Mixing analysis of nutrients, oxygen and dissolved inorganic carbon in the upper and middle North Atlantic ocean east of the Azores

In this paper the distribution of nutrients, oxygen and dissolved inorganic carbon are given along two perpendicular sections in the Northeast Atlantic, between the Azores Islands and the Iberian Peninsula. A mixing model has been established based on the thermohaline properties of the water masses using data from this study and other measured literature. It was found that the model explained most of the variability found in the distribution of the chemical variables. The model is validated using conservative parameter ‘NOʹ [Broecker, W.S., 1974. ‘NOʹ, a conservative water-mass tracer. Earth Planet. Sci. Lett., 23: 100–107]. A chemical characterisation of the water masses was performed using nutrients, oxygen, alkalinity and DIC and calculating the concentration of them in the previously defined end-members. From the thermohaline and chemical concentrations of the end-members, the mixing model can determine the chemical field within this and other oceanic areas with comparative and predictive accuracy. The relative variation of nutrient concentrations, due to the regeneration of organic matter, was also estimated. In addition, from the model residuals, the ventilation pattern described for North Atlantic Central Water (NACW) shows a north–south gradient associated with the subtropical gyre and the Azores Current.