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Abstract

Explorer and Dangeard Canyons are named limbs of the large, dendritic Whittard Canyon system that incises the Celtic Sea continental slope. The system is known to feature large (order 80-m amplitude) semidiurnal internal tides, assumed to be generated at the shelf break to the southwest and focused into some limbs of the canyon by its steep, converging bathymetry. Interestingly, other limbs of the same system are much less tidally energetic. These large, but spatially heterogeneous internal tides are thought to have a variety of environmental impacts, from benthic faunal distribution to triggering turbidity currents. In summer 2022, a University of Washington DeepGlider was deployed in and around Whittard Canyon for 45 days. After correcting for the internal spring-neap cycle, the largest semidiurnal internal tides (order 120-m amplitude) were observed at the mouths of Explorer and Dangeard Canyons and in both limbs the vertical oscillation of isopycnals progressed up-canyon (at 0.6-1.9 m s−1 in Explorer and 2.0 m s−1 in Dangeard). The associated available potential energy was highest in the lower half of the water column and decreased up the limbs. Finally, a 13-hour yo-yo CTD/LADCP station at the mouth of Explorer Canyon, competed during a coincident habitat mapping and benthic ecosystem survey (JC237), showed the up-canyon energy flux to be 6.7 kW m−1. This evidence suggests very high levels of internal tide dissipation and resulting turbulent mixing within these two canyon limbs, which are likely to have considerable impact on local benthic ecosystems, sedimentological processes, and biogeochemical cycling.