More than methane: quantifying melt-driven biogas production and nutrient export from Eurasian Arctic lowland permafrost

The vulnerability of the carbon stocks in Arctic permafrost to climate change is well known. New research has shown that increased mineralization of soil carbon via aerobic pathways favouring CO2 production instead of anaerobic pathways favoring CH4 represents the most important climate change amplifier within Arctic permafrost. It is, however, less well known how hydrological and geomorphological processes govern the changing distribution of oxic and anoxic sediments in Arctic lowlands. This has been investigated in this project. The project has focused on studies of the biogeochemical conditions of microorganisms in both the active layer and the top permafrost in lowland areas in Svalbard as a proxy for the extensive Arctic permafrost lowland areas in Siberia and North America. In the Norwegian part of this JPI project two young researchers Brendan O'Neill and Ebbe N. Bak have been employed at UNIS and HVL. They have worked intensively on 1) analyzing the ice content and ice types of the active layer and permafrost top (cryostratigraphical studies) and 2) performing incubation studies of cores from the active layer and top permafrost with measurements of microbiological parameters both from the LowPerm study areas in Svalbard. At UNIS also internal PhD student, Graham Gilbert have collaborated with the project, and he has obtained two 20 m long cores, that have been shared with colleagues in LowPerm for improved access to deeper permafrost in the LowPerm study area. The Norwegian part of the project has primarily focused on characterizing the ice content and physical process dynamics of the active layer and top permafrost, in addition to describing the changes in the microbial populations and their functional potential in the active layer and top permafrost. The results from the work comprises reconstructing the Holocene landscape development in the LowPerm Adventdalen lowland study area with focus on the delta development down through the valley and on the development of the different permafrost landforms with varying ice content. One of the most important landforms with respect to the potential for release of greenhouse gasses from the permafrost is ice-wedge polygons, which have as particularly high ice content near the top of the permafrost, and which due to winter thermal contraction cracking can provide a direct release of greenhouse gasses to the atmosphere even in winter. We have therefore studied the geomorphological process activity of these landforms and made an analysis of ice-wedge cracking registration using new technology in the form of 1D mini acceleration loggers, which has shown very useful for this purpose. We have additionally collected and analyzed a set of shorter active layer ? top permafrost cores from ice-wedge polygons in the Adventdalen area. The ice-wedge polygons are covered by loess deposits in some parts of the study area, just as some are located in wetland areas. The top permafrost and the active layer in Adventdalen is of late Holocene age, and thus relatively young and with very varying ice content. Five shallow permafrost cores from Adventdalen were additionally collected in April/May 2016. These cores have been used for numerous experiments, including high-resolution XRF (ITRAX), batch incubations, chemical analyses, and microbial community analyses (DNA extraction, qPCR). A UK PhD student has also analyzed the cores with respect to ice content as part of the LowPerm project. Most experiments and analytical work have now ended, but a few long-term incubation experiments will be running into 2018. Changes in consumption/production of CO2 and CH4 in incubation experiments were quantified by gas chromatography with a thermal conductivity detector for CO2 and a flame ionization detector for CH4. The preliminary results indicate that methane production plays a much smaller role than previously assumed for Arctic lowlands. This is supported by results from gas samples done in collaboration with other non-Norwegian LowPerm project researchers. Emission of CO2 seems to be much more important than CH4 emission from Arctic lowlands with respect to the relevance of these gases? effect on radiative forcing. We see a shift in the composition of the microbial ecosystem from the top of the permafrost to the active layer, which reduces CH4 emission from Arctic lowlands. Non-Norwegian LowPerm project researchers use seasonal measurements of greenhouse gas emission from the different Arctic landforms studied in this project to upscale the emission to the entire lowland landscape from Kapp Linne to Adventdalen. In addition stable water isotopes have been analyzed from the rivers of the study area. The seasonal dynamics of the isotopic composition of the rivers show systematic differences in the contributions from the tributary rivers through the year. These results will be used together with the hydrochemical analyses to improve the understanding of the nutrient transport in r

The importance of the oceans for heat transfer into the Arctic means that the low altitude and very extensive permafrost lowlands here can respond quickly and significantly to climate change. In the Eurasian Arctic this causes the early onset of melt, increased active layer thickness and enhanced microbial activity. It is now known that the vast soil carbon stocks of Arctic permafrost are vulnerable to these changes, but accurate forecasting of its influence on the global climate system cannot be achieved until the following knowledge gaps are addressed: 1) Microbially-mediated processes at the active layer/permafrost interface will control the in-situ production of new biogases and nutrients in response to warming by (extrinsic) climate forcing. However, at the landscape scale, these crucial biogeochemical processes are governed by poorly understood intrinsic (hydrological, geomorphological and ecological) drivers yet to be incorporated into regional models. 2) Runoff from extensive permafrost lowlands in the Eurasian Arctic is a quantitatively important source of iron, nitrogen, phosphorus and organic matter to already highly productive marine ecosystems. The fertilisation potential of such chemical fluxes entering the sea must be urgently quantified as it will induce further change in the CO2 budget, via biological production, and thus initiate marine ecosystem change. This project will address these key issues with an integrated programme of field work, laboratory experimentation, numerical modelling and workshops. We will use Russian and Norwegian field logistics from West Spitsbergen to Siberia, and laboratories in the UK and Denmark. Major polar science practitioners from outside the consortium with expertise in regional modelling, isotope geochemistry, marine ecosystem change and biogeochemical cycling will enhance the international profile and impact of the project via knowledge exchange activities that include two workshops.