Side and moon pool deployments from the RSV Nuyina
Deploying equipment over the side (or stern) of the ship works well in the open ocean and in good weather. But when the weather is particularly rough, or the ship is in sea ice, some research has to stop. But not anymore.
The moon pool is a 13 metre vertical shaft, four metres square, which runs from the science deck, through the ship’s hull, to the open ocean. When its top and bottom hatches are opened the moon pool allows the deployment of equipment such as CTDs (conductivity, temperature and depth instruments), nets, underwater vehicles and other instruments, within the relative comfort and protection of the ship.
CTDs will regularly be deployed from the icebreaker through a side door or the moon pool. These metal rosettes contain up to 36 12-litre plastic bottles and are used to collect water samples at different depths, up to 6500 metres. The rosette is lowered by a cable from a door out over the side of the ship (or down through the moon pool) to the required depth – usually to the bottom. As the rosette descends and ascends over a few hours, a remotely triggered device allows the water bottles to be closed selectively, so that samples of water are collected from different depths. These water samples are then analysed to provide oceanographers with information about the physical and chemical properties of different water masses.
Using CTDs and other water profiling instruments, scientists have been able to observe that the Southern Ocean is warming, freshening, become less oxygenated and more acidic. These measurements are important for understanding the response of the Southern Ocean to climate change and changes in its ability to take up heat and carbon dioxide, which in turn will affect local and regional climates.
Trace metal rosettes have a similar setup to CTDs but are prepared for deployment in a very clean environment, free of trace metals such as iron. They are used to study elements that exist in very low (trace) amounts in the ocean, and that are important for biological and chemical processes – iron, for example, is critical to the growth of phytoplankton.