The climatic event El Nio, literally the Baby Jesus, was given its name because it generally occurs at Christmas time along the Peruvian coasts. This expression of climatic variability, also called El Nio Southern Oscillation (ENSO), results from a series of interactions between the atmosphere and the tropical ocean. It induces drought in areas that normally receive abundant rain and, conversely, heavy rainfall and floods in usually arid desert zones. Scientists term this phenomenon a quasi-cyclic variation because its periodicity, which varies from 2 to 7 years, shows no regular time pattern. Research conducted over the past 25 years, by oceanographers, climatologists and meteorologists has much improved knowledge on the mechanisms generating an El Nio event. However, possible influence of other systems of climate variability on the ENSO regime is more difficult to fathom. More particularly, it is not known if the intensity and frequency of the event is susceptible to modification in a situation of global warming.
The research work recently published by a team of Chilean and IRD scientists sheds new light on El Nios variability. Several geochemical factors contained in a drill core sediment sampled from 80 m depth under the Bay of Mejillones, in northern Chile, were determined. Analysis of breakdown byproducts from diatoms, unicellular planktonic algae, yielded an accurate trace of this regions trends in sea surface temperature between 1650 and 2000. Data for the period 1820-1878 showed a fall of over 2C. This temperature decrease was also detected in two cores collected near the South-American coasts, over 1000 km to the North and South of Mejillones.
These samplings confirmed that the decrease in ocean temperature observed from 1820 affected the whole Pacific seaboard, from central Chile up to the North of Peru. All the oceanic area situated on the path of the Humboldt current system was therefore the scene of significant cooling during this per
|Contact: Gregory Flechet|
Institut de Recherche Pour le Dveloppement