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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

Float trajectories in coordinates of salinity and normalized time. (a) Statistics of the final vertical distribution of the floats; (b) spaghetti diagram of all the float trajectories. Red lines correspond to those following the downstream path and the blue lines those following the upstream path. The thick lines are the mean trajectories along the respective paths. Time in Figure 9b is normalized by the time that each float took to reach the shelfbreak. Thus, all the floats with a normalized time smaller than 1 are still over the shelf.
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fig09: Float trajectories in coordinates of salinity and normalized time. (a) Statistics of the final vertical distribution of the floats; (b) spaghetti diagram of all the float trajectories. Red lines correspond to those following the downstream path and the blue lines those following the upstream path. The thick lines are the mean trajectories along the respective paths. Time in Figure 9b is normalized by the time that each float took to reach the shelfbreak. Thus, all the floats with a normalized time smaller than 1 are still over the shelf.

Mentions: To better quantify the impact of mixing, we gathered all the floats trajectories and normalized their travel time by the time that it took each float to reach the shelfbreak. Thus, a normalized time >1 corresponds to floats that are in the deep ocean while those with a normalized time <1 are over the shelf (regardless of the speed at which the float moved). The superposition of all the trajectories generates a spaghetti diagram that highlights the wide range of SSS variability captured by the floats during their journey toward the deep ocean (Figure 9). The thick lines superimposed on this diagram correspond to the mean SSS variations along the upstream (blue) and the downstream (red) pathways. On average, a float following the downstream path takes approximately 284 days to reach the shelfbreak while a float following the upstream path takes 123 days. These estimates included the approximately 40 days that it takes the floats to travel from their release site in the inner portion of the estuary to the mouth of the RdlP. The salinity signatures of the two pathways start to diverge as soon as the floats leave the estuary (Figure 9b). The downstream pathway shows a steeper salinity increase. It takes, for example, ∼0.45 units of normalized time (on average 127 days of real time), to go from 10 to 30 PSU along the downstream pathway and ∼0.91 units of normalized time (on average 113 days) along the upstream pathway. The difference, ∼2 weeks, is accentuated by the fact that water parcels following the upstream path are very close to the shelfbreak while those following the downstream path have not yet reached the middle point of their journey. The upstream pathway shows an abrupt increase of salinities near the shelfbreak (Figure 9b). This increase is produced by an onshore intrusion of the Malvinas Current, which forms a midshelf jet flowing past the BMC [Palma et al., 2008; Matano et al., 2010]. At the shelfbreak there is an approximate difference of 3 PSU between the two pathways.


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)

Float trajectories in coordinates of salinity and normalized time. (a) Statistics of the final vertical distribution of the floats; (b) spaghetti diagram of all the float trajectories. Red lines correspond to those following the downstream path and the blue lines those following the upstream path. The thick lines are the mean trajectories along the respective paths. Time in Figure 9b is normalized by the time that each float took to reach the shelfbreak. Thus, all the floats with a normalized time smaller than 1 are still over the shelf.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig09: Float trajectories in coordinates of salinity and normalized time. (a) Statistics of the final vertical distribution of the floats; (b) spaghetti diagram of all the float trajectories. Red lines correspond to those following the downstream path and the blue lines those following the upstream path. The thick lines are the mean trajectories along the respective paths. Time in Figure 9b is normalized by the time that each float took to reach the shelfbreak. Thus, all the floats with a normalized time smaller than 1 are still over the shelf.
Mentions: To better quantify the impact of mixing, we gathered all the floats trajectories and normalized their travel time by the time that it took each float to reach the shelfbreak. Thus, a normalized time >1 corresponds to floats that are in the deep ocean while those with a normalized time <1 are over the shelf (regardless of the speed at which the float moved). The superposition of all the trajectories generates a spaghetti diagram that highlights the wide range of SSS variability captured by the floats during their journey toward the deep ocean (Figure 9). The thick lines superimposed on this diagram correspond to the mean SSS variations along the upstream (blue) and the downstream (red) pathways. On average, a float following the downstream path takes approximately 284 days to reach the shelfbreak while a float following the upstream path takes 123 days. These estimates included the approximately 40 days that it takes the floats to travel from their release site in the inner portion of the estuary to the mouth of the RdlP. The salinity signatures of the two pathways start to diverge as soon as the floats leave the estuary (Figure 9b). The downstream pathway shows a steeper salinity increase. It takes, for example, ∼0.45 units of normalized time (on average 127 days of real time), to go from 10 to 30 PSU along the downstream pathway and ∼0.91 units of normalized time (on average 113 days) along the upstream pathway. The difference, ∼2 weeks, is accentuated by the fact that water parcels following the upstream path are very close to the shelfbreak while those following the downstream path have not yet reached the middle point of their journey. The upstream pathway shows an abrupt increase of salinities near the shelfbreak (Figure 9b). This increase is produced by an onshore intrusion of the Malvinas Current, which forms a midshelf jet flowing past the BMC [Palma et al., 2008; Matano et al., 2010]. At the shelfbreak there is an approximate difference of 3 PSU between the two pathways.

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