Evaluation of High Arctic terrestrial habitats as potential hotspots of nitrous oxide emissions (Hornsund region, South Spitsbergen)

Carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) are the main greenhouse gases (GHGs) contributing to the ongoing climate crisis. Among those N 2 O has the highest global warming potential and is mainly of microbiological origin. Tropical rainforests are considered the primary natural source, although in recent years fluxes of N 2 O from polar ecosystems have been reported at comparable levels. In this study we aimed to identify High Arctic terrestrial habitats with the highest potential to become sources of N 2 O emissions. A microbiological and geochemical analysis was performed on soil procured from the biologically and geomorphologically diverse South Spitsbergen region in search of biotic and abiotic determinants of a N 2 O emission hotspot. Terrestrial sites within this High Arctic area vastly differed in their potential to emit substantial N 2 O amounts. External organic matter inputs were pivotal in maintaining a pool of inorganic nitrogen compounds for microbially-mediated N 2 O-generating processes such as denitrification. The examined planktivorous seabird colony presented a unique, potential N 2 O emission hotspot as it featured persistent acidification of the surrounding soil, a steady ammonia release and nitrate presence even after breeding season closure. Soils of the majority of analyzed sites did not display detectable nitrate and/or ammonia levels, with some areas having the characteristics of a N 2 O-sink rather than an emitter, especially postglacial moraine deposits. The presented data encourage further, more targeted investigations of High Arctic N 2 O emission hot- and coldspots to progressively improve N 2 O emission estimates for permafrost affected regions worldwide.