1499 Permafrost Degradation and Inlux of Biogeogases into the Atmosphere E. Rivkina Institute of Physicochemical and Biological Problems in Soil Science, Pushchino, Russia G. Kraev Institute of Physicochemical and Biological Problems in Soil Science, Pushchino, Russia Abstract The data on methane content and pattern of its distribution across permafrost of different age and origin on late Cenozoic permafrost of Northeastern Arctic are summarized. We have found that methane is present in the epycryogenic Holocene and early Pleistocene layers and is absent in the syncryogenic late Pleistocene ice complex. Incubation under anaerobic conditions triggered the process of methane formation in Holocene and early Pleistocene layers and did not initiate it in the ice complex sediments. Based on the analysis of microbial community, organic matter, and potential for methane formation in various genetic types of permafrost sediments, we concluded that ice complex sediments, and to a lesser extent than epycryogenic ones, have the potential to produce methane in consequence of permafrost degradation. Keywords: permafrost; methane production; methanogenic arhaea; isotopic composition. Introduction In the framework of global change studies in the last decades, attention has been given to CO 2 and CH 4 emission from high-latitude ecosystems (Whalen & Reeburgh 1990, Christensen, 1993, Fyodorov-Davydov 1998, Reeburgh et al. 1998, Worthy et al. 2000, Zamolodchikov & Fyodorov- Davydov 2004, Wagner et al. 2003, van Huissteden et al. 2005). However, signiicant amounts of these greenhouse gases have been isolated from biogeochemical cycling and conserved in permafrost (Rivkina et al. 1992,) together with organic matter (Schirrmeister et al. 2002, Kholodov et al. 2004) and viable anaerobic microorganisms (Rivkina et al. 1998, Gilichinsky 2002). Thus, permafrost is a huge deposit and potentially, a large source of old organic carbon. It is important to assess the consequences of permafrost degradation because at least four pathways of carbon moblilization are inluenced by permafrost thaw: 1. The reservoir of carbon dioxide and methane bound in upper permafrost horizons that, unlike the deep high- pressure gas hydrates, could be easily liberated in the case of thawing in the polar regions. 2. The paleomicrobial community of viable methanogens expected to retain activity and be anew involved in biogeochemical processes, including generation of greenhouse gases (Rivkina et al. 2006). 3. Labile organic matter conserved in permafrost will be consumed by these microorganisms as an energy source for greenhouse gas production. 4. Increased production of methane in the active zone. This is in fact observed on northeastern Arctic exposures under present conditions with associated release methane, which is of similar magnitude to the direct production in Arctic tundra (Rivkina et al. 2001). Recent studies have provided a new impetus to such discussion, as they forecast high gas emission in response to permafrost degradation (Walter et al. 2006, Zimov et al. 2006). These papers, describing the lux of greenhouse gases from thermokarst ponds, have stimulated signiicant public and scientiic interest. Quantiication of methane release from thawing permafrost is of prime importance in climate research. Our objective is to clearly recognize the concentration and features of distribution of carbon sources in permafrost, based on its history (Sher 1974, Schiermeister et al. 2002). The present paper, based on the analysis of microbial community, organic matter and content of CO 2 and CH 4 , as well as on the possibility of methane formation and oxidation in various genetic types of permafrost sediments, will discuss the potential of greenhouse gases emission to the atmosphere in response to permafrost degradation and speciically, the late Pleistocene Icy Complex thawing upon which most activities are now focused. Study Area and Object of Investigation Investigations were carried out in continuous permafrost area in tundra and forest tundra zone landscapes on north- eastern Arctic coastal lowlands (125–162°E, 68–72°N), located between the Lena and Kolyma River deltas (Fig. 1). Sites were located outside the oil and gas basins, and were characterized by different Quaternary deposits (early Pleistocene to Holocene) and permafrost of both syn- and epicryogenic origin (Kaplina et al. 1984, Schirrmeister et al. 2002). Permafrost here had begun to form 3 million years ago and until now has not been deeply affected by global thawing. Studies were carried out down to 100 m depths on ine dispersed late Cenozoic stratotypes, which have been well described by many authors (Kaplina et al. 1981, 1988, Sher et al. 2005) on the bases of radiocarbon, palynological, paleontological, paleomagnetic, cryolithological, and physicochemical data. Distribution, thickness and area of the following strata