Are we causing a mass extinction in our oceans?
Research shows that many areas of today's oceans have conditions that parallel those of 250 million years ago, when 95 percent of marine species quickly died out.
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What's more, the ocean surface is warming, driven by the emission of carbon dioxide and other greenhouse gases. This keeps the deeper waters, which are rich in nutrients but low in oxygen, from mixing with the oxygenated surface. According to a 2007 report from the International Panel on Climate Change (IPCC), global surface temperatures increased by 1.1 degrees Fahrenheit (0.6 degrees Celsius) throughout the 21st century, and, according to the National Oceanic and Atmospheric Administration (NOAA), this decade is the warmest since record-keeping began in 1880.Skip to next paragraph
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At the time of the third of the Big Five extinctions, the Permian-Triassic, there was only one massive continent and one massive ocean, conditions that disrupted ocean circulation and inhibited oxygen circulation in an already warm world, according to Lee Kump, a geoscientist at Pennsylvania State University. That set the stage for the ultimate trigger, a series of massive volcanic eruptions in Siberia.
The eruptions pumped massive amounts of carbon dioxide into the atmosphere. This warmed the ocean further, exacerbating its oxygen problem. Meanwhile, more storms on land washed more oxygen-eating nutrients into the ocean. Bacteria began producing hydrogen sulfide, which was ultimately expelled into an atmosphere already toxic with carbon dioxide, according to Kump.
A comparison of carbon dioxide release then versus now is telling, Kump said. Siberian volcanoes emitted tens of thousands of gigatons of carbon dioxide into the air over what was probably thousands of years. Humans currently are producing 9 gigatons per year from fossil fuel reservoirs that contain up to 4,000 gigatons.
The rate of carbon dioxide release matters, Kump said, because life has to have time to adapt.
"It's: Would you rather be squeezed or punched?" Kump said. "The Permian extinction was a squeeze that gradually got tighter and tighter … It may ultimately have been more fatal than the punch we are going to get, but the punch is going to hurt more."
Crumbling at the base
The parallel in ocean chemistry between the past and present isn't limited to oxygen depletion. The Permian ocean became more acidic as the climate changed, just as the modern ocean is doing.
The ocean has absorbed about 30 percent of human-produced carbon dioxide to date, and as a result, its waters have experienced a 30 percent increase in acidity, according to Richard Feely, a senior scientist with NOAA's Pacific Marine Environmental Laboratory. If trends continue, ocean acidity will increase by up to 150 percent by the end of this century, he said.
Increased carbon dioxide and ocean acidity played a role in all of the Big Five mass extinctions, but in those cases the change in acidity was tens to hundreds of times slower than what's happening now. When changes happen quickly, "the ocean system itself doesn't have time to adapt," Feely said.
Increasingly acidic waters affect a number of species that are key parts of the ocean's ecosystems.
Acidification interferes with the ability of oysters, marine snails and other creatures to build shells or skeletons from calcium carbonate. In oyster hatcheries on the West Coast of the United States, more-acidic waters prevent oyster larvae from forming shells, and have been shown to dissolve the shells of pteropods — small marine snails that feed salmon and other commercially caught fish — from around the living creatures, Feely said.