Oceans Acidifying Faster today Than in Past 300 Million Years
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"We know that life during past ocean acidification events was not wiped out--new species evolved to replace those that died off. But if industrial carbon emissions continue at the current pace, we may lose organisms we care about--coral reefs, oysters, salmon."
The oceans act like a sponge to draw down excess carbon dioxide from the air.
The gas reacts with seawater to form carbonic acid, which over time is neutralized by fossil carbonate shells on the seafloor.
If too much carbon dioxide enters the ocean too quickly, it can deplete the carbonate ions that corals, mollusks and some plankton need for reef and shell-building.
In a review of hundreds of paleoceanographic studies, the researchers found evidence for only one period in the last 300 million years when the oceans changed as fast as today: the Paleocene-Eocene Thermal Maximum, or PETM.
In ocean sediment cores, the PETM appears as a brown mud layer flanked by thick deposits of white plankton fossils.
About 56 million years ago, a mysterious surge of carbon into the atmosphere warmed the planet and turned the oceans corrosive.
In about 5,000 years, atmospheric carbon doubled to 1,800 parts per million (ppm), and average global temperatures rose by about 6 degrees Celsius.
The carbonate plankton shells littering the seafloor dissolved, leaving the brown clay layer that scientists see in sediment cores today.
As many as half of all species of benthic foraminifera, a group of one-celled organisms that live at the ocean bottom, went extinct, suggesting that deep-sea organisms higher on the food chain may have also disappeared, said paper co-author Ellen Thomas, a paleoceanographer at Yale University.
"It's really unusual that you lose more than 5 to 10 percent of species," she said.
Scientists estimate that ocean acidity--its pH--may have fallen as much as 0.45 units as the planet vented stores of carbon into the air.
"These scientists have synthesized and evaluated evidence far back in Earth's history," said Candace Major, program officer in the National Science Foundation's (NSF) Division of Ocean Sciences, which funded the research.
"The ocean acidification we're seeing today is unprecedented," said Major, "even when viewed through the lens of the past 300 million years, a result of the very fast rates at which we're changing the chemistry of the atmosphere and oceans."
In the last hundred years, rising carbon dioxide from human activities has lowered ocean pH by 0.1 unit, an acidification rate at least 10 times faster than 56 million years ago, says Honisch.
The Intergovernmental Panel on Climate Change (IPCC) predicts that pH will fall another 0.2 units by 2100, raising the possibility that we may soon see ocean changes similar to those observed during the PETM.
More catastrophic events have happened on Earth before, but perhaps not as quickly.
The study finds two other analogs for modern day ocean acidification--the extinctions triggered by massive volcanism at the end of the Permian and Triassic eras, about 252 million and 201 million years ago, respectively.
But the authors caution that because ocean sediments older than 180 million years have been recycled back into the deep Earth, scientists have fewer records to work with.
During the "Great Dying" at the end of the Permian, about 252 million years ago, about 96 percent of life disappeared.
Massive eruptions from what is known as the Siberian Traps in present-day Russia are thought to have triggered earth's biggest extinction.
Over 20,000 years or more, carbon in the atmosphere rose dramatically.
Scientists have found evidence for ocean dead zones, and preferential survival of organisms predisposed to carbonate-poor seawater and high blood-carbon levels, but so far they have been unable to reconstruct changes in ocean pH or carbonate.
At the end of the Triassic, about 201 million years ago, a second burst of mass volcanism associated with the break-up of the supercontinent Pangaea doubled atmospheric carbon and touched off another wave of die-offs.
Coral reefs collapsed and an entire class of sea creatures, the eel-like conodonts, vanished.
On land, large plant-eating animals gave rise to meat-eating dinosaurs like Tyrannosaurus rex as the Jurassic era began.
A greater extinction of tropical species has led some scientists to question whether global warming rather than ocean acidification was the main killer at this time.
This study finds that the most notorious of all extinctions, the one that ended the Age of Dinosaurs with a falling asteroid 65 million years ago, may not have been associated with ocean acidification.
The asteroid impact in present-day Mexico 65 million years ago released toxic gases and possibly set off fires that sent surges of carbon into the air.
Though many species of plankton went extinct, coral reefs and benthic foraminifera survived.
In lab experiments, scientists have tried to simulate modern ocean acidification, but the number of variables currently at play--high carbon dioxide and warmer temperatures, and reduced ocean pH and dissolved oxygen levels--make predictions difficult.
An alternative to investigating the paleo-record has been to study natural carbon seeps from offshore volcanoes that are producing the acidification levels expected by the year 2100.
In a recent study of coral reefs off Papua New Guinea, scientists found that during long-term exposure to high carbon dioxide and pH 0.2 units lower than today--at a pH of 7.8 (the IPCC projection for 2100)--reef biodiversity and regeneration
Via Terra Daily @ http://www.terradaily.com/reports/Oceans_Acidifying_Faster_today_Than_in_Past_300_Million_Years_999.html
Trouble in Paradise: Ocean Acidification This Way Comes
Sustainability of tropical corals in question, but some species developing survival mechanisms
The following is part five in a series on the National Science Foundation's Long-Term Ecological Research (LTER) Network. Visit parts one, two, three, four, six, seven and eight in this series.
