Complementary analyses on certain minerals contained in the sediment samples confirmed that these minerals were transported by the winds from the continent. Therefore the reinforcement of such prevailing winds, the trade winds, would have favoured the rise of colder waters up from deeper reaches, along the Pacific coasts of South America, by pushing the ocean surface layer westwards. Confirmation of this hypothesis came from measurement of the organic carbon flux which is directly linked to growth in nutrient concentration. The increase in this flux accords with the phase of falling sea temperatures between 1820 and 1878 which proves that the rise in nutrient concentration stems from a rising up of cold water by the process of upwelling (2).
The hypothesis the researchers postulate suggests that, in a situation of climate warming like the one that followed the end of the Little Ice Age, the large continentocean temperature (and hence thermal) contrast would be responsible for this accentuation of the trade wind regime. Whereas the Atacama, a coastal-zone desert, warmed rapidly during this period, the sea surface temperature would have risen much more slowly. The long-term persistence of a substantial temperature difference between ocean and continent would have caused an intensification of the prevailing winds. Then by pushing the surface water towards the west, these winds would have induced cooling of the coastal waters, changing the normal feature of the El Nio regime which is a warming of the waters. Between the end of the Little Ice Age and the beginning of the global warming attributable to human activities the ENSO regime was modified. Historical climatology studies founded on chroniclers accounts and descriptions of floods caused by these El Nio events also showe
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Institut de Recherche Pour le Dveloppement