Depth distribution of δ13 of dissolved ΣCO2 in seawater off eastern Taiwan: effects of the Kuroshio current and its associated upwelling phenomenon

This paper presents depth variations of dissolved 02, ΣCO2, alkalinity, and δ13 C of ΣCO2 in seawater off eastern Taiwan. O2 decreases from an averaged surface value of approximately 4.6 ml l−1 to a minimum of about 2.0 ml I−1 at a depth of 1000 m, and then increases gradually to about 3.5 ml l−1 near the seafloor. ICO2 concentrations increase from typical values of 1900–2050 μmol kg−1 at the surface to 2100–2300 μmol kg−1 at depths of more than 1000 m, corresponding to an increase in alkalinity from about 2250μeq kg−1 at the surface to 2450μeq kg−1 in the bottom water. δ13 C of ΣCO2 at the surface averages about +0.25% and becomes lighter with increasing depth to approximately −1.0%. The observed depth distributions of O2, :ΣCO2, alkalinity andδ13 of ΣCO2 are thus similar to those reported in the open ocean and can be attributed to OZ utilization and CO2 production during organic decomposition. On a close examination, however, rates of O2 decrease and ΣCO2 and alkalinity increases are less profound than those observed in the open ocean, particularly in the Pacific. Furthermore, values ofδ13 C measured are invariably lighter than those reported in the Pacific. The discrepancy is attributed largely to the presence of the Kuroshio current and its associated upwelling phenomenon in the continental margin off eastern Taiwan.