Seafloor morphology and sediment distribution on a semi-arid continental shelf, Western Equatorial Atlantic

This study on the Ceará continental shelf (Western Equatorial Atlantic) analyzes seafloor morphology and sediment distribution to map and classify geomorphic habitats. The region represents a transitional setting between siliciclastic and carbonate sedimentation systems, where bathymetric and sedimentological data were integrated to identify and describe distinct geohabitat types using Benthic Terrain Modeling (BTM) and sediment distribution. The results revealed nine physical habitats, including flat and rugged seafloor, submerged dunes, paleovalleys, and reef structures. The predominant sediments were siliciclastic, with sand accounting for 71.2%, gravel for 21.8%, and a smaller fraction of mud for 7%. Bioclastic and mixed (lithobioclastic and biolithoclastic) sediments were the secondary components (~ 33%) across the shelf. Rocky outcrops and reefs increase habitat heterogeneity and biodiversity, whereas flatter areas, dominated by siliciclastic sediments, tend to support less diverse benthic communities. These features reflect sea-level fluctuations, hydrodynamic forces, and relict sediment deposition. Paleovalleys at depths of 30–40 m likely formed during low sea levels and were later shaped by transgressive phases. Submerged rocks, reefs, and stepped surfaces provide key evidence of Holocene sea-level stabilization. These geomorphological structures are similar to those observed on other continental shelves, indicating that local and regional factors shape seafloor morphology. Despite some data limitations, this study improves understanding of the Ceará shelf’s marine landscapes and supports future research on sediment dynamics, biodiversity, and conservation.