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| Titel |
Planktic foraminiferal shell thinning in the Arabian Sea due to anthropogenic ocean acidification? |
| VerfasserIn |
H. Moel, G. M. Ganssen, F. J. C. Peeters, S. J. A. Jung, D. Kroon, G. J. A. Brummer, R. E. Zeebe |
| 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 ; 6, no. 9 ; Nr. 6, no. 9 (2009-09-23), S.1917-1925 |
| Datensatznummer |
250003994
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| Publikation (Nr.) |
 copernicus.org/bg-6-1917-2009.pdf |
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| Zusammenfassung |
| About one third of the anthropogenic carbon dioxide (CO2) released into
the atmosphere in the past two centuries has been taken up by the ocean. As
CO2 invades the surface ocean, carbonate ion concentrations and pH are
lowered. Laboratory studies indicate that this reduces the calcification
rates of marine calcifying organisms, including planktic foraminifera. Such
a reduction in calcification resulting from anthropogenic CO2 emissions
has not been observed, or quantified in the field yet. Here we present the
findings of a study in the Western Arabian Sea that uses shells of the
surface water dwelling planktic foraminifer Globigerinoides ruber in order to test the hypothesis
that anthropogenically induced acidification has reduced shell calcification
of this species. We found that light, thin-walled shells from the surface
sediment are younger (based on 14C and δ13C measurements)
than the heavier, thicker-walled shells. Shells in the upper, bioturbated,
sediment layer were significantly lighter compared to shells found below
this layer. These observations are consistent with a scenario where
anthropogenically induced ocean acidification reduced the rate at which
foraminifera calcify, resulting in lighter shells. On the other hand, we
show that seasonal upwelling in the area also influences their calcification
and the stable isotope (δ13C and δ18O) signatures
recorded by the foraminifera shells. Plankton tow and sediment trap data
show that lighter shells were produced during upwelling and heavier ones
during non-upwelling periods. Seasonality alone, however, cannot explain the
14C results, or the increase in shell weight below the bioturbated
sediment layer. We therefore must conclude that probably both the processes
of acidification and seasonal upwelling are responsible for the presence of
light shells in the top of the sediment and the age difference between thick
and thin specimens. |
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