Arrest of deep scattering layer migration by a positive thermal gradient

Abstract

LIGHT and temperature are considered to be the factors that influence did vertical migrations of populations of biological sound scatterers (deep scattering layers) in the sea^1–3. While light is probably the most important, temperatures which surpass the physiological tolerances of the organisms should play a major role in setting vertical limits. With positive thermal gradients (temperature increasing with depth) as are found in arctic and sub-arctic seas, sufficiently low temperatures near the surface could limit the evening ascent. This situation was observed in March, 1966 over the Kurile Trench along the eastern coast of the Kamchatka Peninsula (50°30′N, 162°30′E), an area influenced by the Oya Shio current system. Data were collected from USNS Charles Davis; acoustic records were made on a Westrex MK 10A Precision Depth Recorder using a Gifft transceiver to drive a hull-mounted UQN transducer at 12kHz. The records were made on the 1.5-s sweep scale of the recorder.