The anomalous circulation over the southwest South Atlantic shelf in austral autumn 2016

ALBERTO R. PIOLA; ELBIO D. PALMA; CAROLINA VERA

Montreal

Congreso; 27 IUGG General Assembly; 2019

IUGG

The western South Atlantic continental shelf hosts one of the most productivemarine ecosystems in the southern hemisphere. In contrast with eastern boundaryupwelling regimes the productivity in these regions is thought to be mostlysustained by nutrients supplied from the western boundary currents. South of~38ºS the northward flowing Malvinas Current marks the offshore edge of theshelf, while the region further north is under the influence of the southward flowingBrazil Current. Close to the confluence of the western boundary currents the Platariver discharges about 25,000 m3/s. This discharge, the western boundary currentsand the along-shore winds are the main factors controlling the shelf circulation.This presentation is focused on an extreme event observed in the austral fall of2016, which led to an unprecedented toxic bloom along the coast of southernBrazil. The combined analysis of satellite and in-situ observations, together withnumerical simulations and atmospheric reanalysis products indicate that the eventwas triggered by anomalous atmospheric circulation patterns that led to strongsoutherly winds lasting several weeks and extending throughout the western SouthAtlantic shelf. These anomalous winds drove a coastal sea-level rise during most ofMay and June, developing a strong coastal current which combined withanomalously high river discharge created an extraordinary river plume whichimpacted the coastal ecosystems beyond 1200 km from the estuary.