Assessing the Local Effects of El Niño on the OMZ-core in the Pacific off Central Mexico

The vertical structure of the Oxygen Minimum Zone includes three layers: the upper oxycline, the core and the lower oxycline. The position of the oxycline and the core can be affected by El Niño, that advect oxygenated waters from the equator. In the eastern tropical North Pacific, studies about the effects of El Niño in the vertical distribution of oxygen are scarce. Only a recent work found a positive anomaly of the oxygen concentration in the oxycline within the Gulf of California. However, the authors did not report changes in the OMZ-core and did not use data in the open ocean. Here, we focused on the effects of El Niño on the upper limit of the OMZ-core in the Pacific off Mexico, because in there occur a chlorophyll maxima associated with the suboxic waters. Thus, the changes in the position of the OMZ-core upper limit can induce changes in the ecosystem. The preliminary results showed that the depth of the upper limit of the OMZ-core was not affected by the 2015-2016 El Niño. Also, we found that the temporal evolution of the sea temperature anomalies do not follow the anomalies in the El Niño 3.4 region. Hence, we pointed out that an assessment of the El Niño should consider its local expression, the vertical structure of the water column and the temporal evolution of the phenomena. Finally, we presented the challenges to assess the spatial variations of El Niño effects in the water column and how we are proposing to deal with them.