While we are now close to monitoring oceanic CO2 uptake on decadal and regional scales, meaningful predictions of its future behaviour are difficult. Climate change affects ocean biology and physics and could lead to reduced efficiency of the carbon sinks, a process that atmospheric data and ocean models indicate is already occurring in the Southern Ocean. Attempts to set a baseline stabilization target for the atmospheric CO2 concentration will ultimately depend on our understanding and prediction of oceanic CO2 sinks. There is a critical and urgent need to better understand the ocean processes regulating CO2 uptake and to identify research and observational priorities for the future. This workshop reviews the current knowledge base and enhance international cooperation to resolve the magnitude, variability and processes governing ocean sources and sinks of carbon, from observations, process-based models and atmospheric and oceanic inversions.