Early signals of El Niño 2023 in the Gulf of California?

Abstract

After a long La Niña event (2020-2023), the US National Oceanographic and Atmospheric Administration warned of a quick transition to an El Niño phase. As a monitoring of sea surface temperature (SST) and chlorophyll-a (Chl-a) levels in the Gulf of California, Mexico, this study aims to show the evolution of both parameters during the first seven months of 2023. It compares them with the first seven months of 2015 when an extreme El Niño event occurred. Satellite data from the Moderate Resolution Imaging Spectroradiometer were obtained from which maps of both variables were constructed to quantitatively assess the changes in the SST and the Chl-a levels during the selected periods. Satellite data/pixels were extracted from the southern region of the gulf, in the connection between the gulf and the open Pacific Ocean. The results showed a gradual increase in the SST values from February to July of 2023 with 20.43, 22.29, 22.77, 27.88, 28.72 and 31.64ºC, respectively (a thermal variation of 11.21ºC), while Chl-a levels showed a decrease over the same period, from 1.81, 1.10, 0.78, 0.24, 0.19 mg m-3 to unusually low values of 0.11 mg m-3, respectively (a reduction of 1.70 mg m-3). A similar pattern was found in 2015, with increased SST and decreased Chl-a. Were the observed patterns in 2023 the early signals of El Niño in the Gulf of California?