Distributed Permafrost Observation Network in Western Alaska: the First Results

Abstract:

The area of Western Alaska including the Selawik National Wildlife Refuge (SNWR) is generally underrepresented in terms of permafrost thermal monitoring. Thus, the main objective of this study was to establish a permafrost monitoring network in Western Alaska in order to understand the spatial variability in permafrost thermal regime in the area and to have a baseline in order to detect future change. Present and future thawing of permafrost in the region will have a dramatic effect on the ecosystems and infrastructure because the permafrost here generally has a high ice content, as a result of preservation of old ground ice in these relatively cold regions even during the warmer time intervals of the Holocene. Over the summers of 2011 and 2012 a total of 26 automated monitoring stations were established to collect temperature data from the active layer and near-surface permafrost. While most of these stations were basic and only measured the temperature down to 1.5 m at 4 depths, three of the stations had higher vertical temperature resolution down to 3 m. The sites were selected using an ecotype (basic vegetation groups) map of very high resolution (30 m) that had been created for the area in 2009. We found the Upland Dwarf Birch-Tussock Shrub ecotype to be the coldest with a mean annual ground temperature at 1 meter (MAGT1.0) of -3.9 °C during the August 1^st, 2012 to July 31^st, 2013 measurement period. This is also the most widespread ecotype in the SNWR, covering approximately 28.4% by area. The next widespread ecotype in the SNWR is the Lowland and Upland Birch-Ericaceous Low Shrub. This ecotype had higher ground temperatures with an average MAGT1.0 of -2.4 °C during the same measurement period. We also found that within some ecotypes (White Spruce and Alder-Willow Shrub) the presence or absence of moss on the surface seems to indicate the presence or absence of near surface permafrost. In general, we found good agreement between ecotype classes and permafrost characteristics such as temperature, active layer thickness, and freeze back duration. Thus, we believe it might be possible to translate the ecotype map into a very high spatial resolution (30 m) permafrost map using our measurements. Such a map would be useful in decision making with respect to land use and understanding how the landscape might change under future climate scenarios.