Can an improving monsoon in East Asia induce a global cooling? – Eurasia Review


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The study of the orogenic effects of the uprising of the Tibetan plateau on the global climate during the Cenozoic has focused almost exclusively on the India-Asia collision zone, the Himalayas. Heavy erosion in the Himalayas was believed to be the main driver of atmospheric CO in the Cenozoic2 decline and global cooling primarily by accelerated chemical weathering of silicates in the India-Asia collision zone or by efficient burying of organic carbon in the neighboring Bengal fan in South Asia.

However, the size of the India-Asia collision and the associated closure of the Tethys Ocean had a significant effect on the reorganization of climate models beyond the collision zone. In an article co-authored with Yibo Yang and Albert Galy at the Institute of Tibetan Plateau Research, Chinese Academy of Sciences and Petrographic and Geochemical Research Center, CNRS-University of Lorraine, and ten other colleagues, these researchers stated: “ the Oligocene-Miocene limit The Asian climatic reorganization linked to the northward migration of the East Asian monsoon towards subtropical China is a potentially important atmospheric CO but poorly constrained2consumption process.

These twelve researchers made a first-order estimate of the difference in CO2 consumption induced by the alteration of silicates and the burying of organic carbon in subtropical China linked to the advance of the monsoon around the end of the Oligocene. They found in the study, which was published in Science China Earth Sciences, that the northward advance of the East Asian monsoon over tectonically inactive subtropical China induced a globally significant alteration of the atmospheric CO silicate.2 sink. That is, a long-term increase in CO2consumption by weathering of silicates varies from 0.06 to 0.87 × 1012 mol year-1 according to reconstructions of erosion fluxes, with a contribution of about 50% of Mg-silicate alteration since the end of the Oligocene. The landfill flow of organic carbon is approximately 25% of contemporary CO2 consumption by alteration of silicates.

The first order calculation of CO2 consumption has highlighted the very important role of weathering of the Mg-rich craton of the Yangtze and surrounding terranes, as the unusual nature of the eroded Mg-rich crust not only enhances the tectonic forcing of the climate, but may also contribute to the increase in the Mg content of the Neogene ocean.

The study provided a new perspective on the Cenozoic carbon cycle linked to the magnesium-rich nature of the crust affected by such uplift-induced climate change and illustrated how disruptions to global climate and atmospheric CO can be complex.2 levels by orogenic uplift, and how important is the nature of the crust not only involved in the collision but also around the collision. In recent decades, the role of crustal and / or lithosphere heterogeneity has long been demonstrated in other geoscience disciplines, and the distinction between mantle rocks and upper crustal rocks was already well integrated. in the long term climate. scientific community.

“But to our knowledge”, wrote the twelve researchers, “the main conclusions of this study (the importance of the composition of the crust, and the spatial extent of the disturbances of the global climate and atmospheric CO2 by orogenic uplift) suggests that tectonics affect Cenozoic cooling via modulation of the carbon geologic cycle in various ways, and such forcing might not be fully extrapolated to the older global orogeny.

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