Changes and variability in ocean biogeochemistry are poorly observed despite its profound impacts on ocean ecosystems and associated services, and sensitivity to and for climate. The overall aim of BioGeoSea is to significantly close the research and knowledge gaps on biogeochemical Essential Ocean Variables (BGC EOVs), validate them in-situ and in models, and use them to feed ocean metrics in the form of indicators and data products that reflect their relevance to the society. This aim includes updating EOVs requirements and specifications to enhance their usefulness in providing ocean biogeochemistry indicators, which BioGeoSea will develop and deliver. These indicators will reflect different spatial and temporal scales, and be focused around: 1) ocean acidification; 2) ocean deoxygenation 3) the biological carbon pump; and 4) greenhouse gas fluxes. BioGeoSea will: 1) improve the requirement setting of BGC EOVs; 2) Improve the observational capability of BGC EOVs over a large range of temporal and spatial scales; 3) Provide better representation of biogeochemical processes in models and more accurate predictions; 4) Improve ocean BGC data products that are invaluable to understand complex ocean phenomena; 5) Deliver ocean BGC indicators and engage actively with stakeholders. Key results will be communicated to international networks and entities for endorsement, approval and efficient dissemination of the outcomes. This project will help to better observe and deliver biogeochemical ocean data and information, and ultimately advance our understanding about ocean health and its role in climate regulation. BioGeoSea will demonstrate the importance of long-term observations of the ocean, focusing on BGC EOVs. The quality of information from all BGC EOVs will be improved, and four innovative BGC indicators will be delivered, at a technological readiness level that responds to the needs of an economically viable and healthy society.