In:
Biogeosciences, Copernicus GmbH, Vol. 16, No. 19 ( 2019-10-07), p. 3835-3852
Abstract:
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 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 Stainforthia fusiformis to higher diversity and
abundance and dominance of the Elphidium 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 (〈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.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-16-3835-2019
DOI:
10.5194/bg-16-3835-2019-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2158181-2
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