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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-199
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-199
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 12 Jun 2019

Submitted as: research article | 12 Jun 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Biogeosciences (BG).

Rapid environmental responses to climate-induced hydrographic changes in the Baltic Sea entrance

Laurie M. Charrieau1, Karl Ljung1, Frederik Schenk2, Ute Daewel3, Emma Kritzberg4, and Helena L. Filipsson1 Laurie M. Charrieau et al.
  • 1Department of Geology, Lund University, Sweden
  • 2Bolin Centre for Climate Research and Department of Geological Sciences, Stockholm University, Sweden
  • 3Department of System Analysis and Modelling, Centre for Materials and Coastal Research, Geesthacht, Germany
  • 4Department of Biology, Lund University, Sweden

Abstract. The Öresund (the Sound), which is a part of the Danish straits, is linking the marine North Sea and the brackish Baltic Sea. It is a transition zone where ecosystems are subjected to large gradients in terms of salinity, temperature, carbonate chemistry, and dissolved oxygen concentration. In addition to the highly variable environmental conditions, the area is responding to anthropogenic disturbances in e.g. nutrient loading, temperature, and pH. We have reconstructed environmental changes in the Öresund during the last c. 200 years, and especially dissolved oxygen concentration, salinity, organic matter content, and pollution levels, using benthic foraminifera and sediment geochemistry. Five zones with characteristic foraminiferal assemblages were identified, each reflecting the environmental conditions for respective period. The largest changes occurred ~ 1950, when the foraminiferal assemblage shifted from a low diversity fauna, dominated by the species Stainforthia fusiformis to higher diversity and abundance, and dominance of the Elphidium group. Concurrently, the grain-size distribution shifted from clayey – to more sandy sediment. To explore the causes for the environmental changes, we used time-series of reconstructed wind conditions coupled with large-scale climate variations as recorded by the NAO index, as well as the ECOSMO II model of currents in the Öresund area. The results indicate increased changes in the water circulation towards stronger currents in the area since the 1950's. The foraminiferal fauna responded quickly (< 10 years) to the environmental changes. Notably, when the wind conditions, and thereby the current system, returned in the 1980's to the previous pattern, the foraminiferal species assemblage did not rebound, but the foraminiferal faunas rather displayed a new equilibrium state.

Laurie M. Charrieau et al.
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Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Laurie M. Charrieau et al.
Laurie M. Charrieau et al.
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Short summary
We reconstructed environmental changes in the Öresund during the last 200 years, using foraminifera (microfossils), sediment and climate data. Five zones were identified, reflecting oxygen, salinity, food content, and pollution levels for each period. The largest changes occurred ~ 1950, towards stronger currents. The foraminifera responded quickly (< 10 years) to the changes. Moreover, they did not rebound when the system returned to the previous pattern, but displayed a new equilibrium state.
We reconstructed environmental changes in the Öresund during the last 200 years, using...
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