{"id":3515690,"date":"2025-08-26T11:38:01","date_gmt":"2025-08-26T11:38:01","guid":{"rendered":"https:\/\/www.resilience.org\/?p=3515690"},"modified":"2025-08-26T11:38:01","modified_gmt":"2025-08-26T11:38:01","slug":"the-tiny-ocean-organisms-that-could-help-the-climate-in-a-big-way","status":"publish","type":"post","link":"https:\/\/www.resilience.org\/stories\/2025-08-26\/the-tiny-ocean-organisms-that-could-help-the-climate-in-a-big-way\/","title":{"rendered":"The tiny ocean organisms that could help the climate in a big way"},"content":{"rendered":"

“This story was originally published by Grist<\/a>. Sign up for Grist’s weekly newsletter here<\/a>.”<\/em><\/p>\n

Some of the littlest organisms in the ocean wield incredible influence, both on their ecosystems and on the planet. Like plants do on land, phytoplankton absorb sunlight and carbon dioxide and expel oxygen. They process so much of those two gases, in fact, that they\u2019re responsible for half of the carbon<\/a> sequestered by photosynthesis worldwide and half of the oxygen<\/a> in the atmosphere. Phytoplankton also sit at the base of the food web as essential cuisine for their animal counterparts, the zooplankton, which in turn feed many other creatures, from fishes to crustaceans.<\/p>\n

As humanity lags far behind where it should be in reducing its greenhouse gas emissions, researchers are turning to phytoplankton for help. They\u2019re exploring how to fertilize the oceans like farmers fertilize crops, helping more of these microscopic organisms grow and eventually sink into the depths, taking carbon with them. But scientists are still exploring the many unknowns swirling around this sort of ocean fertilization, like where best to apply nutrients and in what forms, amounts, and proportions. And then they have to consider what unintended side effects might ripple through ecosystems.<\/p>\n

\u201cYou can generate a lot of biomass with relatively small amounts of micronutrient introductions, predominantly iron, and therefore the cost effectiveness is potentially pretty promising as well,\u201d said Eric Schwaab, senior fellow at Ocean Visions, which is exploring research directions for phytoplankton fertilization. \u201cBut obviously the big \u2018but\u2019 is the huge questions.\u201d<\/p><\/blockquote>\n

To answer such questions, last month scientists published a study<\/a> in the journal One Earth, in which they modeled the interaction between phytoplankton and nutrients in the Southern Ocean, which encircles Antarctica. Researchers have long known that adding iron to the sea leads to blooms of phytoplankton (back in the 1980s, one scientist declared: \u201cGive me a half tanker of iron, and I will give you an ice age\u201d), and they\u2019ve done so on a small scale. But this modeling included other elements the organisms crave, like cobalt<\/span>, zinc, and silicon.<\/p>\n

That\u2019s a critical consideration, the researchers say, because different species of phytoplankton use nutrients in different proportions. While all species need iron, a group known as diatoms rapidly consume zinc and silicon, the latter of which they use to build shells. But another group, the flagellates, more rapidly consume cobalt.<\/p>\n

So if researchers want to experiment with fertilizing the Southern Ocean, they might use this modeling to target diatoms, because they\u2019re bigger than flagellates and can store more carbon. They also sink faster, due to their shells. \u201cYou can guide the development of one of the species more than the other by selecting the elements that they need, so that they will preferentially proliferate compared to the other ones,\u201d said Willy Baeyens, an environmental scientist at the Free University of Brussels and lead author of the paper.<\/p>\n

This is where the ecological considerations come in, as ecologists will have to study the implications of tinkering with nature. \u201cCould we stimulate the wrong kinds of diatoms, like toxic Pseudo-nitzschia<\/em><\/a>, that then produce a lot of domoic acid, and that\u2019s damaging to the ecosystem?\u201d asked Katherine Barbeau, an ocean biogeochemist at the Scripps Institution of Oceanography, who studies the interaction of metals and plankton but wasn\u2019t involved in the research. (Domoic acid is a potent neurotoxin that sickens marine mammals like sea lions<\/a>, and can reach humans through tainted seafood<\/a>.) \u201cCertainly, people have raised these types of concerns.\u201d<\/p>\n

