Potential Contributions of Ammonia-Oxidizing Microorganisms to the Distributions of Nitrous Oxide in the Northern Bering Sea

Oceanic N2O is a major source of atmospheric N2O gas and is involved in global warming and ozone depletion. It is thought to be mainly produced by nitrification, denitrification and nitrifier denitrification processes mediated by ammonia-oxidizing bacteria, ammonia-oxidizing archaea (AOA) and denitrifying bacteria. The Bering Sea, especially its continental shelf area, is considered a typical source of atmospheric N2O. During the 7th Chinese National Arctic Research Expedition (CHINARE2016), the distributions of N2O and ammonia-oxidizing microorganisms (AOOs) in the Bering Sea continental shelf and abyssal basin water were investigated. At a depth of 50 similar to 900 m within the abyssal basin, the in-situ ammonia oxidation process, particularly performed by AOA, exhibits considerable potential for the formation of supersaturated N2O. Meanwhile, beneath the oxygen minimum zone (depth range is approximately 800 similar to 1,000 m), supersaturated N2O is primarily driven by mixing processes, while the ammonia oxidation mediated by AOA also contributes to a certain extent. In addition, the N2O distribution characteristic exhibits a substantial disparity between the southern and northern Bering Sea shelves, with the former characterized as a mild sink and the latter as a weak source. The water column of the Bering Sea demonstrates a considerable potential for generating supersaturated N2O through ammonia oxidation, as corroborated by the current study. Nitrous oxide (N2O) is an important trace greenhouse gas that also acts as an ozone destroyer. The ocean is one of the main sources of N2O to the atmosphere. As a marginal sea of the Pacific Ocean with high productivity, the distribution mechanism of N2O is very complex affected by water masses mixing and intricate biogeochemical cycle processes. And the N2O flux of Bering Sea has distinct spatio-temporal variability. In this study, by incorporating previous research conclusions on the nitrogen cycle, we investigate the distribution mechanism of N2O and functional genes of ammonia oxidizing microorganisms in the Bering Sea to elucidate the potential contribution of individual nitrogen cycle processes to N2O supersaturation and which kinds of ammonia oxidation microorganisms are involved in this contribution, thus illustrating the distribution mechanisms of N2O in the northern Bering Sea. The flux of Bering Sea in summer was estimated based on the distribution mechanism of N2O. This findings were helpful to understand the mechanism of N2O metabolism in the Bering Sea and improve the accuracy of Marine N2O flux estimation. The source-sink characteristics of N2O in Bering Sea express obvious spatial and temporal variability Ammonia oxidation could potentially play a crucial role in the formation of N2O in the deep waters of the Bering Abyssal Basin The distribution mechanisms of N2O in the southern and northern shelves of the Bering Sea exhibit distinct characteristic