Now for the "logistics"! Divers need to maintain "neutral buoyancy" while in the water. This means that they can "hover" at any desired depth; neither rising nor sinking except for the slight rise and fall that occurs as one breathes. Thanks to our understanding of Boyle's Law, we can do this!Boyle's Law states that as pressure increases, volume decreases. Obviously, as one goes deeper in the water, pressure increases. This causes any air spaces in the body and the suit to be compressed. It may be easier to understand this if you imagine a balloon that is inflated and tied closed. If you hold that balloon at the surface of the water, it will remain "full size." But, as you take that same balloon deeper into the water, the air inside will be compressed, or squeezed, into a smaller space and the balloon will look smaller!
As a diver goes into deeper water, any air spaces in the body and suit will also be compressed. This makes the diver become less buoyant and will cause the diver to start to sink. To compensate for that, the diver can put air into their suit. This adds buoyancy and allows the diver to stay neutrally buoyant at any depth! But, when the diver begins to ascend to the surface, the air that has been put into the suit will start to expand causing the diver to rise even faster. This can be controlled by dumping air out of the suit. Divers are regularly adjusting their buoyancy. It's actually quite fun!
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Inlet valve
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Dump valve
When we collect samples in Antarctica, we are very careful not to disturb the algal mat on the bottom of the lakes. We use a technique nick-named "fin-tipping." We lower ourselves very carefully to the bottom and stick just the tips of our fins into the sediment. Then we slowly lower our body towards the bottom until we can just reach the sediment, being careful not to actually touch it. When our buoyancy is "just right", our bodies will rise slightly with each inhaled breath and will sink slightly with each exhaled breath. It's like rocking in a cradle.... well... sort of!
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Sketch of fin tipping
You can also check out my journals and pictures from previous seasons at: http://www.ryejrhigh.org/ellwood