Modern pollen rain signatures along the Parnaíba River Basin in Northeastern Brazil

Recent studies of marine sediments adjacent to the Parnaíba Basin, in northeastern Brazil, have been used for continental paleoenvironmental reconstructions of the glacial epoch. As the largest basin entirely located within the Northeast region, it spans a critical transition zone between the Cerrado and Caatinga biomes. To characterize the modern pollen rain within this ecotone, we analyzed 41 surface sediment samples and compared the pollen assemblages with published botanical surveys. First, pollen assemblages were characterized using three diagrams: vegetation type, geographical location, and depositional environment. The basin presents a unique mixed signature combining Cerrado elements (e.g., Astronium- type , Tapirira- type) with Caatinga taxa ( Mimosa -type). Spatially, the Upper and Lower sectors exhibited high heterogeneity, contrasting with arboreal consistency in the Mid-Parnaíba. Distinct hydrological markers also emerged: Cyperaceae was strictly linked to lacustrine environments, whereas Mauritia indicated permanently flooded soils within gallery forests and palm swamps. Landscape analysis subsequently confirmed that Arboreal Pollen (AP) frequencies accurately track woody cover, while Borreria -type and Poaceae serve as robust proxies for landscape openness. Multivariate analyses refined these patterns: Cluster Analysis identified six specific floristic groups ( Tapirira-Astronium , mixed, Melastomataceae-Combretaceae, Borreria-Aspidosperma , mixed woody-herbaceous, and Mimosa- type assemblages), while Redundancy Analysis (RDA) identified Mean Annual Temperature (MAT) as a significant environmental driver within the explained variance. Critically, comparison with paleoecological records reveals a sharp floristic shift from cooler, humid glacial periods to the current warmer climate, marked by the scarcity of montane taxa. This study establishes a crucial baseline for interpreting fossil records and understanding ecosystem dynamics in this transition zone. • Modern pollen rain reflects vegetation patterns along the Parnaíba River gradient. • Cerrado, Caatinga, and transitional zones show distinct pollen assemblages. • Analyses reveal floristic structure influenced by edaphoclimatic gradients. • Pollen assemblages are more related to local conditions than spatial location. • Anthropization and distinct grasslands strongly influence pollen assemblages.