Soil characteristics of cryosols from two sites on King George Island, maritime Antarctica

This study presents soil temperature and moisture regimes from March 2008 to January 2009 for two active layer monitoring (CALM-S) sites at King George Island, Maritime Antarctica. The monitoring sites were installed during the summer of 2008 and consist of thermistors (accuracy of ±0.2 °C), arranged vertically with probes at different depths and one soil moisture probe placed at the bottommost layer at each site (accuracy of ± 2.5%), recording data at hourly intervals in a high capacity datalogger. The active layer thermal regime in the studied period for both soils was typical of periglacial environments, with extreme variation in surface temperature during summer resulting in frequent freeze and thaw cycles. The great majority of the soil temperature readings during the eleven month period was close to 0 °C, resulting in low values of freezing and thawing degree days. Both soils have poor thermal apparent diffusivity but values were higher for the soil from Fildes Peninsula. The different moisture regimes for the studied soils were attributed to soil texture, with the coarser soil presenting much lower water content during all seasons. Differences in water and ice contents may explain the contrasting patterns of freezing of the studied soils, being two-sided for the coarser soil and one-sided for the loamy soil. The temperature profile of the studied soils during the eleven month period indicates that the active layer reached a maximum depth of approximately 92 cm at Potter and 89 cm at Fildes. Longer data sets are needed for more conclusive analysis on active layer behaviour in this part of Antarctica.

Characteristics and changes of thermokarst lakes in Canada, Russia and Sweden

Peat plateaus are widespread at high northern latitudes and are important soil organic carbon reservoirs. A warming climate can cause either increased ground subsidence (thermokarst) resulting in lake formation or increased drainage as the permafrost thaws. A better understanding of spatiotemporal variations in these landforms in relation to climate change is important for predicting the future thawing permafrost carbon feedback. In this study, dynamics in thermokarst lake extent during the last 35-50 years has been quantified through time series analysis of aerial photographs and high-resolution satellite images (IKONOS/QuickBird) in three peat plateau complexes, spread out across the northern circumpolar region along a climatic and permafrost gradient. From the mid-1970s until the mid-2000s there has been an increase in mean annual air temperature, winter precipitation, and ground temperature in all three study areas. The two peat plateaus located in the continuous and discontinuous permafrost zones, respectively, where mean annual air temperatures are below -5°C and ground temperatures are -2°C or colder, have experienced small changes in thermokarst lake extent. In the peat plateau located in the sporadic permafrost zone where the mean annual air temperature is around -3°C, and the ground temperature is close to 0°C, lake drainage and infilling with fen vegetation has been extensive and many new thermokarst lakes have formed. In a future progressively warmer and wetter climate permafrost degradation can cause significant impacts on landscape composition and greenhouse gas exchange also in areas with extensive peat plateaus, which presently still experience stable permafrost conditions.

(Table 1) Carbon pools in different vegetation components in grazed and ungrazed plots near Ny-Ålesund, Spitzbergen

The carbon (C) sink strength of arctic tundra is under pressure from increasing populations of arctic breeding geese. In this study we examined how CO2 and CH4 fluxes, plant biomass and soil C responded to the removal of vertebrate herbivores in a high arctic wet moss meadow that has been intensively used by barnacle geese (Branta leucopsis) for ca. 20 years. We used 4 and 9 years old grazing exclosures to investigate the potential for recovery of ecosystem function during the growing season (July 2007). The results show greater above- and below-ground vascular plant biomass within the grazing exclosures with graminoid biomass being most responsive to the removal of herbivory whilst moss biomass remained unchanged. The changes in biomass switched the system from net emission to net uptake of CO2 (0.47 and -0.77 µmol/m**2/s in grazed and exclosure plots, respectively) during the growing season and doubled the C storage in live biomass. In contrast, the treatment had no impact on the CH4 fluxes, the total litter C pool or the soil C concentration. The rapid recovery of the above ground biomass and CO2 fluxes demonstrates the plasticity of this high arctic ecosystem in terms of response to changing herbivore pressure.