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

Rivers on Ishigaki Island, part of the UNESCO World Heritage Sites in Japan's Ryukyu Archipelago, exhibit exceptionally high alkalinity due to enhanced carbonate dissolution driven by soil-originated CO₂. This results in a significant riverine carbon flux with implications for climate regulation and ocean acidification buffering. A comparative hydrogeochemical study on Ishigaki Island (carbonate-dominated) and Iriomote Island (aluminosilicate-dominated) revealed that Ishigaki's rivers have alkalinity levels surpassing global averages, such as those of the Saint Lawrence and Mississippi rivers. This high inorganic carbon input alters the ratio of carbon to nutrients in river water, potentially making coastal seas a source of atmospheric CO₂. The study highlights the critical role of geological characteristics in shaping riverine carbon dynamics and their broader environmental impacts.

Ushie, H., Kawahata, H., Suzuki, A., Murayama, S., & Inoue, M. (2010). Enhanced riverine carbon flux from carbonate catchment to the ocean: A comparative hydrogeochemical study on Ishigaki and Iriomote islands, southwestern Japan. Journal of Geophysical Research: Biogeosciences, 115(G2). Portico. https://doi.org/10.1029/2009jg001039