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Ocean acidification is the ongoing decrease in the pH of the Earth's oceans, caused by the uptake of carbon dioxide ( CO 2 ) from the atmosphere. The main cause of ocean acidification is the burning of fossil fuels. Seawater is slightly basic (meaning pH > 7), and ocean acidification involves a shift towards pH-neutral conditions rather than a transition to acidic conditions (pH < 7). The issue of ocean acidification is the decreased production of the shells of shellfish and other aquatic life with calcium carbonate shells. The calcium carbonate shells can not reproduce under high saturated acidotic waters. An estimated 30–40% of the carbon dioxide from human activity released into the atmosphere dissolves into oceans, rivers and lakes. Some of it reacts with the water to form carbonic acid. Some of the resulting carbonic acid molecules dissociate into a bicarbonate ion and a hydrogen ion, thus increasing ocean acidity (H+ ion concentration). Between 1751 and 1996, surface ...

The carbon cycle describes the fluxes of carbon dioxide ( CO 2 ) between the oceans, terrestrial biosphere, lithosphere, and the atmosphere. Human activities such as the combustion of fossil fuels and land use changes have led to a new flux of CO 2 into the atmosphere. About 45% has remained in the atmosphere; most of the rest has been taken up by the oceans, with some taken up by terrestrial plants. The carbon cycle involves both organic compounds such as cellulose and inorganic carbon compounds such as carbon dioxide, carbonate ion, and bicarbonate ion. The inorganic compounds are particularly relevant when discussing ocean acidification for they include many forms of dissolved CO 2 present in the Earth's oceans. When CO 2 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 ( H 2 CO 3 ), bicarbonate ( HCO − 3 ) and carbonate ( CO 2− 3 ). The ratio of these species depends on factor...

Dissolving CO 2 in seawater increases the hydrogen ion ( H + ) concentration in the ocean, and thus decreases ocean pH, as follows: CO 2 (aq) + H 2 O ⇌ H 2 CO 3 ⇌ HCO 3 − + H+ ⇌ CO 3 2− + 2 H+. Caldeira and Wickett (2003) placed the rate and magnitude of modern ocean acidification changes in the context of probable historical changes during the last 300 million years. Since the industrial revolution began, the ocean has absorbed about a third of the CO 2 we have produced since then and it is estimated that surface ocean pH has dropped by slightly more than 0.1 units on the logarithmic scale of pH, representing about a 29% increase in H + . It is expected to 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 CO 2 , the impacts being most severe for coral reefs and the Southern Ocean. These changes are predicted to accelerate as more anthropogenic CO 2 is rel...

Overview edit 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 ( CaCO 3 ). 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 CaCO 3 structures, such as coccoliths. After they are formed, such structures are vulnerable to dissolution unless the surrounding seawater contains saturating concentrations of carbonate ions (CO 3 2−). Mechanism edit Of the extra carbon dioxide added into the oceans, some remains as dissolved carbon dioxide, while the rest contributes towards making additional bicarbonate (and additional carbonic acid). This also increases the concentration of hydrogen ions, and the percentage increase in hydrogen is larger than the percentage in...

Increasing acidity has possibly harmful consequences, such as depressing metabolic rates in jumbo squid, depressing the immune responses of blue mussels, and coral bleaching. However it may benefit some species, for example increasing the growth rate of the sea star, Pisaster ochraceus , while shelled plankton species may flourish in altered oceans. The reports "Ocean Acidification Summary for Policymakers 2013" and the IPCC approved "Special Report on the Ocean and Cryosphere in a Changing Climate" from 2019 describe research findings and possible impacts. Impacts on oceanic calcifying organisms edit Although the natural absorption of CO 2 by the world's oceans helps mitigate the climatic effects of anthropogenic emissions of CO 2 , 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,...

Reducing CO 2 emissions edit Members of the InterAcademy Panel recommended that by 2050, global anthropogenic CO 2 emissions be reduced less than 50% of the 1990 level. The 2009 statement also called on world leaders to: Acknowledge that ocean acidification is a direct and real consequence of increasing atmospheric CO 2 concentrations, is already having an effect at current concentrations, and is likely to cause grave harm to important marine ecosystems as CO 2 concentrations reach 450 parts-per-million (ppm) and above; ... Recognize that reducing the build up of CO 2 in the atmosphere is the only practicable solution to mitigating ocean acidification; ... Reinvigorate action to reduce stressors, such as overfishing and pollution, on marine ecosystems to increase resilience to ocean acidification. Stabilizing atmospheric CO 2 concentrations at 450 ppm would require near-term emissions reductions, with steeper reductions over time. The German Advisory Council on Global Change...

