This study explores the carbon stability in the Arctic permafrost following the sea-level transgression since the Last Glacial Maximum (LGM). The Arctic permafrost stores a significant amount of organic carbon sequestered as frozen particulate organic carbon, solid methane hydrate and free methane gas. Post-LGM sea-level transgression resulted in ocean water, which is up to 20 degrees C warmer compared to the average annual air mass, inundating, and thawing the permafrost. This study develops a one-dimensional multiphase flow, multicomponent transport numerical model and apply it to investigate the coupled thermal, hydraulic, microbial, and chemical processes occurring in the thawing subsea permafrost. Results show that microbial methane is produced and vented to the seawater immediately upon the flooding of the Arctic continental shelves. This microbial methane is generated by the biodegradation of the previously frozen organic carbon. The maximum seabed methane flux is predicted in the shallow water where the sediment has been warmed up, but the remaining amount of organic carbon is still high. It is less likely to cause seabed methane emission by methane hydrate dissociation. Such a situation only happens when there is a very shallow (similar to 200 m depth) intra-permafrost methane hydrate, the occurrence of which is limited. This study provides insights into the limits of methane release from the ongoing flooding of the Arctic permafrost, which is critical to understand the role of the Arctic permafrost in the carbon cycle, ocean chemistry and climate change. Arctic permafrost stores similar to 1,700 billion tons of organic carbon. If just a fraction of that melts, the escaping methane would become one of the world's largest sources of greenhouse gas and would severely impact the environment and the climate. Over the last similar to 18,000 years, a quarter of the stored organic carbon in the Arctic permafrost has been flooded by the rising, warm seas. This has melted the ice and degraded the permafrost. But what happens to the carbon pools? This study investigates the stability of the carbon in the Arctic permafrost following the flooding using a newly developed numerical model. Results show that microbial methane is generated and emitted to the seawater immediately following the flooding. This methane is produced by the biodegradation of the previously frozen organic carbon near the seafloor. The maximum methane emission is predicted in the shallow water near the coast where the sediment has been warmed up, but the remaining amount of organic carbon is still high. This study provides insights into the limits of methane release from the ongoing flooding of the Arctic permafrost, which is critical to understand the role of the Arctic permafrost in the carbon cycle, ocean chemistry and climate change. A numerical model is developed to simulate the coupled thermal, hydraulic, microbial and chemical processes in the thawing subsea permafrost The biodegradation of the ancient organic carbon in the thawing subsea permafrost results in seabed microbial methane emission Seabed methane emission is less likely to be caused by methane hydrate dissociation at the Arctic continental shelves

Microorganisms that are halophilic and halotolerant have gradually developed unique structures, physiologies, and genomes to survive. They are essential for ecological restoration and pollution control. This review emphasizes the critical role of halophilic and halotolerant microorganisms in plant stress tolerance, the ability to degrade a wide range of organic pollutants, the potential for cultural heritage conservation and restoration, and the impact on the spread of resistance genes. Halophilic and halotolerant microorganisms tolerate salt by controlling osmotic pressure in the cytoplasm via one of two major mechanisms: compatible solute accumulation or inorganic ion accumulation. Besides, the ability of halophilic and halotolerant microorganisms to survive high salt concentrations is also related to enzymatic proteins with fascinating physicochemical and structural properties. The advantage of halophilic enzymes is their ability to maintain enzyme stability and activity under high salt concentrations and organic reagents. The review of halophilic and halotolerant microorganisms is critically valuable for the reclamation of saline lands and pollutant degradation in highly saline environments.

Increased permafrost thaw due to climate change in northern high-latitudes has prompted concern over impacts on soil and stream biogeochemistry that affect the fate of dissolved organic carbon (DOC). Few studies to-date have examined the link between molecular composition and biolability of dissolved organic matter (DOM) mobilized from different soil horizons despite its importance in understanding carbon turnover in aquatic systems. Additionally, the effect of mixed DOM sources on microbial metabolism (e.g., priming) is not well understood. No studies to-date have addressed potential priming effects in northern high-latitude or permafrost-influenced aquatic ecosystems, yet these ecosystems may be hot spots of priming where biolabile, ancient permafrost DOC mixes with relatively stable, modern stream DOC. To assess biodegradability and priming of DOC in permafrost-influenced streams, we conducted 28 day bioincubation experiments utilizing a suite of stream samples and leachates of fresh vegetation and different soil horizons, including permafrost, from Interior Alaska. The molecular composition of unamended DOM samples at initial and final time points was determined by ultrahigh resolution mass spectrometry. Initial molecular composition was correlated to DOC biodegradability, particularly the contribution of energy-rich aliphatic compounds, and stream microbial communities utilized 50-56% of aliphatics in permafrost-derived DOM within 28 days. Biodegradability of DOC followed a continuum from relatively stable stream DOC to relatively biolabile DOC derived from permafrost, active layer organic soil, and vegetation leachates. Microbial utilization of DOC was similar to 3-11% for stream bioincubations and ranged from 9% (active layer mineral soil-derived) to 66% (vegetation-derived) for leachate bioincubations. To investigate the presence or absence of a priming effect, bioincubation experiments included treatments amended with 1% relative carbon concentrations of simple, biolabile organic carbon substrates (i.e., primers). The amount of DOC consumed in primed treatments was not significantly different from the control in any of the bioincubation experiments after 28 days, making it apparent that the addition of biolabile permafrost-derived DOC to aquatic ecosystems will likely not enhance the biodegradation of relatively modern, stable DOC sources. Thus, future projections of carbon turnover in northern high-latitude region streams may not have to account for a priming effect.