The impact of Atmospheric River events in preserved stable water isotope signature in the snow pack in Finse, Southern Norway

Abstract

Stable water isotopes have become a key element in hydrological and atmospheric research topics. Hydrologists aim to close the water cycle, and the improvement of measurement techniques and models makes that they come closer every time. Especially the atmospheric part of the cycle is not yet fully understood, and this study aims to get an increased understanding about the isotopic signals in the snow pack, and if the snow pack record may be used to derive an improved understanding of the importance of atmospheric river events for the Norwegian snow cover. The Finse area has been chosen as a proxy site for Norway, and 215 samples have been taken to analyze for stable water isotopes. 11 different snow profiles that were computed from snow pits that were excavated during the fieldwork were compared with the isotope values for d18O and d-excess, and with meteorological data provided by the meteorological institute of Norway. The snow pack from the same winter season (2016-2017) was simulated with the model CROCUS, using forecast data from AROME. One of the precipitation events, an atmospheric river event, was picked out and modeled with FLEXPART, to simulate the moisture uptake areas. This was backed up by satellite data and compared to the isotopic signals from the snow pits. The isotopic signal from this event was found in two of the snow pits, in February and May. Other isotopic signals were connected to other precipitation events, and by comparing the signals with the relative humidity and air temperature at the time of deposition the moisture source conditions were interpreted. Most precipitation events seem to have a southerly source, with the signal from the atmospheric river period having its source furthest south. Two of the signals appear to be from a more local (northern) source, and one isotopic signal was concluded not to have been preserved. Further research is needed to get an understanding about the role of different atmospheric and snow processes altering the isotopic signal, and multi-year studies on the isotope signal in seasonal snow is desirable as well, to get an understanding about different atmospheric circulation patterns.