Dispatch 4: First Water Samples from the Arctic     Print

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Mengnan Zhao

September 21, 2015

This morning we were greeted by a fairly windy and wavy day with light snow. I awoke finding myself hardly able to stand in the swaying motion. The wind reached up to 35 knots around midnight, but fortunately the weather slowly improved before we arrived at our first station for CTD/rosette deployment.

This year, unlike previous years, we will make an anticlockwise track around the Beaufort Gyre region. This year is a “low ice” year with more ice to the east and north of us. So we planned to make our buoy deployments on the ice as soon as possible to the east and north, and finish our expedition with the rest of the science stations on the western side of the gyre. By late afternoon, we had arrived at our first station at the mouth of the Amundsen Gulf. The wind had calmed, and conditions were perfect for our first deployment.

The rosette deployment required collaboration between the winch operator, the ship’s bridge, and the CTD lab. As the entire rosette descended from the ocean’s surface to the bottom, we in the CTD lab monitored the real-time temperature, salinity, fluorescence and oxygen profile through the water column. Using these measurements allows us to determine where different water layers sit, and the depths to close bottles to sample their properties. Once the rosette is back in the wet lab, the Niskin bottles (filled with water from different depths) are sampled from to fill a range of different bottles from which to measure salinity, nutrients, dissolved inorganic carbon, chlorophyll, alkalinity, colored dissolved organic matter, oxygen, barium, bacteria, methane, and others. Some water samples are pre-treated before storing; for example, for bacteria, samples are filtered by different sizes and stored in a fridge on the ship for later genetic analysis in labs back home. For other properties, like salt and dissolved inorganic carbon, the water samples are analyzed right away in the lab on the ship. Samples for oxygen require chemical fixing immediately after the water is drawn from the rosette to prevent any possible contamination by atmospheric gases.

Although the entire process sounds straightforward, doing it can be another story! And our first stations were not completely smooth going. During one cast, we had to pull the entire system out of the water shortly after deploying it because of a tiny problem with a bottom connector. It was also my first time operating the computer in the CTD lab. Despite help from scientists Sarah Zimmermann and Mike Dempsey (IOS), I was exhausted after a 6 hour deployment.