Oxygen minimum zone variability off Caldera, northern Chile

Several studies show the increase and intensification of oxygen minimum zones (OMZs) in the eastern edge upwelling systems. However, the models differ from in situ measurements. Additionally, Eastern Boundary Upwelling Systems (EBUS) are subject to interannual and interdecadal variability due to phenomena such as El Niño-Southern Oscillation (ENSO). In this work, we analyze the transoceanic information of dissolved oxygen, temperature, and salinity from six cruises with stations between the coast and 82°W at 27-28°S between 1967 and 2022. During the whole period, the study area presented Equatorial Subsurface Water (ESSW), which deepened and decreased its presence away from the coast, while its temperature and salinity decreased and the concentration of dissolved oxygen increased. The ESSW hosted an intense OMZ close to the coast with the highest zonal coverage during strong El Niño (2015). However, no statistically significant relationships were observed between the Oceanic Nino Index and OMZ or oxygen variability in the ESSW. Nevertheless, the temporal oxygen variability showed different patterns, with a decrease in the most oceanic zone (west of 79°W), no trend between 78 and 75°W, a decrease from 1967 to 2000 and then an increment, between 74 and 72°W, and no trend at 71°W.