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The acid and alkalinity budgets of weathering in the Andes–Amazon system: Insights into the erosional control of global biogeochemical cycles

Torres, Mark A. and West, A. Joshua and Clark, Kathryn E. and Paris, Guillaume and Bouchez, Julien and Ponton, Camilo and Feakins, Sarah J. and Galy, Valier and Adkins, Jess F. (2016) The acid and alkalinity budgets of weathering in the Andes–Amazon system: Insights into the erosional control of global biogeochemical cycles. Earth and Planetary Science Letters, 450 . pp. 381-391. ISSN 0012-821X. https://resolver.caltech.edu/CaltechAUTHORS:20160930-124814278

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Abstract

The correlation between chemical weathering fluxes and denudation rates suggests that tectonic activity can force variations in atmospheric pCO_2 by modulating weathering fluxes. However, the effect of weathering on pCO2 is not solely determined by the total mass flux. Instead, the effect of weathering on pCO_2 also depends upon the balance between 1) alkalinity generation by carbonate and silicate mineral dissolution and 2) sulfuric acid generation by the oxidation of sulfide minerals. In this study, we explore how the balance between acid and alkalinity generation varies with tectonic uplift to better understand the links between tectonics and the long-term carbon cycle. To trace weathering reactions across the transition from the Peruvian Andes to the Amazonian foreland basin, we measured a suite of elemental concentrations (Na, K, Ca, Mg, Sr, Si, Li, SO4, and Cl) and isotopic ratios (^(87)Sr/^(86)Sr and δ^(34)S) on both dissolved and solid phase samples. Using an inverse model, we quantitatively link systematic changes in solute geochemistry with elevation to downstream declines in sulfuric acid weathering as well as the proportion of cations sourced from silicates. With a new carbonate-system framework, we show that weathering in the Andes Mountains is a CO_2 source whereas foreland weathering is a CO_2 sink. These results are consistent with the theoretical expectation that the ratio of sulfide oxidation to silicate weathering increases with increasing erosion. Altogether, our results suggest that the effect of tectonically-enhanced weathering on atmospheric pCO_2 is strongly modulated by sulfide mineral oxidation.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.epsl.2016.06.012DOIArticle
http://www.sciencedirect.com/science/article/pii/S0012821X16302990PublisherArticle
ORCID:
AuthorORCID
Torres, Mark A.0000-0002-9599-2748
West, A. Joshua0000-0001-6909-1471
Clark, Kathryn E.0000-0002-3925-2630
Paris, Guillaume0000-0001-8368-1224
Feakins, Sarah J.0000-0003-3434-2423
Adkins, Jess F.0000-0002-3174-5190
Additional Information:© 2016 Elsevier B.V. Received 25 November 2015, Revised 8 June 2016, Accepted 9 June 2016, Available online 28 June 2016. Financial support was provided by NSF EAR-1227192 and NSF EAR-1455352 to A.J. West. M. Torres was supported by USC and C-DEBI fellowships. K. Clark was supported by NSERC and Clarendon Fund Ph.D. scholarships. We thank ACCA Peru, Incaterra, and CREES for field support; A. Robles Caceres, J.A. Gibaja Lopez, J. Huamán Ovalle, R.J. Abarca Martínez, I. Cuba Torres, A. Alfaro-Tapia, D. Oviedo Licona, A. Ccahuana, and J. Farfan Flores for field assistance. Lou Derry and two anonymous reviewers are thanked for their comments on an earlier version of this manuscript.
Funders:
Funding AgencyGrant Number
NSFEAR-1227192
NSFEAR-1455352
University of Southern CaliforniaUNSPECIFIED
Center for Dark Energy Biosphere Investigations (C-DEBI)UNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Clarendon FundUNSPECIFIED
Subject Keywords:chemical weathering; Andes; Amazon; Pyrite; oxidation
Record Number:CaltechAUTHORS:20160930-124814278
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20160930-124814278
Official Citation:Mark A. Torres, A. Joshua West, Kathryn E. Clark, Guillaume Paris, Julien Bouchez, Camilo Ponton, Sarah J. Feakins, Valier Galy, Jess F. Adkins, The acid and alkalinity budgets of weathering in the Andes–Amazon system: Insights into the erosional control of global biogeochemical cycles, Earth and Planetary Science Letters, Volume 450, 15 September 2016, Pages 381-391, ISSN 0012-821X, http://dx.doi.org/10.1016/j.epsl.2016.06.012. (http://www.sciencedirect.com/science/article/pii/S0012821X16302990)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:70693
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:30 Sep 2016 21:22
Last Modified:09 Mar 2020 13:19

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