Munich, Bavaria (ots) – For hundreds of millions of years, the average temperature on the Earth’s surface has varied by not much more than 20° Celsius, making life possible on our planet. To explain this stable temperature situation, there must be some kind of “thermostat” that regulates the amount of carbon dioxide in the atmosphere, which is crucial for global temperature, over geological time periods. The erosion and weathering of rocks play an important role in this earth thermostat. A team led by geologist Aaron Bufe from the Ludwig Maximilian University of Munich (LMU) and Niels Hovius from the German Research Center for Geosciences (GFZ) has now modeled the influence of these processes on the carbon balance of the atmosphere. The surprising result: CO2 absorption through weathering reactions is highest in low mountain ranges with moderate erosion rates; not in high mountains where rocks erode particularly quickly.
A team led by LMU geologist Aaron Bufe has investigated how erosion and weathering influence the CO2 balance over millions of years.
Model calculations show: There is an erosion rate at which CO2 storage through weathering is maximum.
In low mountain ranges with moderate elevation, erosion is often close to this rate. Weathering in mountains with greater uplift stores less CO2 or even releases it.
As soon as rock is exposed through erosion and exposed to wind and weather, weathering begins. “When silicates weather, carbon is removed from the atmosphere and is later precipitated as lime. Other compounds, however, such as carbonates and sulfides or organic carbon contained in the stone, release CO2 during weathering. These reactions occur much faster than silicate weathering,” explains Hovius. “So there are some complications when it comes to the question of what the effect of erosion and mountain building is on the carbon balance.”
Weathering model shows common mechanisms
To gain a clearer picture, the researchers used mathematical weathering models to analyze data on the extent of sulfide, carbonate and silicate weathering in different study areas – such as Taiwan and New Zealand – and determined how the weathering of the respective rock responds to changes in the erosion rate. “We found similarities for all locations that point to common mechanisms,” says Bufe.
Further model calculations showed that the connection between erosion and CO2 balance is not linear, but that CO2 storage reaches an optimum at an erosion rate of approximately 0.1 millimeters per year. At both lower and higher rates, less CO2 is stored or even more CO2 is released due to weathering. “High erosion rates like those in Taiwan or the Himalayas are driving the system toward a CO2 source because as erosion rates increase, silicate weathering eventually stops increasing, while carbonate and sulfide weathering increases even further,” explains Bufe.
In landscapes with moderate erosion rates of around 0.1 millimeters per year, however, the rapidly weathering carbonates and sulfides have already been largely consumed, while silicate weathering can take place on a large scale. In landscapes with little topography and uplift, where even less material is removed, there is ultimately little left to weather. The largest CO2 sinks are therefore low mountain ranges such as the Black Forest or the Bavarian Forest, whose erosion rates are close to the optimum. “The temperature to which the ‘Earth thermostat’ is set depends primarily on the global distribution of erosion rates over geological time,” says Bufe. In order to further understand the effects of erosion on the Earth’s climate system, he believes that organic carbon sinks and weathering in floodplains would need to be taken into account in future studies.
Contact
Prof. Dr. A.S. Aaron Bufe
Department of Earth and Environmental Sciences
Ludwig Maximilian University of Munich (LMU)
Phone: +49 (0) 89 2180 6714
E-Mail: a.bufe@lmu.de
Website:
publication
Aaron Bufe, Jeremy K.C. Rugenstein, and Niels Hovius: CO2 drawdown from weathering maximized at moderate erosion rates. Science 2024. DOI 10.1126/science.adk0957
Questions & Contact:
Claudia Russo Head of Communications & Press Ludwig-Maximilians-University Munich Leopoldstr. 3 80802 München
