Effects of temperature on silicate weathering: Solute fluxes and chemical weathering in a temperate rain forest watershed,Jamieson Creek,British Columbia |
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| Authors: | Benjamin F Turner Art F White Susan L Brantley |
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| Institution: | 1. Landcare Research, Department Soil and Landscapes, Gerald St, Lincoln 7608, New Zealand;2. University of Minnesota, Department of Soil, Water, and Climate, 439 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108-6028, USA;3. Lincoln University, Department of Soil and Physical Sciences, PO Box 85084, Lincoln 7647, New Zealand;4. University of Massachusetts, Department of Geosciences, 627 North Pleasant Street, 233 Morrill Science Center, Amherst, MA 01003-9297, USA;5. University of Edinburgh, School of GeoSciences, Geography Building, Drummond Street, Edinburgh EH8 9XP, UK;1. Department of Geological Sciences, California State University, Long Beach, CA 90840, USA;2. Department of Geology and Geophysics, School of Ocean and Earth Sciences and Technology, University of Hawaii at Manoa, Honolulu, HI 96822, USA;3. State of Hawaii, Department of Health, Honolulu, HI 96813, USA |
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| Abstract: | Chemical weathering of silicate minerals has long been known as a sink for atmospheric CO2, and feedbacks between weathering and climate are believed to affect global climate. While warmer temperatures are believed to increase rates of weathering, weathering in cool climates can be accelerated by increased mineral exposure due to mechanical weathering by ice. In this study, chemical weathering of silicate minerals is investigated in a small temperate watershed. The Jamieson Creek watershed is covered by mature coniferous forest and receives high annual precipitation (4000 mm), mostly in the form of rainfall, and is underlain by quartz diorite bedrock and glacial till. Analysis of pore water concentration gradients indicates that weathering in hydraulically unsaturated ablation till is dominated by dissolution of plagioclase and hornblende. However, a watershed scale solute mass balance indicates high relative fluxes of K and Ca, indicating preferential leaching of these solutes possibly from the relatively unweathered lodgement till. Weathering rates for plagioclase and hornblende calculated from a watershed scale solute mass balance are similar in magnitude to rates determined using pore water concentration gradients.When compared to the Rio Icacos basin in Puerto Rico, a pristine tropical watershed with similar annual precipitation and bedrock, but with dissimilar regolith properties, fluxes of weathering products in stream discharge from the warmer site are 1.8 to 16.2-fold higher, respectively, and regolith profile-averaged plagioclase weathering rates are 3.8 to 9.0-fold higher. This suggests that the Arrhenius effect, which predicts a 3.5- to 9-fold increase in the dissolution rate of plagioclase as temperature is increased from 3.4° to 22 °C, may explain the greater weathering fluxes and rates at the Rio Icacos site. However, more modest differences in K and Ca fluxes between the two sites are attributed to accelerated leaching of those solutes from glacial till at Jamieson Creek. Our findings suggest that under conditions of high rainfall and favorable topography, weathering rates of silicate minerals in warm tropical systems will tend to be higher than in cool temperate systems, even if the temperate system is has been perturbed by an episode of glaciation that deposits regolith high in fresh mineral surface area. |
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