Interdecadal changes in seasonal freeze and thaw depths in Russia

Abstract

[1] Seasonal freezing and thawing processes in cold regions play a major role in ecosystem diversity, productivity, and the Arctic hydrological system. Long-term changes in seasonal freeze and thaw depths are also important indicators of climate change. Only sparse historical measurements of seasonal freeze and thaw depths are available for permafrost and seasonally frozen ground regions. Using mean monthly soil temperature data for for 242 stations located throughout Russia, we employed a linear interpolation method to determine the depth of the 0°C isotherm based on soil temperature data measured between 0.2 m and 3.2 m depth. The relationship between available observed annual maximum freeze and thaw depths and our interpolated values indicates a perfect correlation. A comprehensive evaluation of long-term trends in these new interpolated data for Russia indicates that in permafrost regions, active layer depths have been steadily increasing. In the period 1956-1990 the active layer exhibited a statistically significant deepening by approximately 20 cm. The changes in the seasonally frozen ground areas are even greater: The depth of the freezing layer decreased 34 cm between 1956 and 1990. Potential forcings of the observed changes include air temperature, freezing and thawing index, and snow depth. Correlation and multiple regression reveal that active layer depth is most strongly related to snow depth. Air temperature, both mean annual and thawing index, is also significantly related to changes in the active layer. Freeze depth is influenced most strongly by the freezing index and mean annual air temperature, although snow depth is also a significant contributor. Air temperature and snow depth have been changing less in the seasonally frozen ground regions of Russia compared to permafrost regions, although observed changes in freeze depth are greater than changes in active layer depth for . This indicates that the seasonally frozen ground regions of the Russian high latitudes are more susceptible to climate change than the Russian permafrost. However, as temperatures have been rising, especially in the high-latitude continental regions, both permafrost and seasonally frozen ground regions are being greatly impacted. These changes can potentially result in increased river runoff and changes in discharge throughout the Russian Arctic drainage basin, as well as changes in high-latitude ecosystems.

Modeling permafrost thaw and ecosystem carbon cycle under annual and seasonal warming at an Arctic tundra site in Alaska

“…However, we found insignificant difference in soil water content between warming and ambient condition during the growing season (Figure 2b). In addition, the earlier thawing increased the entire growing season thaw depth and active layer thickness, which is consistent with former studies [Hinkel et al, 1997;Waelbroeck et al, 1997;Anisimov et al, 2002;Hinkel and Nelson, 2003;Frauenfeld et al, 2004;Zimov et al, 2006a;Beer et al, 2007;Khvorostyanov et al, 2008a;Smith et al, 2009;Burke et al, 2012;von Deimling et al, 2012]. However, this warming effect appears to have extended growing season 0°days (i.e., >137 versus 134).…”

“…For example, the altered rate and timing of snow cover termination can regulate permafrost thaw depth [Frauenfeld et al, 2004;Zhang, 2005] and further influence CO 2 sequestration in Arctic tundra ecosystems [Humphreys and Lafleur, 2011]. Thawing of the active layer and artificial drainage significantly decreased tundra tussock ecosystem C fluxes and global warming potential [Merbold et al, 2009].…”

Observed soil temperature trends associated with climate change in the Tibetan Plateau, 1960–2014

“…In terms of spatial distribution, these stations, mainly located on the northeast, interior, and southwest sections of the TP, are typically established close to densely inhabited areas. Depending on the ST at 3.2 m, Frauenfeld (Frauenfeld 2004) has previously classified the location as either permafrost or seasonally frozen ground. The individual location was deemed as seasonally frozen ground while the ST at 3.2 m is above zero, otherwise the permafrost.…”

Isoprene emissions from a tundra ecosystem

“…Additionally, many climate models predict a decrease in thermohaline circulation, which impacts the heat budget of vast regions of the Arctic . Finally, Arctic warming trends drastically change the state of an ecosystem by eroding the permafrost layer and increasing active layer depth (Chen et al, 2003;Frauenfeld et al, 2004).…”