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| Titel |
Polar amplification of the early Eocene indicated by δ2H values of lignin methoxyl groups of mummified wood |
| VerfasserIn |
Tobias Anhäuser, Benjamin Hook, Jochen Halfar, Markus Greule, Frank Keppler |
| 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 |
250145325
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| Publikation (Nr.) |
 EGU/EGU2017-9257.pdf |
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| Zusammenfassung |
| A number of well-preserved mummified wood samples have been excavated during diamond
mining operations in early Eocene (55-50 Ma) kimberlite deposits located near the Arctic
Circle (64∘ N, 110∘ W) in the Canadian Northwest Territories. The preserved wood,
containing multi-decadal length tree-ring information, therefore allows the reconstruction
of an unprecedented snapshot of terrestrial high-latitude climate during the early
Eocene. Here we used wood-derived stable hydrogen isotopes (δ2H) as proxy for
paleoclimatic interpretations. While cellulose extractions are commonly used for
the analysis of modern wood-derived δ2H values, the mummified wood samples
had been affected by selective degradation leading to a strong or even complete
loss of cellulose while leaving a lignin-rich material behind. We have therefore
analyzed δ2H values of the lignin methoxyl groups that have previously been shown
to reflect the δ2H values of the local precipitation and can thus be used to infer
paleoclimate information such as temperature changes. We applied this proxy to specimens
found in three adjacent kimberlite pipes (30 km apart) which represent a range of
early Eocene ages (Rb/Sr dating: 55.5 ± 0.7, 55.2 ± 0.3 and 53.3 ± 0.6 Ma [2σ
standard deviation]). The δ2H values were measured at annual resolution for the three
mummified wood series (length of individual time series: 82, 62 and 40 years)
and the mean δ2H value of precipitation for the three decadal-scale time slices
was reconstructed. Finally, we used existing relationships between early Eocene
temperatures and stable isotopes in precipitation to quantify temperature changes.
Warming phases such as the one covered here (culminating in the Early Eocene
Climatic Optimum [52 to 50 Ma]) are commonly accompanied by a stronger increase
in arctic/subarctic surface air temperatures in comparison to the global average
(the ratio of these temperature differences is referred to as the polar amplification).
Our estimation shows for the period between 55.5 and 53.3 Ma a mean subarctic
temperature increase of 7.3 ± 3.7 ∘C. Globally, for the same period, a mean temperature
increase of 1.5 ∘C has previously been derived from the δ18O values of benthic
foraminifera. This suggests a polar amplification with a magnitude of 5 (±3). Despite
uncertainties regarding both the age determination and the temperature reconstructions, the
magnitude of our estimation is broadly in line with polar amplifications estimated
for other Cenozoic global warming intervals, which have shown magnitudes of
3 to 4. Even though occurring on a much shorter time scale, the current global
warming shows a similar polar amplification pattern as post industrial revolution Arctic
temperatures, which are projected to amplify significantly in the near future, have already
increased up to 3 ∘C as compared to a lower latitude temperature increase of 1 ∘C. |
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