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Unformatted text preview: I t’s not hard to imagine a tonne of water: it is a week’s worth of not-very-deep baths. Get- ting to grips with a billion tonnes of water is more of a challenge. That would be a simi- lar bath for every man, woman and child on the planet; a week’s worth of flow for the Nile. To really expand your mind, go further still, to a billion billion tonnes — enough water to give every human a day’s worth of the Nile instead of a shallow bath. There are dwarf planets that weigh less than a billion billion tonnes. Yet Earth’s oceans weigh more. If it is hard to imagine something so vast, it is perhaps even harder to imagine changing it. But humanity is changing the oceans. From the tropics to the Arctic, the seas are sucking up human-driven emissions of carbon diox- ide — about half of the excess belched into the atmosphere over the past two centuries from fossil-fuel burning and cement manufactur- ing plants 1 . When carbon dioxide dissolves in water, carbonic acid is produced: as a result the oceans are becoming more acidic. “It’s basic chemistry,” says Joanie Kleypas, a marine ecol- ogist at the National Center for Atmospheric Research in Boulder, Colorado. “It’s hard to say that this is not happening.” Over the past few years, scientists have docu- mented how increasingly acidic seas could eat away the armour of many creatures — blunt- ing the spikes on sea urchins and dissolving the covering on cor- als. In artificially acidified waters, some animals, such as squid, have problems swimming because the corrosive water affects their res- piration rate. Others, particularly tiny organ- isms with carbonate shells, lose their protec- tive shields as the acid eats away at them 2 . But research into low-pH oceanography is, as yet, sparse. “We’re just starting to grapple with what low pH will mean for ocean com- munities,” says Jim Barry, a marine biologist at the Monterey Bay Aquarium Research Institute (MBARI) in Moss Landing, California. This ocean acidification is unlike the atmos- pheric warming also being caused by carbon dioxide in that it is fairly predictable; plotting its future course requires little more than school chemistry, as opposed to sophisticated model- ling. The rate of acidification is pretty much unprecedented. Before the industrial revolu- tion, the rise in the level of carbon dioxide in the atmosphere was relatively slow — giving oceans time to circulate the waters being made more acidic in the shallows with acid-neutral- izing carbonate sediments in the depths. In the past few decades, carbon dioxide has been building up far more quickly, and the ocean is becoming acidified at a rate that outpaces the action of sedimentary antacids....
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This note was uploaded on 06/04/2011 for the course PCB 4043 taught by Professor Osenberg during the Fall '10 term at University of Florida.
- Fall '10