Anticyclonic Eddies Connecting the Western Boundaries of Indian and Atlantic Oceans

Abstract

Abstract The Indo‐Atlantic interocean exchanges achieved by Agulhas Rings are tightly linked to global ocean circulation and climate. Yet they are still poorly understood because they are difficult to identify and follow. We propose here an original assessment on Agulhas Rings, achieved by TOEddies, a new eddy identification and tracking algorithm that we applied over 24 years of satellite altimetry. Its main novelty lies in the detection of eddy splitting and merging events. These are particularly abundant and significantly impact the concept of a trajectory associated with a single eddy, which becomes less obvious than previously admitted. To overcome this complication, we have defined a network of segments that group together in relatively complex trajectories. Such a network provides an original assessment of the routes and the history of Agulhas Rings. It links 730,481 eddies into 6,363 segments that cluster into Agulhas Ring trajectories of different orders. Such an order depends on the affiliation of the eddies and segments, in a similar way as a tree of life. Among them, we have identified 122 order 0 trajectories that can be considered as the major trajectories associated to a single eddy, albeit it has undergone itself splitting and merging events. Despite the disappearance of many eddies in the altimeter signal in the Cape Basin, a significant fraction can be followed from the Indian Ocean to the South Brazil Current with, on average, 3.5 years to cross the entire South Atlantic.