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Enhanced riverine carbon flux from carbonate catchment to the ocean: A comparative hydrogeochemical study on Ishigaki and Iriomote islands, southwestern Japan

2010; American Geophysical Union; Volume: 115; Issue: G2 Linguagem: Inglês

10.1029/2009jg001039

2156-2202

Hiroyuki Ushie, Hodaka Kawahata, Atsushi Suzuki, Shohei Murayama, Mayuri Inoue,

Methane Hydrates and Related Phenomena

Riverine carbon transportation is an important carbon flux connecting reservoirs of the atmosphere, continents, and oceans. The flux is strongly related to the important roles of rivers such as regulation of climate change and buffering of ocean acidification. Here, to evaluate the linkage of such functions of rivers and geological characteristics of the watersheds, we present the results of a comparative hydrogeochemical study conducted on small subtropical watersheds of aluminosilicate‐dominated Iriomote Island and carbonate‐based Ishigaki Island, southwestern Japan. Rivers on Ishigaki Island exhibited much higher alkalinity than rivers on Iriomote Island, which was even higher than the mean value of major rivers in the world, such as the Saint Lawrence and the Mississippi. This high alkalinity was the result of carbonate dissolution enhanced by soil‐originated CO 2 . As a result of this high inorganic carbon input, the ratio of inorganic carbon and nutrients of the river water was higher than that of marine organic matter such as the Redfield ratio, making the coastal seas a potential source of CO 2 for the atmosphere.