Dramatic ENSO related Southwestern Atlantic ecosystem shifts

Abstract

ENSO (El Niño Southern Oscillation) events are becoming more frequent and more intense as climate change continues. Although ENSO effects are known to propagate into the southwest Atlantic, knowledge of how these anomalies result in ecological impacts is yet to be documented. A 3600 km transect in the southwest Atlantic from the Falkland Islands (Malvinas) to Tristan da Cunha during La Niña (March 2018) found a more abundant and speciose seabird assemblage, with more filter-feeding seabird and cetacean species, and a shallower and more concentrated pelagic biomass, than a near identical transect during El Niño (March 2019). Changes in wind and sea surface temperature anomalies correlated, through a one-to-three-month lag, to the peak BEST (Bivariate ENSO Index) index. Stronger winds and greater near surface ocean mixing are for the first time described as mechanisms through which ENSO events can propagate across the southwest Atlantic Ocean basin to alter pelagic ecosystem structure and communities. Main Text.