Growing ocean dead zones leave fish gasping

New Scientist Environment blog: "Dead zones" containing too little oxygen for fish to breathe are growing as global temperatures increase. Warmer water dissolves less oxygen, so as temperatures rise, oxygen vanishes from oceans. Marine biologists are warning that if dead zones continue expanding, oceanic "deserts" could massively deplete marine life and fish stocks.

Previous studies have shown that surface layers of the ocean can be depleted of oxygen by pollution draining out from rivers, as in the Gulf of Mexico. However the new study finds depletion at intermediate ocean depths, between 300 and 700 metres. There has also been evidence of oxygen depletion closer to the sea bed in some regions, such as the Arabian Sea, but no one has looked before in detail at intermediate depths.

"From our observations we can only tell what happened in the past 50 years, but we need to find out what will happen in the future," says Lothar Stramma of the University of Kiel, Germany.

…The combined data set shows that, over the past 50 years, large volumes of ocean previously rich in oxygen have become "oxygen minimum zones" (OMZs) containing less than 120 micromoles of oxygen per kilogram of water. These are the concentrations at which fish, squid, crustaceans and other marine creatures begin to suffocate and die…..

Marine life killed by a lack of oxygen, photo by "Kils," Wikimedia Commons, under the GNU Free Documentation License