Ocean acidification may be worst in 300 million years: study

AFP Yahoo News 2 Mar 12;

High levels of pollution may be turning the planet's oceans acidic at a faster rate than at any time in the past 300 million years, with unknown consequences for future sea life, researchers said Thursday.

The acidification may be worse than during four major mass extinctions in history when natural pulses of carbon from asteroid impacts and volcanic eruptions caused global temperatures to soar, said the study in the journal Science.

An international team of researchers from the United States, Britain, Spain, Germany and the Netherlands examined hundreds of paleoceanographic studies, including fossils wedged in seafloor sediment from millions of years ago.

They found only one time in history that came close to what scientists are seeing today in terms of ocean life die-off -- a mysterious period known as the Paleocene-Eocene Thermal Maximum about 56 million years ago.

Though the reason for the carbon upsurge back then remains a source of debate, scientists believe that the doubling of harmful emissions drove up global temperatures by about six degrees Celsius and caused big losses of ocean life.

Oceans are particularly vulnerable because they soak up excess carbon dioxide from the air which turns the waters more acidic, a state that can kill corals, mollusks and other forms of reef and shell organisms.

"We know that life during past ocean acidification events was not wiped out -- new species evolved to replace those that died off," said lead author Barbel Honisch, a paleoceanographer at Columbia University's Lamont-Doherty Earth Observatory.

"But if industrial carbon emissions continue at the current pace, we may lose organisms we care about -- coral reefs, oysters, salmon."

Honish and colleagues said the current rate of ocean acidification is at least 10 times faster than it was 56 million years ago.

"The geological record suggests that the current acidification is potentially unparalleled in at least the last 300 million years of Earth history, and raises the possibility that we are entering an unknown territory of marine ecosystem change," said co-author Andy Ridgwell of Bristol University.

The UN Environment Program released a report in 2010 that warned carbon emissions from fossil fuels may bear a greater risk for the marine environment than previously thought.

Rising acidity levels have an impact on calcium-based lifeforms, ranging from tiny organisms called ptetropods that are the primary food source, to crabs, fish, lobsters and coral, it said.

The UN report called for cuts in human-made CO2 emissions to reduce acidification and support for further work to quantify the risk and identify species that could be most in peril.

Oceans' acidic shift may be fastest in 300 million years
Deborah Zabarenko Reuters Yahoo News 2 Mar 12;

WASHINGTON (Reuters) - The world's oceans are turning acidic at what could be the fastest pace of any time in the past 300 million years, even more rapidly than during a monster emission of planet-warming carbon 56 million years ago, scientists said on Thursday.

Looking back at that bygone warm period in Earth's history could offer help in forecasting the impact of human-spurred climate change, researchers said of a review of hundreds of studies of ancient climate records published in the journal Science.

Quickly acidifying seawater eats away at coral reefs, which provide habitat for other animals and plants, and makes it harder for mussels and oysters to form protective shells. It can also interfere with small organisms that feed commercial fish like salmon.

The phenomenon has been a top concern of Jane Lubchenco, the head of the U.S. National Oceanic and Atmospheric Administration, who has conducted demonstrations about acidification during hearings in the U.S. Congress.

Oceans get more acidic when more carbon gets into the atmosphere. In pre-industrial times, that occurred periodically in natural pulses of carbon that also pushed up global temperatures, the scientists wrote.

Human activities, including the burning of fossil fuels, have increased the level of atmospheric carbon to 392 parts per million from about 280 parts per million at the start of the industrial revolution. Carbon dioxide is one of several heat-trapping gases that contribute to global warming.

To figure out what ocean acidification might have done in the prehistoric past, 21 researchers from the United States, the United Kingdom, the Netherlands, Germany and Spain reviewed studies of the geological record going back 300 million years, looking for signs of climate disruption.

Those indications of climate change included mass extinction events, where substantial percentages of living things on Earth died off, such as the giant asteroid strike thought to have killed the dinosaurs some 65 million years ago.

