Active layer thickening and controls on interannual variability in the Nordic Arctic compared to the circum‐Arctic (original) (raw)
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CATENA, 2018
This article focuses on short-term changes in the thermal conditions and thickness of the active layer during the summer season of 2015, observed in test fields located in the tundra and the beach areas in the Kaffiøyra region Svalbard. The purpose was also to attempt a detailed analysis of short-term relationships between the rate and the dynamic of ground thaw and air temperature, as well as to determine the influence of the local surface features and geological structures on the thaw rate. Active layer thickness in the Kaffiøyra region is considerably diversified both spatially and temporally. Throughout the analysed timeframe average ground temperatures on the beach and in the tundra were above zero and a delayed response of ground temperature to changes in air temperature was generally observed. The increase in the thickness of the active layer on the beach was 0.8 cm per day, whereas in the tundra it averaged 1.3 cm. One essential factor conditioning the short-term variability of the thickness and thermal conditions of an active layer is the activity of contemporary morphogenetic processes, which affect the dynamic of changes in the morphology of permafrost areas and their geological structure. Examples of such changes can be found in coastal zones exposed to tidal activity and undergoing glacial processes. The research demonstrated the substantial influence of local morphology and lithological and geological structures of the active layer on the variable thaw intensity and thickness growth rate in the tundra and beach environments.
Bulletin of Geography. Physical Geography Series, 2016
This article describes and discusses the results of observations concerning short-term changes in the thermal conditions and the thickness of the active layer in a test field located in the tundra of the Kaffiøyra (NW Spitsbergen) during the summer season of 2015. One of the objectives was to find a correlation between the dynamic of the changes and the local topography. In recent years, thawing of the active layer in the Kaffiøyra region has been considerably varied in individual summer seasons. The test field area was 100 square meters, comprised 36 measurement points and was situated at approximately 3 m a.s.l. in the tundra. The measurements of the thickness and temperature of the active layer were carried out in July, August and early September of 2015. The greatest thickness of the active layer in the tundra was found near the moraine, in the area with the sharpest slope (156 cm to 212 cm). Ground temperatures were observed to follow the prevailing weather conditions with a de...
Journal of Geophysical Research, 1998
Active-layer thickness was determined in late August 1995 and 1996 at 100 m intervals over seven 1 km 2 grids in the Arctic Coastal Plain and Arctic Foothills physiographic provinces of northern Alaska. Collectively, the sampled areas integrate the range of regional terrain, soil, and vegetation characteristics in this region. Spatial autocorrelation analysis indicates that patterns of active-layer thickness are governed closely by topographic detail, acting through near-surface hydrology. On the coastal plain, maximum variability occurs at scales involving hundreds of meters, and patterns were similar in the two years. Substantially less spatial structure and interannual correspondence were found within the foothill sites, where high variability occurs over smaller distances. The divergence in patterns of thaw depth between the two provinces reflects the scale of local terrain features, which predetermines the effectiveness of fixed sampling intervals. Exploratory analysis should be performed to ascertain the scale s) of maximum variability within representative areas prior to selection of sampling intervals and development of long-term monitoring programs. 1994], the active layer could thicken and release water and carbon stored in the upper permafrost [Hinzman and Kane, 1992; Anisimov et al., 1997; !/Vaelbroeck et al., 1997]. Additional direct effects include surface subsidence and thermokarst, which could have negative impacts on the landscape and infrastructure [Nelson et al., 1993; Williams, 1995]. For these reasons, active-layer and permafrost dynamics are considered to be an integral component of Arctic ecosystems, and their effects are being incorporated in local, regional, and global models [Waelbroeck, 1993; Savtchenko, 1998]. Active-layer thickness varies both spatially and temporally, partly in response to air temperature. Although warmer summers are generally associated with thicker thawed layers at particular locations, this relation is not absolute because winter snow cover, summer rainfall, soil properties, and vegetation characteristics can influence thaw depth [e.g., Smith, 1975; Goodrich, 1982; Hinkel et al., 1993; Zhang et al., 1996b]. The depth of thaw can also vary substantially across small lateral distances. Because the flux of trace gases from the tundra to Paper number 98JD00534. 