Seasonal methane emissions from Lagoon Pingo West in Svalbard

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Methane is a potent greenhouse gas, with an even stronger climate forcing than carbon dioxide. Therefore, it is important to measure methane emissions. Recent studies on natural methane emissions from the Arctic, focused on methane release from the active layer and shallow permafrost, for example in wetlands. In contrast, pingos might act as emission sources for methane from reservoirs beneath the permafrost. A pingo is a landform in permafrost with an inner ice-core. Over the summer season, the icy parts of the pingo might thaw and form a lake. A study in Svalbard in the summer of 2017, measured the methane concentration in samples of a pingo lake, and modelled the flux of methane to the atmosphere. The seasonal methane flux amounted to 46.0 gCH4/100 d/m2. As the seasonal flux was higher than those of surrounding wetlands, pingos were characterized as emission "hotspots" in the Arctic landscape of Svalbard. This study aims to quantify the methane concentration and methane flux from Lagoon Pingo West for the summer seasons of 2020 and 2021. Lagoon Pingo West is fed by the same pingo spring as Lagoon Pingo East, where the study has been conducted in 2017. I used 11 samples over the summer season taken in irregular time intervals between 3-16 days to monitor the methane concentration. In addition, I used an automatic methane analyzer that measured the methane concentration in one-hour steps. The methane flux was calculated using a diffusion model that employed the results of the samples and the analyzer. In August 2021, I could apply chamber measurements that allowed for estimates of the methane flux. I found higher methane concentrations near the inflow in the central part of the lake than at the margins or at the outflow. I could observe a seasonal pattern in methane concentration, that varied with the positions and years. However, all data showed low methane concentrations after the melt season. The seasonal mean of the methane flux was higher in 2021 than in 2020. The diffusion model, using the analyzer data yielded higher results than the chamber measurements. The lowest results were obtained using the diffusion model with the data of the samples. The estimates for the seasonal methane fluxes were lower than those of Lagoon Pingo East in 2017. In 2020, the seasonal flux amounted to 1.69 gCH4/ 100 d/m2 at Lagoon Pingo West, calculated for the average of the sample positions, and in 2021 it amounted to 8.17 gCH4 / 100 d /m2. The results show that the methane flux from Lagoon Pingo West is higher than estimates from other Arctic lakes. In future works, the frequency of sampling could be increased to better understand the seasonal pattern of the methane concentration. The estimates of methane fluxes could be improved by daily or weekly measurements of the ebullition flux from the lake water.

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Koehnen, H. (2022): Seasonal methane emissions from Lagoon Pingo West in Svalbard , Bachelor thesis, Universität Potsdam.

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