Growing Acid Problem Thins Shells of Ocean Creatures

Andrea Thompson, LiveScience.com 8 Mar 09

Scientists have started to see some of the expected effects of Earth's increasing carbon dioxide burden: The shells of microscopic animals in the ocean are becoming thinner thanks to the ocean's absorption of some of that excess carbon dioxide, a new study shows.

The shells of those creatures studies are about one-third lighter.

As carbon dioxide from the burning of fossil fuels has accumulated in the atmosphere, some of it has been absorbed by the ocean. As the gas dissolves in the water, it forms a week acid (the same kind that's in bubbly soft drinks), causing the ocean itself to become gradually more acidic.

As ocean water becomes more acidic, it also lowers the amount of calcium carbonate available to aquatic animals that use the mineral to build shells or skeletons, such as corals. These organisms can be important links in the marine food chain.

Scientists have predicted that the increase in ocean acidification could significantly reduce the ability of these creatures to build their casings, potentially devastating them and causing rippling effects through the ecosystem. But "until now the potential impact on ocean chemistry and marine life has been based on projections and models" and laboratory experiments, said leader of the new study, Will Howard of the Antarctic Climate & Ecosystems Cooperative Research Centre in Australia.

With funding from the Australian Government Department of Climate Change, Howard and his colleagues collected microscopic marine animals - called planktonic foraminifera, or forams - from the South Tasman Rise region of the Southern Ocean. They compared the weights of the shells of these modern forams to those trapped in ocean sediments before the industrial revolution and the build-up of carbon dioxide.

They found that the modern shell weights were 30 to 35 percent lower than those of the older forams.

The researchers also found a link between higher atmospheric carbon dioxide levels and lowr shell weights in a 50,000-year-long record from a marine sediment core (a long column drilled out from the ocean floor that shows layers of sediments as they were laid down over time).

"Today's results publish the first evidence from nature, rather than a laboratory, that the two are linked," Howard said.

The findings are detailed in the March 8 issue of the journal Nature Geoscience.

If the results are applicable to the rest of the ocean, they could lead to large ecosystem shifts.

"The potential knock-on effects pose significant implications for the oceanic food chain and the findings are a worrying signal of what we can expect to see elsewhere in the future," Howard said. "The Southern Ocean is giving us a strong indication of an acidification process that will spread throughout the global ocean."

Rising ocean acidity cutting shell weights - study
David Fogarty, Reuters 8 Mar 09;

SINGAPORE, March 9 (Reuters) - Acidifying oceans caused by rising carbon dioxide levels are cutting the shell weights of tiny marine animals in a process that could accelerate global warming, a scientist said on Monday.

William Howard of the University of Tasmania in Australia described the findings as an early-warning signal, adding the research was the first direct field evidence of marine life being affected by rising acidity of the oceans.

Oceans absorb large amounts of CO2 emitted by mankind through the burning of fossil fuels. The Southern Ocean between Australia and Antarctica is the largest of the ocean carbon sinks.

But scientists say the world's oceans are becoming more acidic as they absorb more planet-warming CO2, disrupting the process of calcification used by sea creatures to build shells as well as coral reefs.

Laboratory experiments had earlier predicted these impacts.

Howard and co-author Andrew Moy, also of the University of Tasmania, studied the shells of tiny amoeba-like animals called foraminifera in the Southern Ocean and compared the shell weights to data from sediment core records dating back 50,000 years.

Their findings, which appear in the latest issue of Nature Geoscience, show shell weights of modern-day foraminifera falling between 30 and 35 percent.

"The big challenge will be how do we scale up this kind of change to understand what it means for the ecosystem. And to be honest, we don't know yet," he told Reuters.

The implications for climate change were clearer, he said.

CARBON TRANSFER

Foraminifera, which live on the ocean's surface, play a major role in trapping CO2 and transporting it to the ocean depths where it can be locked away for decades or more.

Disrupting this process could accelerate climate change.

Foraminifera, he said, comprise a significant proportion of all the carbonate shell material produced in the ocean.

"Their presence and production helps facilitate the sinking of organic matter from the surface layers of the ocean into the deep ocean," said Howard, project leader of the ocean acidification team at the Antarctic Climate and Ecosystems Cooperative Research Centre.

"That translates into the transfer of carbon from the atmosphere into the deep ocean. If these organisms are not calcifying as much it may translate into a reduction in the carbon transfer from the atmosphere."

Oceans are alkaline and Howard said that a century ago, oceans had a pH of 8.2, with a pH of 0 being battery acid and 13 being household bleach.

Oceans were now just under 8.1, he said.

"We've already changed the pH of the ocean by about 0.1. At these levels this represents about a 30 percent increase in the acidity of the oceans," Howard said.

"Anything that makes a shell is going to have a hard time making that shell."

The big challenge was understanding the ocean's response to climate change and what happens to ecosystems. The Southern Ocean was one of the first areas scientists will see this kind of shift, Howard said, in part because it is a major carbon sink.

"There's no question acidification is going to affect every part of the ocean because every part of the ocean is taking up CO2 from man-made emissions," he said. (Editing by Paul Tait)

Proof on the Half Shell: A More Acid Ocean Corrodes Sea Life
Ocean acidification is taking a toll on tiny shell-building animals
David Biello, Scientific American 8 Mar 09;

The shells of tiny ocean animals known as foraminifera—specifically Globigerina bulloides—are shrinking as a result of the slowly acidifying waters of the Southern Ocean near Antarctica. The reason behind the rising acidity: Higher carbon dioxide (CO2) levels in the atmosphere, making these shells more proof that climate change is making life tougher for the seas' shell-builders.

Marine scientist Andrew Moy at the Antarctic Climate & Ecosystems Cooperative Research Center (ACE) in Hobart, Tasmania, and his Australian colleagues report in Nature Geoscience this week that they made this finding after comparing G. bulloides shells in ocean cores collected along the South Tasman Rise in 1995 with samples from traps collected between 1997 and 2004. The cores provide records that stretch back 50,000 years.

"We knew there were changes in carbonate chemistry of the surface ocean associated with the large-scale glacial-interglacial cycles in CO2 [levels], and that these past changes were of similar magnitude to the anthropogenic changes we are seeing now," says study co-author William Howard, a marine geologist at ACE. "The Southern [Ocean] works well [to study this issue] as it is a region where anthropogenic CO2 uptake, and thus acidification, has progressed more than in other regions. Other variables, such as temperature, have changed, but not as much."

The researchers found that modern G. bulloides could not build shells as large as the ones their ancestors formed as recently as century ago. In fact, modern shells were 35 percent smaller than in the relatively recent past—an average of 17.4 micrograms compared with 26.8 micrograms before industrialization. (One microgram is one millionth of a gram; there are 28.3 grams in an ounce.)

"We don't yet know what impact this will have on the organisms' health or survival," Howard says, but one thing seems clear: the tiny animals won't be storing as much CO2 in their shells in the form of carbonate. "If the shell-making is reduced, the storage of carbon in the ocean might be, as well."

That's bad news for the climate, because the ocean is responsible for absorbing at least one quarter of the CO2 that humans load into the air through fossil fuel burning and other activities—and it is the action of foraminifera and other tiny shell-building animals, along with plants like algae that lock it away safely for millennia.

It will be harder to get such a clear sign in a shell from other ocean regions—as variables like temperature and the amount of minerals available can significantly change the chemistry of a given ocean region. As Howard noted, the Southern Ocean has absorbed lots of manmade CO2 while temperatures and nutrients have not changed as much, making it more ideal for studying ocean acidification than other areas. Scientists examining foraminifera in the Arabian Sea, however, have found similar results, and Howard speculates the situation may be similar in the North Atlantic region, because it also absorbs a significant chunk of manmade CO2.

Howard says that CO2 emissions must be cut or captured and stored permanently in some fashion to halt this gradual acidification of the world's oceans. In the meantime, he adds, it's likely that many of the other shell-building oceanic animals are suffering similar fates as G. bulloides.

