Stramma, Lothar and Schmidtko, Sunke (2019) Global evidence of ocean deoxygenation. In: Ocean deoxygenation: everyone’s problem. Causes, impacts, consequences and solutions. , ed. by Laffoley, D. and Baxter, J. M.. IUCN, Gland, Switzerland, pp. 25-36. ISBN 978-2-8317-2013-5 DOI 10.2305/IUCN.CH.2019.13.en.

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Abstract

Summary
• The global oxygen inventory has decreased by ~2% over the period 1960 to 2010, this finding is supported by
regional time series data that indicate a continuous decrease in oceanic dissolved oxygen.
• Ocean model simulations predict a decline in the dissolved oxygen inventory of the global ocean of 1 to 7%
by the year 2100, caused by a combination of a warming-induced decline in oxygen solubility and reduced
ventilation of the deep ocean.
• Open-ocean deoxygenation is resulting mainly from a warming ocean, increased stratification and changing
circulation which interact with eutrophication-induced hypoxia (oxygen concentration below ~60 to 120 μmol
O2 kg-1) and biological activity in shelf regions.
• Climate change related longer-term oxygen trends are masked by oxygen variability on a range of different
spatial and temporal scales.
• The decline in the oceanic oxygen content can affect ocean nutrient cycles and the marine habitat, with
potentially detrimental consequences for fisheries, ecosystems and coastal economies.
• Oxygen loss is closely related to ocean warming and acidification caused by CO2 increase driven by CO2
emissions as well as biogeochemical consequences related to anthropogenic fertilization of the ocean; hence a
combined effort investigating the different stressors will be most beneficial to understand future ocean changes.

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