And because these organisms are food for zooplankton, researchers must ensure a change in the population of a certain phytoplankton doesn\u2019t cause further problems up the food web. Indeed, these zooplankton are essential for storing CO2: They gobble up the phytoplankton and excrete the carbon as fecal pellets, which sink to the seafloor.<\/p>\n

Phytoplankton fertilization could also change ocean chemistry. When the tiny organisms die, bacteria feast on them and soak up oxygen from the water. When phytoplankton blooms get especially big they create \u201cdead zones,\u201d where fishes and other organisms perish en masse<\/a>. \u201cOf course, you would have to fertilize on a really large scale to cause those kinds of perturbations,\u201d Barbeau said. \u201cBut I guess if you\u2019re trying to also fertilize on a scale large enough to make a dent in atmospheric CO2, that\u2019s what you\u2019re aiming to do.\u201d<\/p>\n

Exactly how much carbon dioxide the technique can capture remains an open question. Scientists need to confirm, for instance, the amount of carbon that ends up in diatoms and gets packaged in zooplankton fecal pellets, how much of that sinks, and how long it stays on the seafloor. Models can predict these things, but researchers must do longer-term experiments in the ocean to confirm.<\/p>\n

\u201cWe believe in the potential of this as a technology to help stabilize the climate, but are very interested in addressing concerns about if it works, how it works, and what kinds of consequences there might be,\u201d said Sarah Smith, an oceanographer and assistant professor at Moss Landing Marine Laboratories, who\u2019s on the steering committee for the research group Exploring Ocean Iron Solutions<\/a>. \u201cWe\u2019re really interested in ensuring that the cure isn\u2019t worse than the disease.\u201d<\/p><\/blockquote>\n

Scientists have been able to observe what happens when the planet itself fertilizes the oceans. In 2019 and 2020, wildfires in Australia spewed iron-rich smoke that fell onto the Southern Ocean, creating massive phytoplankton blooms<\/a>. And in 2019, Hawai\u02bbi\u2019s K\u012blauea released a five-mile-high plume of ash that created perhaps the largest bloom recorded in the North Pacific Ocean<\/a>.<\/p>\n

Humans, too, have been unknowingly running a vast phytoplankton-fertilizing experiment. When industries in East Asia smelt metals or burn coal, they release iron in air pollution, which rains down into the North Pacific Ocean: A recent study<\/a> found that 39 percent of iron in seawater sampled there came from human activity, supercharging phytoplankton growth<\/a>.<\/p>\n

These natural and accidental experiments, though, were free. The Southern Ocean is far from just about everything, and deploying phytoplankton-fertilizing ships will come at a cost. Yet this body of water is an enticing target exactly because of its isolation: In other oceans bordered by plenty of land, like the Atlantic, rivers and winds gather metals from the landscape and dump them into the sea, providing nutrients for phytoplankton. With so little land around the Southern Ocean \u2014 Antarctica is locked in ice \u2014 there\u2019s more potential to supplement the nutrients and encourage more growth. \u201cYou cannot go with a small rowing boat in the middle of the Southern Ocean,\u201d Baeyens said. \u201cThat\u2019s now the very big challenge, where to find sponsors that are interested in doing some pilot experiments.\u201d<\/p>\n

The experts exploring all of this are quick to note that humans can\u2019t fertilize their way out of the climate crisis. Yes, the U.N.\u2019s Intergovernmental Panel on Climate Change has said that countries will have to deploy these sorts of negative-emissions techniques, but they must first and foremost stop burning fossil fuels.<\/p>\n

\u201cNone of these things are useful at all if we don\u2019t first get control over our climate pollution,\u201d Schwaab said. \u201cNever would any responsible person see this as a substitute for decarbonizing our economy to appropriate levels.\u201d<\/p><\/blockquote>\n

This article originally appeared in Grist<\/a> at https:\/\/grist.org\/climate\/the-tiny-ocean-organisms-that-could-help-the-climate-in-a-big-way\/<\/a>.<\/p>\n

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Grist is a nonprofit, independent media organization dedicated to telling stories of climate solutions and a just future. Learn more at Grist.org<\/a><\/p>\n