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
• Format: Text
• Language: English
• Published: 2022
• Subjects: North Atlantic
• Online Access: https://doi.org/10.5194/egusphere-2022-360; https://egusphere.copernicus.org/preprints/2022/egusphere-2022-360/

Methane (CH 4 ) 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 CH 4 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 CH 4 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 CH 4 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 CH 4 appeared to be associated to phosphorus depleted waters and to a peak of regions of elevated phytoplankton abundance. Further investigations indicated a correlation between CH 4 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 CH 4 , mainly produced by phytoplanktonic activity in surface waters.