Detailed temperature–salinity distribution in the Northeast Atlantic from ship and Argo vertical casts

Abstract. The present study defines new interpolation functions for hydrological data. These functions are applied to generate climatological maps of temperature–salinity distribution with 25 m depth interval and 30 km space interval (MEDTRANS data-set). The data underwent a rigorous data quality control, having passed several filtering procedures. The gridding was done on neutral density surfaces, which allows better representation of the relative intensity of thermohaline fronts for the same gridding radius. The gridding was done using multi-pass Barnes' Optimum Interpolation procedure with spatially variable size of the gridding window. The shape of the window accounted for topographic influence: the dominant along-slope direction of water mass transport. One of the new features was the use of a local ratio of topographic to planetary β-effects to define the shape of the window as a function of the relative importance of the topographic influence. The N/f ratio was used for simulation of the baroclinic decrease of the topographic influence on water mass transport with the distance from the bottom. The gridded fields are available at the web-site of the Center of Oceanography of the University of Lisbon (http://co.fc.ul.pt/en/data). The new MEDTRANS climatology gives more details to the distribution of water characteristics in the Subtropical Northeast Atlantic, in particular near the Iberian Peninsula. The geostrophic currents relative to the 1900 m reference level demonstrate the local circulation features, in good correspondence to the theory and to previous studies: the acceleration in the meanders of the Azores current; the cyclonic gyre in the Gulf of Cadiz; the splitting and separation of the Mediterranean Water outflow from the continental slope near the Gorringe and the Galicia banks. Those features are not reproduced by the alternative climatologies. Seasonal climatologies, computed for the warm (May–October) and cold (November–April) seasons, revealed stronger zonal extension of the upper ocean patterns during the warm season, as compared to the cold one. At the Iberian continental slope, the seasonality manifested itself in more saline and denser lower core of the Mediterranean Water during the warm season as compared to the cold season.