HR: 10:50h
AN: PP52C-03    [Abstracts]
TI: Recent and Past High Resolution Organic Sedimentation in an Upwelling Cell of Humboldt Current System; Mejillones bay, Northern Chile.
AU: * Jorge, V
EM: jvaldes@uantof.cl
AF: Laboratorio de Sedimentologia y Paleoambientes Facultad de Recursos del Mar Universidad de Antofagasta, Av. Coloso s/n., Antofagasta, 170 Chile
AU: Abdel, S
EM: Abdel.Sifeddine@ird.bondy.fr
AF: UR 055 PALEOTROPIQUE, Institut de Recherche pour le Développement, 32 avenue Henri-Varagnat, F-93143 Bondy Cedex, France, Bondy, F-93143 France
AU: Luc, O
EM: Luc.Ortlieb@ird.bondy.fr
AF: UR 055 PALEOTROPIQUE, Institut de Recherche pour le Développement, 32 avenue Henri-Varagnat, F-93143 Bondy Cedex, France, Bondy, F-93143 France
AU: Gabriel, V
EM: gvargas@ing.uchile.cl
AF: Departamento de Geologia, Universidad de Chile, Plaza Ercilla 803, Santiago, 130 Chile
AU: Catherine, P
EM: cpierre@lodyc.cl
AF: LOCEAN, IRD-CNRS-MNHN-UPMC, Université Paris VI, 4 Place Jussieu Case 100 75252 Paris Cedex 05, Paris, 05 France
AB: In this study, we present information of annual hydrographic variability, surface sediments distribution and one sedimentary core analyses to reconstruct the past 200 years of oceanographic history of Mejillones, focusing on the productivity and oxygenation factors. Spatial differences in surface water productivity were evaluated using periodical „13C measurements of dissolved inorganic carbon. The organic composition of the superficial sediment, analyzed by statistical approach, reflects the three principal zones identified by their degree of bottom oxygenation. The oxic coastal zone preserves principally non-metabolizable organic matter with high Oxygen Index (OI) and low Hydrogen Index (HI), total carbon (TC), total organic carbon (TOC) and nitrogen content (NT). In this area, the organic fraction is dominated by dispersed amorphous organic matter. This suggests an environment where most of metabolizable organic matter has been degraded within the water column and/or at the benthic surface sediments. The microxic hemipelagic zone located deeper than 65 meters, is marked by low OI values and high HI, TC, TOC and NT values. Palynofacies study of sediments collected in this zone reveals the presence of abundant agglomerated amorphous organic matter. All these results suggest high primary productivity and increased flocculation (self-sedimentation) of organic matter, which partly permitted its preservation. The sedimentary organic matter deposited in the transitional disoxic zone, located between the costal and hemipelagic areas, is characterized by the same values of TC and NT than the microxic zone, but do not present the same petrographical parameters. Based on this calibration study, we identified three differents periods in the oceanographic evolution of the embayment, during the past 200 years. Before the nineteenth century, the sedimentary record suggests an enhanced oxygenation and/or depleted productivity Abrupt alternations of the two oceanographic state described previously seem to have occurred during the nineteenth century. During the major part of the twentieth century the sedimentary record indicates a higher primary productivity coupled to an intensification of microxic/anoxic condition of the water column.
DE: 4999 General or miscellaneous
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005