Home Career Window of opportunity for methane to slip through natural filters – ScienceDaily

Window of opportunity for methane to slip through natural filters – ScienceDaily

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Warmer oceans could lead to the release of large amounts of methane from the seafloor, which could exacerbate climate warming. New research develops a method to understand the role of microorganisms in increasing methane emissions from the seafloor.

Huge reservoirs of the powerful greenhouse gas methane are stored under the sea in solid water ice. This solid is known as methane hydrate. For more than three decades, there have been various concerns that warming seabeds could cause this methane to be released rapidly, possibly even reaching the atmosphere, where it would further warm the climate. Fortunately, this methane hydrate is mostly found under the seabed and under hundreds of meters of seawater. Even if warming melts this methane hydrate and releases the methane, the natural microbial filters present on the seafloor are expected to destroy most of the methane before it reaches open seawater.

However, there are gaps in our knowledge of the relevant processes on the seafloor. Specifically, could seafloor warming be fast enough for methane hydrate to melt so quickly that the released methane would overwhelm and eventually bypass natural microbial filters? “The microbial filter layer in the sediment – we call it the ‘sulphate-methane transition’ where the methane is removed – is quite fragile,” explains Associate Professor Christian Stranne from Stockholm University’s Department of Geological Sciences. “The filter bed takes many years to form and reach maximum methane consumption efficiency. A filter is a living thing consisting of microorganisms that consume methane under anaerobic conditions (without oxygen). The filter also moves up and down the nozzle, depending on the rate at which the methane reaches it.”

In a new study just published in Communications Earth and environmentStranne and his colleagues at Stockholm University and Linnaeus University combined a new model of the biological behavior and vertical movements of this microbial filter with existing models of the physical behavior of seafloor sediments. The physical parts of the model include processes such as the formation of cracks and methane can move up the sediment after the melting of methane hydrates.

Christian Stran explains: “Imagine that the amount of methane rising through the sediment increases suddenly, as might happen if methane hydrate begins to melt faster. It may take decades for the filter to adjust to the new rate of methane consumption. Our new study shows , that during the time that the filter is not regenerated, a significant amount of methane can escape past the filter and into the ocean water.

Despite this “window of opportunity”, methane from hydrate melting that reaches seawater faces further methane degradation processes. These processes make it virtually impossible for a significant amount of methane to enter the atmosphere as a result of the melting of methane hydrate. However, the techniques demonstrated in this study could be applied to other regions where methane released by the seabed is much smaller and more likely to enter the atmosphere, such as the Arctic continental shelves, according to Christian Stranne.

“Methane hydrates are a huge store of carbon, so it remains important to understand how they interact with changes in the ocean and potentially the atmosphere over long and, in the case of our study, fairly short timescales. We now know that there is indeed a possible melting process of methane hydrates to temporarily bypass what was previously thought to be a strong filter in the sludge,” says Christian Stranne.

The rate of warming, however, matters a lot: “Our results show that if our oceans are warming at rates well below 1 °C per 100 years, the filter can keep up with that rate and remain very effective. Unfortunately, we’re seeing higher rates of warming than some of our oceans.”

The study was funded by the Swedish Research Council, VR.

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Materials is provided Stockholm University. Note: Content can be edited for style and length.

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