Abstract: Understanding the meteorological drivers of precipitation isotopic composition is crucial for the
interpretation of paleoclimate archives, such as the past precipitation records found in the ice
cores, as well as to successfully constrain atmospheric models including the explicit
representation of water isotopes. This is of particular importance in the context of climate change,
and in particular in the Arctic where climate models project enhanced hydrological cycle and
temperature increase which might in turn have significant impacts on the global climate (through
e.g. the sea-ice retreat, water vapour feedback or cloud cover). Indeed, large discrepancies on the
future Arctic precipitation exist amongst different climate models.
Condensing water vapour being the first stage of a precipitation event, its isotopic composition
influences that of the precipitation and must therefore be fully understood in order to find the
causes for the inter-model spread. The water vapour isotopic composition is believed to be
influenced by changes in moisture sources and fractionation history during transport. It thus
provides valuable and independent information on moisture source origins and represents a
crucial tool for assessing the realism of models and the interpretation of meteorological archives.
During the last 5 years, new laser methods have permitted to achieve such measurements of water
isotopes.
In the present work, new in situ continuous measurements of the isotopic composition of water
vapour in Svalbard between the end of June 2014 and March 2015 are studied. Given its location,
Svalbard allowed us to expand the monitoring of water vapour isotopic composition and
atmospheric circulation towards the Arctic so as to explore their relationship to the moisture
source conditions. In order to do so, Lagrangian backtrajectories were computed and associated
with the processed data.
A clear distinction between trajectories coming from over the Arctic sea-ice area and those from
the North Atlantic Ocean could be observed in the isotopic composition. The latter also displayed
seasonal variations attributed to seasonal changes in atmospheric transport. Moreover, during
days with low isotopic depletion, deviations from the expected global meteoric water line were
observed and studied. Finally, days displaying a significant and rapid change in the isotopic
composition were explained by a corresponding sudden change in the air mass past trajectory.
This work opens the possibility to quantify the effects of evaporation conditions on isotopic data,
provides a new dataset for the evaluation of atmospheric models, and will provide a basis to
revise the climatic interpretation of Svalbard ice core records.