Spatio-temporal Patterns of Chlorophyll-a in a Wide and Low-relief Shelf Sea of the Gulf of Mexico: Insights of Inter-annual Climatic Forcing on the Phytoplankton Biomass Varying Behavior

Chlorophyll-a concentrations were recorded in three oceanographic surveys (GOMEX-4, GOMEX-5, GOMEX-6) during 2015-2018 throughout the Yucatan shelf, southeast Gulf of Mexico (GoM). Such campaigns encompassed El Niño Southern Oscillation (ENSO), cold-phase ENSO, and non-ENSO conditions, as well as a progressively increasing upwelling intensification scenario. The objective of the multiyear GOMEX series was tackle the interplay between the upwelling, precipitation regime, and wind patterns influencing the distribution, magnitude and timing of the phytoplankton biomass. Boreal frontal systems improved the coastal Chl-a (1.69 ± 0.07mg m^-3). This pattern was subject the modulation of large-scale climatic oscillations (ENSO). The upwelling pulses depicted a wide-shelf influence over the Chl-a concentration (0.47 ± 0.01 mg m^-3 and 0.53 ± 0.03 mg m^-3 avg. concentrations in the marine and coastal areas, respectively), with and onshore excursion of cold water masses intermingled with seasonal precipitation traits sustaining high nearshore Chl-a in zones influenced by subaqueous freshwater input characterizing the karstified Yucatan seascape (varying within the interval of 1.50-2.76 mg m^-3). These results suggest that, similarly to riverine-influenced areas in the northern GoM, intense ENSO events have the potential to strongly alter the phytoplankton biomass in karstified shelves as well. This large-scale pattern overlaps processes occurring over a broad spatial and temporal scale, like seasonal rainfall and upwelling, establishing recurrent environmental gradients driving biogeochemical fronts along the seascape. These relationships allow a better grasp of sound ecologically processes as phytoplankton blooms along the Yucatan shelf, which might be also sensitive to human-driven disturbances.