Microbial driven methane dynamic in the Siberian Arctic during glacial-interglacial climate changesJ. GRIESS1,2, K. MANGELSDORF2, D. WAGNER11 Alfred Wegener Institute, Research Unit Potsdam, Telegrafenberg A45, 14473 Potsdam, Germany2 Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Telegrafenberg B423, 14473 Potsdam, GermanyArctic permafrost environments play an important role within the global methane cycle. Thawing of permafrost and the suggested release of this climate relevant trace gas, due to an increased microbial turnover of organic carbon and from ancient methane reservoirs, represent a potential risk to global warming. For the prediction of a future development of the permafrost environment and its contribution to the global atmospheric carbon budget, it is important to understand how this system reacted to environmental changes in the past. These changes in climate may cause chemical and physical variations in sedimentary column and thus, we expected changes in the composition of key microorganisms being implicated in methane cycle. Therefore, quantitative and qualitative analyses of the variations in composition of bacterial and archaeal communities involved in the Siberian methane cycle in Holocene and Late Pleistocene were conducted. The El'gygygtgyn permafrost core and lake sediments of 142 m and 517 m length, respectively, were recovered within the ICDP project Scientific Drilling in Elgygytgyn Crater Lake from November 2008 to May 2009. In addition to that, a 23 m long permafrost core drilled in 2002 on Kurungnakh Island, Lena-Delta, Siberia, was examined. Permafrost environments can be quite different. Whereas the terrestrial core from El'gygytgyn represent a dry and TOC poor habitat, the permafrost core drilled on Kurungnakh Island was taken in a water saturated and TOC rich environment. These two sites will be compared. However, in the current abstract we will focus on the results of the Kurungnakh permafrost core. Our studies on the reconstruction of the methane cycle in Siberian permafrost deposits combines biogeochemical and molecular microbiological methods. As a general result it was shown, that it was possible to recover lipid biomarker and intact DNA throughout the Kurungnakh permafrost sequence that comprises sediments of the holocene and late pleistocene. First analyses of intact glycerol dialkyl glycerol tetraethers (GDGTs) were conducted. GDGTs provide paleo-signals of archaeal and bacterial communities, since these core lipids are relatively stable outside intact cells. Highest amounts of ether lipids were found in the upper layer and at the bottom of the core. Generally, the results of GDGT analyses correlate to measured contents of total organic carbon (TOC) and concentrations of in-situ methane of the deposits. Total GDGT contents show highest concentrations with 495 ng/g sediment at 122 cm depth, with of 70 ng/g sediment at 1184 to 1745 cm and with about 400 ng/g sediment at 2320 cm depth. Furthermore, these biomarkers can be distinguished between biomarkers representing signals of paleo-archaeal and paleo-bacterial communities (depending on the tetraether alkyl bridges). Archaeol concentration varied between 3.84 and 62.5 ng/g sediment. The highest amounts were measured on top and bottom of the core and at a peak at 1745cm depth.Additionally, the presence of aerobic methane oxidizing bacteria (MOB) was analyzed using diploptene (Hop-22(29)ene), a biomarker that can be found in methane oxidizing bacteria. The variability of the diploptene distribution correlates to measured rates of methane and content of TOC. Diploptene can be regarded as a paleo-signal for MOBs being present during time of sedimentation of the respective deposits (upper aerobic active layer). The fact that sedimentary intervals with high amounts of trapped methane (presumably intervals with in-situ methane production) also contain high contents of diploptene suggests that these sediments released also high amounts of methane in the past being the host of considerable aerobic methanotrophic communities.To complete our information on the qualitative composition of microbial communities, DNA-based analyses were conducted using archaeal and methanotrophic specific primer combinations, whereas amplicons were subsequently analyzed by DGGE and clone libraries. Fingerprints of archaeal 16 S rRNA gene sequences of the different permafrost samples show variations within the vertical profile. Sequence analyses showed a distinct diversity of methanogens affiliated with Methanobacteriaceae, Methanosarcinaceaea and Methanomicrobiaceae. Highest diversity of methanogens could be detected at depth of 1507 cm and 1745 cm, which were also characterized by high amounts of archaeol.Both biogeochemical as well as molecular methods revealed variation within the composition of past and present microbial communities and showed indications of response to climate changes.