25 years of Malvinas Current volume transport at its northernmost extension: variability and drivers

ARTANA, CAMILA; FERRARI, RAMIRO; KOENIG, ZOÉ; MARTIN SARACENO; PIOLA, ALBERTO R.; CHRISTINE PROVOST; NATHALIE SENNÉCHAEL

Congreso; 25 Years of Progress in Radar Altimetry Symposium,; 2018

The Malvinas Current (MC), the northward flowingwestern boundary current of the Southwestern AtlanticOcean is an offshoot of the Antarctic CircumpolarCurrent and extends up to 38°S. Currentmeter mooringdata in the northernmost extension of MC have beenobtained at 41°S at three opportunities: in 1993-1995(contribution to WOCE project, [1]), 2001-2003(contribution to CLIVAR project, [2]) and 2014-2015(CASSIS Malvinas project). For each period, velocitiesderived from satellite altimetry data are highlycorrelated (> 0.8) with 20-day low-pass filtered in-situvelocities from current meters deployed at 300 m depth[3]. Gridded data are preferred to along-track data [3].Combining satellite altimetry and the in situ data setsfrom the three 10-years apart mooring deployments, a24-year long volume transport time series of the MC at41°S was produced [4] using a look-up table method [5]. Three types of shear were used to estimate theuncertainty attached to the lack of information on thevelocity shear in the upper 300 m of the water column[5]. The accurate look-up table method provides a reevaluationof the mean transport with respect toprevious estimates performed using a classic method [6,2]. On the occasion of the ?25 years of Progress in RadarAltimetry? Symposium, we updated the transport timeseries (1993-2017).The drivers of the MC transport variations at 41°Sexamined in [7] were revisited [5, 8]. Transport extremaat 41°S are not driven by upstream conditions on theslope. Instead, transport maxima appear to be relatedwith cyclonic eddies detached from the Polar Frontwhich propagate northward above the 4000 m isobathup to 41°S. Transport minima are due to positiveanomalies shed by the Brazil Current overshoot thatmanage to move westward onto the slope. Altimetryand Argo floats show that at times, the MC is cut fromits source downstream of Drake Passage by anticyclonicanomalies propagating westward along the MalvinasEscarpment at 48°S [8]. These blocking events arerecurrent and last about a month. However, they do notseem to affect the MC flow at 41°S, as a cyclonicrecirculation cell is established between 38°S and 48°S,with the MC being its western boundary. The MalvinasPlateau restricts the northward penetration ofmesoscale activity. Consequently, variations of sea levelanomalies south of 53°S do not impact the MC furthernorth.