Patterns of bottom current flow deduced from dune asymmetries over the Gulf of Cadiz shelf (southwest Spain)

The analysis of dune-like morphologies on the Gulf of Cadiz continental shelf, using high-resolution seismic reflection profiles and sediment samples, reveals a well-defined distribution pattern controlled by the area's hydrodynamics. These bedforms are considered to be modern features from the Holocene, and therefore they provide information about the bottom circulatory patterns established over the continental shelf. Most of the submarine dunes have been identified over a shallow physiographic feature named the Barbate High. The current flows that generate the bedform fields can be attributed to a complex interaction of several hydrodynamic agents, in which the process of current direction reversal related to the tidal cycle in the Straits of Gibraltar seems to be involved. Eastward-oriented submarine dunes located on the onshore zones of the inner shelf are generated by the Atlantic inflow, which over these shallow zones is mainly orientated towards the east during high-tide conditions in the Straits of Gibraltar. Bedforms oriented westwards and west-northwestwards in the offshore zones indicate that a previously undescribed flow occurs on the Gulf of Cadiz continental shelf. This flow is attributed to the influence of ebb tidal currents, which move preferentially towards the west over these zones. As a result of this complex bottom flow pattern, a clockwise sand transport pattern over the Barbate High is established.