Provenance of intermediate waters in the western North Pacific deduced from thermodynamic imprint on δ13C of DIC -: art. no. 3347

[1] Stable carbon isotopes of dissolved inorganic carbon (delta(13)C(DIC)), together with phosphate concentrations (PO43-) of the western North Pacific marginal area are presented. Although delta(13)C(DIC) controlled not only air-sea exchange but also biological activities, by subtracting PO43- as a biological factor from the delta(13)C(DIC), the thermodynamic imprint on the carbon isotopic composition (delta(13)C(as)) is used as a conservative tracer. The linear relationship between delta(13)C(as) and temperature with the delta(13)C(as)/temperature slope of -0.104parts per thousand/degreesC is observed in the North Pacific subtropical region. This relationship can be extended to the Weddell Sea deep waters. Therefore oceanic DIC is apparently in temperature-dependent isotopic equilibrium with atmospheric CO2. To characterize each water mass, the "isotopically labeled temperature'' (T-iso), which is derived from delta(13)C(as)-temperature relationship obtained for the subtropical gyre water and Weddell Sea Water, is introduced. In contrast, the delta(13)C(as)-temperature relationship is not necessarily linear for the northern Japan Sea Water, the Kuroshio-Oyashio Mixed Water and the Okhotsk Sea Water. This nonlinearity implies apparent air-sea carbon isotopic disequilibria resulting from water cooling without accompanying air-sea carbon isotope equilibrium. By using the potential temperature (T-pot) and the T-iso, the source waters constituting intermediate waters (26.8sigma(theta)) have been estimated. The results clearly indicate that (1) the intermediate water in the southern Okhotsk Sea contains up to 20% Japan Sea Water, and that (2) "new'' North Pacific Intermediate Water (NPIW) consists of Okhotsk Sea Water, subarctic gyre water, and "old'' subtropical NPIW.