Preservación y abundancia de escamas de pecesen sedimentos del margen continental de Chile (21-36° S)

Abstract

The relationship between fish scale preservation and variations in the sediment redox conditions on Chile's continental shelf are evaluated herein through fish scale counts and normalized concentrations of redox sensitive elements (Mo/Al, S/Al, Fe/Al) using eight sediment cores taken from sites under the influence of the oxygen minimum zone off Chile (Iquique: 20°15' S, Mejillones Bay: 23° S, Concepcín: 36° S). Off northern Chile (Iquique and Mejillones), fish scales from anchovy (Engraulis ringens) and the Myctophidae family are dominant (mean = 90 and 120 scales 1,000 cm-3, respectively), whereas off central-southern Chile (Concepcín), jack mackerel (Trachurus murphy) scales are the most abundant (mean = 140 scales 1,000 cm-3). The abundance of hake (Merluccius gayi gayi) and sardine (Sardinops sagax) scales is approximately one order of magnitude lower than that of anchovy or jack mackerel. In general, the highest values and widest ranges of variation in the Mo/Al, S/Al, and Fe/Al ratios are found in Mejillones (Mo/Al ∼ 0.8-12 mg g-1, S/Al 0.2-4.6 g g-1, Fe/Al 0.3-0.7 g g-1), followed by Iquique (Mo/Al ∼ 0.2-1.8, S/Al 0.2-0.7, Fe/Al 0.5-0.8); Concepcín has lower, less variable values (Mo/Al ∼ 0.07, S/Al ∼ 0.15, Fe/Al ∼ 0.5). According to the Mo/Al ratio, used as an indicator of paleo-oxygenation, reducing conditions in the Mejillones Bay and Iquique sediments are relatively more intense than in those off Concepci∼n. At all three sampling sites, the relationship between the abundance of anchovy scales and the logarithm of the Mo/Al ratio is statistically significant (r2 = 0.46, P < 0.0001), indicating a dependence between these two variables. In particular, for Mo/Al 1 mg g -3, small changes in the redox conditions can affect considerably scale preservation in the sediment, whereas this dependence decreases with Mo/Al > 1 mg g-1.