Because the partial pressure of carbon dioxide (pCO2) at the ocean surface is the main determinant of the air–sea CO2 flux, understanding what causes pCO2 to vary is important to the issue of carbon sequestration. The strength of the CO2 flux is strongly influenced by wind speed and, in polar regions, the presence of sea ice which affects gas exchange efficiency. In this study, oceanographic measurements were made near the Mertz Glacier at 140–150°E during the 2018–2019 austral summer to clarify the effects of melting sea ice and glacial ice and biological production on surface ocean pCO2. Water column samples were collected and analyzed for stable oxygen isotopic ratios and concentrations of dissolved inorganic carbon, total alkalinity, and nutrients. We evaluated the direct effects of meteoric water and sea ice meltwater on pCO2, finding that, at 10 dbar, they reduced pCO2 by 8 ± 1 µatm and 8 ± 2 µatm, respectively, relative to pCO2 of Circumpolar Deep Water, 447 ± 21 µatm. We then evaluated the indirect effects of biological production, finding that the reduction of pCO2 due to biological production, calculated from nutrient uptake during winter and summer, was 107 ± 31 µatm. The reduction of pCO2 at 10 dbar (113 ± 29 µatm) relative to pCO2 of Circumpolar Deep Water in the coastal region of the Mertz Glacier was influenced significantly by biological production. Iron limitation was assessed based on the ratio of nutrient consumption (ΔSi/ΔN) of phytoplankton from winter to summer. Net community production was higher and ΔSi/ΔN was lower closest to the continent. As low ΔSi/ΔN indicates iron-replete conditions, the implication is that iron had enhanced biological production. These results support the hypothesis that iron supplied by glacial meltwater and coastal sediments controls biological production and pCO2 variability in this area.
SAMORI et al. (Thu,) studied this question.