Expedition Reveals Missing Ingredient in Climate Models

Expedition Reveals Missing Ingredient in Climate Models

The Earth system has a number of built-in processes triggered by changes to the climate. Understanding these feedback loops, as they're called, is essential to create accurate models of how the planet might respond to a warmer future.

A positive feedback loop - despite the name - can be deeply problematic, reinforcing, or even accelerating, a change like rising temperatures. Melting of white ice, for example, reduces the brightness of the planet, so that it absorbs, rather than reflects, more of the sun's energy and warms even faster. On the flipside, warmer ocean temperatures may lead to a proliferation of plant-like phytoplankton, which can then take more carbon dioxide out of the atmosphere through photosynthesis, an example of a negative feedback loop that could help stabilize the climate.

Most climate models make that optimistic assumption. In reality, though, observations from the nutrient-rich Southern Ocean suggest that productivity has, counterintuitively, decreased in recent decades.

This winter, an international group of researchers, including Bigelow Laboratory for Ocean Sciences' own Ben Twining, headed south to figure out why.

For six weeks, the team sailed aboard the RRS Sir David Attenborough around the rapidly warming West Antarctic Peninsula to unravel the role of certain metal elements in regulating biological productivity in the ocean. They're particularly interested in manganese. This "trace" metal appears in minute concentrations in the environment but is an essential ingredient to life. It historically has been overlooked in climate models, but the team thinks it may be key to understanding this concerning conundrum.

"There are too many factors in the Earth system to consider them all in models, so we only include those things we think are the most important, which hasn't, to date, included manganese," said Twining, a senior research scientist. "These are the models that underpin our climate predictions and goals, so it's an important question. But to even begin incorporating these processes into models, we need a lot more data."

Mighty Macronutrients

The Southern Ocean plays a critical role in the biogeochemical processes that regulate the climate, "punching above its weight," Twining explained, when it comes to how much carbon it absorbs from the atmosphere.

"What happens in the window of time when surface waters are in contact with the atmosphere in this corner of the ocean has a significant influence on the climate," he said. "And that process is controlled by iron. At least that's been our theory."

Iron is considered a micronutrient, not because it's less important than macronutrients like nitrogen - iron is essential for most forms of life - but because it's needed at much lower concentrations. In iron-limited bodies of water like the Southern Ocean, where there's a relative dearth of the element compared to other nutrients, the availability of iron is thought to ultimately determine how much plant and algae life can grow.

Scientists are just coming to appreciate, though, how important other micronutrients are.

In the last handful of years (thanks in part to the global GEOTRACES program that Twining is part of), researchers have collected extensive measurements on the abundance of several metals across the ocean. They've found that, as with iron, manganese can also be limiting in the waters around Antarctica, making this region somewhat unique in the global ocean.

That's what motivated Twining's recent expedition.

The Iron-Man project, funded by the Natural Environment Research Council and led by a researcher at the University of Liverpool, aims to illuminate the sources of iron and manganese to the Southern Ocean, how these elements move through the water column, and how quickly they're consumed and recycled by different types of plankton - with the ultimate goal of creating more nuanced models of the climate.

"The project really is multidisciplinary," Twining said. "We're led by a modeler, but we have experts in field sampling and experimental science working together to understand how manganese affects productivity and how we can start incorporating this missing piece into models."

Experiments at Sea

Sailing out of Punta Arenas, Chile, Twining and his co-scientists spent six weeks across January and February sampling at 25 sites across what Twining described as "three acts."

The first set of sites, in the far southern reaches of the Pacific, are "upstream" of the West Antarctic Peninsula given prevailing winds and currents. There, the team could observe ocean conditions before the water comes into contact with Antarctica. The final sets of sites, conversely, were in the southern edge of the Atlantic to capture conditions "downstream" of land. For the middle act, researchers sampled at several sites in the shallow waters along the continent.

At each station, researchers deployed a piece of equipment called a rosette, which can collect water samples at different depths - over 10,000 feet deep in some cases - to provide a snapshot of conditions across the entire water column. Small fans above the ship also collected tiny aerosol particles to measure how much metal-laden dust is being carried from land and dropped into the ocean (dust blown from the Sahara Desert is actually the main source of iron in the entire Atlantic Ocean).

Meanwhile, a torpedo-like device called a towfish towed alongside the ship collected surface water, pumping it directly to the labs on board where the team undertook a number of experiments. Some researchers incubated samples of algae, letting them grow over several days to see how they respond to additions of different metals and whether some favor iron over manganese. Others focused on zooplankton to understand whether these tiny animals recycle (through basic functions like peeing and pooping) the metals at different rates.

When analyzed, all of this information will give the team a more complete picture of how the relative availability of iron and manganese control the growth of plankton in the Southern Ocean - the first step to understand how future changes will reshape this critical ecosystem.

Building that knowledge in one of the most extreme parts of the ocean, known for high winds and rough seas, is no easy task (even on the state-of-the-art Attenborough, the flagship of the British research fleet). There's also the social dynamics when you have scientists from five countries living in close quarters for almost two months.

Add to that the challenges of sampling for iron from a ship made of steel. Given the trace amounts of metals they're measuring, the researchers needed to take several precautions to avoid contamination from the ship, like using specially designed, metal-free equipment and extensive filtering protocols in the labs. Even the fans for measuring aerosols were closely controlled so they could turn the equipment on and off when the winds shifted.

Twining, though, said he wouldn't change a thing.

"For six weeks, you're working together, talking about interesting ideas with people that are leaders in their field, all trying to better understand the ocean and its future," Twining said. "The science is important, but the act of doing it was inspiring. This is exactly the kind of experience for which I became a scientist."

Hear directly from Twining about his experience in Antarctica this winter at: currents.bigelow.org

Photo Captions

All photos credit Ben Twining.

Photo 1: Seawater collected with the towfish was supplied to on-board "clean" laboratories using an air-powered teflon diagphragm pump, providing researchers on-demand access to very low-iron water.

Photo 2: Senior Research Scientist Ben Twining posed for a picture in front of the Attenborough in Punta Arenas, Chile, on January 20, 2026.

Photo 3: On its way from Rothera Research Station to Palmer Station, the Attenborough sailed through the Gunnel Channel along the east side of Adelaide Island.

Photo 4: Uncontaminated water samples were collected for trace metal analysis using a special rosette.

Photo 5: The towfish was towed outboard from the ship, allowing researchers to collect surface seawater that was not contaminated by the vessel's metal hull.

Photo 6: As the expedition's conclusion neared, the towfish was retrieved at sunset in the Drake Passage on February 24, 2026.