Bioproductivity of the surface waters in the Guiana Basin (Atlantic ocean): new integrated approach

The purpose of this research to assess bioproductivity and trophicity of surface waters in the Guiana Basin to identify favorable conditions for the development of phytoplankton – a marker of the ocean ecosystem state. We use of data on phytoplankton (species and quantitative analysis) and biochemical parameters (concentrations of adenosine triphosphate and chlorophyll a) to determine the maturity stages and nutritional type of the communities using a new integrated approach. These data are obtained either from in situ measurements and sampling during a cruise in winter 2022, or satellite observations. An analysis of the phytoplankton distribution was carried out in conjunction with abiotic factors (temperature, salinity, dissolved oxygen, phosphate concentrations) for the photic layer 0–50 m. Generally, the main finding of our study is that in the Vema Fracture zone (mesotrophic waters) autotrophs prevail with the dominance of diatom microalgae (corresponding to equilibrium community); whereas in the Guiana section oligotrophic waters) heterotrophs prevail with the dominance of dinophytic microalgae (corresponding to developed and mature communities). This distribution is confirmed by the heterotrophic photoautotrophic index values (HPI). Concluding a discussion, we show that winter distribution of phytoplankton and the maturity degree of its community in the study area, are associated with the supply of nutrients due to the advection of Amazon waters by the North Brazil Current – North Equatorial Countercurrent system.