Methane emissions from the North Sea tend to decrease

Last June, a team of researchers found a large concentration of methane in the surface waters of the North Sea. A recent study lead by Alberto Borges, a researcher at the University of Liège, shows that if methane emissions at the coast are higher, they have tended to decline since 1990.

Methane (CH₄) is a powerful greenhouse gas. It is also classified in second place, behind carbon dioxide (CO₂), although its lifetime in the atmosphere is shorter (about ten times shorter over a period of 10 years than CO₂) . A better understanding and reduction of methane emissions in the atmosphere could be a promising key to effectively slow global warming. But this implies that we must indentify their sources and wells that are numerous. While oceans are considered to be modest sources of methane, their coastal areas record very high emissions. This was demonstrated by a study published in 2016 (1) in which Alberto Borges and his colleagues highlighted the high concentrations of methane found on our belgian coasts. In coastal areas methane emissions are linked to two conditions:

1. A significant transfer of methane from marine sediments to the water column.
Production will be more important as the production of methane by microalgae (phytoplankton) will itself be important.
2. A small depth

The Belgian coastal zone combines these two conditions: it is very productive and shallow (less than 30 cm deep).  A new study, still carried out by Alberto Borges - in collaboration with the Université Libre de Bruxelles (ULB) (2) - has demonstrated that methane emissions in the Belgian coastal zone tend to be 300 to 1300 times higher than in the deep part od the oceans! However, this study also shows that methane emissions from the Belgian coastal zone have decreased from 1990 to the present day. This is linked to a reduction in eutrophication (pollution from agricultural and wastewater nutrients) since the 1990s, in response to the improvement of water quality in the Scheldt estuary. Encouraging results!

Scientific references

(1)    The North Sea : high levels of methane emissionshttp://reflexions.ulg.ac.be/en/methanenorthsea

(2)    Borges AV, Speeckaert G., Champenois W., Scranton M.I. & Gypens N. (2017) Productivity and temperature as drivers of seasonal and spatial variations of dissolved methane in the Southern Bight of the North Sea, Ecosystems, DOI: 10.1007/s10021-017-0171-7 https://link.springer.com/article/10.1007/s10021-017-0171-7

Illustrations

Bathymetry of the Belgian coastal zone and the nine stations sampled in 2016 (circles), station WS1 that was sampled from 2009 to 2013 (diamond), the platform where wind speeds were measured at sea (Westhinder, WH, square) and the two National Centers for Environmental Prediction (NCEP) grid points (crosses in the inset map). Acoustic turbidity coverage is derived from Le Bot and others (2005).