Olivine Weathering Implications in Coastal Environment: an experimental approach.
Supervisors: Nils Moosdorf, Murugan Ramasamy (ZMT, Bremen)
Ocean alkalinity enhancement (OAE) is a potential ocean-based carbon removal strategy involving the dispersal of crushed olivine rock to sequester atmospheric CO2. However, much of the olivine settles before weathering, and the environmental impact remains unclear. This study examines the effects of various sediment types on olivine dissolution, the natural behaviour of benthic areas without olivine, and the role of microbes in olivine dissolution.

A 60-day column experiment was conducted with coarse and fine sediments, including controls and autoclaved treatments in a tidal set-up. Porewater samples from columns (n=14) were collected from water, sediment, and olivine layers from three replicates of each treatment and analysed for total alkalinity (TA), dissolved inorganic carbon (DIC), dissolved silica (DSi), and pH. Post-experiment, olivine samples were examined using scanning electron microscopy with energy-dispersive X-ray spectroscopy (EDX), revealing dissolution evidence and textural changes compared to fresh olivine. In the coarse olivine treatment, TA values ranged from 2483 ± 99 to 2866 ± 101 μmol/L. Fine grain olivine treatment showed initial TA values between 3670 ± 145 and 4267± 81 μmol/L, decreasing over time. Coarse without olivine TA water increased from 2291±117 to 4272±115 μmol/L, while fine grain without olivine TA reached 3502±113 μmol/L by the experiment’s end. Among all treatments, autoclaved had the lowest TA variation. Other chemical parameters confirmed this TA pattern. The primary difference between fine and coarse olivine treatments is due to permeability differences, with slower tidally induced water flow in fine grain restricting chemical exchange. Increased chemical signals in water can inhibit weathering due to saturation over time, thus reducing OAE’s long-term effectiveness. Without olivine treatments, natural alkalinity input is evident, with a more pronounced effect in coarse grain > fine, indicating that more space between grains accelerates natural alkalinity production in alkaline sources. Microbes have a significant influence on olivine dissolution. The finding suggests coarse grain settings are optimal for long-term OAE.

Keywords: Ocean alkalinity enhancement, enhanced weathering, climate change, olivine