Preprints
https://doi.org/10.5194/egusphere-2022-360
https://doi.org/10.5194/egusphere-2022-360
 
23 May 2022
23 May 2022
Status: this preprint is open for discussion.

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

Anna Kolomijeca1,2, Lukas Marx3, Sarah Reynolds3, Thierry Cariou1,4, Edward Mawji5, and Cedric Boulart1 Anna Kolomijeca et al.
  • 1UMR 7144 CNRS Sorbonne Université, Station Biologique de Roscoff, 29680 Roscoff, France
  • 2MARUM, Center for Marine Environmental Sciences, D-28359 Bremen, Germany
  • 3School of the Environment, Geography and Geosciences, University of Portsmouth, PO1 2UP Portsmouth, UK
  • 4IRD, UAR191, Instrumentation, Moyens Analytiques, Observatoires en Géophysique et Océanographie (IMAGO), Technopôle de Brest-Iroise, 29280 Plouzané, France
  • 5National Oceanography Centre, European Way, Southampton, SO14 3ZH, UK

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.

Anna Kolomijeca et al.

Status: open (until 21 Jul 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-360', Leonard Ernst, 19 Jun 2022 reply

Anna Kolomijeca et al.

Anna Kolomijeca et al.

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Short summary
More and more studies indicate that the Open Ocean can be a significant source of methane, the second greenhouse gas after CO2. Our study in the North subtropical Atlantic Ocean shows that a significant part of the methane flux to the atmosphere is related to cyanobacteria, a ubiquitous phytoplankton, that produce methane as part of their metabolic activity. This study is a response to the lack of data on the role of the oceans on the methane budget in the context of the climate change.