Scientia Marina, Vol 76, No S1 (2012)

Mixing dynamics on the inner shelf of the Ebro Delta


https://doi.org/10.3989/scimar.03605.18A

Imma Bastida
Universitat de Girona, Department of Physics, Group of Environmental Physics, Spain

Jesús Planella
Universitat de Girona, Department of Physics, Group of Environmental Physics, Spain

Elena Roget
Universitat de Girona, Department of Physics, Group of Environmental Physics, Spain

Jorge Guillén
Institut de Ciències del Mar, Marine Geology Department, CSIC, Spain

Pere Puig
Institut de Ciències del Mar, Marine Geology Department, CSIC, Spain

Xavier Sánchez
Universitat de Girona, Department of Physics, Group of Environmental Physics, Spain

Abstract


Turbidity, CTD, and temperature and shear microstructure data recorded along a 25 km transect from 8 to 69 m depth across the Ebro Delta shelf (northwestern Mediterranean) are presented. The water column was stratified and prior to the campaign the regional southwest flow was measured to have superimposed diurnal and sub-inertial components. The bottom boundary layer (BBL) at all stations deeper than 20 m has a vertical extension of 3 to 9 m, increasing to 12 m at the deeper stations and even to 14 m at a station at 45 m depth outside the studied transect. The law of the wall was identified at almost all stations with an extension ranging from 40% to 100% of that of the BBL. At some stations high dissipation rates were found in the interior of the bottom layer. The study shows the correspondence between the turbidity contents and the local mixing processes at the BBL and suggests that sub-critical reflection of internal waves could play an important role in boundary mixing. Our data also suggest that during the campaign, after two consecutive short episodes of high winds, the first baroclinic mode shifted to the second one.

Keywords


bottom boundary layer; nepheloid layer; inner shelf; turbulence; turbidity; internal waves; mixing

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References


Alford M., Pinkel A. 2000. Observations of Overturning in the Thermocline: The Context of Ocean Mixing. J. Phys. Oceanogr. 30: 805-832. http://dx.doi.org/10.1175/1520-0485(2000)030<0805:OOOITT>2.0.CO;2

Cacchione D.A., Drake D.E. 1986. Nepheloid layers and internal waves over continental shelves and slopes. Geo-Mar. Let. 6: 147-152.

Cacchione D.A., Drake D.E., Losada M.A., Medina R. 1990. Bottom-boundary-layer measurements on the continental-shelf off the Ebro river, Spain. Mar. Geol. 95: 179-192. http://dx.doi.org/10.1016/0025-3227(90)90115-Z

Chant R.J. 2001. Evolution of near-inertial waves during an upwelling event on the New Jersey inner shelf. J. Phys. Oceanogr. 31: 746-764. http://dx.doi.org/10.1175/1520-0485(2001)031<0746:EONIWD>2.0.CO;2

Dauxois T., Didier A.D., Falcon E. 2004. Observation of near-critical reflection of internal waves in stably stratified fluid. Phys. Fluid. 16:1936-1941. http://dx.doi.org/10.1063/1.1711814

Davis AG., Soulby R.L., King H.L. 1988. A numerical model of the combined wave and current bottom boundary layer. J. Geophys. Res. C. 93: 491-508. http://dx.doi.org/10.1029/JC093iC01p00491

de Juan S., Demestre M., Thrush S. 2009. Defining ecological indicators of trawling disturbance when everywhere that can be fished is fished: A Mediterranean case study. Mar. Policy. 33: 472-478. http://dx.doi.org/10.1016/j.marpol.2008.11.005

Demestre M., de Juan S., Sarto P., Ligas A. 2008. Seasonal closures as a measure of trawling effort control in two Mediterranean trawling grounds: Effects on epibenthic communities. Mar. Pollut. Bull. 56: 1765-1773. http://dx.doi.org/10.1016/j.marpolbul.2008.06.004 PMid:18649897

Díaz J.I., Nelson C.H., Barber J.H., Giró S. 1990. Late pleisocente and holocene sedimentary facies on the Ebro continental-shelf. Mar. Geol. 95: 333-352. http://dx.doi.org/10.1016/0025-3227(90)90123-2

Emery W.J., Thomson R.E. 2001. Data analysis methods in physical oceanography. Elsevier, 638 pp.

