A groundbreaking new study has unveiled compelling evidence of enhanced marine burial of terrestrial organic carbon during one of Earth’s most dramatic climate events: the Palaeocene–Eocene Thermal Maximum (PETM). Spanning roughly 55 million years ago, the PETM represents a window into rapid global warming, often considered a natural analogue to modern anthropogenic climate change. This research harnesses innovative biomarker proxies paired with sophisticated mixing models and climate simulations to unravel the complex pathways of carbon cycling between land and ocean during this pivotal interval.

At the heart of this investigation lie branched glycerol dialkyl glycerol tetraethers (brGDGTs) and long-chain n-alkanes, molecular fossils derived from bacterial and terrestrial plant sources, respectively. These biomarkers serve as unique fingerprints that allow scientists to distinguish inputs of organic carbon originating from soils and vascular plants, versus that synthesized or deposited within marine systems. By compiling and analyzing brGDGT and n-alkane data from multiple PETM-aged sediment cores spread across geographically diverse sites—from the High Arctic to the Tasman Sea—the researchers bridged geographic and depositional contexts to create a comprehensive view of carbon sourcing.

The methodology builds on carefully extracted lipid fractions separated via microwave-assisted and accelerated solvent extractions, followed by advanced chromatographic and mass spectrometric techniques. Gas chromatography tandem mass spectrometry (GC-MS/MS) was leveraged for hydrocarbon analyses such as n-alkanes, while high-performance liquid chromatography mass spectrometry (HPLC-MS) targeted polar fractions containing brGDGTs. These high-resolution extraction and detection methods ensured robust molecular quantification critical for downstream proxy calculations.

Several key indices were calculated to differentiate terrestrial versus marine organic carbon sources. The branched-to-isoprenoid tetraether (BIT) index quantitatively captures the balance between soil-derived branched GDGTs and marine archaeal crenarchaeol, with soil endmember values derived from an extensive modern peat and soil database, and marine endmember values from distal ocean sediments. Complementarily, the terrestrial-to-aquatic ratio (TAR), based on the abundance of long-chain versus short-chain n-alkanes, serves as a proxy for vascular plant contributions. These indicators were integrated into a rigorous three-endmember mixing model, facilitating the quantification of soil, plant, and marine fractions in PETM sedimentary organic carbon.

A significant innovation in the study is how the mixing model accounts for conservative tracers insensitive to certain endmembers, enabling refined calculations even when biomarkers partially constrain source inputs. This non-negative least squares approach, solved within a Monte Carlo framework incorporating endmember uncertainty and allowing for minor contributions from uncharacterized sources, generates statistically robust source apportionment. The approach was validated against modern Gulf of Mexico sediments, demonstrating high fidelity in reconstructing known terrestrial versus marine carbon contributions.

Quantifying historical carbon mass accumulation rates (MARs) involved integrating fractionated organic carbon proportions with independently derived sedimentation rates and bulk densities from multiple PETM sedimentary records. Standardizing dry bulk density assumptions based on typical detrital and clay mineral densities ensured consistency across sites. This multi-site MAR assessment revealed nuanced shifts in terrestrial carbon burial efficiency during the PETM, reflecting changes in sediment supply, organic carbon preservation, and coastal-marine interactions under extreme warming conditions.

Climate modeling experiments provided the contextual framework for interpreting these geochemical findings. Utilizing the DeepMIP ensemble within the Paleoclimate Modelling Intercomparison Project (PMIP4) and the Coupled Model Intercomparison Project Phase 6 (CMIP6), simulations were executed with varying atmospheric CO₂ concentrations, ranging from pre-industrial levels to multiples up to sixfold. Normalized mean annual precipitation fields extracted from multi-model means enabled the assessment of hydrologic impacts of elevated greenhouse gas forcing on terrestrial and marine carbon dynamics.

Further nuance is provided by the Hadley Centre’s coupled atmosphere-land model configuration incorporating the MOSES2.1 land surface scheme and TRIFFID dynamic vegetation and carbon cycle model. Spanning two key atmospheric CO₂ scenarios bracketing the PETM transition, this framework allowed estimation of changes in vegetation distribution, soil carbon stocks, and ecosystem productivity under palaeoclimate boundary conditions. These models affirm the plausibility of enhanced terrestrial organic carbon export and subsequent marine burial under PETM warming, as observed in empirical sediment biomarker records.

