The Role of Erosion in Cooling the Earth

Between one and two billion tons of sediment are eroded yearly from the Himalaya mountains and transported to the Indian Ocean by the Ganges and Brahmaputra, rivers which spill out into the Bengal fan. The debris contains significant amounts of organic substances which, if allowed to decompose, would contribute to CO₂ emissions.
An international team of scientists, including Christian France-Lanord from CRPG,¹ has completed the first detailed and conclusive study² on this erosion system, the largest in the world.



France-Lanord and his student Valier Galy quantified the amount of atmospheric CO₂ that is effectively buried in the process, examining all stages of Himalayan erosion: the original make-up of the eroded surface, the composition of debris transported by the watercourses, and the nature of sediment that finally reaches the ocean.
They found that the process represents between 10 and 20 percent of all terrestrial organic carbon matter buried at sea worldwide. Crucially, the unusually high sedimentation rates in the Bay of Bengal significantly starve the organic carbon of oxygen, arresting decomposition. This efficient CO₂ sink contrasts with that of the Amazon delta, where exposed erosion sediment is re-oxidized before ocean burial.
For billions of years, water-borne continental erosion has played a major role in the Earth’s capacity to counter volcanic CO₂ emissions by regularly sweeping away vast amounts of organic and inorganic carbon substances for burial under the sea. The process contributes to regulating the greenhouse gases which largely govern world climate. While the recent sharp increase in man-made CO₂ emissions has provoked the current trend of global warming, continental erosion on a geological timescale is crucial to explaining past climate changes and in establishing long-term models of future climate evolution.
“The variations in intensity of continental erosion may be the cause of major geological fluctuations in world climate,” comments France-Lanord. “The creation of the Himalaya-Tibet mountain range, and the increase of the continental erosion flux which resulted over the past 30 million years, could be at the origins of the glacial period that the Earth has known since the Miocene epoch.”
Graham Tearse