Ocean acidification

Estimated change in sea water pH caused by human created CO2 between the 1700s and the 1990s, from the Global Ocean Data Analysis Project and the World Ocean Atlas

Ocean acidification is the name given to the ongoing decrease in the pH of the Earth's oceans, caused by the uptake of anthropogenic carbon dioxide (CO2) from the atmosphere.[1] About 30–40% of the carbon dioxide released by humans into the atmosphere dissolves into the oceans, rivers and lakes.[2][3] To maintain chemical equilibrium, some of it reacts with the water to form carbonic acid. Some of these extra carbonic acid molecules react with a water molecule to give a bicarbonate ion and a hydronium ion, thus increasing the ocean's "acidity" (H+ ion concentration). Between 1751 and 1994 surface ocean pH is estimated to have decreased from approximately 8.25 to 8.14,[4] representing an increase of almost 30% in H+ ion concentration in the world's oceans.[5][6]

This increasing acidity is thought to have a range of direct undesirable consequences such as depressing metabolic rates in jumbo squid[7] and depressing the immune responses of blue mussels.[8]

Other chemical reactions are also triggered which result in an actual net decrease in the amount of carbonate ions available. In the oceans, this makes it more difficult for marine calcifying organisms, such as coral and some plankton, to form biogenic calcium carbonate, and existing such structures become vulnerable to dissolution.[9] Thus, ongoing acidification of the oceans also poses a threat to the food chains connected with the oceans.[10][11]

Carbon cycle

The CO2 cycle between the atmosphere and the ocean.

The carbon cycle describes the fluxes of carbon dioxide (CO2) between the oceans, terrestrial biosphere, lithosphere,[12] and the atmosphere. Human activities such as the combustion of fossil fuels and land use changes have led to a new flux of CO2 into the atmosphere. About 45% has remained in the atmosphere; most of the rest has been taken up by the oceans,[13] with some also taken up by terrestrial plants.[14]

The carbon cycle involves both organic compounds as well as inorganic carbon compounds such as carbon dioxide and the carbonates. The inorganic compounds are particularly relevant when discussing ocean acidification for it includes the many forms of dissolved CO2 present in the Earth's oceans.[15]

When CO2 dissolves, it reacts with water to form a balance of ionic and non-ionic chemical species: dissolved free carbon dioxide (CO2(aq)), carbonic acid (H2CO3), bicarbonate (HCO
3
) and carbonate (CO2−
3
). The ratio of these species depends on factors such as seawater temperature and alkalinity (as shown in a Bjerrum plot). These different forms of dissolved inorganic carbon are transferred from an ocean's surface to its interior by the ocean's solubility pump.

The resistance of an area of ocean to absorbing atmospheric CO2 is known as the Revelle factor.

Acidification

Dissolving CO2 in seawater increases the hydrogen ion (H+) concentration in the ocean, and thus decreases ocean pH, as follows:

CO2 (aq) + H2O $\leftrightarrow$ H2CO3 $\leftrightarrow$ HCO3 + H+ $\leftrightarrow$ CO32− + 2 H+.

Caldeira and Wickett (2003)[1] placed the rate and magnitude of modern ocean acidification changes in the context of probable historical changes during the last 300 million years.

Average surface ocean pH[9]
Time pH pH change relative
to pre-industrial
Source H+ concentration change
relative to pre-industrial
Pre-industrial (18th century) 8.179 analysed field[16][not in citation given]
Recent past (1990s) 8.104 −0.075 field[16] + 18.9%
Present levels ~8.069 −0.11 field[5][17][6][18] + 28.8%
2050 (2×CO2 = 560 ppm) 7.949 −0.230 model[9] + 69.8%
2100 (IS92a)[19] 7.824 −0.355 model[9] + 126.5%

