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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 () from the atmosphere. An estimated 30–40% of the carbon dioxide from human activity released into the atmosphere dissolves into oceans, rivers and lakes. To achieve 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 ocean acidity (H+ ion concentration). Between 1751 and 1994 surface ocean pH is estimated to have decreased from approximately 8.25 to 8.14, representing an increase of almost 30% in H+ ion concentration in the world's oceans.〔(Report of the Ocean Acidification and Oxygen Working Group, International Council for Science's Scientific Committee on Ocean Research (SCOR) Biological Observatories Workshop )〕 Earth System Models project that within the last decade ocean acidity exceeded historical analogs and in combination with other ocean biogeochemical changes could undermine the functioning of marine ecosystems and disrupt the provision of many goods and services associated with the ocean. Increasing acidity is thought to have a range of possibly harmful consequences, such as depressing metabolic rates and immune responses in some organisms, and causing coral bleaching. Other chemical reactions are triggered which result in a net decrease in the amount of carbonate ions available. This makes it more difficult for marine calcifying organisms, such as coral and some plankton, to form biogenic calcium carbonate, and such structures become vulnerable to dissolution.〔 Ongoing acidification of the oceans threatens food chains connected with the oceans. As members of the InterAcademy Panel, 105 science academies have issued a statement on ocean acidification recommending that by 2050, global emissions be reduced by at least 50% compared to the 1990 level.〔, Secretariat: TWAS (the Academy of Sciences for the Developing World), Trieste, Italy.〕 Ocean acidification has been called the "evil twin of global warming"〔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〕〔The other carbon dioxide problem http://www.rsc.org/chemistryworld/2014/07/ocean-acidification〕〔Global warming’s evil twin: ocean acidification http://theconversation.com/global-warmings-evil-twin-ocean-acidification-19017〕 and "the other problem".〔〔 Ocean acidification has occurred previously in Earth's history. The most notable example is the Paleocene-Eocene Thermal Maximum (PETM), which occurred approximately 56 million years ago. For reasons that are currently uncertain, massive amounts of carbon entered the ocean and atmosphere, and led to the dissolution of carbonate sediments in all ocean basins. ==Carbon cycle== The carbon cycle describes the fluxes of carbon dioxide () between the oceans, terrestrial biosphere, lithosphere,〔(【引用サイトリンク】work=Encyclopædia Britannica Online )〕 and the atmosphere. Human activities such as the combustion of fossil fuels and land use changes have led to a new flux of 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 and the carbonates. The inorganic compounds are particularly relevant when discussing ocean acidification for it includes many forms of dissolved present in the Earth's oceans. When dissolves, it reacts with water to form a balance of ionic and non-ionic chemical species: dissolved free carbon dioxide (), carbonic acid (), bicarbonate () and carbonate (). 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 is known as the Revelle factor. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「ocean acidification」の詳細全文を読む スポンサード リンク
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