2012, Oceanography 25(2):124–131, http://dx.doi.org/10.5670/oceanog.2012.47
Hans van Haren | NIOZ Royal Netherlands Institute for Sea Research, Den Burg, the Netherlands
Louis Gostiaux | INP/UJF-Grenoble 1, Laboratoire des Ecoulements Géophysiques et Industriels, Grenoble, France
The sun inputs huge amounts of heat to the ocean, heat that would stay near the ocean's surface if it were not mechanically mixed into the deep. Warm water is less dense than cold water, so that heated surface waters "float" on top of the cold deep waters. Only active mechanical turbulent mixing can pump the heat downward. Such mixing requires remarkably little energy, about one-thousandth of the heat stored, but it is crucial for ocean life and for nutrient and sediment transport. Several mechanisms for ocean mixing have been studied in the past. The dominant mixing mechanism seems to be breaking of internal waves above underwater topography. Here, we quantify the details of how internal waves transition to strong turbulent mixing by using high-sampling-rate temperature sensors. The sensors were moored above the sloping bottom of a large guyot (flat-topped submarine volcano) in the Canary Basin, North Atlantic Ocean. Over a tidal period, most mixing occurs in two periods of less than half an hour each. This "boundary mixing" dominates sediment resuspension and is 100 times more turbulent than open ocean mixing. Extrapolating, the mixing may be sufficiently effective to maintain the ocean's density stratification.
van Haren, H., and L. Gostiaux. 2012. Energy release through internal wave breaking. Oceanography 25(2):124–131, http://dx.doi.org/10.5670/oceanog.2012.47.
Armi, L. 1978. Some evidence for boundary mixing in the deep ocean. Journal of Geophysical Research 83:1,971–1,979, http://dx.doi.org/10.1029/JC083iC04p01971.
Armi, L. 1979. Effects of variations in eddy diffusivity on property distributions in the oceans. Journal of Marine Research 37:515–530.
Aucan, J., M.A. Merrifield, D.S. Luther, and P. Flament. 2006. Tidal mixing events on the deep flanks of Kaena Ridge, Hawaii. Journal of Physical Oceanography 36:1,202–1,219, http://dx.doi.org/10.1175/JPO2888.1.
Bonnin, J., H. van Haren, P. Hosegood, and G.-J.A. Brummer. 2006. Burst resuspension of seabed material at the foot of the continental slope in the Rockall Channel. Marine Geology 226:167–184, http://dx.doi.org/10.1016/j.margeo.2005.11.006.
D’Asaro, E.A., and R.-C. Lien. 2000. The wave-turbulence transition for stratified flows. Journal of Physical Oceanography 30:1,669–1,678, http://dx.doi.org/10.1175/1520-0485(2000)030<1669:TWTTFS>2.0.CO;2.
Dillon, T.M. 1982. Vertical overturns: A comparison of Thorpe and Ozmidov length scales. Journal of Geophysical Research 87:9,601–9,613, http://dx.doi.org/10.1029/JC087iC12p09601.
Farmer, D.M., M.H. Alford, R.-C. Lien, Y.J. Yang, M.-H. Chang, and Q. Li. 2011. From Luzon Strait to Dongsha Plateau: Stages in the life of an internal wave. Oceanography 24(4):64–77, http://dx.doi.org/10.5670/oceanog.2011.95.
Garrett, C. 1990. The role of secondary circulation in boundary mixing. Journal of Geophysical Research 95:3,181–3,188, http://dx.doi.org/10.1029/JC095iC03p03181.
Garrett, C. 1991. Marginal mixing theories. Atmosphere-Ocean 29:313–339, http://dx.doi.org/10.1080/07055900.1991.9649407.
Gerkema, T. 1996. A unified model for the generation and fission of internal tides in a rotating ocean. Journal of Marine Research 54:421–450, http://dx.doi.org/10.1357/0022240963213574.
Gerkema, T., and H. van Haren. 2007. Internal tides and energy fluxes over Great Meteor Seamount. Ocean Science 3:441–449.
Gregg, M.C. 1989. Scaling turbulent dissipation in the thermocline. Journal of Geophysical Research 94:9,686–9,698, http://dx.doi.org/10.1029/JC094iC07p09686.
Groen, P. 1948. Contribution to the theory of internal waves. Koninklijk Nederlands Meteorologisch Instituut Mededelingen en Verhandelingen B11:1–23.
Helfrich, K.R., and W.K. Melville. 2006. Long nonlinear internal waves. Annual Review of Fluid Mechanics 38:395–425, http://dx.doi.org/10.1146/annurev.fluid.38.050304.092129.
Hosegood, P., J. Bonnin, and H. van Haren. 2004. Solibore-induced sediment resuspension in the Faeroe-Shetland Channel. Geophysical Research Letters 31, L09301, http://dx.doi.org/10.1029/2004GL019544.
Klymak, J.M., and J.N. Moum. 2003. Internal solitary waves of elevation advancing on a shoaling shelf. Geophysical Research Letters 30, 2045, http://dx.doi.org/10.1029/2003GL017706.
