Marine robots are exploring the ocean's role in climate control

Far from shore, between Greenland and Canada, the Labrador Sea is known for its winter gales and ice-crusted swells. Yet 3,300 meters beneath that forbidding surface, a quiet army of cameras, gliders, and drifting floats is tracking one of the planet’s most powerful – yet least understood – climate regulators: the biological carbon pump.

Microscopic algae at the surface draw carbon dioxide from the air, turn it into organic matter, and – after death or digestion – become “marine snow” that drifts slowly downward. If those particles sink fast enough, or are flushed deep by winter convection currents, the carbon can remain locked away for centuries.

“Without the biological carbon pump, atmospheric CO₂ would be 50% higher,” said Filipa Carvalho of the UK’s National Oceanography Center (NOC). She also leads the year-long ReBELS project (Resolving Biological Carbon Export in the Labrador Sea).

Probing the ocean’s twilight zone

Tracking that pump is notoriously difficult. Much of the action occurs in the dim “twilight zone,” 100–1,000 meters below the surface. It’s well beyond divers and largely invisible to satellites.

Traditional sediment traps, lowered from ships, capture only brief snapshots. ReBELS combines a string of autonomous platforms in a first-of-its-kind attempt to record the entire annual cycle.

The backbone of the experiment is a tall mooring deployed by the research vessel James Cook. Suspended at 100 meters and 300 meters are two custom FluxCAM units, each a pair of high-resolution cameras that photograph falling particles every few minutes throughout the year.

“This is really exciting, allowing us to capture the particles’ true sinking speed, linked to their size and composition,” Carvalho said.

Tracking carbon in the ocean

Those images feed an AI routine that identifies, measures, and tracks every fleck that drifts into view – anything sinking slower than one meter a day or as fast as 200 meters a day.

“Because it’s hard using traditional methods to capture the huge range of particle sizes that there are, you could be making big assumptions and terribly underestimating or overestimating the amount of carbon flux,” Carvalho said.

By linking size to speed, the team hopes to tighten the error bars on global climate models that depend on accurate carbon export rates.

A drifting float with new sensors

Fifty nautical miles away, a free-drifting profiling float follows the same water mass the particles are sinking through. Unlike conventional floats that surface every ten days, this one rises and falls every 36 hours, stopping at 200 meters, 500 meters, 1,000 meters, and 2,000 meters.

It carries extra batteries and an optical transmissometer that acts “as an optical sediment trap,” as Carvalho put it.

The float’s camera (an Underwater Vision Profiler) judges whether large shapes are organic fluff or living zooplankton. A hyperspectral radiometer records light signatures that hint at which phytoplankton species dominate the surface bloom.

Gliders that patrol and chase

Two autonomous gliders complete the robotic fleet. One hovers near the mooring, providing high-resolution background conditions and helping match FluxCAM observations with bulk optical readings.

The second glider follows the drifting float, mapping the three-dimensional context around the moving parcel of water. Together, the instruments let researchers watch how zooplankton migrate – rising at night to feed, sinking by day – and how quickly their waste pellets plunge into the dark.

“Taking these different approaches helps to fill the gaps we might otherwise have,” Carvalho said.

The stationary mooring tracks year-round change at one spot. The float follows one water mass, while the glider maps variability. A follow-up cruise next summer will calibrate the sensors and retrieve terabytes of stored data.

Carbon hotspot in the deep sea

Each winter, the Labrador Sea undergoes deep-water convection. As frigid air cools the surface, dense water sinks, dragging surface water – and freshly formed organic particles – downward.

Rapid deep convection in the Labrador Sea could make it a major site for carbon export and long-term ocean storage. Yet no one has taken continuous, year-round measurements of both the biological and physical mechanisms at work.

The key unknown is the race between sinking and decay. If bacteria consume particles before they leave the upper ocean, the carbon escapes back to the atmosphere; if the particles descend fast, the carbon is locked away.

By measuring and tracking thousands of individual sinking rates and linking them to water-column physics, ReBELS hopes to reveal how much carbon the Labrador Sea truly sequesters.

Engineering challenges and help from AI

Designing gear that survives a year in 3°C water under crushing pressure is no small feat. NOC engineers built FluxCAM with titanium housings and custom electronics.

The AI image-analysis pipeline, trained on millions of labeled frames, will process data automatically so scientists can focus on interpreting results.

Ground-truthing is critical. Sediment traps on the mooring still collect bulk material for chemical analysis, letting the team check whether AI-derived flux estimates match lab-measured carbon content.

“Through our ground truthing and being able to better calculate the biogeochemical and biological variables, we will have less uncertainty from the measurements we get from our autonomous platforms,” Carvalho said.

Designing the next carbon watch

If all goes well, researchers will recover the moorings and float in late summer, and technicians will begin months of downloading data. This research could deliver a full seasonal record of marine-snow export tied to overturning – something current climate models lack.

The goal is to learn whether the Labrador Sea’s behavior represents a global carbon-pump “hot spot” or a broader pattern.

With atmospheric CO₂ still climbing, precise knowledge of ocean uptake is urgent. “This makes it hard to model, hindering our ability to predict how this really important process could change,” Carvalho said.

By tracking carbon in the ocean’s twilight zone, the robotic flotilla may soon deliver the clarity climate science need.

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