Several years of continuous low-frequency underwater ambient noise data from 0.1 to 125 Hz have been made available for examination by the United Nations Comprehensive Nuclear Test Ban Treaty Organization. Narrow-band noise time records between 0.5 and 10 Hz were selected for study, chosen deliberately to address noise sources tied primarily to the environment. Power spectra of the variable narrow-band time records were found to display sharp spectral lines at fluctuation frequencies that match lunar and solar diurnal and semidiurnal ocean tides.