The Surface Pathways of the South Atlantic: Revisiting the Cold and Warm Water Routes Using Observational Data

Abstract

The relative contributions of the Atlantic Meridional Overturning Circulation upper limb source waters in the South Atlantic (SA) remain largely unresolved. We contribute to a resolution by using observational data to explore water mass pathways feeding into the Benguela Current, considered a major component of the Atlantic Meridional Overturning Circulation upper limb in the SA. We focus on the pathways from the Pacific Ocean via the Drake Passage (traditionally termed the “cold” water route) and the Indian Ocean via Agulhas Leakage (traditionally termed the “warm” water route). We employ two main observational data sets: (1) surface drifter trajectories from the National Oceanic and Atmospheric Administration's Global Drifter Program and (2) the Ocean Surface Current Analysis Real-time product. Based on our Lagrangian analysis, the majority of particles originating in the Drake Passage remain in the Antarctic Circumpolar Current, with a small portion reaching the northern limb of the SA subtropical gyre, and a few infiltrating the Agulhas Current region. The majority of particles released in the Agulhas Current follow the Agulhas Return Current and recirculate in its vicinity. Only a small portion leaks into the SA. Observed pathways reveal strong interactions between the two source waters in the Brazil-Malvinas Confluence, the SA subtropical gyre, the Benguela Current, and the Agulhas Current region. Results from backward trajectories suggest a sizable contribution of waters from the Drake Passage to the Benguela Current but show disagreement between the two datasets in the magnitude of this contribution.