Observational evidence of diapycnal upwelling within a sloping submarine canyon

• Main Authors: Wynne-Cattanach, Bethan, Alford, Matthew, Couto, Nicole, Drake, Henri, Ferrari, Raffaele, Boyer, Arnaud Le, Mercier, Herle, Messias, Marie-Jose, Garabato, Alberto Naveira, Polzin, Kurt, Ruan, Xiaozhou, Spingys, Carl, van Haren, Hans, Voet, Gunnar
• Other Authors: Scripps Institution of Oceanography (SIO - UC San Diego), University of California San Diego (UC San Diego), University of California (UC)-University of California (UC), University College of London London (UCL), Laboratoire d'Océanographie Physique et Spatiale (LOPS), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), University of Exeter, National Oceanography Centre Southampton (NOC), University of Southampton, Woods Hole Oceanographic Institution (WHOI), Royal Netherlands Institute for Sea Research (NIOZ)
• Format: Report
• Language: English
• Published: HAL CCSD 2023
• Subjects: [SDU]Sciences of the Universe [physics]; Munk; North Atlantic
• Online Access: https://hal.science/hal-04299678; https://doi.org/10.21203/rs.3.rs-3459062/v1

Abstract Small-scale turbulent mixing drives the upwelling of deep water masses in the abyssal ocean as part of the global overturning circulation (Wunsch & Ferrari 2004). However, the processes leading to mixing and the pathways through which this upwelling occurs remain insufficiently understood. Recent observational and theoretical work suggests that deep water upwelling may be focused in bottom boundary layers on the ocean’s sloping seafloor; however, direct evidence of this is lacking (Ledwell et al. 2000, St. Laurent et al. 2001, Ferrari et al. 2016, de Lavergne et al. 2016). Here, we present observations from a near-bottom dye release within a canyon on the North Atlantic continental slope showing upwelling across density surfaces at a rate of 250 +/- 75 m/day over three days, ∼10,000 times higher than the global average value required to account for ∼30 Sv of upwelling globally (Munk 1966). The vigourous upwelling is coupled with adiabatic exchange of near-boundary and interior fluid. These results provide direct evidence of strong, bottom-focused diapycnal upwelling in the deep ocean, supporting previous suggestions that mixing at topographic features, such as canyons, leads to upwelling.