10 January, 2003
1/10/03 A Successful Last Day On Lake Fryxell
This day would be our last on Lake Fryxell and we were all glad to say goodbye. The long walk across the ice had grown increasingly difficult. So it was nice that our last day was successful. We removed some nice sediment cores from the lake. We had bored through 5.5 meters of ice and down 20 meters to the lake bottom. We managed to collect core samples approximately 2 meters into the sediment. The photos below show some of the cores we removed.
The coring process involves feeding a coring tube down a hole in the ice to reach the lakebed below. A coring tube is a four foot long, 2 inch diameter stainless steel pipe with a long oblong rod inside it that runs the length of the tube. The oblong rod keeps material out of the core barrel, by holding a piston (like a rubber stopper) in place at the end of the barrel until we are ready to collect a sample. On top of the coring rod sits a 20 kilogram (45 pounds) weight that acts as a hammer during the coring process. The coring equipment is lowered into the lake on long extension poles, but is also held steady by a rope supporting the weight and by a strong cable that can be controlled with a winch.
We lower the coring tube into the hole and add extension poles as we lower it down. Once the corer reaches the lake bottom, the oblong rod is raised up by the extension poles until it gets to the top of the corer, leaving the core barrel in place. There it is given a one-quarter turn, which locks the oblong rod in the up position. The goal is to collect a one meter core sample each time the corer is lowered. To measure this, we make a mark on the extension poles from the top of the ice and up one meter. Then the 20 kg weight is raised and lowered onto the coring tube to hammer it into the sediment. The hammer is lifted and dropped until the one meter of extension pole gets to ice level. This is how we know we have cored one meter into the sediment.
We then begin the process of raising the corer. A tripod is set up above the hole so that we can use pulleys to help us lift the weight and to use the winch to reel in the steel cable. We even attached a bungee cable to the weight that made lifting this hammer easier. As the corer is raised, extension poles are removed. Each one is attached with a bolt and two nuts, so it takes a few minutes to remove them and requires you to remove your gloves. The metal and cold water make that an uncomfortable task and so we take turns with that job. Often times the extension poles won't separate easily, so we then have to attach a chain clamp to each pole and twist them apart. All these things take time and cause you to remove your gloves. As the day progresses and your hands get colder and colder, performing these tasks becomes frustrating as your coordination deteriorates.
Once the corer is removed, we place the apparatus out across the ice. We then slowly push the piston rod back into the corer and force the sediment back out. The sediment is collected on a one meter long piece of two inch diameter PVC tube that has been cut in half horizontally.
When the sediment has been removed and is sitting in the PVC, the other half of the PVC is placed on top so that it looks like a whole tube again. We need to cut the sediment core longitudinally (in half the long way). To do this, a thin wire is run down the length of the PVC between the two halves, thus cutting the sample much like one would use a cheese cutter to slice cheese.
Although the sample has been cut, it tends to stick together, so a knife is carefully inserted between the PVC tube to gently pry the sediment apart into two even halves. Once apart, the sediments are examined and a description is recorded into a journal. Each sample is labeled with the date, lake name, the assigned site number, and the geographic location as identified using a GPS. A photograph of the core is also taken at the site and each tube is wrapped and secured with plastic wrap and taped up for removal from the ice.
Boring through the ice, obtaining a sediment core, and preparing the sample can all take several hours. We put in long days on the ice, but everyone works hard and supports one another. When things go wrong, it is discouraging, but the team stays optimistic and just becomes more determined. Like with most situations in life that don't seem to go as planned, we have found that humor carries us until the problem is rectified.
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