biostudies-literatureUnknown630(8018)Wynne-Cattanach BLSmall-scale turbulent mixing drives the upwelling of deep water masses in the abyssal ocean as part of the global overturning circulation¹. However, the processes leading to mixing and the pathways through which this upwelling occurs remain insufficiently understood. Recent observational and theoretical work^2-5 has suggested that deep-water upwelling may occur along the ocean's sloping seafloor; however, evidence has, so far, been indirect. Here we show vigorous near-bottom upwelling across isopycnals at a rate of the order of 100 metres per day, coupled with adiabatic exchange of near-boundary and interior fluid. These observations were made using a dye released close to the seafloor within a sloping submarine canyon, and they provide direct evidence of strong, bottom-focused diapycnal upwelling in the deep ocean. This supports previous suggestions that mixing at topographic features, such as canyons, leads to globally significant upwelling^3,6-8. The upwelling rates observed were approximately 10,000 times higher than the global average value required for approximately 30 × 10⁶ m³ s^-1 of net upwelling globally⁹.Nature884-890https://www.ebi.ac.uk/biostudies/studies/S-EPMC11208136biostudies-literatureObservations of diapycnal upwelling within a sloping submarine canyon.PMC11208136Couto NFerrari RLe Boyer ARuan XVoet GSpingys CPNaveira Garabato ACvan Haren HWynne-Cattanach BLMercier HAlford MHPolzin KMessias MJDrake HFfalseObservations of diapycnal upwelling within a sloping submarine canyon.Small-scale turbulent mixing drives the upwelling of deep water masses in the abyssal ocean as part of the global overturning circulation¹. However, the processes leading to mixing and the pathways through which this upwelling occurs remain insufficiently understood. Recent observational and theoretical work^2-5 has suggested that deep-water upwelling may occur along the ocean's sloping seafloor; however, evidence has, so far, been indirect. Here we show vigorous near-bottom upwelling across isopycnals at a rate of the order of 100 metres per day, coupled with adiabatic exchange of near-boundary and interior fluid. These observations were made using a dye released close to the seafloor within a sloping submarine canyon, and they provide direct evidence of strong, bottom-focused diapycnal upwelling in the deep ocean. This supports previous suggestions that mixing at topographic features, such as canyons, leads to globally significant upwelling^3,6-8. The upwelling rates observed were approximately 10,000 times higher than the global average value required for approximately 30 × 10⁶ m³ s^-1 of net upwelling globally⁹.2024-01-01T00:00:00Z2024 Jun2025-04-21T20:15:25.724Z2025-04-05T17:58:21.385ZS-EPMC112081363892661310.1038/s41586-024-07411-2