Abstract

Precipitation is a key element when studying the polar climate as it directly effects the ice sheet mass balance. Additionally, its isotopic composition, which is stored in ice cores, can be used to reconstruct local temperatures on much longer timescales than available from direct observations. Nonetheless, making a robust temperature reconstruction remains a challenging task, as a large number of physical processes can alter the isotopic composition of the precipitation. For example, a correct representation of the environmental conditions under which the moisture evaporates into the atmosphere at the source regions is crucial. Critical quantities like surface temperature and relative humidity are known to be also spatially heterogeneous and consequently, a shift in source regions could have a large impact on the initial isotopic composition as well.

To investigate the importance of source variability for Greenland, we studied the variability of the moisture source regions for Greenland on both interannual and seasonal timescales between 1987-2016, using an offline trajectory model (ROTRAJ) forced with reanalysis data (ERA-Interim). Using the reanalysis data, it is found that there exists a strong seasonal variability in the moisture uptake locations for the precipitation observed over Greenland. During winter, moisture sources are mainly located over the Atlantic Ocean, while the largest contributor of moisture for Greenland precipitation during summer is the North American continent. Interestingly, the detailed source locations in winter are highly dependent on the circulation patterns, while in summer source regions are more constant and mainly vary in strength. These results suggest that changes in precipitation seasonality as well as changes in atmospheric circulation can have a large influence on the isotope signature of Greenland precipitation and should therefore be considered carefully when reconstructing temperatures from ice cores.