Maintaining of the Eastern South Pacific Oxygen Minimum Zone (OMZ) off Chile

[1] Processes regulating OMZs persistence in the oxygenated ocean remain poorly understood. Four cruises (21 degrees-30 degrees S) and fixed-point monitoring (36 degrees S) between 2000 and 2002 using techniques adapted to O-2 conditions as low as 1 mu M allow a preliminary analysis of the entire Chilean OMZ structure. A shallow OMZ is observed in the three studied areas, although its structure differs. Off northern and central Chile, the OMZ is a permanent feature, more pronounced at the coast than further offshore. On the shelf, it forms in spring and erodes in fall. A conceptual model of two intermittent active or passive phases (intense or low biogeochemical O-2 consumption) is proposed as a key mechanism for the local OMZ maintaining. The highest O-2 consumptions are paradoxically favoured at the oxycline when the OMZ is less intense as offshore and on the shelf in spring and fall, suggesting a control by O-2 availability of the OMZ remineralization.