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| Titel |
Orbital control on late Miocene climate and the North African monsoon: insight from an ensemble of sub-precessional simulations |
| VerfasserIn |
A. Marzocchi, D. J. Lunt, R. Flecker, C. D. Bradshaw, A. Farnsworth, F. J. Hilgen |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 11, no. 10 ; Nr. 11, no. 10 (2015-10-01), S.1271-1295 |
| Datensatznummer |
250117430
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| Publikation (Nr.) |
 copernicus.org/cp-11-1271-2015.pdf |
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| Zusammenfassung |
| Orbital forcing is a key climate driver over multi-millennial timescales. In
particular, monsoon systems are thought to be driven by orbital cyclicity,
especially by precession. Here, we analyse the impact of orbital forcing on
global climate with a particular focus on the North African monsoon, by
carrying out an ensemble of 22 equally spaced (one every 1000 years)
atmosphere–ocean–vegetation simulations using the HadCM3L model, covering one
full late Miocene precession-driven insolation cycle with varying obliquity
(between 6.568 and 6.589 Ma). The simulations only differ in their prescribed
orbital parameters, which vary realistically for the selected time period. We
have also carried out two modern-orbit control experiments, one with late
Miocene and one with present-day palaeogeography, and two additional
sensitivity experiments for the orbital extremes with varying
CO2 forcing. Our results highlight the high sensitivity of
the North African summer monsoon to orbital forcing, with strongly
intensified precipitation during the precession minimum, leading to a
northward penetration of vegetation up to ~ 21° N. The
modelled summer monsoon is also moderately sensitive to palaeogeography
changes, but it has a low sensitivity to atmospheric CO2
concentration between 280 and 400 ppm. Our simulations allow us to explore
the climatic response to orbital forcing not only for the precession
extremes but also on sub-precessional timescales. We demonstrate the
importance of including orbital variability in model–data comparison studies,
because doing so partially reduces the mismatch between the late Miocene
terrestrial proxy record and model results. Failure to include orbital
variability could also lead to significant miscorrelations in
temperature-based proxy reconstructions for this time period, because of the
asynchronicity between maximum (minimum) surface air temperatures and minimum
(maximum) precession in several areas around the globe. This is of particular
relevance for the North African regions, which have previously been
identified as optimal areas to target for late Miocene palaeodata
acquisition. |
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