Sunday, July 3, 2011
ACID Oceans by CO2...!
ACID OCEANS AND CO2
CO2 and bad gases from Jets-Cars-Coal Generators-Tar Sands extraction-Methane of Cattle-dESALINATION PLANTS-THERMOELECTRIC PLANTS
Acid Oceans Threatening Marine Food Chain, Experts Warn
Scott Norris in San Francisco, California
for National Geographic News
February 17, 2007
The world's oceans are turning acidic due to the buildup of carbon dioxide (CO2) in the atmosphere, and scientists say the effects on marine life will be catastrophic.
In the next 50 to 100 years corrosive seawater will dissolve the shells of tiny marine snails and reduce coral reefs to rubble, the researchers say (coral photos, facts, more).
Four leading marine experts delivered this grim prognosis yesterday at the annual meeting of the American Association for the Advancement of Science in San Francisco, California.
The scientists stressed that increased ocean acidity is one of the gravest dangers posed by the buildup of atmospheric CO2.
"Ocean chemistry is changing to a state that has not occurred for hundreds of thousands of years," said Richard Feely of Seattle's Pacific Marine Environmental Laboratory.
"Shell-building by marine organisms will slow down or stop. Reef-building will decrease or reverse."
Already, Feely said, ocean acidity has increased about 30 percent since industrialization began spurring harmful carbon emissions centuries ago. Unless emissions are reduced from current levels, an increase of 150 percent is predicted by 2100.
Such an increase would make the oceans more acidic than they've been at any time in the last 20 million years, he added.
Sea Creatures' Uncertain Fate
The organisms most directly affected are those that build hard shells or other mineral structures of calcium carbonate. These include numerous species of corals, marine snails, and crust-building algae.
As oceans absorb CO2 from the air, the gas reacts with water to produce carbonic acid. The acid in turn consumes the carbonate that sea creatures need to build their shells.
"This is a problem that no living corals have encountered in their past evolutionary history," said Charlie Veron, of the Australian Institute of Marine Science.
Acid Oceans Threatening Marine Food Chain, Experts Warn
Over time, coral reefs have been able to adjust to changes in ocean temperature and sea level, Veron said. But acidification appears to be a problem that the ancestors of today's corals were unable to solve.
Mass extinctions of marine life in the distant past, he said, were probably caused by chemical changes similar to those happening today.
"It took coral reefs about four to ten million years to recover each time," he added.
In shallow waters where most corals presently grow, carbonate is not in short supply. But at greater depths carbonate concentration decreases until it reaches a point beyond which shell- and reef-production is no longer possible.
That critical threshold is rising closer to the surface as oceans grow increasingly acidic, limiting the depths at which corals and other organisms can live.
Feely said that this limit has already risen several hundred meters, particularly in the Indian and Pacific oceans. Recent measurements in the Gulf of Alaska found that carbonate was in short supply less than 325 feet (100 meters) below the surface.
James Orr, of the International Atomic Energy Agency's Marine Environmental Laboratory in Monaco, said that by the end of this century, shell- and reef-building sea creatures will be unable to live at any depth across a huge area of the world's oceans.
"Two-thirds of cold-water corals will be exposed to corrosive waters by 2100," Orr said.
Initial concerns about ocean acidification have focused on corals, which are already experiencing die-offs and "bleaching" due to warmer water temperatures.
(Read related story: "Global Warming Has Devastating Effect on Coral Reefs, Study Shows".)
Unfortunately, Veron said, "the very corals that will escape mass bleaching are those most prone to the effects of ocean acidification."
Scientists now recognize that the danger extends to other organisms as well. Robert Buddemeier, of the Kansas Geological Survey, said mineral-producing "coralline" algae are especially vulnerable.
The algaes' cementlike secretions are the "glue" that helps hold coral reefs together, Buddemeier said, and also help stabilize coastlines in nonreef areas.
Perhaps even more alarming is the threat to marine snails called pteropods.
Populations of these tiny creatures can reach up to ten thousand individuals per cubic meter (35 cubic feet) in the Southern Ocean. Their loss, Orr said, would have far-reaching effects.
"They're an integral component of marine food webs, a huge food source for many marine predators," he said.
