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located in the Bay of Bengal, which is strongly in
uenced by this major river system.
Furthermore, the terrestrial vegetation model Biome4 (Haxeltine and Prentice 1996 ;
Kaplan et al. 2003 ) was forced with input from the KCM to simulate climate-induced
changes in the distribution of plant functional types (PFT), whereby the C 4 /C 3
balance was de
ned as the fraction of net primary production produced by C 4 PFT.
For comparison, past changes in the relative proportions of C 4 and C 3 plants can be
derived from the
13 C isotopic signature of leaf wax n-alkanes measured in marine
sediments. As a sensitivity test we here show that air temperature, precipitation, and
atmospheric CO 2 levels are the most important climate factors in
uencing the C 4 /C 3
13 C signal registered in
signature of terrestrial vegetation, thus
finally shaping the
the sediment core.
3 Key Findings
The Indian summer monsoon is one of the major systems contributing to tropical
climate variability. In particular, there are large seasonal variations with intensive
rainfall during summer. The
D of multiple n-alkanes, a proxy for the amount of
continental rainfall, implies increased precipitation during the early Holocene and
the Eemian at a similar magnitude (Fig. 1 a). Also Ti/Ca ratios, a proxy for litho-
genic vs. marine input (not shown), support the hypothesis for enhanced monsoon
rainfall since higher precipitation and river run off are the primary driver for larger
terrigenous mineral
13 C of four
individual n-alkanes is shifted towards more depleted values during the interglacials
compared to glacial values, indicating an expansion of C 3 vegetation or/and
increased humidity in a warmer climate (Fig. 1 a). The differences between
fluxes during the Holocene and Eemian. The
13 C
values for individual n-alkanes in each sample analysed are very likely due to the
different proportional contributions from different vegetation types (Wang et al.
2013 ). However, quite similar
13 C values within 2
for Holocene and Eemian
samples suggest similar vegetation types during both interglacials. Our preliminary
results imply that despite the difference in insolation forcing, the amelioration of
vegetation and increase in monsoonal precipitation over India experienced similar
magnitudes for the Holocene and the Eemian.
According to climate model simulations the strength of the Indian Monsoon was
more intense in both the early Holocene and the early Eemian compared to pre-
industrial (Fig. 1 b, lower panels). Although both interglacial periods underwent
comparable temporal changes in orbital con
gurations, an overall higher eccen-
tricity during the Eemian resulted in a greater magnitude of insolation change than
during the Holocene (Fig. 1 a). Consequently, the mean annual summer precipita-
tion (June-August; JJA) is enhanced by up to 7 mm/day in the Early Holocene and
by up to 9 mm/day during the Early Eemian relative to preindustrial in our model
simulations. Also changes in net precipitation (precipitation-evaporation) indicate
wetter conditions for the Eemian than for the Holocene, a general northern hemi-
sphere pattern which also holds true for the African and South American Monsoon
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