• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.24 no.3
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• pp.389-399
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• 2019

The calcium carbonate saturation state in the Ulleung Basin of East Sea was calculated using bottle data set of pH, dissolved inorganic carbon and total alkalinity obtained from the year 1999, 2014, 2017, and 2018 cruise. In the 2010s calcium carbonate saturation state was significantly lowered at all depth compared to the 1999 reference state. Accordingly calcite saturation horizon and aragonite saturation horizon shoaled to 500 m and 200 m, respectively. A key chemical species for the calcium carbonate saturation state, carbonate ion showed distinctive profile between upper and deep waters: it is moderately high (${\sim}175{\mu}mol\;kg^{-1}$) in upper waters and very low (< ${\sim}50{\mu}mol\;kg^{-1}$) in the deep waters. However the decreasing trend of carbonate ion concentration was pronounced in the upper water than deep waters, suggesting atmospheric $CO_2$ penetration is largely confined to the upper waters in the 2000s.