Friday, November 14, 2025

A significant amount of dissolved organic carbon in the Arctic Ocean comes from land

New study shows that 16 percent of the Arctic Ocean’s organic carbon comes from terrestrial sources, such as thawing permafrost and eroding coastlines – and presents a new approach to assess its capacity as a carbon sink

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research

Duration thawing area "Slump D" on Herschel Island, Yukon, Canada — image:
New study shows that 16 percent of the Arctic Ocean’s organic carbon comes from terrestrial sources, such as thawing permafrost and eroding coastlines.
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Credit: Alfred-Wegener-Institut / Jaroslav Obu

Climate change and the associated rising temperatures are melting more and more frozen ground in the Arctic. This dissolved matter contains large amounts of organic carbon which is flowing into the central Arctic ocean. In a new study, scientists led by Alfred-Wegener-Institute quantified how much terrestrial organic matter accumulates in the central Arctic Ocean. Using chemical fingerprints, they were able to assess how fast it degrades, thus releasing additional CO2 to the ocean. These findings are an important basis to project how inputs from land affect Arctic marine ecosystems and the ability of the ocean to store CO2 in a warming climate. The results are published in the journal Nature Geoscience.

When permafrost thaws in the Arctic, it releases very old organic matter from plants, microorganisms or animals, containing carbon that was frozen in the soil for hundreds or thousands of years. Rivers transport this material into the Arctic Ocean, where it dissolves and turns into “dissolved organic matter (DOM)”. “This matter constitutes a large reservoir of organic carbon in the ocean, rivalling the amount of atmospheric CO2 in scale”, says Dr. Xianyu Kong, scientist at Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and first author of the study. “Compared to most other oceans, the Arctic Ocean receives more freshwater and a disproportionally large amount of terrestrial organic matter from extensive inputs from permafrost thaw, river discharge, and coastal erosion.”

Together with German, Norwegian and Danish colleagues, the AWI scientist has now quantified, how much organic carbon is accumulated in the central Arctic Ocean. „Our study reveals that about 16 percent of all dissolved organic carbon here originates from land, much of it persisting even in deep waters, where we surprisingly found a consistently high terrestrial contribution,” says Xianyu Kong. “This suggests that some of land-derived organic matter is chemically stable enough to survive long transport and move from the central Arctic ocean to the North Atlantic Deep Water. This connects Arctic processes with the global carbon cycle.”

Terrestrial dissolved organic carbon is also transported in surface waters: The so-called Transpolar Drift is a surface current that transports freshwater, sea ice as well as nutrients across the Arctic Ocean towards the North Atlantic. The amount of organic carbon in regions that are affected by the Transpolar Drift was about twice as high in neighboring regions. From this, the research team estimated that around 39 million tons of terrestrial carbon are transported from the Arctic to the Atlantic every year.

Map Shows Terrestrial Dissolved Organic Carbon in the Arctic Ocean

DOM from terrestrial sources impacts the organic carbon cycle in the Arctic Ocean by changing light attenuation, nutrient availability, or microbial processes. “Previous studies show that the concentration of dissolved organic carbon increases in freshwater environments as a response to climate change”, says Prof. Boris Koch, co-author of the study and chemical oceanographer at AWI. “For the Arctic Ocean, however, there is no data available that shows similar trends, partly due to the lack of appropriate methods.” With their results, the AWI researchers are filling a knowledge gap in the understanding of how much carbon enters the Arctic Ocean from land, how it is distributed, and how it changes in the ocean. “As Arctic warming accelerates, inputs of terrestrial organic matter are expected to increase, potentially altering carbon cycling and broader biogeochemical processes in the Arctic Ocean”, says Xianyu Kong. Previous climate models do not yet reflect these findings. “These findings are an important basis for predicting how inputs from land affects Arctic marine ecosystems and the Arctic carbon inventory in a warming climate.”

