| Summary: | 234 páginas [EN] This thesis analyses the hydrographic and chemical data collected during the 4x cruise carried out in summer 1997 within the World Ocean Circulation Experiment (WOCE) program and, named 4x as it repeated section 4 across the southern boundary of the Subpolar North Atlantic gyre sampled during the International Geophysical Year in 1957-58. The water mass structure, spreading and mixing in the Subpolar North Atlantic is analysed by means of an optimum multiparameter analysis. The proposed mixing model is proved to be reliable and robust. Some deficiencies are detected and discussed in the back-calculation technique more widely accepted to estimate the anthropogenic carbon (CANT) signal in the ocean. A new approach for estimating the preformed alkalinity (TA0) in the North Atlantic Ocean is suggested. We recalculate the CANT content in a section along the Eastern North Atlantic using this new TA0, the Mehrbach et al. (Measurements of the apparent dissociation constant of carbonic acid in seawater at atmospheric pressure. Limn. Oceanogr. 8, 897–907, 1973) CO2 dissociation constants, and including the effect of water vapor pressure on estimation of the pre-industrial pCO2. Our findings lead us to conclude that the CO2 disequilibrium when water masses are formed is small and not significant. Direct and indirect evidence based on available high-quality CO2 data taken in formation areas in late winter conditions support this argumentation. The circulation pattern across the 4x section is diagnosed using inverse methods. The flow is constrained with measured mass transports at specific sites, while conserving mass and salt for the region north of the section and forcing the silicate flux to the river input north of the section. The fluxes of physical (heat and freshwater) and chemical (nutrients, oxygen, alkalinity, total inorganic carbon and anthropogenic carbon) properties are estimated and decomposed into barotropic, baroclinic and horizontal components. Combining our fluxes with those across ...
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