Profiling Floats by Chanelle

I have been traveling around Tasmania a couple of days now, but the reality of the upcoming S04P cruise didn’t entirely set in until I saw the R/V Palmer docked in Hobart yesterday afternoon. As an undergraduate who works at the University of Washington Argo float lab, I always see the instruments from our lab get shipped to these places all over the world, but I never thought I would one day be able to go with them.

Our lab builds over 100 floats a year as part of the Argo program, which is an international collaboration to better understand the world’s oceans with a global array of profiling floats. There are 32 participating countries in the program, and collectively over 3000 floats have been deployed. Argo floats are autonomous sensor platforms that measure the salinity and depth of the upper 2000 meters of the water column. They are distributed throughout the world’s oceans and the data collected from the floats has increased the understanding of global scale circulation and improved climate models and predictions.

In addition to constructing floats for the traditional Argo array, our lab also builds floats for the SOCCOM project, which stands for Southern Ocean Carbon and Climate Observations and Modeling. The Southern Ocean is a particularly important study region because this ocean is responsible for a large amount of sequestration of carbon dioxide and heat from the atmosphere. Additionally, this region is projected to be particularly impacted by ocean acidification. However, despite the importance of the Southern Ocean to global climate and its vulnerability to ocean acidification, this region is poorly understood because of its inaccessibility for much of the year. The goal of the SOCCOM project is to use a network of autonomous profiling floats throughout the Southern Ocean to collect data up to 2000 meters depth year round. This data will be used to better understand this region and create better projections and models of Earth’s climate and the ocean’s biogeochemistry.

The floats built for the SOCCOM project are outfitted with additional biogeochemical sensors that measure nitrate, chlorophyll, dissolved oxygen, and pH. There will be 6 SOCCOM floats deployed on the Palmer from our lab. The last time I saw these floats, I was putting them in crates for their long voyage to Hobart. Before the floats were ready for shipment, though, they had been in the lab for months being prepared and undergoing countless quality checks.

The first step that I as an undergraduate technician did in helping prepare these SOCCOM floats for deployment was performing pressure calibration tests on them. I use a deadweight tester to exert pressure on the sensors, and I make sure that the pressures being read by the sensors are within a certain range of what they should be reading. Usually, the readings are within range, but occasionally I get readings that are out of specification, so I send the CTD head (the part of the float that houses the salinity, temperature, and depth sensors) back to an oceanographic instrument facility called Seabird to be recalibrated. This process ensures that the floats that are deployed will have accurate readings of their depth.

Another quality check I perform on the floats is telemetry testing of the SIM cards.  When the floats are in the middle of the ocean, they transmit their data back to shore via satellite, which they do with SIM cards that are similar to what you have in your cell phone. Before the SIM cards are installed in the floats, I make sure they are able to connect to satellites and to both of our lab computers via both an internet connection and a modem to modem connection.

My next task is to prepare the floats for ballasting. Since the floats take profiles up to 2000 meters of depth, they must be made to be neutrally buoyant at this depth through a process called ballasting. This process involves putting them in a pressure vessel and determining what weight needs to be added to the float in order to make it neutrally buoyant at depth. I do not do any of the ballasting, but I make sure the floats are ready for it by temporarily mounting the FLBB (sensor that measures chlorophyll) at the top of the float where it will be out of the way while in the pressure vessel.

Once the ballasting is done, we know how much weight needs to be added to the float, which is achieved with a combination of battery packs and strips of lead.  Once the float has been all built up with the correct amount of weight, I perform buoyancy checks on the floats to ensure that they are weighted correctly. This consists of me putting the floats in a test tank located in the UW Oceanography building and ensuring that the floats are able to return to the surface. Once the float gets back to the surface, I push it around to make sure it is able to correct itself and is sitting correctly in the water.

 I am lowering a SOCCOM float into the test tank to do a buoyancy check.

  

After the buoyancy check is complete, we put the floats through “dock testing” where we put the floats outside and let them go through mission sequences. This is our final run through to make sure everything is running properly and that the float is able to connect to the satellites and transmit files. After this check, the float is pretty much ready to go and be crated for shipment. At this point, my work is usually done with the float, but now I am lucky enough to have the opportunity to participate in the deployment process of these S04P floats.

The tasks I described are just a few of the things I do at the lab, and this post has barely scratched the surface of what our lab does and the greater Argo and SOCCOM programs. I am grateful to have worked with a fantastic cohort of people at the UW Argo float lab and to be a part of a program that is doing so much to help better our understanding of the ocean.  I’m looking forward to continuing my work with these instruments while on S04P.

--Chanelle