A biological acoustic survey in the marginal ice-edge zone of the Bellingshausen Sea

An acoustic survey at 38 kHz was carried out from R.R.S. Discovery in the Bellingshausen Sea from 23 November to 7 December 1992 as part of the U.K. Joint Global Ocean Flux Study (JGOFS) Southern Ocean investigations [Turner D. and N. J. P. Owens (1995) Deep-Sea Research II, 42, 907–932]. A total of 285 targets were identified and described from the chart record of the echo sounder. Mean volume backscattering strength data were collected using an echo integration system. These data are used to describe the spatial and temporal variability of krill (Euphausia superba) distribution and biomass in the marginal ice-edge zone. Krill biomass density varied from a mean of 42 g m−2 during the first survey phase to 20 g m−2 on the second survey phase. The number of small swarms detected during the second phase was greater than during the first phase. On this first survey a large swarm (2.8 km in extent) had a potential biomass of 3.7 × 104 tonnes. Some calculations are presented to show the potential impact of krill on the flux of carbon in the area of the survey