Since the industrial revolution began, it is estimated that surface ocean pH has dropped by slightly more than 0.1 units on the logarithmic scale of pH, representing an approximately 29% increase in H+, and it is estimated that it will drop by a further 0.3 to 0.5 pH units (an additional doubling to tripling of today's post-industrial acid concentrations) by 2100 as the oceans absorb more anthropogenic CO2, the impacts being most severe for coral reefs and the Southern Ocean.[1][9][20] These changes are predicted to continue rapidly as the oceans take up more anthropogenic CO2 from the atmosphere. The degree of change to ocean chemistry, including ocean pH, will depend on the mitigation and emissions pathways[21] society takes.[22]

Although the largest changes are expected in the future,[9] a report from NOAA scientists found large quantities of water undersaturated in aragonite are already upwelling close to the Pacific continental shelf area of North America.[23] Continental shelves play an important role in marine ecosystems since most marine organisms live or are spawned there, and though the study only dealt with the area from Vancouver to Northern California, the authors suggest that other shelf areas may be experiencing similar effects.[23]

Rate

Similarly, one of the first detailed datasets examining temporal variations in pH at a temperate coastal location found that acidification was occurring at a rate much higher than previously predicted, with consequences for near-shore benthic ecosystems.[24][25] Thomas Lovejoy, former chief biodiversity advisor to the World Bank, has suggested that "the acidity of the oceans will more than double in the next 40 years. This rate is 100 times faster than any changes in ocean acidity in the last 20 million years, making it unlikely that marine life can somehow adapt to the changes."[26]

Current rates of ocean acidification have been compared with the greenhouse event at the Paleocene–Eocene boundary (about 55 million years ago) when surface ocean temperatures rose by 5–6 degrees Celsius. No catastrophe was seen in surface ecosystems, yet bottom-dwelling organisms in the deep ocean experienced a major extinction. The current acidification is on a path to reach levels higher than any seen in the last 65 million years,[27] and the rate of increase is about ten times the rate that preceded the Paleocene–Eocene mass extinction. The current and projected acidification has been described as an almost unprecedented geological event.[28] A National Research Council study released in April 2010 likewise concluded that "the level of acid in the oceans is increasing at an unprecedented rate."[29][30] A 2012 paper in the journal Science examined the geological record in an attempt to find a historical analog for current global conditions as well as those of the future. The researchers determined that the current rate of ocean acidification is faster than at any time in the past 300 million years.[31][32]

A review by climate scientists at the RealClimate blog, of a 2005 report by the Royal Society of the UK similarly highlighted the centrality of the rates of change in the present anthropogenic acidification process, writing:[33]

"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 CO2−
3
into the ocean from dissolving rocks on land, called weathering. These processes stabilize the pH of the ocean, by a mechanism called CaCO3 compensation...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 [present] 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."

In the 15-year period 1995–2010 alone, acidity has increased 6 percent in the upper 100 meters of the Pacific Ocean from Hawaii to Alaska.[34] According to a statement in July 2012 by Jane Lubchenco, head of the U.S. National Oceanic and Atmospheric Administration "surface waters are changing much more rapidly than initial calculations have suggested. It's yet another reason to be very seriously concerned about the amount of carbon dioxide that is in the atmosphere now and the additional amount we continue to put out."[35]

Calcification

Changes in ocean chemistry can have extensive direct and indirect effects on organisms and their habitats. One of the most important repercussions of increasing ocean acidity relates to the production of shells and plates out of calcium carbonate (CaCO3).[20] This process is called calcification and is important to the biology and survival of a wide range of marine organisms. Calcification involves the precipitation of dissolved ions into solid CaCO3 structures, such as coccoliths. After they are formed, such structures are vulnerable to dissolution unless the surrounding seawater contains saturating concentrations of carbonate ions. The saturation state of seawater for a mineral (known as Ω) is a measure of the thermodynamic potential for the mineral to form or to dissolve, and is described by the following equation:

${\Omega} = \frac{\left[\textrm{Ca}^{2+}\right] \left[\textrm{CO}_{3}^{2-}\right]}{K_{sp}}$

