Ocean acidification

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Ocean acidification is the name given to the ongoing decrease in the pH of the Earth's oceans, caused by their uptake of anthropogenic carbon dioxide from the atmosphere. Between 1751 and 1994 surface ocean pH is estimated to have decreased from approximately 8.179 to 8.104 (a change of -0.075).^[1][1]

Contents 1 Carbon cycle 2 Acidification 3 Possible impacts 4 Gallery 5 See also 6 References 6.1 Further reading 7 External links 7.1 Carbonate system calculators

Carbon cycle

In the natural carbon cycle, the atmospheric concentration of carbon dioxide (CO₂) represents a balance of fluxes between the oceans, terrestrial biosphere and the atmosphere. Human activities such as land-use changes, the combustion of fossil fuels, and the production of cement have led to a new flux of CO₂ into the atmosphere. Some of this has remained in the atmosphere (where it is responsible for the rise in atmospheric concentrations), some is believed to have been taken up by terrestrial plants, and some has been absorbed by the oceans.

When CO₂ dissolves, it reacts with water to form a balance of ionic and non-ionic chemical species : dissolved free carbon dioxide (CO_{2 (aq)}), carbonic acid (H₂CO₃), bicarbonate (HCO₃^-) and carbonate (CO₃^2-). The ratio of these species depends on factors such as seawater temperature and alkalinity (see the article on the ocean's solubility pump for more detail).

Acidification

Average surface ocean pH^[1]

Time	pH	pH change	Source
Pre-industrial (1700s)	8.179	0.000	analysed field[1]
Recent past (1990s)	8.104	-0.075	field[1]
2050 (2×CO2 = 560 ppm)	7.949	-0.230	model[1]
2100 (IS92a)[1]	7.824	-0.355	model[1]

Dissolving CO₂ in seawater also increases the hydrogen ion (H⁺) concentration in the ocean, and thus decreases ocean pH. The use of the term "ocean acidification" to describe this process was introduced in Caldeira and Wickett (2003)^[1].

Since the industrial revolution began, it is estimated that surface ocean pH has dropped by slightly less than 0.1 units (on the logarithmic scale of pH), and it is estimated that it will drop by a further 0.3 - 0.5 units by 2100 as the ocean absorbs more anthropogenic CO₂^[1][1][1].

Note that, although the ocean is acidifying, its pH is still greater than 7 (that of neutral water), so the ocean could also be described as becoming less alkaline.

A report from NOAA scientists published in the journal Science in May 2008 found that large amounts of water that is undersaturated in aragonite (i.e. a proxy measure indicating relatively acidified / low pH water) are upwelling to within four miles of the Pacific continental shelf area of N. America. This area is a critical zone where most local marine life lives or is born. While the paper only dealt with the areas from Vancouver to northern California, other continental shelf areas may be experiencing similar effects.^[1]

Possible impacts

Pollution v • d • e

Air pollution

Acid rain • Air Quality Index • Atmospheric dispersion modeling • Chlorofluorocarbon • Global dimming • Global warming • Haze • Indoor air quality • Ozone depletion • Particulate • Smog

Water pollution

Eutrophication • Hypoxia • Marine pollution • Ocean acidification • Oil spill • Ship pollution • Surface runoff • Thermal pollution • Wastewater • Waterborne diseases • Water quality • Water stagnation

Soil contamination

Bioremediation • Herbicide • Pesticide • Soil Guideline Values (SGVs)

Radioactive contamination

Actinides in the environment • Environmental radioactivity • Fission product • Nuclear fallout • Plutonium in the environment • Radiation poisoning • Radium in the environment • Uranium in the environment

Other types of pollution

Invasive species • Light pollution • Noise pollution • Radio spectrum pollution • Visual pollution

Inter-government treaties

Montreal Protocol • Nitrogen Oxide Protocol • Kyoto Protocol • CLRTAP

Major organizations

DEFRA • EPA • Global Atmosphere Watch • Greenpeace • National Ambient Air Quality Standards

Related topics

Environmental Science • Natural environment

Although the natural absorption of CO₂ by the world's oceans helps mitigate the climatic effects of anthropogenic emissions of CO₂, it is believed that the resulting decrease in pH will have negative consequences, primarily for oceanic calcifying organisms. These use the calcite or aragonite polymorphs of calcium carbonate to construct cell coverings or skeletons. Calcifiers span the food chain from autotrophs to heterotrophs and include organisms such as coccolithophores, corals, foraminifera, echinoderms, crustaceans and molluscs.

Under normal conditions, calcite and aragonite are stable in surface waters since the carbonate ion is at supersaturating concentrations. However, as ocean pH falls, so does the concentration of this ion, and when carbonate becomes under-saturated, structures made of calcium carbonate are vulnerable to dissolution. Research has already found that corals^[1], coccolithophore algae^[1][1][1][1], coralline algae^[1], foraminifera^[1], shellfish^[1] and pteropods^[1] experience reduced calcification or enhanced dissolution when exposed to elevated CO₂. The Royal Society of London published a comprehensive overview of ocean acidification, and its potential consequences, in June 2005^[1].

