Multiple thermal fronts near the Patagonian shelf break

Abstract

[1] Eighteen year (1985 -2002) sea surface temperature (SST) data are used to study the intraseasonal variability of the Patagonian shelf break front (SBF) in the SW South Atlantic Ocean between 39°and 44°S. The cross-shelf break SST gradients reveal distinct, previously undocumented thermal fronts located both, offshore and inshore of the SBF. Throughout the year the main SBF, identified as a band of negative SST gradient maxima (relatively strong offshore temperature decrease), forms a persistent feature located closed to the 200 m isobath, while two distinct negative gradient maxima are located inshore and offshore of this location. Daily SST images reveal the presence of three branches of cold waters whose edges delineate the above mentioned fronts. The two offshore branches closely follow lines of constant potential vorticity ( f/h) and appear to be associated with the Malvinas Current, while a third branch, located further onshore, is not steered by the bottom topography. South of 40°S the onshore branch forms a quasi permanent front parallel to the SBF. Citation:

Squid as nutrient vectors linking Southwest Atlantic marine ecosystems

“…The sub-Antarctic shelf ecosystem is occupied by waters of sub-Antarctic origin transported onto the Shelf by the western branch of the cold Falkland (Malvinas) Current that mix with shelf waters forming several oceanographic fronts in the Southern Patagonian Shelf (Acha et al, 2004). The eastern branch of the Falkland Current forms the long Falkland/Malvinas Current Front that runs along the Patagonian shelf break and slope and frames the Patagonian large marine ecosystem from east (Acha et al, 2004;Franco et al, 2008). The temperate shelf ecosystem lies within waters of subtropical origin, transported onto the shelf by the Brazil Current and mixed with temperate shelf waters.…”

Malvinas-slope water intrusions on the northern Patagonia continental shelf

“…A plausible explanation for the apparent seasonal modulation of high-frequency SSTa is the seasonal variation in the magnitude of the temperature gradient (∂T /∂x) across the shelf break front. The SST gradient is highest in austral summer and lowest in winter (Saraceno et al, 2004;Franco et al, 2008;Rivas and Pisoni, 2010).…”

“…9) have shown that the high SST gradient band observed along the western edge of the Malvinas Current between 39 and 44 • S closely follows the line of constant potential vorticity (f/H , where f is the Coriolis parameter and H is the bottom depth) equal to 2×10 −7 m −1 s −1 . More recently, Franco et al (2008) have suggested that the surface transition between shelf and Malvinas Current waters is organized as a series of distinct thermal fronts, each following lines of constant potential vorticity, except for the westernmost front located over the outer continental shelf, which is more variable. Variability of the inshore front is presumably due to reduced f/H gradients and a less pronounced topographic control of the flow in the outer shelf.…”

“…From austral spring to fall the Patagonian shelf and MC waters form a moderate sea surface temperature front (>0.1 • C km −1 ) which closely follows the 300 m isobath (Saraceno et al, 2004). Recent studies show that the shelf break front is frequently arranged as a series of narrow along shelf break bands, which appear to be steered by the bottom topography (Franco et al, 2008). The shelf-open ocean transition is also characterized by a salinity front extending from the sea surface to the bottom at the offshore edge of the continental shelf (Romero et al, 2006).…”

A Model of Multiple Zonal Jets in the Oceans: Dynamical and Kinematical Analysis

“…The equatorial currents (Firing 1987) might be dynamically related to the midlatitude, multiple zonal jets through instabilities of large-scale waves (e.g., Hua et al 2008). Multiple-jet zonation of currents is also observed on continental slopes (Franco et al 2008), suggesting the important role for the topographic b effect. Finally, vigorous research on zonal jets is carried out by the plasma physics community-many aspects of this effort have geophysical counterparts; a comprehensive review of the subject is in Diamond et al (2005).…”