Here Ω is the product of the concentrations (or activities) of the reacting ions that form the mineral (Ca2+ and CO2−
3
), divided by the product of the concentrations of those ions when the mineral is at equilibrium (Ksp), that is, when the mineral is neither forming nor dissolving.[36] In seawater, a natural horizontal boundary is formed as a result of temperature, pressure, and depth, and is known as the saturation horizon, or lysocline.[20] Above this saturation horizon, Ω has a value greater than 1, and CaCO3 does not readily dissolve. Most calcifying organisms live in such waters.[20] Below this depth, Ω has a value less than 1, and CaCO3 will dissolve. However, if its production rate is high enough to offset dissolution, CaCO3 can still occur where Ω is less than 1. The carbonate compensation depth occurs at the depth in the ocean where production is exceeded by dissolution.[37]

Bjerrum plot: Change in carbonate system of seawater from ocean acidification.

As shown in the Bjerrum plot, along with the change in pH, adding extra CO2 to the oceans also changes the oceans' concentrations of the different forms of dissolved inorganic carbon. There is a decrease in the concentration of CO32−, which decreases Ω, and hence makes CaCO3 dissolution more likely.

Calcium carbonate occurs in two common polymorphs: aragonite and calcite. Aragonite is much more soluble than calcite, with the result that the aragonite saturation horizon is always nearer to the surface than the calcite saturation horizon.[20] This also means that those organisms that produce aragonite may possibly be more vulnerable to changes in ocean acidity than those that produce calcite.[9] Increasing CO2 levels and the resulting lower pH of seawater decreases the saturation state of CaCO3 and raises the saturation horizons of both forms closer to the surface.[38] This decrease in saturation state is believed to be one of the main factors leading to decreased calcification in marine organisms, as it has been found that the inorganic precipitation of CaCO3 is directly proportional to its saturation state.[39]

Possible impacts

Impacts on oceanic calcifying organisms

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 span the food chain from autotrophs to heterotrophs and include organisms such as coccolithophores, corals, foraminifera, echinoderms, crustaceans and molluscs.[40] As described above, under normal conditions, calcite and aragonite are stable in surface waters since the carbonate ion is at supersaturating concentrations. However, as ocean pH falls, the concentration of carbonate ions required for saturation to occur increases, and when carbonate becomes undersaturated, structures made of calcium carbonate are vulnerable to dissolution. Therefore, even if there is no change in the rate of calcification, the rate of dissolution of calcareous material increases.[41]

Research has already found that corals,[42][43][44] coccolithophore algae,[45][46][47][48] coralline algae,[49] foraminifera,[50] shellfish[51] and pteropods[9][52] experience reduced calcification or enhanced dissolution when exposed to elevated CO2.

The Royal Society published a comprehensive overview of ocean acidification, and its potential consequences, in June 2005.[20] However, some studies have found different response to ocean acidification, with coccolithophore calcification and photosynthesis both increasing under elevated atmospheric pCO2,[53][54][55] an equal decline in primary production and calcification in response to elevated CO2[56] or the direction of the response varying between species.[57] A study in 2008 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.[55] And another study in 2010 from Stony Brook University drew a dismal conclusion that while some areas are overharvested and other fishing grounds are being restored, because of ocean acidification it may be impossible to bring back many previous shellfish populations.[58] While the full ecological consequences of these changes in calcification are still uncertain, it appears likely that many calcifying species will be adversely affected.

When exposed in experiments to pH reduced by 0.2 to 0.4, larvae of a temperate brittlestar, a relative of the common sea star, fewer than 0.1 percent survived more than eight days.[34] There is also a suggestion that a decline in the coccolithophores may have secondary effects on climate, contributing to global warming by decreasing the Earth's albedo via their effects on oceanic cloud cover.[59]