Klymak, J.M., J.N. Moum, J.D. Nash, E. Kunze, J.B. Girton, G.S. Carter, C.M. Lee, T.B. Sanford, and M.C. Gregg. 2006. An estimate of tidal energy lost to turbulence at the Hawaiian Ridge. Journal of Physical Oceanography 36:1,148–1,164, http://dx.doi.org/10.1175/JPO2885.1.
Mohn, C., and A. Beckmann. 2002. The upper ocean circulation at Great Meteor Seamount. Part I: Structure of density and flow fields. Ocean Dynamics 52:179–193, http://dx.doi.org/10.1007/s10236-002-0017-4.
Munk, W. 1966. Abyssal recipes. Deep-Sea Research 13:707–730, http://dx.doi.org/10.1016/0011-7471(66)90602-4.
Munk, W., and C. Wunsch. 1998. Abyssal recipes II: Energetics of tidal and wind mixing. Deep-Sea Research Part I 45:1,977–2,010, http://dx.doi.org/10.1016/S0967-0637(98)00070-3.
Nash, J.D., M.H. Alford, E. Kunze, K. Martini, and S. Kelly. 2007. Hotspots of deep ocean mixing on the Oregon continental slope. Geophysical Research Letters 34, L01605, http://dx.doi.org/10.1029/2006GL028170.
Orr, M.H., and P.C. Mignerey. 2003. Nonlinear internal waves in the South China Sea: Observation of the conversion of depression internal waves to elevation internal waves. Journal of Geophysical Research 108, 3064, http://dx.doi.org/10.1029/2001JC001163.
Osborn, T.R. 1980. Estimates of the local rate of vertical diffusion from dissipation measurements. Journal of Physical Oceanography 10:83–89, http://dx.doi.org/10.1175/1520-0485(1980)010<0083:EOTLRO>2.0.CO;2.
St. Laurent, L., H. Simmons, T.Y. Tang, and Y.H. Wang. 2011. Turbulent properties of internal waves in the South China Sea. Oceanography 24(4):78–87, http://dx.doi.org/10.5670/oceanog.2011.96.
Thorpe, S.A. 1977. Turbulence and mixing in a Scottish loch. Philosophical Transactions of the Royal Society of London A 286:125–181, http://dx.doi.org/10.1098/rsta.1977.0112.
Thorpe, S.A. 1987a. Transitional phenomena and the development of turbulence in stratified fluids: A review. Journal of Geophysical Research 92:5,231–5,248, http://dx.doi.org/10.1029/JC092iC05p05231.
Thorpe, S.A. 1987b. Current and temperature variability on the continental slope. Philosophical Transactions of the Royal Society of London A 323:471–517, http://dx.doi.org/10.1098/rsta.1987.0100.
Thorpe, S.A. 2010. Breaking internal waves and turbulent dissipation. Journal of Marine Research 68:851–880, http://dx.doi.org/10.1357/002224010796673876.
van Haren, H. 2005. Details of stratification in a sloping bottom boundary layer of Great Meteor Seamount. Geophysical Research Letters 32, L07606, http://dx.doi.org/10.1029/2004GL022298.
van Haren, H. 2006. Nonlinear motions at the internal tide source. Geophysical Research Letters 33, L11605, http://dx.doi.org/10.1029/2006GL025851.
van Haren, H., and L. Gostiaux. 2009. High-resolution open-ocean temperature spectra. Journal of Geophysical Research 114, C05005, http://dx.doi.org/10.1029/2008JC004967.
van Haren, H., and L. Gostiaux. 2010. A deep-ocean Kelvin-Helmholtz billow train. Geophysical Research Letters 37, L03605, http://dx.doi.org/10.1029/2009GL041890.
van Haren, H., and L. Gostiaux. 2011. Large internal waves advection in very weakly stratified deep Mediterranean waters. Geophysical Research Letters 38, L22603, http://dx.doi.org/10.1029/2011GL049707.
van Haren, H., and L. Gostiaux. 2012. Detailed internal wave mixing observed above a deep-ocean slope. Journal of Marine Research 70:173–197, http://dx.doi.org/10.1357/002224012800502363.
van Haren, H., L. Gostiaux, M. Laan, M. van Haren, E. van Haren, and L.J.A. Gerringa. 2012. Internal wave turbulence near a Texel beach. PLoS ONE 7(3), e32535, http://dx.doi.org/10.1371/journal.pone.0032535.
van Haren, H., M. Laan, D.-J. Buijsman, L. Gostiaux, M.G. Smit, and E. Keijzer. 2009. NIOZ3: Independent temperature sensors sampling yearlong data at a rate of 1 Hz. IEEE Journal of Oceanic Engineering 34:315–322, http://dx.doi.org/10.1109/JOE.2009.2021237.
Vlasenko, V., and K. Hutter. 2002. Numerical experiments on the breaking of solitary internal waves over a slope-shelf topography. Journal of Physical Oceanography 32:1,779–1,793, http://dx.doi.org/10.1175/1520-0485(2002)032<1779:NEOTBO>2.0.CO;2.