Oceans losing oxygen at unprecedented rate, experts warn

[nitpicker]

https://www.theguardian.com/environment/2019/dec/07/oceans-losing-oxygen-at-unprecedented-rate-experts-warn

Oceans losing oxygen at unprecedented rate, experts warn

Fiona Harvey in Madrid

Sat 7 Dec 2019 09.00 GMT

Oxygen in the oceans is being lost at an unprecedented rate, with “dead zones” proliferating and hundreds more areas showing oxygen dangerously depleted, as a result of the climate emergency and intensive farming, experts have warned.

Sharks, tuna, marlin and other large fish species were at particular risk, scientists said, with many vital ecosystems in danger of collapse. Dead zones – where oxygen is effectively absent – have quadrupled in extent in the last half-century, and there are also at least 700 areas where oxygen is at dangerously low levels, up from 45 when research was undertaken in the 1960s.

The International Union for the Conservation of Nature presented the findings on Saturday at the UN climate conference in Madrid, where governments are halfway through tense negotiations aimed at tackling the climate crisis.

Grethel Aguilar, the acting director general of the IUCN, said the health of the oceans should be a key consideration for the talks. “As the warming ocean loses oxygen, the delicate balance of marine life is thrown into disarray,” she said. “The potentially dire effects on fisheries and vulnerable coastal communities mean that the decisions made at the conference are even more crucial.”

All fish need dissolved oxygen, but the biggest species are particularly vulnerable to depleted oxygen levels because they need much more to survive. Evidence shows that depleted levels are forcing them to move towards the surface and to shallow areas of sea, where they are more vulnerable to fishing.

Some ocean areas are naturally lower in oxygen than others, but these are even more susceptible to damage when their oxygen levels are depleted further, the report’s authors said. Species that can more easily tolerate low oxygen levels, such as jellyfish, some squid and marine microbes, can flourish at the expense of fish, upsetting the balance of ecosystems. The natural oceanic cycles of phosphorus and nitrogen are also at risk.
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[GeorgeGist]

1. Today's moment in ...

We're So Fucked.

[hatrack]

2. Also at NYT - in some tropical ocean areas, oxygen content down 40-50%

EDIT

The decline might not seem significant because, “we’re sort of sitting surrounded by plenty of oxygen and we don’t think small losses of oxygen affect us,” said Dan Laffoley, the principal adviser in the conservation union’s global marine and polar program and an editor of the report. “But if we were to try and go up Mount Everest without oxygen, there would come a point where a 2 percent loss of oxygen in our surroundings would become very significant.”

“The ocean is not uniformly populated with oxygen,” he added. One study in the journal Science, for example, found that water in some parts of the tropics had experienced a 40 to 50 percent reduction in oxygen.

“This is one of the newer classes of impacts to rise into the public awareness,” said Kim Cobb, a climate scientist and director of the global change program at Georgia Tech, who was not involved in the report. “And we see this along the coast of California with these mass fish die-offs as the most dramatic example of this kind of creep of deoxygenation on the coastal ocean.”

This loss of oxygen in the ocean is significant enough to affect the planetary cycling of elements such as nitrogen and phosphorous which are, “essential for life on Earth,” Dr. Laffoley said.

EDIT

https://www.nytimes.com/2019/12/07/climate/ocean-acidification-climate-change.html