The snails' calcium carbonate shells are so thin they are virtually transparent, Orr added, which makes them particularly vulnerable.
"Pteropod shells can start to dissolve in 24 hours," he said, "under [the seawater] conditions we expect for 2100."
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Pollution creating acid oceans
The world's oceans are becoming acidic at a faster rate than at any time in the last 65 million years, threatening marine life and food supplies across the globe, according to a new study.
Researchers from the University of Bristol looked at how levels of acid in the ocean have changed over history.
They found that as ocean acidification accelerated it caused mass extinctions at the bottom of the food chain that could threaten whole ecosystems in the future.
The rapid acidification today is being caused by the massive amount of carbon dioxide being pumped out by cars and factories every year, which is absorbed by the water. Since the industrial revolution acidity in the seas have increased by 30 per cent.
The last time such a fast change occurred is thought to be 65 million years ago, when some natural event caused ocean acidification and the dinosaurs died out.
The study looked at sediments from around 55 million years ago, when temperature rose by up to 6C and acidification was occurring at a similar rate as today.
It found widespread extinction of tiny organisms that live on the bottom of the ocean. Ocean acidification can dissolve the carbonate shells of marine organisms and cause muscle wastage and dwarfism in other species.
Andy Ridgwell, lead author of the paper published in Nature Geoscience, said it could mean problems for humans in the future.
"Unlike surface plankton dwelling in a variable habitat, organisms living deep down on the ocean floor are adapted to much more stable conditions. A rapid and severe geochemical change in their environment would make their survival precarious.
"The widespread extinction of these ocean floor organisms during the Paleocene-Eocene greenhouse warming and acidification event tells us that similar extinctions in the future are possible," he said.
Dr Ridgwell said acidification is actually occurring much faster today than in the examples they looked at from the past therefore "exceeding the rate plankton can adapt" and theatening the basis of much of marine life. This would mean fish and other creatures further up the food chain that human beings eat may be affected as soon as the end of this century.
"There is lots of concern about major disruption to ecosystems. Certainly coral reefs will be eroded, that has an impact on other species. We could see marine ecosystems affected this century," he said.
:: A separate study published in Geoscience found that the glaciers on Greenland are melting much faster than expected because of ocean currents bringing warm water into the area. If the warming continues it could cause sea levels to rise by 3ft, three times as much as previous estimates, by 2100.
It is well known that burning of fossil fuels has increased CO2 in the atmosphere from about 275 ppm (.0275%) to 378 ppm (.0375%) since the Industrial Revolution began in the 1800s. This extra CO2 has contributed to the observed rise in global temperatures of 0.6° C via the greenhouse effect. What is less well known, and is discussed in detail in a March 2006 article in Scientific American called "The Dangers of Ocean Acidification", is that a tremendous amount of the CO2 emitted by fossil fuel burning winds up in the oceans. The oceans have absorbed 48% of all the CO2 emitted since 1800, according to a study published by Sabine et al. in 2004 in Science. Without the action of the oceans to absorb so much of our waste gases we've pumped into the atmosphere, Earth would be a much warmer planet.
Figure 1. Changes in surface oceanic concentration of CO2 (left, in micro-atmospheres), and pH (right) from three locations. Blue is at 29°N, 15°W in the Canary Islands; green is at 23°N, 158°W in the Hawaiian Islands, and red is 31°N, 64°W at Bermuda. The mean seasonal cycle was removed from the data, and the thick black line is smoothed to not include any information less than 1/2 year in period. Note that as CO2 has risen, the pH of the oceans has fallen as the waters become more acid. Image credit: IPCC 2007: The Physical Basis for Climate Change.
The price paid
The oceans are paying a price for this service, though. When CO2 dissolves into the ocean, it creates carbonic acid. The oceans have dissolved so much CO2 during the past 150 years that the acidity of the oceans' surface waters has substantially increased. Before the Industrial Revolution, pH of the ocean surface waters ranged from 8.0 to 8.3 (pH decreases as acidity increases). Ocean pH has dropped a full 0.1 units since then, to the 7.9 to 8.2 range. Unless significant cuts in CO2 emissions are realized in the next few decades, the pH will fall another 0.14-0.35 units by the year 2100 as the oceans continue to acidify, according to the Intergovernmental Panel on Climate Change (IPCC) 2007 Synthesis Report. A 2005 report by the Royal Society of the UK projects the decrease by 2100 will be 0.5 pH units, and notes that it will take more than 10,000 years for the ocean to return to its pre-1800s acidity level.