Eriksen C.C. 1985. Implications of ocean bottom reflection for internal wave spectra and mixing. J. Phys. Oceanogr. 15: 1145-1156. http://dx.doi.org/10.1175/1520-0485(1985)015<1145:IOOBRF>2.0.CO;2

Fernandes A.A., Chandramohan P., Nayak B.U. 1993. Observed current at Bombay high during a winter. Mahasagar 26: 95-104.

Fofonoff N.P., Millard Jr. R.C. 1983. Algorithms for computation of fundamental properties of seawater (1983), UNESCO Technical Papers in Marine Science. No. 44, Division of Marine Sciences. UNESCO, Place de Fontenoy, 75700 Paris.

Font J., Salat J., Tintoré J. 1988. Permanent features of the circulation in the Catalan Sea, Oceanol. Acta. 9: 51-57.

Font J., Salat J., Julià A. 1990. Marine circulation along the Ebro continental-margin. Mar. Geol. 95: 165-177. http://dx.doi.org/10.1016/0025-3227(90)90114-Y

Gargett A., Osborn T., Nasmyth P. 1984. Local isotropy and the decay of turbulence in a stratified fluid. J. Fluid Mech. 144: 231-280. http://dx.doi.org/10.1017/S0022112084001592

Garrett C., Gilbert.D. 1988. Estimates of vertical mixing by internal waves reflected off a sloping bottom. In: "Small Scale Turbulence and Mixing in the Ocean". Proc. 19th Liège Colloq. on Ocean Hydrodynamics, 405-424.

Garrett C. 1990. The role of secondary circulation in boundary mixing. J. Geophys. Res. C. 95: 3181-3188. http://dx.doi.org/10.1029/JC095iC03p03181

Gibson C.H. 1980. Fossil temperature, salinity, and vorticity turbulence in the ocean. In: Nihoul J.C.J. (ed.), Marine Turbulence, Elsevier Publishing Co., Amsterdam, pp. 221-257.

Gill A. 1982, Atmosphere-Ocean Dynamics. Academic Press, 662 pp.

Gonella J. 1972. A rotary component method for analysing meteorological and oceanographic vector time series. Deep-Sea Res. 19: 883-846.

Guillén J., Palanques A. 1997. A historical perspective of the morphological evolution in the lower Ebro River. Env. Geol. 30: 174-180. http://dx.doi.org/10.1007/s002540050144

Guillén J., Jiménez J.A., Palanques A., Gracia V., Puig P., Sánchez-Arcilla, A. 2002. Sediment resuspension across a fetch-limited tideless inner shelf. Cont. Shelf Res. 22: 305-325. http://dx.doi.org/10.1016/S0278-4343(01)00059-0

Howarth, M.J., Souza A.J. 2005. Reynolds stress observations in continental shelf seas. Deep-Sea Res-II. 55: 1075-1086. http://dx.doi.org/10.1016/j.dsr2.2005.01.003

Imberger J., Boashash B. 1986. Application of the Wigner-Ville distribution to temperature gradient microstructure: A new technique to study small-scale variations. J. Phys. Oceanogr. 16: 1997-2012. http://dx.doi.org/10.1175/1520-0485(1986)016<1997:AOTWDT>2.0.CO;2

Ivey G.N., Nokes R.I. 1989. Mixing driven by the breaking of internal waves against sloping boundaries. J. Fluid Mech. 204, 479-500. http://dx.doi.org/10.1017/S0022112089001849

Ivey G. N., Imberger J. 1991. On the nature of turbulence in a stratified fluid. 1. The energetics of mixing. J. Phys. Oceanogr. 21: 650-658. http://dx.doi.org/10.1175/1520-0485(1991)021<0650:OTNOTI>2.0.CO;2

Kundu P.J. 1990. Fluid Mechanics. Academic Press, 638 pp.

