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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

Snapshots of the (a and c) SSS and (b and d) the passive tracer. The white dots mark the location of the BMC, the red dots marks the escape latitude according to the SSS criterion and the green dot marks escape latitude according to the passive tracer. In (a and b), the location of the BMC coincides with the escape latitude according to the tracer. In (c and d), the escape latitude according to the SSS criterion cannot be determined. The red dotted line in Figure 5a shows the shelfbreak section with salinities smaller than the established criterion for RdlP waters. In situations like this, we choose the escape latitude as the middle point of this section.
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fig05: Snapshots of the (a and c) SSS and (b and d) the passive tracer. The white dots mark the location of the BMC, the red dots marks the escape latitude according to the SSS criterion and the green dot marks escape latitude according to the passive tracer. In (a and b), the location of the BMC coincides with the escape latitude according to the tracer. In (c and d), the escape latitude according to the SSS criterion cannot be determined. The red dotted line in Figure 5a shows the shelfbreak section with salinities smaller than the established criterion for RdlP waters. In situations like this, we choose the escape latitude as the middle point of this section.

Mentions: Snapshots of the SSS and the tracer illustrate the causality of the differences between the ELs and the ELt estimates (Figure 5). The snapshots show the locations of the BMC (white dots), ELs (red dots) and Elt (green dots) during the summer and winter seasons. The summer snapshot corresponds to a period of northeasterly winds, which impede the alongshelf advance of the RdlP plume, thus leading to the development of a bulge of relatively freshwaters in front of the river mouth. During this event there is a long swath along the shelfbreak of waters with SSS < 34.0 (dotted red line in Figure 5a). The ELs, which is defined as the midpoint of this region, is located to the north of the BMC. The ELt is located just at the BMC (Figure 5b). The difference between both estimates is relatively small. The winter months show the largest differences between ELs and ELt (Figures 5c and 5d). Downwelling favorable winds during this period trap the freshwater plume along the coast where it is advected alongshore (Figure 5c). After reaching Cape Santa Marta (∼28°S) the plume is returned south by an inshore intrusion of the BC flowing along the shelfbreak. Intense mixing along this pathway increases the plume's salinity so by the time it reaches the BMC these waters have a SSS > 34.0. This explains the gaps of the ELs time series during the winter months (Figure 4a). In the particular example shown here, the ELs coincide with the latitude of the BMC but it does not mark the location where the RdlP waters are detrained from the shelf. Instead, it marks the latitude of detrainment of relatively freshwaters advected from the Patagonian shelf. The RdlP waters (according to the ELt criterion) are detrained farther north, near the mouth of the Patos/Mirim Lagoon (Figure 5d). Similar detrainments through filaments have been reported from in situ observations [Piola et al., 2008b].


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)

Snapshots of the (a and c) SSS and (b and d) the passive tracer. The white dots mark the location of the BMC, the red dots marks the escape latitude according to the SSS criterion and the green dot marks escape latitude according to the passive tracer. In (a and b), the location of the BMC coincides with the escape latitude according to the tracer. In (c and d), the escape latitude according to the SSS criterion cannot be determined. The red dotted line in Figure 5a shows the shelfbreak section with salinities smaller than the established criterion for RdlP waters. In situations like this, we choose the escape latitude as the middle point of this section.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig05: Snapshots of the (a and c) SSS and (b and d) the passive tracer. The white dots mark the location of the BMC, the red dots marks the escape latitude according to the SSS criterion and the green dot marks escape latitude according to the passive tracer. In (a and b), the location of the BMC coincides with the escape latitude according to the tracer. In (c and d), the escape latitude according to the SSS criterion cannot be determined. The red dotted line in Figure 5a shows the shelfbreak section with salinities smaller than the established criterion for RdlP waters. In situations like this, we choose the escape latitude as the middle point of this section.
Mentions: Snapshots of the SSS and the tracer illustrate the causality of the differences between the ELs and the ELt estimates (Figure 5). The snapshots show the locations of the BMC (white dots), ELs (red dots) and Elt (green dots) during the summer and winter seasons. The summer snapshot corresponds to a period of northeasterly winds, which impede the alongshelf advance of the RdlP plume, thus leading to the development of a bulge of relatively freshwaters in front of the river mouth. During this event there is a long swath along the shelfbreak of waters with SSS < 34.0 (dotted red line in Figure 5a). The ELs, which is defined as the midpoint of this region, is located to the north of the BMC. The ELt is located just at the BMC (Figure 5b). The difference between both estimates is relatively small. The winter months show the largest differences between ELs and ELt (Figures 5c and 5d). Downwelling favorable winds during this period trap the freshwater plume along the coast where it is advected alongshore (Figure 5c). After reaching Cape Santa Marta (∼28°S) the plume is returned south by an inshore intrusion of the BC flowing along the shelfbreak. Intense mixing along this pathway increases the plume's salinity so by the time it reaches the BMC these waters have a SSS > 34.0. This explains the gaps of the ELs time series during the winter months (Figure 4a). In the particular example shown here, the ELs coincide with the latitude of the BMC but it does not mark the location where the RdlP waters are detrained from the shelf. Instead, it marks the latitude of detrainment of relatively freshwaters advected from the Patagonian shelf. The RdlP waters (according to the ELt criterion) are detrained farther north, near the mouth of the Patos/Mirim Lagoon (Figure 5d). Similar detrainments through filaments have been reported from in situ observations [Piola et al., 2008b].

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