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Acidifying Oceans Threaten Food Chain

Acidic oceans threaten marine food chain
The Guardian (U.K.) Sept. 29, 2005

Rising carbon dioxide in the atmosphere is threatening to make oceans too corrosive for marine organisms to grow protective shells, according to researchers.

If emissions continue unabated, the entire Southern Ocean, which stretches north from the Antarctic coastline, and subarctic regions of the Pacific Ocean will soon become so acidic that the shells of marine creatures will soften and dissolve making them easy targets for predators. Others will not be able to grow sufficient shells to survive.

The loss of shelled creatures at the lower end of the food chain could have disastrous consequences for larger marine animals. North pacific salmon, mackerel, herring, cod and baleen whales all feed on pteropods or sea butterflies, one of the species under imminent threat.


"These are extremely important in the food chain and what happens if they start to disappear is a great unknown," said Jim Orr, lead scientist on the study at the Laboratory for Science of the Climate and Environment in Gif-sur-Yvette, near Paris.


Previous studies have suggested it would take centuries for emissions to acidify the oceans to such an extent, but the latest report, published today in the journal Nature, claims entire ecosystems will be threatened much sooner. "Within decades, there may be serious trouble brewing in these polar oceans," said Dr Orr. "Unlike climate predictions, the uncertainties here are small."


Carbon dioxide is churned out by the burning of fossil fuels and other industrial processes. Each day, the average person burns enough fuel to emit 11kg (about 24lbs) of carbon dioxide, 4kg of which is absorbed by the oceans. When carbon dioxide is taken up by oceans, it strips out carbonate ions dissolved in surface waters, so there is less available for marine organisms to build calcium carbonate shells and exoskeletons from.


Dr Orr and an international team from Britain, the US, Japan and Australia combined recent measurements from oceans with computer models to work out how CO2 levels are likely to change the acidity of oceans in coming decades if emissions continue as expected.


They found that by 2100, the amount of carbonate available for marine organisms would drop by 60%. By 2050, there could be too little carbonate in surface waters for organisms to form shells.


In a follow-up experiment, Victoria Fabry at California State University San Marcos investigated how marine organisms reacted to the predicted changes by immersing live pteropods in sea water as acidic as the models predicted for 2100. She found the shells began to dissolve rapidly, with pits forming on their surfaces and external layers peeling away.


Life in the polar oceans will be first to feel the brunt of rising carbon dioxide levels. Atmospheric carbon dioxide has increased from pre-industrial levels of around 280 parts per million to 380ppm today.


Higher ocean acidity seen as threat to food chain

Cape Cod Times, Oct. 30, 2005


WOODS HOLE - In 50 to 100 years, rising ocean acidity levels might reach a point where the shells of some marine organisms could dissolve or fail to grow altogether.


This scenario sounds like a scene from a scary sci-fi flick, but researchers say this potential phenomenon is directly related to rising carbon dioxide levels in the ocean that could upset the balance of marine ecosystems.


Ocean acidification is occurring at a faster rate than originally predicted, with the potential to harm marine life and disrupt the ocean's food web, according to Scott Doney, a marine chemist with the Woods Hole Oceanographic Institution.


Doney was a member of an international team of 27 marine biologists and chemists from the U.S., Australia, Europe and Japan who analyzed recently compiled data to create models showing how rising acidification might impact ocean life.


'The food web is going to look very different in 50 to 100 years if we continue to burn carbon dioxide at current levels,' Doney said.

Within that time span, the team concluded in a study published last month in the journal Nature, there could be 'severe consequences' for so-called marine calcifying organisms that build external skeletal material from calcium carbonate, the basic building block of limestone.


Calcifying organisms, which include sea urchins, cold-water corals, coralline algae and plankton known as pteropods, are most threatened by acidification, the study found.


Collectively, these organisms provide essential food and habitat to other marine life, which means their demise could affect entire ocean ecosystems.


'There's a lot of plants and animals that make their shells out of calcium carbonate,' Doney said.


