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| Titel |
Foraminifera Mg/Ca palaeothermometry in a high CO2 world - appropriate correction for secular change in seawater chemistry |
| VerfasserIn |
D. Evans, W. Müller |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250058765
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| Zusammenfassung |
| Palaeotemperature estimates using both the Mg/Ca ratio and δ18O of foraminifera suffer from
uncertainties regarding the composition of seawater, particularly during the Paleogene where
climate reconstruction is a priority. The fundamental difference between these techniques is
that proxy information exists for secular change in seawater Mg/Ca, whereas past
δ18Oseawater values have to be assumed, as even though changes in the bulk composition of
seawater can be calculated (depending on reconstructed ice volume), δ18Oseawater is locally
highly variable. Despite this principal advantage of Mg/Ca thermometry, the majority of
currently published Mg/Ca temperature reconstructions are likely to be inaccurate: The
previously used methodology for the required correction for temporal variation of seawater
Mg/Ca has assumed that a linear relationship exists between Mg-Caseawater and
Mg-Caforaminifera. However, recent studies [e.g. 1] have demonstrated that this is not the
case, and that a power relationship between these two parameters best describes the
data.
We will show the difference between these two correction techniques, focusing on why
assuming a linear correction has led to incorrect foraminiferal constraints regarding the
Mg/Ca ratio of the past oceans, particularly in the Paleogene. Furthermore, we demonstrate
that by comparing Mg/Ca and δ18O results from foraminifera that existed in an ice free world
it is possible to indirectly calibrate the relationship between Mg-Caseawater and
Mg-Caforaminifera. Whilst previous assumptions do not result in error in the reconstructed
magnitude of temperature change over Cenozoic climate transitions, it is likely
that (depending on the assumptions of a particular study) absolute temperature
estimates require revision. This particularly applies to results from time periods
associated with significant Antarctic ice volume, which leads to greater uncertainty in
δ18Oseawater.
[1] Segev & Erez, 2006, Geochem. Geophys. Geosys., 7(2). |
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