Diving under the ice at Casey
This season sees a significant diving program at Casey to assist the Free Ocean CO2 Enrichment (FOCE) project. Antarctic scientific diving under ice may be perceived as risky, but with appropriate planning, equipment, procedures, training, and highly skilled personnel, the risks can be mitigated. The weather needs to be at the better end of the spectrum, with low winds otherwise the divers and tenders would be at greater risk of hypothermia. Entry into the water is via a 90 cm holes cut through the ice by a hydraulically driven brace-and-bit auger. A cloverleaf pattern of three holes is used with one of the holes cut about half depth, so a step is created to facilitate entry and exit. An additional single hole is cut about 15 m away as an emergency exit point.
Antarctic divers require a minimum of ADAS part two (30 m surface supply air) professional diving qualification. Many have part three (50 m) and additional diver medical technician training, the latter so they can manage emergencies if they occur. Divers wear dry suits with inner thermals to insulate from the -1.8°C water. Paradoxically, the effort of getting into the suit often causes them to be excessively warm. Because of the complexity of the dive gear and need for backup redundancy, each diver has a surface attendant to assist with gearing up. In addition, their 'three finger' gloves significantly impair dexterity. The dive supervisor checks and rechecks the gearing up process, and supervises the panel, which delivers air to the divers and also provides communications and direction to the divers via a long bundled 'umbilical'. The umbilical carries primary air supply hose, communications cable, a strong cord for tethering and a further air hose known as a pneumo. The umbilical is the diver’s life-line, and link to the surface.
Once fully kitted in their dry suit, Antarctic divers then don the rest of their gear. This includes a weight belt, buoyancy compensator vest including accessory air supply (via a separate cylinder and regulator), additional integrated weights, fins and a full face mask. The mask doesn't have a traditional scuba mouthpiece, but contains almost a mask within a mask that covers the nose and mouth. This is called an oronasal flange and permits the diver to talk with the surface supervisor. Messages are relayed from the surface through a speaker over one ear. The vest and mask are connected to the umbilical for air supply. The kit weighs as much as 35 kg, making it very difficult to move on land, let alone ice. Assistance from a tender is essential, as the centre of weight is behind the diver. Once fully kitted, divers become quite worn out and hot. Time to enter the water! The only way in is via the hole in the ice, one at a time, assisted by their tender - they sometimes need to get on all fours for the entry.
In the water, the effect of gravity is suddenly removed and the divers have a new sense of freedom but a very real perception of the intense cold. Despite its stunning clarity, the water is quite dark under the ice. Now their professional training and experience comes to the fore. Their gear is complex to operate, and on occasions, may not function properly due to the temperature. They continue close communication with the dive supervisor. They have practiced emergency procedures, and they have back up air supplies and buoyancy. Divers maintain strict buoyancy control so as not to disturb the bottom. They dive well inside established dive table no-decompression time limits to increase their safety margin, and prevent decompression illness (DCI). A backup recompression chamber is available at Casey station, but the diving process is directed at preventing DCI, maintaining safety and diver health. Hypothermia is always a risk, and diver status is carefully monitored by the supervisor. They undertake their assigned tasks methodically.
After completing their work, divers return to the surface and briefly stop at three metres on a 'safety stop', before exiting via the ice hole (see photo below). Their tethering to the surface via the umbilical is a key safety component. Not only does it provide their air supply and communications, but it allows direct return to the ice hole. Out of the water, all of the weight returns and their tender assists them back onto the ice. Their gear is removed, and out of their drysuit they quickly dress in their multilayered clothing to prevent hypothermia. This has described just one dive in a series of many. Over coming months, there will be many underwater tasks to perform as they set up the apparatus for the FOCE project and collect samples. Divers are the operational endpoint of a huge FOCE team effort.
Associate Professor David Smart, Consultant Specialist in Diving Medicine