Sources, Pathways, and Drivers of Sub‐Antarctic Mode Water Formation
Abstract Sub‐Antarctic Mode Waters (SAMWs) form to the north of the Antarctic Circumpolar Current in the Indo‐Pacific Ocean, whence they ventilate the ocean's lower pycnocline and play an important role in the climate system. With a backward Lagrangian particle‐tracking experiment in a data‐ass...
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Wiley
2025-04-01
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| Online Access: | https://doi.org/10.1029/2024AV001449 |
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| author | Bieito Fernández Castro Alberto C. Naveira Garabato Matthew Mazloff Richard G. Williams |
| author_facet | Bieito Fernández Castro Alberto C. Naveira Garabato Matthew Mazloff Richard G. Williams |
| author_sort | Bieito Fernández Castro |
| collection | DOAJ |
| description | Abstract Sub‐Antarctic Mode Waters (SAMWs) form to the north of the Antarctic Circumpolar Current in the Indo‐Pacific Ocean, whence they ventilate the ocean's lower pycnocline and play an important role in the climate system. With a backward Lagrangian particle‐tracking experiment in a data‐assimilative model of the Southern Ocean (B‐SOSE), we address the long‐standing question of the extent to which SAMWs originate from densification of southward‐flowing subtropical waters versus lightening of northward‐flowing Antarctic waters sourced by Circumpolar Deep Water (CDW) upwelling. Our analysis evidences the co‐occurrence of both sources in all SAMW formation areas, and strong inter‐basin contrasts in their relative contributions. Subtropical waters are the main precursor of Indian Ocean SAMWs (70%–75% of particles) but contribute a smaller amount (<40% of particles) to Pacific SAMWs, which are mainly sourced from the upwelled CDW. By tracking property changes along particle trajectories, we show that SAMW formation from northern and southern sources involves contrasting drivers: subtropical source waters are cooled and densified by surface heat fluxes, and freshened by ocean mixing. Southern source waters are warmed and lightened by surface heat and freshwater fluxes, and they are made either saltier by mixing in the case of Indian SAMWs, or fresher by surface fluxes in the case of Pacific SAMWs. Our results underscore the distinct climatic impact of Indian and Pacific SAMWs formation, involving net release of atmospheric heat and uptake of atmospheric freshwater, respectively; a role that is conferred by the relative contributions of subtropical and Antarctic sources to their formation. |
| format | Article |
| id | doaj-art-163a2753f02f48cea89bbbd9eb6ca98a |
| institution | DOAJ |
| issn | 2576-604X |
| language | English |
| publishDate | 2025-04-01 |
| publisher | Wiley |
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| series | AGU Advances |
| spelling | doaj-art-163a2753f02f48cea89bbbd9eb6ca98a2025-08-20T03:09:32ZengWileyAGU Advances2576-604X2025-04-0162n/an/a10.1029/2024AV001449Sources, Pathways, and Drivers of Sub‐Antarctic Mode Water FormationBieito Fernández Castro0Alberto C. Naveira Garabato1Matthew Mazloff2Richard G. Williams3Ocean and Earth Science National Oceanography Centre University of Southampton Southampton UKOcean and Earth Science National Oceanography Centre University of Southampton Southampton UKScripps Institution of Oceanography University of California, San Diego La Jolla CA USADepartment of Earth, Ocean, and Ecological Sciences School of Environmental Sciences University of Liverpool Liverpool UKAbstract Sub‐Antarctic Mode Waters (SAMWs) form to the north of the Antarctic Circumpolar Current in the Indo‐Pacific Ocean, whence they ventilate the ocean's lower pycnocline and play an important role in the climate system. With a backward Lagrangian particle‐tracking experiment in a data‐assimilative model of the Southern Ocean (B‐SOSE), we address the long‐standing question of the extent to which SAMWs originate from densification of southward‐flowing subtropical waters versus lightening of northward‐flowing Antarctic waters sourced by Circumpolar Deep Water (CDW) upwelling. Our analysis evidences the co‐occurrence of both sources in all SAMW formation areas, and strong inter‐basin contrasts in their relative contributions. Subtropical waters are the main precursor of Indian Ocean SAMWs (70%–75% of particles) but contribute a smaller amount (<40% of particles) to Pacific SAMWs, which are mainly sourced from the upwelled CDW. By tracking property changes along particle trajectories, we show that SAMW formation from northern and southern sources involves contrasting drivers: subtropical source waters are cooled and densified by surface heat fluxes, and freshened by ocean mixing. Southern source waters are warmed and lightened by surface heat and freshwater fluxes, and they are made either saltier by mixing in the case of Indian SAMWs, or fresher by surface fluxes in the case of Pacific SAMWs. Our results underscore the distinct climatic impact of Indian and Pacific SAMWs formation, involving net release of atmospheric heat and uptake of atmospheric freshwater, respectively; a role that is conferred by the relative contributions of subtropical and Antarctic sources to their formation.https://doi.org/10.1029/2024AV001449Sub‐Antartic Mode WatersSouthern OceanLagrangian trackingwater mass transformationocean mixing |
| spellingShingle | Bieito Fernández Castro Alberto C. Naveira Garabato Matthew Mazloff Richard G. Williams Sources, Pathways, and Drivers of Sub‐Antarctic Mode Water Formation AGU Advances Sub‐Antartic Mode Waters Southern Ocean Lagrangian tracking water mass transformation ocean mixing |
| title | Sources, Pathways, and Drivers of Sub‐Antarctic Mode Water Formation |
| title_full | Sources, Pathways, and Drivers of Sub‐Antarctic Mode Water Formation |
| title_fullStr | Sources, Pathways, and Drivers of Sub‐Antarctic Mode Water Formation |
| title_full_unstemmed | Sources, Pathways, and Drivers of Sub‐Antarctic Mode Water Formation |
| title_short | Sources, Pathways, and Drivers of Sub‐Antarctic Mode Water Formation |
| title_sort | sources pathways and drivers of sub antarctic mode water formation |
| topic | Sub‐Antartic Mode Waters Southern Ocean Lagrangian tracking water mass transformation ocean mixing |
| url | https://doi.org/10.1029/2024AV001449 |
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