This report sets out the importance of carbon in the open ocean and, through examples, illustrates the significance and values of some of its major carbon pools and sinks. It has been produced to promote better understanding of how atmospheric carbon is captured, stored and mobilized in the ocean, and how this has a significant bearing on sustainability, the welfare of people, and the future scale and intensity of climate change and ocean acidification. The core message is that the significance of carbon processes, pools and sinks in teh open ocean now need to be centrally focused into decision making at all scales. This report demonstrates from multiple angles that continuing with excessive carbon emissions from human activities, whilst ignoring carbon management through the various ways we use and interact with the ocean, is imperiling the ocean system that shields us from more rapid dangerous climate change impacts.