Search for: All records

Abstract We characterize long‐term trends of sea surface temperature (SST), absolute dynamic topography, and chlorophyll‐a(CHL) in the Patagonian shelf break front (SBF) using 27 years (1993–2019) of satellite data. Warming of the Argentinean shelf waters and the southwestward displacement of the Brazil‐Malvinas Confluence (BMC) impact the northernmost extension of the SBF. Cooling of the Malvinas Current (MC) and the concurrent warming of the adjacent shelf waters lead to a significant increase of SST gradients along the outer shelf. The southwestward displacement of the BMC implies a similar shift of the SBF. An increase in CHL trend appears to be associated with southerly wind anomalies along the shelf break. We estimate a southward shift of the northernmost penetration of the MC of −0.11 ± 0.076°/decade. 

Abstract A high‐resolution ocean model is used to characterize the circulation and cross‐shelf exchanges in the Brazilian/Uruguayan portion of the southwestern Atlantic shelf. Cross‐shelf exchanges are strongly modulated by the bottom topography. There is ∼1.2 Sv of on‐shelf transport between 21°S and 25.2°S, and ∼1.6 Sv of off‐shelf transport between 35°S and 25.2°S. North of 25.2°S, the cross‐shelf exchanges show a two‐layer structure with an off‐shelf flow in the upper 50m and on‐shelf flow deep below. A Lagrangian diagnostic shows that ∼0.15 Sv of deep waters from the Brazil Current (z > 200 m) are injected into the shelf. Mixing with ambient waters produces a spicier (warmer and saltier) water mass, which is ejected into the open ocean in the southern region. Backward in‐time particle's trajectories analysis reveals that 95% of the southward shelf transport at 32°S originates in the open ocean at 22°S. Our model diagnostics show that there is a very limited connectivity between the shelf regions north and south of Cabo Frio. Correlation analysis shows no significant influence of El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM) on the time variability of the cross‐shelf transport. Cross‐shelf transports, however, are significantly correlated with the local wind stress variability. 

Abstract The northeast periphery of the Scotia Sea hosts one of the largest chlorophyll‐a blooms of the Southern Ocean. This bloom peaks to the northwest of the island of South Georgia, extending eastward for hundreds of kilometers. Although the Southern Ocean has many islands of similar size, South Georgia is ecologically one of the most significant: It not only sustains one of the Southern Ocean's largest and most diverse ecosystems but also constitutes its single most important region for biological carbon sequestration. While the exceptional nature of South Georgia's blooms has been recognized widely, both the physical processes that contribute to their fertilization and the reasons why these blooms are larger than those of other similar regions (e.g., Kerguelen or Crozet Islands) are poorly understood. We use the results of a high‐resolution ocean model to investigate the physical processes that mediate the entrainment of deep, iron‐rich waters into the surface layers of the South Georgia region. We show that the Southern Antarctic Circumpolar Current Front, the southernmost jet of the Antarctic Circumpolar Current (ACC), pumps iron‐enriched waters from the deep ocean onto the bottom layers of South Georgia's shelf. These waters are upwelled along the northern coast of the island and are then exported into the Georgia Basin, where topographically steered circulation shields them from the dispersive effects of local currents and eddies, thus allowing the bloom development.