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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

(a) Time series of the escape latitude calculated using the SSS criterion (Els). The thin, black line represents the original time series, the thick gray line the interpolated value and the green line the time series of the latitudinal variations of the BMC. (b) Time series of the escape latitude calculated using the passive tracer (ELt, purple line) and using the SSS criterion (ELs, gray line).
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fig04: (a) Time series of the escape latitude calculated using the SSS criterion (Els). The thin, black line represents the original time series, the thick gray line the interpolated value and the green line the time series of the latitudinal variations of the BMC. (b) Time series of the escape latitude calculated using the passive tracer (ELt, purple line) and using the SSS criterion (ELs, gray line).

Mentions: In summary, we found no definite pattern of SSS variability representing the El Niño events. The moderate Niño of 2009/2010, for example, led to an SSS increase while the equally moderate Niño of 2002/2003 led to an SSS decrease. The lack of a definite SSS response pattern to these events reflects the high variability of the alongshelf wind stress associated with them. Some Niños are associated with northeasterly winds (e.g., 2006 and 2009), others with southwesterly winds (e.g., 2002) and still others have no well-defined wind direction (e.g., 2004). Over a longer period, Piola et al. [2005] noted that during 1950–2001 there are relatively few episodes in which southwesterly winds and a marked freshening of the downstream region follow increases of the river discharge. During the period analyzed herein, La Niña events are characterized by below average RdlP discharges and northeasterly winds, both of which tend to increase the shelf's SSSs (in the downstream region) (Figure 2a). During the 1950–2001 period [Piola et al., 2005, Figure 4], however, La Niña events were characterized by a decrease of the RdlP discharge but there was no definite pattern of wind direction.


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)

(a) Time series of the escape latitude calculated using the SSS criterion (Els). The thin, black line represents the original time series, the thick gray line the interpolated value and the green line the time series of the latitudinal variations of the BMC. (b) Time series of the escape latitude calculated using the passive tracer (ELt, purple line) and using the SSS criterion (ELs, gray line).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig04: (a) Time series of the escape latitude calculated using the SSS criterion (Els). The thin, black line represents the original time series, the thick gray line the interpolated value and the green line the time series of the latitudinal variations of the BMC. (b) Time series of the escape latitude calculated using the passive tracer (ELt, purple line) and using the SSS criterion (ELs, gray line).
Mentions: In summary, we found no definite pattern of SSS variability representing the El Niño events. The moderate Niño of 2009/2010, for example, led to an SSS increase while the equally moderate Niño of 2002/2003 led to an SSS decrease. The lack of a definite SSS response pattern to these events reflects the high variability of the alongshelf wind stress associated with them. Some Niños are associated with northeasterly winds (e.g., 2006 and 2009), others with southwesterly winds (e.g., 2002) and still others have no well-defined wind direction (e.g., 2004). Over a longer period, Piola et al. [2005] noted that during 1950–2001 there are relatively few episodes in which southwesterly winds and a marked freshening of the downstream region follow increases of the river discharge. During the period analyzed herein, La Niña events are characterized by below average RdlP discharges and northeasterly winds, both of which tend to increase the shelf's SSSs (in the downstream region) (Figure 2a). During the 1950–2001 period [Piola et al., 2005, Figure 4], however, La Niña events were characterized by a decrease of the RdlP discharge but there was no definite pattern of wind direction.

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