The doctoral thesis was part of the ongoing research project “Tolerance limits of microbial life in terrestrial permafrost” in the scope of the DFG (Deutsche Forschungsgemeinschaft) Priority Program “Mars and the Terrestrial Planets” WA 1554/1-2. In this project, special attention was paid to the survival potential of methanogenic archaea in Siberian permafrost. Field research and sampling were carried out during the expedition Lena Delta 2004 (Samoylov Island, Siberia, Russia). The work was conducted at the Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam and is presented as a Ph.D. thesis at the University of Potsdam, Institute of Biochemistry and Biology. The thesis is composed of an introduction and four main chapters (2-5), followed by synthesis and conclusions. In the first chapter, an introduction of the research topic, the main objectives of this work, study site description and an overview of the publication is given. The main chapters consist of four manuscripts that represent self-contained units which are field on a common thread. Chapter 2 is in preparation for submitting and Chapter 4 has been submitted for publication to various international journals, whereas Chapter 3 and 5 are published already (s. 1.5). A synthesis of the four research articles is given in Chapter 6, including the outline of the basic findings aswell as major conclusions and future perspectives.