UW Argo lab

The view through my terminal window is wet and gloomy and the weather seems to be lulling everyone to sleep. Typical day in Seattle. However, today I am immune to the somnolent spell of the city because, in just a short while, I will depart for Fremantle, Australia to begin my cruise through the Southern Ocean!

Before I leave, I would like to recount my last visit to the UW Argo float lab. Last week, I asked Rick Rupan, our lab manager, to give me a tour of the operation he oversees. He was more than eager to participate. He spared no details as he walked me through all the intricate details of float design, testing, assembly and deployment. That experience left me with great appreciation for all the work that this lab does. I will try to summarize.

Our lab is one of a handful groups in the world that assembles and deploys profiling floats for the Argo program. Argo is a global array of profiling platforms that allows us to remotely monitor the state of the ocean. These floats freely drift through the ocean and sample the upper 2000m of the ocean on roughly 10 day intervals. The first Argo float was deployed more than 15 years ago and the current observing network now boasts over 3900 floats worldwide.

The standard Argo floats measure temperature and salinity. However, a small but growing subset of these floats are now being equipped biogeochemical sensors that can measure ocean properties such as oxygen, nitrate, pH and fluorescence. The floats that I will deploy for the SOCCOM project belong to the latter category.

A close up of the sensors on a biogeochemical Argo float.

Our lab assembles and ships both standard Argo floats and their souped-up biogeochemical counterparts. The UW float team mainly deals with a particular model of floats known as APEX floats, which are manufactured by the Teledyne Webb Research company. More recently, they also have started working with the NAVIS model from Sea-bird electronics. All these floats do essentially the same thing but work in slightly different ways.

When the floats arrive at our lab, they are fully assembled and usually work right out of the box. But, these floats are expensive. A fully equipped biogeochemical float, for example, costs roughly $80,000 USD, so Rick needs to ensure that we can get the maximum performance out of each float.

Rick and Christina tinker with the electronics of an Argo float.

To prolong the lifetime of these instruments, Rick and his crew subject them to a rigorous course of quality control testing. They start by stripping the floats down to their bare essentials and perform tests on each component. Every piece of the float, from the pumping mechanism to the control board to the sensors, is scrutinized for defects and deficiencies. Part of this process also includes ballasting, where they submerge the float in a special tank to calibrate its buoyancy and test its ability to remain upright in the water. Rick's group is able to fix most problems in-house but occasionally they have to return particularly defective components to their manufacturer.

Rick showing the internal electronics of a regular Argo float that only has
temperature and salinity sensors (right) and a SOCCOM float that has
a full suite of biogeochemical sensors (left).

The floats that arrive from APEX only have temperature and salinity sensors on board, so the group has to install all additional sensors. For SOCCOM floats, this step involves shipping them to our partners at the MBARI oceanography center in Monterey Bay, California. The MBARI group installs sensors for pH and nitrate then ships the modified floats back to UW. As you can tell from the picture above, these extra sensors add a lot of bulk to the float. For this reason, SOCCOM floats are slightly larger than regular Argo floats.

Typical turnover time for float testing and rebuilding is usually about 2 weeks. But, after Rick's crew work their magic, each new float is sent out with an expected lifetime of 4-5 5-7 years.

Map showing the location of all current Argo profiles, as of
February 4, 2016

In some ways, the UW lab is like a factory. Even though the group is small, the complicated logistics of the Argo program requires the lab to operate like clockwork. Every float that gets deployed will eventually die, so we have to continually build new floats to maintain the existing coverage. In 2015, the UW float assembled and shipped roughly 120 floats, which is a substantial fraction of the 800 that were built globally.

In this blog post, I only mentioned 2 people, Rick and Christina. However, many more people are involved in the pre- and post-Argo float production process. I would be remiss to not mention Professor Steve Riser (principal investigator and also my advisor),  Dana Swift (senior research engineer and one of the technical masterminds behind the Argo project) and Annie Wong (senior research scientist and data quality control expert). There other important people that I don't have time to acknowledge but you can see full group here. It is through their collective hard work and dedication that the Argo program is as successful as it is today.

That's all for now! My next update will be from Australia. Rick has already flown ahead to retrieve the SOCCOM floats from shipment and load them onto the research vessel.

 -EW