However, some studies have found different response to ocean acidification, with coccolithophore calcification and photosynthesis both increasing under elevated atmospheric pTemplate:CO2^[1][1][1], an equal decline in primary production and calcification in response to elevated CO₂^[1] or the direction of the response varying between species^[1]. Recent work examining a sediment core from the North Atlantic found that while the species composition of coccolithophorids has remained unchanged for the industrial period 1780 to 2004, the calcification of coccoliths has increased by up to 40% during the same time^[1].

While the full ecological consequences of these changes in calcification are still uncertain, it appears likely that many calcifying species will be adversely affected. There is also a suggestion that a decline in the coccolithophores may have secondary effects on climate change, by decreasing the earth's albedo via their effects on oceanic cloud cover^[1]. Aside from calcification, organisms may suffer other adverse effects, either directly as reproductive or physiological effects (e.g. CO₂-induced acidification of body fluids, known as hypercapnia), or indirectly through negative impacts on food resources^[1]. However, as with calcification, as yet there is not a full understanding of these processes in marine organisms or ecosystems.

Leaving aside direct biological effects, it is expected that ocean acidification in the future will lead to a significant decrease in the burial of carbonate sediments for several centuries, and even the dissolution of existing carbonate sediments^[1]. This will cause an elevation of ocean alkalinity, leading to the enhancement of the ocean as a reservoir for CO₂ with moderate (and potentially beneficial) implications for climate change as more CO₂ leaves the atmosphere for the ocean^[1].

Gallery

Image:AYool GLODAP aCO2.png Sea surface "present day" (1990s) anthropogenic CO2

Image:AYool GLODAP invt aCO2.png Vertical inventory of "present day" (1990s) anthropogenic CO2

Image:AYool GLODAP del co3.png Change in surface CO32- ion from the 1700s to the 1990s

See also

• Biological pump
• Carbon dioxide sinks
• Continental shelf pump
• Global Ocean Data Analysis Project
• Seawater pH
• Solubility pump

References

Further reading

• Cicerone, R.; J. Orr, P. Brewer et al. (2004). "The Ocean in a High CO₂ World". EOS, Transactions American Geophysical Union 85 (37): 351–353. doi:10.1029/2004EO370007. ISSN 0096-3941.

• Doney, S. C. (2006). "The Dangers of Ocean Acidification". Scientific American 294: 58–65. ISSN 0036-8733., (Article preview only).

• Feely, R. A.; Sabine, Christopher L.; Lee, Kitack; Berelson, Will; Kleypas, Joanie; Fabry, Victoria J.; Millero, Frank J. (2004). "Impact of Anthropogenic CO₂ on the CaCO₃ System in the Oceans" (abstract). Science 305 (5682): 362–366. doi:10.1126/science.1097329. ISSN 0036-8075.

• Henderson, Caspar. "Ocean acidification: the other CO2 problem", NewScientist.com news service, 2006-08-05. 

• Jacobson, M. Z. (2005). "Studying ocean acidification with conservative, stable numerical schemes for nonequilibrium air-ocean exchange and ocean equilibrium chemistry". Journal of Geophysical Research - Atmospheres 110: D07302. doi:10.1029/2004JD005220. ISSN 0148-0227.

• Kleypas, J.A., R.A. Feely, V.J. Fabry, C. Langdon, C.L. Sabine, and L.L. Robbins. (2006). Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers: A Guide for Further Research, report of a workshop held 18-20 April 2005, St. Petersburg, FL, sponsored by NSF, NOAA and the U.S. Geological Survey, 88pp.

• Kolbert, E. (2006). The Darkening Sea: Carbon emissions and the ocean. The New Yorker magazine. 20 November 2006.

• Sabine, C. L.; Feely, Richard A.; Gruber, Nicolas; Key, Robert M.; Lee, Kitack; Bullister, John L. et al. (2004). "The Oceanic Sink for Anthropogenic CO₂" (abstract). Science 305 (5682): 367–371. doi:10.1126/science.1097403. ISSN 0036-8075.

• Stone, R. (2007). "A World Without Corals?". Science 316 (5825): 678–681. doi:10.1126/science.316.5825.678. ISSN 0036-8075.

External links

• Announcement for Royal Society of London report
• Orr et al. (2005) supplementary material
• The Acid Ocean – the Other Problem with CO₂ Emission, David Archer, a RealClimate discussion
• Task Force on Ocean Acidification in the Pacific, including recent presentations on ocean acidification, Pacific Science Association
• "Coral Bones" - an investigation into the future of coral reefs
• "Growing Acidity of Oceans May Kill Corals", Washington Post
• Ocean Acidification - a multimedia, interactive site from The World Ocean Observatory
• Dropping pH in the Oceans Causing a Rising Tide of Alarm by Tundi Agardy, The World Ocean Observatory
• Regularly-updated "blog" of ocean acidification publications and news
• The Ocean Acidification Network: An Information Network for the International Scientific Community
• CO2-04: Effect of Elevated CO2 on Phytoplankton project of Australia's Antarctic Climate and Ecosystems Cooperative Research Centre
• "Scientists Grapple with Ocean Acidification", ABC News

Carbonate system calculators

The following packages calculate the state of the carbonate system in seawater (including pH):

• CO2SYS, a stand-alone executable (also available in a version for Microsoft Excel/VBA)
• seacarb, a R package for Windows, Mac OS X and Linux (also available here)
• CSYS, a Matlab script

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