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Abstract
Modelling tides in the southern Weddell Sea: updated model with new bathymetry from ROPEX(ROPEX) Laurie Padman Robin Robertson Keith Nicholls A significant fraction of the total oceanic kinetic energy in the southern and western Weddell Sea is supplied by tidal currents [Robertson et al., 1998: denoted "RPE-98"]. The region of strong tides includes the ocean cavity under the Filchner-Ronne Ice Shelves (FRIS), and the adjacent broad southern continental shelf and upper slope. The spatial distribution of tidal energy was estimated using a finite-difference barotropic ocean model as a prelude to investigating the effect of tides on other processes of general climate and glaciological interest. Tides have been shown to play a significant role in the formation of dense, High-Salinity Shelf Water (HSSW), Weddell Sea Bottom Water (WSBW), and Antarctic Bottom Water (AABW). HSSW formation is enhanced by the working of the winter sea-ice pack by tidal shear and strain, and by the increase in mean open water percentage due to periodic tide-forced ice divergence (see, e.g., Foldvik and Gammelsrød [1988]). WSBW and AABW are formed by the mixing of dense shelf water types with Warm (or "Weddell") Deep Water Modified Warm Deep Water (WDW and MWDW) at the shelf/slope front: mixing rates increase near locations where baroclinic tides and other internal gravity waves are generated, very often near the shelf break. Processes under the FRIS are also influenced by tides. The frictional stress caused by tidal currents flowing under the ice shelf causes mixing of the HSSW up to the base of the glacial ice, leading to melting of the ice base and formation of Ice Shelf Water (ISW). This water type is very cold but relatively fresh, and ultimately contributes to WSBW and AABW formation after the ISW leaves the FRIS cavity, flowing primarily through the Filchner Depression, to the shelf break. Tidal currents are, however, very sensitive to bathymetry, both total water depth (or water column thickness under ice shelves), and bottom slope. Depth data are sparse throughout much of the western and southern Weddell Sea, hence our ability to model tidal currents may be quite poor in these areas. In this paper our primary aim is to show how modelled tidal currents in the southern Weddell Sea are modified by the inclusion of new bathymetric data collected during the Ronne Polynya Experiment (ROPEX), which was carried out from the Royal Navy ice-strengthened hydrographic vessel, HMS Endurance, in January and February 1998. |
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