Large amounts of methane are released from fjords

Normally, ocean fjord waters are stratified into distinct layers, one stacked on top of the next. During storms, these layers can be mixed, which can cause the floor of a fjord to become oxygenated. Storms can also cause a release in methane from fjords. 

Now, research from the University of Gothenburg estimates that the amount of methane emissions from fjords is more than the total emissions from all of the deep ocean waters globally combined. This is interesting because fjords cover only 0.13 percent of earth’s oceans compared to the 84 percent covered by deep oceans.   

“It’s been known for some time that many fjords have anoxic environments closest to the bottom and that methane forms in the bottom sediment. Usually, only a small portion of this gas ever reaches the atmosphere because it gets broken down as it ascends through the more oxygen-rich waters closer to the surface. But in our research, we recorded large emissions of methane when the water in the fjord was mixed during storm events, for example,” said Stefano Bonaglia, a researcher in the Department of Marine Sciences at the University of Gothenburg.

Monitoring methane is increasingly important as global climate change continues to impact us all. Scientists estimate that methane accounts for 30 percent of the greenhouse effect. Although oceans naturally release some methane, human activity has increased eutrophication and created anoxic environments on ocean floors. All of this is especially true in fjords and drives their high methane releases. 

“This is because in fjords, carbon-rich sediment is deposited from marine plants and animals as well as from materials entering the fjords from the surrounding land via streams that flow into them,” explained Bonaglia. 

“As fjords are relatively protected from ocean currents, the water tends to remain stratified in layers at different temperatures and with different concentrations of salt and oxygen. The layers closest to the fjord floor are anoxic regions where methane gas forms as the material in the sediment decomposes,” 

Although the current research was carried out in Sweden, the same effects have been seen in fjords in Canada. The researchers hope that by understanding this effect, greenhouse gases will be budgeted and accounted for more accurately in the future.   

The study is published in the journal Limnology and Oceanography Letters.

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By Zach Fitzner, Earth.com Staff Writer