Tidally Forced Lee Waves Drive Turbulent Mixing Along the Arctic Ocean Margins

• Published in: Geophysical Research Letters
• Main Authors: Fer, Ilker, Koenig, Zoé, Kozlov, Igor, Ostrowski, Marek, Rippeth, Tom, Padman, Laurie, Bosse, Anthony, Kolås, Eivind
• Other Authors: Bjerknes Centre for Climate Research (BCCR), Department of Biological Sciences Bergen (BIO / UiB), University of Bergen (UiB)-University of Bergen (UiB), University of Bergen (UiB), Norwegian Polar Institute, Marine Hydrophysical Institute, Satellite Oceanography Laboratory St Petersburg (SOLab), Russian State Hydrometeorological University St.Petersburg (RSHU), Institute of Marine Research Bergen (IMR), School of Ocean Sciences Menai Bridge, Bangor University, Earth and Space Research, Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Arctic; Arctic Ocean; Sea ice; Svalbard
• Online Access: https://hal.science/hal-02968286; https://hal.science/hal-02968286/document; https://hal.science/hal-02968286/file/2020GL088083.pdf; https://doi.org/10.1029/2020GL088083

International audience In the Arctic Ocean, limited measurements indicate that the strongest mixing below the atmospherically forced surface mixed layer occurs where tidal currents are strong. However, mechanisms of energy conversion from tides to turbulence and the overall contribution of tidally driven mixing to Arctic Ocean state are poorly understood. We present measurements from the shelf north of Svalbard that show abrupt isopycnal vertical displacements of 10-50 m and intense dissipation associated with cross-isobath diurnal tidal currents of ∼0.15 m s −1. Energy from the barotropic tide accumulated in a trapped baroclinic lee wave during maximum downslope flow and was released around slack water. During a 6-hr turbulent event, high-frequency internal waves were present, the full 300-m depth water column became turbulent, dissipation rates increased by a factor of 100, and turbulent heat flux averaged 15 W m −2 compared with the background rate of 1 W m −2. Plain Language Summary Turbulent mixing in the Arctic Ocean water column affects sea ice variability through transport of subsurface heat toward the surface. This turbulent mixing is concentrated along the margins, mainly driven by tidal flow over sloping topography. However, processes of energy transfer from tides to turbulence in the Arctic are poorly understood, and the magnitudes and locations of mixing are poorly constrained. Here we present detailed measurements from the shelf north of Svalbard, showing a turbulent event driven by moderate tidal currents. The energy is trapped and accumulated at the time of maximum downslope flow and is released at the turn of the tide when the entire water column becomes highly turbulent. Our observations imply that this process is an important source of mixing in the Arctic Ocean.