World's oceans face an acid test
Roger Harrabin, BBC News 10 Mar 09;

Carbon dioxide emissions from modern society are turning the ocean more acidic and some sea creatures are already suffering, according to research to be discussed at a major global science conference.

Studies in the Southern Ocean by Australian scientists found that the shells of tiny amoeba-like creatures called foraminifera have become thinner since the Industrial Revolution.

The scientists say this shows that increasing CO2 uptake in the ocean has a direct effect on the ability of micro-organisms to make shells.

The paper, being presented at the University of Copenhagen's International Scientific Congress on Climate Change, will add to a rising tide of scientific concern over ocean acidification.

Already, ocean acidity has increased about 32% since pre-industrial times. By 2100, it is projected to have increased by perhaps 130%, which scientists fear could have a potentially catastrophic impact on marine life.

In a study published in Nature Geoscience, William Howard, Andrew Moy and colleagues collected the shells of the organisms as they fell towards the sea floor.

They compared the mass of the shells, about the size of a grain of sand, to the mass of older shells on the sea floor.

The modern shells were 30 to 35% lighter than those that formed prior to the industrial period.

The researchers from the University of Tasmania attribute the change to the acidification of the Southern Ocean, which they say is driven by the uptake of CO2 from factories, cars and power stations.

Mussel test

Other scientists are wary of attributing all the blame for the acidification of the Southern Ocean on humans - there is major upwelling of more acidic water from the deep seas.

Waters from the deep ocean are colder than the surface waters and contain more carbon, which mixes with the seawater to form carbonic acid.

But this will not diminish concern over the problem of ocean acidification in general.

Some of the cutting-edge work in this new field of science is being done at Plymouth Marine Laboratory (PML) in south-west England.

A blustery wind is cutting in from the English Channel when we go to meet the laboratory's Steve Widdicombe, who is gathering mussels from the estuary of the River Exe.

He will use the molluscs to test how they will respond to increasing acidity as CO2 emissions rise.

The Exe is nearly a mile wide at this point and Steve has to work quickly because the tide is about to turn.

The specimens are taken back to the lab where their blood is sampled with a needle thrust through a gap in their shell.

An enzyme test indicates the strength of their immune system.

Then they are placed in tanks where acidity has been increased by bubbling CO2 through the water.

This is a long-term test, and Dr Widdicombe suspects it will show that mussels will be seriously compromised by the levels of acidification expected by 2100.

A previous experiment at PML, published in the Proceedings of the Royal Society, showed that starfish would be killed by a pH of 7.7, which may occur by 2100 if CO2 emissions continue to rise.

Ocean pH levels have previously remained roughly constant at 8.2 for at least half a million years.

"We found that relatively small changes in pH (acid/alkali balance) for a long period cause creatures to use up energy trying to respond to the change," Dr Widdicombe says.

"The more we look at long-term chronic effects of acidification, the more worrying it becomes," he adds.

"It's a continuous stress. We can all respond to temporary stress but if we are under continuous stress we get sick."

The big question with acidification is whether calcifying organisms that need more alkaline conditions to create their shells will be able to adapt to more acidic waters.

"We need to look at evolutionary timescales," Dr Widdicombe explains.

"No-one has done the studies on what if anything would drive the ability to adapt.

"I personally think evolutionary timetables are simply too short to respond to the sort of changes we are making. I really fear the worst."

OCEAN ACIDIFICATION

• Up to one half of the CO2 released by burning fossil fuels over the past 200 years has been absorbed by world's oceans
  
• This has lowered its pH by 0.1
  
• pH is the measure of acidity and alkalinity
  
• The vast majority of liquids lie between pH 0 (very acidic) and pH 14 (very alkaline); 7 is neutral
  
• Seawater is mildly alkaline with a "natural" pH of about 8.2
  
• The IPCC forecasts that ocean pH will fall by "between 0.14 and 0.35 units over the 21st Century, adding to the present decrease of 0.1 units since pre-industrial times"

With an explanation of acid oceans.