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The salinity signature of the cross-shelf exchanges in the Southwestern Atlantic Ocean: Satellite observations.

Guerrero RA, Piola AR, Fenco H, Matano RP, Combes V, Chao Y, James C, Palma ED, Saraceno M, Strub PT - J Geophys Res Oceans (2014)

Bottom Line: However, the combined analysis of SSS, satellite-derived sea surface elevation and surface velocity data suggest that the precise location of the export of shelf waters depends on offshore circulation patterns, such as the location of the Brazil Malvinas Confluence and mesoscale eddies and meanders of the Brazil Current.The satellite data indicate that in summer, mixtures of low-salinity shelf waters are swiftly driven toward the ocean interior along the axis of the Brazil/Malvinas Confluence.Satellite salinity sensors capture low-salinity detrainment events from shelves SW Atlantic low-salinity detrainments cause highest basin-scale variability In summer low-salinity detrainments cause extended low-salinity anomalies.

View Article: PubMed Central - PubMed

Affiliation: Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP) Mar del Plata, Argentina.

ABSTRACT

: Satellite-derived sea surface salinity (SSS) data from Aquarius and SMOS are used to study the shelf-open ocean exchanges in the western South Atlantic near 35°S. Away from the tropics, these exchanges cause the largest SSS variability throughout the South Atlantic. The data reveal a well-defined seasonal pattern of SSS during the analyzed period and of the location of the export of low-salinity shelf waters. In spring and summer, low-salinity waters over the shelf expand offshore and are transferred to the open ocean primarily southeast of the river mouth (from 36°S to 37°30'S). In contrast, in fall and winter, low-salinity waters extend along a coastal plume and the export path to the open ocean distributes along the offshore edge of the plume. The strong seasonal SSS pattern is modulated by the seasonality of the along-shelf component of the wind stress over the shelf. However, the combined analysis of SSS, satellite-derived sea surface elevation and surface velocity data suggest that the precise location of the export of shelf waters depends on offshore circulation patterns, such as the location of the Brazil Malvinas Confluence and mesoscale eddies and meanders of the Brazil Current. The satellite data indicate that in summer, mixtures of low-salinity shelf waters are swiftly driven toward the ocean interior along the axis of the Brazil/Malvinas Confluence. In winter, episodic wind reversals force the low-salinity coastal plume offshore where they mix with tropical waters within the Brazil Current and create a warmer variety of low-salinity waters in the open ocean.

Key points: Satellite salinity sensors capture low-salinity detrainment events from shelves SW Atlantic low-salinity detrainments cause highest basin-scale variability In summer low-salinity detrainments cause extended low-salinity anomalies.

No MeSH data available.


Related in: MedlinePlus

SSS (contours) and SSS anomaly (colors) for (a) September 2010 constructed from SMOS L2 data and (b) August 2012 constructed with Aquarius data, relative to the 2012–2013 mean. The gray thick line indicates the 200 m isobath.
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fig10: SSS (contours) and SSS anomaly (colors) for (a) September 2010 constructed from SMOS L2 data and (b) August 2012 constructed with Aquarius data, relative to the 2012–2013 mean. The gray thick line indicates the 200 m isobath.

