Unique transport paths of 137Cs from the Indian to Southern Oceans

• Published in: Marine pollution bulletin 2024-04, Vol.201, p.116168-116168, Article 116168
• Main Authors: Inoue, Mutsuo, Mashita, Kaisei, Mitsunushi, Hayata, Nagao, Seiya, Kumamoto, Yuichiro
• Format: Article
• Language: English
• Subjects: Current system; Indian Ocean; Low-background γ-spectrometry; Radiocesium; Radium isotopes; Southern Ocean
• ISSN: 0025-326X; 1879-3363
• DOI: 10.1016/j.marpolbul.2024.116168

To assess ocean-scale transport systems, we examined the latitudinal cross-sectional distribution of 137Cs activity concentrations in the Indian and Southern Oceans between December 2019 and January 2020 using low-background γ-spectrometry. At 0°–20°S, 137Cs concentrations exhibited a gradual decrease below the mixing layer (1–0.1 mBq/L). However, the concentrations steeply decreased toward the Southern Ocean along a transect of 30°–60°S (from 0.8 to 0.02 mBq/L) with minor vertical variation at each site. For the 137Cs inventories (0–800 m depth) from 15 to 600 Bq/m2, a maximum value was recorded at 30°S, indicating the downwelling of 137Cs as a reservoir for the Subantarctic Mode Water. The significantly low concentrations (0.02 mBq/L) at 60°S suggest minimal transport of 137Cs to the Southern Ocean. These findings assist in understanding 137Cs circulation patterns and provide valuable insights into the transport pathways of soluble contaminants. •Spatial distribution of 137Cs was examined in Indian–Southern Oceans in early 2020.•Area under 30°–60°S received more surface ventilation than that under 0°–20°S.•Maximum inventory at ~30°S indicated the downwelling transport of 137Cs to SAMW.•Transport of 137Cs between the Indian and Southern Oceans is extremely limited.