Glacial to interglacial primary production and El Nino-Southern Oscillation dynamics inferred from coccolithophores of the Santa Barbara Basin
Résumé
We investigate the long-term stability of El Nino-Southern Oscillation and Pacific Decadal Oscillation based on the examination of coccolithophore assemblages in a largely laminated 35 ka sedimentary record, retrieved in the Santa Barbara Basin (core MD02-2503). At a centennial scale coccolith assemblages indicate low primary production in the basin from 35 to 11.5 ka B. P., whereas the Holocene is characterized by high-productivity conditions. This pattern demonstrates the influence of the glacial-interglacial cycles on productivity and, by inference, on the nutrient supply by the upwelling cell off Point of Conception. On a shorter scale, laminations associated with Dansgaard-Oeschger events appear to be due to an injection of poorly oxygenated waters in the deepest part of the basin rather than anoxia due to high primary production. A seasonal sampling in seven laminated sections (spanning from 20 to 220 years) extracted from Holocene, Bolling-Allerod, and Dansgaard-Oeschger event 3 indicates El Nino probably existed continuously during the last 28 ka. The frequency of El Nino varied through time (between 1/2.5 and 1/5 event a(-1)) and appearing to follow the precession cycle. El Nino exhibits higher (lower) frequencies when the precession values are lower (higher). Finally, the Holocene is characterized by a decrease in El Nino's frequencies due to the reinforcement of El Nino through this period.
Domaines
Océanographie
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