Sampling Seawater

As mentioned previously, we have two different water sampling devices – the GEOTRACES rosette fitted with Go-Flo bottles, and the Niskin rosette fitted with Niskin bottles (the rosette part is the actual frame the bottles are attached to). Pictured below is the Niskin rosette being recovered from a cast. Water sampled from Niskin bottles is analyzed for nutrients and elements that are not prone to contamination. The rosette is moved into a staging bay where spouts on the bottom of the Niskins are used to fill individual sample bottles. In the background of this picture, the GEOTRACES rosette is staged and ready to go. As soon as the Niskin rosette is on deck, the GEOTRACES rosette goes in the water; we try to utilize our station time as efficiently as possible by moving quickly from one sampling event to the next.

Niskin smallAs the Niskin and GEOTRACES rosettes makes their way to the depths of the ocean the grey sampling bottles are open on the top and bottom to allow water to flow through. The gut of the rosette is filled with electronics (pictured below) that communicate temperature, conductivity, density, and turbidity to computers on board the ship. The chief scientists and marine technicians watch the profile unfold on the way down to select specific sampling depths (12 depths per cast). As the rosette makes its way back up to the surface, the bottles are tripped to close at the chosen depths.

CTD small.jpg4The GEOTRACES rosette is used to collect samples that are prone to contamination (like mercury). Go-Flo bottles are stored and processed in a clean laboratory that has HEPA filtered air to cleanse the room of any floating particles or dust that could contaminate the water. To prepare for a cast, the Go-Flos are carried out one-by-one and attached to the rosette (below). Plastic shower caps cover the opened top and bottom of the Go-Flos to avoid contamination on deck, and are promptly removed before entering the water.

loading bottles smallEach Go-Flo bottle is assigned a special tracking number (called a GEOTRACES number), which Laura (below) is assigning right before the cast. Many different samples will be collected from each Go-Flo bottle and all will have the same GEOTRACES number to track and compare results.

laura smallAfter the cast, the Go-Flo bottles are brought back into the clean van and placed into custom fit racks. The sampling team spends hours collecting and organizing samples from each Go-Flo bottle, some that will be analyzed on board the ship and others that will be transported to labs back in the U.S.

sara smallIn the clean van (above) Sara is collecting redox sensitive samples using special syringes – she will flush the air out of the line in order to draw a bubble free sample. Water from these syringes is analyzed for elements that are structurally altered in the presence of oxygen, such as Fe(II).

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