Ocean Science www.ocean-sci.net 1812-0784 1812-0792 5 4 2009 10.5194/os-5-435-2009 http://www.ocean-sci.net/5/435/2009/ http://www.ocean-sci.net/5/435/2009/os-5-435-2009.html http://www.ocean-sci.net/5/435/2009/os-5-435-2009.pdf 435 445 2009-10-26 Observations of turbulence beneath sea ice in southern McMurdo Sound, Antarctica C. L. Stevens c.stevens@niwa.cri.nz N. J. Robinson M. J. M. Williams T. G. Haskell National Institute for Water and Atmospheric Research (NIWA), Greta Point Wellington, New Zealand University of Otago, Dunedin, New Zealand Industrial Research Ltd (IRL), Gracefield, Lower Hutt, New Zealand The first turbulence profiler observations beneath land fast sea ice which is directly adjacent to an Antarctic ice shelf are described. The stratification in the 325 m deep water column consisted of a layer of supercooled water in the upper 40 m lying above a quasi-linearly stratified water column with a sharp step in density at mid-depth. Turbulent energy dissipation rates were on average 3×10−8 m2 s−3 with peak bin-averaged values reaching 4×10−7 m2 s−3. The local dissipation rate per unit area was estimated to be 10 m Wm−2 on average with a peak of 50 m Wm−2. These values are consistent with a moderate baroclinic response to the tides. The small-scale turbulent energetics lie on the boundary between isotropy and buoyancy-affected. This will likely influence the formation and aggregation of frazil ice crystals within the supercooled layer. The data suggest that the large crystals observed in McMurdo Sound will transition from initial growth at scales smaller than the Kolmogorov lengthscale to sizes substantially (1–2 orders of magnitude) greater than the Kolmogorov scale. An estimate of the experiment-averaged vertical diffusivity of mass Kρ yields a coefficient of around 2×10−4 m2s−1 although this increased by a factor of 2 near the surface. Combining this estimate of Kρ with available observations of average and maximum currents suggests the layer of supercooled water can persist for a distance of ~250 km from the front of the McMurdo Ice Shelf. % vor jede Referenz Albrecht, N., Vennell, R., Williams, M., Stevens, C., Langhorne, P., Leonard, G., and Haskell, T.: Observation of sub-inertial internal tides in McMurdo Sound, Antarctica, Geophys. Res. Lett., 33, L24606, doi:10.1029/2006GL027377, 2006. Arrigo, K. R., van Dijken, G., and Long, M.: Coastal Southern Ocean: A strong anthropogenic CO2 sink, Geophys. Res. Lett., 35, L21602, doi:10.1029/2008GL035624, 2008. Dempsey, D., Langhorne, P. J., Robinson, N. J., Williams, M. W. M., Haskell, T. G., and Frew, R.: Observation and modeling of platelet ice fabric in McMurdo Sound, Antarctica, to appear, J. Geophys. Res., doi:10.1029/2008JC005264, in press, 2009. Dillon, T. M.: Vertical Overturns: A Comparison of Thorpe and Ozmidov Length Scales, J. Geophys. Res., 87(C12), 9601–9613, 1982. Fer, I. and Widell, K.: Early spring turbulent mixing in an ice-covered Arctic fjord during transition to melting, Cont. Shelf Res., 27, 1980–1999, 2007. Galbraith, P. S. and Kelley, D. E.: Identifying overturns in CTD profiles, J. Atmos. Ocean. Tech., 13, 688–702, 1996. Goring, D. G. and Pyne, A.: Observations of sea-level variability in Ross Sea, Antarctica, N. Z. J. Mar. Freshwater Res., 37, 241–249, 2003. Hellmer, H. H.: Impact of Antarctic ice shelf melting on sea ice and deep ocean properties, Geophys. Res. Lett., 31, L10307, doi:10.1029/2004GL019506, 2004. Holland, P. R., Feltham, D. R., and Jenkins, A.: Ice Shelf Water plume flow beneath Filchner-Ronne Ice Shelf, Antarctica, J. Geophys. Res., 112, C05044, doi:10.1029/2006JC003915, 