Over the past 50 years, polar diving has yielded a wealth of scientific information and proven to be an indispensable sampling and observational technique. Despite technological advances, exclusively mechanical or remote methods cannot replace divers in the water under the ice. Ice diving is both politically and scientifically interesting and has received international research funding in the fields of medicine, physiology, fisheries and ecology. Basic climate-change research focuses on polar regions because of their global importance.
Preparation
Dedicated ice-diving equipment and specialized training of divers, dive supervisors and medical personnel must feature prominently in the operational logistics of ice diving. Traditional models of dive planning do not transfer well to extreme-environment diving; the margins of error are much narrower. Treating ice-diving operations as remote-environment activities and taking extra steps to prepare for managing decompression illness increase the probability of successful diving missions. Gas-management and emergency-response planning in extreme-environment diving require special consideration — not unlike that required in cave, rebreather or wreck diving.
Diving under polar ice is an obvious example of extreme-environment diving because of the many physiological, equipment-related and training parameters that affect divers. Regulator performance and thermal protection are two principal concerns. In polar regions there is a chance that first- or second-stage scuba regulators will malfunction due to the accumulation of ice in or around the regulator, resulting in complete occlusion of air flow or a massive free-flow that could rapidly expend a diver’s air supply. Factors that influence the likelihood of regulator freeze-up are design and configuration (determined by the manufacturer), quality control (unique to the individual regulator), depth (due to increased gas density), mass flow (a product of depth and respiratory volume), water intrusion, time and temperature. Most free-flow problems occur in second stages, which means careful predive management is essential. Regulators must be kept warm and absolutely devoid of any residual fresh water. Not breathing from the second stage prior to immersion prevents moisture from a diver’s breath from crystallizing on the low-pressure seat, which is a trigger for further ice accumulation and free-flow.
Minimum ice-diving qualification criteria that have proven effective in scientific diving include at least a year as a certified diver, 50 logged open-water dives, 15 logged drysuit dives and 10 logged drysuit dives in the preceding six months. Unpacking a new drysuit for the first time on a liveaboard vessel is not considered good preparation; ice divers must become proficient with the gear and techniques that will be used prior to their deployment on ice-diving expeditions.
Equipment
Divers should be equipped with two fully independent regulators attached to an adequate gas supply whenever they dive under a ceiling. Proper use and pre- and postdive care substantially improve the reliability of regulators. A large volume of air exhausted rapidly through a regulator will almost certainly cause a free-flow. Drysuit inflator hoses are also subject to free-flows and are attached to backup regulators in case the air supply to the primary regulator must be turned off to stem the loss of air. When inflating a drysuit or a BCD, use frequent short bursts of air. The primary cause of regulator free-flow is entry of water into the mechanism and the water freezing once the regulator is used. Fresh water in a regulator from rinsing or melting snow may freeze as soon as the regulator is submerged in seawater or when it is exposed to extremely cold air temperatures. If multiple dives are planned, postpone freshwater rinsing of the regulator until all the day’s dives are completed.
Drysuit fabric (vulcanized rubber, crushed neoprene or trilaminate) depends on the diver’s preference, the requirements for range and ease of motion and the available options. The choice of drysuit underwear is perhaps more important than the choice of drysuit material because it is the underwear that provides most of the thermal protection. Many divers wear an under layer of expedition-weight polypropylene and an outer layer of 400g Thinsulate®.
Drygloves or mitts with inner liners (rather than wetgloves) are most commonly used with drysuits. Diving Unlimited International (DUI) zipseal drygloves see widespread use since they effectively permit the warm air that surrounds the rest of the body to also reach the hands at depth. Two disadvantages of dryglove systems are the complete lack of thermal protection if the gloves flood or are punctured and the related risk of flooding the entire drysuit.
