Winter Ecosystem Respiration and Sources of CO2From the High Arctic Tundra of Svalbard: Response to a Deeper Snow Experiment

Currently, there is a lack of understanding on how the magnitude and sources of carbon (C) emissions from High Arctic tundra are impacted by changing snow cover duration and depth during winter. Here we investigated this issue in a graminoid tundra snow fence experiment on shale‐derived gelisols in Svalbard from the end of the growing season and throughout the winter. To characterize emissions, we measured ecosystem respiration (Reco) along with its radiocarbon (14C) content. We assessed the composition of soil organic matter (SOM) by measuring its bulk‐C and nitrogen (N), 14C content, and n‐alkane composition. Our findings reveal that greater snow depth increased soil temperatures and winter Reco(25 mg C m−2d−1under deeper snow compared to 13 mg C m−2d−1in ambient conditions). At the end of the growing season, Recowas dominated by plant respiration and microbial decomposition of C fixed within the past 60 years (Δ14C = 62 ± 8‰). During winter, emissions were significantly older (Δ14C = −64 ± 14‰), and likely sourced from microorganisms decomposing aged SOM formed during the Holocene mixed with biotic or abiotic mineralization of the carbonaceous, fossil parent material. Our findings imply that snow cover duration and depth is a key control on soil temperatures and thus the magnitude of Recoin winter. We also show that in shallow Arctic soils, mineralization of carbonaceous parent materials can contribute significant proportions of fossil C to Reco. Therefore, permafrost‐C inventories informing C emission projections must carefully distinguish between more vulnerable SOM from recently fixed biomass and more recalcitrant ancient sedimentary C sources. Deeper snow increased winter soil temperatures and CO2emissions of Arctic tundraLate growing season emissions were driven by year‐ to decade‐old C (Δ14C = 62 ± 8‰) and winter emissions by Holocene soil and fossil shale (Δ14C = −64 ± 14‰)In gelisols, weathering of C‐rich parent material may contribute to C emissions