Abstract

A combined study bearing on the downcore variations of metal elements and of organic matter composition in a 48 cm-long sedimentary core provided elements to reconstruct paleoenvironmental conditions of oxygen availability and organic matter preservation in the Bay of Mejillones del Sur (23°S. northern Chile). High concentration of heavy metals like Cd and Mo, both indicators of former conditions of oxygenation, and the values of redox indices V/Cr y Ni/Co in several points of the core, suggest a predominance of disoxic/anoxic conditions at the bottom of the water column all along the last millenium. The transmission Fourier transformed infrared (FTIR) spectroscopy of the soluble organic matter showed that, during the last thousand years, the early diagenesis scarcely affected the organic components of the sediment: the spectra indicate that the functional groups are the same that those of the biological precursors (living organisms). The high content of organic matter and its good state of preservation reflect the general lack of oxygen experienced by the subsuperficial waters of the embayment during the last millenium.