Switchyard Project: Sampling Success

by | 5.9.2011 at 10:16am
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The past 1½ weeks have been very successful. Our team from Lamont-Doherty Earth Observatory was able to obtain water samples from eight stations, while the team from the University of Washington has already broken their all-time record of the past years of 18 stations.

Today (May 7) is actually the first day we can’t fly due to the weather conditions, which do not allow safe landings on ice (a lot of low clouds and fog above the ice). This is certainly a very much-needed day of rest, especially for the field teams that go out and get samples.

Twin Otter with tent attached. Sampling happens inside the tent.

Time to describe how we actually do the sampling of water from the Arctic Ocean.

The sampling is a two-step process. First, we need to get the actual water samples from the Arctic Ocean, and second, we have to sample that particular water and put it into sampling containers for further analysis.

Step 1 is certainly the much more elaborate and straining part. When weather permits, an airplane (a Twin Otter) especially suitable for operating in the Arctic will take part of our team, two to three people, to one or two locations per day where we would like to get water samples.

Dale, Richard and Ryan setting up a tripod inside the tent to operate the CTD-rosette

After landing on the ice, we drill a 12-inch hole through the ice, which can be as thick as 7-8 feet. In order to get water samples, we have designed a special sampling device – a so-called lightweight CTD-rosette. The rosette holds a cassette with the CTD sensors and three cassettes of four sampling bottles – so called Niskin bottles, with a volume of 4 liters each.

The whole package is lowered through the 12-inch hole into the water to depths as deep as 800 meters, while the CTD sensors record and monitor temperature, salinity (conductivity) and dissolved oxygen of the water on the way down. These data already reveal some of the features in the water column that we are interested in, such as regions with strong signatures of freshwater, Atlantic water or Pacific water.

On the way back up to the surface we close one of the bottles at a time at each of the depths that are of particular interest for us. This will isolate and capture a portion of the water in order to bring it back to the station. The whole procedure on the ice needs about 3 to 4 hours. Don’t forget that the time to get to the sampling locations can be as long as 5 hours one-way.

Step 2 takes place in Alert, where we have set up a little laboratory. The rest of our team has already prepared a large number of sampling containers and is awaiting the arrival of the field team. As soon as the water samples arrive (which is usually later afternoon or at night), we fill water from each of the 4-liter Niskin bottles into smaller containers of various size and type (plastic bottles, glass bottles, metal containers). We take 120 samples for each of the locations our field team was able to reach.

Some of the large number of samples are actually being analyzed right here in Alert in our little lab within the next few days by Susan (salinity and oxygen samples), while most of the samples have to be shipped back to Lamont-Doherty.

Three cassettes with four Niskin bottles attached to each.

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