Dissolved organic carbon (DOC) is a major component of both marine (23 μM) and continental (161 μM) rain, present in concentrations greater than nitric and sulfuric acids combined. Rain is a significant source of DOC to surface seawater (90 × 1012 g C yr−1), equivalent to the magnitude of river input of DOC to the open ocean and half the magnitude of carbon buried in marine sediments per year on a global scale. Current models of global carbon cycling focus primarily on inorganic forms of carbon and are unable to account for approximately 20% of the global carbon dioxide, suggesting a significant missing carbon sink. Quantification of the average DOC concentration in marine rain allows calculation of the global rainwater flux of DOC of 430 ± 150 × 1012 g C yr−1. When inorganic carbon is included, this rainwater carbon flux becomes 510 ± 170 × 1012 g C yr−1, which, although not the same carbon, is equivalent in magnitude to over one third of the missing carbon sink.