During the experiment, CO2 will be supplied from large-capacity gas tanks mounted on a bespoke frame, lowered into place from the RRS James Cook at about 100m from the injection site in order to minimise disturbance. A sophisticated gas flow control system and acoustic communications will allow full control from the ship.
Also mounted on the frame are cylinders containing the tracer gases that will be mixed with the CO2 gas before delivery to the experiment. The experiment will require 3 tonnes of CO2 for the 3-week experiment – this may sound like a lot but it’s actually a very small amount. Averaged over the duration of the experiment it equates 214 kg of gas released per day, which is equivalent to less than 2 seconds’ worth of CO2 emissions during the takeoff of a jumbo jet.
The tanks have been assembled in the hangar at NOC, and will be filled with CO2 and the tracer gases a few days before the expedition departs.
The CO2 gas will be mixed with a cocktail of inert, non-toxic chemical tracers prior to its release: Kr, SF6 and C3F8. CO2 is quite a reactive compound in the marine environment, which makes it challenging to differentiate between natural variability and a leak, especially when the leak is small. The addition of chemically distinct tracers to the released gas provides a failsafe for detecting and tracing the fate of the CO2 released during the experiment.