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| Titel |
Encrustation and trace element composition of Neogloboquadrina dutertrei assessed from single chamber analyses – implications for paleotemperature estimates |
| VerfasserIn |
L. Jonkers, L. J. Nooijer, G.-J. Reichart, R. Zahn, G.-J. A. Brummer |
| 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 (2012-11-26), S.4851-4860 |
| Datensatznummer |
250007416
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| Publikation (Nr.) |
 copernicus.org/bg-9-4851-2012.pdf |
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| Zusammenfassung |
| Crust formation is a common phenomenon in planktonic foraminifera. Because
of their different formation mechanism and hence composition, crusts affect
the overall test composition and therefore complicate the use of
crust-bearing foraminifera in paleoceanography. Such species are often used
to estimate subsurface paleotemperatures, and although the influence of encrustation
on the trace element/Ca ratio is recognised, it has not been
systematically explored between and within tests. Here we use laser ablation
ICP-MS to assess the variability in trace element composition of the crust
of Neogloboquadrina dutertrei within individual chambers, as well as the effect of compositional
heterogeneity of the crust on whole test chemistry. Compositionally, the
outer crust differs from inner layer by lower Mg/Ca and Mn/Ca, but is
indistinguishable in Sr/Ca. Crust thickness decreases towards the younger
chambers, and it may be entirely absent from the last chamber. In contrast to
Mn/Ca and Sr/Ca, crustal Mg/Ca ratios show a tendency towards higher values
on the younger chambers. These patterns in crust thickness and in crust
Mg/Ca indicate that temperature is not the dominant factor controlling crust
composition. Temperature estimates based on N. dutertrei, and presumably other
crust-forming species too, are therefore biased towards too low values.
Through comparison of modern and glacial tests, we show that this bias is not
constant and that changes in crust thickness and/or in Mg/Ca values can
spuriously suggest temperature changes. |
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