The marine methane cycle in the Canadian Arctic Archipelago during summer

Summary

In the Arctic Ocean, methane concentrations surpassing global averages are prevalent, especially along sub-Arctic and Arctic continental shelf margins. Despite elevated dissolved methane levels, the Arctic Ocean exhibits minimal methane fluxes to the atmosphere, indicating a potential role of water column oxidation in methane processing. During the Northwest Passage Project in the summer of 2019, we integrated thermohaline, chemical, and biological data with in-situ and in-vitro methane data in Canadian Arctic Archipelago (CAA) waters. Elevated in-situ dissolved methane was prominent in near-surface Pacific waters (between 2 and 7 m), particularly in meltwater regions, with av. concentrations of 5.8 ± 2.5 nM within the upper 30m. While methane oxidation constants were generally low (av. 0.006 ± 0.002 d−1), surface waters in Wellington Channel and Croker Bay exhibited higher rates (av. 0.01 ± 0.0004 d−1), associated with Pacific-origin microbial taxa like Oleispira and Aurantivirga. Deeper layers (>200 m) displayed lower methane concentrations (av. 3.1 ± 1.1 nM) and oxidation rates (av. 0.005 ± 0.001 d−1). Sea ice showed elevated dissolved methane concentrations (av. 9.2 ± 5 nM). Waters in the western CAA exhibited a 25% increase in methane concentrations compared to ice-free areas. The overall picture suggested supersaturation of in-situ methane in shallow waters (between 2 and 50 m), coupled with faster oxidation rates in meltwater and Pacific dominant layers, suggesting rapid seasonal cycling of methane and prevention of the methane migration into the atmosphere.