Linking carbon and iron cycles by investigating transport, fate and mineralogy of iron-bearing colloids from peat-draining rivers - Scotland as model for high-latitude rivers

Understanding the biogeochemical cycle of iron, and how it interacts with the global carbon cycle, is of fundamental importance to better constraining its influence on atmospheric CO2 and ultimately on climate. Recent research has highlighted a gap in our understanding of riverine iron delivery, more specifically the nature of iron transport by dissolved organic carbon (DOC) in rivers emerging from peatland environments. There is growing recognition within marine biogeochemistry that the importance of iron inputs by rivers and/or groundwaters has been grossly underestimated. This situation arose because the global riverine iron input is based on the “average world river”. In turn, these calculations use average compositions and total water discharge to the ocean by major world rivers, most of which exhibit extensive iron removal by flocculation and sedimentation during seawater mixing. Humic-rich, high latitude rivers, which recent work has shown to have a much higher iron-carrying capacity, are underrepresented in these calculations. Therefore it is very likely that a much greater amount of dissolved iron can escape estuarine removal and be transported to the open ocean than previously thought. The nature of this iron-DOC transport from peatland environments requires further research to identify the exact mechanisms by which iron is transported from land to ocean, and to gauge the bioavailability of the DOC-packaged iron and hence its importance to marine photosynthesizing microorganisms in coastal and open ocean ecosystems.

This project will investigate how iron speciation and mineralogy in these organic carbon complexes influences (i) its solubility during transport across the estuarine salinity gradient, and (ii) its bioavailability in coastal waters. The student will employ novel, cutting-edge technologies (Mössbauer spectroscopy and combined ultrafiltration with SeaFAST+ICP-MS) to survey trace metal concentrations, with emphasis on iron concentrations, speciation and mineralogy, across the salinity gradients of three different sea lochs on the West Coast of Scotland (Etive, Sunart, Nevis). The differing geology and land use within each catchment, while remaining within a narrow geographical range, will reveal whether these factors result in distinct differences in iron speciation and mineralogy in the catchment runoff, and hence if there is a consequent influence on the bioavailability of the iron delivered to coastal waters.

The successful candidate will become a member of the ‘Environmental Systems, Change and Protection’ research team in the Biological and Environmental Sciences Department at the University of Stirling. Classical Mössbauer spectroscopy will be carried out at the MöSEE Laboratory in Stirling, while synchrotron-based Mössbauer spectroscopy will take place at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France (proposal-based allocation of time). The field sampling and associated analytical work will require approximately one third of the student’s time to be spent at SAMS in Oban (http://www.sams.ac.uk/) and at the JHI in Aberdeen (http://www.hutton.ac.uk/). The student will become a member of the University of Stirling Graduate School (USGS; http://www.stir.ac.uk/research/stirling-graduate-school/) and will be enrolled in the Marine Alliance for Science and Technology for Scotland (MASTS) Graduate School (http://www.masts.ac.uk/graduate-school/).