5 April, 2000
Question 46: How big do icebergs get?
The weather is only mildly windy and rainy today so our group got in a couple of dives in Hero Inlet, collecting a few target species of macroalgae that we were low on. With shore diving, the tenders watch from shore to make sure there are no problems and assist the divers in entering and exiting the water. It is much easier to put all of the equipment on when you are not standing in a rocking boat!
Before you put on your gear and hop into the water, you have to put your SCUBA unit together. The tank holds the supply of compressed air that you breathe while diving. We are not using any special mix of gasses. We are using single steel 95-cubic-foot tanks with Y-valves, that are filled with approximately 2400 psi of air.
The tank is cinched into the holder on the back of the buoyancy compensator (BC). The BC is worn like a vest over the dry suit. It holds all the equipment in place and can be filled with air to help us float at the surface. It has lots of D-rings and quick release snaps to attach holders and gear to. There is a hose over the left shoulder used to inflate and deflate the BC. I have my dive knife zip-tied there for easy access. To help take the BC on and off at the surface there are quick release clips on the shoulders. A large velcro cummerbund and aquick release clip attach the two sides of the BC together at the front.
The last and most important piece of gear that gets attached to the tank is the regulator (or in our case, regulators). A regulator is the piece of equipment that allows the diver to use the high pressure air from the tank; it both reduces the pressure and gives air to the diver on demand (only when you breathe in). There are two stages to the regulator. The first-stage has a yoke that attaches to the tank valve. The first-stage reduces the air pressure from the tank to 150 psi above the ambient (surrounding) pressure. This intermediate pressure air travels down the hose to the second-stage that is held in the mouth. The second-stage stops the air until the diver breathes in. When the diver inhales, it then reduces the air to equal ambient pressure.
The tank's Y-valve allows us to put two totally separate first-stage regulators on the tank. This reduces the danger of a first-stage freeze-up. Since each first-stage has a second-stage attached to it, we also have two second-stage regulators, a secondary (back-up) and a primary. Both stages of the regulator have air bleed systems to help keep the internal mechanics from freezing. If our regulators freeze, they will usually freeze open, bleeding lots of air rather than shutting off our air supply.
Also on the regulator are two power inflator hoses, one for the BC and one for the dry suit. They both inflate with air from the tank. The other attachment on one first-stage is the gauge console. This contains the instruments that measure how much air remains in the tank (Submersible Pressure Gauge), depth, direction (compass), and time. Our consoles have only two units. One is the SPG and the other is a dive computer that tracks all the other information and computes information about previous dives, current dive and possibilities for future dives.
Answer 45: Sea water in Antarctica does not vary much in temperature between summer and winter or with depth. South of 60 S, there is usually less than a 2 degree difference between seasonal temperatures. Throughout most of the Southern Ocean there is only a 4-5 degree difference between the deepest depths and the surface. The water is usually within the range of 2.0 to -2.0 C. Ice temperature (always below freezing) at the surface tends to be colder as it is exposed to winter air temperatures while the underside of the ice is near the temperature of the sea water (-1.5 to -2.0 C).
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