Internal tides in a dendritic submarine canyon

Abstract

Submarine canyons are a common geomorphological feature along continental slopes worldwide and often found to be ‘hotspots’ of internal tide activity. However, the majority of well-studied submarine canyons are simple linear incisions or have meandering morphology; internal tide energetics in branching (dendritic) canyons has not previously been investigated. Here we present a high-resolution (500-m) numerical modelling study of the internal tide within Whittard Canyon, a large, dendritic submarine canyon system that incises the Celtic Sea continental slope. A modified version of the Princeton Ocean Model is used to simulate the M2 (semidiurnal) internal tide in the Whittard Canyon region, verified against a hydrographic dataset collected by an autonomous ocean glider. Much of the internal tide energy entering Whittard Canyon originates to the southeast, along the Celtic Sea shelf break. Internal tide generation also occurs within the canyon itself, but is in part compensated by areas of negative energy conversion. Depth-integrated internal tide energy fluxes exceed 8kWm−1 in the eastern limb of the canyon. The internal tide is topographically steered through the major limbs and along-canyon energy flux is bottom intensified, suggesting topographic focusing. The down canyon extent of bottom intensification closely corresponds to the point that along-canyon slope becomes near-critical to the semidiurnal internal tide. Energetically, the multiple limbs of Whittard Canyon behave differently, some are net sources of internal tide energy whilst others are net sinks. Internal tide energy dissipation also varies between the canyon limbs; bulk dissipation rates are 2.1-7.7×10-8Wkg-1. In addition, the effect of bathymetric resolution on internal tide generation and propagation is investigated by progressively smoothing the model domain. Decreasing the bathymetric resolution reduces internal tide generation and energy dissipation in both Whittard Canyon and the model domain as a whole, however, internal tide energy flux into the canyon is not consistently changed. At least 1.5-km resolution bathymetry is required to adequately resolve the semidiurnal internal tide field in this region of complex topography.