The distribution of oxygen in the ocean is controlled by physical, biogeochemical and biological processes. Both the supply and consumption of oxygen are sensitive to climate change in ways that are not fully understood. Recent observations suggest that the oxygen content of the ocean is declining (ocean deoxygenation) and the oxygen minimum zones and costal hypoxia sites are expanding with tremendous effects on the ocean’s ecosystems and living organisms. Following the EUR-OCEANS conference on “Ocean Deoxygenation” in Toulouse, France, in 2011, the 46th International Liège Colloquium on “Low Oxygen Environments in Marine, Fresh and Estuarine Waters” in 2014 and the discussion meeting of the Royal Society London on “Ocean Ventilation and Deoxygenation in a Warming World” in 2016, the purpose of the international conference on “Ocean Deoxygenation: Drivers & Consequences – Past|Present|Future” that took place in Kiel, 3–7 Sept 2018 organised by the Collaborative Research Centre 754 “Climate-Biogeochemical Interactions in the Tropical Ocean” was to − focus on the past, present and future state of oxygen in the ocean on global, regional and local scales − analyse mechanisms and feedbacks critical to identify natural and anthropogenic causes of oxygen variability − determine impacts on biogeochemical cycles and ecosystems.

This special issue is open to all submissions on ocean deoxygenation and is not limited to conference participants.

Purpose of special issue: The Collaborative Research Centre 754 “Climate-Biogeochemical Interactions in the Tropical Ocean” has been investigating the newly recognised threat of ocean deoxygenation since 2008. Before the project's end in 2019, the International Conference on Ocean Deoxygenation was organised in Kiel, Germany in September 2018 with over 300 participants (https://conference.sfb754.de/event/1/). Following the conference the proposed inter-journal special issue aims at presenting the recent research advances and highlights in the field of ocean deoxygenation. The special issue shall not be limited to conference participants but be open to all submissions.