Oceanic three-dimensional Lagrangian Coherent Structures: A study of a mesoscale eddy in the Benguela ocean region

TL;DR

This study analyzes three-dimensional Lagrangian Coherent Structures in the Benguela ocean, revealing their geometry, depth variation, and role in transport around a mesoscale eddy using FSLE fields from ROMS model data.

Contribution

It introduces a method to extract 3D LCSs in oceanic regions and characterizes their structure and function around mesoscale eddies.

Findings

LCSs form curtain-like vertical surfaces.

FSLE values decrease with depth, with a local maximum at 100 m.

LCSs act as pathways and barriers for transport.

Abstract

We study three dimensional oceanic Lagrangian Coherent Structures (LCSs) in the Benguela region, as obtained from an output of the ROMS model. To do that we first compute Finite-Size Lyapunov exponent (FSLE) fields in the region volume, characterizing mesoscale stirring and mixing. Average FSLE values show a general decreasing trend with depth, but there is a local maximum at about 100 m depth. LCSs are extracted as ridges of the calculated FSLE fields. They present a "curtain-like" geometry in which the strongest attracting and repelling structures appear as quasivertical surfaces. LCSs around a particular cyclonic eddy, pinched off from the upwelling front are also calculated. The LCSs are confirmed to provide pathways and barriers to transport in and out of the eddy.