Spatiotemporal patterns of rain-on-snow and basal ice in high Arctic Svalbard: detection of a climate-cryosphere regime shift

Bart Peeters,Ketil Isaksen,Brage Bremset Hansen,Jean-Charles Gallet,Åshild Ønvik Pedersen,Audun Stien,Leif Egil Loe,Jack Kohler,Vebjørn Veiberg,Ronny Aanes

doi:10.1088/1748-9326/aaefb3

Abstract

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 of field 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 snowpack measurements from coastal (Ny-Ålesund area; 2000–2017) and central Spitsbergen (Nordenskiöld Land; 2010–2017), Svalbard, to analyze spatiotemporal patterns in basal ice and how they are linked with 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 was modified by accumulated snowfall; a deeper snowpack restricts ice formation following a minor rain event, but enhances ice formation following heavy rain due to an increased contribution of snowmelt. Accordingly, inter-annual variation in snow depth was negatively related to basal ice thickness. Annual fluctuations in basal ice thickness were strongly correlated in space (average correlation ρ = 0.40; 0–142 km distance between plots) due to strong spatial correlation in winter rain (ρ = 0.62; 14–410 km distance between meteorological stations). Models of basal ice based on meteorological time-series (1957–2017) suggested that ice-free winters (i.e. mean basal ice <0.1 cm) had virtually not occurred since 1998, whereas such winters previously (1957–1998) occurred every three–four years on average. This detected cryosphere regime shift was linked to a parallel climate regime shift with increased winter rain amounts. Svalbard is regarded a bellwether for Arctic winter climate change. Our empirical study may therefore provide an early warning of future changes in high-arctic snowpacks.

Highlights

We use time-series of spatially replicated snowpack measurements from coastal (Ny-Ålesund area; 2000–2017) and central Spitsbergen (Nordenskiöld Land; 2010–2017), Svalbard, to analyze spatiotemporal patterns in basal ice and how they are linked with topography, weather, snowpack and climate change
We modelled and predicted historical occurrence and thickness in basal ice using our regression models accounting for weather and topography, and investigated temporal changes linked with the recent warming in high Arctic Svalbard (Hansen et al 2014, Isaksen et al 2016)
The positive effect of rain on basal ice thickness decreased with increasing elevation, because precipitation is more likely to fall as snow at higher altitudes

Summary

Introduction

In the Arctic, winter warm spells with near-surface air temperatures above 0 °C are becoming more frequent due to global warming (Moore 2016, Graham et al 2017). This warming, in combination with enhanced surface evaporation due to the loss of sea-ice cover and poleward atmospheric moisture transport, contributes to an overall increase in precipitation over Arctic land areas (4.5% increase per degree of temperature rise), in late autumn and winter (Serreze et al 2009, Zhang et al 2012, Bintanja and Selten 2014). More frequent ROS and basal ice formation in space and time may have serious socio-economic impacts for reindeer herders (Bartsch et al 2010, Forbes et al 2016, Riseth et al 2016), and for the tourism industry and local communities in the Arctic (Hansen et al 2014)

Methods

Results

Conclusion