Planktonic foraminiferal assemblages and particle fluxes at the entrance of the Gulf of California highlight the effects of the strong El Niño 2015–2016

Abstract

The impacts of El Niño 2015–2016 on planktonic foraminiferal assemblages and particle fluxes (total mass, organic carbon, total nitrogen, and carbonate) were analyzed in a sediment trap record located at the entrance of the Gulf of California from 2015 to 2019. Biweekly data of the sea surface temperature (SST) and sea surface chlorophyll-a (Chl-a) were obtained from satellite images (MODIS-AQUA) during this period. Particle fluxes and planktonic foraminiferal assemblages reflected the seasonal cycles of SST and phytoplankton biomass highlighting the effects of El Niño 2015–2016. During neutral and La Niña conditions, winter-spring upwelling leads to low SST, high Chl-a and particle fluxes, and an assemblage dominated by Globigerina bulloides while the summers are characterized by high SST, low Chl-a and particle fluxes, and a Globorotaloides hexagonus assemblage. In contrast, in normal summers, there is an alternation of G. bulloides and Orbulina universa-Trilobatus sacculifer-Globigerinella siphonifera associations. By late autumn under La Niña conditions, the Globigerinita glutinata assemblage reflects the transition from warm to cold conditions and the beginning of the upwelling season. This general pattern was affected by El Niño during 2015–2016. From late summer 2015 to early winter 2016 (El Niño 2015–2016 maximum intensity), Globigerinoides tenellus dominated, reflecting the intrusion of warm and oligotrophic equatorial waters. These results show the strong influence of El Niño Southern Oscillation (ENSO) on oceanic dynamics and planktonic foraminiferal assemblages at the entrance of the Gulf of California, and allow for a better interpretation of the preservation of these anomalous warm events in the sedimentary record, which can provide a better understanding of the long-term variations and effects of ENSO.