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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

Snapshots of the sea surface salinity (SSS) in the nested model configuration used in this study. (a) The domain of the parent model, which has a horizontal resolution of 1/4°. (b) The first child model, which has a resolution of 1/12°. (b) The second child model, which has a resolution of 1/24°. The three models have the same vertical resolution (40 sigma levels). (c) The extent of Region 1, which is discussed in later sections. The gray line in Figure 1c marks the location of the 200 m isobath (the shelfbreak).
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fig01: Snapshots of the sea surface salinity (SSS) in the nested model configuration used in this study. (a) The domain of the parent model, which has a horizontal resolution of 1/4°. (b) The first child model, which has a resolution of 1/12°. (b) The second child model, which has a resolution of 1/24°. The three models have the same vertical resolution (40 sigma levels). (c) The extent of Region 1, which is discussed in later sections. The gray line in Figure 1c marks the location of the 200 m isobath (the shelfbreak).

Mentions: The model used in this study is the Regional Ocean Modeling System (ROMS), which is a three-dimensional, free surface, hydrostatic, eddy-resolving primitive equation ocean model. ROMS uses orthogonal curvilinear coordinates in the horizontal and sigma, terrain following coordinates in the vertical [Shchepetkin and McWilliams, 2005]. We use the version ROMS_AGRIF (http://roms.mpl.ird.fr/), which offers the capability of a two-way nesting procedure with high-resolution “child” grids embedded into a coarser resolution “parent” grid. The parent grid extends 360° in the longitudinal direction and from Antarctica to 15.2°N (Figure 1). It has a spatial resolution of 1/4°, and 40 sigma levels in the vertical, with enhanced resolution at the surface. The first child grid extends from 82°W to 41°W and from 64°S to 20°S, covering the southern portion of South America with spatial resolution of 1/12° (Figure 1). The nested configuration (parent and first child) is forced by the three day averaged ERA_Interim data set from 1979 to 2012 at the surface and by the climatology Simple Ocean Data Assimilation model (SODA) at the open boundary of the parent model (15.2°N). A detailed technical description of this model configuration, as well as its performance, can be found in Combes and Matano [2014]. The 10 day averaged model solution of this nested configuration is used offline as the lateral boundary conditions for a second child grid from 2000 to 2012. The second child grid extends from 66°W to 44°W and from 44°S to 25°S, thus covering the southwestern Atlantic region with a horizontal resolution of 1/24° (Figure 1), which is ∼3.8 km at the latitude of RdlP mouth. Unlike the two ways nested experiment of the parent and first child grids, we opted for the higher-resolution (0.25°) QuickSCAT (period 2000–2007) and ASCAT (period 2008–2012) daily wind stress as surface momentum forcing. The surface heat and freshwater fluxes are derived from the COADS data set (climatology). The model also includes a daily discharge of the RdlP, a constant discharge from the Patos Lagoon (set to 2000 m3/s) and five tidal components (M2, S2, N2, K1, and O1 harmonics). The 1/24° resolution model had first spun up for the period 2007–2012, which gave the initial condition to the 2000–2012 model integration. The transport pathways and statistics of the RdlP waters are also characterized using a passive tracer advection-diffusion equation that is identical to that used for the temperature and salinity. The tracer is continuously released (set to 1) in the mouth of the RdlP and distributed from surface to bottom. Although surface forcing is averaged daily, all following analyses will use 10 day averaged fields (including wind stress).


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)

Snapshots of the sea surface salinity (SSS) in the nested model configuration used in this study. (a) The domain of the parent model, which has a horizontal resolution of 1/4°. (b) The first child model, which has a resolution of 1/12°. (b) The second child model, which has a resolution of 1/24°. The three models have the same vertical resolution (40 sigma levels). (c) The extent of Region 1, which is discussed in later sections. The gray line in Figure 1c marks the location of the 200 m isobath (the shelfbreak).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig01: Snapshots of the sea surface salinity (SSS) in the nested model configuration used in this study. (a) The domain of the parent model, which has a horizontal resolution of 1/4°. (b) The first child model, which has a resolution of 1/12°. (b) The second child model, which has a resolution of 1/24°. The three models have the same vertical resolution (40 sigma levels). (c) The extent of Region 1, which is discussed in later sections. The gray line in Figure 1c marks the location of the 200 m isobath (the shelfbreak).
Mentions: The model used in this study is the Regional Ocean Modeling System (ROMS), which is a three-dimensional, free surface, hydrostatic, eddy-resolving primitive equation ocean model. ROMS uses orthogonal curvilinear coordinates in the horizontal and sigma, terrain following coordinates in the vertical [Shchepetkin and McWilliams, 2005]. We use the version ROMS_AGRIF (http://roms.mpl.ird.fr/), which offers the capability of a two-way nesting procedure with high-resolution “child” grids embedded into a coarser resolution “parent” grid. The parent grid extends 360° in the longitudinal direction and from Antarctica to 15.2°N (Figure 1). It has a spatial resolution of 1/4°, and 40 sigma levels in the vertical, with enhanced resolution at the surface. The first child grid extends from 82°W to 41°W and from 64°S to 20°S, covering the southern portion of South America with spatial resolution of 1/12° (Figure 1). The nested configuration (parent and first child) is forced by the three day averaged ERA_Interim data set from 1979 to 2012 at the surface and by the climatology Simple Ocean Data Assimilation model (SODA) at the open boundary of the parent model (15.2°N). A detailed technical description of this model configuration, as well as its performance, can be found in Combes and Matano [2014]. The 10 day averaged model solution of this nested configuration is used offline as the lateral boundary conditions for a second child grid from 2000 to 2012. The second child grid extends from 66°W to 44°W and from 44°S to 25°S, thus covering the southwestern Atlantic region with a horizontal resolution of 1/24° (Figure 1), which is ∼3.8 km at the latitude of RdlP mouth. Unlike the two ways nested experiment of the parent and first child grids, we opted for the higher-resolution (0.25°) QuickSCAT (period 2000–2007) and ASCAT (period 2008–2012) daily wind stress as surface momentum forcing. The surface heat and freshwater fluxes are derived from the COADS data set (climatology). The model also includes a daily discharge of the RdlP, a constant discharge from the Patos Lagoon (set to 2000 m3/s) and five tidal components (M2, S2, N2, K1, and O1 harmonics). The 1/24° resolution model had first spun up for the period 2007–2012, which gave the initial condition to the 2000–2012 model integration. The transport pathways and statistics of the RdlP waters are also characterized using a passive tracer advection-diffusion equation that is identical to that used for the temperature and salinity. The tracer is continuously released (set to 1) in the mouth of the RdlP and distributed from surface to bottom. Although surface forcing is averaged daily, all following analyses will use 10 day averaged fields (including wind stress).

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