Chemical weathering regulates atmospheric CO2, leads to soil formation and drives the evolution of the Earth surface. This reaction is taking place within the critical zone, the thin layer at the surface of our planet located between bedrock and the top of the vegetation, involving the main Earth surface geochemical reservoirs (lithosphere, biosphere, atmosphere and hydrosphere). The products of chemical weathering are mainly harvested by rivers, which play the role of integrator at the scale of their catchment.
If some of the potential controlling factors of chemical weathering have already been explored such as temperature, lithology, relief and now acid production, the role of life remains relatively unknown.
First, some biological processes can increase weathering rates: biological respiration in soils produces a large amount of CO2 available for weathering; and incomplete oxidation of organic matter generates organic acids. Second, the biosphere as a geochemical reservoir can store nutrient elements for some time, and thus impact chemical mass budgets at the catchment scale.
Barium (Ba) is an alkali-earth element, fairly soluble, and which can be considered as a nutrient. Recently it has been shown that shifts in the Ba isotopic composition occur during the recycling of nutrients at the soil scale (Bullen and Chadwick, 2016).
The goal of my PhD project is to use Ba concentration and isotopic composition within the solid and dissolved phases of a range of rivers (from mono-lithological catchments to large rivers representing the continental scale) in order to assess the cycling of Ba through biosphere and its potential relationships with other factors such as lithology, climate, and weathering regimes / rates.
T. Bullen, O. Chadwick, Ca, Sr and Ba stable isotopes reveal the fate of soil nutrients along a tropical climosequence in Hawaii, Chem Geol 422 (2016) 25–45