Assessing the biological response to changes in ocean chemistry from increased weathering

er million-year timescales, weathering of silicate and carbonate rocks draws down atmospheric carbon dioxide to be stored within the oceans. This acts as a negative feedback on carbon emissions within the carbon cycle, and prevents "runaway" greenhouse climate effects.

This DPhil project has been funded as part of the NERC-led Greenhouse Gas Removal
Programme. The aim of the NERC-led programme is to establish whether natural weathering rates could be artificially accelerated to draw down atmospheric carbon dioxide on a timescale which could achieve negative emissions i.e. the intentional removal of carbon dioxide from the atmosphere. This could help mitigate the current and future impact of global warming.

However, assuming weathering rates could be artificially accelerated, storing carbon dioxide in the ocean may have significant as yet unconstrained and unquantified ramifications. Increased weathering would raise the alkalinity of the ocean. There are three main aims of this DPhil project:

1) Determine the calcification response of the main marine calcifiers (foraminifera and corals) through laboratory and field experiments. If calcification rates can keep pace with alkalinity addition, then the draw-down of atmospheric carbon dioxide could be reversed, rendering accelerated weathering an inadequate method to achieve negative emissions. Calcein and 135Ba will be used as novel tracers of new growth in calcification rate determination experiments. The results of these experiments will then be integrated into ocean circulation models.
2) Establish the response of phytoplankton groups e.g. diatoms, dinoflagellates, cyanobacteria, coccolithophores to alkalinity addition, again through laboratory and field experiments. This addresses how marine ecosystems may be altered because of raised ocean alkalinity.
3) Investigate how phytoplankton groups respond to contaminants associated with weathering of mine waste, again through laboratory and field experiments. Mining waste is a potential material which could be artificially weathered to achieve negative emissions due to its ready availability and large surface area. This material will inevitably contain heavy metals which could stimulate growth and carbon fixation in ocean biota, or act as a toxin.

The aim is to perform field experiments in controlled reef environments in both the Gulf of Eilat and the Great Barrier Reef, in collaboration with Professor Jonathan Erez at the Hebrew University of Jerusalem and Professor Ove Hoegh-Guldberg at the University of Queensland respectively.

This project brings together a trans-disciplinary team to determine the efficacy of enhanced weathering and ocean alkalinity enhancement for greenhouse gas removal, as well as its technical and socio-economic feasibility, its wider governance, ethical and societal issues, and environmental impact. The project is expected to benefit a range of communities, in different ways and over different timescales:

1. Government policymakers: who are tasked to achieve the goal of keeping global temperatures to 1.5oC above preindustrial level. In support of this task, this project will provide a comprehensive assessment of the quantity of CO2 that could be removed due to enhanced weathering and ocean alkalinity enhancement, and over what timescale. The project will also provide predictions for CO2 uptake for a range of different technologies and technological approaches.

2. Industry, who are committed to reducing levels of greenhouse gas emissions and to developing techniques to manage atmospheric CO2. In this project we will work directly with the mining industry and provide a comprehensive assessment of how they could turn their 'waste' products into a commodity for CO2 reduction thereby reducing the carbon footprint of their activities. Managing levels of CO2 in this way will require industrial capabilities on a large scale that represents an opportunity to develop new income streams to the UK economy.

3. Intergovernmental Panel on Climate Change: Our research on the efficacy of enhanced weathering and ocean alkalinity enhancement is expected to feed in to the 6th IPCC Assessment Report which will have a strong focus on climate change mitigation strategies.

4. Civil Society: Global warming is a global issue that will significantly impact the lives of our children and grandchildren. Civil society is keenly interested in science that works to mitigate these impacts, but is rightly concerned that geoengineering approaches may have unintended consequences that do more harm than good. This project will undertake research to assess the potential costs and benefits of enhanced weathering and ocean alkalinity enhancement approaches. Communicating the results of this work, to both NGOs and the wider public, will be critical for driving this approach to full-scale deployment.