Temporal variations of surface oceanic and atmospheric CO2 fugacity and total dissolved inorganic carbon in the northwestern North Pacific |
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| Authors: | Tomonori Watai Masaaki Kikuchi Takakiyo Nakazawa |
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| Institution: | (1) Center for Atmospheric and Oceanic Studies, Faculty of Science, Tohoku University, 980-77 Sendai, Japan |
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| Abstract: | In order to examine temporal variations of the surface oceanic and atmospheric fCO2 and the DIC concentration, we analyzed air and seawater samples collected during the period May 1992–June 1996 in the northwestern
North Pacific, about 30 km off the coast of the main island of Japan. The atmospheric CO2 concentration has increased secularly at a rate of 1.9 ppmv yr−1, and it showed a clear seasonal cycle with a maximum in spring and a minimum late in summer, produced mainly by seasonally-dependent
terrestrial biospheric activities. DIC also showed a prominent seasonal cycle in the surface ocean; the minimum and maximum
values of the cycle appeared in early fall and in early spring, respectively, due primarily to the seasonally-dependent activities
of marine biota and partly to the vertical mixing of seawater and the coastal upwelling. The oceanic fCO2 values were almost always lower than those of the atmospheric fCO2, suggesting that this area of the ocean acts as a sink for atmospheric CO2. Values varied seasonally, mainly reflecting seasonal changes of SST and DIC, with a secular increase at a rate of 3.7 μatm
yr−1. The average values of the annual net CO2 flux between the ocean and the atmosphere calculated by using the different bulk equations ranged between −0.8 and −1.7 mol
m−2yr−1, and its magnitude was enhanced and reduced late in spring and mid-summer, respectively, due mainly to the seasonally varying
oceanic fCO2. |
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| Keywords: | Carbon dioxide fugacity stable carbon isotope dissolved inorganic carbon surface ocean atmosphere western North Pacific |
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