A missing link between continental shelves and the deep sea: Have we underestimated the importance of land-detached canyons?

Dr Veerle Huvenne, Michael Clare, NOC; Esther Sumner, University of Soton; Rob Hall, University of East Anglia; Ian Kane, Manchester Unit

Submarine canyons are assumed to be globally-significant conduits for the transfer of sediment, nutrients, organic carbon and pollutants between continental shelves and the deep sea. However, efforts to directly quantify contemporary particulate fluxes through submarine canyons have focused solely on a handful of canyons that directly connect to rivers or coastal littoral cells1. Because of the long-standing paradigm that canyons whose heads lie 100s of km from shore are quiescent in terms of sediment transport, these ‘land-detached’ canyons have often been overlooked by hydrodynamic monitoring; despite accounting for more than three quarters of the >9000 submarine canyons worldwide2. Without measurements, we cannot quantify particulate fluxes in land-detached canyons, exposing a major gap in understanding of global sediment routing systems and shelf to deep-sea exchanges. New measurements in the Whittard Canyon, Celtic Margin2 (>250 km from shore) recorded powerful turbidity currents, of a surprisingly similar frequency and magnitude to those reported in major land-attached canyons3. These new results challenge the long-held paradigm, but questions remain concerning what triggers these flows, the volumes of material they transport, and the efficiency by which they bury natural sediments and anthropogenic pollutants. This project will tackle these important questions, using new data from Whittard Canyon.



[1] What triggers turbidity currents in a land-detached canyon? Integration of detailed repeat seafloor surveys of the shelf and canyon head acquired by Autonomous Underwater Vehicles (AUV), glider-based oceanographic measurements, and hydrodynamic modelling will identify for the first time the mechanisms by which material is transferred to the canyon and how flows are triggered.


[2] How efficiently are organic carbon and pollutants transported and buried? Sediment traps sample suspended sediments, while sediment cores record how rapidly that material is buried. These samples will be subject to sedimentological, X-Ray and grain-size analyses. Organic carbon, and microplastic concentrations/type will be quantified using organic geochemistry (NOC) and FTIR (Manchester). Mapping of accumulation hotspots will determine whether turbidity currents flush sediments and pollutants to the deep sea, or lock them up within the canyon.


[3] How do particulate fluxes compare with other canyon systems worldwide? Detailed direct measurements of turbidity currents made using moored Acoustic Doppler Current Profilers will be analysed to provide the first quantification of of sediment, carbon and pollutant fluxes along a land-detached canyon. These values will be compared with other major canyons such as those fed by major rivers (e.g. Congo Canyon1) to appraise the global importance of land-detached canyons.



The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at National Oceanography Centre Southampton within the Ocean BioGeosciences group. The student will join a wider international collaboration focused on Whittard Canyon, including two NERC-funded projects (PISCES and CLASS) that have gathered large amounts of data. The candidate will have the opportunity to join offshore research campaigns to acquire further data. Specific training relevant to a future academic career and across a range of offshore industries include: i) Sedimentology (visual description, grain size, X-Ray Imaging, XRF); ii) Geophysics/remote sensing (Multibeam bathymetry, side scan sonar); iii) Geochemistry (Organic carbon, FTIR polymer identification); iv) Hydrodynamics (moored ADCP, ship hydrographic survey, and glider-acquired data, plus regional hydrodynamic modelling). 


Eligibility & Funding Details: 

Please see https://inspire-dtp.ac.uk/how-apply for details.


Background Reading: 

1.       Talling, P.J., Baker, M.L., Pope, E.L., Ruffell, S.C., Jacinto, R.S., Heijnen, M.S., Clare, M.A., Hage, S., Simmons, S.M., Hasenhündl, M., Heerema, C.J. and McGhee, C., 2022. Longest sediment flows yet measured show how major rivers connect efficiently to deep sea. Nature communications, 13(1), pp.1-15. https://doi.org/10.1038/s41467-022-31689-3

2.       Amaro, T., Huvenne, V.A.I., Allcock, A.L., Aslam, T., Davies, J.S., Danovaro, R., De Stigter, H.C., Duineveld, G.C.A., Gambi, C., Gooday, A.J. and Gunton, L.M., 2016. The Whittard Canyon–A case study of submarine canyon processes. Progress in Oceanography, 146, pp.38-57. https://doi.org/10.1016/j.pocean.2016.06.003

3.         Heijnen, M., Mienis, F., Gates, A., Bett, B., Hall, R., Hunt, J., Kane, I., Pebody, C., Huvenne, V., Soutter, E. and Clare, M., 2022. Challenging the highstand-dormant paradigm for land-detached submarine canyons. Nature Communications. https://doi.org/10.1038/s41467-022-31114-9