Because a drysuit must be inflated to prevent suit squeeze with increasing pressure, it is most efficient to regulate buoyancy at depth by controlling the amount of air in the drysuit, which must be equipped with a hands-free exhaust valve. BCDs are considered emergency equipment to be used only in the event of catastrophic drysuit failure. This procedure eliminates the need to vent two air sources during ascent, reduces the chance of BCD-inflator free flow and simplifies the maintenance of neutral buoyancy during the dive. The main purpose of air in a drysuit, of course, is to provide thermal insulation.
Divers must wear sufficient weight to allow for maintenance of neutral buoyancy with a certain amount of air in the drysuit. Runaway negative buoyancy is as great a safety problem as an out-of-control ascent. Because of the amount of weight commonly worn (30 to 40 pounds) and the serious consequences of accidental release, weight harnesses are favored over weight belts.
Hazards and Emergencies
Extreme underwater visibility may make objects appear closer than they are; this illusion could entice divers to travel farther from the access hole than is prudent. The greatest hazard associated with fast-ice diving is the potential loss of the dive hole. Access holes, leads and cracks in the ice are often highly visible from below because daylight streams through them. However, dive holes may be difficult to see due to low light or from the holes being covered with portable shelters. Therefore, a well-marked down line is required for fast-ice dives. Divers should maintain positive visual contact with the down line during the dive and take frequent note of their position relative to the access hole or lead. Problems requiring an emergency ascent are serious, since a vertical ascent to the surface is impossible except when a diver is directly under the dive hole or lead.
Pack ice is inherently unstable and its conditions can change rapidly, primarily from surface wind conditions. An offshore wind may blow pack ice away from the shoreline and loosen the pack, whereas an onshore wind may move significant quantities of pack ice against shorelines or fast-ice edges, obstructing what may have been clear access areas when divers entered the water.
As with diving in general, the best approach to ice-diving emergencies is prevention. Divers must halt operations any time they become unduly stressed because of cold, fatigue, unease or any other physiological reason. Similarly, terminate the dive in the event of equipment difficulties such as free-flowing regulators, tether-system entanglements, leaking drysuits or buoyancy problems.
To clearly mark access holes, divers deploy well-marked down lines, establish recognizable landmarks (such as specific ice formations) under the hole at the outset of dives, leave a strobe light, flag or other highly visible object on the bottom just below the hole or shovel surface snow off the ice in a radiating spoke pattern that points the way to the dive hole.
Physiological Considerations
Cold is the overriding limiting factor for dive operations, especially with regard to the thermal protection and dexterity of hands. Dives should be terminated before a diver’s hands become too cold to effectively operate gear or grasp a down line. This loss of dexterity can occur quickly (within 5 to 10 minutes if hands are not adequately protected). Holding onto a camera will increase the rate at which a hand becomes cold. Switching the housing from hand to hand or attaching it to the down line may allow hands to rewarm. DUI dryglove systems have greatly improved thermal protection of divers’ hands.
Heat loss occurs through inadequate insulation, exposed areas (such as the head in an insufficient hood arrangement) and from breathing cold air. Scuba-cylinder air is initially at ambient temperature and chills from expansion as it passes through the regulator. Air consumption increases as the diver cools, resulting in additional cooling with increased ventilation. Significant chilling also occurs during safety stops when divers movement is reduced. Polar diving requires significant insulation, which results in decreased mobility and increased potential for buoyancy problems — two challenges ice divers must address.
Besides the dehydrating effect of breathing dry air on a dive, Antarctica and the Arctic are extremely low-humidity environments (polar deserts) in which dehydration can be rapid and insidious. Continuous attention to hydration is required; urine should be clear and copious.
Diving at the Earth’s polar regions does not necessarily mean diving directly beneath the poles. At the South Pole you would find that after drilling down through more than a mile and a half of vertical ice, you would hit bedrock and still be hundreds of horizontal miles away from open ocean. If you delayed your North Pole trip for a few years, drilling through sea ice might not be required at all in the summer, given the observed reduction of up to 75 percent of Arctic sea-ice volume over the last 30 years. And it would be a long distance to travel for an open-water dive with a bottom depth of nearly 14,000 feet.
© Alert Diver — Fall Q4 2012