The research links the issue of deoxygenation to increasing levels of pollution and declining fish stocks. The authors say that patterns of underwater oxygen are unsustainable and could lead to damaging ecosystem collapses in the long term.
Levels of marine oxygen have been falling since the middle of the 20th century as a result of higher carbon dioxide levels and rising temperatures in the ocean. The primary cause of deoxygenation in open oceans is global warming – warmer water holds less oxygen.
Oxygen is no longer so easy for #marine life to obtain. In the past decade #ocean oxygen levels have taken a dive—an alarming trend that is linked to #climatechange. Levels in some tropical regions have dropped by 40% in the last 50 years: https://t.co/fxW6bbOowO via @sciam
— Defenders of Wildlife (@Defenders) March 1, 2019
Experts alarmed by how quickly marine oxygen levels falling
The scale of the change concerned the scientists behind the report. Andreas Oschiles, an Oceanographer and one of the report’s authors, said he and his colleagues “were surprised by the intensity of the changes we saw, how rapidly oxygen is going down in the ocean and how large the effects on marine ecosystems are.”
In some tropical regions, oxygen levels have declined by 40% over the last half-century.
The flow-on effects of deoxygenation can be disastrous for marine life, who need oxygen to undertake usual activities like digesting food and escaping predators.
Marine life can also be important oxygen producers as well consuming oxygen; a recent survey of plankton communities in coastal waters and shelf seas around the UK said oxygen production is one of the vital ecosystem services the organisms undertake.
Oxygen declines are also seen in estuaries and other coastal bodies of water linked to the ocean. In these systems, levels of nitrogen and phosphorus have risen, mainly due to farming, sewage and the use of fossil fuels. Climate change has also worsened oxygen decline in this water.
"The ocean is running out of breath, scientists warn."
— EGU (@EuroGeosciences) February 26, 2019
Californian survey also said global warming has led to deoxygenation
In order to tackle deoxygenation and its associated negative effects “will necessitate a substantial global decrease in greenhouse gas emissions, as well as reductions in nutrient discharges to coastal waters” the study concludes.
Earlier in February, California’s Office of Environmental Health Hazard Assessment (OEHHA) published results of an evaluation of ocean water in the US state. The evaluation also showed evidence of significant deoxygenation.
The office said the declining oxygen levels had been caused primarily by climate change, rising chemical pollution from agriculture and wastewater being deposited into the sea.
While deoxygenation is generally bad news for marine life, the evaluation noted that some species thrive in low oxygen conditions and have been able to expand their territory due to the change. Humboldt’s Squid, for example, has been able to extend its habitat from California to the southern stretches of Alaska.