Every evening, immense numbers of ocean animals rise toward surface waters and descend again before daylight. Discover how sonar exposed the deep scattering layer, why predators and light help drive diel vertical migration, and how this daily movement carries carbon and energy through the ocean. Inside this episode: - The false bottom that appeared on early sonar - Which animals form moving scattering layers - Why many migrants rise at night and descend by day - How migration contributes to the biological carbon pump - What modern water-column sonar reveals Sources include NOAA Ocean Exploration, NOAA water-column sonar records, NOAA Ocean Service material, and peer-reviewed research on vertical ocean ecology. This episode is a researched narrative summary. Historical records may be incomplete, translated differently, or interpreted differently  ...