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Contreras, S, Pantoja S, Neira C, Lange CB.  2007.  Biogeochemistry of surface sediments off Concepcion (~36°S), Chile: El Nino vs. non-El Nino conditions. Progress in Oceanography. 75:576-585.   10.1016/j.pocean.2007.08.030   AbstractWebsite

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 Concepcion (36 degrees S) during the 1997-1998 El Nino with those of a normal year (2002-2003). We found that the primary hydrographic effect of El Nino 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 delta N-15) observed during El Nino 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 delta N-15. Although diminished, export production was preserved in the surface sediments, revealing less degraded organic matter in the upwelling period of the El Nino 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. (c) 2007 Elsevier Ltd. All rights reserved.