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| Titel |
Proxy comparisons for Paleogene sea water temperature reconstructions |
| VerfasserIn |
Marijke de Bar, Lennart de Nooijer, Stefan Schouten, Martin Ziegler, Appy Sluijs, Gert-Jan Reichart |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250138847
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| Publikation (Nr.) |
 EGU/EGU2017-1978.pdf |
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| Zusammenfassung |
| Several studies have reconstructed Paleogene seawater temperatures, using single- or
multi-proxy approaches (e.g. Hollis et al., 2012 and references therein), particularly
comparing TEX86 with foraminiferal δ18O and Mg/Ca. Whereas trends often agree
relatively well, absolute temperatures can differ significantly between proxies, possibly
because they are often applied to (extreme) climate events/transitions (e.g. Sluijs et
al., 2011), where certain assumptions underlying the temperature proxies may not
hold true. A more general long-term multi-proxy temperature reconstruction, is
therefore necessary to validate the different proxies and underlying presumed boundary
conditions.
Here we apply a multi-proxy approach using foraminiferal calcite and organic proxies to
generate a low-resolution, long term (80 Myr) paleotemperature record for the Bass River
core (New Jersey, North Atlantic). Oxygen (δ18O), clumped isotopes (Δ47) and Mg/Ca of
benthic foraminifera, as well as the organic proxies MBT’-CBT, TEX86H, U37K’ index and
the LDI were determined on the same sediments. The youngest samples of Miocene age are
characterized by a high BIT index (>0.8) and fractional abundance of the C32 1,15-diol
(>0.6; de Bar et al., 2016) and the absence of foraminifera, all suggesting high
continental input and shallow depths. The older sediment layers (∼30 to 90 Ma)
display BIT values and C32 1,15-diol fractional abundances <0.3, implying marine
conditions.
The temperature records (∼30 to 90 Ma) show the global transition from the Cretaceous
to Eocene greenhouse world into the icehouse climate. The TEX86H sea surface temperature
(SST) record shows a gradual cooling over time of ∼35 to 20 ˚ C, whereas the δ18O-derived
bottom water temperatures (BWTs) decrease from ∼20 to 10 ˚ C, and the Mg/Ca and
Δ47-derived BWTs decrease from ∼25 to 15 ˚ C. The absolute temperature difference
between the δ18O and Δ47, might be explained by local variations in seawater δ18O
composition. Similarly, the difference in Mg/Ca- and δ18O-derived BWTs is likely caused by
uncertainties in the seawater Mg/Ca model and the relationship between the seawater Mg/Ca
and the incorporation of Mg into the foraminiferal shell. The U37K’ index could not be
calculated as only di-unsaturated alkenones were identified, indicating that SSTs were >
28 ˚ C. In contrast, LDI temperatures were considerably lower and varied only
between 21 and 19 ˚ C. MBT’-CBT derived mean annual temperatures for the ages
of 9 and 20 Ma align well with the TEX86H SSTs. Overall, the agreement of the
paleotemperature proxies in terms of main tendencies, and the covariation with the global
benthic oxygen isotope compilation suggests that temperatures in this region varied in
concert with global climate variability. The fact that offsets between the different
proxies used here remain fairly constant down to 90 Ma ago, indicates that the
fundamental mechanisms responsible for the proxy relation to temperature remained
constant.
de Bar, M. W., et al. (2016), Constraints on the application of long chain diol proxies in
the Iberian Atlantic margin, Org. Geochem., 101, 184-195.
Hollis, C. J., et al. (2012), Early Paleogene temperature history of the Southwest Pacific
Ocean: Reconciling proxies and models, Earth Planet. Sci. Lett., 349, 53-66.
Sluijs, A., et al. (2011), Southern ocean warming, sea level and hydrological change
during the Paleocene-Eocene thermal maximum, Climate of the Past, 7(1), 47-61. |
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