Abstract. High-alpine glaciers are valuable archives of past climatic and environmental conditions. The interpretation of the preserved signal requires a precise
chronology. Radiocarbon (14C) dating of the water-insoluble organic
carbon (WIOC) fraction has become an important dating tool to constrain the
age of ice cores from mid-latitude and low-latitude glaciers. However, in some
cases this method is restricted by the low WIOC concentration in the ice. In
this work, we report first 14C dating results using the dissolved organic
carbon (DOC) fraction, which is present at concentrations of at least a factor
of 2 higher than the WIOC fraction. We evaluated this new approach by
comparison to the established WIO14C dating based on parallel ice core
sample sections from four different Eurasian glaciers covering an age range of
several hundred to around 20 000 years; 14C dating of the two fractions
yielded comparable ages, with WIO14C revealing a slight, barely
significant, systematic offset towards older ages comparable in magnitude with
the analytical uncertainty. We attribute this offset to two effects of about
equal size but opposite in direction: (i) in-situ-produced 14C
contributing to the DOC resulting in a bias towards younger ages and (ii)
incompletely removed carbonates from particulate mineral dust (14C-depleted) contributing to the WIOC fraction with a bias towards older ages.
The estimated amount of in-situ-produced 14C in the DOC fraction is
smaller than the analytical uncertainty for most samples. Nevertheless, under
extreme conditions, such as very high altitude and/or low snow accumulation
rates, DO14C dating results need to be interpreted cautiously. While
during DOC extraction the removal of inorganic carbon is monitored for
completeness, the removal for WIOC samples was so far only assumed to be
quantitative, at least for ice samples containing average levels of mineral
dust. Here we estimated an average removal efficiency of 98±2 %,
resulting in a small offset of the order of the current analytical
uncertainty. Future optimization of the removal procedure has the potential to
improve the accuracy and precision of WIO14C dating. With this study we
demonstrate that using the DOC fraction for 14C dating not only is a
valuable alternative to the use of WIOC but also benefits from a reduced
required ice mass of typically ∼250 g to achieve comparable
precision of around ±200 years. This approach thus has the potential of
pushing radiocarbon dating of ice forward even to remote regions where the
carbon content in the ice is particularly low.
Extraction of Dissolved Organic Carbon from Glacier Ice for Radiocarbon Analysis