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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

Spatial amplitude and time series of the first EOF mode of SSH variability from the AVISO data set. The black line of the time series corresponds to AVISO, the green line to the child model. The spatial amplitude of the first EOF from the model is nearly identical to the AVISO (not shown).
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fig12: Spatial amplitude and time series of the first EOF mode of SSH variability from the AVISO data set. The black line of the time series corresponds to AVISO, the green line to the child model. The spatial amplitude of the first EOF from the model is nearly identical to the AVISO (not shown).

Mentions: To further assess the model realism, we also compared the SSH variability of the model with gridded altimeter sea level anomaly (SLA) data from the AVISO (Archiving, Validation and Interpretation of Satellite Oceanographic data) research quality (delayed delivery) data set. Although concerns about errors in the tidal models have been especially critical over the Patagonia shelf in the past, the tides over the shelf north of 40°S are much less energetic than farther south [Palma et al., 2004b]. In addition, Saraceno et al. [2010] have found good agreement between the tidal models used in AVISO corrections and in situ observations north of 42°S on the Patagonia shelf. Land contamination of the altimeter data within ∼30 km of the coast is less of a problem for this “coastal” Region 1, since most of the SSH signal over this wide shelf originates far from the coast. In Figure 12, we present the first EOF (explaining 57% of the variance) of AVISO SLA (from the weekly ¼° weekly gridded data) over the shelf inshore of the 200 m isobath in Region 1 (27.7°S–34.7°S). This region is far north of the region where large tides may cause problems for the altimeter data retrievals. The gradient in the SLA field from the EOF depicts alongshore geostrophic flow over the outer shelf in the south and the midshelf in the north, with a time series (in black) that is typically positive (indicating equatorward flow) from March–August and negative (poleward) from September–February. The spatial pattern of SSH from the model first EOF (explaining 84% of the variance) is not shown because it is nearly identical to that from the altimeter. The time series from the model first EOF (in green) has been interpolated to the weekly AVISO times and both time series have been smoothed with a 5 point boxcar filter. The agreement between the two time series is exceptionally good (r = 0.79), given that no data have been assimilated into the model. The agreement of the second EOF time series (not shown, explaining another 8–10% of the variance for both) is moderately good, capturing the lower frequency seasonal changes but missing many intraseasonal peaks and troughs (r = 0.36). This level of agreement indicates that the model reproduces a majority of the wind-driven large-scale circulation over the shelf on time scales of 1–2 months and longer, including the seasonal cycle and its variability on intraseasonal and interannual scales. The agreement also serves to validate the use of the altimeter data over the shelf in this region and on these scales, as reported by Saraceno et al. [2010], Strub et al. [2014], and (Strub et al., 2014, in preparation).


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)

Spatial amplitude and time series of the first EOF mode of SSH variability from the AVISO data set. The black line of the time series corresponds to AVISO, the green line to the child model. The spatial amplitude of the first EOF from the model is nearly identical to the AVISO (not shown).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig12: Spatial amplitude and time series of the first EOF mode of SSH variability from the AVISO data set. The black line of the time series corresponds to AVISO, the green line to the child model. The spatial amplitude of the first EOF from the model is nearly identical to the AVISO (not shown).
Mentions: To further assess the model realism, we also compared the SSH variability of the model with gridded altimeter sea level anomaly (SLA) data from the AVISO (Archiving, Validation and Interpretation of Satellite Oceanographic data) research quality (delayed delivery) data set. Although concerns about errors in the tidal models have been especially critical over the Patagonia shelf in the past, the tides over the shelf north of 40°S are much less energetic than farther south [Palma et al., 2004b]. In addition, Saraceno et al. [2010] have found good agreement between the tidal models used in AVISO corrections and in situ observations north of 42°S on the Patagonia shelf. Land contamination of the altimeter data within ∼30 km of the coast is less of a problem for this “coastal” Region 1, since most of the SSH signal over this wide shelf originates far from the coast. In Figure 12, we present the first EOF (explaining 57% of the variance) of AVISO SLA (from the weekly ¼° weekly gridded data) over the shelf inshore of the 200 m isobath in Region 1 (27.7°S–34.7°S). This region is far north of the region where large tides may cause problems for the altimeter data retrievals. The gradient in the SLA field from the EOF depicts alongshore geostrophic flow over the outer shelf in the south and the midshelf in the north, with a time series (in black) that is typically positive (indicating equatorward flow) from March–August and negative (poleward) from September–February. The spatial pattern of SSH from the model first EOF (explaining 84% of the variance) is not shown because it is nearly identical to that from the altimeter. The time series from the model first EOF (in green) has been interpolated to the weekly AVISO times and both time series have been smoothed with a 5 point boxcar filter. The agreement between the two time series is exceptionally good (r = 0.79), given that no data have been assimilated into the model. The agreement of the second EOF time series (not shown, explaining another 8–10% of the variance for both) is moderately good, capturing the lower frequency seasonal changes but missing many intraseasonal peaks and troughs (r = 0.36). This level of agreement indicates that the model reproduces a majority of the wind-driven large-scale circulation over the shelf on time scales of 1–2 months and longer, including the seasonal cycle and its variability on intraseasonal and interannual scales. The agreement also serves to validate the use of the altimeter data over the shelf in this region and on these scales, as reported by Saraceno et al. [2010], Strub et al. [2014], and (Strub et al., 2014, in preparation).

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