Hydrography of the Pontevedra Ria: Intra-annual spatial and temporal variability in a Galician coastal system (NW Spain)

In order to ameliorate the dearth of existing scientific knowledge concerni ng the hydrography of the Pontevedra Ria, a systematic investigation was ca rried out between October 1997-98. Salinity variations were closely related to river discharge whereas bottom waters presented oceanic characteristics over the whole year. Current was controlled by tide, river discharge, and wind in the internal ria where the highest velocities were directed along t he ria channel with a low transverse component. Favorable atmospheric condi tions in spring induced coastal upwelling up the continental shelf. In May the upwelling was sufficiently strong to be detected in the inner ria and i ntensified in July and August, cooling the ria water to 12 degrees -14 degr eesC. Upwelling ceased in September, and from November to March seawater tr ansported by the poleward current (35.9; 15 degreesC) was detected on the s helf. From January until March, unanticipated favorable upwelling condition s provoked an influx of poleward inside the ria. Ria intrusion of poleward water and association with occasional winter upwelling conditions has not b een observed previously. Isopycnic three-dimensional (3-D) surface and 2-D isopycnal maps show that with high river runoff or intense upwelling, lower -salinity water leaves the ria near the northern margin in the surface laye r. Under negative upwelling conditions, the water is partially dammed insid e the ria and exits the ria when the wind speed falls. During upwelling eve nts, ENACW penetrated the ria, especially near the southern shore. Arrival of ENACW at the northern entrance impedes the outward water flow through th is mouth.