For the analysis, the researchers, in collaboration with the Helmholtz Centre for Environmental Research (UFZ), developed a new analytical approach over several years to analyze seawater samples from across the central Arctic Ocean that they have collected during the MOSAiC expedition in 2019 /2020. To measure the organic compounds in the samples, they used ultrahigh-resolution Fourier-transform mass spectrometry (FT-ICR MS). “This method allowed us to identify and quantify thousands of individual organic molecular formulas in seawater and distinguish whether they originated from the ocean and sea ice or terrestrial sources”, says Xianyu Kong. “We were not only able to quantify the concentration of terrestrial carbon, but also to estimate how far the degradation of the organic material has already progressed.” Using this method, the researchers were able to produce the first depth-resolved map of dissolved terrestrial organic carbon in the Arctic Ocean.

Original publication

Kong, X., Lechtenfeld, O.J., Kaesler, J.M. et al. Major terrestrial contribution to the dissolved organic carbon budget in the Arctic Ocean. Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01847-5

Journal

Nature Geoscience

DOI

10.1038/s41561-025-01847-5

Article Title

Major terrestrial contribution to the dissolved organic carbon budget in the Arctic Ocean

Article Publication Date

7-Nov-2025

When ants battle bumble bees, nobody wins

Invasive Argentine ants prevent bees from eating

University of California - Riverside

Bumble on a lupin — image:
Bumble bee and ant at the same flower.
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Credit: David Rankin/UCR

When bumble bees fight invasive Argentine ants for food, bees may win an individual skirmish but end up with less to feed the hive.

Bumble bees are already under pressure from habitat loss, disease, and pesticides. Former UC Riverside entomology graduate student Michelle Miner wondered whether aggressive ants might be adding to that stress.

“With how important bumble bees are as pollinators, it made sense to try and understand more about what’s going on in these tiny nectar wars, because they could have a big impact,” Miner said.

Her research, published in the Journal of Insect Science, analyzed over 4,300 individual behaviors from more than 415 bumble bees.

Performed in UCR professor Erin Wilson Rankin’s lab, the experiments involved six separate bumble bee colonies foraging in a shared arena. The bees could choose feeders that either had ants nearby or were ant-free.

Argentine ants, sometimes called sugar ants, do not sting but they do bite and can overwhelm other insects with sheer numbers.

“They can dominate a food resource just by showing up en masse,” Wilson Rankin said.

Given the choice, bees avoid ants. The more ants at a feeder, the less likely bees were to attempt feeding there. Unsurprisingly, more ants also meant a higher chance of bees being bitten. Still, the ant bites were not fatal. And if provoked, some bees fought back.

“We do see the aggression being bi-directional,” Wilson Rankin said. “Sometimes you’ll see ant heads on the bee legs because they were feeding and in response to an attack, the bee bit the ant and decapitated it.”

Though bumble bees can sting without dying, unlike honeybees, Miner didn’t observe any stings during the study. Instead, battling bees typically used their mandibles to fight their ant adversaries.

“Mandibles are like teeth but not only used to chew,” Miner said. “They can flare open to handle flowers or crunch a foe.”

Thanks in part to their much larger size, bumble bees who responded aggressively to the ants were generally victorious in one-on-one fights in this lab study. But that likely doesn’t translate into a win for the entire bee colony.

Instead of returning to foraging after encountering an ant, bees often stayed locked in further confrontations.

“The ant presence induced prolonged aggressive exchanges,” Wilson Rankin said. “Even though that one bee might benefit from being aggressive in the short term, it may not be beneficial for the colony overall.”

When the bees go into attack mode, they aren’t feeding.

“They’re wasting energy, they could be getting harmed, and they’re not bringing food back,” Wilson Rankin said.

Whether the hive compensates for lost food is unknown.

“We do know that the youngest bees don’t leave the colony. Once they’re old enough to ‘get their licenses’ they go out and forage,” Wilson Rankin said. “We don’t know if the colony sends out additional foragers when one comes back short. That’s the next question it’s important to answer.”

Bees and ants at the same lab feeder.

Credit

Michelle Miner/UCR

An Argentine ant and bumble bee sharing the same flower resource.

Credit

David Rankin/UCR