Tides in the Weddell Sea (original) (raw)
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Baroclinic and barotropic tides in the Weddell Sea
Antarctic Science, 2005
Barotropic and baroclinic tides were simulated for the Weddell Sea using ROMS. The model estimates for both tidal elevations and velocities showed good agreement with existing observations. The rms differences were 9 cm for elevations and 1.2–1.7 cm s−1 for the major axes of the tidal ellipses for the semidiurnal constituents and 6–8 cm and 4.5 cm s−1 for the diurnal constituents, respectively. Most of the discrepancies occurred deep under the ice shelf for the semidiurnal tides and along the continental slope for the diurnal tides. Along the continental slope, the model overestimated the generation of diurnal continental shelf waves. The diurnal tides were barotropic throughout the basin. However, internal tides were generated at semidiurnal frequencies over rough topography. Over the continental slope, semidiurnal baroclinic tidal generation was enhanced by the existence of continental shelf waves, through their harmonics. Baroclinic tides generated over rough topography in the no...
Internal waves and tides in the western Weddell Sea: Observations from Ice Station Weddell
Journal of Geophysical Research, 1997
The upper ocean current and temperature fields in the western Weddell Sea were measured from the drifting pack ice at Ice Station Weddell I (ISW) and nearby sites using a vertical profiler and an array of moored sensors in January-June 1992. These data document the structure and variability of the internal gravity wave field and tidal currents in this remote region. The variance of the internal wave continuum (f < frequency < N) at ISW was 0.2-0.6 of the Garrett-Munk (GM) universal level for the first 60 days, increasing to near GM levels during the final 10 days of the deployment. In contrast, the energy density at site C, 50 km west of ISW and farther up the continental slope, was always near GM levels. Variations may be due to a combination of spatial and temporal gradients of the internal wave field. At ISW, coherence between vertically separated sensors was used to estimate vertical wave number bandwidth. Energy and bandwidth estimates are compared with previous studies in both ice-covered and temperate oceans. Using our measurements of the internal wave field and existing parameterizations of mixing, we estimate the vertical heat flux from the Warm Deep Water toward the surface. At ISW the upward heat flux due to mixing associated with the internal waves was about 1 W m-2, much less than the 20 W m-2 average flux required to balance the heat budget for the Weddell Gyre. Tidal currents contributed significantly to the total measured horizontal velocity variance. The tides were primarily barotropic and increased toward the west in both the semidiurnal and diurnal frequency bands. It is suggested that the stronger tidal currents to the west, over the shallower water of the upper continental slope, are indirectly responsible for the higher internal wave energy at site C relative to ISW.
Numerical Investigation of Tidal Processes and Phenomena in the Weddell Sea, Antarctica
2002
In the framework of the BRIOS ({\it Bremerhaven Regional Ice OceanSimulations}), a three-dimensional tidal model was developed toinvestigate tidal processes in the southern Weddell Sea. Themodel is based on the free surface SCRUM ({\it S-Coordinate Primitive EquationOcean Model}), modified to allow for the inclusion of the horizontalcomponent of the Earth's rotation vector, the equilibrium tide and ice shelves.Barotropic tides are simulated in a regional two-dimensional (x-y) configuration for theAtlantic Sector of the Southern Ocean. In thisinvestigation, the semidiurnal M$_{2}$ and S$_{2}$ andthe diurnal K$_{1}$ and O$_{1}$ frequencies are considered.For both semidiurnal constituents, maxima amplitudes are foundin the southwestern corner of the Filchner-Ronne Ice Shelf (FRIS).Diurnal tides have higher amplitudes at thecontinental shelf break where they excite continental shelf waves ofsame period propagating in the along-slope direction.With the full three-dimensional model, b...
Impact of the Eastern Weddell Ice Shelves on water masses in the eastern Weddell Sea
Journal of Geophysical Research, 2006
We use a primitive equation Ocean General Circulation Model to simulate the ocean circulation regime in the Eastern Weddell Sea. The computer model ROMBAX (Revisited Ocean Model based on Bryan And Cox) is an improved version of an earlier ocean model, which has been developed to allow the simulation of the flow regime in ice shelf covered regions. The Eastern Weddell Ice Shelf (EWIS) region is of particular importance because of its narrow continental shelf and its location at the inflow of water masses from the east into the southern Weddell Sea. We have compared the simulated flow pattern and water properties in the EWIS region with the available sparse observations. While the general observed structure of temperature and salinity is reproduced, the model tends to overestimate the onshore flow of warm deep waters. This discrepancy is not large enough to seriously influence the ice shelfocean interaction, which is in good agreement with estimates based on field observations. The mean net melt rate is found to be 0.88 m yr À1 (2.1 mSv) and has a strong seasonal cycle. Sensitivity studies with different ice shelf configurations (no melting, no ice shelf, closed cavity) show strong impacts on the water mass properties in the EWIS region, with up to 0.7°C difference in temperature and 0.05 in salinity relative to the control run. Our results suggest that the EWIS region is of substantial importance to water mass preconditioning and formation in the Weddell Sea, although no deep or bottom water formation occurs in the eastern Weddell Sea directly.
