報告書番号

V06019

タイトル（和文）

大気中CO2濃度の増加がもたらす海洋酸性化－海洋プランクトンを通じてCO2吸収に与える影響に関する文献調査－

タイトル（英文）

Ocean acidification induced by increasing atmospheric carbon dioxide-A literature review of the impacts of ocean acidification on oceanic uptake of CO2 by marine plankton-

概要 （図表や脚注は「報告書全文」に掲載しております）

海洋の酸性化とこれが海洋植物プランクトンに与える影響に関する最新の知見を調査し，今後解明すべき課題を抽出した。近年の大気中CO2濃度の増加は海洋表層へのCO2吸収量を増加させ，その結果，表層水のpHは産業革命前と比較して0.1低下している。今後の大気中CO2濃度の増加は海洋の酸性化をより進行させると考えられる。海水のpHの低下はCO32-濃度の減少とCO2濃度の増加を伴う。CO32-濃度の減少は海洋生物の炭酸カルシウム外骨格の形成を阻害し，最終的にはこれを溶解させる。一方，CO2濃度の増加は植物プランクトンによる光合成を活発化する可能性が指摘されている。海洋酸性化が海洋プランクトンに与えるこれらの影響は海洋生態系構造を変化させるとともに，海洋炭素循環を変化させる可能性がある。しかしながら，海洋酸性化に対する植物プランクトンの応答を評価するための定量的な実験結果は極めて限られている。実験結果の蓄積により海洋酸性化に対する植物プランクトンの応答を把握するとともに，これの実験結果を海洋生態系モデルを用いた検討に反映させていく。

概要 （英文）

Although CO2 released into the atmosphere as a result of the burning of fossil fuels cause the global warming, the ocean play a significant role on absorbing the CO2 and restraining the rapid increase in the atmospheric CO2 concentration. However, hydrolysis of CO2 in seawater increases the hydrogen ion concentration, and thus lowers pH in the surface seawater. Here, the present knowledge about ocean acidification and its impacts on oceanic uptake of CO2 were researched on literatures, and then the issue, which should be resolved soon, was clarified.
We surveyed 56 of recent publication about the impacts of ocean acidification. Scientific knowledge was summarized as follows. (1) Progress in ocean acidification; recent observations revealed that global average of surface ocean, pH shallower than 25 m depth is 8.1, and the value is already 0.1 unit lower than preindustrial values. The study, using 13 models of the ocean carbon cycle, revealed that pH in the Southern Ocean surface water will begin to become lower than 7.8 by the year 2050. (2) Impacts on plankton; increase in CO2 concentration lowered the production rate of calcium carbonate by pteropods and coccolithophores, and a part of the shell was solved in the water with high CO2 during the incubation experiments. In contrast, increase in CO2 in seawater will increase the photosynthetic rate of phytoplankton. However the effect is different among the species, so the increase in CO2 may induce the change in phytoplankton species composition. (3) Impacts on the absorption of CO2 into the ocean; the less the production of calcium carbonate, the more the CO2 dissolved in seawater. The more the phytoplanktonic photosynthesis, the more the CO2 dissolved in seawater. Thus, both of these two responses will increase the CO2 absorption into the ocean.
Scince experimental results for responses of marine plankton to an ocean acidification are not enough for quantitateve discussions, we will examine the responses of calcification and photosynthesis by phytoplankton to the increase in CO2 and seawater temperature with the incubation experiments in order to clarify the future change in oceanic uptake of CO2. Then, the results from the experiments could be reflected in a progressing marine ecosystem model.

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