ИСТИНА

Presented and discussed the new data of gas properties (total gas content and composition) and water stable isotopes of two climatically contrasted Holocene and Pleistocene syngenetic ice wedges (SIW) and two types of tabular massive ground ice (TMGI) near Marre-Sale polar station, West Yamal, Russia. Our data set also supports the previous assumption that the ice wedges with isotopic signature (-25-23ppm for 18O and -190-180ppm for D) were formed in Pleistocene winters and the ice wedges with isotopic signature (-17-15ppm for 18O and -118-114ppm for D) in Holocene. For carbon dioxide, all ice wedges mixing ratios are clearly higher than the atmospheric values (0,03pct), the highest values being observed in Pleistocene ice wedges (0,97 pct), in Holocene ice wedges - (0,64 pct). Oxygen shows consistently lower values than the atmosphere (of the order of 4-7 pct), and nitrogen is slightly higher, balancing other constituents. On the contrary, methane mixing ratios show their lowest values in Pleistocene SIW (0, 004%), in Holocene SIW - (0,164 pct). Air bubbles trapped in polar ice provide an almost direct record of atmospheric methane over the last 800 kyr (e.g., Loulergue et al., 2008), methane budget for the periods is known: present (0,167 pct), and Last Glacial Maximum (0,036) (e.g., Josueґ Bock et al., 2012) and it is comparable with our data. Different methane mixing ratios in SIW suggest different climatic and environmental conditions. These properties are consistent with SIW developing under relatively warm Holocene conditions and cold in Pleistocene. Methane mixing ratios in TMGI show highest content (till 1, 37 pct). Isotopic measurements of the 13C -70,5ppm, and D -326ppm in methane are typical for gas formed with the participation of vital functions of bacteria. Found that the isotopic values 13C in methane are close to the values of the carbon isotopes of methane horizons at depths of 46-52 and 114-120 m in the Bovanenkovo gas field, West Yamal, and characterized of isotope volume -70,4-76,8ppm. Source of methane in TMGI could not be methane hydrates, because methane hydrates have a specific deuterium isotopic signature of about -190ppm, versus about -290ppm for mean of other sources. This pilot study detailed gas content and composition, and water and gas isotope analyses of ground ice sheds more light on the conditions of ground ice growth under changing environmental conditions. Higher temperatures in a Holocene resulted higher methane content in SIW, relatively high carbon dioxide levels. Lower temperatures in a Late Pleistocene resulted lower methane content in SIW. It is difficult to select potential sources bubbles trapped gas in TMGI. This heterogeneous medium, rich in organic matter, might have favored the anaerobic microenvironmental conditions necessary to explain the maximum methane content levels. Marshy coasts near shallow seas may have contributed to such conditions. The content of marsh gas in TMGI excludes their glacial origin.