Three of the big five mass extinction events in the geologic past were associated with a rapid increase in atmospheric carbon dioxide, probably due to volcanism and/or thermal dissociation of marine gas hydrates. Early research focused on the climatic effects of the elevated CO 2 levels on biodiversity, but in 2004, decreased CaCO 3 saturation due to seawater uptake of volcanogenic CO 2 was suggested as a possible kill mechanism during the marine mass extinction at the end of the Triassic. The end-Triassic biotic crisis is still the most well-established example of a marine mass extinction due to ocean acidification, because (a) volcanic activity, changes in carbon isotopes, decrease of carbonate sedimentation, and marine extinction coincided precisely in the stratigraphic record, and (b) there was pronounced selectivity of the extinction against organisms with thick aragonitic skeletons, which is predicted from experimental studies. Ocean acidification has also been suggested as a ...

"Present day" (1990s) sea surface pH Present day alkalinity "Present day" (1990s) sea surface anthropogenic CO 2 Vertical inventory of "present day" (1990s) anthropogenic CO 2 Change in surface CO 2− 3 ion from the 1700s to the 1990s Present day DIC Pre-Industrial DIC A NOAA (AOML) in situ CO 2 concentration sensor (SAMI-CO2), attached to a Coral Reef Early Warning System station, utilized in conducting ocean acidification studies near coral reef areas A NOAA (PMEL) moored autonomous CO 2 buoy used for measuring CO 2 concentration and ocean acidification studies

Clarke, L.; Edmonds, J.; Jacoby, H.; Pitcher, H.; Reilly, J.; Richels, R. (July 2007). "Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations. Sub-report 2.1A" (PDF) . In U.S. Climate Change Science Program and the Subcommittee on Global Change Research (ed.). Synthesis and Assessment Product 2.1 . Washington, DC., USA: Department of Energy, Office of Biological & Environmental Research. Archived from the original (PDF) on 16 June 2013. Good, P.; Gosling, S. N.; Bernie, D.; Caesar1, J.; Warren, R.; Arnell, N. W.; Lowe, J. A. (2010). An updated review of developments in climate science research since IPCC Fourth Assessment Report (PDF) (Report). London, UK: AVOID Consortium. Report website. UK Royal Society (September 2009). Geoengineering the climate: science, governance and uncertainty (PDF) . London: UK Royal Society. ISBN  978-0-85403-773-5 , RS Policy document 10/09. Report website. UNEP (November 2010). The Emissions Gap Report: Are the Copenh...

Three of the big five mass extinction events in the geologic past were associated with a rapid increase in atmospheric carbon dioxide, probably due to volcanism and/or thermal dissociation of marine gas hydrates. Early research focused on the climatic effects of the elevated CO 2 levels on biodiversity, but in 2004, decreased CaCO 3 saturation due to seawater uptake of volcanogenic CO 2 was suggested as a possible kill mechanism during the marine mass extinction at the end of the Triassic. The end-Triassic biotic crisis is still the most well-established example of a marine mass extinction due to ocean acidification, because (a) volcanic activity, changes in carbon isotopes, decrease of carbonate sedimentation, and marine extinction coincided precisely in the stratigraphic record, and (b) there was pronounced selectivity of the extinction against organisms with thick aragonitic skeletons, which is predicted from experimental studies. Ocean acidification has also been suggested as a ...

"Present day" (1990s) sea surface pH Present day alkalinity "Present day" (1990s) sea surface anthropogenic CO 2 Vertical inventory of "present day" (1990s) anthropogenic CO 2 Change in surface CO 2− 3 ion from the 1700s to the 1990s Present day DIC Pre-Industrial DIC A NOAA (AOML) in situ CO 2 concentration sensor (SAMI-CO2), attached to a Coral Reef Early Warning System station, utilized in conducting ocean acidification studies near coral reef areas A NOAA (PMEL) moored autonomous CO 2 buoy used for measuring CO 2 concentration and ocean acidification studies

Clarke, L.; Edmonds, J.; Jacoby, H.; Pitcher, H.; Reilly, J.; Richels, R. (July 2007). "Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations. Sub-report 2.1A" (PDF) . In U.S. Climate Change Science Program and the Subcommittee on Global Change Research (ed.). Synthesis and Assessment Product 2.1 . Washington, DC., USA: Department of Energy, Office of Biological & Environmental Research. Archived from the original (PDF) on 16 June 2013. Good, P.; Gosling, S. N.; Bernie, D.; Caesar1, J.; Warren, R.; Arnell, N. W.; Lowe, J. A. (2010). An updated review of developments in climate science research since IPCC Fourth Assessment Report (PDF) (Report). London, UK: AVOID Consortium. Report website. UK Royal Society (September 2009). Geoengineering the climate: science, governance and uncertainty (PDF) . London: UK Royal Society. ISBN  978-0-85403-773-5 , RS Policy document 10/09. CS1 maint: ref=harv (link) Report website. UNEP (November 2010). The Emissions...