Something wicked this way comes: ocean acidification arrives in paradises like Mo'orea.
Credit and Larger Version
Credit and Larger Version
The following is part five in a series on the National Science Foundation's Long-Term Ecological Research (LTER) Network. Visit parts one, two, three, four, six, seven and eight in this series.
Double, double toil and trouble;
Fire burn, and caldron bubble.
---Shakespeare, Macbeth
Mo'orea, it's called--this island in French Polynesia that's been dubbed the most beautiful island in the world.
Here Tahitian breezes dance across crystal blue waters and beneath the tropical seas lies a necklace of coral reefs that encircles Mo'orea like a string of brightly colored jewels.
Extensive reefs of a coral named Porites and other species form atolls, or reefs that ring Mo'orea's lagoons.
Porites are colonial corals, also known as Scleractinians, found in shallow tropical waters throughout the Indo-Pacific and Caribbean regions.
Think tropical reef and your mind's eye is likely seeing Porites.
These corals and other calcifying marine life, such as coralline algae, are also the world's primary reef-builders. And therein lies the trouble.
The seas in which these calcifying species dwell are turning acidic, their pH slowly dropping as Earth's oceans acidify in response to increased carbon dioxide in the atmosphere.
As atmospheric carbon rises in response to human-caused carbon dioxide emissions, carbon in the ocean goes up in tandem.
Marine life that depends on calcium carbonate can no longer form shells or, in the case of coral reefs, skeletons. Such marine life are found in waters that are more basic with a higher pH rather than a lower pH, which is more acidic.
Porites reefs, say scientists Peter Edmunds and Robert Carpenter of California State University at Northridge, are among the most sensitive of all corals.
Carpenter and Edmunds are two of the lead scientists at the National Science Foundation's (NSF) Mo'orea Coral Reef Long-Term Ecological Research (LTER) site, one of 26 such LTER sites around the globe.
Mo'orea is the only coral reef site in NSF's LTER network. It is funded by NSF's Divisions of Ocean Sciences and Environmental Biology.
To study the effects of ocean acidification on corals and other calcifying organisms, the biologists have been awarded an NSF SEES (Science, Engineering, and Education for Sustainability) Ocean Acidification grant.
We need to understand the chemistry of ocean acidification and its interplay with other marine processes--while Earth's seas are still hospitable to life as we know it, according to David Garrison, director of NSF's Biological Oceanography Program.
Carpenter and Edmunds hope to learn how fast--and the specific mechanisms by which--ocean acidification is affecting Mo'orea's corals and calcified algae, before the island's pristine reefs join dead and dying corals lining tropical coastlines around the world.
"Is there a way of sustaining healthy coral reefs when our oceans are acidifying?" asks Edmunds.
"Marine animals and plants from pteropods--delicate, butterfly-like plankton--to hard corals and coralline algae are affected by ocean acidification, as are the microbes that fuel ocean productivity and influence the chemical functioning of seawater.
"Corals like Porites, with their extensive distribution in tropical waters, may be ocean 'canaries in the coal mine.'"
At the current rate, he and Carpenter believe, coral reefs could disappear by the turn of the next century.
"The loss of biodiversity," says Carpenter, "would be devastating to the world's oceans--and to all of us. Tourism and fishing, in fact, entire economies, depend on coral reefs."
The scientists' recent findings are cause for hope, however. Porites, it turns out, may be developing an ability to counteract the effects of ocean acidification.
When Edmunds exposed Porites to different water temperatures and pH levels, and to plankton called brine shrimp as a food source, he found that increasing the amount of plankton in the coral's diet reduced the effects of ocean acidification.
The results are published in a recent issue of the journal Limnology & Oceanography.
"It's an intriguing mechanism," says Edmunds. "As seawater became more acidic, the corals continued to deposit calcium carbonate [new hard skeleton]. Although ocean acidification reduced the overall ability of coral tissue to calcify, the corals responded to more food by adding more tissue."
Edmunds thinks that the extra plankton food may allow the coral to "bulk up," thereby changing its internal structure and increasing its ability to manufacture skeleton even in acidifying waters.
"It's a very important finding that corals can mitigate the effects of ocean acidification," says Garrison. "It will be important to uncover the specific mechanism, and to establish whether other species have this ability."
And whether, says Edmunds, it might allow Porites to survive in the more acid oceans of the future.
Edmunds and Carpenter found that the response of tropical reefs to ocean acidification may be species-specific, with some species of corals and coralline algae affected more than others.
They've also discovered that more acid oceans may lead to changes in patterns of biodiversity in a high-carbon dioxide world.
If the tropical seas cauldron continues to bubble with waters turning to acid, the scientists say, it will indeed lead to double, double toil and trouble--for the most beautiful island in the world, and for coral reefs around the globe.
Ultimately, it will affect the sustainability of life on a planet that--made up of 70 percent oceans--might better be called Water than Earth.
- Cheryl Dybas, NSF (703) 292-7734 cdybas@nsf.gov |
From the National Science Foundation @ http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=122642
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