World’s oceans are los­ing oxy­gen rapidly, study finds

Antelope Valley Press (Sunday) - - News - By KEN­DRA PIERRE-LOUIS New York Times

The world’s oceans are gasp­ing for breath, a re­port is­sued Satur­day at the an­nual global cli­mate talks in Madrid has con­cluded.

The re­port rep­re­sents the com­bined ef­forts of 67 sci­en­tists from 17 coun­tries and was re­leased by the In­ter­na­tional Union for Con­ser­va­tion of Na­ture. It found that oxy­gen lev­els in the world’s oceans de­clined by roughly 2% be­tween 1960 and 2010. The de­cline, called de­oxy­gena­tion, is largely at­trib­uted to cli­mate change, although other hu­man ac­tiv­i­ties are con­tribut­ing to the prob­lem. One ex­am­ple is so-called nu­tri­ent runoff, when too many nu­tri­ents from fer­til­iz­ers used on farms and lawns wash into wa­ter­ways.

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% 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% 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,” Laf­fo­ley said.

“What sur­prised me was that, as oxy­gen lev­els low­ered, there would be an ef­fect on those cy­cles,” he added. “We lower these oxy­gen lev­els at our peril.”

De­oxy­gena­tion is just one of the ways the world’s oceans are un­der as­sault. As they ab­sorb car­bon diox­ide, oceans be­comes less ba­sic and more acidic, in some places dis­solv­ing the shells of aquatic life like clams, mus­sels and shrimp in what is some­times called the “os­teo­poro­sis of the sea.”

And, since the mid­dle of last cen­tury, oceans have ab­sorbed 93% of the heat as­so­ci­ated with hu­man-caused green­house gas emis­sions, lead­ing to mass bleach­ing of coral reefs. Warmer wa­ter also takes up more space than cooler wa­ter. NASA says that this ther­mal ex­pan­sion process has caused roughly a third of ex­ist­ing sea level rise.

Ac­cord­ing to Laf­fo­ley, if the heat ab­sorbed by the oceans since 1955 had gone into the lower lev­els of the at­mos­phere in­stead, land tem­per­a­tures would be warmer by 65 de­grees Fahren­heit, or 36 de­grees Cel­sius.

Global av­er­age tem­per­a­tures have risen 2 de­grees Fahren­heit since the late 19th cen­tury and the Paris Cli­mate agree­ment has a tar­get of lim­it­ing fur­ther in­creases to be­low 3.6 de­grees Fahren­heit.

But wa­ter holds less oxy­gen by vol­ume than air does. And as ocean tem­per­a­tures in­crease, the warmer wa­ter can’t hold as much gas, in­clud­ing oxy­gen, as cooler wa­ter. (It’s why soda tends to go flat faster in the hot sum­mer sun.)

Warm­ing tem­per­a­tures also af­fect the abil­ity of ocean wa­ter to mix, so that the oxy­gen ab­sorbed on the top layer doesn’t prop­erly get down into the deeper ocean. And what oxy­gen is avail­able gets used up more quickly be­cause ma­rine life uses more oxy­gen when tem­per­a­tures are warmer.

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