Impact of "the Blob" 2014 and 2019 in the sea surface temperature and chlorophyll-a levels of the Gulf of California: a satellite-based study

Abstract

In 2014, an unexpected and unusual warm patch of ocean water was discovered in the northeast Pacific Ocean (PO) that moved south, reaching the Mexican coasts; this patch, returning in 2019, was nicknamed "the Blob". This paper aimed to assess the impacts of this phenomenon on the sea surface temperature (SST) and chlorophyll-a (CHLA) levels in the Gulf of California (GC), a high-productivity region. Daily satellite images of SST and CHLA with a spatial resolution of 1 km/pixel were obtained for 2014, 2017, and 2019 from the Moderate Resolution Imaging Spectroradiometer (MODIS). Two disc-shaped areas of around 25 km in diameter were selected in the southern portion of the GC to assess the variability of both parameters quantitatively. An additional site was selected in the PO for comparison and, thus, to better characterize and have a complete vision of these events. The results showed that in the PO, during the periods in which the Blob occurred, the SST values were higher concerning the neutral year (2017), and the levels of CHLA were very low (barely 0.15 mg m-3). Within the GC, the results showed the presence of a strong seasonal variability, with maximum values of SST (>30°C) and the lowest concentrations of CHLA (<2 mg m-3) during the summer, with maximum concentrations of CHLA (~10 mg m-3) observed during the winter months. Contrary to expectations, no dramatic changes in SST and CHLA were observed during the years impacted by the Blob. This apparent absence of negative impacts could be related to different mechanisms in the gulf that "protect" to avoid climate disruptions. The presence of complex geomorphology and hydrodynamic processes at different scales induce mixing and fertilizing of the euphotic layer. Could these factors protect the southern gulf from the negative impacts of the Blob?