The making of benthic chambers!

The past couple weeks before our departure were spent preparing last minute items for the trip and packing. This included constructing benthic chambers that we have brought with us to the ice to deploy on the sea floor. The benthic chambers will be used to quantify the flux of methane from the seafloor over a 24-hour period. We will also take pore-water measurements from the chambers allowing us to see the concentration of methane, sulfur and oxygen at various depths within the sediment. To facilitate these research goals, the benthic chambers had to have various features that I’ll outline here. By working with the awesome people at the CEOAS Machine Shop (Ben Russel, John Simpkins and Tige Kurth) we were able to design the chambers using mainly stock PVC plastic and acrylic plastic tubes.

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Solid works design of the caps for the benthic chambers

In designing the chambers, we had a few goals that we had to have many brainstorming sessions to figure out how to achieve. First, we had to make sure that we could gently mix the water periodically to avoid the sediment-water interface from becoming anoxic. It has to be a gentle mixing though, as stirring up sediment would skew our data. We also had to have outlets to sample the overlying water (through use of a gas tight septa) as well as holes for sampling of the pore water beginning at the top of the sediment and continuing at two centimeter increments down. We also had to ensure that the cap would have a gas tight fit so that we could have upmost confidence in our measurements of gas flux from the sediment into the overlying water.

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Finished benthic chamber cap! The red circle you can see is the septa that will allow for us to sample the overlying water in situ with a syringe and the white wheel is the magnetic stirrer

Figuring out how to gently mix the water to avoid the development of anoxic conditions while also not disturbing the sediment was the most challenging task. Most designs employ use of a motor powered turbine, generally battery operated through water and pressure proofed connections. However, we knew that the best option for us would be non-electric – a difficult task to say the least. What we ended up designing can be seen in the animation that Ben Russel from the Machine Shop designed on solid works. It utilizes magnets to hold two propeller shaped pieces on either side of the lid of the benthic chamber. With manual movement (by us during dives) of the top magnetic piece, the bottom piece rotates accordingly gently mixing the water within the chamber.

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Finished product!

In design of these chambers, I got to learn how to use the Lathe for facing, turning and drilling (machine shop lingo for smoothing the ends, countering the bottom, and creating even sides) the chamber tubes once they had been cut on the horizontal band saw. The lids for the chambers, including the outlets for the septa and o-ring groves, were designed in the CNC program and cut into the PVC plastic of the caps with precision by the machine. The ports for the rhizones that will allow for sampling the pore-water in vertical increments down the core were made with a simple drill press. Overall, it was really fun to work in the machine shop designing these chambers and learning how to use all the new equipment. Check back with us to see pictures of them deployed in the field!

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