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| Titel |
Relationships between bottom water carbonate saturation and element/Ca ratios in coretop samples of the benthic foraminifera Oridorsalis umbonatus |
| VerfasserIn |
C. F. Dawber, A. Tripati |
| 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. 8 ; Nr. 9, no. 8 (2012-08-09), S.3029-3045 |
| Datensatznummer |
250007234
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| Publikation (Nr.) |
 copernicus.org/bg-9-3029-2012.pdf |
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| Zusammenfassung |
| Elemental ratios in benthic foraminifera have been used to
reconstruct bottom water temperature and carbonate saturation
(Δ[CO32−]). We present
elemental data for the long-ranging benthic foraminifera
Oridorsalis umbonatus from sediment core tops
that span a narrow range of temperatures and a wide range of saturation
states. B/Ca, Li/Ca, Sr/Ca and Mg/Ca ratios exhibit positive correlations
with bottom water carbonate saturation. The sensitivity of individual
element/calcium ratios to bottom water Δ[CO32−] varies considerably, with B/Ca being most
sensitive and Sr/Ca the least sensitive. The empirically derived sensitivity
of B/Ca, Li/Ca, Mg/Ca and Sr/Ca to bottom water Δ[CO32−] are 0.433 ± 0.053 and
0.0561 ± 0.0084 μmol mol−1 μmol kg−1 and 0.0164 ± 0.0015 and 0.00241 ±
0.0004 mmol mol−1μmol kg−1, respectively. To assess the fidelity of these
relationships and the possibility of applying these relationships to earlier
periods of Earth history, we examine the mechanisms governing elemental
incorporation into foraminiferal calcite. Empirical partition coefficients
for Li and Sr are consistent with Rayleigh fractionation from an internal
pool used for calcification. For O. umbonatus and
other benthic species, we show that the fraction of Ca remaining in the pool
is a function of bottom water Δ[CO32−], and can
be explained by either a growth rate effect and/or the energetic cost of
raising vesicle pH at the site of calcification. Empirical partition
coefficients for Mg and B may also be controlled by Rayleigh fractionation,
but require that either the fractionation factor from the internal pool is
smaller than the inorganic partition coefficient and/or additional
fractionation mechanisms. O. umbonatus element
ratio data may also be consistent with fractionation according to the
surface entrapment model and/or the presence of discrete high- and low-Mg
calcite phases. However, at present we are limited in our ability to assess
these mechanisms. The new X/Ca data for O. umbonatus
provide constraints to test the role of these mechanisms in the
future. |
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