Le site de vulgarisation scientifique de l’Université de Liège. ULg, Université de Liège

The North Sea: high levels of methane emissions
6/14/16

When it approaches the Belgian and English coasts, this peat accumulates at depths of between 10 and 30 metres which is quite close to the surface.  The tidal currents are strong there and mix the different water column. In other words, the surface waters are heated but the water column is not stratified. This heat is redistributed from the surface down to the sea bed. Instead of leading to the creation of a cold layer and a warm layer, lukewarm water therefore extends from the surface to the seabed. The methane released from the sediment easily reaches the surface and can be released into the atmosphere. This phenomenon is likely to accelerate with climate change. Not only do the warmer waters activate the bacterial production of methane, but they also enable it to be released more easily. 

This is one of the first times that a study has shown the behaviour of methane in permanently-mixed bodies of water that are rich in organic matter such as the waters of the Belgian coast. This study therefore marks the beginning of a new avenue of research into the methane cycle and includes the coastal environments and the shallower areas in general. “We knew that the coasts played an important role in the marine methane cycle, but this remains difficult to quantify. One coast is not the same as another, these are particularly heterogeneous environments. However, we estimate that today the coastal areas alone constitute a source of methane that is 5 to 10 times higher than all the deep oceans”. This is an advance that will make it possible to fine-tune knowledge about the contributions of the different sources of methane which remain imprecise today due to the fact that the methane cycle is so complicated to quantify.

CH4  concentration North Sea 

A global ecological problem…

The emission of methane, in terms of mass, is much less significant than that of carbon dioxide (CO2). But in terms of global warming, the molecules of CH4 are twenty-five to thirty times more efficient than CO2. This rather competitive factor means that methane as a greenhouse gas, is second only to CO2. It is responsible for one third of global warming linked to human activity. In addition, methane is a gas which has many sources and sinks to the extent that its cycle easily defies attempts to quantify it. It is therefore difficult to establish a clear estimate of the sources of emission of this gas and to act accordingly. One piece of data is very solid however: the total accumulation of methane in the atmosphere. “This is quite easy to calculate, says Alberto Borges. “We know the volume of the atmosphere. By measuring the concentration of methane in the atmosphere over time, we can determine its accumulation”. 

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