The marine methane cycle in the Canadian Arctic Archipelago during summer

• Published in: Marine Ecology Progress Series
• Main Authors: D'Angelo, Alessandra, Garcia-Eidell, Cynthia, Kerrigan, Zak, Strock, Jacob, Crable, Frances, VanKeersbilck, Nikolas, Raziuddin, Humair, Ewa, Theressa, Umar, Samira, King, Andrew L., Gonzelez-Meler, Miquel, Loose, Brice
• Format: Text
• Language: English
• Published: 2023
• Subjects: Arctic; Arctic Ocean; Canadian Arctic Archipelago; Pacific; Northwest Passage; Wellington Channel; Croker; Croker Bay; Arctic Archipelago; Northwest passage; Northwest Passage Project; Sea ice; Subarctic
• Online Access: https://doi.org/10.5194/bg-2023-157; https://bg.copernicus.org/preprints/bg-2023-157/

In the Arctic Ocean region, methane (CH 4 ) concentrations are higher than the global average, with particularly high concentrations of dissolved CH 4 observed along many subarctic and Arctic continental shelf margins. Despite this, the Arctic Ocean emits only minimal methane fluxes to the atmosphere across the air-sea interface, suggesting that water column oxidation of methane may be an important process. In this study, we paired thermohaline, chemical, and biological data collected during the Northwest Passage Project transit through the Canadian Arctic Archipelago (CAA) waters in the summer of 2019 with in-situ and in-vitro methane data. Our findings suggested that the most elevated in-situ concentration of dissolved methane was present in the near-surface waters of the Pacific, particularly in meltwater regions. The highest methane concentrations were observed within shallow waters, averaging at 5.8 ± 2.5 nM within the upper 30 m depth. Furthermore, the methane distribution showed a distinct pattern from east to west, with higher concentrations and oxidation rate potential in the western region. In our study, we observed generally low methane oxidation rate constants, averaging at 0.006 ± 0.002 d −1 . However, surface waters from Wellington Channel and Croker Bay exhibited relatively higher methane oxidation rates, averaging at 0.01 ± 0.0004 d −1 . These regions were distinguished by a significant proportion of meltwater, including both meteoric water and sea ice meltwater, mixed with water of Pacific origin. We identified microbial taxa of Pacific-origin likely associated with methane oxidation, including Oleispira (γ-proteobacteria) and Aurantivirga (Flavobacteria), in the Pacific and meteoric waters. In contrast, deeper layers (> 200 m depth) showed lower methane concentrations (av. 3.1 ± 1.1 nM) and lower methane oxidation rate constants (av. 0.005 ± 0.001 d −1 ). Within the sea ice, dissolved methane concentrations were found to be higher than the concentrations at equilibrium with atmospheric ...