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

<p>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....

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Main Authors: L. M. Charrieau, K. Ljung, F. Schenk, U. Daewel, E. Kritzberg, H. L. Filipsson
Format: Article
Language:English
Published: Copernicus Publications 2019-10-01
Series:Biogeosciences
Online Access:https://www.biogeosciences.net/16/3835/2019/bg-16-3835-2019.pdf
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spelling doaj-bb3f22bb498047098881c25b6edf4ce12020-11-24T21:44:15ZengCopernicus PublicationsBiogeosciences1726-41701726-41892019-10-01163835385210.5194/bg-16-3835-2019Rapid environmental responses to climate-induced hydrographic changes in the Baltic Sea entranceL. M. Charrieau0K. Ljung1F. Schenk2U. Daewel3E. Kritzberg4H. L. Filipsson5Department of Geology, Lund University, Lund, SwedenDepartment of Geology, Lund University, Lund, SwedenBolin Centre for Climate Research and Department of Geological Sciences, Stockholm University, Stockholm, SwedenDepartment of System Analysis and Modelling, Centre for Materials and Coastal Research, Geesthacht, GermanyDepartment of Biology, Lund University, Lund, SwedenDepartment of Geology, Lund University, Lund, Sweden<p>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 ca. 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 the respective period. The largest changes occurred around 1950, when the foraminiferal assemblage shifted from a low diversity fauna dominated by the species <i>Stainforthia fusiformis</i> to higher diversity and abundance and dominance of the <i>Elphidium</i> species. Concurrently, the grain-size distribution shifted from clayey to sandier sediment. To explore the causes of the environmental changes, we used time series of reconstructed wind conditions coupled with large-scale climate variations as recorded by the North Atlantic Oscillation (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 after the 1950s. The foraminiferal fauna responded quickly (&lt;10 years) to the environmental changes. Notably, when the wind conditions, and thereby the current system, returned in the 1980s to the previous pattern, the foraminiferal assemblage did not rebound. Instead, the foraminiferal faunas displayed a new equilibrium state.</p>https://www.biogeosciences.net/16/3835/2019/bg-16-3835-2019.pdf
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language English
format Article
sources DOAJ
author L. M. Charrieau
K. Ljung
F. Schenk
U. Daewel
E. Kritzberg
H. L. Filipsson
spellingShingle L. M. Charrieau
K. Ljung
F. Schenk
U. Daewel
E. Kritzberg
H. L. Filipsson
Rapid environmental responses to climate-induced hydrographic changes in the Baltic Sea entrance
Biogeosciences
author_facet L. M. Charrieau
K. Ljung
F. Schenk
U. Daewel
E. Kritzberg
H. L. Filipsson
author_sort L. M. Charrieau
title Rapid environmental responses to climate-induced hydrographic changes in the Baltic Sea entrance
title_short Rapid environmental responses to climate-induced hydrographic changes in the Baltic Sea entrance
title_full Rapid environmental responses to climate-induced hydrographic changes in the Baltic Sea entrance
title_fullStr Rapid environmental responses to climate-induced hydrographic changes in the Baltic Sea entrance
title_full_unstemmed Rapid environmental responses to climate-induced hydrographic changes in the Baltic Sea entrance
title_sort rapid environmental responses to climate-induced hydrographic changes in the baltic sea entrance
publisher Copernicus Publications
series Biogeosciences
issn 1726-4170
1726-4189
publishDate 2019-10-01
description <p>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 ca. 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 the respective period. The largest changes occurred around 1950, when the foraminiferal assemblage shifted from a low diversity fauna dominated by the species <i>Stainforthia fusiformis</i> to higher diversity and abundance and dominance of the <i>Elphidium</i> species. Concurrently, the grain-size distribution shifted from clayey to sandier sediment. To explore the causes of the environmental changes, we used time series of reconstructed wind conditions coupled with large-scale climate variations as recorded by the North Atlantic Oscillation (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 after the 1950s. The foraminiferal fauna responded quickly (&lt;10 years) to the environmental changes. Notably, when the wind conditions, and thereby the current system, returned in the 1980s to the previous pattern, the foraminiferal assemblage did not rebound. Instead, the foraminiferal faunas displayed a new equilibrium state.</p>
url https://www.biogeosciences.net/16/3835/2019/bg-16-3835-2019.pdf
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