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Collecting Sediment and Marine Snow

August 18, 2012

Today the science crew started to get pretty busy. We finally arrived at our first station over Norfolk Canyon around 4:30 AM. I am not sure of the exact moment, but I woke up and the first thing that popped into my head was, “We’ve stopped.” That’s right, I managed almost six hours of sleep. The ride was definitely a little smoother, and I think I am getting used to the rocking motion. Much of the day I don’t even notice it. Just now I was watching a shirt hanging on a hook wave back and forth and I barely felt a thing.

Dr. Brendan Roark running the filter apparatus. Photo by Eric Hanneman.

Dr. Brendan Roark running the filter apparatus. Photo by Eric Hanneman.

By 5:30 AM I was on deck standing next to Dr. Brendan Roark, from Texas A&M University. He was watching the line from which the CTD was hanging over the side. It was on its way back up from 1190 meters below, with some water collected near the bottom in Niskin bottles. The water was going to be used to load the sediment collecting bottles on BOBO and ALBEX, the benthic landers that we were going to deploy.

Dr. Mienis assists while Dr. Gerard Duineveld places the bottles in the lander. Photo by Eric Hanneman.

Dr. Amanda Demopoulos and Dr. Furu Mienis add mercuric chloride. Photo by Eric Hanneman.

The bottles will collect sediment and marine snow for a month. Even on the bottom of the sea, life is robust, so to prevent things from growing in the bottles, a small amount of a solution of mercuric chloride, which is toxic, is added to them to preserve the samples. There are a couple of reasons that deep water is desired to fill the rest of the bottle. First, surface waters have a lot more plankton than deep water. The plankton could be filtered out. But along with the plankton come organic molecules such as chlorophyll, nucleic and fatty acids, and these are too small to filter out. Most importantly, however, is having the water in the collecting bottle be as chemically similar, in particular salinity and alkalinity, as the water at the bottom. The marine snow, by falling into water that is not chemically identical, could have substances leach out, changing the weight and chemical nature of the collected sediment. So filtered, deep water is used to fill the bottles, and to keep the mercuric chloride in the bottle and doing its job.

Dr. Mienis assists while Dr. Gerard Duineveld places the bottles in the lander. Photo by Eric Hanneman.

Dr. Mienis assists while Dr. Gerard Duineveld places the bottles in the lander. Photo by Eric Hanneman.

After the lander is loaded with the collecting bottles, a lot of preparation happens really fast. The electronics get a final going over to make sure all the wires are connected and everything is working. Then the crane lifts the lander over the stern of the boat and into the water. Once in position, a sharp tug on the quick release happens, and the lander plunges to the bottom.

View of the sediment trap from below, filled with sample bottles. Photo by Eric Hanneman.

View of the sediment trap from below, filled with sample bottles. Photo by Eric Hanneman.

After a year goes by, our crew will come back and send a radio signal to the lander, which will cause it to release its 600 pounds of ballast weight. Then the floats mounted on the sides of the lander will rapidly bring it to the surface, where flashing lights and a beacon will help locate it.

Bon voyage, see you in a year! Photo by Eric Hanneman.

Bon voyage, see you in a year! Photo by Eric Hanneman.

Tomorrow, when we arrive at Baltimore Canyon, it’s going to get even busier, with three more landers to launch and the possibility of an ROV dive. I better get some sleep.

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3 Comments leave one →
  1. lizbaird permalink
    August 18, 2012 9:25 pm

    Wow! Leaving the lander out for a year. How may other groups launch landers? Does anyone know the percentage of landers that are recovered? i would hope most of them!

    • Eric Hanneman permalink
      August 21, 2012 7:14 pm

      Dr. Duineveld has been launching landers off Ireland and Portugal for years. He has had them pop up unexpectedly, but has not lost one yet. Dr. Ross has been sending landers down for awhile too, in the Gulf of Mexico and SE Atlantic. There is currently one lander that is unresponsive. They know where it is, and are planning to recover it using some cutting gear borrowed from the oil industry to free the ballast weight. But usually, they are recovered.

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