In coastal waters, a substantial fraction of the dissolved organic carbon (DOC) pool is optically active and referred to as coloured dissolved organic matter (CDOM). In this presentation, we discuss results from a collaborative research effort that explored spatial and temporal variability in the relationships between DOC and CDOM across global coastal systems. Data obtained from 45 coastal systems globally revealed both system-specific patterns and broader, consistent global relationships between the DOC and CDOM pools. These findings provide a basis for enabling standardised optical proxies for DOC. Such a proxy could improve DOC quantification on a global scale using optical observation.