Meridional Distribution of Surface CO2 along 67°E of the Indian Ocean

Surface seawater carbon dioxide was observed from 3 °S to 27 °S along 67 °E of the Indian Ocean in April 2018 and 2019. Partial pressure of CO₂(pCO₂) in the surface seawater and the atmosphere were observed every two minutes using an underway CO2 measurement system (General Oceanics Model 8050) installed on R/V Isabu. Surface water temperature and salinity were measured as well. The pCO₂ was measured using Li-7000 NDIR. Standard gases were measured every 8 hours in five classes with concentrations of 0 µatm, 202 µatm, 350 µatm, 447 µatm, and 359.87 µatm. The fCO₂ of atmosphere remained nearly constant at 387 ± 2 µatm, but the surface seawater fCO₂ peaked at about 3 °S and tended to decrease toward the north and south. The distribution of fCO₂ in surface seawater according to latitude tends to be very similar to that of sea surface temperature. In order to investigate the factors that control the distribution of fCO₂ in surface seawater, we analyzed the sea surface temperature, sea surface salinity, and other factors. The effects of salinity are insignificant, and the surface fCO₂ distribution is mainly controlled by sea surface temperature and other factors that can be represented mainly by biological activity and mixing.