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.
Highlights
The Antarctic Circumpolar Current (ACC) in the Southern Ocean (> ~ 60° S) is the largest eastward current in the global ocean, surrounding Antarctica
This study examined the spatial distributions of 226Ra and 228Ra concentrations at depths of 10–830 m from the northwestern Indian Ocean to the Southern Ocean and obtained a comprehensive understanding of temporal and ocean-scale spatial variations, incorporating the results from previous s tudies[19,20,21,22,23,24,25,26,27]
Based on the salinity and dissolved oxygen (DO) profiles, water columns from depths of > 100–800 m at sites MR19-73 and -104 predominantly comprised the Subantarctic Mode Water (SAMW) and AAIW, which is formed via the convection of Antarctic Surface Water, existing between the upper layer and Upper Circumpolar Deep Water (UCDW)[6,30,31]
Summary
The Antarctic Circumpolar Current (ACC) in the Southern Ocean (> ~ 60° S) is the largest eastward current in the global ocean, surrounding Antarctica. This study examined the spatial distributions of 226Ra and 228Ra concentrations at depths of 10–830 m from the northwestern Indian Ocean to the Southern Ocean and obtained a comprehensive understanding of temporal (over the last 50 years) and ocean-scale spatial variations (between the western and eastern Indian Ocean and the Southern Ocean), incorporating the results from previous s tudies[19,20,21,22,23,24,25,26,27] It clarified ocean-scale current circulations in this area, focusing on the waters connecting the Southern and southern Indian Oceans
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
