Exploring the Potential for Internal Tides to Reshape the Continental Shelf Edge Seafloor

Abstract Studies in the literature have argued anecdotally that strong near-bottom flow induced by internal tides could transport sediment and modify shelf-edge topography over the long term. To explore this argument, this study quantitatively investigates the topographic influence of internal tides using an idealized quasi-two-dimensional model that represents modern-day conditions at the shelf edge of the Mid-Atlantic Bight off the U.S. northeast coast. Observed temporal evolution of the internal tide amplitude and phases at the Mid-Atlantic Bight shelf edge over a 2-month period is used in conjunction with the model. We i) investigate two sources of semi-diurnal internal tides at the shelf edge, locally generated internal tides (LIT) and incident internal tides (IIT), and ii) consider transport of both suspended and bedload sediment. Model results indicate that LIT alone are inadequate to induce sediment transport, but a combination of tides, LIT and IIT can mobilize sediment at the shelf edge. Modeled sediment transport exhibits a tendency to compensate for changes in shelf-edge curvature and sea level from present-day conditions. However, the present-day shelf-edge profile does not represent a stable condition, as the sediment transport is stronger for the modern configuration than for other hypothetical shelf-edge geometries. Projecting short-term topographic change induced by the combined internal tides over longer timespans (with several major assumptions) indicates that, within the covered parameter range, the shelf-edge seafloor change induced by combined tides and internal tides over 10,000 years had an upper bound of 1-2 m. Sensitivity simulations show that although rates of bed change are affected by bottom roughness, shelf-edge curvature and sea level, the order of magnitude of the seafloor change remains unchanged across the parameter space considered here. This order of magnitude of modeled sediment transport and bed change suggests that it is unlikely for internal tides alone to have significantly shaped the edge of the Mid-Atlantic Bight continental shelf, at least for the conditions considered here. However, whether internal tides have interacted with other oceanographic processes and modified the shelf edge topography and what oceanic processes have shaped the shelf edge topography are questions that remain to be answered.