The events that seemed similar to what is happening now included mass extinctions about 252 million and 201 million years ago, as well as the warming period 56 million years in the past.

The researchers reckoned the 5,000-year hot spell 56 million years ago, likely due to factors like massive volcanism, was the closest parallel to current conditions at any time in the 300 million years.

To detect that, they looked at a layer of brown mud buried under the Southern Ocean off Antarctica. Sandwiched between layers of white plankton fossils, the brown mud indicated an ocean so acidic that the plankton fossils from that particular 5,000-year period dissolved into muck.

During that span, the amount of carbon in the atmosphere doubled and average temperatures rose by 10.8 degrees F (6 degrees C), the researchers said. The oceans became more acidic by about 0.4 unit on the 14-point pH scale over that 5,000-year period, the researchers said.

That is a fast warm-up and a quick acidification, but it is small compared with what has happened on Earth since the start of the industrial revolution some 150 years ago, study author Baerbel Hoenisch of Columbia University's Lamont-Doherty Earth Observatory said by telephone.

EXTINCTIONS ON THE SEAFLOOR

During the warming period 56 million years ago, known as the Paleocene-Eocene Thermal Maximum, or PETM, and occurring about 9 million years after the extinction of the dinosaurs, acidification for each century was about .008 unit on the pH scale, Hoenisch said.

Back then, many corals went extinct, as did many types of single-celled organisms that lived on the sea floor, which suggests other plants and animals higher on the food chain died out too, researchers said.

By contrast, in the 20th century, oceans acidified by .1 unit of pH, and are projected to get more acidic at the rate of .2 or .3 pH by the year 2100, according to the study.

The U.N. Intergovernmental Panel on Climate Change projects world temperatures could rise by 3.2 to 7 degrees F (1.8 to 4 degrees C) this century.

"Given that the rate of change was an order of magnitude smaller (in the PETM) compared to what we're doing today, and still there were these big ecosystem changes, that gives us concern for what is going to happen in the future," Hoenisch said.

Those skeptical of human-caused climate change often point to past warming periods caused by natural events as evidence that the current warming trend is not a result of human activities. Hoenisch noted that natural causes such as massive volcanism were probably responsible for the PETM.

She said, however, that the rate of warming and acidification was much more gradual then, over the course of five millennia compared with one century.

Richard Feely, an oceanographer at the U.S. National Oceanic and Atmospheric Administration who was not involved in the study, said looking at that distant past was a good way to foresee the future.

"These studies give you a sense of the timing involved in past ocean acidification events - they did not happen quickly," Feely said in a statement. "The decisions we make over the next few decades could have significant implications on a geologic timescale."

(Editing by Peter Cooney)

Ocean Acidification Rate May Be Unprecedented, Study Says
ScienceDaily 1 Mar 12

The world's oceans may be turning acidic faster today from human carbon emissions than they did during four major extinctions in the last 300 million years, when natural pulses of carbon sent global temperatures soaring, says a new study in Science. The study is the first of its kind to survey the geologic record for evidence of ocean acidification over this vast time period.

"What we're doing today really stands out," said lead author Bärbel Hönisch, a paleoceanographer at Columbia University's Lamont-Doherty Earth Observatory. "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. But if CO2 goes into the oceans too quickly, it can deplete the carbonate ions that corals, mollusks and some plankton need for reef and shell-building.

That is what is happening now. In a review of hundreds of paleoceanographic studies, a team of researchers from five countries found evidence for only one period in the last 300 million years when the oceans changed even remotely as fast as today: the Paleocene-Eocene Thermal Maximum, or PETM, some 56 million years ago. In the early 1990s, scientists extracting sediments from the seafloor off Antarctica found a layer of mud from this period wedged between thick deposits of white plankton fossils. In a span of about 5,000 years, they estimated, a mysterious surge of carbon doubled atmospheric concentrations, pushed average global temperatures up by about6 degrees C, and dramatically changed the ecological landscape.

