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| Titel |
Erosional response of active mountain belts to Milankovitch-cycle climate forcing : time lag and amplification |
| VerfasserIn |
Jean Braun, Alexandra Gourlan, Christophe Voisin, Catherine Chauvel |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076780
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| Zusammenfassung |
| We investigated the erosional response of a steady-state mountain belt (i.e. that has reached a
balance between tectonic uplift and erosion) to variations in rainfall intensity using a simple
stream-power law to represent river bedrock incision. In the stream power law, the erosion
rate is assumed to be proportional to slope (to the power n) and discharge (to the power
m) We show that, when precipitation is forced to vary periodically, the erosional
response is offset by a time lag that depends on the period of the climate forcing
and the value of both exponents (n and m). Furthermore, for large values of these
exponents, variations in sedimentary flux are amplified with respect to the imposed
climate variations, explaining why even small periodic variations in precipitation
rate can lead to a large and thus observable signal in the sedimentary record. To
support our findings we used geochemical observations from site ODP-758 in the
Indian Ocean that show a clear offset between a record of climate variability at the
Milankovitch periods (23, 41 and 100 ky) derived from Oxygen isotope measurements
and the erosional response from the nearby Himalayan orogen measured by Nd
seawater isotopic composition. Using this dataset, we were able to constrain the
values of the exponents n and m that best reproduce the observed time lags as
a function of the forcing period, and, from them, we estimated the amplification
factor, which can be as high as 3 to 4. This finding may explain why small amplitude
variations in climate (precipitation) can lead to substantial and thus measurable
variations in sedimentary flux out of large-scale orogens such as the Himalayan system. |
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