Surface mesoscale structures and wind variability in the northern Gulf of California (NGC) were analyzed using data from SeaWiFS (1 km) and QuikSCAT (1 day). The months of February and March were selected as representative of winter and the months of August and September were selected as representative of summer. Chlorophyll‐a (Chla) and wind time series were constructed using 16 points to analyze temporal variability and wind magnitude‐Chla temporal and spatial linear correlation. Wind components along and across the NGC were found to play an equally significant role regarding wind variability, contrary to what is currently recognized. Wind magnitude tended to be stronger in winter and had less wind direction variability than in summer. A bimodal wind pattern was registered for each season, each wind direction explaining less than 30% of total variability. The zone with minimum variability in wind direction and maximum variability in wind magnitude was located northwest of the NGC, the same area where wind magnitude‐Chla correlation was significant (p < 0.05). Winter and summer surface circulation patterns are more complex than currently documented. Summer is characterized by numerous plumes and eddies (especially anticyclonic), some traveling from coast to coast, enhancing the exchange of suspended material. Winter varied greatly interannualy, also showing many plumes and eddies (especially cyclonic), but was very heterogeneous, opposite to summer. Significant summer correlation was mostly positive, whereas in winter the significant correlation was equally positive and negative, maybe as a consequence of higher nutrient availability during this season.

The vertical diffuse attenuation coefficient $K_d$ ($\mathrm{PAR}$) is used for calculating the euphotic zone, the first optical depth that is important for primary productivity models. Currently, $K_d \left(\mathrm{PAR}\right)$ can be estimated using an irradiometer or a Secchi disk ($\mathrm{SD}$). The main objective of this work is to define a model that can be applied to a wide range of optical marine conditions to estimate $K_d \left(\mathrm{PAR}\right)$ by $\mathrm{SD}$. We used irradiance profiles and $\mathrm{SD}$ depth ($Z_{SD}$) from 679 stations in various marine regions. Three parametric models were developed, and their statistical performance was evaluated in view of previous approaches reported and remote sensing data. The best results were obtained with an adaptive model representing three cases: clear-water, turbid-water, and a transition zone (R² = 0.965, MAE = 0.083, RMSD = 0.239, BIAS = 0.01, and MPI = 0.854). Previous models considering a single optical depth figure at which the $SD$ disappears did not capture the marine optical complexity. Our classification of 113 stations with spectral absorption data into Jerlov water types indicated that no unique correspondence existed between estimated $K_d$ (PAR) and water type, making it ambiguous to associate compatible inherent optical properties and chlorophyll with $Z_{SD}$. Although obtaining $K_d$ ($\mathrm{PAR}$) from $Z_{SD}$ is simple/low-cost, care should be taken in the methodology used to measure $Z_{SD}$ to ensure consistent results across different optical marine conditions.

In this study, we report the response of phytoplankton community composition to cold and warm interannual events affecting the waters off the Baja California Peninsula from 2007 to 2016 based on data obtained from a single marine station (31.75° N/116.96° W). Included variables were satellite chlorophyll a, sea surface temperature (MODIS/Aqua), upwelling intensity, and field data (phytoplankton pigments, inorganic nutrients, light penetration). Phytoplankton pigments were determined by high performance liquid chromatography, and CHEMTAX software was used to determine the relative contributions of the main taxonomic groups to chlorophyll a. Our results confirm the decrease in phytoplankton biomass due to the influence of the recent Pacific Warm Anomaly (2014) and El Niño 2015–2016. However, this decrease was especially marked at the surface. When data from the entire water column was considered, this decrease was not significant, because at the subsurface Chla did not decrease as much. Nevertheless, significant changes in community composition occurred in the entire water column with Cyanobacteria (including Prochlorococcus) and Prymnesiophytes being dominant at the surface, while Chlorophytes and Prasinophytes made a strong contribution at the subsurface. Analysis of the spatial distribution of SST and satellite chlorophyll a made it possible to infer the spatial extension of these anomalies at a regional scale.

Tetraselmis suecica is a green microalga that thrives under a wide range of conditions, used in the commercial culture of fish, mollusk, and crustacean larvae for supplementing the demand for fertilizers. Its pigments have applications in human health care as drug products, vitamins, and cosmetics. Growth and pigment concentration of T. suecica were evaluated in experimental cultures with different nutrient concentrations and light intensities to determine the most appropriate culture conditions to optimize the production of biomass and pigments. Chlorophyll-a, chlorophyll-b, lutein, violaxanthin, α, β-carotene, and neoxanthin concentrations were evaluated under three different nutrient conditions (441.5/18.1, 883/36.3, and 1766/76.2 μM of NaNO3/NaH2PO4) and four light intensities (50, 150, 300, and 750 μmol quanta m-2 s-1). Increases in either or both of these factors lead to increases in the concentration of all pigments. Chlorophyll-a reached up to 5×103 mg m-3, chlorophyll-b up to 2500 mg m-3, lutein 600 mg m-3, violaxanthin 300 mg m-3, α, β-carotene 500 mg m-3, and neoxanthin 400 mg m-3. Growth rate (μ) attained values of 1.6 d-1. An index to evaluate the efficiency of pigment production by light intensity (called LER) was computed. The highest LER was recorded at 50 μmol quanta m-2 s-1 and a nutrient concentration of 1766/76.2 μM (NaNO3/NaH2PO4); this treatment optimizes pigment production with the lowest light intensity. Our results show that the optimum light intensity should be selected according to the objective of the culture, either maximizing pigment concentration for harvesting at higher concentrations or reducing production costs regarding light consumption.