The sophisticated integration of geochemical proxies, sedimentological data, and model simulations collectively advances our understanding of carbon cycling feedbacks during hyperthermal intervals. Accelerated burial of terrestrial organic carbon in marine sediments would have acted as an important carbon sink mechanism, potentially modulating atmospheric CO₂ levels and climate evolution through the PETM. This insight bridges a critical knowledge gap regarding organic carbon fluxes from continents to oceans during rapid warming events in Earth’s deep past.

Moreover, the study’s methodological framework—combining conservative tracer endmember mixing with uncertainty quantification—represents a transferable approach applicable to other geological intervals characterized by coupled climate-carbon perturbations. It highlights the vital role of molecular-level biomarker analyses in reconstructing paleoecosystem structure and sedimentary carbon sources, deepening our ability to predict carbon cycle sensitivity to future climatic changes.

These findings challenge simplistic interpretations of terrestrial carbon loss during warming, revealing instead that significant portions were transferred and buried in marine environments, emphasizing complex cross-system connectivity. This underlines the importance of integrated biogeochemical and climate modeling perspectives to reconstruct feedbacks governing Earth system resilience and tipping points.

Crucially, the validation of biomarker endmembers via modern analogs—such as the Mississippi–Atchafalaya River system—strengthens confidence in the approach’s accuracy and relevance. By demonstrating model outputs consistent with contemporary river-coastal sediment organic carbon distributions, the study underscores the robustness of proxy-based quantitative source apportionment.

This multidisciplinary effort pushes the frontier in paleoenvironmental science, with implications extending from fundamental deep-time carbon cycle reconstructions to informing projections of future organic carbon dynamics under anthropogenic climate forcing. It exemplifies how state-of-the-art analytical chemistry, sedimentology, and Earth system modeling converge to unravel complex Earth processes critical to understanding planetary climate stability.

Further research building on these results might explore finer temporal resolution biomarker studies, integration with isotopic measurements, and expanded geographic coverage to refine the spatial heterogeneity of organic carbon sources and burial efficiencies. Additionally, investigating mechanisms underpinning organic matter preservation in marine sediments under elevated temperatures could illuminate pathways controlling long-term carbon sequestration.

In conclusion, this seminal work presents unprecedented insights into the enhanced burial of terrestrial organic carbon in marine settings during the PETM, a period typified by rapid, profound climate change. Through an elegant fusion of biomarker geochemistry and climate simulation, it opens new vistas in deciphering Earth’s carbon cycle responses and offers a potent analog to contemporary global warming scenarios.

Subject of Research: Enhanced marine burial of terrestrial organic carbon during the Palaeocene–Eocene Thermal Maximum

Article Title: Enhanced marine burial of terrestrial organic carbon through the Palaeocene–Eocene Thermal Maximum

Article References:
Inglis, G.N., Hemingway, J.D., Stockey, R.G. et al. Enhanced marine burial of terrestrial organic carbon through the Palaeocene–Eocene Thermal Maximum. Nat. Geosci. (2026). https://doi.org/10.1038/s41561-026-02012-2

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41561-026-02012-2

Humanity has littered the sky with the refuse of fossil fuel use, releasing enough CO₂ to change the planet’s climate. We are also chucking incredible sums of carbon in the form of plastics into landfills and into the environment around (and inside of) us. What if cleaning up one of these problems could also help clean up the other?

A new study led by Ruth Ebenbauer at Aarhus University experiments with this idea by upcycling discarded polystyrene into (part of) a material commonly used in carbon-capture systems.

Adding amines

This material is based on amines—a simple chemical group that conveniently acts like a sponge for CO₂. An amine will grab CO₂ molecules when exposed to them, but let go of the CO₂ when heated or depressurized, leaving it ready to go again. The first “CO₂ scrubbers” tried in smokestacks used amines dissolved in water to do this, but solid amines are used in all kinds of carbon-capture systems now because they require less energy. These solid materials—often made into granules similar to the activated carbon in a water filter—have high surface area and high porosity, so the amines can efficiently partner up with CO₂ molecules.

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Thousands of electric vehicles in Waymo’s autonomous robotaxi fleet may eventually give up their used batteries for a very different purpose—contributing up to hundreds of megawatt-hours of stationary energy storage to local power grids.

