Arctic surface snow interactions with the atmosphere: Spatio-temporal isotopic variability during the MOSAiC expedition

Snow on sea ice is crucial in moderating sea ice and atmosphere interactions, yet fully grasping snow’s isotopic composition and the processes shaping it presents substantial challenges, including sublimation and wind redistribution. This study utilizes a year of stable water isotope datasets from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in 2019/2020 to explore the complex interactions between snow deposition processes and postdepositional changes affecting snow on Arctic sea ice including seasonal and spatial dynamics. We compare snow data with water vapor isotope measurements by examining 911 individual snow isotope measurements and integrating these discrete snow samples with continuous water vapor isotope data. Autumn shows a pronounced δ18O offset between snow and vapor. In winter, δ18O and d-excess in surface snow and water vapor diverge sharply, indicating kinetic fractionation under extremely cold temperatures as research vessel Polarstern drifted from the Siberian to the Atlantic Arctic. While water vapor δ18O responds rapidly to air temperature and humidity changes, surface snow δ18O values are modulated by postdepositional processes like sublimation and wind redistribution. We found that these 2 processes play a key role in isotopic enrichment that is intensified by the snow’s prolonged surface residence. Wind-driven snow redistribution, occurring during 67% of the winter period, leads to an average surface snow δ18O of −22‰ across the sea ice by redistributing and mixing fresh snow with more metamorphosed snow. This study provides new insights into how wind-driven redistribution and prolonged surface residence not only alter isotopic values in surface snow but also obscure seasonal isotopic patterns, complicating the interpretation of snow isotope records in the Arctic. Our research to understand the differences between the isotopic values of vapor and the isotopic values of snow provides insight into interactions between snow and the atmosphere, as well as the processes that alter isotopic values internally within the Arctic snowpack. Our study highlights the complexity of surface snow isotope geochemistry across the Arctic from the eastern to the central basin during the MOSAiC expedition window and how the underlying processes of water vapor transport, temperature–isotope relations, and the role of secondary processes, including wind redistribution and sea ice formation all contribute to the horizontal and vertical geochemistry patterns.