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The salinity signature of the cross-shelf exchanges in the Southwestern Atlantic Ocean: Numerical simulations.

Matano RP, Combes V, Piola AR, Guerrero R, Palma ED, Ted Strub P, James C, Fenco H, Chao Y, Saraceno M - J Geophys Res Oceans (2014)

Bottom Line: Dynamical analysis reveals that the cross-shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean.The net cross-shelf volume flux is 1.21 Sv.This outflow is largely compensated by an inflow from the Patagonian shelf.

View Article: PubMed Central - PubMed

Affiliation: College of Earth, Ocean and Atmospheric Sciences, Oregon State University Corvallis, Oregon, USA.

ABSTRACT

A high-resolution model is used to characterize the dominant patterns of sea surface salinity (SSS) variability generated by the freshwater discharges of the Rio de la Plata (RdlP) and the Patos/Mirim Lagoon in the southwestern Atlantic region. We identify three dominant modes of SSS variability. The first two, which have been discussed in previous studies, represent the seasonal and the interannual variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes. During the austral winter (JJA), the plumes leave the shelf region north of the BMC. During the austral summer (DJF), the plumes are entrained more directly into the BMC. A sensitivity study indicates that the high-frequency component of the wind stress forcing controls the vertical structure of the plumes while the low-frequency component of the wind stress forcing and the interannual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross-shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross-shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf.

No MeSH data available.


Related in: MedlinePlus

Float trajectories. (a) Upstream pathway; (b) downstream pathway. The color corresponds to the salinities along those trajectories. The inset of Figure 8b shows the SSS observed by Piola et al. [2008]. The dotted circles mark the location of offshore detrainments. The black contour marks the location of the shelfbreak (200 m isobath).
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fig08: Float trajectories. (a) Upstream pathway; (b) downstream pathway. The color corresponds to the salinities along those trajectories. The inset of Figure 8b shows the SSS observed by Piola et al. [2008]. The dotted circles mark the location of offshore detrainments. The black contour marks the location of the shelfbreak (200 m isobath).

Mentions: The float trajectories span the entire latitudinal range from the BMC to Cape Santa Marta (28°S). To illustrate the salinity evolution along the two most extremes cases we chose two subgroups of float trajectories representing the downstream pathway (floats that went past 28°S), and the upstream pathway (floats that crossed the shelfbreak south of 36°S) (Figure 8). The upstream pathway represent summer conditions, when upwelling favorable winds move the floats southward along the coast of Argentina until an opposing flow from the Patagonian shelf displaces them toward the shelfbreak; there the BMC circulation rapidly advects the floats into the deep ocean (Figure 8a). The downstream pathways represent the winter conditions, when the winds reverse direction moving the floats in the downstream direction along the coasts of Uruguay and Brazil, whence they are funneled into the Brazil Current and advected toward the BMC (Figure 8b). Water parcels following the upstream pathway arrive at the shelfbreak with a lower salinity than those following the downstream pathway. The difference is partly attributed to the shortness of the upstream path and partly to the fact that upstream excursions are accompanied by the formation of a bulge of relatively freshwaters, which screens the bulk of the RdlP waters from intense mixing with the ambient waters (Figure 5a). In contrast, the narrow and elongated corridor associated with the downstream spreading favors more mixing with the ambient waters (Figure 5b). In addition, water parcels diverted in the upstream direction mix with relatively fresh Sub-Antarctic Shelf Waters while those diverted downstream are mixed with the much saltier Subtropical Shelf Waters.


The salinity signature of the cross-shelf exchanges in the Southwestern Atlantic Ocean: Numerical simulations.

Matano RP, Combes V, Piola AR, Guerrero R, Palma ED, Ted Strub P, James C, Fenco H, Chao Y, Saraceno M - J Geophys Res Oceans (2014)

Float trajectories. (a) Upstream pathway; (b) downstream pathway. The color corresponds to the salinities along those trajectories. The inset of Figure 8b shows the SSS observed by Piola et al. [2008]. The dotted circles mark the location of offshore detrainments. The black contour marks the location of the shelfbreak (200 m isobath).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4508930&req=5

fig08: Float trajectories. (a) Upstream pathway; (b) downstream pathway. The color corresponds to the salinities along those trajectories. The inset of Figure 8b shows the SSS observed by Piola et al. [2008]. The dotted circles mark the location of offshore detrainments. The black contour marks the location of the shelfbreak (200 m isobath).
Mentions: The float trajectories span the entire latitudinal range from the BMC to Cape Santa Marta (28°S). To illustrate the salinity evolution along the two most extremes cases we chose two subgroups of float trajectories representing the downstream pathway (floats that went past 28°S), and the upstream pathway (floats that crossed the shelfbreak south of 36°S) (Figure 8). The upstream pathway represent summer conditions, when upwelling favorable winds move the floats southward along the coast of Argentina until an opposing flow from the Patagonian shelf displaces them toward the shelfbreak; there the BMC circulation rapidly advects the floats into the deep ocean (Figure 8a). The downstream pathways represent the winter conditions, when the winds reverse direction moving the floats in the downstream direction along the coasts of Uruguay and Brazil, whence they are funneled into the Brazil Current and advected toward the BMC (Figure 8b). Water parcels following the upstream pathway arrive at the shelfbreak with a lower salinity than those following the downstream pathway. The difference is partly attributed to the shortness of the upstream path and partly to the fact that upstream excursions are accompanied by the formation of a bulge of relatively freshwaters, which screens the bulk of the RdlP waters from intense mixing with the ambient waters (Figure 5a). In contrast, the narrow and elongated corridor associated with the downstream spreading favors more mixing with the ambient waters (Figure 5b). In addition, water parcels diverted in the upstream direction mix with relatively fresh Sub-Antarctic Shelf Waters while those diverted downstream are mixed with the much saltier Subtropical Shelf Waters.

Bottom Line: Dynamical analysis reveals that the cross-shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean.The net cross-shelf volume flux is 1.21 Sv.This outflow is largely compensated by an inflow from the Patagonian shelf.

View Article: PubMed Central - PubMed

Affiliation: College of Earth, Ocean and Atmospheric Sciences, Oregon State University Corvallis, Oregon, USA.

ABSTRACT

A high-resolution model is used to characterize the dominant patterns of sea surface salinity (SSS) variability generated by the freshwater discharges of the Rio de la Plata (RdlP) and the Patos/Mirim Lagoon in the southwestern Atlantic region. We identify three dominant modes of SSS variability. The first two, which have been discussed in previous studies, represent the seasonal and the interannual variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes. During the austral winter (JJA), the plumes leave the shelf region north of the BMC. During the austral summer (DJF), the plumes are entrained more directly into the BMC. A sensitivity study indicates that the high-frequency component of the wind stress forcing controls the vertical structure of the plumes while the low-frequency component of the wind stress forcing and the interannual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross-shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross-shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf.

No MeSH data available.


Related in: MedlinePlus