Higher acidity in the ocean creates problems for a number of organisms. Corals and other creatures that build shells out of calcium carbonate are particularly vulnerable, since they cannot form their shells if the acidity passes a critical level--their shells will dissolve. Several shell-building planktonic organisms, such as coccolithophorids, pteropods, and foraminifera, form an important basis of the food chain in the cold waters surrounding Antarctica. The effect of ocean acidification is more pronounced at colder temperatures, and it is believed that these important micro-organisms will die out or be forced to move to warmer waters in order to survive in the coming decades. What this will mean to the birds, fish, marine mammals, and humans that depend on the oceans for their livelihood is unknown. Major die-offs of many species are quite possible, which would have serious impacts for nations such as Chile, where marine-related activities provide more jobs than any other sector of the economy. The effects on the Atlantic are expected to be delayed several decades compared to the Southern Hemisphere oceans, but are still expected to be significant by the end of the century.
Corals in tropical and subtropical waters will not dissolve in the more acidic waters, but the increased acidity will cause them to grow more slowly. When this added stress is added to the already significant impacts of coral bleaching from global warming, pollution, and destruction due to dynamiting of reefs to harvest fish, the outlook for coral reefs this century is exceedingly bleak. About one-third of the world's coral reefs have already been damaged or destroyed in the past century, with another one-third at serious risk of destruction by 2030.
The effect of higher oceanic acidity and CO2 levels on higher organisms such as fish, birds, and sea mammals is largely unknown. A 2008 study found that purple sea urchins are unable to build their spiny shell in acid water. Fish are also likely to be adversely impacted, since high levels of CO2 are sometimes used by researchers to euthanize fish.
Higher dissolved CO2 in the oceans will benefit a number of species. For example, many higher plants such as sea grasses use dissolved CO2 directly to help them grow, and should prosper from higher CO2 levels in the ocean, just as many plants on land are expected to benefit from higher atmospheric CO2 levels. Some types of phytoplankton will probably benefit as well, although laboratory studies on this are not conclusive. Other species of phytoplankton will likely be unaffected. The Royal Society of the UK report concluded, "the increase of CO2 in the surface oceans expected by 2100 is unlikely to have any significant direct effect on photosynthesis or growth of most micro-organisms in the oceans."
What the future holds
Ocean life can adapt to higher acidity. One study (Spivack et al., 1993) found that pH levels in the ocean 7.5 million years ago were about 7.4, well below today's pH. The big concern with the current increase in acidity and drop of ocean pH levels is that it is being compressed into such a short period of time. Past changes in oceanic acidity have presumably occurred over tens of thousands of years, giving time for life to adapt. A July 2006 study, Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers: A Guide for Future Research, put out by 50 of the world's leading experts in ocean chemistry, warned that modern sea life will probably adapt poorly to more acidic waters. This is because the oceans have not been as acidic as they now are for at least 650,000 years, and probably millions of years beyond that. Modern ocean life has evolved for a great deal of time under balanced ocean conditions, and the current change may occur so fast that a partial collapse of the food chain in some regions may occur. One note of optimism: similar concerns were voiced when the Antarctic ozone hole opened up, exposing phytoplankton in the Southern Hemisphere oceans to a rapid and unprecedented increase in levels of damaging ultraviolet radiation. It was widely feared that this increase in UV light would destroy enough phytoplankton to trigger a collapse of the food chain in the waters off of Antarctica. This has not happened. One study (Smith et. al., 1992) found a 6-12% decrease in phytoplankton during the time the ozone hole opens up, typically about 10-12 weeks of the year. So, at least in this one case, the marine ecosystem was able to adapt to a rapid, unprecedented change and not collapse.
