Massive marine methane emissions from near-shore shallow coastal areas.
Methane is the second most important greenhouse gas contributing to climate warming. The open ocean is a minor source of methane to the atmosphere. We report intense methane emissions from the near-shore southern region of the North Sea characterized by the presence of extensive areas with gassy sediments. The average flux intensities (~130 μmol m(-2) d(-1)) are one order of magnitude higher than values characteristic of continental shelves (~30 μmol m(-2) d(-1)) and three orders of magnitude higher than values characteristic of the open ocean (~0.4 μmol m(-2) d(-1)). The high methane concentrations (up to 1,128 nmol L(-1)) that sustain these fluxes are related to the shallow and well-mixed water column that allows an efficient transfer of methane from the seafloor to surface waters. This differs from deeper and stratified seep areas where there is a large decrease of methane between bottom and surface by microbial oxidation or physical transport. Shallow well-mixed continental shelves represent about 33% of the total continental shelf area, so that marine coastal methane emissions are probably under-estimated. Near-shore and shallow seep areas are hot spots of methane emission, and our data also suggest that emissions could increase in response to warming of surface waters.
Université de Liège, Unité d'Océanographie Chimique, Institut de Physique (B5), B-4000, Belgium.
Alberto V
AV
Borges
Université de Liège, Unité d'Océanographie Chimique, Institut de Physique (B5), B-4000, Belgium.
Willy
W
Champenois
Université Libre de Bruxelles, Laboratoire d'Ecologie des Systèmes Aquatiques, CP221, Boulevard du Triomphe, B-1050, Belgium.
Nathalie
N
Gypens
Université de Liège, Unité d'Océanographie Chimique, Institut de Physique (B5), B-4000, Belgium.
Bruno
B
Delille
Université de Liège, Unité d'Océanographie Chimique, Institut de Physique (B5), B-4000, Belgium.
Jérôme
J
Harlay