Enhanced Warming and Wetting of the Active Layer Caused by Rain and Snow, Svalbard

julia.boike [ at ] awi.de


The active layer situated between the permafrost and the ground surface has changed greatly over the last decades at a site in Ny-Ålesund, Svalbard. While permafrost is defined as ground (soil or rock) which has been below a temperature of 0 °C for at least two consecutive years, the active layer is thawing every summer and refreezing in autumn. Svalbard has the warmest permafrost compared to other Arctic sites at the same latitude. In this study, meteorological data from 1998-2018 as well as soil temperature and active layer volumetric water content data were analysed. While the mean annual air temperature in Ny-Ålesund has increased over the past 20 years by about 1.46 °C (+/- 0.05 °C) per decade, the annual liquid precipitation sum increased by 76 mm (+/- 44 mm) per decade. Furthermore, the timespan when the ground is covered by snow has shortened. The active layer has doubled in thickness from around 90 cm in 1998 to more than 150 cm in 2018. The freezing period starts later compared to 20 years ago, leading to a shortening of the period when the soil is frozen of 31 days (+/- 17 days) per decade. During the 20 years of observation, the active layer always completely refroze in winter, but the liquid volumetric water content remained partly above 10 %. The analysis of the active layer temperature and the liquid volumetric water content revealed a general warming and wetting trend within the 20 years of observation. In the active layer soil warming is normally reduced as energy is used for melting of ground ice. This process usually increases the liquid volumetric water content. Still, over the 20 year period the soil temperature increased by 0.9 °C to 1.6 °C (+/- 0.6 °C) per decade as a range for all measured depths (4 cm – 133 cm). The mean annual LVWC in the active layer at 10 cm to 94 cm depth increased as a range for the depths between 0.6 % and 3.2 % (+/- 1.2 %) per decade. The main correlating parameters to the changes in soil temperature and liquid volumetric water content of the soil for each month were assessed using a correlation matrix. The main correlation factor seems to be in winter and spring the lengthening of the thawing period, in summer the earlier vanishing snow cover and in autumn the delayed start of the freeze-back period. However, these parameters are in turn influenced by air temperature and precipitation changes. Surface volumetric water content declined slightly over the 20 years by about 1.7% (+/- 0.6 %) per decade, probably due to stronger evapotranspiration or due to the deepening of the active layer. If the trend of the past 20 years continued, permafrost degradation on Svalbard could be increasing over the next years causing landscape changes, landslides and stronger erosion, posing a potential-risk to infrastructure.

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Bacher, S. (2019): Enhanced Warming and Wetting of the Active Layer Caused by Rain and Snow, Svalbard , Bachelor thesis, University of Potsdam.

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