Oceans Are Losing Oxygen—and Becoming More Hostile to Life

Marlin and Sailfish are staying within 800 meters of the surface in Guatemala and Costa Rica, instead of deep diving as usual, to avoid suffocation.

Declining ocean oxygen is as significant as water warming and acidification. Midwater fish which support the Pacific food chain have declined 63% since the 1950s.

... a disturbing trend: Warming temperatures are sucking oxygen out of waters even far out at sea, making enormous stretches of deep ocean hostile to marine life.

This phenomenon could transform the seas as much as global warming or ocean acidification will,...

“Two hundred meters down, there is a freight train of low-oxygen water barreling toward the surface,”...

These are not coastal dead zones, like the one that sprawls across the Gulf of Mexico, but great swaths of deep water that can reach thousands of miles offshore. Already naturally low in oxygen, these regions keep growing, spreading horizontally and vertically. Included are vast portions of the eastern Pacific, almost all of the Bay of Bengal, and an area of the Atlantic off West Africa as broad as the United States.

Globally, these low-oxygen areas have expanded by more than 1.7 million square miles  (4.5 million square kilometers) in the past 50 years.

Over the next decade, researchers figured out that this change already was driving marine creatures—sailfish, sharks, tuna, swordfish, and Pacific cod, as well as the smaller sardines, herring, shad, and mackerel they eat—into ever narrower bands of oxygen-rich water near the surface.

“It leaves just a very thin lens on the top of the ocean where most organisms can live,”...

... fish often credited with keeping marine systems functioning soundly—tiny midwater bristlemouths, the region’s most abundant marine species, as well as viperfish, hatchetfish, razor-mouthed dragonfish, and even minnow-like lampfish.

All are significant parts of the seafood buffet that supports life in the eastern Pacific, and all are declining dramatically with the vertical rise of low-oxygen water.

“If it was a 10 percent change, it wouldn’t have been worth noting, but they’ve declined by 63 percent,” says Koslow, of the Scripps Institution of Oceanography. And “what’s been amazing is it’s across the board—eight major groups of deep-sea fishes declining together—and it’s strongly correlated with declining oxygen.” [emphasis mine]

Oxygen minimum zones affect global ocean chemistry by removing available nitrogen. Map is for 2009.

Around 30- 50% of global marine N-loss takes place in these areas, which represent only ca. 0.1% of the ocean´ s volume.

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Thanks for posting, Ruth. I always read you threads, but I don't know how to reply in the face of disaster.

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