Structure of the Mediterranean Undercurrent and Mediterranean Water spreading around the southwestern Iberian Peninsula

Abstract

[1] RAFOS float and hydrographic data are analyzed to investigate the pathways, rates, and mechanisms of Mediterranean Water (MW) spreading into the North Atlantic from the Gulf of Cadiz, with an emphasis on processes other than meddies. We find that the transition of the Mediterranean outflow from a density current to an intermediate-depth jet occurs as it enters Portimao Canyon south of Portugal due to rapidly steepening topography and associated turbulent entrainment. This feature was not seen in recent plume model simulations due to their use of smoothed topography. In addition to the traditional lower salinity maximum (or core), a denser, deeper continuous vein of MW was also traceable from Portimao Canyon to Cape St. Vincent. The mean velocity structure of the Mediterranean Undercurrent changes from a ∼30-km-wide jet with peak mean westward speed of ∼0.2 m s−1 along the southern Iberian slope, to a broader, much weaker northward flow with maximum mean speed of only ∼0.06 m s−1 along the western Iberian slope, due in part to changes in the bottom slope. Lower core MW spread mainly (1) southward into the interior Gulf of Cadiz, (2) northward along the western Iberian slope, and (3) westward into the deep Tagus Abyssal Plain. The average spreading rate was 0.01–0.02 m s−1 toward the west–northwest direction. Meddies forming near the slope were found to have an indirect but profound impact on MW spreading, often diverting MW approaching from upstream into the interior. The results are compared to recent hydrography-based studies of MW spreading pathways.