Mentions: From data collected in October 1984, Gordon [1989] also noted the presence of a warmer variety of low-salinity waters on the western branch of the Brazil Current, which he suggested were originated further north, either by excess precipitation over the coastal region or as a result of northward flow of RdlP waters along the coast which were then diffused offshore, forming a low-salinity cap over the southward flowing Brazil Current. The two varieties of low-salinity waters were also apparent in observations collected in winter 2003. These data presented several warm-fresh (∼15–17°C, <34) filaments detaching from the RdlP coastal plume near 29°S and 31°S and a significantly colder variety (∼11°C) close to the Confluence [Piola et al., 2008b]. These data suggested that in winter, when under the sustained influence of southwesterly winds the RdlP plume is well-developed as a narrow coastal band extending northeastward from the river mouth, the primary export route of low-salinity waters is along the offshore edge of the plume. The winter 2003 survey further indicates that as these waters mix with the salty Brazil Current they rapidly lose their low-salinity signal [Piola et al., 2008b]. Similar detachments of low-salinity waters are suggested by the trajectories of particles released in a numerical model [Matano et al., 2014]. On the other hand, the hydrographic data collected further south across the BMC shows that the cold variety of low-salinity waters is mostly composed of undiluted SASW from the northern Patagonia continental shelf [Piola et al., 2008b, their Figure 11]. Though SASW is ∼0.3 fresher than surface waters within the Malvinas Current (SSS > 34), the salinity difference is probably too small for clear detection by the satellite sensors. Thus, in winter, the export of PPW waters and undiluted SASW create a salinity signal much weaker than in summer. These results explain why only three low-salinity export events apparent in the satellite data are observed in winter (2S in April–June 2010, 3S in August–September–October 2010, Table2, and 4A in August 2012, Table1). All the events were intense (mean SSS ∼ 33) and each lasted from 5 to 16 weeks (see Tables1 and 2). Each of these winter events was preceded by the most intense wind reversals observed between 2010 and 2014 (Figures 7c and 7d). We argue that these wind reversals from southwesterly to northeasterly winds caused the offshore expansion of RdlP waters, thus providing a more intense export of low-salinity waters along the coast of southern Brazil, and a stronger salinity anomaly in the open ocean. The export of shelf waters to the open ocean creates extensive negative salinity anomalies (<−0.5) over the southward flowing Brazil Current between 27°S and 35°S (Figures 10a and 10b). Likewise, in winter the numerical simulations present extensive negative salinity anomalies in the open ocean north of about 36°S [Matano et al., 2014, Figure 10]. Given the relatively high sea surface temperatures advected within the Brazil Current, similar features are probably the source of the warm variety of low-salinity waters reported in previous studies [Gordon, 1989; Piola et al., 2008b].


The salinity signature of the cross-shelf exchanges in the Southwestern Atlantic Ocean: Satellite observations.

Guerrero RA, Piola AR, Fenco H, Matano RP, Combes V, Chao Y, James C, Palma ED, Saraceno M, Strub PT - J Geophys Res Oceans (2014)

SSS (contours) and SSS anomaly (colors) for (a) September 2010 constructed from SMOS L2 data and (b) August 2012 constructed with Aquarius data, relative to the 2012–2013 mean. The gray thick line indicates the 200 m isobath.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4508963&req=5

