Inter-annual variability of the Pelagic-Benthic coupling in the upwelling system off central Chile

摘要

The coastal region of central Chile (36° S) is one of the mostproductive coastal systems, characterized by a marked seasonality in theupwelling regime, that brings subsurface waters rich in nutrient and poor inoxygen (ESSW) into the euphotic zone. This oceanographic condition dependsbasically on the equatorward wind strength and is modified on different timescales, with the El Niño-Southern Oscillation (ENSO) phenomenon as themain source of interannual variability in the Pacific Ocean. Here we presentan effort to integrate physical and biogeochemical variability associatedwith in situ information and experiments at coastal stations off centralChile (36° S) in order to improve the knowledge on the pelagic-benthiccoupling in this upwelling system during the warm ENSO phase or El Niño.Carbon fluxes exported from the water column to the sediments and theammonium exchange across the sediment-water interface are discussed togetherwith oceanographic and benthic conditions. All measurements and estimationswere carried out from May 1997 until April 2001 at two stations, one locatedinside Concepción Bay (~28 m depth), and the other on thecontinental shelf at ~36° S (~88 m depth). The results showthat the pelagic and benthic systems are strongly coupled off central Chile(36° S). Oceanographic variability associated with upwelling events(seasonal scale) and an El Niño event (interannual scale) was observed.The carbon fluxes exported to the sediments, the benthic conditions (i.e.,quantity and quality of the sediment organic matter), and the ammoniumexchange across the sediment-water interface, responded to the seasonalregime of upwelling during non El Niño years as well as to the ENSOrelated oceanographic variability.