Metals content in surface waters of an upwelling system of the northern Humboldt Current (Mejillones Bay, Chile)

Physical–chemical parameters (temperature, salinity, dissolved oxygen, nutrients, and chlorophyll concentration) of surface waters were used to evaluate the influence of biological and physical processes over the metal concentrations (Cd, Ni, V, Mo, Mn, and Fe) in different periods of a normal annual cycle (June 2002 and April 2003), in Mejillones Bay (23° S), one of northern Chile's strongest upwelling cells. Two points were sampled every 2 months, but statistical analysis of these parameters did not show any spatial differences in surface water composition (annual average) in this bay. The order of total and dissolved metals by abundance (annual mean) in the Mejillones Bay surface waters during the sampling period was Cd < Ni < Mn < Fe < V < Mo.The surface concentration of metals does not appear to be explained by anthropogenic inputs (at least not during the year of this work), and variability observed in this study appears to be natural. The lack of correlation between physical–chemical parameters and metals could indicate a more complex combination of factors acting on surface concentrations. Moreover, the mixture of water masses and the Oxygen Minimum Zone which characterizes the Mejillones bay should have an important influence on surface distribution of trace metals and can explain the high temporal variability observed in most of the metals analyzed in this work. A two-box conceptual model is proposed to suggest possible influences on metals in surface waters of this coastal ecosystem.