Lorke A., Umlauf L., Jonas T., Wu.est A. 2002. Dynamics of Turbulence in Low-Speed Oscillating Bottom-Boundary Layers of Stratified Basins. Environ. Fluid Mech. 2: 291-313. http://dx.doi.org/10.1023/A:1020450729821

Lorke A., Peeters F., Wuest A. 2005. Shear-induced convective mixing in bottom boundary layers on slopes. Limnol. Oceanogr. 50: 1612-1619. http://dx.doi.org/10.4319/lo.2005.50.5.1612

Lozovatsky I., Roget E., Fernando H.J.S., Figueroa M., Shapovalov S. 2006. Sheared turbulence in low-speed oscillating bottom.boundaary layers of stratified basins. Deep-Sea Res. I 53: 87-407.

MacKinnon J.A., Gregg M.C. 2005. Near-inertial waves on the New England shelf: The role of evolving stratification, turbulent dissipation, and bottom drag. J. Phys. Oceanogr. 35: 2408-2424 http://dx.doi.org/10.1175/JPO2822.1

McPhee-Shaw E.E., Kunze E. 2002. Boundary layer intrusions from a sloping bottom: A mechanism for generating intermediate nepheloid layers' J. Geophys. Res. 107: 3050. http://dx.doi.org/10.1029/2001JC000801

Millot C., Crepon M. 1981. Inertial oscillations on the continental-shelf of the gulf of Lions - observations and theory. J. Phys. Oceanogr. 11: 639-657. http://dx.doi.org/10.1175/1520-0485(1981)011<0639:IOOTCS>2.0.CO;2

Moum J.N., Perlin A., Klymak J.M., Levine M.D., Boyd T., Kosro P.M. 2004. Convectively driven mixing in the bottom boundary layer. J. Phys. Oceanogr. 34: 2189-2202. http://dx.doi.org/10.1175/1520-0485(2004)034<2189:CDMITB>2.0.CO;2

Osborn T.R. 1980. Estimates of local rate of vertical diffusion from dissipation measurements. J. Phys. Oceanogr. 10: 83-89. http://dx.doi.org/10.1175/1520-0485(1980)010<0083:EOTLRO>2.0.CO;2

Palanques A., Drake D.E. 1990. Distribution and dispersal of suspended particulate matter on the Ebro continental-shelf, northwestern Mediterranean-sea. Mar. Geol. 95: 193-206. http://dx.doi.org/10.1016/0025-3227(90)90116-2

Palanques A., Puig P., Guillén J., Jiménez J., Gracia V., Sánchez-Arcilla A., Madsen O. 2002. Near-bottom suspended sediment fluxes on the microtidal low-energy Ebro continental shelf (NW Mediterranean). Cont. Shelf Res. 22: 285-303. http://dx.doi.org/10.1016/S0278-4343(01)00058-9

Panchev S., Kesich,D. 1969. Energy spectrum of isotropic turbulence at large wavenumbers. Comptes rendus de l'Académie Bulgare des Sciences. 22: 627-630.

Perlin A., Moum J.N., Klymak J.M., Levine M.D., Boyd T. Kosro P.M. 2005. A modified law-of-the-wall applied to oceanic bottom boundary layers. J. Geophys. Res. 110: C10S10. http://dx.doi.org/10.1029/2004JC002310

Phillips O.M., Shyu J.H., Salmun H. 1986. An experiment on boundary mixing - mean circulation and transport rates. J. Fluid Mech. 173: 473-499. http://dx.doi.org/10.1017/S0022112086001234

Piera J., Roget E., Catalan J. 2002. Turbulent patch identification in microstructure profiles: a method based on wavelet denoising and Thorpe displacement analysis. J. Atmos. Ocean. Tech. 19: 1390-1402. http://dx.doi.org/10.1175/1520-0426(2002)019<1390:TPIIMP>2.0.CO;2

Prandke H., Stips A. 1998. Test measurements with an operational microstructure turbulence profiler: detection limit of dissipations rates. Aquat. Sci. 60: 191-209. http://dx.doi.org/10.1007/s000270050036

Prandke H. 2005. Microstructure sensors. In: Marine Turbulence: Theories, Observations and Models, edited by Baumert H Z., Simpson J.H., Sundermann J. Cambridge Univ. Press, pp.101-109.

