Abstract
The Malvinas Current (MC) 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. The number and spatial disposition of jet-cores organizing the MC are found to vary in time influenced by topographic waves propagating along the current. The Lagrangian analysis reveals that permanent jet-cores tend to approach one another upstream, yet do not merge into a single jet as the Eulerian analysis of the data suggests. Independent support for the existence of multiple jets is provided by trajectories of surface drifters from a deployment of unparalleled dimensions for the region and ocean color images. The drifters develop the characteristic boomerang-shaped patterns into which passive tracers straddling jet-cores deform and exhibit Lagrangian metrics that are largely consistent with those derived from altimetry data. Ocean color imagery reveals similar "chevrons" and suggest upwelling along the jets, which is consistent with a new solution of arrested topographic wave dynamics. This observation and the finding that the MC jet system is influenced by propagating waves suggests that the MC variability may have major implications in the modulation of primary productivity on synoptic timescales. Drifters flowing into the open ocean, exhibit organizing patterns that are largely shaped by mesoscale circulation and essentially differ from those observed along the MC. Evidence of this observation is provided on the basis of LCS analysis and the calculation of a quasi-objective Lagrangian metric derived directly from drifter trajectories.
The ocean circulation exhibits complex motions ranging across a large span of spatio-temporal scales. Despite this complexity, distinguished material curves known as Lagrangian Coherent Structures (LCSs) may underlie the system dynamics and provide the backbones of flow organization. These structures may represent the centerpieces of passive tracer filaments, they may delineate the axes of Lagrangian jets, or they may provide boundaries to material eddies. In this work, we apply LCS methods to extract the organizing structure of the ocean currents in the Southwestern Atlantic, where the Malvinas Current (MC) flows. Surface Lagrangian dynamics, as resolved by satellite altimetry data, are interpreted together with trajectories of surface drifting buoys from a deployment of unprecedented dimensions for the region and ocean color imagery. The main finding of this multidata approach is that the MC is structured as a time-varying system of multiple Lagrangian jets. These structures are found to be modulated by trapped topographic waves characteristic of synoptic timescales. A minimal model of the MC associates upwelling to these jets, which suggests potential implications for primary productivity in the region.
Original evidence derived from a dedicated drifter experiment characterizes the Malvinas Current as a system of multiple Lagrangian jets The longitudinal position of the jets are modulated by trapped topographic waves propagating along the current Ocean color suggests upwelling along the jets, consistent with arrested topographic wave dynamics