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144 CHAPTER 3. TERRESTRIAL SYSTEMS
3.2.5 Analyses of dissolved organic carbon (DOC) at low levels in Alpine
and polar glaciers
Participating scientists Martin Schock, Steffen Greilich ∗ and Jean-Robert Petit ∗∗
∗ Heidelberger Akademie der Wissenschaften, Forschungsstelle Archaeometrie
∗∗ LGGE-CNRS, Grenoble
Abstract Deploying a novel method for ultra-low DOC analysis, DOC in high Alpine precipitation
was found to be increased by a factor of 2-4 (to up to 4 · 10 −7 gC/g) since preindustrial times, wheras
DOC level less than about 10 −8 gC/g are seen in Antarctic ice cores.
Background The bulk quantity DOC constitutes
an important part of the impurity content
of non-temperated glaciers. Related retrospective
studies would be highly relevant therefore in terms
of radiative forcing, past atmospheric carbon cycles
and englacial microbial activity. However no
systematic ice core analyses of DOC were available,
yet, due to unsolved contamination problems
and insufficient sensitivity of conventional TOC
analysers. In this context a dedicated flow injection
system, based on UV induced DOC degregation
has been developed (along with an appropriate
decontamination procedure as to cope with the
challenge to analyse ice cores, drilled in kerosene
filled bore holes).
Funding EU-CARBOSOL project : ”Present
and Retrospective State of Organic versus Inorganic
Aerosol over Europe : Implications for Climate”
Methods and results Sample decontamination,
(deploying partial melting or a melting
probe) is shown to control the precision and
quantitative detection limit (presently around
5 · 10 −9 gC/g). Extensive comparison with a high
temperature combustion method revealed that the
UV degradation efficiency for most of the relevant
DOC species seems to be close to 90% .
Various high Alpine ice cores have been systematically
analysed for DOC (partly in seasonal resolution),
indicating a significant change by typically
a factor of 2 to 4 since the pre industrial era.
This presumably anthropogenic effect is however
clearly lower, compared to concurrent changes of
man made inorganic species, like sulphate (Preunkert
et al., 2001).
DOC-surveys of a cold, low elevation Alpine ice
cap (Bengel, 2005), in view of radiocarbon dating
of the ice body genesis via DOC indicated, that
about 1 kg ice would be needed for this purpose.
Most difficult in terms of reliable measurements
have been Antarctic ice cores, where DOC levels
approach the limit of detection. Including polar
ice cores, no big difference is seen in the pre
industrial DOC level between Alpine and Greenland
sites, wheras an interhemispheric difference
by one order of magnitude shows up with respect
to Antarctica. Here, DOC analyses in accreted ice
from Lake Vostok gave a mean DOC level lower
by roughly a factor of 50, than previously reported
by Priscu et al., (1999), giving much less room for
viable micro biological activities, than hitherto assumed
(Bulat et al 2004).
Figure 3.19: Range of dissolved organic carbon
(DOC) content in various ice bodies (including accreted
ice from Lake Vostok), displayed by median
as well as by 25% and 75% percentils, respectively
Outlook/Future work Radiocarbon dating of
the DOC fraction in Alpine ice.
Main publication J.-R. Petit , J. Flückiger, M.
Leuenberger, W. Haeberli, R. Psenner , Dissolved
organic carbon (DOC) in ice samples from nontemperated,
polar and Alpine glaciers. Geophysical
Research Abstracts, Vol. 7, 08671, 2005
Schock et al. [2005]