Measurements of Diurnal Changes in Bioluminescence From the Sea Surface to 2,000 Meters Using a New Photometric Device1

At stations in the western and central North Atlantic Ocean, the transparency was found to change with depth in the upper 300 m and to be very high in the strata below. Using 3 photomultiplier photometers, the rate of light diminution during the sunset period was shown to be essentially the same at the surface, 100, and 300 m. Using a newly designed light‐tight agitator, which pumps water past the window of the deep‐sea photometer, luminescent flashing was recorded from the surface to depths as great as 2,000 m in both day and night tests. Some luminescence was detected at all depths during the day at certain stations. At night, Flashing increased very greatly in the upper 50 m, considerably at 200 m, and somewhat at intervening depths. Changes in luminescence with depth, sometimes abrupt, occurred at widely varying levels between 40 and 85 m at different stations, usually near the thermocline, and always associated with vertical temperature changes. Netting placed over the intake of the agitator showed that most of the luminescent organisms in the upper few hundred meters were smaller than 0.24 mm. Additional tests with the unrestricted photometer indicated that much of the luminescence recorded at greater depths was from larger animals.