Weathering of rocks can lead to association or release of carbon dioxide – in active mountain ranges, the release of carbon dioxide is strongly dominated
Taiwan is an extreme island: Earthquakes and severe typhoons hit the region frequently and change the landscape, sometimes being catastrophic. This makes Taiwan a great laboratory for geosciences. Erosion, for example, occurs a thousand times faster in the center of the island than in its southernmost tip. This difference in erosion rates affects chemical weathering of rocks and gives insight into our planet’s carbon cycle over a scale of millions of years. Now a group of researchers led by Aaron Bove and Niels Hofius of the German Research Center for Geosciences (GFZ) has now taken advantage of the different rates of erosion and studied how the uplift and erosion of rocks determine the balance of carbon emissions and uptake. The surprising result: at high erosion rates, the weathering processes release carbon dioxide; At low rates of erosion, they trap carbon from the atmosphere. The study will be published in Natural Earth Sciences.
Behind all of this are tectonic and chemical processes. Particularly in fast-growing mountains, tectonic uplift and erosion are constantly causing new rock material to emerge from underground. There it is exposed to acidified water circulating that dissolves or changes the rocks. Depending on the type of rocks, this weathering has very different effects on Earth’s climate. For example, if carbonic acid from the soil comes into contact with silicate minerals, limestone (calcium carbonate or calcium carbonate) precipitates, in which carbon binds for a very long time. In the case of a mixture of sulfur minerals, such as pyrite and limestone, the opposite occurs. The sulfuric acid that forms when pyrite comes into contact with water and oxygen dissolves the carbonate minerals, thus producing carbon dioxide. This relationship between mountain building and chemical weathering is thought to affect our planet’s climate on a scale of millions of years. But how exactly does alpine or Himalayan growth affect the climate? Is the process of silicate weathering accelerating causing a cooler climate or is the degradation of limestone by sulfuric acid dominant, leading to an increase in the concentration of carbon dioxide in the atmosphere, with the attendant global warming?
This question can be answered in southern Taiwan. Taiwan is in a subduction zone, as the ocean plate slides under the Asian continent. This subduction causes rapid mountain growth. While the center of the island has been tall for several million years, the southern tip has just come out of the sea. There, the mountains are low-lying and erode relatively slowly. In the far north, where mountains are steep and long, new rocks are quickly brought to Earth’s surface for the weather. It is advantageous that the rocks of southern Taiwan are typical of many young mountain ranges around the world, and contain mostly silicate minerals with some carbonate and pyrite.
In their study, the researchers sampled rivers that collect water from these mountains with different erosion rates. From material dissolved in rivers, researchers estimated the proportion of minerals sulfide, carbonates, and silicates in weathering. These results allowed them to estimate both the amount of carbon dioxide that is isolated and the amount of carbon dioxide emitted from weathering reactions. First author Aaron Boff reports, “We found that in the southern part of Taiwan, carbon dioxide sequestration predominates in the atmosphere. However, in the far north, as mountains erode faster, rates of carbonate and sulfide weathering are dominated and carbon dioxide is released.”
So, will the weathering of mountain ranges lead to an increase in carbon dioxide in the atmosphere? “We can make relatively good statements about Taiwan,” says Aaron Bove. Chemical weathering in these more active mountain belts appears to be a net source of carbon dioxide emissions into the atmosphere due to chemical weathering. But the story may change when sediments eroded from mountains are trapped in the plains. Vast alluvial placer; as is the case at the foot of the Himalayas or the Alps. These deposits are often rich in silicates, which the weathering process isolates carbon dioxide. In addition, mountain building not only brings sedimentary rocks with pyrite and carbonate to the surface of the earth. “, But also the types of rocks that are formed from solid magma and contain many fresh silicates that are affected quickly. Researchers have some mountains to climb before we fully know the net effect of weather factors on Earth’s climate.”
Original study: Co-variation in the weathering of silicates, carbonates, and sulfides leads to the release of carbon dioxide with corrosion
DOI: 10.1038 / s41561-021-00714-3
Active bedrock seepage with yellow-brown weathering fluids; Lushan – Taiwan. (Photo: Kristin Cook, GFZ)
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Metamorphic micro-sediment (schist) with pyrite (gold) grains and carbonate precipitate (white). (Photo: Albert Galle, University of Lorraine)
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Dr.. Aaron Bove
Scientist in the Department of Geomorphology
Phone: +49 331 288 27544[email protected]