Investigating the Upper-Ocean Pathways, Dynamics, and Geometry of the South Atlantic

Abstract

The South Atlantic has been of special interest to the overturning circulation as its source waters may have the ability to influence deep water convection in the subpolar North Atlantic, and hence affect the overturning variability or strength. As such, it is important to have a thorough understand of the pathways that regulate the upper-ocean flow in the South Atlantic. This dissertation revisits previously studied aspects of the circulation from an observational perspective focusing on the use of Lagrangian data and statistical tools that complement the observational data. More specifically, surface drifter trajectories, Argo float trajectories, and satellite altimetry products are used to investigate the cold and warm water routes, the subtropical gyre circulation, and the connection between the North Brazil Current and the tropical North Atlantic. The statistical tools used throughout this dissertation are rooted in Markov chain theory, which allows for the construction of probability distribution maps that represent mean pathways and artificially extend the lifetime of observational trajectories. In addition, a new method derived from transition path theory is used to specifically identify pathways that connect a desired source and target region. The results reveal that the cold and warm water routes share multiple pathways throughout the South Atlantic and contribute comparable amounts to the Benguela Current waters. The cold water route follows internal pathways suggesting a significant role in the subtropical gyre circulation in setting pathways. The analysis of sea surface height data shows no significant trends in the subtropical gyre size and strength over the past 25 years. Finally, this work highlights the importance of pathways following the Atlantic interior to the tropical North Atlantic from the North Brazil Current. Future work will focus on understanding the differences between the two-dimensional pathways revealed from the observational trajectories and three-dimensional pathways simulated by model trajectories.