Intergovernmental Oceanographic Commission of UNESCO (IOC-UNESCO)
Authors: Breitburg, D., Grégoire, M. and Isensee, K. (eds.). Global Ocean Oxygen Network 2018. IOC Technical Series, No. 137
Oxygen is critical to the health of the ocean. It structures aquatic ecosystems, impacts the biogeochemical cycling of carbon, nitrogen and other key elements, and is a fundamental requirement for marine life from the intertidal zone to the greatest depths of the ocean.
Nearly all ocean organisms larger than a single cell, and even many microbes, require oxygen for survival. They depend on oxygen in the water in the same way that animals on land depend on oxygen in the air. A reduction in ambient oxygen below required levels causes physiological stress, behavioural changes and ultimately death of key marine species. ‘If you can’t breathe, nothing else matters’.
Climate change is decreasing oxygen concentrations in the open ocean. The combined effects of climate change and excess nutrients (nitrogen and phosphorus from sources such as agricultural runoff and human waste) are leading to oxygen loss in coastal marine systems and semi-enclosed seas that are strongly influenced by their watershed. Global and regional models predict that the oxygen content of marine waters will continue to decline as atmospheric and ocean temperatures rise and human population size increases. Ocean health is expected to decline and human well-being may ultimately suffer.
This technical brief presents a summary of scientific experiments, observations and numerical models addressing the following questions: How has the oxygen content in the open ocean and coastal waters changed over the past century and through geological time? What are the mechanisms behind this oxygen decline? How is ocean oxygen content predicted to change over the rest of the twenty-first century? What are the consequences of low and declining oxygen concentrations in the marine environment?