Mild Impact of the 2023 El Niño on Oceanographic and Biological Conditions in the Humboldt Current System

Resumen: El Niño is an oceanographic-atmospheric perturbation that originates at the equator and subsequently moves poleward along the coasts of the American continent, altering environmental and biological conditions of marine ecosystems. Upwelling supplies nutrients and concentrates plankton near the surface in some of these ecosystems, although it also promotes the transport of water and plankton to the open ocean. We recorded the ecosystem alterations associated with the El Niño 2023 in the Humboldt Archipelago, a biodiversity hotspot situated in a Chilean upwelling region of the Humboldt Current System. To this end, the abundance of plankton organisms (both phytoplankton and zooplankton), particulate carbon and oceanographic conditions were assessed during eight nearly-monthly campaigns. Plankton abundance in the archipelago depends also on local currents that disperse or concentrate particles. These currents originate from the interaction of winds and a canyon crossing the archipelago. Upwelling persisted during the period despite the arrival of a warm Kelvin wave in June–July that elevated the sea level and temperature. The phytoplankton abundance was the lowest after the warm wave, whereas particulate carbon and zooplankton were stable, but there was a significant surface increase during spring. The zooplankton abundance was related to local environmental conditions, such as food and currents.