Unique current connecting Southern and Indian Oceans identified from radium distributions

• Published in: Scientific Reports
• Main Authors: Mutsuo Inoue, Shotaro Hanaki, Hiroaki Kameyama, Yuichiro Kumamoto, Seiya Nagao
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Portfolio 2022
• Subjects: Medicine; R; Science; Q; Antarctic; Southern Ocean; The Antarctic; Indian; Antarc*
• Online Access: https://doi.org/10.1038/s41598-022-05928-y; https://doaj.org/article/21d856ed92604a5c8ce7006c0f6c1f70

Abstract We examined the spatial variations in 226Ra and 228Ra (activities) concentrations from the surface to a depth of 830 m in the Indian and Southern Oceans from December 2019 to January 2020. 226Ra concentrations at the surface increased sharply from 30° S to 60° S along a ~ 55° E transect (1.4–2.9 mBq/L), exhibiting small vertical variations, while 228Ra decreased southward and became depleted in the Southern Ocean. These distributions indicated the ocean-scale northward lateral transport of 226Ra-rich and 228Ra-depleted currents originating from the Antarctic Circumpolar Current (ACC). 226Ra concentrations indicated that the fractions of the ACC at depths of 0–800 m decreased from 0.95 to 0.14 between 60° S and 30° S. The ACC fractions in the subantarctic western Indian Ocean were higher than those previously reported in the eastern Indian region, indicating preferential transport of the ACC. The fractions obtained were approximately equivalent to those in the western Indian Ocean in the 1970s. This could be attributed to the minimal southward shift of the polar front due to global warming over the last 50 years.