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| Titel |
Fluid inclusion stable isotopes and clumped isotopes thermometry study of Eastern Mediterranean paleoclimate |
| VerfasserIn |
A. Matthews, M. Bar-Matthews, H. P. Affek, A. Ayalon, H. B. Vonhof, S. Zaarur, Y. Burstyn |
| 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 |
250064008
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| Zusammenfassung |
| Fluid inclusion (FI) stable isotopes and clumped isotopes thermometry provide powerful
tools for reconstructing paleoclimates using speleothems. Clumped isotopes thermometry is a
unique tool for paleotemperature determination using the mass 47 anomaly (Δ47), but its
application to speleothems is complicated by the occurrence of a kinetic isotope effect (KIE)
that accompanies CO2 degassing during carbonate precipitation1. Experimental studies
involving the surface precipitation of synthetic calcite2 provide a Δ47 thermometer
calibration that takes KIE into account and allows its direct application to speleothems.
Complementary, the δDw and δ18Ow values of speleothem FI provide an important proxy for
cave water-rainfall paleo-hydrological conditions, together with the data required for
construction of the meteoric water line (MWL) relationship. Until recently the main studied
parameter is δDw, and the reliability of FI δ18Ow has been questioned because of the
possibility of post-depositional isotope exchange with the surrounding calcite. When
speleothem calcite δ18Occ is measured, Δ47 temperatures allow δ18Ow to be independently
calculated using the calcite-water fractionation relationship. Methods for FI analysis
using crushing in a helium stream, TC/EA and continuous flow mass spectrometry
(Amsterdam system3) enable both δDw and δ18Ow to be determined, thus allowing
measured δ18Ow values to be compared with those calculated from Δ47 temperatures
and δ18Occ. We apply these methodologies to paleoclimate study in the Eastern
Mediterranean (EM) region during the last 150 ky: in the Soreq Cave from the
glacial stage 6 to the last interglacial stage 5e and the last glacial maximum (LGM)
to the Holocene, and to the Alpine karst system of the Hermon mountain range
(MS) cave4 during the last interglacial and brief warm intervals during the last
glacial.
Soreq Cave Δ47 data show temperature minima at the termination of stage 6 and the
LGM, but the LGM temperatures (ca 9Ë C) were several degrees lower than for glacial stage
6. Both minima were followed by sharp temperature rises into stage 5e and Holocene,
respectively. Δ47 thermometry of the MS cave speleothems confirm that temperatures rose to
several degrees above freezing during brief warming events in the otherwise frozen last
glacial at this altitude (2224m). MWL relationships over the last 150 ky using FI δDw and
calculated δ18Ow suggest that glacial periods are characterized by a MWL closer
to that of the global system, whereas interglacial periods in the Soreq cave and
warm glacial intervals in the MS cave show higher “d excesses” characteristic of
the present day EM region. The MWL relationships of Soreq Cave speleothems
in stage 5e are consistent with the ‘amount effect’ controlling δ18Ow, as found
today and in the Holocene5. Comparison of measured with calculated δ18Ow values
show that it may also be possible to retrieve accurate values for δ18Ow in suitable
speleothems.
1. Affek, H., et al (2008). Geochim. Cosmochim. Acta 72, 5351-5360. 2. Zaarur, S. and
Affek, H. In preparation. 3. Vonhof, H., et al. (2006). Rapid Comm. Mass Spectrom. 20,
2553-255. 4. Ayalon et al (2012) In submission. 5. Bar Matthews, M., et al (2003). Geochim.
Cosmochim. Acta 67, 3181-3199. |
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