Malvinas current at 44.7°S: First assessment of velocity temporal variability from in situ data

Abstract

We report current meter measurements obtained by four moorings deployed across the Malvinas Current (MC) at 44.7°S during 18 months between December 2015-June 2017. Previous measurements of the MC strength have been reported only close to the Brazil-Malvinas Confluence, hindering the interpretation of the flow variability. The record-length time averaged velocities and variance ellipses indicate a strong northward along-isobath. The MC flow is dominated by its barotropic component. The meridional velocities at the western and eastern moorings are not correlated and show large amplitude oscillations which are coherent with the passage of mesoscale features over the moorings. Satellite altimetry data, that are highly correlated with 20-day low-pass filtered in situ velocities (r ~ 0.80), show that the MC variability is affected by the propagation of sea level anomalies (SLA) along the Patagonian slope with phase speeds that range between 0.21 ± 0.04 m s−1 and 0.14 ± 0.01 m s−1. SLAs propagate northward along the slope following contours of constant planetary potential vorticity and its phase speeds decrease towards the east along the slope. SLA arriving at 44.7°S originate near the North Scotia Ridge and along the Malvinas Escarpment, along the northern edge of the Malvinas Plateau. We suggest that the interaction between mesoscale features and the complex bathymetry at those locations generate instabilities that enhance the generation of SLAs that propagate in the flow direction along the western boundary of the Argentine Basin and affect the variability of the MC velocities observed at 44.7°S.