19 November, 2004
Location: Lake Hoare
We had two goals for our dives today. The first goal was for me to take my underwater camera, a ruler, and Kay's fancy dive light to the bottom and get some photographs of the algal matt that would show the scale of the mat pinnacles. The second goal was for Ian to put the Oxygen sensor through another mat and to take two more core samples.
When diving among these algal mats, buoyancy control is critical. Bumping into the bottom of the mat can destroy hundreds, even thousands, of years worth of growth. Some disturbance is inevitable, but we are trying very hard to keep the disturbances to a minimum. A slightly miss placed kick of the fin could lift a considerable amount of algae off the bottom.
Such sensitive substrate makes it very difficult to get close enough to the bottom for close up pictures without causing disturbances. I believe I was quite successful! I first searched for a site that had some sand near the mat that I could place the tips of my fins into without disturbing the matt. I wore ankle weights in order to keep my fins in position once they were placed. I then lowered myself, face/belly first, towards the mat. There are two valves on a dry suit; one valve allows the diver to put air into the suit, the other allows the diver to empty air out of the suit. I fiddled with the valves until I was neutrally buoyant just above the mat. When one is neutrally buoyant, one neither sinks nor floats; it's rather like hovering in mid air. I fine-tuned my buoyancy, and then got to work.
I placed the ruler into the mat, horizontally at first. I then started taking pictures. I tried several different lighting scenarios in order to get the best shots. I tried no lights at all, just natural sunlight through the ice. I tried Kay's light on high, and low settings, and I tried my camera flash. Each method created quite different results, so I took many pictures with each option. With my buoyancy being just right, when I inhaled, I rose up from the matt just a few inches, when I exhaled, I lowered back down towards the mat; using my fin tips in the sand as a fulcrum. I took each picture on an exhalation so I could be closest to the matt without touching. It was rather like rocking in a cradle. It was very soothing and relaxing; I could have taken a nap!
After my dive, Ian dove and collected his samples. His dive also went with tremendous success. He is getting valuable data which will help answer his questions about the oxygen levels within this lake's substrate. I am fortunate to be able to lend a hand with his research!
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