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 44.7ºS 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 flow with an equivalent-barotropic structure. 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 potential vorticity and its phase speeds decrease towards the east across the slope. SLAs that mostly affect the western mooring originate in the northern flank of the North Scotia Ridge while SLAs that mostly affect the eastern mooring originate along the Malvinas Escarpment, along the northern edge of the Malvinas Plateau. We suggest that the interaction between eddies and the complex bathymetry at those locations generate instabilities that enhance the generation of mesoscale structures that propagate in the flow direction along the western boundary of the Argentine Basin affecting the variability of the MC velocities.

Multiple Lagrangian Jet‐Core Structures in the Malvinas Current

“…Current knowledge of the variability of the MC transport and the study of the current structure has been addressed in the literature on the basis of in situ data: ADCP transects and drifters (e.g., Piola et al., 2013), moorings (e.g., Paniagua et al., 2018), satellite altimetry and color imagery (e.g., Artana, Ferrari, et al., 2018), regional models (e.g., Combes & Matano, 2018), and ocean reanalysis (e.g., Artana, Lellouche, et al., 2018). The variability of the MC transport on synoptic timescales, a scale relevant to the present study, has been attributed to the passage of trapped topographic waves and the interaction with mesoscales motions on the eastern side of the MC (Paniagua et al, 2021; Poli et al., 2020). Propagating patterns have been reported to traverse the Drake Passage and have been traced back to their origins in the Pacific Basin.…”

“…The origin of the waves is traced back to the southwestern region of the Atlantic and may possibly be related to wave trains entering the Atlantic from the Pacific Ocean at the Drake Passage, as shown by Paniagua et al. (2021) and discussed by Poli et al. (2020).…”

Dynamic Structure of Eddies of the Brazil‐Malvinas Confluence Zone Revealed by Direct Measurements and Satellite Altimetry

“…The measurements revealed low Richardson numbers well below the mixed layer indicating possible mixing between Antarctic Intermediate Water (AAIW) and the upper ocean layer. Temporal variability of the MC was studied based on moored velocity observations at 41°S (Artana et al., 2018; Lago et al., 2021) and at 44.7°S (Paniagua et al., 2021). Two opposite regimes of the BMC, namely weak and strong Malvinas flow, have been described in several studies (Ferrari et al., 2017; Paniagua et al., 2018).…”