2026/05/04 by Yu Hong, Yan Du, Yifan Xia +1
Earth and Planetary Sciences · Environmental Science · #Geology and Paleoclimatology Research #Methane Hydrates and Related Phenomena #Geological Studies and Exploration
paper · doi:10.1175/jpo-d-25-0147.1
Abstract Antarctic Intermediate Water (AAIW), occupying a broad region at intermediate depths in the Southern Hemisphere oceans, plays a crucial role in global heat and freshwater redistribution. However, its origin at the sea surface remains a subject of ongoing debate. A recently defined distance metric, which distinguishes similar water parcels, is applied to Argo data to trace the surface origins of the AAIW cores in each ocean basin. By examining the spatial distribution of distances to the AAIW cores, we identify that the Pacific and Atlantic AAIW cores primarily originate from localized surface regions, specifically near the Subantarctic Front in the southeast Pacific and the Falkland Plateau in the southwest Atlantic. Further investigation indicates that through subduction in the deep mixed layer, low-salinity water penetrates to intermediate depths in these regions. North of the subduction sites, water masses primarily circulate within the subtropical gyre in the South Pacific, whereas to the south, they are advected eastward by the Antarctic Circumpolar Current into the Atlantic Ocean. In the Indian Ocean, the AAIW core, distinguished by its relatively low oxygen concentration, originates both from eastward inflow carried by the Antarctic Circumpolar Current from the southeast Pacific and local surface sources near 90°E. Our findings confirm the reliability of the distance metric and emphasize the importance of localized physical processes in the penetration of AAIW into the ocean interior. Significance Statement Antarctic Intermediate Water (AAIW), found in Southern Hemisphere intermediate depths, is essential for global heat and freshwater distribution. Using a newly defined distance metric, it is found that AAIW originates primarily from the Subantarctic Front in the southeast Pacific and the Falkland Plateau in the southwest Atlantic, where low-salinity water subducts into deeper layers. In contrast, the Indian Ocean lacks this direct path, with its AAIW formed by the inflow of AAIW from the Atlantic via the Antarctic Circumpolar Current. These findings improve our understanding of AAIW origins and pathways within the ocean.