The fluid in the internal compartments where corals grow their exoskeleton is also extremely important for calcification growth. When the saturation rate of aragonite in the external seawater is at ambient levels, the corals will grow their aragonite crystals rapidly in their internal compartments, hence their exoskeleton grows rapidly. If the level of aragonite in the external seawater is lower than the ambient level, the corals have to work harder to maintain the right balance in the internal compartment. When that happens, the process of growing the crystals slows down, and this slows down the rate of how much their exoskeleton is growing. Depending on how much aragonite is in the surrounding water, the corals may even stop growing because the levels of aragonite are too low to pump in to the internal compartment. They could even dissolve faster than they can make the crystals to their skeleton, depending on the aragonite levels in the surrounding water.[60]

Ocean acidification may also force some organisms to reallocate resources away from productive endpoints such as growth in order to maintain calcification.[61]

Other biological impacts

Aside from the slowing and/or reversing of calcification, organisms may suffer other adverse effects, either indirectly through negative impacts on food resources,[20] or directly as reproductive or physiological effects. For example, the elevated oceanic levels of CO2 may produce CO2-induced acidification of body fluids, known as hypercapnia. Also, increasing ocean acidity is believed to have a range of direct consequences. For example, increasing acidity has been observed to: reduce metabolic rates in jumbo squid;[7] depress the immune responses of blue mussels;[8] and make it harder for juvenile clownfish to tell apart the smells of non-predators and predators,[62] or hear the sounds of their predators.[63] This is possibly because ocean acidification may alter the acoustic properties of seawater, allowing sound to propagate further, and increasing ocean noise. This impacts all animals that use sound for echolocation or communication.[64]

However, as with calcification, as yet there is not a full understanding of these processes in marine organisms or ecosystems.[65]

Shelled plankton species may flourish in altered oceans.[66]

Nonbiological impacts

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.[67] This will cause an elevation of ocean alkalinity, leading to the enhancement of the ocean as a reservoir for CO2 with implications for climate change as more CO2 leaves the atmosphere for the ocean.[68]

Possible solutions

Carbon negative fuels

Carbonic acid can be extracted from seawater as carbon dioxide for use in making synthetic fuel.[69][70] If the resulting flue exhaust gas is subject to carbon capture, then the process is carbon negative over time, resulting in permanent extraction of inorganic carbon from seawater and the atmosphere with which it is in equilibrium. Based on the energy requirements, this process is expected to cost about \$50 per tonne of CO2.[71]

Iron fertilization

It has been proposed that iron fertilization of the ocean could stimulate photosynthesis in phytoplankton (see Iron Hypothesis). The phytoplankton would convert the ocean's dissolved carbon dioxide into carbohydrate and oxygen gas, some of which would sink into the deeper ocean before oxidizing. More than a dozen other open-sea experiments confirmed that adding iron to the ocean increases photosynthesis in phytoplankton by up to 30 times.[72] While this approach has been proposed as a potential solution to the ocean acidification problem, it could potentially mitigate some amount of surface ocean acidification at the cost of increasing acidification in the deep ocean.[73]

