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| Titel |
Mg/Ca and Mn/Ca ratios in benthic foraminifera: the potential to reconstruct past variations in temperature and hypoxia in shelf regions |
| VerfasserIn |
J. Groeneveld, H. L. Filipsson |
| 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 ; 10, no. 7 ; Nr. 10, no. 7 (2013-07-29), S.5125-5138 |
| Datensatznummer |
250018366
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| Publikation (Nr.) |
 copernicus.org/bg-10-5125-2013.pdf |
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| Zusammenfassung |
| Shelf and coastal regions are exceptionally important for many countries as
they provide the main habitat for many economically important fish and
shellfish species. With ongoing climate change and human-induced
eutrophication the shelf regions are especially affected, resulting in
increased temperatures and stratification as well as oxygen depletion of the
bottom waters. In order to be able to predict the magnitude of these changes
in the future, it is necessary to study how they varied in the past. Commonly
used foraminiferal climate and environmental proxies, e.g., stable isotopes
and trace metal/Ca ratios, that are applied in open-ocean settings are not
necessarily applicable in shelf regions, either as faunas are significantly
different or as conditions can change much faster compared to the open ocean.
In this study we explore the use of Mg/Ca as paleothermometer and Mn/Ca as a
potential proxy for changing dissolved oxygen conditions in bottom water on
the benthic foraminifera Bulimina marginata and
Globobulimina turgida. Living specimens were collected from the
Skagerrak and the Gullmar Fjord (SW Sweden); the latter is hypoxic for
several months a year. As the specimens were alive when collected, we assume
it unlikely that any diagenetic coatings have already significantly affected
the trace metal/Ca ratios. The Mg/Ca ratios are similar to previously
published values but display much larger variation than would be expected
from the annual temperature change of less than 2 °C. An additional
impact of the difference in the calcite saturation state between the
Skagerrak and the Gullmar Fjord could explain the results. Mn/Ca ratios from
G. turgida can potentially be related to variations in dissolved
oxygen of the habitat where the foraminifera calcify. Samples from the
Skagerrak display increased Mn/Ca in specimens that lived deeper in the
sediment than those that lived near the surface. G. turgida samples
from the low-oxygen Gullmar Fjord showed significantly increased Mn/Ca, being
highest when bottom water dissolved oxygen was at a minimum. Our study
suggests that trace metal/Ca ratios in benthic foraminifera from shelf
regions have the potential to record past variations in bottom water
temperature and dissolved oxygen concentrations, but an additional impact of
the inorganic carbonate chemistry cannot be excluded. |
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