Spatiotemporal patterns of rain on snow and basal ice in high Arctic Svalbard: detection of a climate cryosphere regime shift
Arctic winters have become increasingly warmer and rainier.Where permafrost prevails, winter rain (or rain on snow) is known to occasionally cause extensive ice layers at the snow/ground interface, i.e. 'basal ice' or 'ground ice' with potentially large ecological and socio economic implications. However, an overall lack offield data has so far restricted our predictive understanding of the environmental conditions shaping spatiotemporal variation in basal ice. Here, we use time series of spatially replicated snowpackmeasurements from coastal (Ny Alesund area; 2000 2017) and central Spitsbergen (Nordenskiold Land; 2010 2017) Svalbard, to analyze spatiotemporal patterns in basal ice and how they are linkedwith topography, weather, snowpack and climate change. As expected, both the spatial occurrence and thickness of basal ice increased strongly with the annual amount of winter rain. This effect wasmodified by accumulated snowfall; a deeper snowpack restricts ice formation following aminor rain event, but enhances ice formation following heavy rain due to an increased contribution of snowmelt. Accordingly, inter annual variation in snowdepthwas negatively related to basal ice thickness. Annual fluctuations in basal ice thickness were strongly correlated in space (average correlation r=0.40; 0 142 kmdistance between plots) due to strong spatial correlation inwinter rain (r=0.62; 14 410 kmdistance betweenmeteorological stations).Models of basal ice based onmeteorological time series (1957 2017) suggested that ice free winters (i.e.mean basal ice<0.1 cm)had virtually not occurred since 1998, whereas suchwinters previously (1957 1998) occurred every three four years on average. This detected cryosphere regime shift was linked to a parallel climate regime shift with increasedwinter rain amounts. Svalbard is regarded a bellwether for Arctic winter climate change.Our empirical studymay therefore provide an early warning of future changes in high arctic snowpacks.