Water masses and chlorophyll-a distribution in a semi-enclosed bay of the southern Gulf of California, Mexico, after the “Godzilla El Niño”

Abstract

During 2015–2016, a strong El Nino event, nicknamed the “Godzilla El Nino,” similar to events in 1982–1983 and 1996–1997 occurred in the Pacific Ocean. Based on in situ and satellite observations, this paper aims to assess the water masses and chlorophyll-a surface distribution in the Bay of La Paz, Gulf of California, Mexico, after this event. A conductivity, temperature, and depth (CTD) rosette system equipped with a fluorescence sensor was used to obtain high-resolution measurements and surface water samples for spectrophotometric determinations of chlorophyll-a. Satellite images of sea surface temperature and chlorophyll-a were obtained for the dates when the cruise took place. The results showed the presence of three water masses: Gulf of California Water, Subtropical Subsurface Water, and Pacific Intermediate Water, the last present in Boca Grande. The highest surface chlorophyll-a concentrations observed were 4.51 mg m-3, 4.63 mg m-3, and 1.00 mg m-3 from the fluorescence sensor, spectrophotometric determination, and satellite observations, respectively. The horizontal distribution patterns for the three methods employed matched well. Despite the fact that Godzilla El Nino had several adverse effects in different regions, at the Bay of La Paz, they seem to have had no dramatic effect on the chlorophyll-a at the time of our observations, even though the values observed were higher compared to previous reports. This apparent lack of effect on the surface waters due to this climate disruption could be associated to the seasonal variability of the phytoplankton productivity, which presents a peak during autumn and winter and to the local fertilization mechanisms reported in the study area; however, further observations are required to confirm this.