The next ocean: humanity's extra C[O.sub.2] could brew a new kind of sea

Science News, March 15, 2008 by Susan Milius

Terrie Klinger is starting to wonder about the future of kelp sex. It's a delicate business in the best of times, and the 21st century is putting marine life to the acid test.

Klinger, of the University of Washington in Seattle, studies the winged and bull kelps that stretch rubbery garlands up from the seafloor off the nearby Pacific coast. These kelp fronds do no luring, touching, fusing of cells or other sexy stuff. Fronds just break out in chocolate-colored patches.

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The patches release spores that swim off to settle on a surface and start the next generation. The new little kelps don't look as if they belong to the same species, or even the same family, as their parents. The little ones just grow into strings of cells, but these are about sex.

"Those of us who have spent far too long looking at this can tell the males from the females," says Klinger. The subtly female-shaped filaments form eggs and release kelp pheromones to call in the male filaments' sperm.

Sex filaments have kept kelp species going for millennia, but Klinger says she wants to know what's happening now that carbon emissions are changing seawater chemistry. The intricate reproductive cycle of kelp is an example of a delicate system that can experience big effects from seemingly small changes in ocean chemistry.

This chemistry is already shifting, powered by the increased concentration of carbon dioxide in the atmosphere from human activity. Not all the carbon dioxide from burning fossil fuels stays in the air. The oceans have absorbed about half of the C[O.sub.2] released from burning fossil fuels since the beginning of the industrial age, says Richard Feely of the National Oceanic and Atmospheric Administration in Seattle. The ocean takes in about 22 million tons of C[O.sub.2] a day, he says.

The influx causes what scientists call ocean acidification. It's a term of convenience. The ocean isn't acid now, nor do Feely and other ocean chemists expect that seawater will become acid in the foreseeable future. However, the extra C[O.sub.2] is driving the oceans closer to the acidic side of the pH scale. By the end of this century, Feely says, the upper 100 meters or so of ocean water will be more acidic than at any time during the past 20 million years.

Klinger is just one of the biologists trying to figure out what a shift in seawater chemistry will do to seaweed, corals, fish, and other marine life. The filaments of both bull and winged kelps grow noticeably slower in acidic seawater, she reported last week at the 2008 Ocean Sciences Meeting in Orlando, Fla.

Biologists are discussing what the chemistry change will do to marine creatures: It looks like bad news for calcium users and a new dawn for slimy rocks. It could begin an age of simplification for ocean ecosystems. Either way, there's a rising consensus that, by changing the oceans' chemistry and biology, burning fossil fuels is essentially making new oceans.

SEA CHANGE Researchers say the oceans of today already register a chemical change, though it may sound deceptively small at first.

Feely now rates the upper layer of seawater on average at 8.10 on the pH scale. That scale goes from 14 to 0 and describes the increasing concentration of hydrogen ions. Plain water, defined as neutral, ranks as 7, and lower numbers indicate increasingly strong acids and larger numbers of hydrogen ions. Since the beginning of the industrial age,

Feely says, the seawater pH has slipped about 0.11 of a pH unit. That's a considerable change, says a 2005 report on ocean acidification from the United Kingdom's Royal Society. The pH scale works logarithmically, so 7 means 10 times more ions than 8. The industrial age has increased the concentration of hydrogen ions by roughly a third.

The pH change from this century could be even bigger. The business-as-usual scenario for carbon emissions will drive the pH of the ocean surface waters down another 0.3 to 0.4 units by the end of the century, says Feely.

That's still not acidic, though. To push the ocean pH below 7, models predict that people would have to burn all of the fossil-fuel carbon on the planet plus a good deal of methane hydrates, he says.

Still, describing the process as ocean acidification isn't wrong. Seawater is acidifying in the sense of creeping toward the acid zone on the scale. Even if the ocean isn't turning into lemon juice, biologists predict that smaller dips in pH could do big things to marine life. It's a peril humans easily fail to appreciate. We can bathe in milk (pH 6.7) or chug orange juice (pH 3 or 4) and call ourselves refreshed. Thanks to fancy protective coatings, such as skin, and robust physiological mechanisms, a milk-soaked juice drinker's blood still hovers around pH 7.35 to 7.45. But our bodies don't have to build coral reefs.

Marine species from corals to snails to floating dots of life called coccolithophores create structures of calcium carbonate. A C[O.sub.2] boost makes this job harder.

A key ingredient in making calcium carbonate is the carbonate ion, C[O.sub.3.sup.-2]. When it reacts with water, C[O.sub.2] forms carbonic acid, [H.sub.2]C[O.sub.3]. "It's the same as adding C[O.sub.2] to pop to make it fizzy," says Feely. The carbonic acid dissociates, releasing hydrogen ions that react with the carbonate ions in the water--thus making them unavailable to calcifiers such as corals building reefs. Feely says the carbonate concentration in the warmer waters where corals live today has already decreased 16 percent since the preindustrial era.