Enigmatic Deep-Water Seafloor Depressions East of Tortue Island, Northern Haiti Margin

Abstract

A widespread area of seafloor depressions - circular, arcuate to elongated-shaped - has been found along the Northern Haitian coast, at water depths between 600 and 2,000 m. Characterized by wavelengths spanning several hundred meters and heights of tens of meters, these depressions are linked with a series of narrow ridges boasting varied morphologies. Our analysis integrating multichannel seismic reflection, high-resolution bathymetry data, and sedimentological and geochemical evaluations of surface sediment cores indicates that present-day seafloor morphology results from the interaction of slope bottom currents with the seafloor. The analyzed sediment cores exhibit hemipelagites, silty and sandy contourites, fine-grained turbidites and reworked sand layers, implying sedimentation in a contourite drift system. This is further corroborated by seismic reflection data depicting wavy reflectors and aggradational stacking features typical of contourite drifts. Seafloor depressions are likely erosional features formed on the top of a contourite drift formed by the interaction of bottom currents with an irregular seafloor morphology. The seafloor equilibrium was initially disturbed by mass-wasting events. Subsequently, the quasi-steady flow of along-slope bottom currents influenced sedimentary distribution and controlled the morphology of the seafloor depressions-constant re-shaping through erosion on their flanks. The resulting rough seafloor could have facilitated the destabilization of bottom currents and the development of erosive eddies responsible for the current morphology of the seafloor depressions. This study highlights the interplay between sedimentary processes (accumulation and compaction) and bottom currents, showing how their combined effects influence slope sedimentation and seafloor geomorphology, forming unique erosional features.