Seasonal progression of active-layer thickness dependent on microrelief

Introduction Active-layer thickness is a major factor for all physical and biological processes in permafrost soils. It is closely related to the fluxes of energy, water and carbon between permafrost landscapes and the atmosphere. Active-layer thickness is mainly driven by air temperature, but also influenced by snow cover, summer rainfall, soil properties and vegetation characteristics (Nelson et al., 1998). The typical polygonal tundra of the Lena Delta is characterised by a pronounced microrelief, which causes a high small-scale heterogeneity of soil and vegetation properties. Consequently, also the active-layer thickness varies substantially across small lateral distances of decimetres to metres. In order to up-scale results of process studies to the landscape scale, a quantification of the heterogeneity of active-layer thickness is of great interest

Impacts of small scale surface variations on the energy balance of wet polygonal tundra on Samoylov Island in the Lena-River-Delta

Climate data are hardly available in remote areas like high arctic permafrost regions. Upscaling of climate processes becomes therefore an essential element in predicting the impacts of changing climate conditions.Methods for upscaling the major energy exchange processes between ground and atmosphere in permafrost regions are developed within the HGF-Project: Sensitivity of permafrost systems water and energy balance under changing climate: A multiscale perspective (SPARC). The project includes the important aspect of changing surface characteristics and their impact on permafrost energy balance. Field works for this purpose took place in July and August 2007 on the island Samoylov in the center of the Lena-River-Delta. The focus of this work rests upon energy balance variation within polygonal structures, which are the most dominant surface elements of this region. Surface properties of two typical polygons in different development stages are considered under the aspect of energy exchange processes between soil and atmosphere. This includes a more general analysis of the thermal properties of specific vegetation units in association with micro relief and moisture content. For evaluating inter polygonal energy balance variations, climate data have to be measured in a very high spatial resolution. Standard climate stations usually record temporal variations of energy balance on point scale. They are not able to provide information about spatial variations. This problem is sometimes bypassed by using multiple or mobile climate stations. However this generally results in very coarse data of spatial differences. Thus a climate station has been modified to a 10m long scanner system for getting a more detailed picture of the spatial energy balance variations between the chosen polygon types. This system allows the record of spatial variations in combination with high frequent measurements of a standard climate station.The scanner system measures short and long wave radiation balance, reflected photosynthetic active radiation, air temperature and humidity in 70 cm height. Variables like air temperature and humidity in 2 m height, as well as air pressure and wind speed that are not supposed to change significant along the running way are measured in a common manner. Soil temperature and moisture sensors where installed underneath the scanner track.The scanner technique gives a more detailed picture of the relation between energy fluxes and surface structures. The results will be used to close the gap between point based and spatial climate models. They also enhance the potentials of remote sensing data when surface information is related to energy fluxes

Accumulation stake readings in western Dronning Maud Land (Antarctica) along the Neumayer-Kottas-Kohnen traverse 2005 to 2006

This data collection contains readings of accumulation stake along the approximately 800 km long traverse route Neumayer-Kottas-Kohnen, Dronning Maud Land, Antarctica. By comparing the readings of an individual stake in two different seasons the amount of surface accumulation (i.e. snow deposition) or erosion (e.g. from sublimation of wind scour) can be determined. Stake readings were conducted approximately every year starting from season 1995/1996 to 2005/2006 as part of the European Project for Ice Coring In Antarctica (EPICA). The readings were carried out by a dedicated two to three person team accompanying the traverse from Neumayer station to Kohnen station. The readings were performed by a simple measurement of the visible length of the stake above the snow surface. For tilted stakes, the vertical height above the surface as well as the length of the stake was measured. New stakes were deployed when less than about 1.5 m of the previous stake was visible or a stake was lost (e.g. from breaking off or falling over and finally get burried in snow). Consequently, at some locations more than one stake is visible for several years (e.g. when the average snow accumulation was rather low). In those cases all visible stakes were recorded at the same location of such a stake cluster and added to the table as Height_1, Height 2, Height 3). Positions were measured with a simple GPS with coarse acquisition accuracy (order of several meters to tens of meters), which is sufficiently accurate to separate different stake locations (usually 500 m apart and horizontal displacement smaller than about 150 m/a, with largest displacements on the Ekström ice shelf). In very few cases, empty lines originate from missing stakes and the required position. In very few cases, a second line with the same coordinate corresponds to the same location with a fourth stake deployed as a new stake. From Neumayer station to Kottas camp stakes were deployed at approximately a 500 m interval. As the spatial variation of accumulation on the polar plateau is smaller than in the lower foreland (in this case the Ritscherflya) the stake distances was increased to 1 km to several kilometers from Kottas camp onto the polar plateau to Kohnen station. Additional field comments made by observing personal were removed from the files. However, original field notes in notebooks are available from AWI's Archive for German Polar Research (Oerter et al., 2013). Although surface accumulation is still one of the major unknowns to determine the the total surface mass balance of the Antarctic ice sheet, especially under climate change, direct long-term observations of surface accumulation are still one of the major gaps in field observations (Eisen et al., 2008). This time series of stake readings provides the basis for calculation the change in accumulation in space and time (e.g. Rotschky et al., 2007). It is thus fundamental for a decade-long record of the spatio-temporal characteristics of surface accumulation, which can be put into context to meteorological and oceanographic changes in the region