Dr. Emma Tomlinson

Land-use has changed soil dynamics in agricultural landscapes and huge amounts of metal pollutants are continuously released into the environment by industrial and domestic activities. In other places, metal deficiency in soils is observed. These modifications affect the nutrient status of soils and freshwater. This project will will determine and use the distinct isotope fingerprint of these anthropogenic influences on the environment and will investigate the potential for using novel stable isotopes as environmental tracers (e.g. find pollution sources).

The abundances and distributions of halogens (F, Cl, Br, I) in the Earth's mantle are virtually unknown, yet the mantle is the source of magmas emplaced in the crust and erupted at the surface. This project will aims to address this gap in knowledge by: 1) developing a new analytical approach for halogens by electrothermal vaporization ICP-MS/OES; 2) characterizing the elemental and isotopic halogen composition of the primitive mantle, using samples from Baffin Island and West Greenland; and 3) to assess halogen recycling and the mantle residence time of recycled halogens thorough investigation of mafic alkaline rocks from the Greenlandic portion of the North Atlantic Craton. This will provide a unique insight into this significant and unexplored halogen reservoir and will make it possible to distinguish between primitive halogens from the deep mantle and those introduced into the mantle via subduction.

The formation and evolution of the Earth's mantle is key to the growth and stabilzation of the planet's continents and the formation of a habitable planet. The aim of this project is to combine geochemical and crystallographic data in order to test the two competing hypothesis for the formation of the sub-continental lithospheric mantle (SCLM). Oceanic mantle peridotite forms by the extraction of basaltic melt to form the crust. However, the SCLM is fundamentally different, being enriched in Si, Al and Ca and having an overabundance of orthopyroxene, which cannot be explained by melting. The favoured model for the formation of the SCLM requires that peridotite mantle initally underwent melting, leading to incompatible element depletion, and was subsequently enriched, or metasomatised, by precolating sililic fluids. However, several observations are difficult to explain, such as: the close spatial distribution of garnet and orthopyroxene in SCLM peridotites, and their low water content. I favor a model in which that the SCLM formed by unmixing (exsolution) of garnet and orthopyroxene from a precursor mineral. In an exsolution scenario, we expect undisturbed exsolution pairs to display a topotaxic relationship, therefore I will analyse the relative crystallographic orientations of garnet inclusions in orthopyroxene in SCLM peridotite. We also expect exsolution pairs to display chemical equilibrium, therefore I will analyse the ultra-trace element and isotopic compostions of proposed exsolution pairs. This novel dataset will be also used to assess the extent of metasomatism. Using the combined crystallographic and geochemical data, I will develop a model for the nature and origin of the percursor and the formation of the SCLM. The SCLM has a strong influence on continental dynamics, relative sea-level change and long term climate change. Thus, understanding the formation and evolution of the SCLM is central to many issues in Earth Sciences.

The effect of volcanism on climate is well known: explosive volcanic eruptions cause global cooling through stratospheric injection of sulphur. However, it is now understood that climatic warming and deglaciation leads to an increase in the frequency of volcanic eruptions in places such as Iceland. A significant increase in volcanic activity in Iceland would make ash clouds over Europe a more frequent occurence, disrupting aviation and transport. I will investgate the relationship between climatic warming and increased volcanism in the past using volcanic signatures in peat. Layers of volcanic ash (tephra) are deposited from volcanic plumes, however tephra records are incomplete. This project will combine traditional tephrochronology with a novel approach to identify volcanic aerosols and thus provide a more comprehensive record of past volcanism in Iceland. This will be used to resolve some of the uncertainty of the effect of climate change on volcanic hazards in the 21st century.

Many volcanic systems exhibit remarkable cyclic behaviour, starting with eruptions of less evolved magma and transitioning to infrequent eruptions of more evolved magma before culminating in cataclysmic eruption. Cyclic variations with periods of 104-105 years are within the range of orbitally forced climatic variations (Milankovitch cycles), indeed, layers of volcanic ash in sediment cores document an increase in volcanic eruption frequency following deglaciation. This project will investigate the tempo of past volcanic eruptions at Campi Flegrei (Italy) using tephra layers preserved in a sedimentary core from Lago Grande di Monticchio, an annually layered lake spanning 3-133 ka located downwind of Campi Flegrei. The aim is to explore the interplay between magmatic and climatic processes and to test the hypothesis that the timing and tempo of volcanism at Campi Flegrei is controlled by climatic variations.