The pathway of the water exchange over the Gdańsk-Gotland Sill of the Baltic Sea and its impact on habitat formation during the stagnation period

• Published in: Oceanologia 2021-04, Vol.63 (2), p.163-178
• Main Authors: Krek, Alexander, Gusev, Andrey, Krek, Elena, Krechik, Viktor, Kapustina, Mariia, Kondrashov, Aleksei, Dudkov, Ivan
• Format: Article
• Language: English
• Subjects: Advection; Gdańsk-Gotland Sill; Habitats; Near-bottom water exchange; Southern Baltic Sea; Stagnaton period
• ISSN: 0078-3234
• DOI: 10.1016/j.oceano.2020.11.003

•Pathway of near-bottom water exchange through the Gdańsk-Gotland Sill is studied.•Permanent water exchange through the erosional trench of the Gdańsk-Gotland Sill exists.•The oxygen-rich water from the Słupsk Furrow led to the development of unique habitat.•Communities of benthic organisms form and live for a long time in the erosional trench. Water exchange between the deep basins of the Baltic Sea during stagnation periods ventilates the bottom layer. Such exchange may be local and associated with the seabed topography features. The aim of this study is to investigate the possible pathway of water exchange within the Gdańsk-Gotland Sill. A comprehensive study was conducted near the one of the local erosional trenches (depressions), comprising bathymetric survey using multibeam echosounder, water column CTD-sounding, tilt current meters mooring, and sampling of seabed deposits and macrozoobenthos. The absence of pelitic sediments even in the natural trench depressions was identified. The seabed is composed of dense clays with surface erosion signs. The presence of a current towards the Gotland Basin was recorded in the bottom layer of the erosional trench. This layer was characterized by increased salinity and dissolved oxygen concentration. The trench was also an area with macrozoobenthos richer in species composition and biomass. Moreover, indicator species of the North Sea waters were found exclusively within the erosional trench. Macrozoobenthic community structure and the age of benthic organisms confirm the existence of permanent water exchange directly from the Słupsk Furrow through the erosional trench, and indicate one of the advective pathways of water exchange between the deep Baltic Sea basins.