Spatial and temporal variability in active layer thickness over the Russian Arctic drainage basin

Abstract

[1] Changes in active layer thickness (ALT) over northern high-latitude permafrost regions have important impacts on the surface energy balance, hydrologic cycle, carbon exchange between the atmosphere and the land surface, plant growth, and ecosystems as a whole. This study examines the 20th century variations of ALT for the Ob, Yenisey, and Lena River basins. ALT is estimated from historical soil temperature measurements from 17 stations , Lena basin only), an annual thawing index based on both surface air temperature data and numerical modeling . The latter two provide spatial fields. Based on the thawing index, the long-term average ALT is about 1.87 m in the Ob, 1.67 in the Yenisey, and 1.69 m in the Lena basin. Over the past several decades, ALT over the three basins shows positive trends, but with different magnitudes. Based on the 17 stations, ALT increased about 0.32 m between 1956 and 1990 in the Lena. To the extent that results based on the soil temperatures represent ground ''truth,'' ALT obtained from both the thawing index and numerical modeling is underestimated. It is widely believed that ALT will increase with global warming. However, this hypothesis needs further refinement since ALT responds primarily to summer air temperature while observed warming has occurred mainly in winter and spring. It is also shown that ALT exhibits complex and inconsistent responses to variations in snow cover.Citation: Zhang, T., et al. (2005), Spatial and temporal variability in active layer thickness over the Russian Arctic drainage basin,

Contemporary estimates of Pan‐Arctic freshwater discharge from GRACE and reanalysis

“…These changes may be amplified through increased greenhouse gas emissions associated with increasing active layer thickness and permafrost degradation [Lawrence and Slater, 2005;Zhang et al, 2005]. As net precipitation increases and the region thaws in response to progressively warming climate, observed increases in freshwater discharge to the Arctic Ocean [Peterson et al, 2002;Meier and Carter, 2006;McClelland et al, 2006] may have important consequences for North Atlantic Deep Water formation and heat transport by the thermohaline circulation [e.g., Stocker and Raible, 2005].…”

Changes in Freezing-Thawing Index and Soil Freeze Depth Over the Heihe River Basin, Western China

“…We defined the annual freezing period from 1 July through 30 June of the next year, and the thawing period from 1 January through 31 December (Steurer and Crandell, 1995;Zhang et al, 2005;Frauenfeld et al, 2007;Wu et al, 2011).The FI and TI could be estimated using the following:…”

“…However, despite the vast extent and importance of seasonally frozen ground (SFG), it has received much less attention (Shiklomanov, 2012). Changes in SFG have important impacts on the surface energy balance, the hydrologic cycle, carbon exchange between the atmosphere and the land surface, plant growth, and ecosystems as a whole (Zhang et al, 2005). Soil freeze depth was a key factor reflecting changes of SFG.…”

“…Of these, the annual freezethaw index is most widely used to determine the seasonal freeze and thaw depths in cold regions, primarily by using the Stefan equation (Nelson et al, 1997;Shiklomanov and Nelson, 2002;Zhang et al, 2005;Anisimov et al, 2007;Smith et al, 2009).…”

“…There are several methods to estimate soil freeze and thaw depths in cold regions: (1) using soil temperature data to estimate freeze-thaw depths (Frauenfeld et al, 2004;Zhang et al, 2005), (2) estimating the depths from the freeze-thaw index, and (3) using numerical models to estimate depths (Zhang and Stamnes, 1998). Of these, the annual freezethaw index is most widely used to determine the seasonal freeze and thaw depths in cold regions, primarily by using the Stefan equation (Nelson et al, 1997;Shiklomanov and Nelson, 2002;Zhang et al, 2005;Anisimov et al, 2007;Smith et al, 2009).…”