The research team projected that the ocean's coldest waters, such as in the Weddell Sea of Antarctica, will become corrosive to pteropods much sooner than originally thought.


Pteropods, also known as sea butterflies, belong to a subclass of small marine gastropod mollusks that propel themselves through the water column by beating wing-like structures.


Ocean acidification occurs when carbon dioxide - a product of combustion and respiration - combines with seawater. The addition of carbon dioxide, or CO2, to the ocean lowers the pH of seawater.

The average pH value for the ocean remains slightly basic at 7.8, with global variations ranging from 7.5 to 8.5.


The pH scale measures how acidic or basic a substance is, in this case seawater. Values between 1-6 are considered acidic, while values between 8-14 are considered alkaline, or basic.


As acidity levels rise, the shells of pteropods may simply dissolve as atmospheric CO2 reaches the levels projected in about 50 years, the study concluded.


Over the past 200 years, the pH of surface seawater has declined by 0.1 units. By 2100, that level is expected to drop by another 0.5 units if CO2 emissions continue to rise at the projected rate.


If that rate is maintained, scientists say it will produce ocean acidity levels unseen for millions of years. In addition, researchers say these changes in ocean chemistry could reduce the ocean's ability to absorb CO2 from the atmosphere and accelerate global warming.


'Up until now, we've mostly thought of climate change in terms of changes in temperature or rainfall,' Doney said, adding that the ocean is equally susceptible to climate modifications.


The ocean serves as a big CO2 repository, Doney said. And the research conducted by his team and a host of others 'shows the negative consequences of the ocean being a big sink,' he said.


'We have recognized for several decades that the buildup of carbon dioxide in the atmosphere from fossil-fuel combustion will lead to ocean acidification,' Doney said. 'We know it's due to human activities; there's no controversy to that.'


Previous studies have noted that changes in ocean chemistry are harmful to warm-water species such as corals that build shells out of calcium carbonate, though it typically takes hundreds of years for such problems to occur.


However, Doney's team focused on the impact to cold-water ecosystems, which, he said, 'appear to be even more sensitive to ocean acidification and on shorter time-scales of the next few decades.'


As atmospheric CO2 continues to rise, scientists project that by the end of this century the entire Southern Ocean - comprising southern portions of the Atlantic, Pacific and Indian oceans - and northern sections of the Pacific Ocean will become so corrosive that many calcifying organisms may not be able to grow shells.


Scientists say this problem could be especially pronounced in polar waters. If populations of polar pteropods decline significantly, researchers say it could trigger a chain reaction throughout the entire ocean ecosystem. Pteropods are an important part of the diet of many marine species, including whales.


Cold-water corals already imperiled by open-ocean trawling will be further threatened by ocean acidification, according to researchers. The corals are abundant in northern portions of the Atlantic Ocean, where they form massive deep reefs.


Doney's team predicted polar and subpolar Atlantic waters will become mostly corrosive by the end of this century, due to fossil-fuel emissions.


Meanwhile, researchers from the Royal Society - the British equivalent of the U.S. National Academy of Sciences - in a report this year determined that reducing CO2 emissions is the only way to stem rising ocean acidification.


The report found that excess atmospheric CO2 from fossil-fuel burning has increased the acidity of the world's oceans to a level irreversible in our lifetime.


Scientists on both sides of the Atlantic fear marine life won't be able to adapt to these changes quickly enough, with higher CO2 levels making it harder for fish and shellfish to breathe and reproduce.

Many in the international scientific community now view ocean acidification as a so-called sister problem to global climate change, particularly since the world's oceans have absorbed about 50 percent of all man-made CO2 produced in the past 200 years.


According to WHOI data, the average person on the planet burns enough fossil fuel each day to emit 24 pounds of carbon dioxide into the atmosphere, 9 pounds of which is taken up by the ocean.


As a marine chemist, Doney said, 'My role is to provide information to society, and not just to the policymakers.'