Oxygen minimum zones (OMZs) are oxygen deficient regions of the ocean that are hotspots for nutrient and climate active trace gas cycling. Forming at intermediate depths (~1001000 m) in response to high biological oxygen demand and reduced ventilation, OMZs occur naturally in regions of high productivity and nutrient-rich upwelling. Global climate change and enhanced run-off from our farms and cities also contributes to OMZ formation and expansion. An expansive and permanent OMZ persists in the Eastern Tropical South Pacific (ETSP) along the coast of northern Chile and Peru. Studies in the ETSP-OMZ have been critical in charting the microbial communities and metabolic processes driving coupled biogeochemical cycling in coastal and open ocean OMZs throughout the global ocean.