Seismic characterisation and geomorphological interpretation of the summit area palaeoenvironment of Tropic Seamount, offshore Western Sahara: A sediment starved, ferromanganese crust and nodule rich guyot

To understand and reconstruct the palaeoenvironmental development of Tropic Seamount, a guyot offshore Western Sahara, an assessment of landforms morphology and seismic facies interpretation was conducted. High resolution multibeam echosounder bathymetry and backscatter, two hours of ROV footage and 23 TOPAS-acquired seismic lines were analysed to derive a morphological model and define seismic facies and units. The seabed morphology was classified into seven morphological classes. Eight seismic (sub)facies were identified on the basis of their internal configuration, forming five seismic units separated by reflectors with distinct morphological geometries. The link between geomorphologies and seismic units allows for the reconstruction of the morphogenetic processes which have likely originated the landforms. According to the reconstructed geological history, Tropic Seamount, a former volcanic island, began to sink after the end of its eruptive activity. Wave action and erosion washed away the islands' terrigenous sediment. Tropic Seamount may then have experienced reefal deposition, with the formation of syn-depositionally cemented hardgrounds. The continuous sinking may have brought its summit in correspondence of the oxygen minimum zone where reduced Fe and Mn ions have undergone oxidation and precipitation on the seamount's summit, leading to the formation of Fesingle bondMn crusts and nodules. The onset of the glacial/interglacial climate pattern and the consequent aridification of the Sahara may have led to ocean fertilization due to iron-rich continental dust input, which enhanced pelagic sedimentation. Finally, submarine resedimentation processes have reshaped the seamount's summit. The reconstruction of Tropic Seamount's depositional history may help shed light on the geological evolution of deep-sea environments and on the processes shaping them.