0148-0227/98/98JD-00534509.00 the atmosphere is related to the thickness of the active layer, the ability to assess the spatial heterogeneity of active-layer thickness is a critical component of efforts to estimate regional emissions of COg and CH 4 in the Arctic [Weller et al., 1995; Nelson et al., 1997b]. Little is known, however, about variations of thaw depth over extensive areas that incorporate diverse surface and subsurface characteristics, particularly on an interannual basis. Many strategies for calculating the thickness of the seasonally thawed layer have been developed, ranging from relatively simple analytic techniques to complex numerical modeling schemes. One of the most fundamental relations involved in assessing active-layer development is its proportionality with the square root of seasonal degree-days of thaw [e.g., Jumikis, 1977; Hinkel and Nicholas, 1995; Nelson et al., 1997b]. Spatial integration is not straightforward, however, because many of the factors influencing thaw depth can vary over short lateral distances. Although substantial progress has been obtained recently [Peddle and Franklin, 1993; Leverington and Duguay, 1996; McMichael et al., 1997], remote sensing has not yet provided an effective solution to the general problem of treating spatial variations of thaw depth. Statistical analysis of data collected directly in the field is therefore currently the primary vehicle for addressing the spatial and temporal variability of active-layer thickness. Nelson et al. [1997b] mapped variations in active-layer thickness over a 26,278 km 2 area in north central Alaska. Mean values of thaw depth in representative 1 ha land cover units were associated with temperature data, a topoclimatic index, and digital terrain and land cover maps to produce a spatial time series of active-layer thickness at weekly intervals. Errors in predicted values of active-layer thickness were less than 10% of measured averages in representative 1 km 2 units arrayed over the north-south extent of the mapped area, indicating that the controlling variables were specified effectively at the scale of the study. Although values used to represent the 90,000 m 2 map pixels reflect average conditions under specific land cover 28,963 28,964
Twenty years of cold surface layer thinning at Storglaciaren, sub-Arctic Sweden, 1989–2009
Journal of Glaciology, 2012
This paper presents the changes in the thermal structure of the polythermal glacier Storglaciären, northern Sweden, over the 20 year period 1989-2009 derived by comparing maps of the depth of the englacial transition between cold ice (permanently frozen) and temperate ice (which contains water inclusions). The maps are based on interpreted ice-penetrating radar surveys from 1989, 2001 and 2009. Complex thinning of the cold layer, first identified between 1989 and 2001, is still ongoing. A volume calculation shows that Storglaciären has lost one-third of its cold surface layer volume in 20 years, with a mean thinning rate of 0.80 ± 0.24 m a-1. We suggest that the thinning of the cold layer at Storglaciären is connected to the climatic warming experienced by sub-Arctic Scandinavia since the 1980s and we argue that repeated ice-penetrating radar surveys over the ablation area of polythermal glaciers offer a useful proxy for evaluating glacier responses to changes in climate.
2008
The relationships between meteorological conditions, permafrost active layer thickness and thermal structure were studied for a dry, polar climate site, next to Petunia− bukta (central Spitsbergen), during four successive summer seasons (2000)(2001)(2002)(2003). In addi− tion to determination of the ground sedimentological and mineralogical properties, the fol− lowing parameters were measured: air temperature, air humidity (both at 2 m and 0.05 m above the ground), wind direction and velocity (at 2 m), precipitation, cloudiness, thickness of the permafrost active layer and ground temperature at 0.05, 0.1, 0.25, 0.5 and 0.75 m be− low the surface. The permafrost level was lowered 0.7 to 1.1 cm day −1 during days with tem− perature above freezing, reaching a maximum depth of 1.2 m. The temperature of the top 0.1 m of the ground reacted within one to two days to changes in air temperature. The reac− tion period of the ground temperature at 0.5 m was several days. Rainfall events were of mi− nor importance to thermal ground structure, in contrast to sites with a more marine climate. Other meteorological factors had a very small influence on the ground temperature. During summer, a well developed thermal gradient reaching over 12°C m −1 was observed, followed by isothermal conditions with temperature of 0°C at the beginning of fall, and reversal of the thermal gradient (−6.7°C m −1 ) in late fall. The interannual variations were mainly due to changes in summer temperature and to the length of period with snow cover in spring, which limited the beginning of thawing. The thermal structure of active layer is governed by seasonal conditions, regardless of overall climatic change.
High-resolution field data for the period 2000-2014 consisting of active layer and permafrost temperature, active layer soil moisture, and thaw depth progression from the UNISCALM research site in Adventdalen, Svalbard, is combined with a physically based coupled cryotic and hydrogeological model to investigate active layer dynamics. The site is a loess-covered river terrace characterized by dry conditions with little to no summer infiltration and an unsaturated active layer. A range of soil moisture characteristic curves consistent with loess sediments is considered and their effects on ice and moisture redistribution, heat flux, energy storage through latent heat transfer, and active layer thickness is investigated and quantified based on hydro-climatic site conditions. Results show that soil moisture retention characteristics exhibit notable control on ice distribution and circulation within the active layer through cryosuction and are subject to seasonal variability and sitespecific surface temperature variations. The retention characteristics also impact unfrozen water and ice content in the permafrost. Although these effects lead to differences in thaw progression rates, the resulting inter-annual variability in active layer thickness is not large. Field data analysis reveals that variations in summer degree days do not notably affect the active layer thaw depths; instead, a cumulative winter degree day index is found to more significantly control interannual active layer thickness variation at this site. A tendency of increasing winter temperatures is found to cause a general warming of the subsurface down to 10 m depth (0.05 to 0.26 • C yr −1 , observed and modelled) including an increasing active layer thickness (0.8 cm yr −1 , observed and 0.3 to 0.8 cm yr −1 , modelled) during the 14-year study period.