Temporal variation of the partial pressure of CO2 in surface seawater of Iyo Nada in the Seto Inland Sea, Japan

Abstract

The temporal variation of the partial pressure of carbon dioxide $$(P_{CO_2 } )$$ in surface seawater of Iyo Nada in the western Seto Inland Sea was measured by infrared absorption of carbon dioxide (CO2) in air equilibrated with seawater. The variation of $$P_{CO_2 } $$ from January to late May in 1994 was relatively small (from 270 to 340 μatm). on the contrary, the $$P_{CO_2 } $$ measured in September 1993 ranged from 200 to 450 μatm. It seems that the relative high $$P_{CO_2 } $$ observed in the north and the south of Iyo Nada in September were caused by destruction of a stratification owing to tidal currents at straits between Hiroshima Bay and Iyo Nada and Hayasui Straits, respectively. The low $$P_{CO_2 } $$ observed in the central Iyo Nada in September was ascribed to a tidal front where high concentrations of chlorophyll-a and a relation between $$P_{CO_2 } $$ and chlorophyll-a in negative sense were found. Except the observation in the north of Iyo Nada in September, the $$P_{CO_2 } $$ in the surface seawater of Iyo Nada were lowe than the atmospheric $$P_{CO_2 } $$ (about 367 μatm). The results obtained by this work and Kimotoet al. (1993) lead to the conclusion that Iyo Nada acts as a sink of the atmospheric CO2 on the average.