Characterizing the Distribution of Nepheloid Layers and Their Response to Hydrodynamics in the NE Rockall Trough, NE Atlantic Ocean

Abstract

Suspended and slow‐sinking particles, especially those concentrated within nepheloid layers, can act as pivotal mediators of oceanic carbon transport and benthic‐pelagic coupling. However, identifying nepheloid layers and distinguishing their composition (i.e., inorganic particles, phytoplankton, zooplankton, and fish) using only acoustic systems remains challenging due to limited multidisciplinary observations. Here, multi‐frequency acoustic data, multisensory biogeochemical observations, and optical cameras are integrated to identify suspended and sinking particles, plankton, and fish off NW Ireland, Rockall Trough (NE Atlantic Ocean). Observed nepheloid layers exhibited high values in turbidity, particle abundance, buoyancy frequency, and synthetic seismograms, which are clearly distinct from plankton and fish shoals, as validated by direct camera observations. They mainly developed at 200–800 m depths and extended at least 40 km across the continental slope. Maximum thickness and echo intensity occurred on the upper slope, where internal waves break, and M ₂ internal tide generation rates are high. Internal waves can cause particle resuspension, inducing nepheloid layers. Internal waves laterally transported particles and lifted them to the upper water column. During the neap‐to‐spring tidal transition, intensified tides enhanced bottom currents and turbulent mixing, vertically diffusing and thickening the nepheloid layers. A cyclonic mesoscale eddy transported particles from the slope to the deeper ocean, thereby further expanding nepheloid layers laterally. This study characterizes the spatiotemporal variability of nepheloid layers, explores their hydrodynamic responses in the NE Rockall Trough, and highlights their role as efficient particle transport highways.