Puig P., Palanques A., Guillén J. 2001. Near-bottom suspended sediment variability caused by storms and near-inertial internal waves on the Ebro mid continental shelf (NW Mediterranean). Mar. Geol. 178: 81-93. http://dx.doi.org/10.1016/S0025-3227(01)00186-4

Roget E., Lozovatsky I., Sánchez X., Figueroa. M. 2006. Microstructure measurements in natural waters: Methodology and applications. Prog. Oceanogr. 70: 126-148. http://dx.doi.org/10.1016/j.pocean.2006.07.003

Rippeth T.P., Simpson J.H., Player R.J., Garcia M. 2002. Current oscillations in the diurnal-inertial band on the Catalonian shelf in spring. Cont. Shelf Res. 22: 247-265. http://dx.doi.org/10.1016/S0278-4343(01)00056-5

Salat J., Tintoré J., Font J., Wang D. P., Vieira M. 1992. Near-inertial motion on the shelf-slope front off northeast Spain. J. Geophys. Res. 97: 7277-7281. http://dx.doi.org/10.1029/92JC00588

Sánchez X., Roget E. 2006. Microstructure measurements and heat flux calculations of a triple-diffusive process in a lake within the diffusive layer convection regime. Deep-Sea Res-I 53: 387-407.

Soloviev A., Klinger, B. 2001. Open Ocean Convection. In: Encyclopedia of Ocean Sciences, Vol.4 Academic Press, pp. 2015-2022. http://dx.doi.org/10.1006/rwos.2001.0118

Stansfield K., Garrett C., Dewey R. 2001. The probability distribution of the Thorpe displacement within overturns in Juan de Fuca Strait. J. Phys. Oceanogr. 31: 3421-3434. http://dx.doi.org/10.1175/1520-0485(2001)031<3421:TPDOTT>2.0.CO;2

Staquet C., Sommeria J. 2002. Internal gravity waves: From instabilities to turbulence. Annu. Rev. Fluid Mech. 34: 559-593. http://dx.doi.org/10.1146/annurev.fluid.34.090601.130953

Stillinger, D.C., Hellnad, K.N., Van Atta, C.W., 1983. Experiments on the transition of homogeneous turbulence to internal waves in a stratified fluid. J. Fluid Mech. 131: 91-122. http://dx.doi.org/10.1017/S0022112083001251

Thorpe S.A. 1977. Turbulence and mixing in a Scottish Loch. Philos. T. R. Soc. Lon. A 286: 125-181. http://dx.doi.org/10.1098/rsta.1977.0112

Thorpe S.A. 1987. On the reflection of a train of finite amplitude internal waves from a uniform slope. J. Fluid Mech. 78: 279-302. http://dx.doi.org/10.1017/S0022112087001228

Thorpe S.A. 1997. On the interaction of internal waves reflecting from slopes. J. Phys. Oceanogr. 27: 2072-2078. http://dx.doi.org/10.1175/1520-0485(1997)027<2072:OTIOIW>2.0.CO;2

Thorpe, S.A. 2004. Recent developments in the study of ocean turbulence. Annu. Rev. Earth Planet Sci. 32: 91-109 http://dx.doi.org/10.1146/annurev.earth.32.071603.152635

Tintoré J., Wang D.P., García E., Viudez A. 1995. Near-inertial motions in the coastal ocean. J. Marine Syst. 6, 301-312. http://dx.doi.org/10.1016/0924-7963(94)00030-F

van Haren J.J.M., Maas L.R.M. 1987. Temperature and current fluctuations due to tidal advection of a front. Neth. J. Sea Res. 21: 79-94. http://dx.doi.org/10.1016/0077-7579(87)90024-X

Wells M., Cenedese C., Caulfield C.P. 2010. The relationship between flux coefficient and entrainment ratio in density currents. J. Phys. Oceanogr. 40: 2713-2727. http://dx.doi.org/10.1175/2010JPO4225.1

Wolk F., Yamazaki H., Seuront L., Lueck R.G. 2002. A new free-fall profiler for measuring biophysical microstructure. J. Atmos. Ocean. Tech. 19: 780-793. http://dx.doi.org/10.1175/1520-0426(2002)019<0780:ANFFPF>2.0.CO;2




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