Water bioproductivity estimate of the equatorial Atlantic under the influence hydrological, hydrochemical and hydrooptical factors in winter 2022

Abstract

Based on contact observation data obtained in the 60th cruise of the RV “Akademik Ioffe”, water bioproductivity was estimated based on the distribution of chlorophyll a (CCl) and microplankton adenosine triphosphate (CATP) concentrations under changing environmental conditions. These parameters were studied in the western equatorial Atlantic (Vema Fracture Zone, 11°N; Guiana Basin–Guiana section, 4°N–7°N) in the winter of 2022. For the first time, the stages of production–destruction succession were estimated based on the heterotrophic–photoautotrophic index (HPI), and water trophicity was investigated according to ATP content in the study area. According to the data obtained on CCl, CATP, and HPI, in the Vema Fracture Zone, waters were mesotrophic, with prevalence of communities of mixed nutrition — heterotrophs and autotrophs (an equilibrium community; HPI 15–25). In the Guiana section area, waters were oligotrophic, with prevalence of heterotrophic nutrition (developed and mature communities; HPI: 25–112 and 112–163). At the first bioproductivity depth maximum (10 m), significant relationships were obtained between spatial distribution of concentrations of chlorophyll a and phosphates (r > 0.5) and oxygen (r > 0.68), as well as between microplankton ATP and phosphates and pH (r > 0.5); negative relationships were recorded microplankton CATP, CCl with temperature (r = -0.42, -0.85) and salinity (r = -0.68, -0.41). At the second bioproductivity depth maximum (50 m), significant relationships were established between HPI and temperature (r=0.64); a negative relationship was found with pH (r = -0.44). The continuity of ATP and chlorophyll a concentrations distribution with depth was shown in the 30-m layer; the heterogeneity of HPI distribution with depth was revealed as well.Finally, the research based on our own instrumental measurements shows a low productivity in the western part of the Equatorial Atlantic in winter 2022. This is caused by the features of water circulation and chemical parameters distribution.