The determination of pH sub(T) in the equatorial Atlantic Ocean and its role in the sound absorption modeling in seawater

The observations carried out during the CITHER 1 cruise (January-March 1993), part of the WOCE Hydrographic Programme, enable a detailed description (3600 analyzed water samples) of the distribution of the pH sub(T) in the Atlantic equatorial belt with a precision of plus or minus 0.003 pH sub(T) units. They show a minimum of pH sub(T) < 7.75 at 400-500 dbar associated with the vertical oxygen minimum characteristic of the equatorial zone, and a maximum (pH sub(T) > 8.00) centered at 1900-2000 dbar, i.e. at the salinity and oxygen maxima level in the North Atlantic Deep Water (NADW). The results of pH sub(T) are used to propose a multiple linear regression directly connecting the pH sub(T) to the hydrological parameters and nutrients, which are more largely available than pH measurements. This is in order to extend the description of the pH sub(T) field to the whole tropical Atlantic zone (30 degree N-30 degree S), and thus, to provide a model of sound absorption at low frequencies (< 1 kHz) in the ocean, which depends on the pH with an uncertainty of about plus or minus 5% in the absorption coefficient for this oceanic area.