Abstract
In this paper, we study the region of the Agulhas leakage origin. The study region is limited by 20–46° S, 0–24° E; it includes the Cape Basin and is crossed by Walvis Ridge. This region is characterized by high dynamic activity of mesoscale eddies and variability of hydrographic parameters in a wide range of spatial and temporal scales. The main element of large-scale circulation is represented by a phenomenon called the Agulhas leakage which is influenced by the South Atlantic Gyre, Benguela Current, and Benguela upwelling. Water particles of various origins are mixed and affect the thermohaline properties of mesoscale eddies, which form a source of the Agulhas leakage. We divided the region into three zones and showed that eddies and their properties differ in each of them. The Agulhas leakage is formed only by long-lived eddies, mainly anticyclones, while cyclones have smaller trajectories and shorter lifespans. In this research, we apply statistical analysis using AMEDA (Angular Momentum Eddy Detection Algorithm), Lagrangian analysis, and the study of vertical thermohaline cross-sections. We establish that in the Cape Basin, the waters of the Agulhas leakage mix with waters of the South Atlantic Gyre and the Benguela Current, and the thermohaline properties of the Agulhas eddies change since the warm and salty waters of the Indian Ocean mix with fresher and colder ones of the Atlantic Ocean. The water particles of the South Atlantic Gyre cross the western border of the region and travel a distance exceeding 500 km in the eastern direction mixing with other particles. We demonstrate that the eddies generated in the Cape Basin are also significantly influenced by the waters of the South Atlantic Gyre. These waters are transported to the Cape Basin region from the west and southwest. This explains the existence of a two-mode water structure noted by other researchers.
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Data Availability
We used the GLORYS12V1 (Global Ocean Physics Reanalysis) data, a global ocean vortex-resolving reanalysis with a spatial resolution of 1/12 at 50 levels is available via the CMS (Copernicus Marine Service): https://datamarinecopernicuseuproductGLOBAL_MULTIYEAR_PHY_001_030/description.
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Acknowledgements
The work of T.B. and A.M. was supported by Russian Science Foundation, grant number 22-27-00004, and St Petersburg State University, grant number 94033410. The work of M.B. and A.U. on Lagrangian modelling and computing was supported by the POI FEBRAS Program (State Task No 121021700341-2).
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This work was supported by Russian Science Foundation grant number 22-27-00004 St Petersburg State grant number 94033410, POI FEBRAS Program (State Task No 121021700341-2).
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TB and MB: conceived of the presented idea. MB and AU: developed the theory and performed the computations. TB and AM: verified the analytical methods. TB and MB: encouraged AM: and AU: to investigate a specific aspect and supervised the findings of this work. MB, AM, and AU: prepared figures. All authors discussed the results and contributed to the final manuscript.
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Belonenko, T.V., Budyansky, M.V., Malysheva, A.A. et al. Observing the Agulhas Leakage Source in the Water Mixing Area. Pure Appl. Geophys. 180, 3401–3421 (2023). https://doi.org/10.1007/s00024-023-03331-w
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DOI: https://doi.org/10.1007/s00024-023-03331-w