[1] Meteorological and soil temperature and moisture data for the period 1998-2005 are presented from a long term monitoring station in the central Lena River Delta at 72°N, 126°E. The investigation site, Samoylov Island, is situated in the zone of continuous permafrost and is characterized by wet polygonal tundra. The summer energy and water balance of the tundra was analyzed for the dry year 1999 and the wet year 2003. The summer water balance of the tundra was found to be mainly controlled by precipitation. The partitioning of the available energy was controlled by precipitation via the soil moisture regime, and by the synoptic weather conditions via radiation and the advection of maritime cold or continental warm air masses. In 2003, regular high precipitation resulted in a constant recharge of polygonal ponds. Of the available energy, 61% were partitioned into latent heat flux and 17% into ground heat flux; hence, the tundra behaved like a typical wetland. In 1999, low precipitation resulted in a loss of polygonal pond waters and a drying of upper soil layers. This led to lower latent heat flux (31% of available energy), higher ground heat flux (29%), and a considerably higher soil thaw depth compared to 2003. Surface and subsurface water flow had a significant influence on the tundra water balance. In 2003, the formation of new surface flow channels through thermo-erosion was observed, which is expected to have a strong and lasting influence on the hydrologic system of the tundra.

Although ponds make up roughly half of the total area of surface water in permafrost landscapes, their relevance to carbon dioxide emissions on a landscape scale has, to date, remained largely unknown. We have therefore investigated the inflows and outflows of dissolved organic and inorganic carbon from lakes, ponds, and outlets on Samoylov Island, in the Lena Delta of northeastern Siberia in September 2008, together with their carbon dioxide emissions. Outgassing of carbon dioxide (CO2) from these ponds and lakes, which cover 25% of Samoylov Island, was found to account for between 74 and 81% of the calculated net landscape‐scale CO2 emissions of 0.2–1.1 g C m−2 d−1 during September 2008, of which 28–43% was from ponds and 27–46% from lakes. The lateral export of dissolved carbon was negligible compared to the gaseous emissions due to the small volumes of runoff. The concentrations of dissolved inorganic carbon in the ponds were found to triple during freezeback, highlighting their importance for temporary carbon storage between the time of carbon production and its emission as CO2. If ponds are ignored the total summer emissions of CO2‐C from water bodies of the islands within the entire Lena Delta (0.7–1.3 Tg) are underestimated by between 35 and 62%.

Water bodies are ubiquitous features in Arctic wetlands. Ponds, i.e., waters with a surface area smaller than 10 4 m 2 , have been recognized as hotspots of biological activity and greenhouse gas emissions but are not well inventoried. This study aimed to identify common characteristics of three Arctic wetlands including water body size and abundance for different spatial resolutions, and the potential of Landsat-5 TM satellite data to show the subpixel fraction of water cover (SWC) via the surface albedo. Water bodies were mapped using optical and radar satellite data with resolutions of 4 m or better, Landsat-5 TM at 30 m and the MODIS water mask (MOD44W) at 250 m resolution. Study sites showed similar properties regarding water body distributions and scaling issues. Abundance-size distributions showed a curved pattern on a log-log scale with a flattened lower tail and an upper tail that appeared Paretian. Ponds represented 95% of the total water body number. Total number of water bodies decreased with coarser spatial resolutions. However, clusters of small water bodies were merged into single larger water bodies leading to local overestimation of water surface area. To assess the uncertainty of coarse-scale products, both surface water fraction and the water body size distribution should therefore be considered. Using Landsat surface albedo to estimate SWC across different terrain types including polygonal terrain and drained thermokarst basins proved to be a robust approach. However, the albedo-SWC relationship is site specific and needs to be tested in other Arctic regions. These findings present a baseline to better represent small water bodies of Arctic wet tundra environments in regional as well as global ecosystem and climate models.

