Becca Neely

IMG_8073I am a Ph.D candidate / Early stage researcher at the University of Iceland and Landsvirkjun having graduated from the Masters of Earth Science course at the University of Oxford (2011). My research interests lie in the application of novel stable isotopes (in particular molybdenum (Mo)) to a variety of problems in the Earth and Environmental sciences.

Molybdenum isotopes in aqueous systems

Molybdenum is a transition metal, one of the most abundant in the oceans but least abundant in the terrestrial biosphere. Life as we know it requires Mo. It is a bioessential element, an enzyme cofactor in nearly all organisms and of particular importance in nitrogen fixation. Mo redox chemistry makes it particularly susceptible to changes in oxygen availability and as such it has been used as a palaeoproxy for both oceanic anoxic events (OAEs) and the great oxidation event (GOE).

When applying an isotope system to geological time it is important to understand the sources, sinks, and processes (with associated fractionations) affecting the element. The aim of this project is to further constrain some of the processes associated with the Mo isotope system, and so improve its application whilst learning more about the natural environment.

The Mo project is split into two sections: low temperature aqueous systems and high temperature, geothermal systems. 

Riverine fluxes and estuarine processes

Previous studies show that the riverine particulate Mo phase is isotopically lighter than the dissolved phase (Archer and Vance, 2008; Pearce et al., 2010; Neubert et al., 2011; Voegelin et al., 2012) but the processes causing this are not well constrained.

There is an extensive river sampling program in Iceland dating back to the 1970s. The combined area of monitored catchments totals more than 50% of the land area of Iceland. This monitoring allows direct comparison between glacial and direct run-off river catchments. This will give an idea of how riverine inputs to the oceans may vary through the climate changes of earth history (glacial and interglacial periods, for example). The riverine monitoring will also shed light on seasonal variations in weathering and the subsequent effect on Mo isotope fractionation and riverine fluxes.

In oxygenated environments Mo is highly mobile and as such, readily enters the dissolved phase. However, increasingly numerous studies are indicating that for many elements, the particulate phase is of particular significance for fluxes to the oceans. If dissolution occurs upon mixing with the higher salinity waters in the estuarine environment then this particulate phase can become a significant flux. By looking at two estuarine environments in Iceland it is possible to see if these estuarine processes are similarly affecting Mo. This project aims to see if riverine Mo enters the ocean via pure mechanical mixing or if some adsorption/dissolution is also occurring in the low salinity mixing zone.

Hydrothermal processes

Hydrothermal waters in Iceland are of particular interest both for commercial exploitation (for the generation of heating and power) and for their contributions to the aqueous biosphere as a potential source of micronutrients (such as Mo). Beyond this, Mo in hydrothermal systems is increasingly drawing interest due to the significance of hydrothermal ore forming processes and mid-ocean-ridge circulation.

Iceland offers a unique setting to study hydrothermal fluids due to the extensive drilling and monitoring of geothermal areas allowing access to both liquid and vapour phases of high temperature areas. In addition, there is an abundance of natural surface hydrothermal waters and springs. These hydrothermal systems are fed by both meteoric and sea-water resulting in distinct and interesting Mo isotope end members and an excellent opportunity to study Mo in hydrothermal waters.

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ARCHER, C. & VANCE, D. 2008. The isotopic signature of the global riverine molybdenum flux and anoxia in the ancient oceans. Nature Geoscience, 1, 597-600.

NEUBERT, N., HERI, A. R., VOEGELIN, A. R., NÄGLER, T. F., SCHLUNEGGER, F. & VILLA, I. M. 2011. The molybdenum isotopic composition in river water: Constraints from small catchments. Earth and Planetary Science Letters, 304, 180-190.

PEARCE, C. R., BURTON, K. W., VON STRANDMANN, P. A. E. P., JAMES, R. H. & GÍSLASON, S. R. 2010. Molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain. Earth and Planetary Science Letters, 295, 104-114.

VOEGELIN, A. R., NÄGLER, T. F., PETTKE, T., NEUBERT, N., STEINMANN, M., POURRET, O. & VILLA, I. M. 2012. The impact of igneous bedrock weathering on the Mo isotopic composition of stream waters: Natural samples and laboratory experiments. Geochimica Et Cosmochimica Acta, 86, 150-165.