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

• Main Authors: Kolomijeca, Anna, Marx, Lukas, Reynolds, Sarah, Cariou, Thierry, Mawji, Edward, Boulart, Cedric
• Other Authors: Center for Marine Environmental Sciences Bremen (MARUM), Universität Bremen, School of Earth and Environmental Sciences Portsmouth, University of Portsmouth, IRD, UAR 191 IMAGO, National Oceanography Centre (NOC), Adaptation et diversité en milieu marin (AD2M), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Station biologique de Roscoff (SBR), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
• Format: Report
• Language: English
• Published: HAL CCSD 2022
• Subjects: [SDE.MCG]Environmental Sciences/Global Changes; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; North Atlantic
• Online Access: https://hal.archives-ouvertes.fr/hal-03853018; https://doi.org/10.5194/egusphere-2022-360

Abstract. Methane (CH4) is the second most produced greenhouse gas after carbon dioxide, however the role of the open ocean in its natural cycle remains 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. The subtropical North Atlantic Ocean between 26° N 80’W and 26° N 18’W was investigated for the distribution of dissolved CH4 concentrations and associated air-sea fluxes during winter 2020. 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 between 3–7 nmol/l, with the highest values of 7–10 nmol/l found to the east of the transect, consistent with other subtropical regions of the world’s oceans. The high anomalies of dissolved CH4 appeared to be associated to phosphorus depleted waters and to a peak of regions of elevated phytoplankton abundance. Further investigations indicated a correlation between CH4 anomalies, phosphate depletion and the abundance of two ubiquitous pico-cyanobacteria, Synechococcus and Prochlorococcus, although other phytoplanktonic phyla cannot be excluded. The calculation of air-sea fluxes confirms the subtropical North Atlantic Ocean as a source of CH4, mainly produced by phytoplanktonic activity in surface waters.