To reach the Paris climate goals, conventional CO2 mitigation alone will not be sufficient, and large-scale deployment of negative emission technologies (NET) will be needed to extract CO2 back from the atmosphere. At present however, the feasibility, efficiency and environmental impact of currently proposed NETs is poorly constrained. This project will quantitatively investigate these issues for enhanced silicate weathering (ESW) in coastal environments, which is a newly proposed NET. The principle behind ESW is that the weathering of silicates releases alkalinity, which increases the CO2 uptake capacity of the ocean. To get a quantitative and mechanistic understanding of ESW under realistic conditions we will combine experimental work, field sampling and modelling efforts. In a large mesocosm facility, we will investigate the rate of olivine weathering, the effect on local geochemistry, the CO2 sequestration efficiency and the possible release of harmful trace metals (nickel, chromium). To examine effects on a longer timescale, we will perform a detailed geochemical assessment of two specific field sites, which have natural olivine weathering. All results will be analyzed using a comprehensive numeric modelling environment to fully unravel the connection between ESW and other biogeochemical processes. The results of this project will provide a first quantitative insight into the potential of coastal ESW as a negative emission technology.