Permafrost landscapes are a challenge for the validation of remote sensing products. The land surface is characterized by high heterogeneity, patterned ground, disturbances, abundance of small-sized water bodies, and sharp moisture gradients. A significant challenge in the evaluation of remote sensing products for highlatitude permafrost landscapes are the very sparse ground data: there are only a limited number of welldescribed and multi-instrumented field sites. Within the ESA Data User Element DUE PERMAFROST project an important component is the evaluation and the assessment by the users and remote sensing experts to lend confidence in the scientific utility of the DUE PERMAFROST products. The long-term and multi-instrumented Russian-German Samoylov Station in the Lena River Delta (Arctic Siberia) is a prime site for evaluation in DUE PERMAFROST PERMAFROST and serves as an important platform to answer the following questions: • Are plot data representative of surrounding parameters at satellite spatial resolutions? • How are the statistics derived from the matchup analysis against in-situ Diagnostic Data Sets (DDS) (absolute validation)? • How is the credibility of DUE Permafrost products against ‘descriptive truth’ (relative validation)?
The risk of carbon emissions from permafrost ground is linked to ground temperature and thus in particular to thermal insulation by vegetation and organic soil layers in summer and snow cover in winter. This ground insulation is strongly influenced by the presence of large herbivorous animals browsing for food. In this study, we examine the potential impact of large herbivore presence on the ground carbon storage in thermokarst landscapes of northeastern Siberia. Our aim is to understand how intensive animal grazing may affect permafrost thaw and hence organic matter decomposition, leading to different ground carbon storage, which is significant in the active layer. Therefore, we analysed sites with differing large herbivore grazing intensity in the Pleistocene Park near Chersky and measured maximum thaw depth, total organic carbon content and decomposition state by δ13C isotope analysis. In addition, we determined sediment grain size composition as well as ice and water content. We found the thaw depth to be shallower and carbon storage to be higher in intensively grazed areas compared to extensively and non-grazed sites in the same thermokarst basin. The intensive grazing presumably leads to a more stable thermal ground regime and thus to increased carbon storage in the thermokarst deposits and active layer. However, the high carbon content found within the upper 20 cm on intensively grazed sites could also indicate higher carbon input rather than reduced decomposition, which requires further studies. We connect our findings to more animal trampling in winter, which causes snow disturbance and cooler winter ground temperatures during the average annual 225 days below freezing. This winter cooling overcompensates ground warming due to the lower insulation associated with shorter heavily grazed vegetation during the average annual 140 thaw days. We conclude that intensive grazing influences the carbon storage capacities of permafrost areas and hence might be an actively manageable instrument to reduce net carbon emission from these sites.
During the past decade, we have studied thermokarst and thermo-erosional processes and landforms in Ice Complex deposits of the Lena Delta. Ice Complex deposits are very ice-rich permafrost up to tens of meters thick. They are widespread in the Arctic and have attracted raising attention due to their vulnerability to thaw under climatic warming. In the Lena Delta they occur on the third geomorphological main terrace, which is distributed as several islands in the southern delta. Degradation processes throughout the Holocene have affected these late Pleistocene deposits. Rapid permafrost thaw underneath ponding water (thermokarst) has created thermokarst lakes; when these lakes drain, thermokarst basins remain that can be several kilometers wide and up to twenty meters deep. Rapid permafrost thaw by running water (thermal erosion) has created gullies, valleys and valley networks that are also deeply incised into the terrain surface. All these landforms and associated processes play an important role for the landscape’s hydrology, energy budget and carbon cycle. Our investigations have aimed at 1) understanding the evolution of thermokarst and thermal erosion in the Lena Delta Ice Complex throughout the Holocene, 2) quantifying current terrain changes (permafrost degradation and aggradation) as well as the contribution of different landform types to organic matter export from the Ice Complex to the Lena River, and 3) deducing potential future thermokarst and thermo-erosional activity. Our methodological approach has been a combination of geomorphological analyses in the field and based on satellite imagery and digital elevation models (DEM), sediment and water sampling.
As main results we would like to highlight the following:
- Thermokarst development started during the transition from Pleistocene to Holocene and has evolved throughout the Holocene.
- Only a minor part of the third terrace in the Lena Delta provides the conditions for the future formation of thermokarst and thermo-erosional landforms, because a large area has already been degraded by thermokarst and thermal erosion during the Holocene.
- Newly developing thermokarst landforms will not be able to grow to such large sizes as the existing Holocene thermokarst landforms.
- The existing landforms vary much in their activity: some thermokarst lakes and thermo-erosional valleys are expanding and actively erode the Ice Complex deposits, many have been stable over the last decades and some lakes have shrunk or drained thereby giving way for permafrost to reestablish.
- This variation of erosion activity is also reflected in different hydrogeochemical compositions of the waters in thermokarst lakes and streams in thermo-erosional valleys: water samples from eroding sites have higher concentrations of dissolved organic carbon (DOC) than stable sites, while thermokarst lakes in the drainage pathway act as DOC-reducing landscape components along the transport route.
Acknowledgments. We wish to thank all colleagues who supported our field work in the Lena Delta during the past ten years and helped with sample processing in the lab. A. Morgenstern was supported by the German Academic Scholarship Foundation and by the Helmholtz Association (grant PD-003).
An expected increase of thermokarst activity will lead to a further degradation of ice rich permafrost. Lakes formed by thermokarst processes are known to be a spatially and temporally variable feature indicative for surface wetness and drainage conditions. In order to investigate recent cryomorphogenesis this study is aimed to determine lake and terrain height changes in an ice rich arctic landscape. The investigation area is located in the south of the Lena Delta (Russia). Average sediment discharge of the Lena River is about 21 mil. t/a. In comparison to the whole catchment river bank erosion in the area of the delta contributes to the riverine sediment input to the Arctic Ocean above average. Ice Complex (IC) permafrost deposits of the third geomorphological terrace cover large areas of the southern Lena Delta, which is exceptionally exposed to an increasing river discharge and strong flood waters along the largest delta channels. On Kurungnakh Island belonging to the third terrace a well pronounced alas-Yedoma thermokarst relief is developed. Undissected Yedoma uplands (< 55m high) alternate with large thermokarst depressions (alasses, < 30m deep) formed by thawing of ground ice since the Bolling interstadial. Lakes can be found here within alasses and on the Yedoma uplands (see Morgenstern et al., this conference). Using photogrammetric principles, GIS, and geodetic measurement techniques a geometric consistent dataset was created for monitoring purposes.
