Methane in Ground Ice and Frozen Sediments in the Coastal Zone and on the Shelf of Kara Sea

Abstract

Degradation of permafrost on the continental shelf and shores of the Arctic seas may be a main cause of the methane emission to the atmosphere from marine sediments. To quantify this effect it is necessary to have reliable data on the methane content in the underground ice and frozen Quaternary deposits. Samples of frozen (permafrost) sediments and ground ice, taken in three reference coastal sections made in the Mid-and Late Pleistocene coastal exposures and on the Kara sea shelf, were collected and studied. The samples were analyzed to determine composition, salinity, organic carbon content, and other characteristics of the underground ices. About 270 samples allowed determination of the gas composition and the methane concentration. The gas is present in the pores of the rocks and air bubbles in the ice. Gas was present in pores of sediments and in bubbles within the ice. It has been established that the composition of non-hydrocarbon gases in the underground ice does not correspond to the composition of the atmosphere in the time of formation of them. The methane content in the underground ice and frozen sediments is characterized by very high variability. The highest concentrations of methane are inherent in layers of the massive ground ice and reach up to 23000 ppm; the maximum concentration of methane in the massive vein ices does not exceed 900 ppm. High concentrations of methane in layers of the massive ice confirm their non-glacier formation. The highest, up to 6400 ppm, methane concentrations in permafrost sediments are characteristic for the Late Pleistocene marine clays, while in the Mid Pleistocene marine clays it does not exceed 1700 ppm. The isotopic composition of methane in frozen sediments and ground ice in both, the Cara Sea coast and shelf, is indicative of similar bacterial genesis of the gas. The total organic carbon content plays the limiting role in the methane production and its accumulation in the frozen sediments and ground ice.

Methane in Gas Shows from Boreholes in Epigenetic Permafrost of Siberian Arctic

“…It also provides an input of methane to δ 13 C as low as -87‰, and values from -60‰ to -65‰ were reported for 10 gas-bearing fields in West Siberia at depths below 700 m [25]. The gas from shallower permafrost studied in Russia and Canada, which was both degassed from sediments [17,20] and emitted from accumulations [5,12,26], was mostly biogenic. Methane seeps in Alaska were reported to be thermogenic and of mixed origin [3], which was strongly distinct from the surficial methane sources in closed talik.…”

“…Previous studies showed that epigenetic permafrost always contains methane in an average concentration of 2.7 mg CH 4 m −3 (up to 47.4 g CH 4 m −3 ) of frozen sediment as opposed to syngenetic permafrost, which in most cases did not have any detectable methane [17,18]. High concentrations of methane in permafrost deposits were found in redeposited and refrozen sediments of drained thaw lake basins in Central Yakutia [19], whereas moderate concentrations were detected in loams and the segregation ice of marine deposits on the Yamal Peninsula [20]. Methane in permafrost could be produced at temperatures below zero by methanogenic archaea [21], and it could be converted to interpore gas hydrate [22].…”

Methane Content in Ground Ice and Sediments of the Kara Sea Coast

“…The lower part of profile in this area is composed by Late Pleistocene saline marine clays with the inclusion of sand layers formed during Marine Isotope Stage (MIS) 5 (127-71 kyr BP cal) [38]. The layer has no visible organic inclusions, the mean total organic carbon (TOC) is 0.84% [27]. Marine clays were freezing epigenetically as a result of retreating sea.…”

“…The upper part of the profile is composed of alluvial lacustrine sands and sandy loams formed during MIS 3 (57-24 kyr BP cal) and MIS 2 (24-11 kyr BP cal) [34]. These sediments contain visible organic detritus, but mean organic content is only 0.34% [27]. The thin layer of Holocene sediments is mostly represented by aeolian sands and peatlands tops the profile.…”

“…The analysis of texture ice extracted from the Pechora Sea seafloor (43-45 m water depth) near Kara Gate Straight showed that methane content of trapped gas was above 4390 ppm [21]. Analysis of the gas composition of the massive tabular ground ice (MTGI) was conducted in Canadian Arctic [22][23][24] and Western Yamal [9,[25][26][27]. These studies report high concentrations of methane trapped in the air bubbles within the ice.…”