Tidally Forced Lee Waves Drive Turbulent Mixing Along the Arctic Ocean Margins. Issue 16 (21st August 2020)

• Record Type: Journal Article
• Authors: Fer, Ilker; Koenig, Zoé; Kozlov, Igor E.; Ostrowski, Marek; Rippeth, Tom P.; Padman, Laurie; Bosse, Anthony; Kolås, Eivind
• Is Part Of: Geophysical research letters. Volume 47:Issue 16(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-21
• Subjects: ocean microstructure -- Arctic Ocean -- dissipation rate -- Svalbard -- critical flow -- nonlinear waves; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL088083
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: 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. Key Points: Cross‐isobath diurnal currents generate nonlinear internal waves north of Svalbard Flow becomes supercritical during maximum off‐shelf tidal flow Time‐averaged turbulent heat fluxes increase by a factor of 4 when the turbulent period is included