Cumulatively since preindustrial times, only the ocean has been a significant sink for anthropogenic carbon. The partitioning of carbon between the atmosphere and ocean will be a key determinant of future climate change. Thus, our community must develop the capacity to accurately diagnose the evolving ocean carbon budget and its variability using models, observations and theory. Both external forcing and internal physical and biogeochemical processing modify surface fluxes and the internal redistribution of carbon. Regional patterns of key biogeochemical stressors, most notably ocean acidification, will also be driven by the ocean’s carbon uptake. In this session, we welcome contributions that quantify the rates and processes of the ocean carbon uptake and storage, as well as its consequences for marine ecosystems. Variability and change across timescales from seasonal to millennial are of interest. We welcome studies that focus on open and coastal regions; on the surface or the interior; and that apply observations, models, and theory.