A new acoustically telemetering deep-sea photometer with some observations on underwater light in the northeast Atlantic

Abstract

A new deep-sea photometer that uses a silicon photodiode as a light sensor is described. The photometer is interfaced with the Institute of Oceanographic Sciences' net monitor, and it measures and acoustically telemeters underwater irradiance. Using the photometer in conjunction with the I.O.S. rectangular midwater trawls it is possible simultaneously to collect biological samples and measure irradiance at the depth of the net. The photometer has measured light to a depth of 700 m in the northeast Atlantic. It records at least seven decades of irradiance and its response is independent of temperature between −3 and +30°C. Measurements of the attenuation coefficient at various stations agree with previous results, and observations are presented on the effects of cloud cover on underwater light. A biological sampling programme using the photometer is described. Preliminary analysis of the samples suggests that different animal populations inhabit different light regimes.