06.9.2020

Mountains, erosion and the carbon cycle

Abstract

Mountain building results in high erosion rates and the interaction of rocks with the atmosphere, water and life. Carbon transfers that result from increased erosion could control the evolution of Earth’s long-term climate. For decades, attention has focused on the hypothesized role of mountain building in drawing down atmospheric carbon dioxide (CO2) via silicate weathering. However, it is now recognized that mountain building and erosion affect the carbon cycle in other important ways. For example, erosion mobilizes organic carbon (OC) from terrestrial vegetation, transferring it to rivers and sediments, and thereby acting to draw down atmospheric CO2 in tandem with silicate weathering. Meanwhile, exhumation of sedimentary rocks can release CO2 through the oxidation of rock OC and sulfide minerals. In this Review, we examine the mechanisms of carbon exchange between rocks and the atmosphere, and discuss the balance of CO2 sources and sinks. It is demonstrated that OC burial and oxidative weathering, not widely considered in most models, control the net CO2 budget associated with erosion. Lithology strongly influences the impact of mountain building on the global carbon cycle, with an orogeny dominated by sedimentary rocks, and thus abundant rock OC and sulfides, tending towards being a CO2 source.

Key points

  • Erosion resulting from mountain building increases transfer of carbon between the atmosphere and storage in rocks.
  • The traditional view has focused on carbon dioxide (CO2) drawdown by silicate weathering, and its links to climate and erosion.
  • An emerging view also considers CO2 drawdown by organic-carbon burial and CO2 emissions from oxidative weathering of both rock organic carbon and sulfide minerals.
  • CO2 sources and sinks increase with erosion, and the net balance has now been quantified in a handful of locations.
  • Climate (temperature, hydrology) regulates inorganic and organic CO2 sinks, with complex interdependency on erosion.
  • Lithology is important: a mountain range composed of sedimentary rocks may be a weak CO2 sink (or CO2 source), but volcanic rocks favour CO2 drawdown.
The full (paywalled) article appeared on the Nature Reviews Earth and Environment website at https://www.nature.com/articles/s43017-020-0058-6
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