Global ocean methane emissions dominated by shallow coastal waters.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 31594924.
- Also identified by DOI 10.1038/s41467-019-12541-7 and PMC identifier 6783430.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Oceanic emissions represent a highly uncertain term in the natural atmospheric methane (CH<sub>4</sub>) budget, due to the sparse sampling of dissolved CH<sub>4</sub> in the marine environment. Here we overcome this limitation by training machine-learning models to map the surface distribution of methane disequilibrium (∆CH<sub>4</sub>). Our approach yields a global diffusive CH<sub>4</sub> flux of 2-6TgCH<sub>4</sub>yr<sup>-1</sup> from the ocean to the atmosphere, after propagating uncertainties in ∆CH<sub>4</sub> and gas transfer velocity. Combined with constraints on bubble-driven ebullitive fluxes, we place total oceanic CH<sub>4</sub> emissions between 6-12TgCH<sub>4</sub>yr<sup>-1</sup>, narrowing the range adopted by recent atmospheric budgets (5-25TgCH<sub>4</sub>yr<sup>-1</sup>) by a factor of three. The global flux is dominated by shallow near-shore environments, where CH<sub>4</sub> released from the seafloor can escape to the atmosphere before oxidation. In the open ocean, our models reveal a significant relationship between ∆CH<sub>4</sub> and primary production that is consistent with hypothesized pathways of in situ methane production during organic matter cycling.