Influence of coastal upwelling and El Niño-Southern Oscillation on nearshore water along Baja California and Chile: Shore-based monitoring during 1997-2000

In order to determine the sensitivity of coastal upwelling tracers to seasonal wind forcing and El Niño–Southern Oscillation (ENSO) off Baja California and Chile, nearshore salinity, cadmium (Cd), and nutrients phosphate, silicate, nitrate+nitrite were monitored in surf zone waters at six locations along the North and South American coasts during 1997–2000. The clearest responses to upwelling favorable wind forcing were observed at the southern tip of Baja California (23.3°N) and off central‐southern Chile (36.5°S). Upwelling tracers at 23.3°N were also the most sensitive to El Niño: average summer Cd and nutrient enrichments were 60% lower following El Niño than during the previous non–El Niño upwelling season. At two sites on the northern and central Chile coasts, conditions associated with El Niño resulted in salinity anomalies >1. Such large shifts in nearshore water properties suggest it may be possible to reconstruct past ENSO patterns from geochemical paleonutrient/paleosalinity proxy records preserved in nearshore archives such as mollusc or foraminifera shells.