Troubleshooting and running samples
After a busy start to the summer with not a lot of time to run samples, the rise-velocity chamber has been going strong for the last few weeks. After our initial sample runs this spring there were a few things we wanted to troubleshoot before we got to the rest of the samples.
One issue was that the chamber had a slow leak at the base where the cap attaches to the clear tube. This meant every morning there would be a puddle on the floor and we would have to add more artificial seawater to the chamber. We tested out a couple different adhesives, some would work well when the tube was half full, but would begin to leak when filled to the top. Because the tube is filled with over 8 feet of water, the pressure at the base is substantial. Eventually, we found a winner! A marine-grade epoxy that is meant to work with difficult-to-bind plastic polymers; so far, so good.
After the chamber was repaired, I mixed a batch of artificial seawater, keeping track of the exact weight of salt it took to get to our desired salinity so we can replicate it next time. Then I continued working through a set of microplastic samples collected from our MOCNESS net system. This shipboard sampling technique consists of multiple stacked nets that can open and close allowing us to sample discrete depth layers. The set I am working on has microplastic samples collected from five depths, starting at the surface down to about 10 meters deep. There are over 200 microplastic pieces to run in this one MOCNESS profile, some of them under 1 mm in diameter and can be hard to track as the rise in the tube. So far the fastest piece took under 2 minutes to get to the top of the rise-velocity chamber and the slowest took 9.5 minutes!
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