The Ocean’s Biological Shield Is Failing: Why It’s Stopping CO2 Absorption

Hidden Truth Revealed by 4,000 Deep-Sea Robots

While research vessels slice through the waves and satellites track water temperatures from orbit, a hidden army of robots operates a mile beneath the surface. These cylindrical aluminum devices come equipped with a range of sensors that measure the ocean’s most vital health parameters: acidity, oxygen, other elements, and temperature. Critically, they also help scientists track the progress of global warming.

Dr. Ken Johnson from the Monterey Bay Aquarium Research Institute (MBARI) explained on IEEE Spectrum, “When you feel sick and go to the hospital, they don’t immediately perform an MRI. They first check your vital signs—that’s exactly what these robots do.”

Currently, over 4,000 of these autonomous devices drift in waters worldwide as part of the international Argo network. The American institute MBARI supplied 330 of the most advanced units.

The Alarming Reality of the ocean global warming role

These devices are fully autonomous. First, they submerge to 1,000 meters (about 3,300 feet) and drift freely for ten days. Then, they drop to 2,000 meters before slowly ascending to the surface. Throughout this cycle, they collect detailed data on the surrounding waters, which they immediately transmit to scientists upon resurfacing.

The Argo program began 26 years ago, but continuous monitoring finally allows researchers to see how oceans react to years of marine heatwaves. The analysis of the data, gathered by this underwater robotic army, recently appeared in the journal Nature Communications.

Sea Heatwave Effect: A Scenario Scientists Didn’t Expect

The oceans annually reduce about 25% of all carbon dioxide humanity emits. This occurs thanks to a simple biological cycle: Plankton at the surface absorbs CO2 and small fish eat it. These organisms convert the CO2 into fecal pellets that sink to the seabed. In this form, the carbon remains trapped for centuries, even millennia, without impacting the climate. But what happens if those tiny particles never reach the ocean floor?

The Detrimental Impact of Rising Temperatures

The new study linked data collected by the underwater robots with plankton DNA analyses. Scientists focused particularly on two marine heatwaves in the Gulf of Alaska between 2013–2015 and 2019–2020. These were periods when local water temperatures exceeded the historical average. The analysis results were indeed disturbing.

The researchers concede that the carbon transport system—the process of plankton and the organisms that eat it sending CO2 to the ocean floor—is now disrupted. Higher temperatures caused an increase in the number of small herbivores. These tiny consumers form the weak link in the chain.

In both studied periods, plankton very efficiently absorbed CO2 through photosynthesis. However, the fecal pellets of the small herbivorous fish that ate the plankton were too light to sink to the bottom. Instead, the particles accumulated at depths of around 200 meters (about 660 feet).

Carbon Dioxide Leaks Back into the Atmosphere

Lower storage depth for CO2 carries serious consequences. “If the material only falls 100 meters, bacteria remineralize it, convert it back into CO2, and it simply mixes back in with the atmosphere,” Johnson stated. “But if the material falls 2 kilometers deep, it’s out of contact with the atmosphere for hundreds of years,” he emphasized.

The data analysis from the drifting robot system reveals the complexity of CO2 in its various forms on our planet. The impact of rising temperatures on the ocean’s ability to clean our atmosphere of this greenhouse gas is especially concerning.

Global warming thus becomes a vicious cycle. The warming climate disrupts the very processes that could limit it. The oceanic ecosystem offered a safeguard against excessive temperature increases—but that safety net is disappearing. “We now see that the ocean global warming role, and its ability to continue providing these services, is not a given forever,” Dr. Ken Johnson concluded plainly.

Read this article in Polish: Biologiczna tarcza Ziemi słabnie. Ocean przestaje pochłaniać CO2