[1] A fully three-dimensional nonlinear primitive equation ocean model is applied to study the semidiurnal internal tide in the South Brazil Bight under summer conditions. Along the shelf break and upper slope of this region, the upper layer (0-600 m) is occupied by the southward flowing Brazil Current. Several numerical experiments were conducted to investigate the generation and propagation of the M 2 internal tide. Using horizontally homogeneous and vertically stratified density fields, internal tides were generated over the whole Bight with a clear signal on the continental shelf. When a more realistic summer stratification was considered, a baroclinic jet, representative of the Brazil Current, developed and comparisons between current observations and modeled results were improved. This jet acts as a barrier to the coastward propagation of the internal tide generated over the slope, reflecting it back towards the open ocean. On the negative relative vorticity side of the Brazil Current, located over the shelf, internal tides are trapped, enhancing vertical current variability and, hence, tidally induced mixing. The results highlight the importance of considering background flows when investigating internal tides in regions of strong along-slope baroclinic flows such as western boundary currents.

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The role of seamounts in the formation and evolution of sea ice is investigated in a series of numerical experiments with a coupled sea ice±ocean model. Bottom topography, strati®cation and forcing are con®gured for the Maud Rise region in the Weddell Sea. The speci®c¯ow regime that develops at the seamount as the combined response to steady and tidal forcing consists of free and trapped waves and a vortex cap, which is caused by mean¯ow and tidal¯ow recti®cation. The enhanced variability through tidal motion in particular modi®es the mixed layer above the seamount enough to delay and reduce sea-ice formation throughout the winter. The induced sea-ice anomaly spreads and moves westward and a ects an area of several 100 000 km 2 . Process studies reveal the complex interaction between wind, steady and periodic ocean currents: all three are required in the process of generation of the sea ice and mixed layer anomalies (mainly through tidal¯ow), their detachment from the topography (caused by steady oceanic¯ow) and the westward translation of the sea-ice anomaly (driven by the timemean wind).

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Data collected from moored instruments, deployed over the southeastern Brazilian continental shelf during the summer and winter months of 2001, show internal tide activity near the shelf break. To help to elucidate the observations, a fully three-dimensional nonlinear primitive equation model is applied to simulate the regional barotropic and baroclinic tides. Two semidiurnal (M 2 and S 2 ) and two diurnal (K 1 and O 1 ) tidal frequencies are considered. Tidal surface elevations are relatively small over the whole modeled area, reaching maximum values of about 0.40 m for M 2 and 0.11 m for O 1 . Comparison between observed and computed tide elevation and Greenwich phase shows reasonable agreement. When the baroclinic response of the model is investigated, stratification is prescribed using summer and winter climatology data of potential density. In this case, the model response to summer and winter stratifications is very similar and internal tides are generated over the shelf break and slope, with vertical displacements up to 25 m, and seaward propagation. Modeled semidiurnal tidal ellipses agree well with winter and summer observations. Observed diurnal tidal ellipses in the middle of the continental shelf and close to the shelf break during summer show an intensification through the water column that could not be represented by the model. Estimates of the total baroclinic M 2 offshore energy flux are about 3.5 and 0.5 MW considering winter and summer stratifications, respectively. Although these quantities are three orders of magnitude less than that estimated for regions known for intense internal tides, they refer to offshore fluxes computed for a very small section of the southeastern Brazilian shelf. This is the first published investigation into internal tides in the southwestern Atlantic Ocean off Brazil.