Water isotope (18O & 2H) profiles in Arctic seasonal snowpack provides a proxy moisture source record

The Arctic water cycle is rapidly changing and may be manifested in shifting moisture sources and storm tracks in the north. Storm tracks can be fingerprinted with distinct combinations of stable δ²H, δ¹⁸O isotope and d-excess values because moisture source ocean temperatures, sea ice, humidity and transport processes differ. While we have successfully delineated moisture sources with event-based precipitation and water vapor recently in portions of the Arctic, it is unclear whether seasonal snowpacks retain the winter-long variation in storm tracks.

We sampled snow profiles and event-based snowfall for stable water isotope composition in two northerly locations at approximately 68°N; the North slope of Alaska and Arctic Finland. We use air parcel back trajectory modeling to link large-scale storm tracks to event-based sampling of snowfall, and isotope profiles in snowpack. Storm isotope signals are preserved in the top of the snowpack for the most recent storms, but we observed an enrichment of δ²H, δ¹⁸O by at the base of snowpack. Even so, the seasonal snowpack provided a useful proxy for the Arctic winter-moisture sources when combined with analysis of large scale storm tracks. Our work is also relevant to regional paleoisotope studies, where records from, e.g., ice cores and ice wedges are typically interpreted to reflect the isotopic composition of winter precipitation. Our data suggests that these proxies for winter precipitation might be biased due to isotope fractionation in the seasonal snowpack.