Internal Tides in Whittard Canyon: Spatial Variability and Impacts on Habitat Heterogeneity

Submarine canyons are often termed 'biodiversity hotspots' and it is thought that oceanographic processes within canyons, such as internal tides, can contribute to habitat heterogeneity and hence modulate biological abundance and diversity. The Celtic Sea shelf edge experiences large tidal currents, and barotropic tidal flows over the shelf edge generate internal waves and associated baroclinic energy fluxes. The shelf is incised by a number of submarine canyons, the largest of which is Whittard Canyon, a dendritic canyon comprising of 4 main branches ranging in depth from 200 to 4000 m. Submarine canyons can trap and focus internal waves towards the head of the canyon, and hence Whittard Canyon is likely to be a location of enhanced internal wave activity and turbulent mixing. Using high resolution simulations of the M2 tide in Whittard Canyon utilising the Princeton Ocean Model, we show that there is elevated baroclinic energy within the canyon, but that this is variable between the different limbs and displays a complex 3D structure. The model identifies locations with enhanced near bottom tidal currents within the canyon, where velocities can reach 40 cm s⁻¹, which may have implications for sediment and organic matter re-suspension and transport within the canyon. Initial inclusion of the modelled M2 internal tide parameters within predictive habitat models of the canyon system suggest that internal tides can have a significant influence on fine-scale species spatial patterns, with both direction and magnitude helping in modelling megafaunal species richness and diversity. Further work is needed to quantify the influence of internal tides on ecology in dynamic environments such as Whittard Canyon, however they are clearly a significant but currently under-explored source of habitat heterogeneity.