Nella Dan: ADBEX II Cruise - Hydroacoustic krill survey data

• Other Authors: AADC (originator), AU/AADC > Australian Antarctic Data Centre, Australia (resourceProvider)
• Format: Dataset
• Language: unknown
• Published: Australian Ocean Data Network
• Subjects: biota; oceans; ANIMALS/INVERTEBRATES; EARTH SCIENCE; BIOLOGICAL CLASSIFICATION; CRUSTACEANS; ARTHROPODS; DEVIATION; GEOPOTENTIAL; MARINE; OCEANOGRAPHY; PRESSURE; SALINITY; SAMPLES; TEMPERATURE; VOLUME; SHIPS; AMD/AU; CEOS; AMD; OCEAN > SOUTHERN OCEAN; GEOGRAPHIC REGION > POLAR; Antarctic; Southern Ocean; The Antarctic; Antarc*; Antarctica; Euphausia superba
• Online Access: https://researchdata.ands.org.au/nella-dan-adbex-krill-survey/685638; https://data.aad.gov.au/metadata/records/ADBEX_II_hydro; http://data.aad.gov.au/aadc/pubs/get_pub.cfm?pub_id=2436; http://data.aad.gov.au/aadc/metadata/citation.cfm?entry_id=ADBEX_II_hydro

This voyage is one of six which are studying the abundance and disribution of Euphausia superba and other zooplankton. This provides a good coverage of the area at varying season times and conditions. Ship-board instrumentation: A Simrad echosounding system was used, comprising of an EK-38 echosounder operating at 38 kHz, and EK-120 echosounder operating at 120 kHz, a QD echointegrator and grey scale chart recorders. The EK-38 was only used intermittently. The echosounder transducers were hull mounted approximately 6m below the surface. An additional 120kHz transducer deployed from the stern by a towed body was used when the hull mounted transducer failed. The towed transducer system was deployed at a nominal depth of 30m. Data collection: Three transects were made, in a north-south direction. The 120kHz echosounder was run continuously while MV Nella Dan was in the study area. The QD integrator was set to integrate 8 depth layers between 1m and 200m below the transducer. The effective integration range was 60-230m. The echointegrator output, including the mean volume backscatter strength for each of the eight layers, was recorded on paper tape at the end of each 1 nautical mile integration interval. The mean target strength of krill were calculated from the lengths of the individual krill. Post-cruise processing: Acoustic data were processed on a VAX 11/750 computer. Mean density and variance of the mean were estimated using the ratio estimator, a process adopted at the second post-FIBEX acoustic workshop. Biomass was estimated for an area defined by a box drawn around the transects and extended on two sides by half the mean spacing between the transects. Mean krill biomass, variance of the biomass, and 95% confidence limits about the mean were calculated from the estimated mean and variance of the krill surface density. Please see the documentation reference for further details, and theoretical information. Data are logically consistent, as oceanographic data (CTD measurements) and water collections for phytoplankton pigment analysis were also obtained at the same sampling sites as the hydroacoustic surveys and the krill and zooplankton hauls. Cruise track was determined systematically before the commencement of the cruise, to eliminate any bias. This dataset contains hydroacoustic results from the Antarctic Division Biomass Experiment II (ADBEX II) cruise of the Nella Dan. This cruise is the third in a series of six cruises, performing a long term survey of krill and other zooplankton distribution and abundance. Australia was to have participated in the Second International Biomass Experiment I (SIBEX I), but withdrew due to resupply problems. ADBEX II is a reduced sampling program of what was to have been sampled during SIBEX I. Three transects were made off Antarctica in the Mawson region of the Australian sector, in January to March 1984, covering a survey area of 70,000 square kilometers. Quantitative and geographic krill distribution, abundance, mean and variance of the krill weight density, and total krill biomass were obtained. Biomass estimates for ADBEX II are given as 3.5 million tonnes, obtained by extrapolating over the survey area used on the SIBEX II cruise (1.28x10^6 square kilometers). Temperature, nutrient and salinty data were also obtained, as well as trawl results. Summary results are listed in the documentation. The fields in this dataset are: pressure temperature salinity volume geopotential samples deviation