[A-OS14] Physical, biogeochemical, and ecological processes and variability in the Indian Ocean

[AOS14-P01] ２019年正のダイポールモード影響下における80°Eラインにて観測された亜表層塩分・溶存物変化

*纐纈 慎也¹、村田 昌彦¹、Arulananthan Kanapathipillai² (1.海洋研究開発機構、2.National Aquatic Resources Research and Development Agency)

キーワード：塩分変動、正のダイポールモード、溶存酸素変化

High-accuracy ship-based observations were conducted at 80°E in the Indian Ocean. The salinities below the mixed layer in 2019 were observed to be lower than that in 1995. This decrease in salinity was mainly attributed to anomalous advection associated with one of the strongest positive Indian Ocean dipole (pIOD) events in 2019 through analysis of the gridded time series of the salinity distributions based on the Argo float array. Increments and reductions in nitrate and dissolved inorganic carbon (DIC) and dissolved oxygen (DO), respectively, were also detected on the isopycnal surfaces where reductions in salinity were observed, which suggested that the anomalous upwelling and westward advection associated with the pIOD in the eastern part of equatorial regions resulted in low-salinity, low-oxygen, and nutrient-rich waters in the central off-equatorial region of the Indian Ocean. However, the downward isopycnal heaving, which was also associated with pIOD, was too strong to increase nitrate below the mixed layers and might have suppressed biological activity. The heaving also affects the DIC and DO distributions, and the effect of interannual changes like the Indian Ocean dipole is essential to estimating changes in anthropogenic carbon storage. This result was considered to be a case study, and based on only two occupations, assessment with more intensive observations and realistic numerical simulations are necessary in the future.