인도양 남중서부의 Po-210과 Pb-210 농도 분포

Abstract

Three vertical water column profiles of dissolved (<1.2 μm) and particulate (>1.2 μm) 210Po and 210Pb were measured in the south central western Indian Ocean (5°S at 60°E to 67°E and 20°S 67°E) in April 2018 (Fig. 1). Our three stations are located within the tropical gyre surrounded by South Equatorial Current, Northeast Madagascar Current and South Equatorial Countercurrent. Dissolved 210Po and 210Pb activities were in the ranges of 6.0 - 17.9 dpm 100kg-1 and 8.4 -21.5 dpm 100kg-1, respectively. Dissolved 210Po and 210Pb values are rapidly decreased in the surface mixed layer (<100m) and 210Po/210Pb activity ratio in the dissolved phase was approximately 0.8 - 1.0 in the surface layer and 0.8 - 1.1 in the deep water (>2000m) of the St. 19 and St. 34. But the 210Po/210Pb activity ratio in the deep water was 1.2 - 1.8 at St. 13 probably due to the elevated decomposition of organic matter in the oxygen deficient deep waters. Particulate 210Po and 210Pb to total 210Po and 210Pb account for about 7 to 29 % for 210Po and about 3 to 17 % for 210Pb with lower values in the surface and higher values near the bottom in the south central western Indian Ocean. The earlier GEOSECS in 1978 sampled thoroughly the eastern and western and southern parts of the Indian Ocean except the tropical gyre. We attempted to plot the basin wide distribution of dissolved 210Pb and the activity ratio of 210Po/210Pb in the surface water