That prospect comes from a “strategic supply agreement” announced by Waymo and B2U Storage Solutions on June 4. B2U has been repurposing thousands of used batteries from various electric vehicles by installing them in large stationary energy storage projects. Such energy storage facilities can capture excess renewable energy during low demand periods and release such energy when local power grids are experiencing peak demand periods.

“Our business is getting the full residual value out of electric vehicle batteries after they're no longer suitable for automotive use,” Freeman Hall, CEO of B2U Storage Solution, told Ars. “Waymo puts a lot of miles on EVs and their model is expanding rapidly, and so we're just very pleased and honored to be able to work with them.”

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Over 20 million tons of polystyrene plastic are produced annually, yet only a small fraction is recycled worldwide. Current recycling methods consume large amounts of energy and often rely on harsh and toxic chemicals to break the strong molecular chains that make up polystyrene. One possible solution is the use of sulfur, which is an inexpensive byproduct formed when refining crude oil. Its unique chemical structure allows it to break up strong chemical chains in long plastic molecules. Despite its abundance, sulfur has very limited applications, and converting it into more usable forms tends to require a lot of heat, rendering it unused for long periods of time. 

Researchers at the Dalian Institute of Chemical Physics hypothesized that sulfur could help break down polystyrene waste to form more valuable chemicals. To power this reaction, they converted sunlight into heat energy through a process called photothermal conversion. They used this heat to transform polystyrene and sulfur into valuable chemicals like 2,4-diphenylthiophene, or chemical D, and 1,3,5-triphenylbenzene, or chemical T, which are used to make semiconductors and chemical sensors. 

To test this, the team mixed ground polystyrene and sulfur at a molar ratio of 1:0.5 in a glass test tube. They sealed the tube with a balloon and secured it onto an iron stand. Then, they focused sunlight onto the bottom of the tube using a curved mirror. As the mixture heated up, the yellow-white solids gradually melted and transformed into a reddish-black liquid after 2 minutes. After heating, the researchers removed the mirror and allowed the system to cool before collecting the gaseous products from the balloon and dissolving the remaining solids for further purification and analysis. 

The researchers then adjusted the reaction conditions to understand what factors influenced their results. They tested the reaction without sulfur, varied the sulfur ratios from 0.2 to 0.8, and replaced elemental sulfur with other sulfur-containing compounds. They also explored adding known photothermal agents, specifically metal oxide additives, to the mixture. 

To compare the difference between sunlight and artificial light, the researchers repeated the experiment indoors using a 100 Watt LED bulb and monitored temperature changes with a thermal camera. They also ran a control experiment using only polystyrene to check how sulfur affected the yield under LED light. They also tested exposure times from 1 to 6 minutes in 1-minute increments to determine how long it took to achieve the highest yields under LED. The researchers used these tests to identify which conditions were necessary for the reaction to occur and how different factors influenced its outcome.

They found that without sulfur or with alternative sulfur-containing compounds, the reaction did not produce chemical D or T under sunlight. In contrast, reactions that included sulfur successfully produced these target products, with the highest yields of 34% for D and 16% for T at a sulfur ratio of 0.5. When they added metal oxides, the chemical yields decreased to 22% and 12%, respectively, suggesting that these additives interfered with the desired reactions. In addition, when the researchers switched from sunlight to LED, the reaction yields dropped to 26% for D and 13% for T. 

Next, they examined how reaction time influenced product formation. They found that yields increased gradually before reaching the maximum at 4 minutes and leveling off. They also noted that mixtures containing sulfur heated up from room temperature to 320°C (608°F), while the control setup only showed a slight temperature increase. The researchers interpreted these results as confirmation of sulfur’s dual role as a reactant and a light-to-heat converter that enables the conversion of polystyrene to useful chemicals.

Taking it a step further, the researchers tested their method on real-world polystyrene wastes, including food packaging, cup lids, and foamed plastics. They successfully produced chemicals D and T from these materials, demonstrating that their process works beyond laboratory samples.

The team concluded that their study presents a simple, fast, and solvent-free approach to converting 2 abundant waste materials into valuable chemicals using sunlight. By combining polystyrene waste and excess sulfur, the researchers offer a new pathway for sustainable polymer upcycling that uses clean energy and is broadly applicable to everyday plastics.

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