Investigating surface spring snow : Changes in the isotopic composition and conductivity along an orographic precipitation gradient in northern Fennoscandia

Sammanfattning: Stable isotopes of oxygen (O18) and hydrogen (H2) are used as proxies of past climates when ice preserved in the polar icecaps. The main assumption when doing paleoclimatic reconstructions using these isotopes is that the isotopic composition of the snow that turned into ice reflect the present temperature of the planet during deposition. In this study, I investigate to what extent the composition of O18 and H2 varies as a function of precipitation. I tested the following hypotheses: i) δO18 and δH2 decreases due to fractionation during orographic fallout, and ii) the electric conductivity in the snow decreases with distance from sea due to fading marine inputs. The hypotheses were tested with field samples gathered along a precipitation gradient from the Norwegian coast to Kiruna, Northern Sweden. To support my first hypothesis, I found a decrease from -9.32% δO18 (-54.85% δH2) to -25.48% δO18 (-109.54 % δH2) due to orographic deposition over the Scandes with a drastic drop in Abisko caused by a rain shadow. Similarly, I found a considerable variation and decreasing trend of conductivity along the precipitation gradient. My study raises awareness that δO18 in snow is in fact dependent on precipitation regimes rather than temperature regimes in this area, which should be considered when interpreting environmental records of δO18 in a paleoclimatic context. Lastly, I suggest further studies targeting the effects of post-depositional processes (melting, sublimation, and anthropogenic influence) on the isotopic composition and conductivity, especially with a changing climate.