fig10: SSS (contours) and SSS anomaly (colors) for (a) September 2010 constructed from SMOS L2 data and (b) August 2012 constructed with Aquarius data, relative to the 2012–2013 mean. The gray thick line indicates the 200 m isobath.
Mentions: From data collected in October 1984, Gordon [1989] also noted the presence of a warmer variety of low-salinity waters on the western branch of the Brazil Current, which he suggested were originated further north, either by excess precipitation over the coastal region or as a result of northward flow of RdlP waters along the coast which were then diffused offshore, forming a low-salinity cap over the southward flowing Brazil Current. The two varieties of low-salinity waters were also apparent in observations collected in winter 2003. These data presented several warm-fresh (∼15–17°C, <34) filaments detaching from the RdlP coastal plume near 29°S and 31°S and a significantly colder variety (∼11°C) close to the Confluence [Piola et al., 2008b]. These data suggested that in winter, when under the sustained influence of southwesterly winds the RdlP plume is well-developed as a narrow coastal band extending northeastward from the river mouth, the primary export route of low-salinity waters is along the offshore edge of the plume. The winter 2003 survey further indicates that as these waters mix with the salty Brazil Current they rapidly lose their low-salinity signal [Piola et al., 2008b]. Similar detachments of low-salinity waters are suggested by the trajectories of particles released in a numerical model [Matano et al., 2014]. On the other hand, the hydrographic data collected further south across the BMC shows that the cold variety of low-salinity waters is mostly composed of undiluted SASW from the northern Patagonia continental shelf [Piola et al., 2008b, their Figure 11]. Though SASW is ∼0.3 fresher than surface waters within the Malvinas Current (SSS > 34), the salinity difference is probably too small for clear detection by the satellite sensors. Thus, in winter, the export of PPW waters and undiluted SASW create a salinity signal much weaker than in summer. These results explain why only three low-salinity export events apparent in the satellite data are observed in winter (2S in April–June 2010, 3S in August–September–October 2010, Table2, and 4A in August 2012, Table1). All the events were intense (mean SSS ∼ 33) and each lasted from 5 to 16 weeks (see Tables1 and 2). Each of these winter events was preceded by the most intense wind reversals observed between 2010 and 2014 (Figures 7c and 7d). We argue that these wind reversals from southwesterly to northeasterly winds caused the offshore expansion of RdlP waters, thus providing a more intense export of low-salinity waters along the coast of southern Brazil, and a stronger salinity anomaly in the open ocean. The export of shelf waters to the open ocean creates extensive negative salinity anomalies (<−0.5) over the southward flowing Brazil Current between 27°S and 35°S (Figures 10a and 10b). Likewise, in winter the numerical simulations present extensive negative salinity anomalies in the open ocean north of about 36°S [Matano et al., 2014, Figure 10]. Given the relatively high sea surface temperatures advected within the Brazil Current, similar features are probably the source of the warm variety of low-salinity waters reported in previous studies [Gordon, 1989; Piola et al., 2008b].

Bottom Line: However, the combined analysis of SSS, satellite-derived sea surface elevation and surface velocity data suggest that the precise location of the export of shelf waters depends on offshore circulation patterns, such as the location of the Brazil Malvinas Confluence and mesoscale eddies and meanders of the Brazil Current.The satellite data indicate that in summer, mixtures of low-salinity shelf waters are swiftly driven toward the ocean interior along the axis of the Brazil/Malvinas Confluence.Satellite salinity sensors capture low-salinity detrainment events from shelves SW Atlantic low-salinity detrainments cause highest basin-scale variability In summer low-salinity detrainments cause extended low-salinity anomalies.

View Article: PubMed Central - PubMed

Affiliation: Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP) Mar del Plata, Argentina.

ABSTRACT

: Satellite-derived sea surface salinity (SSS) data from Aquarius and SMOS are used to study the shelf-open ocean exchanges in the western South Atlantic near 35°S. Away from the tropics, these exchanges cause the largest SSS variability throughout the South Atlantic. The data reveal a well-defined seasonal pattern of SSS during the analyzed period and of the location of the export of low-salinity shelf waters. In spring and summer, low-salinity waters over the shelf expand offshore and are transferred to the open ocean primarily southeast of the river mouth (from 36°S to 37°30'S). In contrast, in fall and winter, low-salinity waters extend along a coastal plume and the export path to the open ocean distributes along the offshore edge of the plume. The strong seasonal SSS pattern is modulated by the seasonality of the along-shelf component of the wind stress over the shelf. However, the combined analysis of SSS, satellite-derived sea surface elevation and surface velocity data suggest that the precise location of the export of shelf waters depends on offshore circulation patterns, such as the location of the Brazil Malvinas Confluence and mesoscale eddies and meanders of the Brazil Current. The satellite data indicate that in summer, mixtures of low-salinity shelf waters are swiftly driven toward the ocean interior along the axis of the Brazil/Malvinas Confluence. In winter, episodic wind reversals force the low-salinity coastal plume offshore where they mix with tropical waters within the Brazil Current and create a warmer variety of low-salinity waters in the open ocean.

Key points: Satellite salinity sensors capture low-salinity detrainment events from shelves SW Atlantic low-salinity detrainments cause highest basin-scale variability In summer low-salinity detrainments cause extended low-salinity anomalies.

No MeSH data available.


Related in: MedlinePlus