Internal wave turbulence at a biologically rich Mid-Atlantic seamount

Abstract The turbulence regime near the crest of a biologically rich seamount of the Mid-Atlantic Ridge southwest of the Azores was registered in high spatial and temporal resolution. Internal tides and their higher harmonics dominate the internal wave motions, producing considerable shear-induced turbulent mixing in layers of 10–50 m thickness. This interior mixing of about 100 times open-ocean interior values is observed both at a high-resolution temperature sensor mooring-site at the crest, 770 m water depth being nearly 400 m below the top of the seamount, and a CTD-yoyo site at the slope off the crest 400 m horizontally away, 880 m water depth. Only at the mooring site, additionally two times higher turbulence is observed near the bottom, associated with highly non-linear wave breaking. The highest abundance of epifauna, notably sponges, are observed just below the crest and 100 m down the eastern slope (700–800 m) in a cross-ridge video-camera transect. This sponge belt is located in a water layer of depressed oxygen levels (saturation 63±2%) with a local minimum centered around 700 m. Turbulent mixing supplies oxygen to this region from above and below and is expected to mix nutrients away from this biodegraded layer towards the depth of highest abundance of macrofauna.FUNDING. The construction of the NIOZ temperature sensors has been financed in part by NWO, the Netherlands Organization for Scientific Research. UH is funded by the SponGES project, which received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 679849. RV Pelagia cruise 64PE412 was carried out in the framework of the TREASURE (Towards Responsible ExtrAction of Submarine Resources) project, supported under grant No 13273 by the Technology Foundation STW of the Netherlands Organisation for Scientific Research (NWO), and partners from the Dutch maritime industry. Shiptime was funded by the Topsector Water programme, a collaborative effort of Dutch industry, academia and government. FM is supported financially by the Innovational Research Incentives Scheme of the Netherlands Organisation for Scientific Research (NWO-VIDI grant 016.161.366). DATA AVAILABILITY. Data are freely available from Figshare: https://figshare.com/s/b6282a6c4dca460158e3. COPYRIGHT. © 2017 van Haren et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited