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| Titel |
The benthic foraminiferal community in a naturally CO2-rich coastal habitat of the southwestern Baltic Sea |
| VerfasserIn |
K. Haynert, J. Schönfeld, I. Polovodova-Asteman, J. Thomsen |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 11 ; Nr. 9, no. 11 (2012-11-12), S.4421-4440 |
| Datensatznummer |
250007386
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| Publikation (Nr.) |
 copernicus.org/bg-9-4421-2012.pdf |
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| Zusammenfassung |
| It is expected that the calcification of foraminifera will be negatively
affected by the ongoing acidification of the oceans. Compared to the open
oceans, these organisms are subjected to much more adverse carbonate system
conditions in coastal and estuarine environments such as the southwestern
Baltic Sea, where benthic foraminifera are abundant. This study documents
the seasonal changes of carbonate chemistry and the ensuing response of the
foraminiferal community with bi-monthly resolution in Flensburg Fjord. In
comparison to the surface pCO2, which is close to equilibrium with the
atmosphere, we observed large seasonal fluctuations of pCO2 in the
bottom and sediment pore waters. The sediment pore water pCO2 was
constantly high during the entire year ranging from 1244 to 3324 μatm.
Nevertheless, in contrast to the bottom water, sediment pore water was
slightly supersaturated with respect to calcite as a consequence of higher
alkalinity (AT) for most of the year. Foraminiferal assemblages
were dominated by two calcareous species, Ammonia aomoriensis and Elphidium incertum, and the agglutinated
Ammotium cassis. The one-year cycle was characterised by seasonal community shifts. Our
results revealed that there is no dynamic response of foraminiferal
population density and diversity to elevated sediment pore water
pCO2. Surprisingly, the fluctuations of sediment pore water
undersaturation (Ωcalc) co-vary with the population densities
of living Ammonia aomoriensis. Further, we observed that most of the tests of living calcifying
foraminifera were intact. Only Ammonia aomorienis showed dissolution and recalcification
structures on the tests, especially at undersaturated conditions.
Therefore, the benthic community is subjected to high pCO2 and tolerates
elevated levels as long as sediment pore water remains supersaturated. Model
calculations inferred that increasing atmospheric CO2 concentrations
will finally lead to a perennial undersaturation in sediment pore waters.
Whereas benthic foraminifera indeed may cope with a high sediment pore water
pCO2, the steady undersaturation of sediment pore waters would
likely cause a significant higher mortality of the dominating Ammonia aomoriensis. This shift
may eventually lead to changes in the benthic foraminiferal communities in
Flensburg Fjord, as well as in other regions experiencing naturally
undersaturated Ωcalc levels. |
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