Foraminifera as environmental bioindicators on the Rio Grande Terrace: a preliminary assessment

There is still a significant gap in research that integrates foraminiferal data with water mass characterization within the specific context of marine phosphorite prospecting. Therefore, this study investigates the environmental dynamics of the Rio Grande Terrace, a strategic area for phosphorite prospecting on the southern Brazilian continental margin, using foraminifera as environmental bioindicators. Four surface sediment samples collected between 352 m and 623 m depth were washed, dried, and subjected to picking and taxonomic identification of foraminifera. These results were integrated with temperature and salinity (T-S) diagrams. The preliminary results revealed a predominance of white (87.9%) and well-preserved (74%) tests, with a low dissolution rate, suggesting a low-hydrodynamic environment and relatively recent depositions. The assemblage is dominated by planktic species, notably Globigerinoides ruber (45.6%), which is likely associated with the Tropical Water (TW). In contrast, the presence of Globigerina bulloides and Globoconella inflata indicates the influence of South Atlantic Central Water (SACW) and potential upwelling events in the region. Multivariate cluster analysis and nMDS ordination demonstrated high similarity (>95%) among stations 59, 65, and 89, while sample 75 diverged due to the bathymetric gradient. Species clustering, identified a cohesive group consisting of G. bulloides, G. cultrata, T. trilobus, and G. inflata, associated with habitats above 300 mwhereas G. ruber exhibited isolated behavior. The occurrence of G. bulloides reinforces the link between upwelling-driven primary productivity and the genesis of previously mapped phosphorus anomalies. The results indicate a complex oceanographic interaction between tropical and upwelling waters, highlighting the effectiveness of foraminifera as tools for environmental monitoring in mineral exploration activities.