The ocean is massive. It covers more than 70 percent of Earth's surface. The Pacific Ocean alone blankets 60 million square miles (155 million square kilometers) of the planet. This water regulates our climate and weather patterns by funneling heat from the equator to the poles, produces more than half of the world's oxygen, and absorbs 50 times more carbon dioxide than our atmosphere.
The secrets the ocean holds can tell us a lot about the state of the planet. But, getting to that info can be a challenge for both humans and scientific instruments, especially in treacherous areas where there are rocky seas, raging storms, thick ice and deep pressure-crushing waters.
That's where a fleet of robotic, self-submerging floats come in. They're part of an international program called Argo, and these mini observatories provide researchers with comprehensive, near-real-time data about the physical state of the ocean. That data includes temperature and salinity patterns that help researchers more accurately measure global warming and rising sea levels, improve weather forecasts and climate predictions, and better gauge the intensity of hurricanes.
How Does Argo Work?
Argo is an international collaboration that involves the deployment of nearly 4,000 cylinder-shaped, free-drifting floats spread throughout the ocean. The floats are placed about every 186 miles (300 kilometers) apart — at every 3 degrees latitude by 3 degrees longitude. The standard floats measure the temperature and salinity in the upper 6,561 feet (2,000 meters) of the ocean, says Gregory C. Johnson, Ph.D., an oceanographer at National Oceanic and Atmospheric Administration (NOAA)'s Pacific Marine Environmental Laboratory in Seattle, Washington.
"Our coverage is actually revolutionary," Johnson says. He's been involved in Argo since the program began in 2000, and has used Argo data in his own published research. "To have almost 4,000 core Argo floats out there now gives us so much more data than we've had in previous decades."
Argo is a major component of the Global Ocean Observing System (GOOS) and Global Climate Observing System (GCOS), which provide data for ocean and atmospheric services and high-quality data for climate research, respectively.
To date, 26 countries have deployed Argo floats and continue to process the data from them. Several other countries contribute logistical support and ship access. Each country obtains its own funding to buy floats, which ring in at about $20,000 each.
Another remarkable thing about Argo is that its data is free and available to anyone in the world who wishes to use it. It's stored on two global data servers, one in France and the other in the United States. To access the information, you can visit the "Argo Data Sources" page.
What Do Argo Floats Do?
There are different types of Argo floats, and each can be programmed to run different missions. The standard Argo float's mission runs on a 10-day cycle:
- Day 1: A float is deployed, usually from a ship, into the ocean at a predetermined point. It spends the first six hours descending vertically about 0.62 miles (1,000 meters) into the sea.
- Days 1-9: Once the float reaches 1,000 meters in depth, it drifts with the current for nine days.
- Day 10: On the last day of the cycle, the float drops another 1,000 meters into the ocean, to about 1.2 miles (2,000 meters) below the surface. Then the float makes its way back to up, a process that takes about six to 12 hours, during which it collects a temperature and salinity profile.
Once the float breaks the surface, it spends the next 15 minutes to an hour transmitting the data from an antenna located on the top of the float to a satellite before descending again and repeating the 10-day cycle.
Since 2000, Argo has collected nearly 2 million deep-ocean profiles, providing a complete, near- real-time picture of the ocean.
What's Inside an Argo Float?
Standard Argo floats contain the following materials:
- conductivity, temperature, depth (CTD) sensor that determines the physical properties of the ocean water
- external bladder that controls the float's buoyancy
- internal reservoir that stores oil when it is not inflating the external bladder
- hydraulic pump that moves oil between the internal reservoir and the external bladder
- antenna at the top that enables the float to transmit data to a satellite
- lithium batteries
There are a few different types of Argo floats. Standard Argo floats are designed to go as deep as 1.2 miles (2,000 meters). Advances in technology in the two decades since the Argo program began have led to the creation of more specialized floats.
- Deep Argo Mission floats are specially designed to go to the ocean floor — up to 3.72 miles (6,000 meters) deep. In order to reach those depths, the floats must withstand what the Argo team describes as "pressure comparable to the weight of two minivans concentrated on a single postage stamp." These floats enable researchers to better understand ocean changes such as increasing heat content in the deep ocean.
- BioGeoChemical Argo (BGC-Argo) Pilot Floats are equipped with biogeochemical sensors that measure six additional parameters, including pH, oxygen, nitrate, chlorophyll, suspended particles and downwelling irradiance. This helps researchers better understand and manage ocean resources.
Deploying floats in ice zones has been a challenge since sea ice prevents floats from pushing their antenna to the surface where they can transmit data. To tackle this issue, scientists and engineers have designed improved mission algorithms for floats deployed in places affected by seasonal ice such as those in the Artic and Antarctic. This new algorithm enables them to avoid collisions with ice and store the data until the floats detect open water at the ocean's surface.
How Is Argo Data Used?
The profile data collected by Argo floats have a variety of applications. They can be used to educate students from kindergarten to university level about the temperature of the ocean or how to read graphs and analyze ocean data and climate change issues.
From an operational standpoint, the data is used by weather and climate centers around the world to improve forecasts of El Niño events and climate features like hurricanes, tsunamis and global warming.
On a research level, Argo provides oceanographers and climate scientists with the most comprehensive subsurface ocean data available. More than 200 research papers published each year use Argo data covering a broad range of data including water mass properties, air-sea interaction, ocean circulation, ocean dynamics and seasonal-to-decadal variability.
For Johnson, Argo data was a "very solid indicator that the Earth's energy budget is out of balance." He recently analyzed data collected from 2014-2018 by special deep-water Argo floats to study the near-bottom waters of the Southwest Pacific Ocean. That analysis revealed that not only was the water in the deep ocean warming, the rate at which it was warming was accelerating.
"How much the ocean is warming is pretty important for understanding how much the climate will warm in the future, for a given change in greenhouse gas concentrations," he says. "So, measuring ocean warming is important for validating climate models and assessing them. It's a key number, actually, in the Earth's climate system."
What Is Argo's Environmental Impact?
Argo floats are extremely quiet and energy efficient, Johnson explains. "The entire array of nearly 4,000 floats operates on less than 100 watts, or about as much power as a ceiling fan," he says.
The floats continue working for about four to five years depending on their mission. Floats with more grueling tasks tend to die sooner while some standard floats have lasted 10 years or more. In time, usually when their batteries wear down, all floats die. When they do, they are designed to make as little impact to the environment as possible.
When a float dies, it drifts around in the deep ocean until it begins to corrode, which allows water to leak inside the float causing it to fall to the sea floor. Over time, the aluminum hull slowly degrades into harmless oxides that spread around in the ocean's currents. The remaining plastics and metal are minimal and slowly decompose over time.