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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

Correlations between the time averaged passive tracer concentration over the shelfbreak and the tracer concentration over all the grid points of the child model. (a) Using a time lag of 0 days; (b) using a time lag of 100 days. The thick white line with the stippled line in Figures 6a and 6b mark the shelfbreak region that we used to construct the time series of the averaged shelfbreak tracer concentration. The black contour marks the location of the shelfbreak (200 m isobath).
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fig06: Correlations between the time averaged passive tracer concentration over the shelfbreak and the tracer concentration over all the grid points of the child model. (a) Using a time lag of 0 days; (b) using a time lag of 100 days. The thick white line with the stippled line in Figures 6a and 6b mark the shelfbreak region that we used to construct the time series of the averaged shelfbreak tracer concentration. The black contour marks the location of the shelfbreak (200 m isobath).

Mentions: We use the passive tracer experiment to establish the correlation patterns that lead to the offshore detrainment of the RdlP plume from the shelf. To this end, we calculate point correlations between the time series of the tracer concentration at the shelfbreak and the time series of all the grid points of the model (Figure 6). The shelfbreak time series represents the average tracer concentration in the section that extends from 33°S to 39°S (Figure 6). Maximum correlations are observed at 0 and 100 day time lags. Note that our analysis is based on 10 day averages of the model variables; therefore a 0 day time lag represent processes with a decorrelation time scale smaller than 10 days. The correlations at zero-lag correspond to summer conditions, when the RdlP waters are rapidly exported to the deep ocean (Figure 6a). During this season, the tracer at the shelfbreak is strongly correlated with the tracer over the southern shelf and over the offshore region, and anticorrelated with the tracer along the South American coast. The correlations at the 100 day time lag relate the tracer concentrations at the shelfbreak and along the South American coast (Figure 6b). These patterns correspond with winter conditions, when the tracer is advected along the coast before being detrained into the deep ocean. The 100 day time lag represents the time that it takes the coastal waters to reach the deep ocean. The lack of significant correlations between the shelfbreak and the deep ocean (at this time lag) reflects the fast decorrelation time scales set by the BMC; after reaching the shelfbreak the RdlP waters are rapidly detrained and diluted in the deep ocean waters, so that after a relatively short period the system loses its memory (Figure 6b).


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)

Correlations between the time averaged passive tracer concentration over the shelfbreak and the tracer concentration over all the grid points of the child model. (a) Using a time lag of 0 days; (b) using a time lag of 100 days. The thick white line with the stippled line in Figures 6a and 6b mark the shelfbreak region that we used to construct the time series of the averaged shelfbreak tracer concentration. 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

fig06: Correlations between the time averaged passive tracer concentration over the shelfbreak and the tracer concentration over all the grid points of the child model. (a) Using a time lag of 0 days; (b) using a time lag of 100 days. The thick white line with the stippled line in Figures 6a and 6b mark the shelfbreak region that we used to construct the time series of the averaged shelfbreak tracer concentration. The black contour marks the location of the shelfbreak (200 m isobath).
Mentions: We use the passive tracer experiment to establish the correlation patterns that lead to the offshore detrainment of the RdlP plume from the shelf. To this end, we calculate point correlations between the time series of the tracer concentration at the shelfbreak and the time series of all the grid points of the model (Figure 6). The shelfbreak time series represents the average tracer concentration in the section that extends from 33°S to 39°S (Figure 6). Maximum correlations are observed at 0 and 100 day time lags. Note that our analysis is based on 10 day averages of the model variables; therefore a 0 day time lag represent processes with a decorrelation time scale smaller than 10 days. The correlations at zero-lag correspond to summer conditions, when the RdlP waters are rapidly exported to the deep ocean (Figure 6a). During this season, the tracer at the shelfbreak is strongly correlated with the tracer over the southern shelf and over the offshore region, and anticorrelated with the tracer along the South American coast. The correlations at the 100 day time lag relate the tracer concentrations at the shelfbreak and along the South American coast (Figure 6b). These patterns correspond with winter conditions, when the tracer is advected along the coast before being detrained into the deep ocean. The 100 day time lag represents the time that it takes the coastal waters to reach the deep ocean. The lack of significant correlations between the shelfbreak and the deep ocean (at this time lag) reflects the fast decorrelation time scales set by the BMC; after reaching the shelfbreak the RdlP waters are rapidly detrained and diluted in the deep ocean waters, so that after a relatively short period the system loses its memory (Figure 6b).

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