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| Titel |
Changes in calcification of coccoliths under stable atmospheric CO2 |
| VerfasserIn |
C. Berger, K. J. S. Meier, H. Kinkel, K.-H. Baumann |
| 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 ; 11, no. 4 ; Nr. 11, no. 4 (2014-02-20), S.929-944 |
| Datensatznummer |
250117233
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| Publikation (Nr.) |
 copernicus.org/bg-11-929-2014.pdf |
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| Zusammenfassung |
The response of coccolithophore calcification to ocean acidification has
been studied in culture experiments as well as in present and past oceans.
The response, however, is different between species and strains, and for the
relatively small carbonate chemistry changes observed in natural
environments, a uniform response of the entire coccolithophore community has
not been documented so far. Moreover, previous palaeo-studies basically focus
on changes in coccolith weight due to increasing CO2 and the resulting
changes in the carbonate system, and only few studies focus on the influence
of other environmental factors. In order to untangle changes in
coccolithophore calcification due to environmental factors such as
temperature and/or productivity from changes caused by increasing pCO2
and decreasing carbonate ion concentration, we here present a study on
coccolith calcification from the Holocene North Atlantic Ocean. The
pre-industrial Holocene, with its predominantly stable atmospheric CO2,
provides the conditions for such a comprehensive analysis. For an analysis
on changes in major components of Holocene coccolithophores under natural
conditions, the family Noelaerhabdaceae was selected, which constitutes the
main part of the assemblage in the North Atlantic.
Records of average coccolith weights from three Holocene sediment cores along
a north–south transect in the North Atlantic were analysed. During the
Holocene, mean weight (and therefore calcification) of Noelaerhabdaceae
(Emiliania huxleyi and Gephyrocapsa) coccoliths decreased
at the Azores (Geofar KF 16) from around 7 to 6 pg, but increased at the
Rockall Plateau (ODP site 980) from around 6 to 8 pg, and at the Vøring
Plateau (MD08-3192) from 7 to 10 pg. The amplitude of average weight
variability is within the range of glacial–interglacial changes that were
interpreted to be an effect of decreasing carbonate ion concentration. By
comparison with SEM assemblage counts, we show that weight changes are not
only partly due to variations in the coccolithophore assemblage but also an
effect of a change in calcification and/or morphotype variability within
single species. Our results indicate that there is no single key factor
responsible for the observed changes in coccolith weight. A major increase in
coccolith weight occurs during a slight decrease in carbonate ion
concentration in the late Holocene at the Rockall Plateau and Vøring
Plateau. Here, more favourable productivity conditions apparently lead to an
increase in coccolith weight, either due to the capability of coccolithophore
species, especially E. huxleyi, to adapt to decreasing carbonate ion
concentration or due to a shift towards heavier calcifying morphotypes. |
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