‘Dead zones’ becoming more common as Oceans lose their oxygen

In the past 50 years, the amount of water in the open ocean with zero oxygen has gone up more than four-fold, while in coastal water bodies, including estuaries and seas, low-oxygen sites have increased more than 10-fold since 1950.

In a new review paper published in Science, lead author Denise Breitburg, a Smithsonian Environmental Research Center marine ecologist, and her colleagues conclude that oxygen loss in the oceans is a serious threat to marine life. According to the paper, the open ocean has lost about 77 billion metric tons of oxygen in the past 50 years – nearly two percent of its total concentration.

“Oxygen is fundamental to life in the oceans,” Breitburg said, according to Science News Online. “The decline in ocean oxygen ranks among the most serious effects of human activities on the Earth’s environment.”

Map showing distribution of bottom-water dissolved oxygen from July 28 to August 3, 2015, west of the Mississippi River delta. Black lined areas — areas in red to deep red — have very little dissolved oxygen.

NOAA

Co-author Lisa Levin, a biological oceanographer at Scripps Institution of Oceanography at the University of California San Diego, said in a press release, “It’s a tremendous loss to all the support services that rely on recreation and tourism, hotels and restaurants and taxi drivers and everything else. The reverberations of unhealthy ecosystems in the ocean can be extensive.”

The research clearly defines how rising nutrient loads, coupled with climate change and human activities are changing ocean biogeochemistry and increasing oxygen consumption. To reach the conclusion that oceans are losing their oxygen at increasingly greater levels, multiple analyses’ were conducted.

Analyses of direct measurements at sites around the world indicate that oxygen-minimum zones in the open ocean have expanded by several million square kilometers and that hundreds of coastal sites now have oxygen concentrations low enough to limit the distribution and abundance of the marine animal populations.

A Norwegian fisheries research vessel which surveyed the Myeik archipelago in 1980 and again in 2013 found rampant overfishing had led to a 90 percent fall in the biomass of open ocean species of fish.

Ye Aung THU, AFP

Carry-over effects of low oxygen levels in ocean
Not only does low oxygen levels have an effect on marine life, causing stunted growth, a decrease in populations, and greater susceptibility to disease, but this will carry-over to humans that rely on the ocean for their food and livelihoods. Many populations dependent on the ocean cannot relocate when marine life is depleted or die out.

In the Philippines, fish kills in a single town’s aquaculture pens cost more than $10 million. Coral reefs, a key tourist attraction in many countries, also can waste away without enough oxygen. The paper also notes that while some coastal fisheries may prosper right now because fish are forced to crowd together to escape low oxygen, this will eventually result in overfishing and damage to the economy.

While low ocean oxygen levels may seem to be low on the list of climate change priorities, the authors raise the possibility of this having a perhaps unwanted positive feedback loop. Low oxygen concentrations can cause the production of nitrous oxide, a powerful greenhouse gas.

This global map shows the concentration of nitrogen dioxide in the troposphere as detected by the Ozone Monitoring Instrument aboard the Aura satellite, averaged over 2014.

NASA

This could make the oceans even warmer, leading to the production of even more greenhouse gasses. However, Breitburg told Futurism that there is “disagreement among researchers whether stratified ocean waters would impede that nitrous oxide from reaching the surface.”

A Three-Pronged Approach to winning the war
The researchers do offer a glimmer of hope, but it will take some the international community as well as individuals working together. We need to first address the issues behind climate change and nutrient pollution in our waters. We need better septic systems to protect humans as well as keep nutrients and pollution out of the water.

Protecting vulnerable marine life is a secondary consideration. If we are to keep our fisheries from greater risk, this could mean creating marine protected areas or no-catch zones in areas animals use to escape low oxygen or switching to fish that are not as threatened by falling oxygen levels.

Among the ecosystems most threatened by global warming are coral reefs which bleach as oceans heat up

MENAHEM KAHANA, AFP/File

And lastly, the researchers say we need to improve on our low-oxygen tracking methods worldwide. Enhanced monitoring, especially in developing countries, and numerical models will help pinpoint which places are most at risk and determine the most effective solutions.

“This is a problem we can solve,” Breitburg said. “Halting climate change requires a global effort, but even local actions can help with nutrient-driven oxygen decline.”

Further reading: Data shows oxygen level in world’s oceans has been declining
Further reading: Rising seas set to double coastal flooding by 2050: study