Deoxygenation –
Open Ocean and Coastal Waters

Oxygen is critical to the health of the planet. It impacts the biogeochemical cycling of carbon, nitrogen and other key elements, it structures aquatic ecosystems, and it is a fundamental requirement for aerobic life, from the intertidal to the greatest depths of the ocean.

Climate change, agricultural runoff and human waste cause decreasing oxygen concentrations in the interior of the open ocean, as well as in estuaries and coastal areas. Global and regional models project that the deoxygenation of marine waters will further worsen with continued increases in global temperatures and human population size, leading to widespread consequences for ocean health and ultimately human wellbeing.

© World Ocean Atlas 2013, Garcia et al. 2014 - Annual average oxygen concentration ml l-1 at 200 m depth (one-degree grid, contour interval 0.5 ml l-l).

There are 10 main ocean oxygen concerns:

  1. Increasing temperatures will reduce the capacity of the ocean to hold oxygen in the future;
  2. Oxygen deficiency is predicted to worsen in estuaries, coastal areas and oxygen minimum zones in the open ocean;
  3. The ocean’s capacity to produce oxygen will be reduced in the future.
  4. Habitat loss is expected to worsen, leading to vertical and horizontal migration of species;
  5. Oxygen deficiency will alter biogeochemical cycles and food webs;
  6. Lower oxygen concentrations are projected to result in a decrease in reproductive capacity and biodiversity loss;
  7. There are important local decreases of commercially important species and aquaculture production;
  8. Harmful Algal Blooms might benefit from nutrients released in bottom waters due to hypoxia (e.g. in the Baltic Sea);
  9. Reduced ocean oxygen concentrations will lead to an increase in greenhouse gas emissions, thereby initiating feedbacks on climate change;
  10. Future scenarios for oxygen depend on a combination of drivers related to global environmental change and land-use, including warming, growing human population, and extensive coastal agricultural practices, which, in turn, act together in affecting marine ecosystems – thus, a multi-stressor approach is important.

Global Ocean Oxygen Network


Listening to the calls demanding increased cooperation and communication around low oxygen concentration in the marine environment, IOC-UNESCO initiated an ad hoc network of scientists focused on oxygen in both the open ocean and coastal areas – the Global Ocean Oxygen Network (GO2NE).

The GO2NE expert meeting took place on 12-13 December 2015 to develop terms of reference and a plan for the continuation of this interdisciplinary IOC-UNESCO network. The plan will be presented to the IOC Executive Council in June 2016 for possible adoption.

© Kirsten Isensee - Ocean oxygen scientists convened in December 2015 to create the GO2NE.

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