March 2, 2012
Ocean Acidification Rapid Compared To Ancient Times
The world´s oceans may be acidifying more rapidly than they have at any time in the past 300 million years due to high levels of pollution, according to research published this week in the journal Science.
Researchers, led by Columbia University´s Lamont-Doherty Earth Observatory and the University of Bristol, assessed a number of climate change events in Earth´s history, including an asteroid impact that wiped out the dinosaurs 65 million years ago.
They warn that too much carbon dioxide in the atmosphere is the key factor that will make the oceans more acidic and imperil key parts of the marine food chain. It has happened before, and can happen again, they warn. In fact, ocean acidification appears to be occurring now at an unprecedented pace.
The study is the first of its kind to survey the geologic record for evidence of ocean acidification over such a large time period.
“What we´re doing today really stands out in the geologic record,” said study leader BÃ¤rbel HÃ¶nisch, a paleoceanographer at Columbia University. “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 world´s oceans act like a sponge, drawing excess carbon dioxide from the air, soaking it up. 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 plankton need for reef and shell-building.
In their review of hundreds of paleoceanographic studies, the team of researchers found evidence for only one period of time in the last 300 million years when the oceans changed as fast as they are today: the Paleocene-Eocene Thermal Maximum, or PETM.
The PETM appears as a brown layer of mud in the ocean sediments where thick deposits of white plankton fossils are found. About 56 million years ago, a massive surge of carbon built up in the atmosphere warmed the planet and deeply acidified the world´s oceans.
The atmospheric carbon doubled to 1,800 parts per million over the course of 5,000 years, raising the average global temperature by 6 degrees Celsius (nearly 11 degrees F). The carbonate plankton shells littering the seafloor dissolved, leaving the brown clay layer that scientists see in sediment cores today.
Quickly acidifying seawater not only eats away at coral reefs, which provide habitat for many animals and plants, but can also interfere with small organisms that feed commercial fish like salmon.
Acidification going on today may be worse, as much as ten times worse, than at any of four major mass extinctions that have previously occurred when natural surges of carbon caused from asteroid impacts and volcanic eruptions caused global temperatures to soar, said the study authors.
“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 study co-author Andy Ridgwell of Bristol University.
Human activities, including the burning of fossil fuels, have increased the level of atmospheric carbon 392 parts per million from about 280 parts per million at the start of the Industrial Revolution.
HÃ¶nisch noted that during the PETM acidification for each century was about .008 unit on the pH scale. Many corals and single-celled organisms went extinct due to the strong pH levels.
Ellen Thomas, a Yale University paleoceanographer, and coauthor of the study, said as many as half of all species of benthic foraminifera -- one-celled organisms that live on the ocean floor -- went extinct during the PETM, suggesting that deep-sea organisms higher up on the food chain may have also died out.
“It´s really unusual that you lose more than 5 to 10 percent of species,” she said.
By contrast, in the 20th century, oceans acidified by .1 unit of pH, and are projected to increase to the rate of .2 or even .3 pH by the year 2100, according to the study.
The UN Intergovernmental Panel on Climate Change (IPCC) projects temperature increases of 3.2 to 7 degrees F by the end of 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,” HÃ¶nisch said.
Of course there are skeptics who claim current climate change is not human caused, but by natural events such as those of the past. HÃ¶nisch 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 5,000 years, compared to one century today.
Richard Feely, an oceanographer at the US National Oceanic and Atmospheric Administration (NOAA) 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 told MSNBC in a statement. “The decisions we make over the next few decades could have significant implications on a geologic timescale.”
The study also found two other analogies for modern day ocean acidification -- the extinctions triggered by massive volcanism at the end of the Permian era 252 million years ago and the Triassic era 201 million years ago. However, researchers say that because ocean sediments older than 180 million years have been recycled back into the deep Earth, it gives them fewer records to work with.
On that note, researchers have made reasonable estimates that around 96 percent of life went extinct during the “Great Dying” at the end of the Permian. Massive eruptions are thought to have triggered the greatest extinction level event in Earth´s history.
At the end of the Triassic, a second burst of mass volcanism associated with the break-up of the supercontinent Pangaea doubled atmospheric carbon that led to another wave of extinction. That event caused the collapse of coral reefs and killed off an entire class of sea creatures, known as conodonts.
The study found that the most notorious of all extinctions, however, is the one that ended the Age of the Dinosaurs 65 million years ago when an asteroid collided with Earth. But scientists have not associated that extinction event with ocean acidification.
The prehistoric asteroid impact 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.
Scientists have tried to simulate modern ocean acidification in the lab, but have not been able to produce accurate results.
Dr Daniela Schmidt, a Royal Society Research Fellow in Bristol University´s School of Earth Sciences, the study´s evidence compiler, said: “Laboratory experiments can tell us about how individual marine organisms react, but the geological record is a real time experiment involving the entire ocean.”
The researchers noted there are other alternatives to investigating ocean acidification, such as studying natural carbon seeps from offshore volcanoes that are producing the acidification levels expected by the year 2100.
A recent study of coral reefs off the coast of Papua New Guinea found that during long-term exposure to high carbon dioxide and pH 0.2 units lower than today, reef biodiversity and regeneration suffered.
A UN Environment Program report, released in 2010, warned that carbon emissions from fossil fuels 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 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.
The study includes contributions from 21 scientists from the United States, Britain, Spain, Germany and the Netherlands. The study was funded by the National Science Foundation (NSF), Past Global Changes (PAGES), the USC Wrigley Institution Catalina Island, and the USC Dornsife College of Letters Arts and Sciences, as well as NSERC, SEPM, AAPG, AMNH, GSA, Evolving Earth Foundation, IAS, and the Paleontological Society.
On the Net:
- Lamont-Doherty Earth Observatory
- University of Bristol
- Yale University
- UN Intergovernmental Panel on Climate Change (IPCC)
- US National Oceanic and Atmospheric Administration (NOAA)