On the Wind Contribution to the Variability of Ocean Currents Over Wide Continental Shelves: A Case Study on the Northern Argentine Continental Shelf

Abstract

The southwestern Atlantic Ocean has one of the largest and most productive continental shelves of the southern hemisphere. Despite its relevance, its circulation patterns have been largely inferred from hydrographic observations and numerical models. Here we describe the variability of the shelf circulation based on the analysis of 11 months of multilevel currents measured by two bottom‐mounted acoustic Doppler current profilers deployed over the continental shelf at 39°S. The record‐length mean is 12 and 13 cm/s in the upper layer and decreases to 6 and 8 cm/s near the bottom, at the deployment nearer and further from the coast, respectively. The mean flow direction is toward the NE, following the orientation of the isobaths. Measurements at both sites show that the alongshore barotropic component accounts for 83% of the variability observed and are well correlated (0.86), suggesting a relatively uniform flow, which is presumably driven by large‐scale forcing. Indeed, large‐scale wind stress patterns dominate the temporal variability of the in situ currents and the passage of atmospheric fronts induces significant changes in the observed currents at all depths. We found that for 12% of the measurements the currents reverse the direction to the SW in response to these atmospheric patterns. Furthermore, the analysis of sea surface height reconstructed from bottom pressure measurements at both sites and from a coastal tide gauge reveals that the variability of the alongshore currents is driven by the cross‐shore pressure gradients generated by the alongshore wind stress.

Circulation and Hydrography in the Western South Atlantic Shelf and Export to the Deep Adjacent Ocean: 30°S to 40°S

“…This negative SLA is confirmed by a coastal tide gauge record from San Clemente del Tuyu (supporting information Figure S3). The change in current direction is in agreement with recent current meter observations collected over the central portion of the continental shelf at around 39°S, which show that though the mean flow is about 10-12 cm s −1 toward the northeast, current reversal are likely to occur during periods of northeasterly winds associated with the passage of synoptic weather systems (Lago et al, 2019).…”

“…A schematic circulation summarizing these findings is presented in Figure 10. Over and south of the southernmost section, a northeastward flow (blue solid line) represents the mean path of SASW derived from previous work (Lago et al, 2019) but not observed in the October 2013, when SASW flowed southward (blue dashed line) due to the prevailing northeasterly winds blowing at that time. The circulation schematic is similar to those presented by Möller et al (2008) and Piola et al (2008) with the addition of the splitting SASW path near 37°S.…”

“…The black dots indicate the CTD stations of the SF2013 cruise occurred in 2013 October. SASW: Subantarctic Shelf Water, over and south of the southernmost transect the solid line indicated the mean path (Lago et al., 2019) and the dashed line indicated what was observed during October 2013. STSW: Subtropical Shelf Water, RDP: Río de la Plata water, AAIW: Antarctic Intermediate Water, SACW: South Atlantic Central Water.…”

Volume Transport Variability on the Northern Argentine Continental Shelf From In Situ and Satellite Altimetry Data

“…10.1029/2020JC016813 7 of 16 the along-shore currents is strongly modulated by the cross-shore pressure gradient generated by the alongshore component of the wind stress (Lago et al, 2019). The strong shelf transport response to along-shore winds is readily apparent over the inner and mid-shelf ( Figure 4).…”

“…The location of the CASSIS moorings used in this study are displayed in Figure 1. Given the barotropic nature and the cross-shelf coherency of the along-shore flow reported by Lago et al (2019), the available data may be used to provide a robust estimate of the volume transport over the continental shelf. The following sections of the study present the data sets considered and the methods used for the analysis (Section 2), the results and discussions (Section 3) and main conclusions (Section 4).…”