Eastern boundary circulation and hydrography off Peru during the 2017 Coastal El Nino

In early 2017 sea surface temperatures in the far eastern tropical Pacific were anomalously high while central Pacific SST anomalies remained neutral or negative. Associated to this anomaly pattern were strong anomalous precipitation events in northern Peru causing severe flooding. During April and May 2017 the near-coastal temperature anomalies declined. In-situ observations from four consecutive research cruises and a glider survey collected between 12°S and 14°S off the coast of Peru are used to describe the eastern boundary circulation and hydrography during declining surface temperature anomalies. The observational data base consists of ship-board hydrography, oxygen and upper-ocean velocity observations, hydrography from glider surveys and velocity time series from mooring deployments. Hydrography at 12°S shows a pronounced warm anomaly near the surface and on the shelf where the full water column warmed by more than 2°C with respect to climatology. Further offshore, a weaker warming was observed below the surface layer as well. The oxycline was displaced downwards and well-oxygenated waters occupied the upper 50m of the water column. Poleward velocities of the Peru-Chile Undercurrent strongly intensified in late-April and May reaching velocities above 50 cm s-1. During this period, near-surface temperature anomalies decreased but subsurface temperatures on the shelf remained high. The forcing of the observed variability of the eastern boundary circulation and of the hydrography during the late phase of the “Coastal El Niño” event is investigated and related to local and remote processes