Variability of the Oxygen Minimum Zone in the EASTERN TROPICAL SOUTH PACIFIC: Role of Mesoscale Dynamics

Abstract:

Here, we investigate the contribution of mesoscale eddies on the oxygen variability of the eastern tropical south Pacific, using a coupled physical-biogeochemical model. The contribution of mesoscale eddies is uncovered under a sensitivity experiments, in which an idealized simulation without mesoscale dynamics is compared to a realistic simulation. We found that eddy dynamics intensified the ventilation of both equatorial and oxygen minimum zone (OMZ) core regions of the eastern tropical south Pacific ocean. This increased ventilation was related to the intensified eastward and poleward transport of well oxygenated waters. At the equatorial region, the increased oxygen supply reduced the volume of hypoxic waters in the upper 500 m depth. This reduction of hypoxic waters volume was accompanied by an increase of oxygen content. In contrast, the eddy-driven oxygen supply to the core of the OMZ did not result in a reduction of hypoxic waters volume. The oxygen content in the water column showed reduced concentration. This reduction of oxygen content was related to the eddy-induced shallowing of the thermocline, which have contributed to the upward expansion of low oxygen waters, and increased oxygen consumption by increasing the export production. Our results suggest an influence of eddy variability on the observed interannual oxygen variability along the Peruvian coast. The intense eddy activity during El Niño events might have contributed to the increased oxygen content along the coast. During La Niña events, the weak eddy activity might not have favoured the oxygen increase, therefore the reduction of water column oxygen content.