Interannual variability in the mesoscale distribution of the depth of the upper boundary of the oxygen minimum layer off northern Chile (18–24S): Implications for the pelagic system and biogeochemical cycling

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Abstract
The low oxygen concentration (-1) at relatively shallow depths (-1 iso-oxyline, representing also the oxycline) and investigating the association of its interannual variability with changes in coastal sea level and in the equatorial and local thermoclines. The depth of the upper boundary of the OML undergoes pronounced deepening during the occurrence of warm ENSO (El Niño Southern Oscillation) events over the whole area of study, and this, in turn, determines a condition of higher oxygen concentrations in the top 100 m layer. These changes follow closely the patterns of interannual variability in coastal sea level and depth of the thermocline in the area of study during the 1980-1997 period. Most of this variability can be accounted for, as expected from previous studies, by remote forcing originating in the equatorial zone of the Pacific Ocean, as evidenced from the significant correlation between the above local parameters and the interannual variability in the depth of the equatorial thermocline. The 1982-83 and 1997-98 El Niño events seemed to have been the most important ones in terms of their effects upon sea level and depth of the thermocline and oxycline off northern Chile. The potential impacts of the interannual changes in the depth of the upper boundary of the OML upon the pelagic system and biogeochemical cycling in the region are discussed.

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