ИСТИНА

The chosen borehole (71 41N, 130 21E) characterizes the morphological structure of the tectonic fractal zone that is filled in with "acoustically gassy sediments". We suggest this site exhibits a significant potential to release CH4 into the atmosphere because this area belongs to the Gakkel Ridge so-called "Middle Arctic belt", a linear seismically-active zone which is characterized by a high density and frequency of strong and shallow earthquakes: energy from a shallow earthquake of magnitude >4.0 might be enough to destabilize ocean hydrates. There is reason to believe that ultra-slow-spreading ridges such as the Gakkel Ridge may be especially conducive to the build-up and explosive discharge of volatile-rich magmatic foams. Thus, it is logical to assume that increasing (or even explosive) discharge of a volatile-rich magmatic plume might be observed in the Buor Khaya tectonic fractal zone which is underlain by the thinnest continental crust. During December 2010 (three months before the drilling) two earthquakes struck the Buor Khaya Gulf area (M4.6 and M4.9). These earthquakes have the potential to activate upward migration of deep fluid in the study area. By choosing the right location for the first borehole in the rift zone of the Buor Khaya Gulf we hoped to discover new and critically important information about: 1) the CH4 potential and the availability of this CH4 to be involved in the modern biogeochemical cycles; 2) sub-sea permafrost; 3) signs of deep super-plumes (CH4 and other gases) and pore water and sediment chemical composition. The total borehole depth was 65m; this included ~12m of ice and water column. The total length of the sediment core is 53m with diameter ~127mm. Well tubes used in our drilling were 146mm in diameter. We did not reach sub-sea permafrost: the sediments beneath the upper aleurite pelitic layer were mostly composed of alluvial sand, which traces the course of the ancient Lena fore-delta. High concentrations of CH4, non-CH4 hydrocarbons, and free hydrogen were found. The temperature along the borehole increased from ~ -0.7-0.8C in the sediment upper boundary layer to -0.3-0.4C down by depth. Linear or exponential approximation of available temperature data suggests that the top of the sub-sea permafrost might be found at a depth of ~170m (linear extrapolation), but the existence of sub-sea permafrost at this particular site is questionable. In any case, preliminary data indicate that the seabed at this site functions as a pathway by which volatile gas components are able to migrate upward. The numerical modeling also demonstrated that in areas affected by the inflow of warm water (such as the Lena River plume), the permafrost can significantly degrade from the top down in addition to the "geothermal" down-top thawing ; this may explain both our drilling result, finding no subsea permafrost at a depth >>53 m.