As is the case with many aspects of human-caused climate change, the dangers are enormous, but poorly understood. In the words of the Dr. Doney's Scientific American article, "dramatic alterations in the marine environment appear to be inevitable." The Royal Society's article cautions, "research into the impacts of high concentrations of CO2 in the oceans is in its infancy and needs to be developed rapidly." The report goes on to state, "Ocean acidification is a powerful reason, in addition to that of climate change, for reducing global CO2 emissions. Action needs to be taken now to avoid the risk of irreversible damage to the oceans. We recommend that all possible approaches be considered of prevent CO2 reaching the atmosphere. No option that can make a significant contribution should be dismissed."
Sabine et al., "The Oceanic Sink for Anthropogenic CO2", Science, 305, 367-371, 16 July 2004.
Smith, R., B. Prezelin, K. Baker, R. Bidigare, N. Boucher, T. Coley, D. Karentz, S. MacIntyre, H. Matlick, D. Menzies, M. Ondrusek, Z. Wan, and K. Waters, "Ozone depletion: Ultraviolet radiation and phytoplankton biology in Antarctic waters", Science, 255, 952, 1992.
Spivack, A.J., You, C., and H.J. Smith, "Foraminiferal boron isotope ratios as a proxy for surface ocean pH over the past 21 Myr", Nature, 363, 149-151, 13 May 1993, doi:10.1038/363149a0.
Acid Oceans From Carbon Dioxide Will Endanger One Third Of Marine Life, Scientists Predict
ScienceDaily (Oct. 19, 2007) — The world’s oceans are becoming more acid, with potentially devastating consequences for corals and the marine organisms that build reefs and provide much of the Earth’s breathable oxygen.
The acidity is caused by the gradual buildup of carbon dioxide (CO2) in the atmosphere, dissolving into the oceans. Scientists fear it could be lethal for animals with chalky skeletons which make up more than a third of the planet’s marine life.
“Recent research into corals using boron isotopes indicates the ocean has become about one third of a pH unit more acid over the past fifty years. This is still early days for the research, and the trend is not uniform, but it certainly looks as if marine acidity is building up,” says Professor Malcolm McCulloch of CoECRS and the Australian National University.
“It appears this acidification is now taking place over decades, rather than centuries as originally predicted. It is happening even faster in the cooler waters of the Southern Ocean than in the tropics. It is starting to look like a very serious issue.”
Corals and plankton with chalky skeletons are at the base of the marine food web. They rely on sea water saturated with calcium carbonate to form their skeletons. However, as acidity intensifies, the saturation declines, making it harder for the animals to form their skeletal structures (calcify).
“Analysis of coral cores shows a steady drop in calcification over the last 20 years,” says Professor Ove Hoegh-Guldberg of CoECRS and the University of Queensland. “There’s not much debate about how it happens: put more CO2 into the air above and it dissolves into the oceans.
“When CO2 levels in the atmosphere reach about 500 parts per million, you put calcification out of business in the oceans.” (Atmospheric CO2 levels are presently 385 ppm, up from 305 in 1960.)
“It isn’t just the coral reefs which are affected – a large part of the plankton in the Southern Ocean, the coccolithophorids, are also affected. These drive ocean productivity and are the base of the food web which supports krill, whales, tuna and our fisheries. They also play a vital role in removing carbon dioxide from the atmosphere, which could break down.”
Professor Hoegh-Guldberg said an experiment at Heron Island, in which CO2 levels were increased in the air of tanks containing corals, had showed it caused some corals to cease forming skeletons. More alarmingly, red calcareous algae – the ‘glue’ that holds the edges of coral reefs together in turbulent water – actually began to dissolve. “The risk is that this may begin to erode the Barrier of the Great Barrier Reef at a grand scale,” he says.
“As an issue it’s a bit of a sleeper. Global warming is incredibly serious, but ocean acidification could be even more so.”
Acid oceans will be among the issues explored by Australia’s leading coral scientists at a national public forum at the Shine Dome in Canberra, Australia, October 18. The Coral Reef Futures 07 Forum is on October 18-19, 2007 and is hosted by the ARC Centre of Excellence for Coral Reef Studies (CoECRS).
Australia’s coral reefs, particularly the Great Barrier Reef, Ningaloo Reef, and Lord Howe Island World Heritage Area, are national icons, of great economic, social, and aesthetic value. Tourism on the Great Barrier Reef alone contributes approximately $5 billion annually to the nation’s economy. Income from recreational and commercial fishing on Australia’s tropical reefs contributes a further $400 million annually. Consequently, science-based management of coral reefs is a national priority.
