Ocean-based Carbon Dioxide Removal: Assessing the utility of coastal enhanced weathering

Project Rationale

If the extent of global warming is to be limited to 1.5 degrees above pre-industrial levels then Carbon Dioxide Removal (CDR) approaches need to be able to extract up to 1000 GtCO₂ from the atmosphere by 2100. Meeting these targets requires the rapid implementation of an array of CDR methods, with ocean-based techniques receiving increasing attention due to the potential scale and permanence of CO₂ sequestration that can be achieved. Coastal enhanced weathering, a form of ocean alkalinity enhancement, is one of the most promising ocean-based CDR techniques, with laboratory experiments and model-based estimates implying it may be capable of removing several GtCO₂/yr [e.g. 1]. However, confidence in the viability of this approach is currently limited by uncertainties in the rate of weathering and the potential for environmental and ecosystem impacts [2,3]. This project addresses these knowledge gaps by investigating the weathering processes and fate of trace metals released during olivine dissolution in coastal environments. Working in collaboration with Vesta, who are conducting the world’s first coastal enhanced weathering trials in America and the Caribbean, this study will help establish the rate of weathering and whether potentially bio-limiting and/or toxic metals such as Fe, Si and Ni are released into seawater or retained within the sediments.

Methodology

The viability of coastal enhanced weathering as a CDR mechanism will be assessed through measurements of olivine dissolution in both field and laboratory settings. Physical and chemical analyses of water fluxes, alkalinity, pH and element abundances will be used to help constrain the rate of weathering and atmospheric CO₂ removal, while state-of-the-art isotopic techniques will be used to investigate the exchange of trace metals to/from seawater during mineral dissolution and precipitation processes. For example; d^88/86Sr will be used to monitor carbonate precipitation, d^30/28Si, d^56/54Fe and d^66/64Zn can help characterise the flux of bio-essential nutrients, while d^60/58Ni and d^53/52Cr can be used to investigate the release of potentially toxic trace metals. Samples will be derived from Vesta’s coastal carbon capture trials being conducted in the USA and Dominican Republic and will be complemented by laboratory-based experiments that characterise weathering mechanisms and their associated isotopic and chemical responses under well constrained conditions [e.g. 3]. There will also be opportunities to apply these techniques to improve our understanding of the release of trace metals at terrestrial enhanced weathering trials being conducted in the UK, Illinois USA, and Malaysia through the Leverhulme Centre for Climate Change Mitigation and Greenhouse Gas Removal Demonstrator projects, with potential to visit and conduct fieldwork at those locations.

Training

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted within the Ocean BioGeoscience group at the National Oceanography Centre. Specific training will include:

     i.       Collection of water and sediment samples from Vesta’s coastal weathering pilot study sites, and conducting in-situ physical and chemical measurements (e.g. pH and alkalinity).

    ii.       Determination of trace element concentrations and isotopic ratios by inductively coupled plasma mass spectrometry (ICP-MS), thermal ionization mass spectrometry (TIMS) and multi-collector (MC) ICP-MS.

   iii.       Laboratory-based experiments for quantifying the rate of olivine dissolution and the associated precipitation of secondary minerals and establishing their effect on the chemical and isotopic composition of the surrounding fluid.

   iv.       Use of geochemical models such as PHREEQC and CO2SYS to constrain changes in aqueous geochemistry and mineral saturation states, and coupling with physical parameters such as discharge/flow rates to establish atmospheric CO₂ drawdown.

In addition to exchanges associated with the INSPIRE DTP, the student will also have opportunities to work closely with other national and international collaborators involved in both the coastal and terrestrial enhanced weathering trials and programmes.