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| Titel |
Changing Miocene seasonality patterns in Central Europe deduced from the Crassostrea isotope archive |
| VerfasserIn |
Patrick Grunert, Mathias Harzhauser  , Werner E. Piller , Arne Micheels |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051574
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| Schlagwörter |
Fossilien, Mollusca, Isotope, Paläoklima, Miozän, Tethys |
| Geograf. Schlagwort |
Österreich, Europa, Mitteleuropa |
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| Zusammenfassung |
| The Western Tethyan estuarine oyster Crassostrea gryphoides is an excellent climate archive
due to its large size and rapid growth. The bivalve was a specialist for estuarine habitats,
which, as junction between terrestrial and marine environments, are strongly modulated by
climatic parameters such as precipitation and discharge. Seasonal rhythms of the climate may
thus be detected from the Crassostrea isotope archive.
The analysed shells of the giant oyster Crassostrea gryphoides document a distinct change in
seasonality patterns from the Miocene Climate Optimum (MCO) into the Miocene
Climate Transition (MCT). The Burdigalian and Langhian shells exhibit a markedly
regular seasonality with regularly occurring seasons of high precipitation, reflected
by increased freshwater discharge into the estuaries. Individual growth rates are
about 2-3 times faster than in geologically younger oysters in the Paratethys Sea. In
contrast to the MCO shells, with parallel δ18O and δ13C profiles, the early MCT shell
indicates phytoplankton blooms during autumn, reflected by a slight phase lag.
MCO water temperatures ranged between 17-19°C during cool seasons and c. 28°C
in warm seasons with a characteristic seasonal range of 9-10°C. An extremely
long 4-decade-record of the huge oyster from the early MCT still suggests a strong
seasonality. A slight cooling might be expressed by the annual temperature range from c.
16-25°C. Soon after, the Serravallian shells of Central Europe document a drastic
change of patterns. Successions of dry years with irregular precipitation events
occur, whereas the δ18O record suggests a continuous regular alternation of warm
and cool seasons. The breakdown of isotope correlation may thus be related to
suboptimal nutrition supply which would also explain the small shell-sizes during that
time.
In terrestrial climates the MCO/MCT transition is characterized by an increase in mean
annual range of temperature, mainly due to decreasing cold month temperatures. This trend is
not so obvious in the data presented here for the shells from the late MCT. Rather warm
Paratethyan sea water temperatures during the late Serrvallian, however, are also indicated by
the wide spread ooid formation, which contradicts a pronounced cooling at that time.
Therefore, unstable precipitation on a multi-annual to decadal scale, rather than a simple
temperature decline, may thus be an important forcing mechanism for the MCT climate in
Central Europe.
The study contributes to the FWF-grant P21414-B16. |
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