Fjords emit as much methane as all the deep oceans globally – Is it up because of that?

news7g05/31/2022

8 3 minutes read

Fjords emit as much methane as all the deep oceans globally - Is it up because of that?

GOTHENBURG UNIVERSITY

Waves pounding — IMAGE: IN MULTI-LOVING ENVIRONMENTS, ENVIRONMENTAL SAFETY AT ENGINEERING IN THE PRODUCTION OF METHANE. IN STORAGE, WATER FROM THE BASE IS COMPLETED TO THE SURFACE, GIVING HUGE Methane into the Atmosphere. see more CREDIT: R LINDBLOM

During major storms, layers of water that are normally stratified in oceanic fjords are mixed, leading to fjord oxidation. But these storm events also lead to a spike in methane emissions from the fjords into the atmosphere.

Researchers from the University of Gothenburg have estimated that the total emissions of this climate-warming gas from the fjords are as large as from all of the world’s deep ocean regions combined.

The world’s fjords are created when inland ice recedes and are a relatively rare natural feature, accounting for only 0.13% of all oceans on Earth. However, according to researchers from the University of Gothenburg, methane emissions from the surface of the fjords are comparable to those from the global deep oceans, which cover 84% of the surface area. global sea. These results have been presented in a peer-reviewed journal article Limit letters and oceanography.

“It has been known for a long time that many fjords have anoxic environments closest to the bottom, and that methane forms in bottom sediments. Normally, only a small part of this gas reaches the atmosphere because it decomposes as it passes through more oxygen-rich water closer to the surface. But in our study, we have documented large emissions of methane when the water in the fjord is mixed during storms,” said Stefano Bonaglia, a researcher in marine geochemistry in the Department of Marine Science. at the University of Gothenburg, said.

An anoxic environment produces methane gas

Detecting and budgeting for atmospheric methane emissions is essential for future climate modeling. The researchers estimate that methane emissions cause about 30% of the greenhouse effect. The contribution of the oceans to methane emissions as measured by the budget is significantly smaller than that of land areas. But human activity has increased eutrophication in coastal areas, and this has created larger areas of anoxic water on the seafloor. This is especially evident in fjords, and although they cover only 0.13% of the global sea surface, they account for about half of all methane emissions into the atmosphere.

“This is because in the fjords, carbon-rich sediments are deposited from marine flora and fauna as well as from materials that enter the fjords from the surrounding land through flows into them. Because fjords are relatively protected from ocean currents, water tends to remain stratified at different temperatures and with different concentrations of salt and oxygen. Stefano Bonaglia says the layers closest to the fjord are anoxic regions, where methane forms when material in the sediments decomposes.

Agriculture promotes eutrophication

Researchers from the University of Gothenburg studied By Fjord near Uddevalla between 2009–2021 and conducted field studies to measure methane production in the fjord. Because the Fjord is starved of oxygen and affected by eutrophication. The Bäve River flows into the fjord, bringing with it a high concentration of nutrients from the region’s agriculture. It is clear that during the mixing events in the fjord, the amount of methane released into the atmosphere increased. During these events, anoxic water from the bottom is rapidly lifted to the surface, carrying methane gas, which can then be released into the atmosphere.

1 million tons of methane

“Methane emissions are very high, and American researchers have witnessed similar events in fjords in Canada. We estimate that emissions from all the world’s fjords are of the same magnitude – about 1 Teragram (Tg) or 1 million tonnes per year – as budgeted emissions from the global deep oceans. . This is because the fjord’s bottom-to-surface distance is much shorter than in the deep oceans. This leads to a lot of organic matter being deposited in the sediment and not enough time for the methane to break down on its way to the surface,” says Stefano Bonaglia, adding that if climate change leads to more extreme weather events, then methane. emissions can increase, but only up to a certain point.

“If we see a sharp increase in the number of major hurricanes, then methane emissions will decrease, because the anoxic environment at the bottom of the fjords will disappear if the water is mixed regularly. .”

Article: High amounts of methane from an anoxic fjord driven by mixing and oxidation

Contact Details: Stefan Bonaglia, Senior Associate Lecturer in Marine Chemistry in the Department of Marine Science at the University of Gothenburg. Phone: +46 (0) 737-41 24 97, E-mail [email protected]