Continental weathering and erosion are integral processes responsible for the evolution of the landscape and exert a major control on the transport of material from the continents to the oceans, and on the cycles of many elements at the Earth’s surface. On geological timescales the chemical weathering of Ca-Mg silicates is amongst the primary feedbacks regulating atmospheric levels of the greenhouse gas carbon dioxide (CO2), thereby moderating the Earth’s climate (e.g. ). Continental weathering is also a major source of nutrients to the ocean, thereby playing a crucial role in ocean productivity and the carbon cycle (e.g. ).
Rivers are the dominant means of transport of many elements to the ocean , but the dissolved input from rivers cannot account for the oceanic budget, taken by some to indicate that the oceans are not in steady-state. However, elemental transport by rivers occurs not only via dissolved species, but also as particulate material, and estimates suggest that rivers transport 16-20 Gt/yr of suspended material to the ocean , more than an order of magnitude larger than the dissolved riverine and aeolian fluxes combined.
Riverine particulates incorporate elements through (i) adsorption to the surface exchange complex (ii) carbonate (iii) organic material (iv) clays (v) Fe-Mn oxides and (vi) residual silicate material. Solubilisation of just a small fraction (0.05%) of this particulate material has the potential to dominate the nutrient flux to the oceans (e.g. [5,6]).
This project aims to trace the release of nutrients from river particulates in estuaries, with a particular focus on the transition metals Fe, Cu, Zn and Ni and their stable isotopes (amongst a number of key micronutrients). Fieldwork will involve sampling rivers, estuary waters, suspended particulate material and bedload, from a range of settings. Including the Mackenzie basin, Iceland and the Gironde (France).
Analytical work will involve (i) Quantification of chemical and mineralogical variations in riverine particulate chemistry with weathering intensity and grain size in terrains showing contrasting rock types, temperature, runoff and degrees of weathering (ii) Characterisation of the mineralogical, elemental and isotope behaviour of particulates in estuarine environments. (iii) Complementary experimental work to determine dissolution rates, elemental release/uptake, and the net isotope release and fractionation accompanying dissolution of riverine particulates in seawater. With a particular focus on the behaviour of Fe-Mn oxides and organic material in the estuarine environment.
The overall aim of this project is to trace the release and sources of the micronutrients Fe, Zn, Cu and Ni in the estuarine environment, and their contribution to the oceanic budget.