All seminars will take place from 13:00 to 14.00 in room G.47, Williamson Building, with coffee and tea at 12:30 in the lobby on the first floor of the Williamson Building. These seminars are open to all and are a good opportunity to meet your fellow students and staff.
For details of previous seminars please see our seminar archive.
Title: Letting off steam: New insights into volatile saturation and magma degassing
Abstract: Dissolved magmatic gases (volatiles) are one of the most important controls on the chemical and physical properties of melts and magmas, on magma phase relations and mineral abundances, and on melt viscosity. The release of volatiles into bubbles is the main driver of explosive volcanic eruptions. Consequently the timing of volatile exsolution, and the style and extent of physical segregation of gas from silicate melt, are critical for understanding the potential explosivity of magmatic systems, as well as fractionation and mineralisation processes. In this talk I will explore how hydrous minerals such as apatite and amphibole can have significant advantages over traditional melt inclusion studies in understanding volatile enrichment, saturation and degassing. Apatite is particularly sensitive to the composition of fluids in equilibrium with magma, and amphibole is a useful monitor of trace metals and oxidation state. Together, this provides new insights into the timing of volatile saturation, the conditions of magma storage and eruption, and the composition of exsolved fluids prior to volcanic eruption or magma solidification.
Title: Microbial life and the death of glaciers
Abstract: Glacial ice covers 11% of Earth’s surface and is a critical zone in terms of climate and hydrology. We now recognise glaciers and ice sheets represent active and diverse microbial habitats, and that microbial processes influence the melting of glacial ice surfaces. Understanding microbial interactions with glaciers is therefore an urgent avenue of investigation. However, despite this imperative, the microbial diversity of glacial systems remains poorly characterised. From approximately 200,000 glaciers presently known on Earth, we have fewer than 10 publicly available microbial genomes at the time of writing. This limits our perspective of the genomic diversity of glaciers past, present and future. Here, I shall introduce work aimed at redressing this lacuna, building from insights from conventional, lab-based DNA sequencing investigations of glacier microbial diversity to the portability and long-read sequencing capability of the Oxford Nanopore Technologies MinION. By linking sequencing efforts in the lab and in the field, our coverage of genomic diversity on glaciers can be improved. By iterating between improving genome data from remote environments and field-sequencing informed experimental strategies, the prospect of gleaning insights to glacial genomic diversity before it is deleted by climate warming this century becomes realistic
Title: Volatiles and Volcanic Vigor
Abstract: What causes some eruptions to be more explosive than others? Is it the total driving gas fuel, or how fast the gas escapes? This talk examines both the volatile content and the speed of magma ascent immediately prior to eruption. Chemical zonation preserved inside glass pockets and crystals provides some of the fastest clocks in geology. These timescales of chemical diffusion operate over minutes to hours in the run-up to eruption.
Title: Tracing fluid transfer across subduction zones using iron and zinc stable isotopes.
Abstract: Subduction zones are the main site of volatile element transfer between the downgoing plate, the overriding mantle wedge and the Earth’s deep interior. The breakdown of serpentine minerals within the downgoing slab and the fluids released play a fundamental role in volatile cycling as well as the redox evolution of the sub-arc mantle. Constraining subduction-related serpentinite devolatilisation is essential in order to better understand of the nature and composition of slab-derived fluids and fluid/rock interactions.
Iron and Zn stable isotopes are recently-established geochemical tracers can trace fluid composition and speciation as isotope partitioning is driven by changes in oxidation state, coordination, and bonding environment. In the case of serpentinite devolatilisation, Fe isotope fractionation should reflect changes in Fe redox state and the formation of chloride and sulfide complexes; Zn isotope fractionation should be sensitive to complexation with carbonate, sulfide and sulfate anions.
This study involved targeting samples from Western Alps ophiolite complexes, interpreted as remnants of serpentinized oceanic lithosphere metamorphosed and devolatilized during subduction. A striking negative correlation is present between bulk serpentinite Fe isotope composition and proportion of ferric iron, with the highest grade samples displaying the heaviest Fe isotope compositions and proportion of oxidised iron. The same samples also display a corresponding variation in Zn isotopes, with the highest grade samples displaying isotopically light compositions. The negative correlation between Fe and Zn isotopes and decrease in ferric iron content can be explained by serpentinite sulfide breakdown and the release of fluids enriched in isotopically light Fe and heavy Zn sulphate complexes. The migration of these highly oxidizing sulfate-bearing fluids from the slab to the slab-mantle interface or mantle wedge has important implications for the redox evolution of the sub-arc mantle and the transport of metals from the subducting slab.
Title: Rice agriculture in a warming climate: what will change and what can we do about it?
