Abstract: The dependence of 2.9 and 6.8 kHz sound absorption on pH of the B（OH）₃/CO₂/Ca/ NaCl, B（OH）₃/CO₂/Ca/Mg/NaCl and Mg/CO₂/Ca/NaCl systems has been measured using the cylindrical resonator method. Tht concentration of each constituent in these systems was equal to that in Lyman and Fleming sea water. Measurements were made at atmospheric pressure and 12.4℃. Results show that the B（OH）₃ relaxation frequency is independent of pH for the pH range of the ocean. It seems clear that there is another low frequency relaxation due to MgHCO₃⁺ in the B（OH）₃/CO₂/Ca/Mg/NaCl system. The MgHCO₃⁺ relaxation frequency in this case has been found to be about 3.5 kHz. The measured relaxation parameters of the B（OH）₃, MgCO₃ and MgHCO₃⁺ relaxations for various systems are given in table.