References

1. ^ a b c Caldeira, K.; Wickett, M. E. (2003). "Anthropogenic carbon and ocean pH". Nature 425 (6956): 365–365. Bibcode:2001AGUFMOS11C0385C. doi:10.1038/425365a. PMID 14508477.
2. ^ Millero, Frank J. (1995). "Thermodynamics of the carbon dioxide system in the oceans". Geochimica et Cosmochimica Acta 59 (4): 661–677.
3. ^ Feely, R. A.; et al. (July 2004). "Impact of Anthropogenic CO2 on the CaCO3 System in the Oceans". Science. 305(5682): 362–366.
4. ^
5. ^ a b Hall-Spencer, J. M.; Rodolfo-Metalpa, R.; Martin, S.; et al. (July 2008). "Volcanic carbon dioxide vents show ecosystem effects of ocean acidification". Nature 454 (7200): 96–9. Bibcode:2008Natur.454...96H. doi:10.1038/nature07051. PMID 18536730.
6. ^ a b Report of the Ocean Acidification and Oxygen Working Group, International Council for Science's Scientific Committee on Ocean Research (SCOR) Biological Observatories Workshop
7. ^ a b Rosa, R.; Seibel, B. (2008). "Synergistic effects of climate-related variables suggest future physiological impairment in a top oceanic predator". P.N.A.S. 105(52): 20776–20780.
8. ^ a b Bibby, R.; et al. (2008). "Effects of ocean acidification on the immune response of the blue mussel Mytilus edulis". Aquatic Biology 2: 67–74.
9. Orr, James C.; et al. (2005). "Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms.". Nature 437 (7059): 681–686. Bibcode:2005Natur.437..681O. doi:10.1038/nature04095. PMID 16193043. Archived from the original on 2008-06-25.
10. ^ Cornelia Dean (January 30, 2009). "Rising Acidity Is Threatening Food Web of Oceans, Science Panel Says". New York Times.
11. ^ Robert E. Service (13 July 2012). "Rising Acidity Brings and Ocean Of Trouble". Science 337: 146–148.
12. ^ "carbon cycle". Encyclopædia Britannica Online. Retrieved 11 Feb 2010.
13. ^ Raven, J. A.; Falkowski, P. G. (1999). "Oceanic sinks for atmospheric CO2". Plant, Cell & Environment 22 (6): 741–755. doi:10.1046/j.1365-3040.1999.00419.x.
14. ^ Cramer, W.; et al. (2001). "Global response of terrestrial ecosystem structure and function to CO2 and climate change: results from six dynamic global vegetation models". Global Change Biology 7 (4): 357–373. doi:10.1046/j.1365-2486.2001.00383.x.
15. ^ Kump, Lee R.; Kasting, James F.; Crane, Robert G. (2003). The Earth System (2nd ed.). Upper Saddle River: Prentice Hall. pp. 162–164. ISBN 0-613-91814-2.
16. ^ a b Key, R. M.; Kozyr, A.; Sabine, C. L.; Lee, K.; Wanninkhof, R.; Bullister, J.; Feely, R. A.; Millero, F.; Mordy, C. and Peng, T.-H. (2004). "A global ocean carbon climatology: Results from GLODAP". Global Biogeochemical Cycles 18 (4): GB4031. Bibcode:2004GBioC..18.4031K. doi:10.1029/2004GB002247.
17. ^ "Ocean acidification and the Southern Ocean" by the Australian Antarctic Division of the Australian Government
18. ^ EPA weighs action on ocean acidification post at official blog of EPOCA, the European Project on Ocean Acidification
19. ^ Review of Past IPCC Emissions Scenarios, IPCC Special Report on Emissions Scenarios (ISBN 0521804930).
20. Raven, J. A. et al. (2005). Ocean acidification due to increasing atmospheric carbon dioxide. Royal Society, London, UK.
21. ^ Anderson, Kevin; Bows, Alice (2011). "Beyond 'dangerous' climate change: emission scenarios for a new world". Philosophical Transactions of the Royal Society A. Retrieved 2011-05-22.
22. ^ Turley, C. (2008). "Impacts of changing ocean chemistry in a high-CO2 world". Mineralogical Magazine 72 (1): 359–362. doi:10.1180/minmag.2008.072.1.359.
