David G. Browning
Browning Biotech, 139 Old North Rd., Kingston, RI 02881
Robert H. Mellen
Kildare Corp., New London, CT 06320
Sound is the primary method of communication in the ocean. The absorption of sound in seawater limits the range and fidelity of communication. This absorption is due to three chemical relaxation mechanisms which, of course, would vary with any change in their constituents, such as sulphur, magnesium, or carbon; or any environmental parameters such as temperature. At the low frequencies (below 1 kHz) required for long-range communication, the principal absorption mechanism is also a pH-dependent buffered boric acid reaction. In turn, the pH in the ocean is controlled by the amount of dissolved carbon dioxide. All these factors could vary during the Earth's evolution. Estimates are made of the possible changes in absorption and, hence, ocean communication conditions over the ages, based on the evolution of ocean as put forth by Holland [H. D. Holland. B. Lazar, and M. McCaffrey, Nature 320, 27--33 (6 March 1986)] and others, with emphasis on the time scale, approximately 50 million years, of ocean mammal development.