The impact of moisture sources on the oxygen isotope composition of precipitation at a continental site in central Europe

摘要

The stable isotope composition of precipitation records processes taking place within the hydrological cycle. Potentially, moisture sources are important controls on the stable isotope composition of precipitation, but studies focused on this topic are still scarce. We studied the moisture sources contributing to precipitation at Postojna (Slovenia) from 2009 to 2013. Back trajectory analyses were computed for the days with precipitation at Postojna. The moisture uptake locations were identified along these trajectories using standard hydro meteorological formulation. The moisture uptake locations were integrated in eight source regions to facilitate its comparison to the monthly oxygen isotope composition (delta O-18 values) of precipitation. Nearly half of the precipitation originated from continental sources (recycled moisture), and 40% was from central and western Mediterranean. Results show that moisture sources do not have a significant impact on the oxygen isotope composition at this site. We suggest that the large proportion of recycled moisture originated from transpiration rather than evaporation, which produced water vapour with less negative delta O-18 values. Thus the difference between the oceanic and local vapour source was reduced, which prevented the distinction of the moisture sources based on their oxygen isotope signature. Nevertheless, delta O-18 values of precipitation are partially controlled by climate parameters, which is of major importance for paleoclimate studies. We found that the main climate control on Postojna delta O-18 values of precipitation is the surface temperature. Amount effect was not recorded at this site, and the winter North Atlantic Oscillation (NAO) does not impact the delta O-18 values of precipitation. The Western Mediterranean Oscillation (WeMO) was correlated to oxygen stable isotope composition, although this atmospheric pattern was not a control. Instead we found that the link to delta O-18 values results from