23. ^ a b Feely, R. A.; Sabine, C. L.; Hernandez-Ayon, J. M.; Ianson, D.; Hales B. (June 2008). "Evidence for upwelling of corrosive "acidified" water onto the continental shelf". Science 320 (5882): 1490–2. Bibcode:2008Sci...320.1490F. doi:10.1126/science.1155676. PMID 18497259.
24. ^ Wootton, J. T.; Pfister, C. A. and Forester, J. D. (2008). "Dynamic patterns and ecological impacts of declining ocean pH in a high-resolution multi-year dataset". Proceedings of the National Academy of Sciences 105 (48): 18848–18853. Bibcode:2008PNAS..10518848W. doi:10.1073/pnas.0810079105. PMC 2596240. PMID 19033205.
25. ^ "Ocean Growing More Acidic Faster Than Once Thought; Increasing Acidity Threatens Sea Life". Science Daily. 2008-11-26. Retrieved 26 November 2008.
26. ^ UN: Oceans are 30 percent more acidic than before fossil fuels
27. ^ Rate of ocean acidification the fastest in 65 million years
28. ^ An Ominous Warning on the Effects of Ocean Acidification
29. ^ Report: Ocean acidification rising at unprecedented rate
30. ^
31. ^ JournalistsResource.org, retrieved 14 March 2012
32. ^ Hönisch, Bärbel; Ridgwell, Andy; Schmidt, Daniela N. (2012). "The Geological Record of Ocean Acidification". Science 335 (6072): 1058–1063. Bibcode:2012Sci...335.1058H. doi:10.1126/science.1208277.
33. ^ The Acid Ocean – the Other Problem with CO2 Emission
34. ^ a b How Acidification Threatens Oceans from the Inside Out
35. ^ Huffington Post, 9 July 2012, "Ocean Acidification Is Climate Change's 'Equally Evil Twin,' NOAA Chief Says," http://www.huffingtonpost.com/2012/07/09/ocean-acidification-reefs-climate-change_n_1658081.html?utm_hp_ref=green
36. ^ Atkinson, M.J.; Cuet, P. (2008). "Possible effects of ocean acidification on coral reef biogeochemistry: topics for research". Marine Ecology Progress Series 373: 249–256. doi:10.3354/meps07867.
37. ^ Thurman, H.V.; Trujillo, A.P. (2004). Introductory Oceanography. Prentice Hall. ISBN 978-0-13-143888-0.
38. ^ The Royal Society. Ocean Acidification Due To Increasing Atmospheric Carbon Dioxide, The Clyvedon Press Ltd. (2005): 11.
39. ^ Marubini, F.; Ferrier-Pagès, C.; Furla, P.; Allemand, D. (2008). "Coral calcification responds to seawater acidification: a working hypothesis towards a physiological mechanism". Coral Reefs 27 (3): 491–499. Bibcode:2008CorRe..27..491M. doi:10.1007/s00338-008-0375-6.
40. ^ National Research Council. "Overview of Climate Changes and Illustrative Impacts." Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia. Washington, DC: The National Academies Press, 2011. 1. Print.
41. ^ Nienhuis, S.; Palmer, A.; Harley, C. (2010). "Elevated CO2 affects shell dissolution rate but not calcification rate in a marine snail". Proceedings of the Royal Society B: Biological Sciences 277 (1693): 2553–2558. doi:10.1098/rspb.2010.0206. PMC 2894921. PMID 20392726.
42. ^ Gattuso, J.-P.; Frankignoulle, M.; Bourge, I.; Romaine, S. and Buddemeier, R. W. (1998). "Effect of calcium carbonate saturation of seawater on coral calcification". Global and Planetary Change 18 (1–2): 37–46. Bibcode:1998GPC....18...37G. doi:10.1016/S0921-8181(98)00035-6.
43. ^ Gattuso, J.-P.; Allemand, D.; Frankignoulle, M. (1999). "Photosynthesis and calcification at cellular, organismal and community levels in coral reefs: a review on interactions and control by carbonate chemistry". American Zoologist 39: 160–183.
