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| Titel |
Reconstruction of paleotemperature for a Palaeolithic site - evaluation of uncertainties in calculation based on phosphates' stable oxygen isotope composition |
| VerfasserIn |
Grzegorz Skrzypek, Andrzej Wiśniewski, Pauline Grierson |
| 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 |
250050602
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| Zusammenfassung |
| The presence of Neanderthals in Central Europe during the Weichselian glaciations
(~115–35ka) was sporadic and likely resulted from migration during warm phases only.
However, placing Neanderthals’ migrations within a precise climatic context has been
challenging, owing to significant uncertainty in dating of Palaeolithic sites older than 50ka.
The radiocarbon dating of the bone or tooth samples older than 50ka is usually very difficult
or impossible, due to the low collagen concentration and low resolution of the radiocarbon
method for such old samples. Consequently, most of the >50ka archaeological sites are dated
using Optically Stimulated Luminescence or Thermoluminescence methods only, which
introduce a high level of uncertainty (±5–10ka). As a result of this uncertainty,
chronologically linking a climate model to a particular archaeological site is not usually very
accurate.
To overcome this problem, we propose a new approach by providing a direct estimation
of mean air temperature at the precise time of a site occupation by Palaeolithic
hunters, regardless of the uncertainty in dating. We have used the stable oxygen
isotope composition of phosphates (δ18OP) of teeth from “dining scraps” (including
mammoths and bison) of Palaeolithic hunters from the Hallera site (Wroclaw/Poland) to
estimate temperatures during two past periods: OIS 5a–d (~115–74ka) and OIS 3
(~59ka). We show that during these two phases of Neanderthals’ presence at the
studied site, temperatures were 6.8Ë C and 6.3Ë C, respectively [1]. To provide some
modern context, these temperatures are ~1Ë C warmer than the current climate of
Stockholm.
The applied analytical method required the following steps: first, verification of the
preservation of δ18OP in bioapatite; then, calculation of the δ18OW value of environmental
water consumed by mammals; and finally, calculation of mean air temperature (Tair) based
on the relationship between δ18OW of participation and Tair. However, besides Tair, several
other factors may have complex influences on δ18O of meteoric water. For instance, a
variation in atmospheric circulation, due to expansion or shrinkage of the Scandinavian ice
cap, may have resulted in different amounts of precipitations from air masses coming from
different directions, and therefore in different annual mean δ18OW. We designed a
cross-verification procedure to assess the accuracy of our estimates, accounting for possible
changes in atmospheric circulations. We randomly selected a set of nine GNIP stations
with long δ18OW and Tair records, located ~500–1000km to the east, west and
south of our study site at similar altitudes. If, during the Pleistocene, the climate
was more continental, conditions at our site could have been more similar to those
observed currently, e.g., in Russia. If influences of the Atlantic were higher, conditions
would be expected to more closely resemble those now observed, e.g., in Western
Germany.
The mean Tair calculated for the sampling site varied around 6.8±1.5Ë C for the
older period studied and 6.3±1.3Ë C for the more recent, based on the δ18OP of all
analysed teeth samples and the δ18O–Tair relationship for the closest GNIP station in
Krakow. These uncertainties (±1.5–1.3Ë C) can be attributed to variation among
individuals and species and uncertainty of the analysis. When data for nine other
stations in the range of 1000km were used (6.9±1.6Ë C for the older period and
6.4±1.6Ë C for the more recent), the calculated values and uncertainties were not
significantly different from those calculated based on the data set for the nearest GNIP
station [1]. This consistency in estimated temperatures confirms that the fraction of
precipitation coming from different directions likely had minor influence on the
stable isotope composition of precipitation, and Tair was the major factor governing
δ18OW.
[1] Skrzypek G., WiśniewskiA., GriersonP.F., 2011. Quaternary Science Reviews (in
press). |
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