann et al.

Andreas Lehmann et al.

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Short summary
The salinity in the Baltic Sea is not only an important topic for physical oceanography as such, but it also integrates the complete water and energy cycle. It is a primary external driver controlling ecosystem dynamics of the Baltic Sea. The long-term dynamics is controlled by river runoff, net precipitation and the water mass exchange between North Sea and Baltic Sea. On shorter time scales, the ephemeral atmospheric conditions drive a very complex and highly variable salinity regime.
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