One‐Year Long ADCP Data Reveal the Influence of Tides, Winds, and Coastal‐Trapped Waves on the Deep Cross‐Slope Transport in a Submarine Trench

Abstract

Submarine canyons and trenches are the main pathways for transport of water, sediments, and nutrients across the continental slope. In the North Sea, transport across the slope and into the Norwegian Sea is confined to the Norwegian Trench (NT). From June 2023 to May 2024, we recorded time series data in the middle of the NT (272 m) and close to the Atlantic continental slope (363 m) using moored ADCPs to investigate the hydrodynamic variability. We identified semi‐diurnal and diurnal tidal influence explaining 19% of the variance in the flow in the middle of the NT, and 10% of the variance at the continental slope, respectively. The deep currents respond to local winds and to coastal‐trapped waves (CTWs) on time scales of 1–10 days. Significant correlations between increased water temperature and along‐slope winds from the Southwest show that CTWs enable strong inflows of Atlantic Water, whereas winds from the Northeast favor upwelling of Arctic waters. In the central trench, seasonal signals in velocity, backscatter, and temperature are related to the North Atlantic Oscillation, highlighting the connectivity of the NT to the North Sea. The interactions of remotely forced CTWs and the up‐and downwelling of water masses are typically observed in submarine canyons. With this study we add to a new understanding of the hydrodynamics in the NT, which are comparable to the dynamics observed in canyons around the world.