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3.2. ICE AND CLIMATE 143
3.2.4 Climatic significance of stable water isotope records from Alpine ice
cores.
Participating scientists Markus Pettinger, Susanne Preunkert ∗ , Ralph Böhlert ∗∗ and Reinhard
Böhm ∗∗∗
∗ LGGS - CNRS, Grenoble
∗∗ Glaciology and Geomorphodynamics Group, Department of Geography, University of Zürich
∗∗∗ ZAMG, Wien
Abstract Upstream effects associated with local variations in snow deposition that influence long
term isotopic trends recorded in Alpine ice cores were investigated. Isotope records of two Mont Blanc
ice show the recent warming trend with high isotope sensitivity, whereas long term records show only
weak correlation with instrumental temperature data.
Figure 3.18: δ 18 O- records of a low
(0.2 m w.e./yr, middle) and a high
(1.1 m w.e./yr, bottom) accumulation core
from the Mont Blanc summit range.
Background Isotope δ 18 O and δD records from
high Alpine cold glaciers may provide complementary
records to polar cores, including the unique
possibility to extend the 250 years instrumental
climate time series only available from western
Europe (Schöner et al., 2002). On the other
side various glaciological constrains hamper the
straightforward interpretation of alpine isotope
records in terms of temperature changes. A multicore
study was therefore set up to partly compensate
for this basic shortcoming.
Funding EU-project ALP-IMP (Multicentennial
climate variability in the Alps based on
Instrumental data, Model simulations and Proxy
data)
Methods and results To determine systematic
upstream effects in the cachment area of
Monte Rosa deep ice cores three shallow firn cores
have been drilled along their flow line down to a
reflection layer determined by radio echo sounding
(as to guarantee an common time span). The
systematic change in the core mean δ 18 O value
along the flow line has been used to improve the
overall upstream corrections. The new data exhibit
in the upper region of the flowline a linear
δ 18 O-accumulation relation of 1.9 � per m water
equivalent. Thus, additional corrections up to
0.4� to those of Keck (2001) are necessary for
the long term trends recorded in Monte Rosa ice
cores. A different approach was chosen for the
Mont Blanc ice core in flank position. In this case,
the changes with depth of the winter snow fraction
induced by wind erosion was determined, but
only an insignificant dependance with depth could
be found.
In the time span of 1920 to 1995 both new Mont
Blanc ice cores show no clear correlation with instrumental
temperature, wich may be due to poor
dating. In contrast the recorded recent warming
trend (1980-2000) exhibits ∆δ 18 O/∆T relations
between 1.5 and 3 �/ ◦ C with high significance
in all ice cores. Previous studies show a relation
of 1.7 �/ ◦ C in the period of 1920 to 1995. Different
to existing Monte Rosa records showing an
odd long term trend towards lower isotope values
into the medieval era, the new Mont Blanc ice divide
core exhibits no such trend, but, if any, only
a weak δ 18 O increase by 0.6�. The respective
ice core chronology as based on a flow only model
(Raymond, 1983) is however still uncertain.
Future work Dating and isotopic analysis of
the new Monte Rosa ice core, drilled to get high
resolution records. In addition the model based
dating of the low accumulation Mont Blanc ice
core has to be improved by matching with known
dust and volcanic horizons.
Main publication Pettinger et al. [2005]