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reconstruct water temperature and the MBT/CBT index to reconstruct mean air
temperature) as well as compound-speci
c hydrogen isotopic composition of lipids
derived from land-plant leafwaxes (e.g., long-chain, odd-numbered n-alkanes) to
reconstruct the hydrological cycle. Application of these molecular proxies on a
Holocene fjord sediment record from the center of the SWW and covering the
Holocene shows promising results.
Numerical transient experiments using the comprehensive global climate model
CCSM3 (Community Climate System Model version 3) were carried out in order to
simulate the evolution of the SWW under orbital forcing from the mid-Holocene
[7,000 years (ka) before present (BP)] to pre-industrial modern times (250 years
BP). These simulations were accompanied by a model inter-comparison with
orbitally forced Holocene transient simulations from four other coupled global
climate models (Varma et al. 2012a ). In order to study the response of SWW to
solar variability, model runs with idealized solar forcing were performed (Varma
et al. 2011 ). Finally, we investigated the in
uence of the stratosphere and its ozone
content on SWW variability, using two transient simulations (one with
xed and
one with solar-induced varying stratospheric ozone) with the coupled atmosphere-
ocean general circulation model EGMAM (ECHO-G with Middle Atmosphere
Model) focusing on the periods of the Late Maunder Minimum (LMM: 1675
AD) and Pre-Industrial (PI: 1716
1790 AD) (Varma et al. 2012b ).
3 Key Findings
Our multi-proxy compilation based on fjord and lake sediment records from the
hyperhumid zone of southernmost Chile provides a consistent picture of Holocene
SWW variability (Fig. 1 ; Lamy et al. 2010 ). Precipitation and thus SWW strength
changes deduced from humidity sensitive pollen, precipitation-dependent terrestrial
organic carbon accumulation in lake and fjord sediments (Fig. 1 e), and salinity
dependent decrease in biogenic carbonate accumulation indicate wetter/windier
conditions between
12.5 and
8.5 ka BP, intermediate conditions thereafter
finally reduced precipitation and less intense westerlies
during the late Holocene (Fig. 1 ). At the northern margin of the SWW in central
Chile reconstructed rainfall changes are generally anti-phased to those from the core
zone. A rainfall reconstruction based on Lake Aculeo level changes (34
5.5 ka BP, and
S; Fig. 1 a;
Jenny et al. 2003 ) reveals substantially reduced precipitation during the early and
mid-Holocene in agreement with reduced terrigenous sediment
in Lake
LleuLleu (37
S; Fig. 1 b) and increased input of Andean-derived versus coastal-
derived terrestrial material at the continental margin (41
S; Fig. 1 c; Lamy et al.
2001 ). All three records show a pronounced shift to more humid conditions starting
at ca. 5.5 ka BP and extending throughout the late Holocene. Though these records
only reach back to
10 ka BP, substantially lower rainfall during the early
Holocene and thus reduced westerly in
uence has been reconstructed at many sites
in the region (Latorre et al. 2007 ).
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