石灰藻による炭酸カルシウム形成 : その機構と海洋における規模(<特集>CO_2シンクとしての炭酸塩岩と地球環境)

概要

論文の詳細を見る
It was suggseted that a very delicate carbon balance between atmosphere, hydrosphere and geosphere on the present earth was attained by CO_2 fixation by photosynthesis and by biological calcification in the ocean. The "calcareous algae", which deposit massive calcium carbonate on the thallus, are mostly marine and are widely scattered among Cyanophyta, Rhodophyta, Chlorophyta, Chlomophyta and Haptophyta. The coral reef is especially important for standing crops of macro-calcareous algae and for their productive environment of calcium carbonate. Calcification in the macro-algae takes place extracellularly in the specially separated sites from the outer seawater, i. e., in intercellular space (Halimeda in Chlorophyta) or thickened cell walls (Corallinaceae in Rhodophyta). It seems to be coupled with an increase in pH in the same sites which is caused by CO_2 fixation by photosynthesis. Calcium carbonte is deposited as aragonite (Halimeda) or magnesian calcite (Corallinaceae). Unicellular algae, coccolithophorids in Haptophyta, produce disc-shaped scales of calcite called "coccoliths". The calcified scales are formed intracellularly and then extruded to the outer surface of the cell. The morphology of coccoliths is under genetic control, and an involvement of specific calcium-binding acid polysaccharides is strongly suggested in the formation of fine structure of coccoliths. The coccolith formation is intimately associated with photosynthesis. Emiliania hyxleyi, a species in coccolithophorids, is a cosmopolitan species and a main producer of pelagic carbonate. Annual production of calcium carbonate by calcareous algae are not known in detail, but it may be estimated as sevelal ten parcent of the total annual production of carbonate (2.0x1O^9 ton as CO_2) in the ocean. Calcium carbonate formation in the ocean accompanies CO_2 evolution as follows; 2HCO_3^- +Ca^<2+>→CaCO_3+H_2O+CO_2, although CO_2 fixation by photosynthesis acts as a "driving force" for CaCO_3 precipitation. Therefore, for the evaluation of calcification in the effect on atmospheric CO_2, it must be estimated how photosynthesis overcomes the calcification in rate and what portion of organic matter synthesized in photosynthesis is remained without oxidation back to CO_2.
日本地球化学会の論文
1993-06-15

石灰藻による炭酸カルシウム形成 : その機構と海洋における規模(<特集>CO_2シンクとしての炭酸塩岩と地球環境)

スポンサーリンク

概要

著者

関連論文

スポンサーリンク