Reconstruction of modern and past weathering regimes using boron isotopes in river sediments

Chemical weathering coupled with carbonate precipitation in the oceans is largely responsible for the sequestration of atmospheric CO2, which balances CO2 inputs into the atmosphere from mantle degassing and thus participates in the global climate regulation at the geological time scale. Despite the importance of chemical weathering in maintaining habitable conditions on the Earth's surface, quantification of past and present chemical weathering remains difficult. The intensity of modern chemical weathering is generally determined from the geochemistry of solutes and sediments transported by rivers. However, this approach suffers from the lithological control on the composition of the dissolved load and granulometric/mineralogical sorting during sediment transport. Alternatively, boron (B) isotopes have physicochemical properties suitable to study of water-rock interactions, including those involving a biological component. The processes responsible for B isotope fractionation are adsorption on clay and detrital particles, precipitation in secondary phases, and recycling through vegetation. While several studies have used B isotopes as a proxy to quantify chemical weathering reactions in the dissolved load of rivers, few have focused on river sediments. As a result, the parameters that control B isotope behavior during the production of secondary products and subsequent transport from source areas to the deposition environment are not fully understood. Additionally, the use of B isotopes as potential proxy for paleo-weathering and paleoenvironment reconstruction is relatively unknown...