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| Titel |
A universal carbonate ion effect on stable oxygen isotope ratios in unicellular planktonic calcifying organisms |
| VerfasserIn |
P. Ziveri, S. Thoms, I. Probert, M. Geisen, G. Langer |
| 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. 3 ; Nr. 9, no. 3 (2012-03-15), S.1025-1032 |
| Datensatznummer |
250006841
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| Publikation (Nr.) |
 copernicus.org/bg-9-1025-2012.pdf |
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| Zusammenfassung |
| The oxygen isotopic composition (δ18O) of calcium carbonate of
planktonic calcifying organisms is a key tool for reconstructing both past
seawater temperature and salinity. The calibration of paloeceanographic
proxies relies in general on empirical relationships derived from field
experiments on extant species. Laboratory experiments have more often than
not revealed that variables other than the target parameter influence the
proxy signal, which makes proxy calibration a challenging task.
Understanding these secondary or "vital" effects is crucial for increasing
proxy accuracy. We present data from laboratory experiments showing that
oxygen isotope fractionation during calcification in the coccolithophore
Calcidiscus leptoporus and the calcareous dinoflagellate Thoracosphaera heimii is dependent on carbonate chemistry of
seawater in addition to its dependence on temperature. A similar result has
previously been reported for planktonic foraminifera, supporting the idea
that the [CO32−] effect on δ18O is universal for
unicellular calcifying planktonic organisms. The slopes of the δ18O/[CO32−] relationships range between –0.0243‰ (μmol kg−1)−1 (calcareous
dinoflagellate T. heimii) and the previously published –0.0022‰ (μmol kg−1)−1 (non-symbiotic
planktonic foramifera Orbulina universa), while C. leptoporus has a slope of –0.0048 ‰ (μmol kg−1)−1. We present a simple
conceptual model, based on the contribution of δ18O-enriched
HCO3− to the CO32− pool in the calcifying vesicle, which
can explain the [CO32−] effect on δ18O for the
different unicellular calcifiers. This approach provides a new insight into
biological fractionation in calcifying organisms. The large range in δ18O/[CO32−] slopes should possibly be explored as a means
for paleoreconstruction of surface [CO32−], particularly through
comparison of the response in ecologically similar planktonic organisms. |
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