Abstract
Measurements of velocity and density profiles were used to describe the tidal and mean flow structure across and along a sill in Refugio Channel, a fjord-like inlet in Southern Chile (43.9°S). These are the first oceanographic measurements of any kind effected in Refugio Channel. Current profiles were obtained with a 307.2-kHz acoustic Doppler current profiler during two semidiurnal cycles along a repeated triangular circuit. Two along-channel transects formed the sides of the triangle that crossed the sill and were identified as the western and eastern transects. One cross-channel transect, the base of the triangle, was located on the seaward side of the sill. Density profiles were obtained at the corners of the triangle. The longitudinal mean flow in the western transect showed a two-layer exchange structure over the landward side of the sill. The structure of net seaward flow at the surface and landward flow at depth was disrupted by the sill in such a way that over the seaward side of the sill, only seaward flow was observed throughout the water column. This likely resulted from the blocking of landward net flow by the sill. In the eastern transect, two-layer exchange dominated over most of the transect and was consistent with the observed density profiles. Over the seaward side of the sill, a surface layer, ∼10m deep, flowed landward as a third layer. This feature should have been caused by river input further seaward (to the north) and produced a surface convergence region over the sill. In terms of tidal flows, the greatest tidal current amplitudes were 40cm s−1 over the sill as the flow accelerated through the reduced cross-sectional area of the channel. Near-surface flow convergences were identified over both along-channel transects.
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References
Baines PG (1995) Topographic effects in stratified flows. Cambridge University Press, New York, p 482
Caceres M, Valle-Levinson A (2004) Transverse variability of flow on both sides of a sill/contraction combination in a fjord-like inlet of southern Chile. Estuar Coast Shelf Sci 60:325–338
Caceres M, Valle-Levinson A, Atkinson L (2003) Observations of cross-channel structure of flow in an energetic tidal channel. J Geophys Res 108(C4):3114
Farmer DA, Armi L (1986) Maximal two-layer exchange over a sill and through the combination of a sill and contraction with barotropic flow. J Fluid Mech 164:53–76
Farmer DA, Denton RA (1985) Hydraulic control of flow over the sill in observatory inlet. J Geophys Res 90(c5):9051–9068
Helfrich KR (1994) Time-dependent two layer hydraulic exchange flows. J Phys Oceanogr 25:359–373
Hogg AM, Ivey GN, Winters KB (2001) Hydraulics and mixing in controlled exchange flows. J Geophys Res 106:959–972
Klymak JM, Gregg MC (2001) The three-dimensional nature of flow near a sill. J Geophys Res 106:22295–22311
Lwiza KMM, Bowers DG, Simpson JH (1991) Residual and tidal flow at a tidal mixing front in the North Sea. Cont Shelf Res 11(11):1379–1395
Marsden RF, Greenwood KC (1994) Internal tides observed by an Acoustic Doppler Current Profiler. J Phys Oceanogr 24:1097–1109
Molinet C, Moreno CA, Caceres M, Bello M, Castillo M, Valle-Levinson A (2006) Effects of sill processes on the distribution of epineustonic competent larvae in a stratified system of Southern Chile. Mar Ecol Prog Ser (in press)
Seim HE, Gregg MC (1997) The importance of aspiration and channel curvature in producing strong vertical mixing over a sill. J Geophys Res 102(C2):3451–3472
Stigebrandt A (1976) On the effect of barotropic current fluctuations on the two-layer transport capacity of a constriction. J Phys Oceanogr 7:118–122
Stigebrandt A (1980) Some aspects of tidal interaction with fjord constrictions. Estuar Coast Shelf Sci 11:151–166
Trump CL, Marmorino G (1997) Calibrating a gyrocompass using ADCP and DGPS data. J Atmos Ocean Technol 14:211–214
Valle-Levinson A, Atkinson LP (1999) Spatial gradients in the flow over an estuarine channel. Estuaries 22(2A):179–193
Valle-Levinson A, Blanco JL (2004) Observations of wind influence on exchange flows in a strait of the Chilean Inland Sea. J Mar Res 62(5):720–740
Valle-Levinson A, Jara F, Molinet C, Soto D (2001) Observations of intratidal variability of flows over a sill/contraction combination in a Chilean fjord. J Geophys Res 106(c4):7051–7064
Valle-Levinson A, Cáceres M, Sepúlveda HH, Holderied K (2002) Patrones de flujo en los canales asociados a la boca del seno Aysén. Cienc Tecnol Mar 25(2):5–16
Winters KB, Seim HE (2000) The role of dissipation and mixing in exchange flow through a contraction channel. J Fluid Mech 407:265–290
Acknowledgments
The fieldwork was funded by the Scientific and Technological Development Funding (FONDEF) of Chile. C. Molinet received support from the National Commission for Scientific and Technological Research (CONICYT) of Chile. AVL was supported by NSF project #9983685. We thank the technicians at Santo Domingo and the crew of Bellavista for their support during the fieldwork. Historic sea-level data and ADCP device were kindly provided by Servicio Hidrografico y Oceanografico de la Armada, Valparaiso, Chile, where Mario Cáceres was formerly affiliated.
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Responsible Editor: Alejandro J. Souza
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Cáceres, M., Valle-Levinson, A., Molinet, C. et al. Lateral variability of flow over a sill in a channel of southern Chile. Ocean Dynamics 56, 352–359 (2006). https://doi.org/10.1007/s10236-006-0077-y
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DOI: https://doi.org/10.1007/s10236-006-0077-y