Basal ice but not summer temperature affects land surface greenness in parts of the landscape in high Arctic tundra

Résumé fourni par la source

Abstract Climate warming in the Arctic is very strong compared to other regions on Earth. Arctic winter climate and cryosphere conditions are changing towards more frequent mild spells. Precipitation is often falling as rain, followed by the formation of basal ice on frozen ground, particularly in Gulf Stream-influenced climates as in Svalbard. Such conditions encapsulate tundra plants in ice for several months, which is assumed to reduce land surface greenness due to plant damage. We investigated whether extensive basal ice (presence and thickness) and increased summer temperatures (growing degree days (GDD)) from in-situ time series impact satellite-derived land surface greenness. We measured greenness as the magnitude and timing of growing season maximum normalized difference vegetation index (NDVI). Our study covers Svalbard from 2013 to 2023, a decade with record breaking summer temperatures and many icy winters. We found lower maximum NDVI values when basal ice was present only at higher elevations (Estimated effect size: −0.0119, 95% CI: −0.0207 to −0.0031). We further found an eight-day advance in the timing of maximum NDVI (Estimated effect size: −7.56, 95% CI: −14.81 to −0.31) with basal ice presence in the region that was characterized by spatially and temporally extensive basal ice. Ice thickness, in contrast to presence, or GDD did not influence the magnitude or timing of maximum NDVI. Taken together, our findings indicate that basal ice presence could become a driver of vegetation change in the High Arctic as climatic extremes intensify, which could alter tundra greenness over larger landscapes and ultimately influence Arctic food webs.

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