Spatial and temporal observations of seasonal thaw in the northern Kolyma lowland

Observations carried out in 1996–2002 in the northern part of the Kolyma Lowland reveal spatial and temporal regularities in the seasonal thawing of tundra and northern taiga soils. The main factor determining differences in active-layer thickness in zonal tundra landscapes is the texture (mechanical composition) of soil parent material. Summer thaw in sandy soils is 2–3 times deeper than in loamy soils. The distribution of maximum seasonal thaw depth in watersheds and on hillslopes with loamy soils is influenced strongly by climatic zonality, which manifests itself through an increase in the depth of thaw from the arctic tundra to northern taiga. River floodplains, thermokarst depressions (alasy), and polygonal bogs have thinner active layers than adjoining watersheds. A direct correlation exists between seasonal thaw depth and mean summer air temperature in most zonal landscapes. In many cases a tendency for increased thaw depth was observed in the warm summer of 2000–2002. An inverse correlation between seasonal thaw depth and total summer precipitation occurs in most zonal biogeocenoses with loamy soils and intrazonal landscapes. This relationship was not found in welldrained zonal tundra and taiga biogeocenoses with sandy soils or in the most waterlogged alas we examined.