The present report examines new information and scientific perspectives on the open oceans that have emerged in the 5 year period since GESAMP first addressed this topic. Not all of the topics covered by the 2009 report are addressed in the same degree of detail while coverage of certain other topics has been extended. For example, contamination arising from shipping activities, ballast water and dumping is now considered of lesser priority in the open oceans whereas new information has enabled improved assessments of ocean noise, mercury and micro-plastics.