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Model-Data Synthesis of Monsoon
Amplitudes for the Holocene and Eemian
Birgit Schneider, Ralph R. Schneider, Yiming Wang
and Vyacheslav Khon
Abstract Monsoon intensity is driven by changes in hemispheric summer
insolation. Marine proxy data show distinct glacial-interglacial variability with
changes in vegetation and weathering inferred from the terrigenous fraction, e.g., by
plant lipid and mineral composition. Unfortunately, no quantitative evidence is
available for differences in monsoonal precipitation. A sensitivity study with a
vegetation model implies that C
4
/C
3
ratios are in
uenced by individual changes in
precipitation, CO
2
, and temperature. Therefore, sedimentary
13
C records of land
plant lipids are no unambiguous indicator for humidity-driven changes in paleo-
vegetation. A novel indicator of past humidity over continents, the
δ
D signature of
leaf waxes, suggests similar conditions for the Indian summer monsoon during the
Holocene and Eemian. However, this new proxy requires more detailed regional
studies, since climate model simulations clearly show signi
δ
cant differences in
monsoon strength between interglacial periods. Accordingly, a more intense
hydrological cycle is expected for the Eemian due to an overall warmer climate
driven by precessional forcing.
Keywords Paleomonsoon
Precipitation reconstructions
Marine and terrestrial
proxy data
Climate modeling
Coupled atmosphere-ocean hydrological cycle
1 Introduction
The frequencies of climate extremes associated with the hydrological cycle in low
latitudes have increased during the last decades due to global warming (IPCC
2007
).
It is important to know how the hydrological cycle responds to global warming,
because intra- and interannual changes associated with monsoon rainfall have
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