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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

Mean vertical structure of the cross sections shown in Figure 4. The background colors represent the salinity field and the white contours are for the velocities (cm/s). The light-blue contours mark the 34 isohaline, which represents the limit of the LPR waters.
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fig15: Mean vertical structure of the cross sections shown in Figure 4. The background colors represent the salinity field and the white contours are for the velocities (cm/s). The light-blue contours mark the 34 isohaline, which represents the limit of the LPR waters.

Mentions: Vertical profiles across the box boundaries illustrate the relation between volume and salinity fluxes (Figure 15). The southern cross section (A–B) is characterized by the presence of low-salinity waters against the coast, which are associated with the upstream (southward) extension of the RdlP plume. The plume is vertically homogeneous in the inner shelf, detaches from the bottom at ∼25 m depth and extends offshore as a surface-trapped plume. The corresponding velocity field shows an upstream jet near the coast that advects the RdlP plume waters south and a stronger midshelf jet flowing in the opposing direction. The northern cross section (C–D) shows a deep, midshelf channel filled with saltier Subtropical Shelf Waters flowing poleward underneath the fresher waters from the RdlP plume. Farther offshore, this cross section shows a northward flowing jet, which is an onshore intrusion of the Malvinas Current [Palma et al., 2008; Combes and Matano, 2014]. Past the shelfbreak there is the poleward flow of the Brazil Current, which carries saltier waters toward the BMC. The eastern cross section (B–C) shows a dominant off-shelf flow of 10–20 cm/s in the north (34.5°S–35.5°S) and 5–10 cm/s in the south (35.5°S–37.5°S). The corresponding salinity field shows a shallow layer (h < 20 m) of freshwaters capping the saltier waters of the Brazil Current. The seasonal anomalies of the off-shelf flow are relatively small (e.g., Figure 14). During the winter there is a decrease of the off-shelf velocities south of 35°S (∼1–2 cm/s) and an increase farther north (<1 cm/s). These patterns reverse during the summer but the flow always maintains its barotropic structure, which indicates that SSS anomalies represent motions of the entire water column.


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)

Mean vertical structure of the cross sections shown in Figure 4. The background colors represent the salinity field and the white contours are for the velocities (cm/s). The light-blue contours mark the 34 isohaline, which represents the limit of the LPR waters.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig15: Mean vertical structure of the cross sections shown in Figure 4. The background colors represent the salinity field and the white contours are for the velocities (cm/s). The light-blue contours mark the 34 isohaline, which represents the limit of the LPR waters.
Mentions: Vertical profiles across the box boundaries illustrate the relation between volume and salinity fluxes (Figure 15). The southern cross section (A–B) is characterized by the presence of low-salinity waters against the coast, which are associated with the upstream (southward) extension of the RdlP plume. The plume is vertically homogeneous in the inner shelf, detaches from the bottom at ∼25 m depth and extends offshore as a surface-trapped plume. The corresponding velocity field shows an upstream jet near the coast that advects the RdlP plume waters south and a stronger midshelf jet flowing in the opposing direction. The northern cross section (C–D) shows a deep, midshelf channel filled with saltier Subtropical Shelf Waters flowing poleward underneath the fresher waters from the RdlP plume. Farther offshore, this cross section shows a northward flowing jet, which is an onshore intrusion of the Malvinas Current [Palma et al., 2008; Combes and Matano, 2014]. Past the shelfbreak there is the poleward flow of the Brazil Current, which carries saltier waters toward the BMC. The eastern cross section (B–C) shows a dominant off-shelf flow of 10–20 cm/s in the north (34.5°S–35.5°S) and 5–10 cm/s in the south (35.5°S–37.5°S). The corresponding salinity field shows a shallow layer (h < 20 m) of freshwaters capping the saltier waters of the Brazil Current. The seasonal anomalies of the off-shelf flow are relatively small (e.g., Figure 14). During the winter there is a decrease of the off-shelf velocities south of 35°S (∼1–2 cm/s) and an increase farther north (<1 cm/s). These patterns reverse during the summer but the flow always maintains its barotropic structure, which indicates that SSS anomalies represent motions of the entire water column.

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