Day 2: Pings, rosettes and sea dust
By Greta Creed
This transit voyage from Brisbane to Darwin has a number of amazing projects on board. The primary aim of the voyage is to relocate the ship to Darwin ahead of the next research voyage, but this doesn’t mean there isn’t science on board, quite the opposite! The Chief Scientist on this voyage will be collecting geophysical data to explore the continental slope of the Great Barrier Reef. Four areas, known to have submarine canyons and landslides, will be surveyed in greater detail. The research is being led by Principal Scientist Dr Robin Beaman (James Cook University). Sea floor measurements are occurring continuously, with the ‘pings’ of the monitoring equipment clearly audible on the lower decks of the ship.
CTD being winched up onto the RV Investigator. Image: Greta Creed
After RV Investigator left Brisbane, the ship first stopped in deep waters to the east of Fraser Island. Here, the CTD (conductivity, temperature and depth) rosette was deployed as part of work led by Dr Dirk Erler (Southern Cross University). This project’s objective is to obtain the first measurements of the isotopic composition of nitrates and nitrous oxides. This will assist in filling in knowledge gaps about the nature of nitrate upwelling in the Coral Sea. The rosette has 24 bottles designed to collect water samples at multiple depths. The CTD rosette was launched at night and was spectacular with the ship’s lights illuminating the initial stages of the descent of the rosette into waters more than 3 kilometres deep, and its subsequent return. Four further CTD collection sites are scheduled in shallower waters along the Queensland margin.
Peter Hughes, CSRIO MNF Hydrochemist taking water samples from the CTD.
Another project piggybacking on the launch of the CTD is Trichodesmium sampling. Trichodesmium (‘sea dust’) forms slicks on the ocean surface. Many slicks were apparent as RV Investigator sailed past the Sunshine Coast. Some are so vast they are visible on satellite imagery. Despite being widespread, little is known of the organism responsible. Samples are being collected in a plankton net at each of the five scheduled launches of the CTD rosettes. Samples are also being retrieved from the CTD’s surface Niskin bottle to facilitate culturing and genetic analysis of the Trichodesmium microorganism. The Educator on Board team and others have been trained in the collection and storage of these samples.
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