Large stocks of permafrost soil organic carbon and nitrogen in Arctic river deltas

Arctic deltas are highly dynamic environments at the land-ocean interface that have acted as long-term sinks of sediment, carbon (C), and nitrogen (N). Climate impacts Arctic deltas and their upstream catchments through sea-level rise, altered river discharge, increased sediment fluxes, intensified biogeochemical cycling, and permafrost thaw. As a result, soil C and N in Arctic delta deposits are becoming more bioavailable. Here, we present a C and N inventory for Arctic delta compiled from over 1600 soil samples spanning 17 river deltas. We estimate that Arctic delta deposits store 57.5 ( + 9.2/−8.2) Pg C and 3.8 ( + 0.8/−0.7) Pg N across a combined area of nearly 100,000 km², representing large and potentially vulnerable biogeochemical pools. Our findings underscore the potentially pivotal role of Arctic deltas in the pan-Arctic carbon cycle and highlight their importance as dynamic zones of both C and N storage and release in a rapidly changing Arctic. This study estimates that Arctic deltas contain vast amounts of soil organic carbon (57.7 Pg) and soil nitrogen (3.8 Pg). This highlights the importance of these vulnerable permafrost landscapes at the land-ocean interface in a changing Arctic.