Martin Saraceno (Departamento de Ciencias de la Atmósfera y los Océanos; Facultad de Ciencias Exactas y Naturales Universidad de Buenos Aires (DCAO, FCEN-UBA) Ciudad Autónoma de Buenos Aires, Argentina; Centro de Investigaciones del Mar y la Atmósfera (CIMA/CONICET-UBA); , Argentina); Laura A. Ruiz-Etcheverry (Departamento de Ciencias de la Atmósfera y los Océanos; Facultad de Ciencias Exactas y Naturales Universidad de Buenos Aires (DCAO, FCEN-UBA) Ciudad Autónoma de Buenos Aires, Argentina; Centro de Investigaciones del Mar y la Atmósfera (CIMA/CONICET-UBA); , Argentina); Claudia Gloria Simionato (Departamento de Ciencias de la Atmósfera y los Océanos; Facultad de Ciencias Exactas y Naturales Universidad de Buenos Aires (DCAO, FCEN-UBA) Ciudad Autónoma de Buenos Aires, Argentina; Centro de Investigaciones del Mar y la Atmósfera (CIMA/CONICET-UBA); , Argentina); Fernando Andrade-Canto (Departamento de Observación y Estudio de la Tierra, la Atmósfera y el Océano; El Colegio de la Frontera Sur; Chetumal, Quintana Roo, Mexico, México); Francisco Javier Beron-Vera (Department of Atmospheric Sciences; Rosenstiel School of Marine, Atmospheric & Earth Science University of Miami Miami, Florida, USA, USA); Olascoaga María Josefina (Department of Ocean Sciences; Rosenstiel School of Marine, Atmospheric & Earth Science University of Miami Miami, Florida, USA, USA)

The Malvinas Current in the Southwestern Atlantic is characterized as a system of multiple Lagrangian jets. This is done by applying geodesic theory of Lagrangian Coherent Structures (LCSs) on altimetry-derived velocity, which portrays the jets as shearless-parabolic LCSs. The number, geometry, and spatial disposition of flow-invariant jet-cores organizing the Malvinas Current system are found to vary in time constrained by the regional mesoscale circulation. Independent support for this characterization is provided by trajectories of surface drifters from a deployment of unparalleled dimensions for the region and ocean color images (Fig. 1). The drifters develop the characteristic boomerang-shaped patterns into which passive tracers straddling shearless-parabolic LCSs deform (Fig. 1 left panel). Satellite-derived surface chlorophyll reveals similar ``chevrons,'' which organize about attracting hyperbolic LCSs extracted from altimetry (Fig. 1 right panel). The LCS analysis of altimetry reveals that the jets tend to approach one another upstream, yet not to merge into a single jet as the Eulerian analysis of the data suggests. Consistent with a new solution of arrested topographic wave dynamics, the ocean color imagery also suggests upwelling along the multiple, upstream-approaching Lagrangian jets forming the Malvinas Current system, which may contribute to the modulation of primary productivity in the region. The mesoscale circulation, well-resolved by altimetry, is seen to drive many aspects of the Lagrangian motion in the Southwestern Atlantic, including the effects of mesoscale elliptic LCSs on shaping the evolution of the drifters.



Fig. 1 The left panel displays drifter trajectory pieces (blue) centered on 9th September 2021 (a dot indicates the central day position), overlaid on attracting LCSs (colored according to a measure of attracting intensity) and shearless parabolic LCSs, which constitute jet-cores (black curves and dashed curve) extracted from altimetry flow by applying geodesic LCS analysis in forward time in a 30 days time window. The right panel depicts a shearless parabolic LCS (black curve) and two hyperbolic LCSs (dashed curves) overlaid on surface chlorophyll-a concentration (logarithmic scale). The development of a chevron feature is readily osbervable. The time window for the LCS extraction was set to 15 days, a timescale representative of the chlorophyll time span.