Globally, the welfare of 500 million people is closely linked to the goods and services provided by coral reef biodiversity. Uniquely among tropical and sub-tropical nations, Australia has extensive coral reefs, a small population of relatively wealthy and well-educated citizens, and well developed infrastructure. Coral reef research is one area where Australia has the capability, indeed the obligation, to claim world-leadership.
The Acid Ocean – the Other Problem with CO2 Emission
— david @ 2 July 2005
The Royal Society has just issued a summary report on the effects of CO2 on the pH chemistry of seawater and aquatic organisms and ecosystems. In addition to its pivotal role in the atmosphere in the regulation of global climate, CO2 and its sister chemical species, HCO3- and CO32- comprise the carbonate buffer system which regulates the pH of seawater. The new report can be found here. Acidifying the ocean is particularly detrimental to organisms that secrete shell material made of CaCO3, such as coral reefs and a type of phytoplankton called coccolithophorids [Kleypas et al., 1999]. The ocean pH change will persist for thousands of years. Because the fossil fuel CO2 rise is faster than natural CO2 increases in the past, the ocean will be acidified to a much greater extent than has occurred naturally in at least the past 800,000 years [Caldeira and Wicket, 2003].
For those of you who look back on your freshman chemistry days with less than fondness, the acidity or pH of an aqueous solution is a measure of the concentration of H+ ions in the solution, with low pH meaning high H+ concentration. H+ ions are aggressive little guys, and too much H+ in water can burn the skin off your hand or make a coral limestone go fizz. The link between CO2 and H+ arises by the combination of CO2 and water, H2O, to form carbonic acid, H2CO3. An acid is a chemical species that releases H+ ions into solution, as does H2CO3 to form HCO3- and CO32-. Adding CO2 to water causes the pH to drop.
The pH of seawater is buffered by the chemistry of carbon, just as is the chemistry of blood and cellular fluids. The buffering action arises from the fact that the concentrations of the various carbon species are much higher than is the concentration of H+ ions. If some process tries to add or remove H+ ions, the amount of H+ ions required will be determined by the amount of the carbon species that have to be converted from one form to another. This will be an amount much higher than the actual change in H+ concentration itself.
Most of the carbon in seawater is in the form of HCO3-, while the concentrations of CO32- and dissolved CO2 are one and two orders of magnitude lower, respectively. The equilibrium reaction for CO2 chemistry in seawater that most cogently captures its behavior is
CO2 + CO32- + H2O == 2 HCO3-
where I am using double equal signs as double arrows, denoting chemical equilibrium. Since this is a chemical equilibrium, Le Chatlier’s principal states that a perturbation, by say the addition of CO2, will cause the equilibrium to shift in such a way as to minimize the perturbation. In this case, it moves to the right. The concentration of CO2 goes up, while the concentration of CO32- goes down. The concentration of HCO3- goes up a bit, but there is so much HCO3- that the relative change in HCO3- is smaller than the changes are for CO2 and CO32-. It works out in the end that CO2 and CO32- are very nearly inversely related to each other, as if CO2 times CO32- equaled a constant.
Coral reefs are built from limestone by the reaction Ca2+ + CO32- == CaCO3, where Ca is calcium. Acidifying the ocean decreases the concentration of CO32- ions, which by le Chatlier’s principal shifts the equilibrium toward the left, tending to dissolve CaCO3. Note that this is a sort of counter-intuitive result, that adding CO2 should make reefs dissolve rather than pushing carbon into making more reefs. It’s all because of those H+ ions.
