The determination of pH(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, in the Atlantic equatorial belt with a precision of +/-0.003 pH(T) units. They show a mini mum of pH(T) < 7.75 at 400-500 dbar associated with the vertical oxygen min imum characteristic of the equatorial zone, and a maximum (pH(T) > 8.00) ce ntered at 1900-2000 dbar, i.e. at the salinity and oxygen maxima level in t he North Atlantic Deep Water (NADW). The results of pHT are used to propose a multiple linear regression directly connecting the pHT to the hydrologic al parameters and nutrients, which are more largely available than pH measu rements. This is in order to extend the description of the pHT field to the whole tropical Atlantic zone (30 degreesN-30 degreesS), and thus, to provi de a model of sound absorption at low frequencies ( < 1 kHz) in the ocean, which depends on the pH with an uncertainty of about +/-5 % in the absorpti on coefficient for this oceanic area. (C) 2001 Elsevier Science B.V. All ri ghts reserved.