Sea level anomaly on the Patagonian continental shelf: Trends, annual patterns and geostrophic flows

Abstract

We study the annual patterns and linear trend of satellite sea level anomaly (SLA) over the southwest South Atlantic continental shelf (SWACS) between 54ºS and 36ºS. Results show that south of 42°S the thermal steric effect explains nearly 100% of the annual amplitude of the SLA, while north of 42°S it explains less than 60%. This difference is due to the halosteric contribution. The annual wind variability plays a minor role over the whole continental shelf. The temporal linear trend in SLA ranges between 1 and 5 mm/yr (95% confidence level). The largest linear trends are found north of 39°S, at 42°S and at 50°S. We propose that in the northern region the large positive linear trends are associated with local changes in the density field caused by advective effects in response to a southward displacement of the South Atlantic High. The causes of the relative large SLA trends in two southern coastal regions are discussed as a function meridional wind stress and river discharge. Finally, we combined the annual cycle of SLA with the mean dynamic topography to estimate the absolute geostrophic velocities. This approach provides the first comprehensive description of the seasonal component of SWACS circulation based on satellite observations. The general circulation of the SWACS is northeastward with stronger/weaker geostrophic currents in austral summer/winter. At all latitudes, geostrophic velocities are larger (up to 20 cm/s) close to the shelf‐break and decrease toward the coast. This spatio‐temporal pattern is more intense north of 45°S.

On the Wind Contribution to the Variability of Ocean Currents Over Wide Continental Shelves: A Case Study on the Northern Argentine Continental Shelf

“…Numerical simulations suggest that the inner and middle shelf circulation is primarily driven by the alongshore component of the wind stress (Palma et al, ). Seasonal geostrophic currents derived from satellite altimetry data south of 36°S present a mean flow to the north all year‐round, with weak seasonal variability, and a slight wind‐driven increase in autumn‐winter (April–July; Strub et al, ; Ruiz‐Etcheverry et al, ). Short‐term observations (Lanfredi, ; Lanfredi & Capurro, ) along with numerical models (Combes & Matano, ; Forbes & Garraffo, ; Glorioso & Flather, ) also show a mean flow in the ACS toward the NNE and indicate that tidal currents north of 40°S are relatively weak.…”

The horizontal heat advection in the Middle Atlantic Bight and the cross‐spectral interactions within the heat advection

“…They found that the MDT shows a consistent pattern over the continental shelves comparing with in situ measurements and the geostrophic velocities from MADT have errors in the order of 12 cm/s over the broad Gulf Stream Current Area (20°N–60°N, 275°E–340°E) [ Rio et al ., ]. Despite the uncertainty of the SLA over the shallow waters, this data set is valuable to describe physical processes on the continental shelf [e.g., Ruiz et al ., ; Gawarkiewicz et al ., ; Strub et al ., ; Ruiz Etcheverry et al ., ]. Moreover, if taken monthly mean, the error of the derived velocities will be further reduced (e.g., 4∼6 cm/s given a SLA decorrelation scale of 4 days) [ Ponte , ].…”

Late Quaternary nearshore molluscan patterns from Patagonia: Windows to southern southwestern Atlantic-Southern Ocean palaeoclimate and biodiversity changes?

“…southwestern Atlantic (SWA): BC, Brazilian warm current; MC, Malvinas/Falkland cold current (branch of the ACC); PC, Patagonian coastal cold current (Subantarctic shelf waters); ACC, Antarctic Circumpolar Current; BMCZ, Brazil-Malvinas Confluence Zone; SAF, Subantarctic Front; PF, Polar Front; ACC, Antarctic Circumpolar Current; SSW: southern westerly winds; PE: Polar easterlies; arrows indicate direction of winds (darker arrows correspond to maximum wind speeds). In the Southeastern Pacific: CHC, Cabo de Hornos Current; HC, Humboldt Current; WWW, West Wind Drift = Antarctic Convergence Current (ACC); information taken from Acha et al, 2004;Bianchi et al, 2005;Palma et al, 2008, Piola andFalabella, 2009;Glembocki et al, 2015;Olguín-Salinas et al, 2015;Ruiz-Etcheverry et al, 2016;Kahl et al, 2017;Piola et al, 2018;Combes and Matano, 2018;Franco et al, 2018; other references therein and in A.6). Biogeographical regions: A, Argentinean malacological province; M, Magellanean malacological province.…”

“…Apart from that, higher δ 18 O values can be linked to higher salinity and/or to enhanced upwelling of cold nutrient-rich waters at coastal fronts (Bianchi et al, 2005). For instance, the modern δ 18 O -and δ 13 C -maxima occur in the northern Golfo San Matías (NSAO), where the influence of warm waters together with a reverse circulation and a longer residence time for shallow waters, are responsible for enhanced evaporation and higher salinity (Piola and Rivas, 1997;Guerrero and Piola, 1997;Rivas and Pisoni, 2010;Ruiz-Etcheverry et al, 2016), leading to higher δ 18 O values (Figs. 3, 4, 9).…”