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Biogeochemistry of surface sediments off Concepción (∼36°S), Chile: El Niño vs. non-El Niño conditions |
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| Authors: | Sergio Contreras Silvio Pantoja Carina B Lange |
| Institution: | a Programa de Postgrado en Oceanografía, Departamento de Oceanografía, Universidad de Concepción, Casilla 160-C, Concepción, Chile b Departamento de Oceanografía y Centro de Investigación Oceanográfica en el Pacífico Sur-Oriental (FONDAP-COPAS), Universidad de Concepción, Casilla 160-C, Concepción, Chile c Integrative Oceanographic Division, Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093-0218, USA |
| Abstract: | We compared the signals of several water column properties (upwelling intensity, sea level anomaly, temperature, nutrients, dissolved oxygen, chlorophyll-a, and surface sediments) of the continental shelf off Concepción (36°S) during the 1997-1998 El Niño with those of a normal year (2002-2003). We found that the primary hydrographic effect of El Niño 1997-1998 was a reduction in the input of nutrient-rich, oxygen-poor Equatorial Subsurface Water over the shelf. This affected the biology of the water column, as evidenced by the reduced phytoplankton biomass. Surface sediment properties (biogenic opal, organic carbon, bulk δ15N) observed during El Niño 1997-1998 reflected a reduced export production and the sediments failed to show the water column seasonality that occurs under normal conditions. In addition, weakened denitrification and/or upper water column fertilization could be inferred from the sedimentary δ15N. Although diminished, export production was preserved in the surface sediments, revealing less degraded organic matter in the upwelling period of the El Niño year than in the normal year. We suggest that the fresher organic material on the seafloor was probably associated with a severe reduction in the polychaete Parapronospio pinnata, which is considered to be the most important metazoan remineralizer of organic carbon at the sediment-water interface in the study area. |
| Keywords: | El Niñ o 1997-1998 Upwelling index Sea level anomaly Organic carbon Biogenic opal Chile |
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