Climatic forcing of terrestrial methane gas escape through permafrost in Svalbard

The release of methane from the summer thaw layer above permanently frozen ground (permafrost) is a well-known problem in Arctic science, because it constitutes a potentially harmful greenhouse gas emission source. However, too little is understood about how deeper methane sources within and beneath the permafrost are also able to escape to the atmosphere. Permafrost thaw and glacier retreat are two climate-driven processes that make this possible. Our project therefore monitored these two scenarios in Svalbard. In so doing we have found that groundwaters emerging from deep beneath the permafrost either in the valley bottom or next to retreating glaciers can carry methane at very high concentrations. The rate of groundwater flow to the land surface is therefore of critical importance. The project has mapped all groundwater springs containing methane in Central Svalbard, an area ca. 6300 km2. We found one or more active seeps at 94 locations and estimated emissions up to 270 tons per year. If representative of the entire Svalbard land area, total emissions are equivalent to 10% of emissions associated with Norway’s oil and gas sector. Glacial springs are by far the most common (84%) and are mostly found close to the front of rapidly retreating glaciers. We have also found very high gas emission sites in front of an advancing glacier (due to a surge) and from the sea bed just in front of several marine-terminating glaciers. Numerical modelling of these different groundwater flows has shown very long residence times (1000s of years) beneath the permafrost in the valley bottom, but much shorter residence times (days) beneath the glaciers. Continuous monitoring at both types of groundwater springs has shown how the physical conditions at their point of emergence are very important for regulating the amount of gas that can escape to the atmosphere. Those that emerge in lakes or deep fjords experience the most significant losses of methane before it has the chance to enter the atmosphere. Those that emerge via turbulent springs experience far lower rates of removal. At the most important sites, emission is dominated by gas bubbles formed after a drop in water pressure. This means there is less time available for emission because the bubbles rise quickly to the surface. The first microbial analysis of the springs show that a great proportion of the microorganisms near their point of emergence use the methane as an energy source and thus contribute to this removal. Other microorganisms are associated with the production of methane, but the evidence suggests that the most active and abundant microorganisms are associated with methane removal. Our geochemical measurements indicate that most of the methane is geological in origin. However, in Adventdalen and Fulmardalen, the gas is microbial in origin. It is not clear why the distribution of gas sources varies like this. However, we suspect that most of the biogenic methane has been trapped for beneath the permafrost for several thousand years. The main concern regarding climate change is that the escape of methane from in front of retreating glaciers will increase rapidly because more glacial melting will increase groundwater pressure. Since it is thought that most of the gas has accumulated beneath the permafrost over thousands of years, the emissions will eventually decline. However, it is also thought that the current rate of gas escape is very low compared to the total volume of gas. This is because permafrost remains an effective seal for the time being. Retreating glaciers are therefore the main concern because they expose new land where permafrost has yet to form, or where it is much thinner.

1) We have put Svalbard "on the map" with respect to the research being undertaken to understand methane emission from permafrost landscapes. This has occurred in tandem with a similar development of research into sea floor gas emissions from Svalbard's coastal and continental shelf environments. We have demonstrated that Svalbard's methane emissions are quite unlike those in other well-studied parts of the Arctic due to its high relief periglacial landscape, rapid climate warming and ongoing isostatic uplift. 2) We have identified novel microorganisms responsible for methane removal and we have identified that potential important microorganisms usually encountered in the deep sea may be sampled far more easily on foot at seepages in lowland Svalbard permafrost. 3) Future research impact linked to the above will involve the integration of terrestrial and marine methane dynamics, a process we have already begun via our publications describing methane in Svalbard fjords and will continue via our next publications and grant applications. We will therefore help foster an interdisciplinary understanding of changes in regional methane dynamics as a consequence of climate change. 3) The Project owners (UNIS) have embedded CLIMAGAS research into its teaching and learning, further adding to the unique opportunities we can offer to the next generation of Arctic scientists. 4) The project reached tens of thousands of visitors to Svalbard Museum due to the exhibition led by Hanne Christiansen, which ran throughout the Easter and summer tourist seasons during the post-covid "more business than usual" return of tourism to Svalbard. 5) The research has the potential to influence the Longyearbyen community's ongoing search for an alternative energy supply. The gas resource beneath the permafrost could provide local energy for some time, but the politics of its utilisation are very difficult to navigate. We are discussing the best way of improving our dialogue with relevant stakeholders whilst also trying to quantify and explain the risk of leaving the methane to escape to the atmosphere via natural processes responding to further climate change.

The release of methane from beneath retreating glaciers and thawing permafrost is a major source of uncertainty in the prediction of future greenhouse gas emissions from the Arctic. Presently we have no basis for predicting these fluxes on account of major uncertainty in the integrated physical, chemical and biological processes that govern how methane is produced, stored and released from these environments. There is great urgency to understand these processes in cases where methane can avoid oxidation or consumption by methanotrophic bacteria. Such removal processes are extremely effective in the case of methane diffusing through the sea floor or the soil's active layer, but we have found that they can be almost completely ineffective in some of the terrestrial groundwater springs of Svalbard and Greenland. Our project faces challenges linked to the observation of processes occurring beneath Arctic glaciers and permafrost. We will therefore use our exceptional data resources from the Adventdalen area, where the sub-surface environment has already been characterised to 900m depth. We will also employ new field techniques developed through pilot research to further quantify the system. These will then be incorporated into a groundwater biogeochemistry model with the capacity to predict methane emissons at the ground surface under current and future conditions. We will draw significant, international research attention to Svalbard, by establishing a "super-site" in the immediate vicinity of Longyearbyen. Here, the rich history of research, mining and polar exploration will greatly facilitate stakeholder engagement. We expect interest from engineers seeking the safe management or exploitation of permafrost methane emissions, Earth scientists seeking improved understanding of Arctic carbon cycling and greenhouse gas dynamics, and policy makers trying to balance poorly known, highly variable natural emissions with more controllable anthropogenic emissions.