44. ^ Langdon, C.; Atkinson, M. J. (2005). "Effect of elevated pCO2 on photosynthesis and calcification of corals and interactions with seasonal change in temperature/irradiance and nutrient enrichment". Journal of Geophysical Research 110 (C09S07): C09S07. Bibcode:2005JGRC..11009S07L. doi:10.1029/2004JC002576.
45. ^ Riebesell, Ulf; Zondervan, Ingrid; Rost, Björn; Tortell, Philippe D.; Zeebe, Richard E. and François M. M. Morel (2000). "Reduced calcification of marine plankton in response to increased atmospheric CO2". Nature 407 (6802): 364–367. doi:10.1038/35030078. PMID 11014189.
46. ^ Zondervan, I.; Zeebe, R. E., Rost, B. and Rieblesell, U. (2001). "Decreasing marine biogenic calcification: a negative feedback on rising atmospheric CO2". Global Biogeochemical Cycles 15 (2): 507–516. Bibcode:2001GBioC..15..507Z. doi:10.1029/2000GB001321.
47. ^ Zondervan, I.; Rost, B. and Rieblesell, U. (2002). "Effect of CO2 concentration on the PIC/POC ratio in the coccolithophore Emiliania huxleyi grown under light limiting conditions and different day lengths". Journal of Experimental Marine Biology and Ecology 272 (1): 55–70. doi:10.1016/S0022-0981(02)00037-0.
48. ^ Delille, B.; Harlay, J., Zondervan, I., Jacquet, S., Chou, L., Wollast, R., Bellerby, R.G.J., Frankignoulle, M., Borges, A.V., Riebesell, U. and Gattuso, J.-P. (2005). "Response of primary production and calcification to changes of pCO2 during experimental blooms of the coccolithophorid Emiliania huxleyi". Global Biogeochemical Cycles 19 (2): GB2023. Bibcode:2005GBioC..19.2023D. doi:10.1029/2004GB002318.
49. ^ Kuffner, I. B.; Andersson, A. J., Jokiel, P. L., Rodgers, K. S. and Mackenzie, F. T. (2007). "Decreased abundance of crustose coralline algae due to ocean acidification". Nature Geoscience 1 (2): 114–117. Bibcode:2008NatGe...1..114K. doi:10.1038/ngeo100.
50. ^ Phillips, Graham; Chris Branagan (2007-09-13). "Ocean Acidification – The BIG global warming story". ABC TV Science: Catalyst (Australian Broadcasting Corporation). Retrieved 2007-09-18.
51. ^ Gazeau, F.; Quiblier, C.; Jansen, J. M.; Gattuso, J.-P.; Middelburg, J. J. and Heip, C. H. R. (2007). "Impact of elevated CO2 on shellfish calcification". Geophysical Research Letters 34 (7): L07603. Bibcode:2007GeoRL..3407603G. doi:10.1029/2006GL028554.
52. ^ Comeau, C.; Gorsky, G., Jeffree, R., Teyssié, J.-L. and Gattuso, J.-P. (2009). "Impact of ocean acidification on a key Arctic pelagic mollusc ("Limacina helicina")". Biogeosciences 6 (9): 1877–1882. doi:10.5194/bg-6-1877-2009.
53. ^ Buitenhuis, E. T.; de Baar, H. J. W. and Veldhuis, M. J. W. (1999). "Photosynthesis and calcification by Emiliania huxleyi (Prymnesiophyceae) as a function of inorganic carbon species". Journal of Phycology 35 (5): 949–959. doi:10.1046/j.1529-8817.1999.3550949.x.
54. ^ Nimer, N. A.; Merrett, M. J. (1993). "Calcification rate in Emiliania huxleyi Lohmann in response to light, nitrate and availability of inorganic carbon". New Phytologist 123 (4): 673–677. doi:10.1111/j.1469-8137.1993.tb03776.x.
55. ^ a b Iglesias-Rodriguez, M. D.; Halloran, P. R., Rickaby, R. E. M., Hall, I. R., Colmenero-Hidalgo, E., Gittins, J.R., Green, D.R.H., Tyrrell, T., Gibbs, S.J., von Dassow, P., Rehm, E., Armbrust, E.V. and Boessenkool, K.P. (2008). "Phytoplankton Calcification in a High-CO2 World". Science 320 (5874): 336–340. Bibcode:2008Sci...320..336I. doi:10.1126/science.1154122. PMID 18420926.
56. ^ Sciandra, A.; Harlay, J., Lefevre, D. et al. (2003). "Response of coccolithophorid Emiliania huxleyi to elevated partial pressure of CO2 under nitrogen limitation". Marine Ecology Progress Series 261: 111–112. doi:10.3354/meps261111.
