Deploying Biogeochemical Argo Floats in the Western Pacific

In my role as a staff research associate at UC San Diego’s Scripps Institution of Oceanography, I spend time at sea about once a year deploying robotic floats with biogeochemical sensors. The floats are part of a vast network covering the world’s oceans, and my most recent trip took me to the tropical western Pacific. I joined the Exploration Vessel Nautilus in Guam and, over the course of a week, deployed six floats as the ship transited to the Solomon Islands. 

The E/V Nautilus houses an impressive remotely operated vehicle named Hercules and runs livestreams from the ship of its operations and dives. While I was aboard, ROV Hercules stayed snug in its hangar and the livestream mostly showed a calm blue ocean sliding by as we steadily headed southeast. Nautilus is equipped with sonar mapping capabilities so we did capture some great data about the seafloor as we crossed over the Mariana Trench, through the Federated States of Micronesia, across the equator, and into the Solomon Islands. 

The six floats we deployed on this trip are part of the Global Ocean Biogeochemistry array (GO-BGC), funded by the National Science Foundation. They also join the larger Argo network, an international program which has over 4,000 floats with temperature and salinity sensors to monitor global ocean health. Biogeochemical floats also report dissolved oxygen, pH, nitrate, backscatter and chlorophyll; more recent floats also report irradiance (light levels). 

When explaining the float program, I often say that I am slowly replacing myself with robots. It is a joke, but also partially true. For much of my career at Scripps Oceanography, I did chemical analyses to report the nutrient, dissolved oxygen and salinity values in seawater from the surface to the seafloor. As my career changed, I left the lab and now work for programs that collect that data and more using autonomous instruments. This massive dataset is invaluable. After all, the floats work in all weather and sea conditions for years on end — something that people on research vessels just can’t do. 

Since there were no other science operations that required Nautilus to stop, the crew slowed the ship to about two knots (from our transit speed of close to 10 knots) for each deployment to make sure the floats were safely lowered into the water. Each float sinks to 2,000 meters (6,600 feet), or about 1.25 miles deep, collecting data as it rises back to the ocean surface. The journey back up takes about seven hours. Once the float sends all the information via satellite, it will “park” itself back at a depth of 1,000 meters (3,300 feet). There it drifts with the current for 10 days before beginning the process again. 

The data is all open access and available to anyone. The data sets for chemistry and temperature pH and temperature have supported many publications to better understand climate change and how much extra carbon is piling up in the oceans, causing acidification. The many parameters also support studies of ocean currents, tracking where each float descends and pops up, and even a paper about penguin populations using information about chlorophyll blooms.

All six floats I deployed from E/V Nautilus had been adopted and named by classrooms from around the world through our Adopt-a-Float program. Since the ship has such a great satellite connection to shore, I was even able to video call with some of the classrooms while onboard. I brought along a life-size cutout of a float, nicknamed "Floaty," to show off to classrooms via those interactions. The science party and crew also loved taking photos with it. The teachers and students will be able to track their float’s progress and data over the next five or so years.

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I have deployed dozens of floats during my 15 years in oceanography and really enjoyed my experience sailing aboard E/V Nautilus. Most of the time, I’m at my desk in San Diego, sending emails and updating spreadsheets. It’s always wonderful to be at sea, helping to get the floats into the water after so much planning. 

Our program relies on ships of opportunity, meaning we piggyback on research vessels, cruise ships and more that are traveling to interesting places and can spare a bit of time to slow down and deploy our floats. I’m part of a big interdisciplinary team from multiple institutions across the U.S., which in turn has counterparts in many other countries around the world. Everyone has a specialty — engineering, computer science, chemistry, data wrangling and more — and it takes all of us to be successful. But it all comes down to getting the floats safely in the water and reporting data! We’re so thankful that the Nautilus team welcomed me onboard and accommodated the deployments and hope to work with them again in the future.

Nautilus is different from the academic research vessels in the Scripps fleet. It’s operated by the Ocean Exploration Trust, which was founded by Robert Ballard, an oceanographer famous for leading the expedition that found the Titanic wreckage back in 1985. He actually joined the ship once we arrived in the Solomon Islands to lead the next cruise to find and record many World War II shipwrecks in Iron Bottom Sound, off the coast of Guadalcanal. The photos and videos from that archaeological expedition were truly remarkable to see as well. You can check out the ship’s livestream 24 hours a day to see what's happening on board!
 

– Melissa Miller is a staff research associate working for physical oceanographer Lynne Talley at Scripps Institution of Oceanography. Miller recently sailed as a guest scientist aboard E/V Nautilus. She also works at the Comic-Con Museum to bring scientific content to pop culture events.