Tracking turbidity currents induced by storms in the Capbreton submarine canyon

The Capbreton submarine canyon is the major canyon on the French Atlantic coast. The canyon remains active and hence a major sedimentary connection between the shelf and the deep sea in the all Bay of Biscay. Being an active... [ view full abstract ]

The Capbreton submarine canyon is the major canyon on the French Atlantic coast. The canyon remains active and hence a major sedimentary connection between the shelf and the deep sea in the all Bay of Biscay. Being an active canyon at the present sea level, the Capbreton canyon may also be the source and the conduit for catastrophic events such as slope failures, down-slope gravity flows or proximal tsunamis, which may impact coastal populations and infrastructures and deep-water infrastructures.
A multidisciplinary study is being developed in order to quantify the present turbidity activity by estimating along the canyon the turbidity currents intensity, return periods of the events and major trigger mechanisms. The developed methodology mixes (1) multiple bathymetric surveys (2013 and 2015) providing differential bathymetries and morphological evolutions from the head of the canyon down to 300 m deep meanders, (2) sediment cores preserving the sediment-water interface (radionuclides datation, ecology of benthic foraminifera, lithofacies analysis) collected from both the thalweg and adjacent terraces along the canyon, (3) moorings with sediments traps and ADCP current meters, (4) processes-based numerical modelling.
Results show a fairly coherent picture of the turbidity activity in the canyon popping out from different proxies and physical evidence. Major storms in the Bay of Biscay onset gravity flows in the canyon producing major (up to 10 m) morphological changes down to 300 m deep. Numerical modelling illustrates how the induced turbidity currents may propagate along the canyon, how far the sand from the head may be transported and how terraces may be fed and preserve turbidites.
Radionuclide activities and ecological characteristics of benthic foraminifera show off a pluriannual and regular perturbation of the deposits and hence interpretations fully coherent with the physical evidence of the turbiditic activity observed and modelled.
The Capbreton submarine canyon stays regularly active in the present highstanding demonstrating that submarine canyons remaining connected to sedimentary sources may preserve their potential for sedimentary hazards along the continental margins.

This work is part of the TANDEM project and partially supported by a grant by the French National Research Agency (ANR) as part of the “Investissements d'Avenir” Programme. The authors thank all the technical support during the Gitan (Ifremer, 2015) and the Volt cruises (Ifremer, 2015 and 2016).