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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

Correlation coefficient between an SSS proxy and (a) the alongshelf component of the wind stress forcing and (b) the LPR discharge. The SSS proxy was constructed using satellite estimates of surface chlorophyll-a concentration collected during the period 1998–2005. Adapted from Piola et al. [2008].
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fig11: Correlation coefficient between an SSS proxy and (a) the alongshelf component of the wind stress forcing and (b) the LPR discharge. The SSS proxy was constructed using satellite estimates of surface chlorophyll-a concentration collected during the period 1998–2005. Adapted from Piola et al. [2008].

Mentions: The first two EOF modes of our model, which represent the alongshelf displacements of the RdlP and the Patos/Mirim freshwater plumes, are in good agreement with observational results. Piola et al. [2008a], for example, found that the highest correlations between the alongshelf winds and a SSS proxy are observed along a relatively narrow corridor hugging the South American coast (Figure 11a) [adapted from Piola et al., ,]. There is a close correspondence between the correlation patterns found by Piola et al. [2008a] and the spatial amplitudes of the first EOF of the model (Figure 3). Both estimates, for example, show dipole structures with lobes of opposite signs in the upstream and downstream portions of the continental shelf. Piola et al. [2008] also reported that the largest correlations between the alongshelf winds and the SSS proxy have a 2 month time lag. This time lag corresponds well with the 45 days estimated from our spectral analysis. The 2 week difference between the two estimates is accounted by the fact that Piola et al. [2008a] used monthly mean winds while we used daily winds. The second EOF of the model also compares well with the correlation patterns estimated by Piola et al. [2008a] (Figure 1b). In agreement with the model results they also found that the largest correlations between the RdlP discharge and the SSS proxy are constrained to the mouth of the river, thus reinforcing the conclusion that the variations of the river discharge do not contribute significantly to the SSS variability away from the source region.


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)

Correlation coefficient between an SSS proxy and (a) the alongshelf component of the wind stress forcing and (b) the LPR discharge. The SSS proxy was constructed using satellite estimates of surface chlorophyll-a concentration collected during the period 1998–2005. Adapted from Piola et al. [2008].
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig11: Correlation coefficient between an SSS proxy and (a) the alongshelf component of the wind stress forcing and (b) the LPR discharge. The SSS proxy was constructed using satellite estimates of surface chlorophyll-a concentration collected during the period 1998–2005. Adapted from Piola et al. [2008].
Mentions: The first two EOF modes of our model, which represent the alongshelf displacements of the RdlP and the Patos/Mirim freshwater plumes, are in good agreement with observational results. Piola et al. [2008a], for example, found that the highest correlations between the alongshelf winds and a SSS proxy are observed along a relatively narrow corridor hugging the South American coast (Figure 11a) [adapted from Piola et al., ,]. There is a close correspondence between the correlation patterns found by Piola et al. [2008a] and the spatial amplitudes of the first EOF of the model (Figure 3). Both estimates, for example, show dipole structures with lobes of opposite signs in the upstream and downstream portions of the continental shelf. Piola et al. [2008] also reported that the largest correlations between the alongshelf winds and the SSS proxy have a 2 month time lag. This time lag corresponds well with the 45 days estimated from our spectral analysis. The 2 week difference between the two estimates is accounted by the fact that Piola et al. [2008a] used monthly mean winds while we used daily winds. The second EOF of the model also compares well with the correlation patterns estimated by Piola et al. [2008a] (Figure 1b). In agreement with the model results they also found that the largest correlations between the RdlP discharge and the SSS proxy are constrained to the mouth of the river, thus reinforcing the conclusion that the variations of the river discharge do not contribute significantly to the SSS variability away from the source region.

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