Mountain growth affects the greenhouse effect

Active leakage of foundation rocks with yellow-brown weather fluids; Lushan – Taiwan. Credit: Kristen Cook (GFZ)

Taiwan is an island of extremes: strong earthquakes and typhoons repeatedly hit the region and change the landscape, sometimes catastrophically. That makes Taiwan a fantastic laboratory for geosciences. For example, erosion processes occur a thousand times faster in the center of the island than in its extreme south. This difference in erosion rates affects the chemical-weather effects of rocks and provides insight into the carbon cycle of our planet on a scale of millions of years.

A team of researchers led by Aaron Bufe and Niels Hovius of the German Research Center for Geosciences (GFZ) have now taken advantage of different erosion rates and investigated how rock uplift and erosion determine the balance of carbon emissions and inputs. Surprising result: at high erosion rates, time processes release carbon dioxide; at low erosion rates they separate carbon from the atmosphere. The study will be published in Nature Geoscience.

Behind all this are tectonic and chemical processes. Especially in fast-growing mountains, tectonic uplift and erosion constantly bring fresh rock material from underground. There it is exposed to circular acidic water that dissolves or changes rocks. Depending on the type of rock, these weather effects have very different effects on the Earth’s climate. For example, if carbonic acid from the soil comes in contact with silicate minerals, limestone (calcium carbonate or CaCO3) precipitates in which carbon binds for a very long time.

In the case of a combination of sulfur minerals, such as pyrite and limestone, the exact opposite happens. The sulfuric acid formed when pyrite comes in contact with water and oxygen dissolves carbonate minerals, thus forming CO2. It is believed that this relationship between the construction of mountains and the chemical weather influence affects the climate of our planet on a scale of millions of years. But how exactly does the growth of the Alps or the Himalayas affect the climate? Is silicate weather accelerating, causing the climate to cool? Or the dissolution of limestone with sulfuric acid dominates, which leads to the concentration of atmospheric CO2 up, with accompanying global warming?

This question can be answered in southern Taiwan. Taiwan is located in the subduction zone, where the oceanic plate slides below the Asian continent. This subduction causes rapid mountain growth. Although the center of the island stands several million years high, the southern peak has just emerged from the sea. There, the mountains are poorly relief and erode relatively slowly. Further north, where the mountains are steep and high, fresh rocks are quickly brought to the Earth’s surface to be affected by the weather. Usefully, the rocks in southern Taiwan are typical of many young mountain ranges around the world, containing mostly silicate minerals with some carbonate and pyrite.

Mountain growth affects the greenhouse effect

Metamorphosed fine sediment (shale) with pyrite grain (gold) and carbonate precipitation (white). Credit: Albert Galy, University of Lorraine

In their study, the researchers sampled rivers that collect water from these mountains at different erosion rates. From the material dissolved in the rivers, the researchers estimated the share of sulfide, carbonate and silicate minerals in the weathering. These results allowed them to estimate the amount of CO2 which is sequestered and the amount of CO2 freed from reactions to weather conditions. First author Aaron Bufe reports: “We have discovered that in the southernmost part of Taiwan atmospheric CO2 sequestration dominates. However, further north, where the mountains erode faster, carbonate and sulphide weather conditions and CO2 was released. “

So, do weather conditions on mountain ranges increase CO2 in the atmosphere? Aaron Bufe says, “we can make relatively good statements about Taiwan. The chemical weather in this most active mountain zone seems to be net CO2 into the atmosphere due to chemical weathering. But perhaps the story changes when sediments washed from the mountains are trapped in vast alluvial plains; as in the foothills of the Himalayas or the Alps.

These sediments are often rich in silicates, the weathering of which will separate CO2. In addition, the construction of mountains brings to the Earth’s surface not only sedimentary rocks with pyrite and carbonate, but also types of rocks formed from hardened magma and containing many fresh silicates that spend time quickly. Researchers must climb some mountains before we fully understand the net effect of weather conditions on the Earth’s climate. ”


A first look at the weather on an Angstrom scale


More information:
Aaron Bufe et al., Co-variation of silicate, carbonate and sulphide weathering stimulates CO2 release with erosion, Nature Geoscience (2021). DOI: 10.1038 / s41561-021-00714-3

Provided by Helmholtz Association of German Research Centers

Citation: Mountain Growth Affects Greenhouse Effect (2021, April 8) retrieved April 8, 2021 from https://phys.org/news/2021-04-mountain-growth-greenhouse-effect.html

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