CaCO3 tends to dissolve in the deep ocean, both because of the high pressure and because the waters have been acidified by CO2 from rotting dead plankton. Surface waters, however, are supersaturated with respect to CaCO3, meaning that there is enough Ca2+ and CO32- in surface waters that you could give up some, and still not provoke CaCO3 to dissolve. However, it has been documented that corals produce CaCO3 more slowly as the extent of supersaturation decreases. This is also true for planktonic CaCO3-secreters such as coccolithophorids and foraminifera. We should note that for coral reef communities, the acid ocean is only one problem that they face, and it’s not the worst. Rising temperatures are tightly correlated with coral bleaching events, the expulsion of symbiotic algae, often followed by death of the coral. There is a terrifying time-series of temperature and coral bleaching from Tahiti in Hoegh-Guldberg, 1999]. When you look at the temperatures that killed the coral, and project future temperatures, it looks to be all over for corals. Coral communities are also impacted by water turbidity, resulting from fertilizer runoff, and by overfishing.
Elevated CO2 levels also affect fish and other aquatic organisms, in part because of the decrease in pH, but also because CO2 is what heterotrophic organisms try to exhale. However, we should note that dissolved CO2 levels were substantially higher than today in the geologic past, and organisms were able to cope with this OK, so apparently there can be some acclimation of populations to higher CO2.
The natural pH of the ocean is determined by a need to balance the deposition and burial of CaCO3 on the sea floor against the influx of Ca2+ and CO32- into the ocean from dissolving rocks on land, called weathering. These processes stabilize the pH of the ocean, by a mechanism called CaCO3 compensation. CaCO3 compensation works on time scales of thousands of years or so. Because of CaCO3 compensation, the oceans were probably at close to their present pH of around 8 even millions of years ago when atmospheric CO2 was 10 times the present value or whatever it was. The CaCO3 cycle was discussed briefly in regards to the uptake of fossil fuel by the ocean, here. The point of bringing it up again is to note that if the CO2 concentration of the atmosphere changes more slowly than this, as it always has throughout the Vostok record, the pH of the ocean will be relatively unaffected because CaCO3 compensation can keep up. The fossil fuel acidification is much faster than natural changes, and so the acid spike will be more intense than the earth has seen in at least 800,000 years.
There are several feedbacks between decreasing the rate of calcification that organisms do in the ocean, and the carbon cycle. Removing CaCO3 from surface waters tends to raise the CO2 concentration of the waters (it should be possible for you to work that out for yourself based on the chemical reactions above). This is a negative feedback, tending to remove excess CO2 from the atmosphere, but it is a small effect. Decreasing the flux of CaCO3 to the sea floor tends to diminish the amount of CaCO3 that gets buried in sediments, which hastens the pH-recovery from the CaCO3 compensation mechanism. This may not be a small effect at all, but it is a slow effect: thousands of years.
Caldeira, K., and Wickett, M.E. Anthropogenic carbon and ocean pH. Nature: 425, 365, 2003.
Hoegh-Guldberg, O. Climate change, coral bleaching and the future of the world’s coral reefs. Mar. Freshwater Res.: 50, 839-8–66, 1999.
Kleypas, J., R.W. Buddemeier, D. Archer, J.-P. Gattuso, C. Langdon, and B. Opdyke (1999) Geochemical consequences of increased atmospheric CO2 on coral reefs. Science 284: 118-120.
Shutting Down the Oceans
Act I: Acid Oceans
Global warming and acidification are damaging the phytoplankton at the basis of the oceans’ enormous food web, putting the entire biosphere in jeopardy. Dr. Mae-Wan Ho
A fully referenced version of this article is posted on ISIS members’ website. Membership details here
Imagine vast expanses of oceans devoid of life as far and wide as you can project your senses, no whales, no fish, no seabirds and no corals beneath. The warm seawater is thick with floating plastic wastes and slime, and the oppressive heavy air putrid with death and decay.
That’s not a scene from a science-fiction film, but a likely future scenario unless we take appropriate action now: stop polluting and exploiting the oceans and shift comprehensively to renewable energy options to drastically reduce carbon emissions (Which Energy?).
Increase in carbon dioxide concentration in the atmosphere and global warming are threatening the oceans’ phytoplankton that supports all marine life from zooplankton to whales. Phytoplankton is also the fastest assimilator of carbon, clearing carbon dioxide from the atmosphere to prevent it building up as a greenhouse gas that warms the earth.
When phytoplankton is in jeopardy, all life is in jeopardy, on land and at sea. Marine life will literally starve to death, and the decay and decomposition that follow would release enormous amounts of carbon dioxide from the estimated 800 Gt of the ocean’s standing biomass, resulting in further global warming on a massive scale.
