Gas hydrate melt enhances ocean acidification

Climate-related methane release is slower, but has worse consequences for marine ecology than thought

Gas hydrates © USGS
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Marine researchers have good and bad news for our future: The Good: Over the next hundred years, there is no reason to fear increased methane emissions from the gas hydrate stored in the seabed. The bad news: The emerging climate gas increases ocean acidification more than previously thought. In particular, the corals and crustaceans living in low-lying, near-surface layers of water would be affected, according to the scientists in the journal Geophysical Research Letters.

Scientists have warned for some years that methane hydrates, which are stored as ice in the seabed, could "thaw" as a result of global warming. As a result, the strong greenhouse gas methane would be increasingly released into the atmosphere and driving climate change further. Now researchers from the Leibniz Institute for Marine Sciences (IFM-GEOMAR) in Kiel have for the first time quantified the effect of ocean currents on the warming of the Arctic seabed and calculated their effects. In their study, the Kiel experts have for the first time combined past and future modeling with calculations for the gas hydrate stability zone (GHSZ), in which solid gas hydrates are produced under high pressure and low temperatures from methane gas.

No increased methane emissions in the next hundred years

With their results they give - to a certain extent - the all-clear: "Our calculations with different computer models clearly show that the climate in the next hundred years, no additional danger from increased methane leakage threatens, " summarizes Arne Biastoch, the lead author of the study. "The gas hydrates dissolve with a time delay, so that more likely in two to three hundred years to expect consequences - a period on which today can say little definitive. We should take these long-term effects into account when discussing climate change. But we should not dramatize the situation. "

Map of ocean temperatures on the seabed today and in 100 years. Biastoch et al., IFM-GEOMAR

Alarm in terms of acidification

However, researchers are alarming with regard to "the other CO2 problem": ocean acidification. So far, it has mainly been considered that seawater absorbs carbon dioxide (CO2) from the atmosphere. Chemical reactions cause the pH of the water to drop. Especially the cold water in the northern latitudes, which absorbs a lot of CO2, quickly becomes corrosive. The result: corals, shells, snails or plankton, can not their calcareous shells

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Residents of low-lying strata particularly affected

Even a small methane hydrate melt accelerates this phenomenon: "We assume that after one hundred years, about twelve percent of the methane stored in the seabed will be released, " according to marine researcher Lars R pke. "We also assume that around half of them are still being picked up by highly specialized microorganisms and deposited as solid matter, " adds Tina Treude. However, the remainder of the gas could rise directly into the atmosphere or, after microbial decomposition to CO2 in seawater, reduce the pH. As a result, the pH value of the Arctic Ocean could drop twice as fast as previously thought in the lower water layers.

It is precisely these layers that biologists and marine chemists have so far been least affected by ocean acidification. Older studies had only the CO2 in view, from the atmosphere

comes and is taken over the sea surface. As a result, it was believed that the upper layers in particular were acidic, says Treude. For the Arctic, we have now proved that the areas near the ground are also at risk.

The ocean currents in the Atlantic are particularly responsible for the rise in temperature on the Arctic seabed. Although the calculations of the Kiel scientists are great

Seasonal and decadal fluctuations have revealed an average warming of 2.5 degrees Celsius per century for the future. The temperatures in the shallower water on the continental shelves are rather above and the continental slopes at the transition to the deep sea are rather below this value.

(Joint Press Release of the Leibniz Institute for Marine Science (IFM-GEOMAR) and the Cluster of Excellence "Ocean of the Future", 28.04.2011 - NPO)