2007. Imberger, J. and Boashash, B.: Application of the Wigner-Ville distribution to temperature gradient microstructure: a new technique to study small-scale variations, J. Phys. Oceanogr., 16, 1997–2012, 1986. Imberger, J. and Ivey, G. N.: On the nature of turbulence in a stratified fluid. Part II: Observations, J. Phys. Oceanogr., 21, 659–675, 1991. Jacobs, S. S., Huppert, H. E., Holdsworth, G., and Drewry, D. J.: Thermohaline steps induced by melting of the Erebus Glacier Tongue, J. Geophys. Res., 86, 6547–6555, 1981. Jacobs, S., Hellmer, H. H., and Jenkins, A.: Antarctic ice sheet melting in the Southeast Pacific. Geophys. Res. Lett., 23, 957–960, 1996. Keeler, R. N., Bondur, V. G., and Gibson, C. H.: Optical satellite imagery detection of internal wave effects from a submerged turbulent outfall in the stratified ocean, Geophys. Res. Lett., 32, L12610, doi:10.1029/2005GL022390, 2005. Leonard, G. H., Purdie, C. R., Langhorne, P. J., Haskell, T. G., Williams, M. J. M., and Frew, R. D.: Observations of platelet ice growth and oceanographic conditions during the winter of 2003 in McMurdo Sound, Antarctica, J. Geophys. Res., 111, C04012, doi:10.1029/2005JC002952, 2006. Lueck, R.: Horizontal and vertical turbulence profilers, in: Marine Turbulence: Theories, Observations and Models, edited by: Baumert, H. Z., Simpson, J. H., and Sundermann, J., Cambridge Univ. Press, 89–100, 2005. Macoun, P. and Lueck, R. G.: Modelling the spatial response of the air-foil shear probe using different sized probes, J. Atmos. Ocean. Tech., 21, 284–297, 2004. McGuiness, M. J., Williams, M. J. M., Langhorne, P. J., Purdie, C., and Crook, J.: Frazil deposition under growing sea ice, J. Geophys. Res., 114, C07014, doi:10.1029/2007JC004414, 2009. McPhee, M. G.: Turbulent heat flux in the upper ocean under sea ice, J. Geophys. Res., 97, 5365–5379, 1992. McPhee, M. G.: Turbulent stress at the ice/ocean interface and bottom surface hydraulic roughness during the SHEBA drift, J. Geophys. Res., 107, 8037, doi:10.1029/2000JC000633, 2002. McPhee, M. G.: A spectral technique for estimating turbulent stress, scalar flux magnitude, and eddy viscosity in the ocean boundary layer under pack ice, J. Phys. Oceanogr., 34, 2180–2188, 2004. McPhee, M. G.: Air-ice-ocean-interaction: Turbulent Ocean Boundary Layer Exchange Processes, Springer, 215~pp., 2008. McPhee, M. G. and Morison, J. H.: Turbulence and diffusion: Under-ice boundary layer, in: Encyclopedia of Ocean Sciences, Academic Press, London, 3071–3078, 2001. McPhee, M. G. and Stanton, T. P.: Turbulence in the statically unstable oceanic boundary layer under Arctic leads, J. Geophys. Res., 101(C3), 6409–6428, 1996. Mitchell, W. M. and Bye, J. A. T.: Observations in the boundary layer under the sea ice in McMurdo Sound, in: Oceanology of the Antarctic Continental Shelf, edited by: Jacobs, S. S., Antarctic Research Series, 63, 167–176, 1985. Morison, J. H., Andersen, R. H., Larsen, N., D'Asaro, E. A., and Boyd, T.: The correction for thermal inertia effects in Sea-Bird CTD data, J. Atmos. Ocean. Tech., 11, 1151–1164, 1994. Muench, R., Padman, L., Gordon, A., and Orsi, A.: A dense water outflow from the Ross Sea, Antarctica: Mixing and the contribution of tides, J. Mar. Sys., 77, 369–387, doi:10.1016/j.jmarsys.2008.11.003, 2009. Osborn, T.: Estimates of the local rate of vertical diffusion from dissipation measurements, J. Phys. Oceanogr., 10, 83–89, 1980. Payne, A. J., Holland, P. R., Shepherd, A. P., Rutt, I. C., Jenkins, A., and Joughin, I.: Numerical modeling of ocean-ice interactions under Pine Island Bay's ice shelf, J. Geophys. Res., 