2006
The ice front region of Ronne Ice Shelf lies near the critical latitude of the semidiurnal M 2 tide, the principal tidal constituent in the southern Weddell Sea. Here the Coriolis frequency almost equals the M 2 tidal frequency, resulting in a strong dependence of the M 2 tidal currents on depth and stratification and a boundary layer that can occupy the entire water column. Using data from four long-term moorings along Ronne Ice Front, we confirm the presence of strongly depth-dependent semidiurnal tidal currents and their sensitivity to changes in stratification. The time series show dramatic seasonal changes in tidal current profiles and significant interannual variability. During periods of stratification, the amplitude of the semidiurnal tides in the mid-water column shows a twofold increase and, despite being several kilometers offshore from the ice front, the tidal currents clearly show a second boundary layer originating from the adjacent ice shelf base. Together, these two boundary layers occupy most of the water column, up to 600 m deep, until intense sea ice formation and the production of High-Salinity Shelf Water erodes the vertical stratification. During winter when homogeneous conditions prevail, a single bottom boundary layer occupies the entire water column at some locations. This strong seasonality and sensitivity of the M 2 tidal current to stratification highlights the difficulties of interpreting current data from short-term moorings while demonstrating that it is the best indicator for characterizing changes in stratification after direct observations of density variations.
A numerical study of the circulation in the northwestern Weddell Sea
Deep Sea Research Part II: Topical Studies in Oceanography, 2002
An eddy-permitting simulation is used to study the circulation of the northwestern Weddell Sea and its interaction with the Scotia Sea. The analysis focuses on the circulation pathways, associated stratification, and volume transports. Comparison between model results and observations show reasonable agreements with respect to the modeled thermohaline stratification and circulation such as export of Weddell Sea Deep Water through the Weddell-Scotia Confluence region. Using the model results, we estimated the relative contributions of the two main routes of escape of the Weddell Sea deep waters into the Scotia Sea and the South Sandwich Trench. The main route for inter-basin exchange is found to be through the Scotia Sea (via the South Orkney Passage and the Bransfield Strait). Our simulation does not show advective transport of deep or bottom waters through the South Sandwich Trench, and Lagrangian analysis of float trajectories indicates that the fluxes in this region are more likely related to eddy-driven mixing than to mean flow advection. The model shows, in addition, some sub-basin scale features that have not been reported in the observations. The Weddell western boundary current is seen as a diffuse, filamentous feature. A southflowing jet was present over the outer shelf off the Antarctic Peninsula. Retroflection and return southward flow is seen for from the South Sandwich Trench, and there was a small inflow of Scotia Sea waters into the Powell Basin. r
High-frequency ice motion and divergence in the Weddell Sea
Journal of Geophysical Research, 2000
We describe the spatial variability of high frequency ice velocity in the Weddell Sea using satellite-tracked ice-mounted buoys. Ice motion is analyzed separately for "diurnal" (1/36-1/18 cph) and "semidiurnal" (1/18-1/6 cph) bands. Ice motion in both bands is caused by a combination of ocean tidal currents and wind stress. Monthly mean diurnal band ice speeds over the deep basin range from 2 to 4 cm s 'l depending on wind stress variance and ice concentration (Cite). Higher speeds (-10 cm s-1) are found in the semidiurnal band in regions of low Cite, notably the northern Weddell Sea, where the ice velocity is dominated by the inertial response to wind stress variations. Monthly mean tidal band ice speeds over the continental slope and shelves often exceed 10 cm s-•. We use comparisons between buoy velocities, moored current meter data, and an ocean tidal model to demonstrate that ice motion is frequently a good indicator of ocean tidal currents in strongly tidal regions. The standard deviation of the divergence of ocean tidal currents estimated from an oceanonly tidal model is small (<0.1x10 '6 s 'l) over most of the Weddell Sea but has values of 1-5x10 '6 s-1 along the Ronne Ice Front and the continental shelf break. High frequency ice divergence is dominated by ice response to wind stress rather than by tides except along the shelf break and ice fronts. In these tidally dominated regions the periodic divergence maintains a mean lead (open water) area of-2-5%. This increased lead fraction implies an increase in area-averaged winter ocean-toatmosphere heat exchange rate of-4-10 W m '2 and an increase in salt flux into the upper ocean as new ice forms in the leads.
A barotropic inverse tidal model for the Arctic Ocean
Geophysical Research Letters, 2004
1] We describe high-resolution (5-km grid) lineardynamics and inverse models of Arctic Ocean barotropic tides obtained with the OSU Tidal Inversion Software (OTIS) package. The 8-constituent dynamics-based model uses the latest ''IBCAO'' bathymetry, and open boundary forcing from the recent TPXO.6.2 global barotropic tidal solution. This model performs significantly better than the present benchmark Arctic tidal model (14-km grid) by Z. Kowalik and A. Proshutinsky, as judged by comparisons with $300 coastal tide gauges. The greatest improvements are found in the Canadian Arctic Archipelago, Nares Strait, and the Baffin Bay and Labrador Sea, and can be explained by the higher resolution of the new model in these topographically complex regions. The new Arctic inverse model assimilates coastal and benthic tide gauges and TOPEX/Poseidon and ERS altimetry for further improvements of the 4 dominant constituents M