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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

Mean SSS anomaly (colors) and mean dynamic topography (contours, cm) for December–January–February. The salinity anomaly is relative to the 2012–2013 mean. The gray thick line indicates the 200 m isobath.
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fig09: Mean SSS anomaly (colors) and mean dynamic topography (contours, cm) for December–January–February. The salinity anomaly is relative to the 2012–2013 mean. The gray thick line indicates the 200 m isobath.

Mentions: Data from both satellite sensors present substantial intraseasonal variability in the outer shelf and upper slope (Figures 7a and 7b). The most conspicuous manifestations of intraseasonal variability of SSS in the upper slope are the low-salinity detrainment events described in section 3 (Figures 6, 7, and S5, and Tables1 and 2). The Hovmöller diagrams constructed with Aquarius along-track SSS data along CT and ST (Figures 6b and 6c) and the SSS-Aq distributions (Figures 8 and S2) show that these events can drive low-salinity waters (SSS-Aq < 33.5) several hundred km away from the shelf. This is in agreement with earlier observations of low-salinity surface water near the BMC. Based on the analysis of hydrographic data collected in October 1984, Gordon [1989] noted that low-salinity waters, which were too warm to be derived from the Malvinas Current, formed elongated filaments or “cells” along the Confluence and suggested that they were first advected offshore by the cyclonic loop described by the Malvinas Current near 39°S, and southward by eddies and filaments of the Malvinas Return Current. Similarly, Provost et al. [1996] observed low-salinity waters along the BMC, presumably derived from the Rio de la Plata and extending about 500 km away from the estuary. SSS distributions derived from high-resolution numerical models also suggested the offshore advection of low-salinity plumes at the BMC [Palma et al., 2008]. Though none of these data allowed mapping the extent or precisely determining the source of the anomalous waters, the SSS-SMOS and SSS-Aq distributions (Figures 5a, 5b, and 8) clearly indicate that the lowest-salinity waters (SSS < 33.5) are derived from the Rio de la Plata. Moreover, our analyses suggest that these waters are advected away from the shelf region via the BMC and that the export events occur primarily during the austral summer (Tables1 and 2). The export of shelf waters in summer creates an extensive region of negative salinity anomalies relative to the record length mean (2012–2013), which extends ∼320 km southeastward form the shelf break (Figure 9). The summer anomalies detrain from the shelf near 37°S (Figure 9), in close agreement with the concentrated exit point of particles released in a numerical simulation [Matano et al., 2014]. On average, in summer the path of these low-salinity waters closely follows the BMC as revealed by the summer mean dynamic topography (40–50 cm contours in Figure 9).


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)

Mean SSS anomaly (colors) and mean dynamic topography (contours, cm) for December–January–February. The salinity anomaly is 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

fig09: Mean SSS anomaly (colors) and mean dynamic topography (contours, cm) for December–January–February. The salinity anomaly is relative to the 2012–2013 mean. The gray thick line indicates the 200 m isobath.
Mentions: Data from both satellite sensors present substantial intraseasonal variability in the outer shelf and upper slope (Figures 7a and 7b). The most conspicuous manifestations of intraseasonal variability of SSS in the upper slope are the low-salinity detrainment events described in section 3 (Figures 6, 7, and S5, and Tables1 and 2). The Hovmöller diagrams constructed with Aquarius along-track SSS data along CT and ST (Figures 6b and 6c) and the SSS-Aq distributions (Figures 8 and S2) show that these events can drive low-salinity waters (SSS-Aq < 33.5) several hundred km away from the shelf. This is in agreement with earlier observations of low-salinity surface water near the BMC. Based on the analysis of hydrographic data collected in October 1984, Gordon [1989] noted that low-salinity waters, which were too warm to be derived from the Malvinas Current, formed elongated filaments or “cells” along the Confluence and suggested that they were first advected offshore by the cyclonic loop described by the Malvinas Current near 39°S, and southward by eddies and filaments of the Malvinas Return Current. Similarly, Provost et al. [1996] observed low-salinity waters along the BMC, presumably derived from the Rio de la Plata and extending about 500 km away from the estuary. SSS distributions derived from high-resolution numerical models also suggested the offshore advection of low-salinity plumes at the BMC [Palma et al., 2008]. Though none of these data allowed mapping the extent or precisely determining the source of the anomalous waters, the SSS-SMOS and SSS-Aq distributions (Figures 5a, 5b, and 8) clearly indicate that the lowest-salinity waters (SSS < 33.5) are derived from the Rio de la Plata. Moreover, our analyses suggest that these waters are advected away from the shelf region via the BMC and that the export events occur primarily during the austral summer (Tables1 and 2). The export of shelf waters in summer creates an extensive region of negative salinity anomalies relative to the record length mean (2012–2013), which extends ∼320 km southeastward form the shelf break (Figure 9). The summer anomalies detrain from the shelf near 37°S (Figure 9), in close agreement with the concentrated exit point of particles released in a numerical simulation [Matano et al., 2014]. On average, in summer the path of these low-salinity waters closely follows the BMC as revealed by the summer mean dynamic topography (40–50 cm contours in Figure 9).

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