Abstract: Rice is a staple food for more than half of the people in the world, and global demand for rice is projected to increase from 644 million tons in 2007 to a projected 827 million tons in 2050. However, rice production is also a major source of the potent greenhouse gas methane (CH4). Little is known about the response of yield and CH4 emissions to environmental factors beyond farmers’ direct control, such as atmospheric CO2 concentrations and climate change. In this talk, I will discuss some of my research in this area. Through meta-analysis and several large-scale experiments, my colleagues and I have tried to quantify the effects of management practices, rising CO2 concentrations and warming on yield and GHG emissions from rice agriculture. Our results suggest that the effects of warming on rice yields may be smaller than previously thought, because negative effects in some areas are partly negated by positive effects in others. I will also discuss several management practices through which farmers may simultaneously increase rice yields while reducing CH4 emissions, and the central role of soil microbes in making these practices work.
Title: Lime mud production: The microbial biofilm connection
Abstract: Microbial biofilms are ubiquitous in aqueous environments and have probably been so since the Early Proterozoic. They are capable of constructing ‘stromatolites’ which can be conveniently gathered into two groups: Those that stick and bind pre-existing sediment particles into mats; and those associated with internal precipitates (most skeletal stromatolites). A third (pelagic) microbial association is dispersed within shallow waters. These drive precipitation within the water column to form whitings.
This presentation focusses on microbial biofilms in which peloidal calcium carbonate precipitation dominates (thrombolite microherms). It explores novel ways of studying biofilm process and product using freshwater lab-based mesocosm experiments. The effects of light, temperature, pH, and turbulence on biofilm metabolism were investigated from the viewpoint of biofilm structure and calcium carbonate precipitation. In particular, the importance of EPS (extracellular metabolic substances) in precipitating spherules, micropeloids, micrite and microspar was studied. Much of the precipitate was incorporated into thrombolite skeletal micro-fabrics but significant amounts were also shed to the surrounding environment as peloids and ultrafine lime mud particles.
Conclusions from these studies have been applied to resolving lime mud production problems associated with two contrasting geological case studies: 1. A freshwater lake (phytoherm and ramp) association from the Quaternary of Central Spain and; 2. A marine ramp and sea mount example from the Quaternary of Sicily, Italy. Collectively these illustrate that very significant quantities of calcium carbonate are generated within microbial mats within the photic zone and that up to 70% of the carbonate product is resedimented downslope and into the basins.
Title: From Atoms to Planets: Understanding Planetary Magnetic Records Using Multiscale and Multidimensional Microscopy
Abstract: Traditional paleomagnetism focuses on the measurement and characterisation of ensemble magnetic properties found in bulk macroscopic samples. Owing to the development of high-sensitivity magnetometers and novel synchrotron techniques, a new paradigm in paleomagnetic studies is currently being established which allows for the study of rare and unique samples from the earliest eras of the earth’s and the solar system’s history. In these samples the critical questions revolve around the ability to establish a direct link between the nanostructural properties (composition, chemical ordering and distribution of magnetic inclusions) and the magnetic signal measured. This talk will explore how advanced microscopy techniques provide for a multiscale understanding of these new systems and allows for exploration into the fundamental rock magnetic behaviour
Title: Basaltic degassing mechanisms and eruptive dynamics revealed by textural, geochemical and geophysical monitoring of Piton de la Fournaise (2014-2017)
Abstract: Since 2013 we have started a routine observational system (DynVolc), Dynamics of Volcanoes, within the French National Observation Service for Volcanology (SNOV), to provide data for the on-going activity at Piton de la Fournaise (PdF), France. This multidisciplinary monitoring approach combines detailed study of the pyroclastic deposit (grain size and componentry) with bulk texture analysis (density, vesicularity, connectivity, permeability, morphology, vesicle distribution and crystal content) and petro-chemical study (bulk rock, glass, minerals, melt inclusions) of the same clasts and/or fragment of lava, collected during explosive/effusive activity at PdF. The objective of this effort is to (i) characterize the ongoing activity at PdF in terms of the textural, chemical and/or geochemical signatures of the eruptive products (both pyroclasts and lava), (ii) gain insights into the mechanisms triggering and driving the current very-mildly-explosive/effusive eruptive events (with shallow sources), and (iii) identify the signatures that announce changes in the activity and/or system (pauses or increases in intensity). The overall aim is to use these parameters as standards to observe and track ongoing activity. I will present here a series of data obtained during the recent eruptive episode, from June 2014 to August 2017, provide some interpretation, and raise some open questions on best protocols and strategies to follow when executing such a multidisciplinary surveillance approach.