Microbial Life in Terrestrial Permafrost: Methanogenesis and Nitrification in Gelisols as Potentials for Exobiological Process (original) (raw)

Dry permafrost over ice-cemented ground at Elephant Head, Ellsworth Land, Antarctica

Antarctic Science, 2019

Dry permafrost - ground with temperature always below 0°C and containing negligible ice - overlying ice-cemented ground has been reported in the Dry Valleys of Antarctica and on Mars. Here we report on a new site (79°49.213'S, 83°18.860'W, 718 m elevation) located on the side of Mount Dolence in Ellsworth Land, Antarctica. Year-round temperature and humidity measurements indicate that dry permafrost is present between depths of 13.5 and 49.0 cm - the location of ice-cemented ground. The mean annual frost point of the ice-cemented ground is -17.0 ± 0.2°C and the mean annual frost point of the atmosphere is -22.7 ± 1°C. The corresponding mean annual temperatures are -19.2°C and -20.3°C. Neither the temperature of the ice-cemented ground nor the air rise above freezing. Both the dry permafrost and the ice table may be habitable. In the dry soil at 3 cm depth there are 80 hours in the summer when temperature exceeds -5°C and water activity exceeds 0.8. At the ice table, temperat...

Permafrost Landscapes on Earth: Lessons for Mars and Europa

2003

The cold and hyper-arid Dry Valleys of Antarctica have long been recognized as having environmental conditions on Earth closest to those on Mars. They contain valuable clues about the presence and character of ice in the permafrost, and about surficial processes on Mars. Extensive regions in the Dry Valleys are commonly mantled by poorly sorted glacial or rock fall material ranging in size at the surface from boulders to small pebbles. The abundance of coarse material at the surface reflects vertical sorting due to re-current thermally induced volumetric changes and to vertical cracks forming (and closing) in the upper few meters of the permafrost, as well as removal of fines from the surface by eolian transport. In Beacon Valley, an area underlain by massive ice, the low relief (1 to 10 m) ground surface with scattered 50-100m-wide depressions is veneered with ˜0.5m of sublimation till. The existence of this till, which formed over 1-10 million years as debris initially contained i...

Permafrost Microbial Community Structure Changes Across the Pleistocene-Holocene Boundary

Frontiers in Environmental Sciences , 2020

Despite the presence of well-documented changes in vegetation and faunal communities at the Pleistocene-Holocene transition, it is unclear whether similar shifts occurred in soil microbes. Recent studies do not show a clear connection between soil parameters and community structure, suggesting permafrost microbiome-climate studies may be unreliable. However, the majority of the permafrost microbial ecological studies have been performed only in either Holocene-or Pleistocene-aged sediments and not on permafrost that formed across the dramatic ecosystem reorganization at the Pleistocene-Holocene transition. In our study, we used permafrost recovered in proximity to the Pleistocene-Holocene transition subsampled under strict sterile conditions developed for ancient DNA studies. Our ordination analyses of microbial community composition based on 16S RNA genes and chemical composition of the soil samples resulted into two distinct clusters based on whether they were of late Pleistocene or Holocene age, while samples within an epoch were more similar than those across the boundary and did not result in age based separation. Between epochs, there was a statistically significant correlation between changes in OTU composition and soil chemical properties, but only Ca and Mn were correlated to OTU composition within Holocene aged samples; furthermore, no chemical parameters were correlated to OTU composition within Pleistocene aged samples. Thus, the results indicate that both soil chemical and microbial parameters are fairly stable until a threshold, driven by climate change in our study, is crossed, after which there is a shift to a new steady state. Modern anthropogenic climate change may lead to similar transitions in state for soil biogeochemical systems and microbial communities in Arctic regions.