A little girl who was taken to the beach for the first time in her life was moved to declare she loved the ocean because it was “always open”. It is unthinkable that the final curtains may soon fall over the oceans.
Oceans take up carbon dioxide passively by dissolving it in the water of the surface layers, and as carbon dioxide increases in the atmosphere, so too does the concentration of carbon dioxide in the water. This makes the surface water more acidic and interferes with calcification in organisms that make their shells or external skeletons from calcium carbonate . The ‘calicifers’ span the marine food web from phytoplankton that make their own food by means of photosynthesis, to practically all other organisms that depend directly or indirectly on phytoplankton for food. Califiers include coccolithophores among the phytoplankton; foraminifera and pteropods (tiny marine snails) among the zooplankton; and corals. Under normal conditions, calcite and aragonite (forms of calcium carbonate) are stable in surface waters where the carbonate ion is at supersaturating concentrations. However as the water becomes more acidic, the concentration of carbonate ion falls, and structures made of calcium carbonate can now dissolve.
Researchers have already found that corals, coccolithophore algae and pteropods have reduced calcification or enhanced dissolution of their shells and skeletons when exposed to elevated levels of carbon dioxide.
Acidity is measured as pH, the negative logarithm to the base 10 of the concentration of hydrogen ion, H+. The scale of pH goes from 0 to 14, pH 7 is neutral, pH greater than 7 is alkaline and less than 7 acidic. The pH of the oceans is slightly alkaline at 8.0 to 8.2; and has dropped 0.1 unit since the industrial revolution. By the end of this century, it will become another 0.3-0.4 unit lower, representing a 100 to 150 percent increase in hydrogen ion concentration.
As pH drops, so does the concentration of carbonate, making it more difficult for marine organisms to form calcium carbonate. There is substantial experimental evidence indicating that calcification rates will decrease in both low latitude corals that form reefs out of aragonite, the metastable form of calcium carbonate, and phytoplankton that form their shells out of calcite, the stable form of calcium carbonate.
Theoretical predictions and experiments match up
An international team of 27 climate scientists from France, the United States, Japan, Switzerland Germany, Australia, and UK used 13 models of the ocean carbon cycle to assess calcium carbonate saturation under the ‘business as usual’ scenario . In their projections, the surface water of the Southern Ocean (that which surrounds the Antarctica) will begin to become under-saturated with respect to aragonite by 2050. By 2100, this could extend throughout the entire Southern Ocean and into the sub-Arctic Pacific Ocean. When live pteropods were exposed to the predicted level of under-saturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution.
The researchers said their findings indicate that conditions harmful to ecosystems at high-latitude could develop within decades and not centuries as previously thought.
They computed modern-day ocean carbonate chemistry from the observed alkalinity and dissolved inorganic carbon (DIC) from data collected during the CO2 Survey of the World Ocean Circulation Experiment (WOCE), part of the World Climate Research Programme (WCRP) which used resources from nearly 30 countries to make in situ and satellite observations of the global ocean between 1990 and 1998 , and the Joint Global Ocean Flux Study (JGOFS), an international multi-disciplinary programme involving 20 nations to study carbon fluxes between the atmosphere and the surface and interior of the oceans and their sensitivities to climate change .
Modern-day surface carbonate ions concentration varies with latitude from 105 mmol/kg in the Southern Ocean (all waters south of 60 S) to 240 mmol/kg in the tropics. Low temperature and large amounts of upwelled deep water in the Southern Ocean containing high levels of carbon dioxide from organic matter decomposition is responsible for the low concentrations of carbonate there.
Carbon dioxide generated by human activities has already reduced modern surface carbonate by more than 10 percent since the industrial revolution (29 mmol/kg in the tropics and 18mmol in the Southern Ocean.).
