| Summary: | This dissertation aims at extending our knowledge of the ESP OMZ through two main approaches. The first approach is based on tracer analysis and inverse modeling techniques. Such techniques are applied to hydrographic datasets in order to examine the water mass structure, its variability and its role on the ventilation of the ESP OMZ. The second approach brings a more dynamical perspective to the study of the ventilation of the ESP OMZ, with the assessment of the annual-mean advective and turbulent oxygen transports into the ESP OMZ from Argo and dissolved oxygen datasets. We describe the distribution of water masses offshore Chile, Peru and Ecuador and discuss their spreading pathways. A thorough characterization of the water masses has been accomplished, resulting in the first set of ESP water types accounting for inorganic nutrients and dissolved oxygen. The low oxygen waters that compose the ESP OMZ are mainly Equatorial Subsurface Water (ESSW). The ESP OMZ is ventilated from the south by the Antarctic Intermediate Water (AAIW) and by the shallower Subantarctic Water (SAAW). These water masses are transported into this region by the Peru Chile Current (PCC) or by the adjacent flow that forms part of the subtropical gyre. We also examine the changes induced by two opposite phases of ENSO in water mass distribution and biogeochemical activity. During La Niña, vigorous upwelling promotes the rise in depth of the upper part of the ESP OMZ and denitrification strengthens in the subsurface layer. Furthermore, the upward displacement of isopycnals induced by La Niña favors the ventilation of a different depth range of the OMZ by the upper portion of the AAIW. The opposite occurs during El Niño conditions. We find that, with a larger oxygen supply, respiration increases balancing most of the extra oxygen gain. This suggests that there is an excess of organic matter waiting to be remineralized whenever oxygen supply increases slightly and this situation favors the maintenance of the ESP OMZ. Furthermore, our results ...
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