Will continental carbonates produce less or more deposition as we move into the Anthropocene?

Understanding future climate, and understanding carbon sequestration strategies, requires that we enhance our understanding of how carbon behaves in the Earth System. One area that has been comparatively overlooked is the flow of carbon through karstlands, where geologically stored carbon is released from limestone and converted into atmospheric CO2, alkalinity supplied to the ocean and into new limestone deposited as continental microbialites (“tufa”). Rough estimates of carbon fluxes in freshwater carbonate streams globally are at least 40Tg a-1, but this value is built on minimal field data and poor understanding of the processes. A critical part of the problem is that we don’t really know how carbon coming into karst rivers from soils and dissolved limestone is partitioned between gas, aqueous and sediment inventories. We aim to provide this data, by constraining the carbon fluxes occurring in a key karst river and through unique laboratory experiments. An exciting part of these experiments will be to investigate how changing the CO2 in the air above the river will change the partitioning. This means we will be able to understand how carbon flux in these rivers was different during the last glacial, and will be different as human activity continues to emit CO2.

 

Field experiments

The critical limitation to understanding karstland carbon fluxes is the lack of knowledge about how much carbon goes “up” into the atmosphere, how much goes “down” to form new calcite and how these balances change within the river system. Carbon also ultimately ends up in the ocean as dissolved bicarbonate, or deposited as organic carbon in the river sediment and these budgets are also not well constrained. The fundamental controls are partially geochemical, but also partially hydraulic – as the fluxes of carbon vertically within the water will be in eddies. Our field experiments will address both issues, using two well-known rivers, which form tufa carbonate today the Lathkill in Derbyshire and at Ddol Uchaf in North Wales. We will capture a unique set of carbon budget constraints, establishing how much carbon goes to atmosphere, to sediment and how much stays in the river. This work will use a mixture of electrochemistry, ICP techniques, titration and isotope measurements to make the most complete evaluation possible. We will also capture a unique set of hydraulic mesurements supported by a new field-deployable particle imaging velocimetry approach. This will allow us to establish how much more carbon is released “up” and “down” in waterfalls compared to relatively static pools. This will be exciting and challenging work, in which you will be developing a new approach to solving a long-standing research problem.

Laboratory experiments

It is important to base our new research in the “real world”, but field data is complicated and we cannot manipulate the conditions to reveal how the system would respond to change. So, between periods working in the field you will perform a unique series of laboratory experiments. Initially, these will be used to develop the same outputs as the field data, with the exception that as many measurements as possible will be automated, hugely increasing the size and power of the dataset. Once the “baseline” is established, the experiment will use supplied gasses to explore how much the system changes when atmospheric CO2 concentration is altered. The key aspect is where the system finds its equilibrium, meaning that some of these experiments will run for several weeks – providing additional opportunity to extract unique and powerful datasets.

 

What you will do?

You will plan and implement field deployments of our mobile analytical facilities, helping us draw up new protocols for bringing this new analytical technology into the question of karstland carbon budgets. You will complete these experiments, organise and analyse the data and write up the conclusions as Research Papers, and for your thesis. Between employments, you will design and implement the experiments, organise and analyse the data and write up further papers about how the budgets would have been different in the past, and will be different in the future. A key element of this will be investigating whether microbial biofilms alter the behaviour of the system (and we expect they will). Using biofilms in these experiments is a long established approach at Hull, and we will use material form the river Lathkill as we have successfully done before.

You will also present these results at international audience, both to engage the global science community with our new approaches and methods, and with our new and important findings.

The project is hosted within the Department of Geography, Geology and Environmental Science (Prof. Mike Rogerson) and the Energy and Environment Institute (Dr. Rob Thomas) at the University of Hull. This newly formed, interdisciplinary partnership has the expertise and field knowledge to find and analyse the field sites the student will study, and the instruments and specialist skills needed to complete the experiments. The project is an exciting opportunity for a physical geography or geology student with interests in Earth System Science, wanting to do some genuinely creative research.

Student profile

The prospective student should have, or expect to receive, a first class BSc degree, or a distinction at Masters level, in an appropriate discipline. They should have interests and experience in most, if not all, of the following topics: geochemistry (including doing measurements), sedimentology or geomorphology, laboratory work and fieldwork. This experience together with other skills and interests that the applicant wishes to develop can be supported by the supervisors and developed during the project. A range of funding sources are available for the project which the candidate can apply to in collaboration with the supervisors. Skills and training in interdisciplinary research skills will include presenting your ongoing results and receiving constructive feedback from peers in the Hull University Geochemistry & Geobiology (HUGG) group, the Energy and Environment Institute, and at a Faculty postgraduate research day. An additional important part of the research training will be to attend national and international conferences to present results and gain feedback. The student will be encouraged to write and submit papers for publication during the project. Discipline specific skills will be developed in geochemistry, hydraulics, microbial carbonate sedimentology and analytical method development. Full training in field and office-based techniques will be provided, although it is anticipated that the successful candidate will have a background in the skills outlined above. This project will involve data collection in the field in the UK, and may also extend to sites elsewhere depending on progress, funding, permits and logistics.