Snow cover evolution, on 2009-2014, at the Limnopolar Lake CALM-S site on Byers Peninsula, Livingston Island, Antarctica.

- We studied the snow cover evolution at the Limnopolar Lake CALM site, Antarctica.
- Mean annual air temperature and snow thickness were constant in the 2009-2014.
- Snow cover duration increased from 267 (in 2011) to 338 (in 2014) days.
- Changes on n-factor and surface offset reveal an increase in ground isolation.
- In result, ground temperature increases and active layer thickness decreases.

In February 2009, a new Circumpolar Active Layer Monitoring (CALM) site was established in the Limnopolar Lake drainage basin, in Byers Peninsula, Livingston Island (South Shetland Archipelago), Antarctica (62°38′59.1″S, 61°06′16.9″W). The first results from active layer thickness and thermal monitoring reported interannual variations, without relevant changes in the air temperature conditions, leaving the snow cover as the most suitable agent controlling the reported changes. Here we study in detail the snow cover evolution on thickness, timing and duration during the 2009-2014 period, by the analysis of mean daily air and ground surface temperature, as well as the snow depth monitored in a stake. Freezing indexes, n-factor, and snow indexes calculations were analyzed to establish the effects of snow cover on the ground thermal regime. The evolution of the snow cover during the 2009-2014 period resulted in about similar snow depths, with mean values of about 45 cm. The snow onset remained about constant with small variations of 10 days in early March. However, the snow offset had significant variations, increasing in more than 60 days in the last three years. This delay on the snow offset resulted in an increase in the snow cover duration from 267 (2011) to 338 (2014) days. Air temperature seems not to be strongly involved in this snow cover timing variation since the highest variation on this period of the maximum and mean annual temperatures only diminished, about 1.6° and 0.5° C respectively, but remaining constant the minimum temperatures (between − 12° and − 18 °C). In consequence, the surface temperature evolved to become less variable along the year directly related to the annual snow layer duration, trending to longer zero curtain periods. In conclusion, the increase in the snow duration is resulting in a reduction of the thaw period in the ground, but remaining similar snow cover onset dates. The consequent decrease in the snow-free period each year could result in a thinner active layer.