Oxygen is critical to the health of the planet. It affects the cycles of carbon, nitrogen and other key elements, and is a fundamental requirement for marine life from the seashore to the greatest depths of the ocean. Nevertheless, deoxygenation is worsening in the coastal and open ocean. This is mainly the result of human activities that are increasing global temperatures (CO2-induced warming) and increasing loads of nutrients from agriculture, sewage, and industrial waste, including pollution from power generation from fossil fuels and biomass.
Facts: During the past 50 years the area of low oxygen water in the open ocean has increased by 4.5 million km2. The world’ oceans are now losing approximately 1 gigaton of oxygen each year. The Millennium Ecosystem Assessment released by the UN in 2005 reported that nitrogen containing compounds (e.g. sewage, fertilizers) release into the oceans grew 80 percent from 1860 to 1990. Increasing temperatures will reduce the capacity of the ocean to hold oxygen in the future. Oxygen deficiency is predicted to worsen in estuaries, coastal areas and oxygen minimum zones in the open ocean. The ocean’s capacity to produce oxygen will be reduced in the future.
Habitat loss is expected to worsen, leading to vertical and horizontal migration of species.
Oxygen deficiency will alter biogeochemical cycles and food webs. Lower oxygen concentrations are projected to result in a decrease in reproductive capacity and biodiversity loss. There are important local decreases of commercially important species and aquaculture production. Harmful Algal Blooms will be exacerbated from nutrients released in bottom waters due to hypoxia (e.g. in the Baltic Sea).Reduced ocean oxygen concentrations will lead to an increase in greenhouse gas emissions, thereby initiating feedbacks on climate change.
Excerpts from UNESCO, Jan. 2018
Background paper (pdf)
Global Ocean Oxygen Network: Through the participation of high level scientists from across the world, the IOC expert group, the Global Ocean Oxygen Network GO2NE, established in 2016, is committed to providing a global and multidisciplinary view of deoxygenation, with a focus on understanding its multiple aspects and impacts.