Tag Archives: deep ocean pollution

Turning Oceans into Muck

image from http://recon.sccf.org/events

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

View Extensive Abstract

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.

Looking Desperately for the Pristine


Not far off the coast of Guam lies the deepest point on Earth’s surface, the Mariana trench. Its floor is 10,994 metres below sea level. If Mount Everest were flipped upside down into it, there would still be more than 2km of clear water between the mountain’s base and the top of the ocean. Such isolation has led many to assume that it and similar seabed trenches will be among the few remaining pristine places on the planet. However, a study led by Alan Jamieson of Newcastle University, in England, has shown that nothing could be further from the truth. As Dr Jamieson and his colleagues report this week in Nature Ecology and Evolution, trenches are actually loaded with pollutants….

No vents are known to exist below 5,000 metres, though, and no sunlight penetrates a trench. The organisms found in them thus depend entirely on dead organic material raining down upon them from far above.  Since these nutrients, having once flowed into a trench, never make their way out again, Dr Jamieson found the notion that trenches have somehow remained untouched by human activities questionable. He suspected that long-lived pollutants such as polychlorinated biphenyls (which were once used widely in electrical equipment) and polybrominated diphenyl ethers (employed in the past as flame retardants) might have made their way into the bodies of organisms living in trenches.

To test this idea out, he and his colleagues sent an unmanned lander to the bottom of the Mariana trench and also to the bottom of the Kermadec trench, near New Zealand. This lander fell to the seabed and spent between eight and 12 hours there, capturing amphipods (a type of crustacean,) using funnel traps baited with mackerel. At the end of its mission it jettisoned some ballast and floated back to the surface with its prey.
When the team looked for pollutants in the captured amphipods, they found that polybrominated diphenyl ethers were indeed present, but at moderate concentrations. Levels of polychlorinated biphenyls, however, were almost off the scale.

Exceprts Oceanic pollution: Entrenched, Economist, Feb. 18, 2017, at 67