57. ^ Langer, G.; Geisen, M., Baumann, K. H. et al. (2006). "Species-specific responses of calcifying algae to changing seawater carbonate chemistry". Geochemistry, Geophysics, Geosystems 7 (9): Q09006. Bibcode:2006GGG.....709006L. doi:10.1029/2005GC001227.
58. ^ "Acidification Of Oceans May Contribute To Global Declines Of Shellfish, Study By Stony Brook Scientists Concludes" (Press release). School of Marine and Atmospheric Sciences at Stony Brook University. 27 September 2010. Retrieved 4 June 2012.
59. ^ Ruttiman, J. (2006). "Sick Seas". Nature 442 (7106): 978–980. Bibcode:2006Natur.442..978R. doi:10.1038/442978a. PMID 16943816.
60. ^ Cohen, A.; Holcomb, M. (2009). "Why Corals Care About Ocean Acidification: Uncovering the Mechanism". Oceanography 24: 118–127.
61. ^ Hannah L. Wood, John I. Spicer and Stephen Widdicombe (2008). "Ocean acidification may increase calcification rates, but at a cost". Proceedings of the Royal Society B: Biological Sciences 275 (1644): 1767–1773. doi:10.1098/rspb.2008.0343. PMC 2587798. PMID 18460426.
62. ^ Dixson, D. L.; et al. (2010). "Ocean acidification disrupts the innate ability of fish to detect predator olfactory cues". Ecology Letters 13 (1): 68–75.
63. ^ Simpson, S. D.; et al. (2011). "Ocean acidification erodes crucial auditory behaviour in a marine fish". Biology Letters.
64. ^ Acid In The Oceans: A Growing Threat To Sea Life by Richard Harris. All Things Considered, 12 August 2009.
65. ^ "Swiss marine researcher moving in for the krill". The Australian. 2008.
66. ^ Some like it acidic April 17, 2013 Science News
67. ^ Ridgwell, A.; Zondervan, I.; Hargreaves, J. C.; Bijma, J.; and Lenton, T. M. (2007). "Assessing the potential long-term increase of oceanic fossil fuel CO2 uptake due to CO2-calcification feedback". Biogeosciences 4 (4): 481–492. doi:10.5194/bg-4-481-2007.
68. ^ Tyrrell, T. (2008). "Calcium carbonate cycling in future oceans and its influence on future climates". Journal of Plankton Research 30 (2): 141–156. doi:10.1093/plankt/fbm105.
69. ^ DiMascio, Felice; Willauer, Heather D. ; Hardy, Dennis R. ; Lewis, M. Kathleen ; Williams, Frederick W. (July 23, 2010). ﻿Extraction of Carbon Dioxide from Seawater by an Electrochemical Acidification Cell. Part 1 - Initial Feasibility Studies﻿ (memorandum report). Washington, DC: Chemistry Division, Navy Technology Center for Safety and Survivability, U.S. Naval Research Laboratory. Retrieved September 7, 2012.
70. ^ Willauer, Heather D.; DiMascio, Felice; Hardy, Dennis R.; Lewis, M. Kathleen; Williams, Frederick W. (April 11, 2011). ﻿Extraction of Carbon Dioxide from Seawater by an Electrochemical Acidification Cell. Part 2 - Laboratory Scaling Studies﻿ (memorandum report). Washington, DC: Chemistry Division, Navy Technology Center for Safety and Survivability, U.S. Naval Research Laboratory. Retrieved September 7, 2012.
71. ^ Eisaman, Matthew D.; et al. (2012). "CO2 extraction from seawater using bipolar membrane electrodialysis". Energy and Environmental Science 5 (6): 7346–52. doi:10.1039/C2EE03393C. Retrieved September 7, 2012.
72. ^ Trujillo, Alan (2011). Essentials of Oceanography. Pearson Education, Inc. p. 157. ISBN 9780321668127.
73. ^ Cao, L.; Caldeira, K. (2010). "Can ocean iron fertilization mitigate ocean acidification?". Climatic Change 99 (1-2): 303–311. doi:10.1007/s10584-010-9799-4.