Seasonal and spatial variability of the euphotic zone in Bahía de Banderas

Background. The euphotic zone (EUZ) is the most superficial section of the water column where solar radiation is sufficient to produce photosynthesis. In situ depth is measured using light profiler probes but can also be monitored using remote sensing. Objective. To determine the temporal and spatial variability of Bahía de Banderas Euphotic Zone (EUZ) and its relationship with other variables that contribute to turbidity. Methods. Different data sources (OceanColor, Copernicus, NOAA, CONAGUA) were used to obtain time series (2003 to 2020) of particulate inorganic matter (PIM), Chlorophyll-a (Chl-a), diffuse attenuation coefficient at 490 nm (Kd490), depth of the Secchi disk (ZSD), ZEU, daily precipitation and water level of the Ameca and Pitillal rivers and a correlation analysis was made between these variables, and a cluster analysis to determine if there are spatial differences in the bay, as well as scatter plots to observe trends among environmental parameters. Two seasonal maps (rainy and dry season) were drawn based on the climatic medians of ZEU and the prevailing geostrophic currents. Results. The euphotic zone (EUZ) was deeper from June to August (48.54 ± 21.93 m) and shallower from February to April (22.95 ± 12.98 m); the cluster analysis determined that the bay is divided into two areas: the north, whose ZEU is shallower (higher correlation with MIP and Chl-a), and the south, where it is deeper (higher correlation with Chl-a). Conclusions. The parameter that has the greatest effect on the depth of the ZEU is the Chl-a, and only the area closest to the mouth of the Ameca and Pitillal rivers presents an inverse relationship between the ZEU with the MIP and the Chl-a.