Satellite observations of the effect of the “Godzilla El Niño” on the Tehuantepec upwelling system in the Mexican Pacific

Abstract

During 2015-2016, a strong El Niño, the “Godzilla El Niño,” which is similar to El Niño events that occurred in 1982/1983 and 1997/1998, occurred in the Pacific Ocean. In this paper, we report on the influence of the “Godzilla El Niño” on the sea surface temperature (SST) and chlorophyll-a (Chla) concentrations in the Tehuantepec upwelling system using satellite observation data. A time-series of the SST and Chla levels in a circular site with a diameter of approximately 54 km centered at the fixed position (15°N, 94.75°W) for the period from January 2003 to December 2016 was obtained using a Moderate Resolution Imaging Spectroradiometer. To estimate the vertical water velocity, a wind velocity time series was obtained from the Copernicus Marine Environment Monitoring Service to assess its variation over the period from January 2014 to December 2016. The results showed unusually high SSTs (> 28 °C) and atypically low Chla concentrations (< 0.1 mg m−3) in the domain of interest during the winter of 2015/2016. In the region of study, the SST in January 2016 was 5.13 °C higher than it had been in January of 2015, whereas the Chla concentration was 1.56 mg m−3 lower over this period. We found that the “Godzilla El Niño” impacted the Tehuantepec upwelling system in the following ways: (1) the wind and vertical water velocity during the winter of 2015/2016 were slightly higher than those observed during the winters of 2013/2014 and 2014/2015; (2) the coastal SST values were elevated during the winter of 2015/2016 compared to their levels during the previous two winters, revealing nutrient-poor water advection; and (3) the Chla concentrations during the 2015/2016 winter season were unusually low compared to their levels during the previous two winters. Our interpretation of these results is that in the Tehuantepec Gulf the wind was strong and induced vertical water velocities reaching up to 6 m day−1 during the “Godzilla El Niño” event (winter 2015/2016); however, the levels of Chla during this period were lower than they had been in previous years. In particular, the levels were lower than they had been during the previous winters. This suggests that, although the wind during the event favored strong upwelling, the water that was advected to the upper layer was nutrient poor.