Basal ice formation in snow cover in Northern Finland between 1948 and 2016

Sirpa Rasmus,Sonja Kivinen,Masoud Irannezhad

doi:10.1088/1748-9326/aae541

Abstract

Basal ice formation in the terrestrial snow cover is a common phenomenon in northern circumpolar areas, one having significant impacts on ecosystems, vegetation, animals and human activities. There is limited knowledge on the spatial and temporal occurrence of basal ice formation because of the sparse observation network and challenges involved in detecting formation events. We present a unique dataset on the annual extent of ice formation events in northern Finland between 1948 and 2016 based on reindeer herders’ descriptions of the cold season in their management reports. In extreme years, basal ice can form over wide geographical extents. In approximately half of the herding districts studied, it occurred more frequently in the period 1983–2016 than in the period 1948–1982. Furthermore, five out of seven of the most extensive basal ice formation events (90th percentile) occurred between 1991 and 2016. The most commonly reported processes related to ice formation were thaw or rain-on-snow events followed by freezing of the snow cover. Years with extensive basal ice formation were often characterized by above-average October–December air temperatures, air temperature variations around 0 °C and relatively high precipitation. However, basal ice did not occur during all warm and wet early winters, and formation events were generally weakly linked to the large-scale atmospheric teleconnections. Another risk factor for reindeer grazing associated with warm and rainy early winters is the growth of mycotoxin-producing molds below the snow. Approximately 24% of all reported mold formation events co-occurred with basal ice formation. The prevalence and frequency of basal ice formation events can be assessed based on our results. Our work contributes to understanding long-term fluctuations and changes in snow and ice conditions and the impacts of this variability in circumpolar areas.

Highlights

Snow is a challenging habitat for life, as the microstructure, stratigraphy, and depth of the snowpack vary continuously in response to weather changes (Pomeroy and Brun 2001)
Basal ice formation events in 1948–2016 Basal ice formation was reported in 0–18 winters in each of the herding districts studied for the period 1948–2016 (figure 2(a))
No change was observed in 17% of the districts, whereas basal ice occurred less frequently in 35% of the districts in the period 1983–2016 compared to the earlier period

Summary

Introduction

Snow is a challenging habitat for life, as the microstructure, stratigraphy, and depth of the snowpack vary continuously in response to weather changes (Pomeroy and Brun 2001). Frequent accumulation of refreezing wet snow layers is possible, if temperature repeatedly fluctuates around the freezing point. Basal ice formation is often related to short-lived (lasting from hours to days), unusual winter weather events, in early winter, examples being heavy liquid precipitation or the influx of warm air masses (Rennert et al 2009, Hansen et al 2014, Pedersen et al 2015). These events may be caused by different weather phenomena operating at different spatial scales (Bokhorst et al 2016). The warming climate and increasing frequency of extreme warm events during the cold season (Hansen et al 2014, Vikhamar-Schuler et al 2016, Kivinen et al 2017) are likely to lead to more frequent formation of basal ice in the future (Rasmus et al 2014, 2016)

Methods

Results

Discussion

Conclusion