Variación temporal de los afloramientos costeros frente a Chile Central (36°S; 74°W), mediante los isótopos estables de oxígeno de foraminíferos planctónicos, durante El Niño 2006

Abstract

The ocean off south-central Chile is characterized by seasonal coastal upwelling. The upwelling of nutrient-rich waters turns this part of the Chilean margin in a high productivity region. As the temporal variability of the upwelling settings may change under El Niño conditions, the impact of the 2006 El Niño event on the fluxes and the stable oxygen isotope composition δ18O) of planktonic foraminifera collected with time-series sediment traps off Concepcion has been investigated. We used sediment trap samples collected between January and October 2006 at 1,000 and 2,300 m water depth, offshore south-central Chile (36°S; 74°W). The shells of planktonic foraminifera are sensitive to record environmental conditions, and here the thermal structure of the water column has been assessed by comparing the data of the planktonic foraminifera species Globigerina bulloides d'Orbigny, 1826 and Neogloboquadrina incompta (Cifelli 1961). The values of these planktonic foraminifera and their differences (Δδ^) reveal the presence of upwelling during summer under normal conditions (January - April). During this period the was < 0.3 990 indicative for a well-mixed water column and the flux and the diversity of the foraminifera as well as the calcium carbonate flux were significantly increased. Following this upwelling period, the 2006 El Niño event began which between April and October was marked by an extended period of water column stratification with low fluxes of foraminifera, calcium carbonate and low species diversity.