By year 2100, as atmospheric carbon dioxide reaches 788 ppm (parts per million) under the business as usual scenario, average tropical surface carbonate will decline to 149 +14 mmol/kg, a 45 percent reduction relative to pre-industrial levels, and that agrees with previous estimates. In the Southern Ocean however, surface concentrations will dip to 55 + 5 mmol/kg, which is 18 percent below the threshold (66 mmol/kg) at which aragonite becomes under-saturated. These changes extend well below the sea surface. Throughout the Southern Ocean, the entire water column becomes under-saturated with respect to aragonite. The aragonite saturation horizon shifts from its present average depth of 730 m all the way to the surface. Simultaneously, in a portion of the sub-Arctic Pacific, the aragonite saturation horizon moves from its present depth of about 120 m to the surface. In the North Atlantic, surface waters remain saturated with respect to aragonite, but the saturation horizon shallows dramatically. North of 50 deg N, it shallows from 2 600 m to 115 m. The greater erosion in the North Atlantic is due to deeper penetration and higher concentrations of anthropogenic carbon dioxide, a tendency already evident in present-day estimates based on data and in models.
The changes in aragonite concentration could have severe consequences for calcifying organisms, particularly shelled pteropods, the major planktonic producers of aragonite. Pteropod population densities are high in polar and subpolar waters, but only 5 species typically occur in such coldwater regions, and of these only one or two species are common at the highest latitudes. High latitude pteropods have one or two generations per year and form integral components of food webs, and are typically found in the upper 300 m where they may reach densities of hundreds to thousands of individuals per cubic millilitre. In the strongly seasonal high latitudes, sedimentation pulses of pteropods frequently occur just after summer. In the Ross Sea, pteropods account for the majority of the annual export flux of both carbonate and organic carbon to the sea floor. South of the Antarctic Polar Front, pteropods also dominate the export flux of calcium carbonate to the sea floor.
Pteropods may already be unable to maintain shells in waters under-saturated with respect to aragonite. Data from sediment traps indicate that empty pteropod shells show pitting and partial dissolution as soon as they fall below the agaronite saturation horizon. In vitro measurements confirm the rapid rates of pteropod shell dissolution. New experimental findings suggest that even the shells of live pteropods dissolve rapidly once surface waters become under-saturated with aragonite. The authors show that when live subartic pteropod Clio pyramidata is exposed to a level of under-saturation similar to that predicted for Southern Ocean surface waters in the year 2100 under business as usual scenario, a marked dissolution at the growing edges of the shell occurs within 48 hours.
Marine food web at risk
The failure of pteropods to thrive will affect many species, as they contribute to the diet of diverse species of other zooplankton, small fishes, the North Pacific Salmon, mackerel herring, cod and baleen whales.
Surface dwelling calcite plankton such as foraminifera and coccolithophorids may fare better in the short term. However, the beginning of high-latitude-calcite under-saturation will only lag aragonite by 50 to 100 years. The diverse bottom-dwelling calcareous organisms in high latitude regions may also be threatened, including cold-water corals, which provide essential fish habitat. Cold-water corals seem much less abundant in the North Pacific than in the North Atlantic where the aragonite saturation horizon is much deeper. Some important groups in the Arctic and Antarctic bottom-dwelling communities secrete magnesium calcite, which can be more soluble than aragonite. These include gorgonians, coralline red algae and echinoderms. At twice the normal concentration of carbon dioxide, juvenile echinoderms stopped growing and produced more brittle and fragile exoskeletons in a subtropical six-month experiment. Experimental evidence from many lower-latitude, shallow-dwelling calcifiers reveals a reduced ability to calcify with a decreasing carbonate saturation state. At twice the normal carbon dioxide concentration, calcification rates in some shallow-dwelling calcareous organisms may decline by up to 50 percent.
...if it took millions of millions f years for the Oceans to "self-develop" to the correct Bioma Ecosystem of the years 1900, is not relevant !
...what is relevant is that Governments are on a willful downward path of "suicide and self destruction" OF THEMSELVES AND THE PLANET ...!
...AND THE ONLY INSANE REASON, IS "EVOLUTIONARY MONEY DRIVEN WORLD MARKETS CAPITALISM"...! AND an egotistical spirit of survival of the fittest, and a barbaric big end to how we new the WORLD !
WHAT IS WORSE, the use of destroyed OCEANS with algae for "bio-fuels" to complete the destruction !
WORLD WAKE UP, WE ARE IN THE HANDS OF NEARLY INSANE DECREPIT WORLD GOVERNMENTS !