112, C10019, doi:10.1029/2006JC003733, 2007. Pease, C. H., Salo, S. A., and Overland, J. E.: Drag measurements for first-year sea ice over a shallow sea, J. Geophys. Res., 88, 2853–2862, 1983. Prandke, H.: Microstructure sensors, in: Marine Turbulence: Theories, Observations and Models, edited by: Baumert, H. Z., Simpson, J. H., and Sundermann, J., Cambridge Univ. Press, 101–109, 2005. Rainville, L., Winsor, P.: Mixing across the Arctic Ocean: Microstructure observations during the Beringia 2005 Expedition, Geophys. Res. Lett., 35, L08606, doi:10.1029/2008GL033532, 2008. Robertson, R. A., Padman, L., and Levine, M. D.: Finestructure, microstructure, and vertical mixing processes in the western Weddell Sea, J. Geophys Res., 100, 18517–18535, 1995. Robinson, N. J., Williams, M. J. W., Barrett, P. J., and Pyne, A. R.: Observations of flow and ice-ocean interactions beneath the McMurdo Ice Shelf, Antarctica, J. Geophys. Res., accepted, 2009. Roget, E., Lozovatsky, I., Sanchez, X., and Figueroa, M.: Microstructure measurements in natural waters: Methodology and applications, Prog. Oceanogr., 70, 126–148, 2006. Shaw, W. J., Stanton, T. P., McPhee, M. G., Morison, J. H., and Martinson, D. G.: Role of the upper ocean in the energy budget of Arctic sea ice during SHEBA, J. Geophys. Res., 114, C06012, doi:10.1029/2008JC004991, 2009. Shih, L. H., Koseff, J. R., Ivey, G. N., and Ferziger, J. H.: Parameterization of turbulent fluxes and scales using homogeneous sheared stably stratified turbulence simulations, J. Fluid Mech., 525, 193–214, 2005. Smedsrud, L. H. and Jenkins, A.: Frazil ice formation in an ice shelf water plume, J. Geophys. Res., 109, C03025, doi:10.1029/2003JC001851, 2004. Stacey, M. T., Monismith, S. G., and Burau, J. R.: Observations of turbulence in a partially stratified estuary, J. Phys. Oceanogr., 29, 1950–1970, 1999. Stacey, M. T., Burau, J. R., and Monismith, S. G.: Creation of residual flows in a partially stratified estuary. J. Geophys. Res., 106, 17013–17037, 2001. Stevens, C.: Turbulence in an Estuarine Embayment: Observations from Beatrix Bay, New Zealand, J. Geophys. Res., 108(C2), 3030, doi:10.1029/2001JC001221, 2003. Stevens, C. L. and Smith, M. J.: Temperature microstructure beneath surface gravity waves, J. Atmos. Ocean. Tech. 21, 1747–1757, 2004. Stevens, C. L., Williams, M. J. M, Robinson, N. J., Albrecht, N., and Haskell, T. G.: Observations of the Stratified Turbulent Boundary-layer and Platelet Ice Beneath McMurdo Sound Sea Ice, Proc. Sixth International Symposium on Stratified Flows, edited by: Ivey, G. N., Perth, Australia, 2006. St Laurent, L.: Turbulent dissipation on the margins of the South China Sea, Geophys. Res. Lett., 35, L23615, doi:10.1029/2008GL035520, 2008. Stroeve, J., Holland, M. M., Meier, W., Scambos, T., and Serreze, M.: Arctic sea ice decline: Faster than forecast, Geophys. Res. Lett., 34, L09501, doi:10.1029/2007GL029703, 2007. Svensson, U. and Omstedt, A.: Simulation of supercooling and size distribution in frazil ice dynamics, Cold Reg. Sci. Technol., 22, 221–233, 1994. Tennekes, H. and Lumley, J. L.: A First Course in Turbulence, MIT Press, 300~pp., 1972. Wesson, J. C. and Gregg, M. C.: Mixing at Camarinal Sill in the Strait of Gibraltar, J. Geophys. Res., 99, 9847–9878, 1994. Williams, M. J. M., Grosfeld, K., Warner, R. C., Gerdes, R., and Determann, J.: Ocean circulation and ice-ocean interaction beneath the Amery Ice Shelf, Antarctica, J. Geophys. Res., 106, 22383–22399, 2001. Zaron, E. D. and Egbert, G. D.: Estimating open-ocean barotropic tidal dissipation: The Hawaiian Ridge, J. Phys. Oceanogr., 36, 1019–1035, 2006.