AbStRACt. Arctic wetland environments are sensitive to ongoing climate change as seen by the recent loss of lakes and ponds in southern Alaska, Siberia, and northern Ellesmere island, Canada. A clearer picture of the mechanisms accounting for these losses or the persistence of ponds is presently required. to better understand and quantify the hydrologic processes that are leading to the sustainability or demise of High Arctic ponds, a detailed study was conducted during the summer seasons of 2006 at Somerset Island, Nunavut (72˚43' N, 94˚15' W). A water balance framework that quantifies water inputs, losses, and storage was employed on four ponds situated in three broad geomorphic areas (coastal, bedrock, and glacial terrain, which includes plateau and moraine). The initial snow cover amount influenced the water level pattern for the summer season. Large end-of-winter snow accumulations in the deep bedrock pond ensured large initial water storage and seasonal sustainability despite variable climatic conditions and a coarse substrate, which encouraged subsurface outflow. Connectivity to a stream draining an upland area and a melting late-lying snowbed nearby allowed the small Moraine pond to maintain stable water levels throughout both years. Sandy soils typical of the Coastal and Plateau ponds favored seepage and subsurface water losses, leading to desiccation of these ponds during dry periods. Lateral water losses from the Coastal pond were enhanced by the presence of a downslope frost crack that formed a steep hydraulic gradient with the pond. High initial snowfall and substantial rain maintain pond water levels, but in years with low snowfall and dry conditions, ponds are vulnerable to disappearance unless a range of dependable hydrological linkages exists.Key words: Arctic hydrology, climate change, connectivity, low-gradient wetland, sustainability RÉSuMÉ. Les milieux humides de l'Arctique sont sensibles aux changements climatiques continus, tel que l'atteste la perte récente de lacs et d'étangs du sud de l'Alaska, de la Sibérie et du nord de l'île d'Ellesmere, au Canada. À l'heure actuelle, il faut obtenir une meilleure idée des mécanismes à la source de ces pertes ou à la source de la persistance des étangs. Afin de mieux comprendre et de quantifier les processus hydrologiques qui entraînent la durabilité ou la disparition des étangs de l'Extrême arctique, une étude détaillée a été réalisée au cours des étés 2005 et 2006 à l'île Somerset, au Nunavut (72˚43' N, 94˚15' O). À quatre étangs situés dans trois grandes zones géomorphologiques (côtière, roche de fond et terrain glaciaire, ce qui comprend plateaux et moraines), on a utilisé un cadre de référence de bilan hydrique quantifiant les gains, les pertes et le stockage d'eau. La quantité de couverture de neige initiale exerçait une influence sur le modèle de niveau d'eau pendant la saison d'été. Les fortes accumulations de neige en fin d'hiver dans la profonde roche de fond des étangs donnaient lieu à un important stockage initial de l'eau et à la durabi...

The accelerated warming of the Arctic climate may alter the local and regional surface energy balances, for which changing land surface temperatures (LSTs) are a key indicator. Modeling current and anticipated changes in the surface energy balance requires an understanding of the spatio-temporal interactions between LSTs and land cover, both of which can be monitored globally by measurements from space. This paper investigates the accuracy of the MODIS LST/Emissivity Daily L3 Global 1 km V005 product and its spatio-temporal sensitivity to land surface properties in a Canadian High Arctic permafrost landscape. The land cover ranged from fully vegetated wet sedge tundra to barren rock. MODIS LSTs were compared with in situ radiometer measurements from wet tundra areas collected over a 2-year period from July 2008 to July 2010 including both summer and winter conditions. The accuracy of the MODIS LSTs was −1.1°C with a root mean square error of 3.9°C over the entire observation period. Agreement was lowest during the freeze-back periods where MODIS LST showed a cold bias likely due to the overrepresentation of clear-sky conditions. A multi-year analysis of LST spatial anomalies, i.e., the difference between MODIS LSTs and the MODIS LST regional mean, revealed a robust spatiotemporal pattern. Highest variability in LST anomalies was found during freeze-up and thaw periods as well as for open water surface in early summer due to the presence or absence of snow or ice. The summer anomaly pattern was similar for all three years despite strong differences in precipitation, air temperature and net radiation. Summer periods with regional mean LSTs above 5.0°C showed the greatest spatial diversity with four distinct 2.0°C classes. Summer anomalies ranged from −4.5°C to 2.6°C with an average standard deviation of 1.8°C. Dry ridge areas heated up the most, while wetland areas and dry areas of sparsely vegetated bedrock with a high albedo remained coolest. The observed summer LST anomalies can be used as a baseline against which to evaluate both past and future changes in land surface properties that relate to the surface energy balance. Summer anomaly classes mainly reflected a combination of albedo and surface wetness. The potential to use this tool to monitor surface drying and wetting in the Arctic should therefore be further explored. A multi-sensor approach combining thermal satellite measurements with optical and radar imagery promises to be an effective tool for a dynamic, process-based ecosystem monitoring scheme.