EU-funded researchers are developing a new generation of ocean sensors that can monitor previously hard-to-reach areas, and are expected to provide clearer insights into how marine ecosystems are responding to climate change.
The world’s oceans support important marine ecosystems and provide more than just food and recreation. They help regulate Earth’s climate, absorbing vast amounts of heat and carbon dioxide, and acting as one of Earth’s most important buffers against climate change.
But despite this important role, scientists still struggle to track exactly where and how the ocean absorbs and stores CO2, and how that process is changing.
According to EU data, the ocean absorbs around a third of anthropogenic CO2 emissions every year. However, observations are sparse, leaving large blind spots in our understanding.
Expansion of ocean observation
Scientists have long relied on commercial ship-based measurements and fixed moorings to study ocean chemistry, but these approaches do not provide comprehensive coverage.
“There really aren’t that many observations,” explains Finnish marine scientist Janne Markus Rintala, based at the Integrated Carbon Observing System (ICOS), a European research network that measures greenhouse gases in the atmosphere, land and ocean.
That data helps scientists understand where carbon comes from, where it ends up, and how quickly the system is changing.
“Sometimes it seems like we know a lot more than we actually do, because the models give the impression that we’ve been watching everywhere.” In reality, direct observations only cover about 3% of the ocean, he explained.
Rintala leads an international team aimed at expanding ocean observation capabilities by developing sensors for platforms that can operate deep beneath the surface, beyond normal transport routes, far from ships and human intervention.
Their goal is to continuously monitor ocean carbon over months and even years, including in areas that have hitherto been largely inaccessible.
The work is part of an EU-funded initiative called GEORGE, which ends in 2027.
Coordinated by ICOS, it will bring together leading experts from across Europe. These include three major research infrastructures: ICOS, the European Multidisciplinary Seabed and Water Column Observatory (EMSO), and Euro-Argo, the European arm of the Argo Global Ocean Observing Network.
Measuring deep carbon
At the heart of this effort is the development of the world’s first autonomous sensor that can accurately measure total alkalinity in the ocean, from the ocean floor to the surface.
Total alkalinity is an important chemical metric that scientists use to understand the ocean carbon system and estimate how much CO2 seawater can absorb and store.
It is also important for tracking ocean acidification. This acidification, caused by rising CO2 levels, lowers the pH of seawater and threatens marine ecosystems, especially the plankton and molluscs that make shells.
“Ocean acidification is extremely harmful to many marine species,” Rintala said. “That can cause cascading effects that ripple through the food web.”
To date, total alkalinity has typically been measured by collecting fixed seawater samples from ships and later analyzing them in land-based laboratories. This approach provides valuable data, but only at isolated points in time and space.
“If you’re interested in the carbon content of the entire ocean, you need to measure deeper,” says Sokratis Loukaides, a marine scientist based at the UK’s National Oceanographic Center (NOC).
Loucaides and his colleagues at NOC are leading the development of a completely different approach. It is a compact lab-on-a-chip sensor that performs miniature chemical experiments inside the instrument itself.
Inside the device, a small sample of seawater is mixed with an acid of known strength and a dye that changes color depending on its acidity. A light-based sensor then reads those color changes and calculates the alkalinity of the surrounding seawater.
By doing this directly in the deep ocean, sensors can build a more detailed picture of how carbon is stored and transported over time, potentially revealing early warning signs of change.
Built to survive in the deep sea
Before being deployed, the sensor had to prove that it could withstand the most extreme conditions on Earth: the crushing pressures of the deep ocean.
This was done at a high-pressure facility in the UK and tested at pressures equivalent to depths of up to 6 kilometers.
The team then tried it out in real-world environments, from shallow estuaries to underwater landing craft and self-driving cars.
In the most rigorous test to date, the sensor was lowered nearly 5,000 meters below the surface of the North Atlantic Ocean.
There, it was loaded onto an undersea lander and then lowered into position at the Porcupine Abyssal Plane Persistence Observatory, a remote open ocean monitoring station some five kilometers below the waves.
Real-time communication is impossible at that depth. The sensors are battery-powered and will store data internally until the lander is retrieved.
“We won’t know exactly how this deployment turned out until we retrieve everything in May 2026,” Loukaides said.
reach the dead end of the sea
Looking to the future, researchers hope to use autonomous underwater vehicles to collect data from seafloor sensors, extending their lifetime and reducing the cost and risk of deployment.
The wide-ranging effort also aims to reach parts of the ocean rarely visited by research ships, such as remote areas and storm-prone areas like the Southern Ocean. This is the task of another research initiative named TRICUSO, which is based on research conducted at GEORGE.
To achieve this, scientists are developing sensors that can be mounted on self-driving vehicles, from torpedo-shaped underwater gliders to wind- and solar-powered watercraft and drifting instruments that move on ocean currents.
Some sensors measure multiple carbon-related parameters at once, while others collect and store seawater samples during long voyages for later laboratory analysis.
Miniaturization and precision are key, Rintala said. Smaller, lighter instruments require less power and chemical reagents, making them easier to deploy over large areas and over long periods of time.
As climate change accelerates, a growing network of autonomous sensors could transform scattered measurements from small parts of the ocean into denser, more detailed maps of the carbon cycle.
Over time, that information could reveal where the ocean is changing most rapidly, where it is approaching critical mass, and how its ability to absorb carbon is evolving.
“We are facing big changes and big unknowns,” Rintala said. “We need many more measurements than we currently have to understand what is happening and how fast it is happening.”
The research for this article was funded by the EU’s Horizon program. The views of the interviewees do not necessarily reflect the views of the European Commission.
This article was originally published in Horizon, EU Research and Innovation Magazine.
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