Temporal Variability of the Dissolved Oxygen in the Southern California Current System

Hydrographic data from approximately two decades of quarterly sampling efforts of the Investigaciones Mexicanas de la Corriente de California (IMECOCAL) program were used to model dissolved oxygen concentration (O₂) in the water column.Results off waters of Ensenada suggest that during the season of upwelling the oxygen concentration below 100 µmol kg^-1 of the water column were shoaling onshore. This is a consequence of vertical transport of water from greater depths towards surface layers with others chemical characteristics. Based on a seasonal climatology generated via correction with sampling O₂ and hydrographic variables, coastal station presented greater seasonal variability. The depth where 100 µmol kg^-1 could be detected during spring was ∼50 m, but in winter occurred ∼100 m. However, in the oceanographic stations furthest from the coast (> 50 km), the effect of upwelling decreased. Besides, the advection of water masses that occur in the region can impact the biogeochemical characteristics that occur in the water column and, consequently, affects the depth to which O₂ concentration of 100 µmol kg^-1 located. This result is one of the most significant as it is possible to detect the presence of Subarctic Water (SAW) in the study area, which can modulate the deepening or shoaling of this depth. Moreover, these processes change year to year in response to interannual events. Reflecting that during positive Oceanic Niño Index (ONI) values of the tend to be deeper (160 m) than during negative values (60 m). This result suggests that not all El Niño and La Niña events are equal and indicates significant changes in the O₂ characteristics of the water column.