Beneath the Laptev Sea , a thick permafrost layer has developed during the last glacials when the now flooded shelf was exposed and not glaciated. The permafrost may still exist today in a submarine environment after the last transgression, since the low seawater temperatures prevented melting. Even if the existence of the submarine permafrost is proven by drilling at several locations, the distribution of the permafrost and its possible degradation in different areas is still unknown. Therefore, high-resolution multi-channel seismic data as well as sediment echosounder and sidescan data were collected during Expedition Transdrift X. This expedition was carried out in September 2004 in a Russian-German cooperation between the GEOMAR ( Kiel , Germany ), the VNIIO ( St. Petersburg , Russia ) and the University of Bremen ( Germany ). As seismic source, a Mini GI Gun was used; the seismic signals were received with a new 48-channel streamer especially designed for shallow water conditions. The main goal of the expedition was to image the distribution and character of the top of the permafrost as well as to analyze and interpret seismic facies in the working area. Finally, the results will be used to determine optimum locations for a drilling campaign planned for summer 2005.

On the poster, we will present seismic data showing the different seismic facies types and structural features found in the Laptev Sea as neotectonic faults and deep structures interpreted as former terrestrial surfaces. A main target of the survey was an acoustically hard interface, which in shape and scale seems to mimic the thermokarst landscapes of the Sibirian coastlands today including ice-complexes and filled thermokarst lakes. The strong reflection of the interface indicates the presence of frozen sediments. A dense grid of seismic and acoustic data was collected crossing this prominent reflector to get a 3-D image of its distribution and shape. Processing and mapping should verify the hypothesis, that this reflector may represent the top of old permafrost developed before the last transgression.