Snow–vegetation–atmosphere interactions in alpine tundra

Abstract. The interannual variability of snow cover in alpine areas is increasing, which may affect the tightly coupled cycles carbon and water through snow–vegetation–atmosphere interactions across a range spatio-temporal scales. To explore role for land–atmosphere exchange CO2 vapor tundra ecosystems, we combined 3 years (2019–2021) continuous eddy covariance flux measurements net ecosystem (NEE) evapotranspiration (ET) from Finse site Norway (1210 m a.s.l.) with ground-based ecosystem-type classification satellite imagery Sentinel-2, Landsat 8, MODIS. While conditions 2019 2021 can be described as typical, 2020 features an extreme accumulation associated strong negative phase Scandinavian pattern synoptic atmospheric circulation during spring. This caused 1-month delay melt-out date, falls 92nd percentile distribution yearly dates period 2001–2021. follow consistent fine-scale spatial relationship types years. Mountain lichen heathlands melt out more heterogeneously than fens flood plains, while late snowbeds up to 1 month later other types. summertime average normalized difference vegetation index (NDVI) was reduced considerably extreme-snow year 2020, it reached same maximum all but one (late snowbeds), indicating that delayed onset growth compensated productivity. Eddy estimates NEE ET are gap-filled separately two wind sectors using random forest regression model account complex nonlinear ecohydrological interactions. differ markedly composition magnitudes, their response controlled by drivers estimated predictor importance model, well high correlation magnitudes (correlation coefficient r=0.92 r=0.89 ET) between both areas. start snow-free season total annual 50 % compared growing-season assimilation turn moderate sink (−31 −6 gC m−2 yr−1) source (34 20 yr−1). These results underpin dependence structure functioning on dynamics, whose anomalies result important ecological events ecosystems.