Surface snow fractionation during snow-atmosphere humidity exchange alters annual mean climate signal in ice core records

• Main Authors: Dietrich, L., Steen-Larsen, H., Wahl, S., Fettweis, X., Jones, T., Town, M., Werner, M.
• Format: Conference Object
• Language: English
• Published: 2023
• Subjects: Greenland; ice core; Ice Sheet
• Online Access: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5021532

Snow-atmosphere humidity fluxes change the isotopic composition of the surface snow after deposition. However, to date, it is unclear which role these post-depositional processes play in the formation of the climate signal recorded in ice cores. Quantifying the post-depositional impact on the isotope record in ice cores is challenging due to the poor humidity flux representation over ice sheets in isotope-enabled climate models. Here, we present results from the isotope-enabled SNOWISO exchange and snowpack model. We run a 30-year (8.5 m) snow core simulation for the EastGRIP drilling site on the Greenland Ice Sheet with and without humidity flux induced fractionation of the surface snow implemented. To guarantee reliable forcing, we combine isotopic input from the global climate model ECHAM-wiso with accurate surface humidity flux simulations from the polar regional climate model MAR. Implementing fractionation induced by the humidity flux increases the mean annual δ18O by +2.1 ‰ and reduces the mean annual d-excess by -6.2 ‰ with a limited effect on the year-to-year variability. We further show that capturing the diurnal cycle of the humidity flux instead of using daily or monthly means is essential to correctly simulate the post-depositional effect on the snow core simulation. Our results shed new light on the current proxy interpretation of stable water isotopes in ice cores and open new opportunities to infer temperature and vapor source region signals more accurately.