David Amblas, Scott Polar Research Institute, University of Cambridge, UK
Julian A. Dowdeswell, Scott Polar Research Institute, University of Cambridge, UK
Miquel Canals, CRG Marine Geosciences, University of Barcelona, Spain
Anna Sanchez-Vidal, CRG Marine Geosciences, University of Barcelona, Spain
Ricardo Silva Jacinto, Institut Français de Recherche Pour L'exploitation de la Mer, Brest, France
Seabed imprint of dense shelf water cascading
Dense shelf-water cascading (DSWC) is an atmosphere-driven seasonal phenomenon that occurs in marine regions around the globe. DSWC starts when surface waters over the continental shelf become denser than surrounding waters (by cooling, evaporation or sea-ice formation with brine rejection) and sink, generating a near-bottom gravity flow that moves downslope along the seabed, often using submarine canyons as preferential conduits. This process contributes to deep-ocean ventilation, plays a role in the global thermohaline circulation (and hence global climate), and involves the massive transfer of energy and matter (including sedimentary particles, organic carbon and pollutants) from shallow to deep waters.
DSWC is highly sensitive to temperature change in both the lower atmosphere and the sea surface. In the coming decades global warming will likely modify the frequency and intensity of DSWC, which could significantly affect the functioning of the deep-sea ecosystems. Overall, dense-water formation is expected to decline over both continental shelves and offshore, particularly in Arctic and sub-polar latitudes where sea-ice production is declining.
Field observations show that DSWC can rapidly reshape the seafloor, particularly in submarine canyons. It has been suggested that DSW fluxes could generate continental slope gullies in Polar Regions too. In situ near-bottom velocities up to 1.25 m s-1
have been measured for these currents, which are similar to those attained by turbidity currents. The large volumetric fluxes created by DSWC can result in appreciable sediment erosion and downslope transport. However, very few field studies discuss DSWC as an effective seafloor-sculpting agent, and none of them at global scale. Here we present a new project that considers the morphological signature of DSWC events on modern continental shelves and slopes. The project aims to contribute to a better characterization of the distribution, hydrodynamics and sculpting capacity of dense shelf water currents, as well as the long-term morphodynamics where they are or have been in action in geologically recent times. It also aims to better understand the past and future effects of climate change on the formation of DSWC, in addition to shedding new light to the on-going discussion about the potential vulnerability of deep-sea ecosystems that largely rely on the arrival of nutrients transported during DSWC events.
Theme 1: Canyon processes in the space-time continuum (formation, evolution, circulation)
dense shelf water cascading, slope gullies, sediment erosion, downslope transport