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| Titel |
Are oxygen isotopes in Amazon tree rings a good proxy for Amazon rainfall? |
| VerfasserIn |
Roel Brienen, Gerd Helle, Thijs Pons, Emmanuel Gloor |
| 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 |
250054381
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| Zusammenfassung |
| The Amazon is the world’s largest drainage basin, transporting about one fifth of the annual
global river runoff. Its hydrological cycle is tightly linked with the carbon cycle of the
Amazon rainforest, one of the largest terrestrial carbon pools, and small changes in the
hydrological cycle of the Amazon therefore affects climate globally. The increase in
extreme droughts of the Amazon over the last decade, possibly due to anthropogenic
forcing, emphasizes the need for understanding the magnitude of historical variability
of hydrological circulation patterns within the Amazon. However, instrumental
climate records of the Amazon are scarce and of limited length. In this study, we
investigate oxygen isotopes in tree rings as a proxy for the hydrological cycle of the
Amazon. To this end, we established a 100 yr long chronology of oxygen isotopes in
tree ring cellulose (TR-δ18O) of Cedrela odorata from northern Bolivia (11o55’S,
65o40’W).
In temperate regions oxygen isotopic measurements in tree rings have been extensively
used as climate proxies reflecting significant influences of several external and internal
factors, but only weakly the isotopic variations in source water. In the tropics such studies are
very scarce. Our site record from individual trees show that TR-δ18O is highly correlated
with δ18O in meteoric water over the Amazon (r=0.83) with depleted values of δ18O during
high rainfall years (i.e., so-called “amount-effect”). This suggests that Cedrela
odorata relies on superficial soil water and that TR-δ18O is a reliable measure of
historical variation in δ18O in meteoric water. The long-term inter-annual record of
TR-δ18O correlated well with inter-annual variation in (summer) rainfall over the
entire basin (r=-0.46) and with (maximum) river run-off levels of the Rio Negro at
Manaus (r=-0.62). Pronounced dry years over the last century are clearly visible in
the oxygen isotope chronology as anomalously high values of TR-δ18O. TR-δ18O
is also a good proxy for large-scale controls of Amazon precipitation, showing
strong correlations with ENSO indices (SOI; r=- 0.52) and Tropical North Atlantic
SSTa (r=0.45), two of the main drivers of Amazon precipitation. These correlation
patterns are not stable over time and show decadal-scale variations, indicating that
large-scale controls of Amazon basin hydrology may have varied over historical time
periods.
Our study shows that δ18O in tree rings of Cedrela odorata is a powerful proxy for
historical variability in the Amazon hydrological cycle and will improve our knowledge of
long-term precipitation changes, which is of great importance for future predictions of the
hydrological cycle in the Amazon. |
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