Global silicate weathering flux overestimated because of sediment–water cation exchange

Tipper, Edward T. and Stevenson, Emily I. and Alcock, Victoria and Knight, Alasdair C. G. and Baronas, J. Jotautas and Hilton, Robert G. and Bickle, Mike J. and Larkin, Christina S. and Feng, Linshu and Relph, Katy E. and Hughes, Genevieve (2021) Global silicate weathering flux overestimated because of sediment–water cation exchange. Proceedings of the National Academy of Sciences of the United States of America, 118 (1). e2016430118. ISSN 0027-8424 Online ISSN 1091-6490 DOI https://doi.org/10.1073/pnas.2016430118

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Official URL: https://doi.org/10.1073/pnas.2016430118

Abstract

Rivers carry the dissolved and solid products of silicate mineral weathering, a process that removes CO2 from the atmosphere and provides a key negative climate feedback over geological timescales. Here we show that in some river systems, a reactive exchange pool on river suspended particulate matter, bonded weakly to mineral surfaces, increases the mobile cation flux by 50%. The chemistry of both river waters and the exchange pool demonstrate exchange equilibrium, confirmed by Sr isotopes. Global silicate weathering fluxes are calculated based on riverine dissolved sodium (Na+) from silicate minerals. The large exchange pool supplies Na+ of non- silicate origin to the dissolved load, especially in catchments with widespread marine sediments, or where rocks have equilibrated with saline basement fluids. We quantify this by comparing the riverine sediment exchange pool and river water chemistry. In some basins, cation exchange could account for the majority of sodium in the river water, significantly reducing estimates of silicate weathering. At a global scale, we demonstrate that silicate weathering fluxes are over-estimated by 12-28%. This over-estimation is greatest in regions of high erosion and high sediment loads where the negative climate feedback has a maximum sensitivity to chemical weathering reactions. In the context of other recent findings that reduce the net CO2 consumption through chemical weathering, the magnitude of the continental silicate weathering fluxes and its implications for solid Earth CO2 degassing fluxes needs to be further investigated.

Item Type: Article
Uncontrolled Keywords: 2020AREP; IA76
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
06 - Part-III Projects
08 - Green Open Access
12 - PhD
Journal or Publication Title: Proceedings of the National Academy of Sciences of the United States of America
Volume: 118
Page Range: e2016430118
Identification Number: https://doi.org/10.1073/pnas.2016430118
Depositing User: Sarah Humbert
Date Deposited: 23 Dec 2020 21:45
Last Modified: 21 Jun 2021 00:01
URI: http://eprints.esc.cam.ac.uk/id/eprint/5981

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