Week 6: Diving Operations

An important part of our research  involves diving to perform experiments, to collect animals, and to measure environmental conditions.  While our team dives often, diving in the Antarctic is far from routine.  Each individual dive is handled by all involved with the utmost focus.  Diving in cold water, particularly under ice, carries with it many hazards and concerns.
When diving under ice, the first thing that needs to be done is to cut a dive hole in the sea ice (image 1).  Using a chainsaw, or an ice saw, and a breaker bar (a thick iron bar which can be used to break up ice), we set out to cut three dive holes (image 2, 3).  Because the dive hole is the only place that a diver can surface, it is  considered a good idea to cut more than one.  We cut two accessory dive holes on either side of the main one, as "emergency exits" should the divers become disoriented or should they need to surface immediately.  Then we shoveled lines of snow away in the shape of a giant asterisk with arrows pointing to the dive hole.  From  the air it must look not unlike those mysterious crop patterns that are found in England.  However because the snow on the ice blocks light from penetrating the water, from under the ice the backlit designs can be seen from deep in the water, directing the diver to the main dive hole.
 The most important part of any diver's gear is his or her SCUBA (Self Contained Underwater Breathing Apparatus).  This is the system of tanks, valves and hoses that allow a diver to be able to breathe air underwater.  In addition, for Antarctic divers the use of a dry suit is a must.  Early Antarctic divers used wet suits, and their dives were consequently short and very uncomfortable.  With the advent of compressed neoprene and vulcanized rubber suits, it was possible to create a suit that excluded water, and so the body could be insulated from the seemingly infinite heat sink that is the Antarctic Ocean.  So our divers would spend a good half an hour gearing up.  They  put on, in order, thermal polypropylene underwear, fleece underwear, layers of socks or thermal booties, the neoprene dry suit (image 4), hand insulation (usually wool or polypropylene glove liners),  rubber gloves, wrist sealers, and finally, the dive mask.  The suit has weak points, places that are prone to failure.  Perhaps the most common site of failure are the hand coverings.  Because they are not continuous with the suit, the seal that keeps water from flooding the gloves is the most common place for water leakage.  Many of our dives ended with the divers coming out of the water with numb hands.  The suit doesn't flood because of an effective seal around the wrists that keeps water out of the suit.  A neck seal also keeps water from leaking in around the neck.  Finally the dive suit's zipper is a weak point of concern.  If it fails, the whole suit floods and the diver is in some serious trouble.  However, great care is taken to keep the zipper in good condition and the suits are checked for leaks regularly.
  Now it was time to put on the SCUBA gear (image 5).  The gear we use consisted of a single air tank which was connected to two separate regulators.  One is used as a back up, should the first fail.  Because of the physics of air decompression, regulators are particularly prone to malfunction in extremely cold water, such as that found in the Antarctic.  So it is important to have a back up system.  The regulators are each connected to a separate hose that runs to a mouth piece. There is also a hose that runs from the regulator directly into the suit.  The diver can use the air in the tank to inflate the suit with air, creating a little more insulation within the suit from the frigid water.  Because the suit is water tight, it is also airtight, so when it is put on, air gets trapped in the suit, making the diver buoyant.  Regulating buoyancy is a concern to divers because if a diver ascends from the deep too fast, he or she will experience nitrogen bubbling out of his or her blood.  This condition is commonly referred to as the bends.  There is no treatment for the bends on station, so prevention is the key.   Divers who use dry suits must use a weightbelt to counteract the buoyancy.  The suit also has a set of venting valves that the diver can use to release air from the suit if he or she feels that the suit is too buoyant, even for the weightbelt.  The goal is for the diver to remain as close to neutrally buoyant as possible.   Each SCUBA system is equipped with a set of gauges and a small computer so the diver can keep track of depth, air reserve, and time spent underwater.   All of this data is important particularly when diving under ice, where it is impossible to just head straight up to the surface in an emergency (the divers must allow for enough time to swim back to the dive hole).  All told the divers weigh approximately twice as much with all the dive equipment on.
 Once suited up, the divers must carry themselves, weighing three hundred and fifty pounds or more, to the dive hole.  This is difficult, when foot deep snow lies between you and the dive hole.  While the divers are suiting up, the tenders (Mario and I) go to the dive hole, clear away any ice that formed over it over night, and lay a down line.  The down line is a rope that is dangled from the surface and serves as a marker for the divers, and provides them with something that they can attach their tether to.  Diving under ice requires the divers to be tethered to the surface.  Otherwise, if the divers lose their way, or become disoriented and lose sight of the dive hole, they are in serious trouble.  Open water diving carries none of these concerns, as the divers can surface wherever they want to.  At the dive hole, the equipment is checked by both the tenders and the divers.  The tenders then help the divers into the water (image 6, Image 7), and the divers swim out of sight.  In the mean time, the tenders nervously wait around the dive hole, keeping the dive hole clear of ice and debris, and, when it warranted, keeping a watchful eye out for leopard seals.  Usually we would bring snacks with us, some nuts, or beef jerky or dried fruit.  Something to pass the time (image 8).  Waiting for the divers to come back up felt like an eternity at times.   We can only imagine what is going on beneath our feet (see "Going Under in McMurdo", by John Pearse). After about twenty to thirty minutes, we see groups of bubbles at the surface, a telltale indicator that the divers are on their way back to the surface.  We prepare for them by clearing away any equipment from around the dive hole.  The divers surface and hand us their bag of goodies (usually animals that they had collected).  Then the tenders help the divers heave themselves out of the dive hole.  Usually the tenders would then bring all the equipment back to the dive locker, following behind the divers.  The divers must get back to the dive locker soon after leaving the water.  Despite the copious measures taken to insulate them from the water, they still experience mild hypothermia (a lowering of the body's core temperature), and so it is very important that they get out of their suits and into a warm shower as soon after the dive as possible.   Usually, one or more of the divers' gloves will have leaked, and so oftentimes the tenders will have to help the divers out of their cumbersome drysuits, their own hands too cold and numb.
 Open water dives are considerably less complicated.  Diving from a boat is much simpler than diving from shore, as the divers can gear up in the boat, and they don't have to swim out to the site of interest.  The only hazard that exists in open water diving is the presence of leopard seals.  This aggressive but graceful species has been known to threaten divers, who by comparison are clumsy and ungainly.  Our divers carried narrow piece of PVC piping, one end having been crafted into a sharp spear.  The weapon was dubbed the "leopard seal be cool tool"  It was the divers' only defense from a seal attack.  The primary defense against leopard seal attacks came from the surface.  The tenders always keep a watchful eye out as leopard seals surface frequently, particularly when they are hunting (this behavior is called spy-hopping).   If one is spotted, then the tenders will rev the boat engine as a signal to the divers to get out of the water.  We have been surprisingly lucky this season.  We only had one unconfirmed sighting during a dive.
      Despite all the potential hazards of diving here, we have completed a successful dive season, without a single mishap in the water.  Primarily due to the expertise of the divers (image 10) and the careful measures taken by the team, we have been able to collect the animals and take the measurements we need to complete our research project here at Palmer Station.