Spatial heterogeneity of the bioluminescence field of the tropical Atlantic Ocean and its relationship with internal waves

Abstract

Field research was conducted during a number of cruises (1982-1986) to the western part of the tropical Atlantic Ocean. A survey taken in summer of 1985 was selected for detailed evaluation because it consisted of: (1) transects, based on continuous bioluminescence records made when the vessel was underway, (2) drift stations with simultaneous measurements of bioluminescence (110 m depth), temperature, salinity, density and current profiles (1000 m depth) and (3) 4 buoy stations with current and temperature autonomous recorders. Spectra of bioluminescence fluctuations obtained from continuous records have a number of peaks, most of which developed at 12 to 13, 8 and 5 km wavelengths, and, in the vertical bioluminescence structure, heterogeneities ranging in size from 10 to 50 m were registered. These horizontal and vertical scales correspond to the scales of the near-inertial gravity waves, which were observed in data from the buoy stations, and vertical current and density profiling. The waves behave as quasi-stationary fluctuations, generating the conditions for aggregation of the bioluminescent organisms along the horizontal and in the vertical planes. The concept that the origin of fluctuations in bioluminescence is to be found in near-inertial gravity waves also explains the latitudinal effect of the changes in variance of the size and dispersion of bioluminescence heterogeneities averaged latitudinally over 5°intervals over the Tropical and Subtropical Atlantic Ocean.