The result: carbonate plankton shells littering the seafloor dissolved, leaving the brown layer of mud. As many as half of all species of benthic foraminifers, a group of single-celled organisms that live at the ocean bottom, went extinct, suggesting that organisms higher in the food chain may have also disappeared, said study co-author Ellen Thomas, a paleoceanographer at Yale University who was on that pivotal Antarctic cruise. "It's really unusual that you lose more than 5 to 10 percent of species over less than 20,000 years," she said. "It's usually on the order of a few percent over a million years." During this time, scientists estimate, ocean pH -- a measure of acidity--may have fallen as much as 0.45 units. (As pH falls, acidity rises.)

In the last hundred years, atmospheric CO2 has risen about 30 percent, to 393 parts per million, and ocean pH has fallen by 0.1 unit, to 8.1--an acidification rate at least 10 times faster than 56 million years ago, says Hönisch. The Intergovernmental Panel on Climate Change predicts that pH may fall another 0.3 units by the end of the century,to 7.8, raising the possibility that we may soon see ocean changes similar to those observed during the PETM.

More catastrophic events have shaken earth before, but perhaps not as quickly. The study finds two other times of potential 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 the timing and chemical changes of these events is less certain. Because most ocean sediments older than 180 million years have been recycled back into the deep earth, scientists have fewer records to work with.

During the end of the Permian, about 252 million years ago, massive volcanic eruptions in present-day Russia led to a rise in atmospheric carbon, and the extinction of 96 percent of marine life. Scientists have found evidence for ocean dead zones and the survival of organisms able to withstand 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 doubled atmospheric carbon. Coral reefs collapsed and many sea creatures vanished. Noting that tropical species fared the worst, some scientists question if global warming rather than ocean acidification was the main killer at this time.

The effects of ocean acidification today are overshadowed for now by other problems, ranging from sewage pollution and hotter summer temperatures that threaten corals with disease and bleaching. However, scientists trying to isolate the effects of acidic water in the lab have shown that lower pH levels can harm a range of marine life, from reef and shell-building organisms to the tiny snails favored by salmon. In a recent study, scientists from Stony Brook University found that the larvae of bay scallops and hard clams grow best at pre-industrial pH levels, while their shells corrode at the levels projected for 2100. Off the U.S. Pacific Northwest, the death of oyster larvae has recently been linked to the upwelling of acidic water there.

In parts of the ocean acidified by underwater volcanoes venting carbon dioxide, scientists have seen alarming signs of what the oceans could be like by 2100. In a 2011 study of coral reefs off Papua New Guinea, scientists writing in the journal Nature Climate Change found that when pH dropped to 7.8, reef diversity declined by as much as 40 percent. Other studies have found that clownfish larvae raised in the lab lose their ability to sniff out predators and find their way home when pH drops below 7.8.

"It's not a problem that can be quickly reversed," said Christopher Langdon, a biological oceanographer at the University of Miami who co-authored the study on Papua New Guinea reefs. "Once a species goes extinct it's gone forever. We're playing a very dangerous game."

It may take decades before ocean acidification's effect on marine life shows itself. Until then, the past is a good way to foresee the future, says Richard Feely, an oceanographer at the National Oceanic and Atmospheric Administration who was not involved in the study. "These studies give you a sense of the timing involved in past ocean acidification events -- they did not happen quickly," he said. "The decisions we make over the next few decades could have significant implications on a geologic timescale."

The study was funded by the U.S. National Science Foundation.

Journal Reference:

Bärbel Hönisch, Andy Ridgwell, Daniela N. Schmidt, Ellen Thomas, Samantha J. Gibbs, Appy Sluijs, Richard Zeebe, Lee Kump, Rowan C. Martindale, Sarah E. Greene, Wolfgang Kiessling, Justin Ries, James C. Zachos, Dana L. Royer, Stephen Barker, Thomas M. Marchitto Jr., Ryan Moyer, Carles Pelejero, Patrizia Ziveri, Gavin L. Foster, and Branwen Williams. The Geological Record of Ocean Acidification. Science, March 2, 2012 DOI: 10.1126/science.1208277