An oceanographic research was developed for the first time in the Northern Galician Rias, where hydrographical, biogeochemical and phytoplankton information was obtained in the Barqueiro Ria. Monthly cruises were carried out onboard the R/V Mytilus and R/V Lura from January/08 to January/09 in a fixed station located at 43°45,509' N and 07°39,493' W. Temperature and salinity profiles were measured with a General Oceanic Rosette, including a Sea-Bird 25 CTD with PAR and Fluorescence sensors. The water column was sampled using General Oceanic (5 or 12 L) bottles. Aliquots were collected at standard depths (0, 5, 10 and 20 m) from surface to near the bottom to analyze: (1) dissolved oxygen concentration and their saturation percentages using the Winkler method; (2) nutrient salts: nitrate, nitrite, ammonium phosphate, silicate, (3) organic matter: dissolved and particulate organic carbon and nitrogen, ( 4) chlorophyll-a and phytoplankton abundances. During the sampling period, the nutrient salts ranged between 0.0-6.1 μM for nitrate, 0.0-0.4 μM for nitrite, 0.1-2.8 μM for ammonium, 0.01-0.39 μM for phosphate and 0.3-5.7 μM for silicate, respectively. The higher value for nitrate and phosphate were found during winter, while higher levels of ammonium occurred in summer as result of remineralisation process. The annual cycle showed an spring bloom with the higher levels of chlorophyll (up to 2.2 μg Chl-a·L·') and primary production close to 17 mg C m·2·h·1); an autumn bloom was also observed were primary production reached the maximum values (19.7 gC·m·2·h·1). The physical, chemical and biological process in the Barqueiro Ria were mainly controlled by the ocean influence as the fluvial contributions were low: the Sor River (annual average flow of 6.0 m3·s·1; -.6 m3·s·1 for the year 2008) levels of nutrient salts were in the range of 27-90 μM for dissolved inorganic nitrogen, 0.01-0.29 μM for phosphate and 64-111 μM for silicate respectively. Therefore, and according to available information, four oceanographic periods can be defined in that Northern Galician Ria: spring, summer stratification, autumn and winter mixing. Moreover, nutrient values, Chl-a, primary production and phytoplankton abundance for productive periods were lower than those reported for the Middle (exemplified in the Corme-Laxe Ria) and Western Rias (i.e. Arousa Ria), and in the range of those reported for the Cantabrian shelf

This communication is a contribution to the research project CTM2007-62546-C03-0l/MAR (CICYT): Influence of metheorological forcing, land geochemistry and estuarine zone in the hydrodynamic, biogeochemical cycle of trace metal and rare earth and plankton transport in the .Vorthern Galician Rias (NW Sapin). (acronym: INTERESANTE)

XII International Symposium on Oceanography of the Bay of Biscay, Brest, France, 3-6 May 2010

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