Seafloor morphology and sedimentology in the Brazilian semi-arid continental shelf: a high-resolution geophysical baseline from the Ceará Basin

Continental shelves along tropical semi-arid margins remain sparsely mapped at high resolution, limiting process-based interpretations of bedforms dynamics and reducing quality of baseline information required for marine spatial planning and offshore development. In this study we present an integrated geomorphological and sedimentological baseline for two middle- to outer-shelf sectors of the Ceará Basin, on Northeast Brazil. We combined multibeam echosounder bathymetry and backscatter, side-scan sonar imagery, and sediment sampling to map bedform morphology and sediment textures in detail across more than 12 km2 in total. High-resolution mapping reveals strong spatial contrasts in seabed morphology and acoustic texture across the two areas. The Western Area comprises a heterogeneous mosaic of geomorphic elements, including a channel, clustered circular depressions, and a terrace-like bench, associated with marked variability in backscatter and grain size, from granule-grade sediment on the bench to sandier substrates in depressions and channel-floor domains. The Eastern Area is dominated by sand-wave and organized into a crest–trough system, with geomorphometric patterns and side-scan sonar textures pointing to spatial variability in seabed roughness and bedform expression. Together, these results highlight how inherited shelf morphology and present-day hydrodynamic reworking interact on a sediment-limited shelf to produce contrasting bedform–sediment domains over short along-shelf distances. The mapped bedform-sediment domains provide a robust physical baseline to guide future process studies and to inform monitoring and risk-aware planning for infrastructure and marine spatial management on the Brazilian semi-arid continental shelf.