The role of storms and resulting sediment transport in maintaining the activity of land‐detached canyons

ABSTRACT

Land‐detached submarine canyons are typically developed on broad continental shelves, where direct fluvial sediment supply is absent. This often leads to their interpretation as inactive sediment conduits, contrasting with recent monitoring studies revealing the presence of turbidity currents in these canyons. The northeastern South China Sea is characterised by a wide shelf with limited sediment input from large rivers, though it experiences frequent tropical storms. This unique setting provides an ideal opportunity to investigate the effects of storm‐enhanced sediment transport on submarine canyon activity. This work quantifies the contribution of storms to sediment transport from the continental shelf to submarine canyons using numerical calculations based on surface sediment grain size, bathymetric data and regional wave field conditions obtained from the ERA5 model. Using an extensive dataset from the South China Sea, the results demonstrate that under storm‐wave conditions, the combination of extreme wave heights and shallow water depths increases the likelihood of shelf‐sediment transport during storms, a process that affects up to 64% of the continental shelf. Our results reveal a dual mechanism sustaining canyon activity: First, storm waves remobilise shelf sediments that are subsequently advected toward canyon heads by currents, preconditioning the slopes through gradual accumulation. Second, during the most energetic events, local remobilisation near the shelf edge generates suspended sediment concentrations exceeding the ~40 g l ⁻¹ threshold, directly triggering sediment gravity flows on steep canyon slopes. The analysis presented here provides valuable insights into the role of storms in facilitating sediment transport from the shelf to canyon heads, and elucidates how storms influence the activity of land‐detached submarine canyons.