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3 Key Findings
For the mid-Holocene, high obliquity results in more high-latitude summer inso-
lation at the expense of low-latitude summer insolation. Obliquity explains most of
the variance in the annual insolation, and the effect is symmetric between the
hemispheres but asymmetric between the tropics and high latitudes. The seasonal
template model (Laepple and Lohmann
2009
) largely reproduces the Holocene
temperature trends as simulated by coupled climate models and provides a theo-
retical framework for our project.
Our multi-proxy mapping reveals contrasting Holocene SST trends, depending
upon the proxy used. To reconcile these mismatches between proxies, we
nd that
foraminiferal Mg/Ca and alkenones paleothermometers may be skewed toward
speci
c seasons (Leduc et al.
2010a
)
(Fig.
1
). Following on a seasonality
hypothesis, a
first attempt to test and quantify the degree to which SST databases
are seasonally-skewed was conducted in data-model comparisons aiming at
filtering
model output for different seasons and compare it to the SST database (Leduc et al.
2010a
; Lohmann et al.
2013
).
Using the coupled atmosphere-ocean general circulation model COSMOS with
applied orbital forcing, we investigate the climate evolution and variability of the last
two interglacial periods, the mid-Holocene (6 thousand years (ka) before present
(BP)) and the Last Interglacial (LIG) (125 ka BP). Earth
s orbital parameters in these
two periods lead to an increase in the Northern Hemisphere
'
'
s seasonal insolation
Fig. 1 Left panels modern-day seasonal anomalies in SST in the North Atlantic Ocean (in
°
C) and
locations of marine sediment cores corresponding to the records shown in right panels. Right
panels records for paleo-SST covering the last 10 ka and estimated from alkenone unsaturation
index and planktonic foraminifera Mg/Ca measurements. Adapted from Leduc et al. (
2010a
)
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