An update on dissolved methane distribution in the subtropical North Atlantic Ocean

• Published in: Ocean Science
• Main Authors: Kolomijeca, Anna, Marx, Lukas, Reynolds, Sarah, Cariou, Thierry, Mawji, Edward, Boulart, Cédric
• Other Authors: Center for Marine Environmental Sciences Bremen (MARUM), Universität Bremen, Adaptation et diversité en milieu marin (ADMM), Institut national des sciences de l'Univers (INSU - CNRS)-Station biologique de Roscoff = Roscoff Marine Station (SBR), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), School of Earth and Environmental Sciences Portsmouth, University of Portsmouth, Instrumentation, Moyens analytiques, Observatoires en Géophysique et Océanographie (IMAGO), National Oceanography Centre (NOC), Ship time was funded by NERC as part of the Climate Linked Atlantic Sector Science (CLASS) research program and as a UK contribution to the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP). A. Kolomijeca’s participation in the cruise and dissolved gas analyses was funded by the Region Bretagne SAD “FULMAR” project, the Foundation Air Liquide SMIS-4M project and the CNRS (LEFE Memestra). The participation of Lukas Marx and Sarah Reynolds was funded by the University of Portsmouth PhD bursary scheme and the UK NERC National Capability program CLASS (Climate Linked Atlantic Sector Science) ECR fellowship.
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2022
• Subjects: [SDE.BE]Environmental Sciences/Biodiversity and Ecology; [SDE.MCG]Environmental Sciences/Global Changes; North Atlantic
• Online Access: https://hal.science/hal-03841334; https://hal.science/hal-03841334v2/document; https://hal.science/hal-03841334v2/file/Kolomijeca%20et%20al%202022%20os-18.pdf; https://doi.org/10.5194/os-18-1377-2022

International audience Methane (CH4) is a potent greenhouse gas and plays a significant role in recent increasing global temperatures. The oceans are a natural source of methane contributing to atmospheric methane concentrations, yet our understanding of the oceanic methane cycle is poorly constrained. Accumulating evidence indicates that a significant part of oceanic CH4 is produced in oxygenated surface waters as a by-product of phytoplanktonic activity. This study focused on the subtropical North Atlantic Ocean (26∘ N, 80′ W and 26∘ N, 18′ W) where the distribution of dissolved CH4 concentrations and associated air–sea fluxes during winter 2020 were investigated. Water samples from 64 stations were collected from the upper water column up to depths of 400 m. The upper oxic mixed layer was oversaturated in dissolved CH4 with concentrations ranging 3–7 nmol L−1, with the highest concentrations of 7–10 nmol L−1 found to the east of the transect, consistent with other subtropical regions of the world's oceans. The high anomalies of dissolved CH4 were found to be associated with phosphate-depleted waters and regions where the abundance of the ubiquitous picocyanobacteria Synechococcus and Prochlorococcus were elevated. Although other phytoplanktonic phyla cannot be excluded, this suggests that cyanobacteria contribute to the release of CH4 in this region. The calculation of air–sea fluxes further confirmed the subtropical North Atlantic Ocean as a source of CH4. This study provides evidence to corroborate the key role that picocyanobacteria play in helping to explain the oversaturation of CH4 found in surface mixed layer of the open ocean, otherwise known as the “ocean methane paradox”.