📄 earth_science

Carbon release from Chatham Rise pockmarks may have been climatically relevant during the last deglaciation

This study uses a 2D hydromechanical model to demonstrate that rapid fluid release from Chatham Rise pockmarks during the last deglaciation could have emitted approximately 2 Petagrams of CO2 per year, a rate significantly higher than that of the Paleocene-Eocene Thermal Maximum, suggesting such geologic carbon release was a major, previously underappreciated driver of deglacial atmospheric CO2 trends.

Original authors: Katrina Magno, Jess Hillman, Ludovic Räss, Lowell Stott, Jenny Suckale

Published 2026-08-20

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CC BY 4.0

Original authors: Katrina Magno, Jess Hillman, Ludovic Räss, Lowell Stott, Jenny Suckale

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Deep beneath the ocean floor, vast reservoirs of ancient carbon lie trapped within layers of rock and sediment. For decades, scientists have known that the Earth's climate is tightly linked to the amount of carbon dioxide in the atmosphere, but the precise mechanisms that move this carbon between the deep Earth and the air have remained somewhat mysterious. One key question has been how quickly and in what quantities this geologic carbon can escape to the surface, particularly during times when the planet is warming up and ice sheets are melting. When massive amounts of ice melt, the weight pressing down on the ocean floor changes, and this shift can trigger the release of fluids from deep underground. If these fluids carry carbon dioxide, they could potentially accelerate global warming, creating a feedback loop where warming leads to more carbon release, which leads to more warming. Understanding these hidden pulses of gas is crucial for reconstructing the climate of the past and predicting the behavior of the Earth system in the future.

Off the coast of New Zealand, a submarine plateau known as the Chatham Rise holds a massive, silent clue to this process. The seabed there is pockmarked with over 45,000 crater-like depressions, formed by the expulsion of fluids from below. While similar craters in other parts of the world are often linked to the release of methane gas from melting ice, the Chatham Rise was never covered by glaciers, and its craters do not contain methane. Instead, chemical evidence suggests these craters are vents for ancient carbon dioxide that has been locked away for millions of years in limestone rocks deep within the Earth's crust. The timing of these craters appearing points directly to the last time the world was coming out of an ice age, a period known as deglaciation. This raises a compelling possibility: that the rapid rise in sea level during that time acted like a switch, unlocking deep carbon reservoirs and pumping them into the ocean and atmosphere.

To test this idea, a team of researchers built a computer simulation of the ocean floor beneath the Chatham Rise. They focused on the thick layers of clay-rich sediment that sit between the deep carbon reservoirs and the seafloor. In normal times, when sea levels are stable, fluids move slowly and evenly through these sediments, like water soaking through a sponge. However, the researchers modeled what happens when sea levels rise quickly, as they did during the end of the last ice age. Their model showed that this rapid increase in water weight pushes the clay sediment into a state where it cannot drain fast enough. This pressure builds up and forces the fluid to find the path of least resistance, breaking through the sediment in narrow, powerful channels rather than seeping out gently. These channels eventually reach the surface, creating the craters seen on the seafloor today.

The simulation revealed that once these channels form, they transport fluid at a rate roughly a thousand times faster than the slow, steady seepage that occurs in between ice ages. By applying this model to the 476 small craters that have been mapped in detail, the researchers estimated the volume of fluid that could have been released during the first wave of this activity. They calculated that the fluid volume moving through these pathways was approximately 1,800 cubic kilometers per year. To understand the climate impact, the team then converted this fluid volume into a mass of carbon dioxide. Even using the most conservative estimates—assuming the fluid contained only a tiny fraction of carbon dioxide and was in a gaseous state—the result was staggering. The release rate came out to about 2 petagrams of carbon dioxide per year.

This number is significant when placed in the context of Earth's history. The researchers compared their finding to the onset of a famous ancient warming event called the Paleocene-Eocene Thermal Maximum, which caused massive extinction and global temperature spikes. Their estimate suggests that the carbon release from the Chatham Rise pockmarks alone was about four times faster than the rate of carbon release inferred for the start of that ancient catastrophe. While the study focused on a specific subset of craters and used a simulation rather than direct measurement, the results suggest that geologic carbon release from fields like the Chatham Rise may have been a major, yet previously overlooked, driver of climate change during the last deglaciation. The study indicates that the Earth's deep carbon cycle is capable of responding rapidly to surface changes, potentially delivering massive pulses of greenhouse gases that could have helped shape the climate of the past.

Technical Summary: Carbon Release from Chatham Rise Pockmarks

Problem Statement
Rapid release of geologic carbon from continental margins during Late Pleistocene deglaciations is hypothesized to have contributed to atmospheric CO₂ trends, yet the climatic relevance of individual release events remains unquantified. While pockmark fields on formerly glaciated margins (e.g., Barents Sea, North Sea) are linked to methane release via gas hydrate dissociation driven by ice-sheet retreat, the Chatham Rise off New Zealand presents a distinct mechanism. This region, never glaciated, hosts over 45,000 pockmarks. Geochemical evidence indicates these features are not driven by shallow methane but by deep, ancient carbon sourced from subducted Mesozoic limestones of the Hikurangi Plateau. The central problem addressed is whether the transition from distributed seepage to localized fluid release through these deep pathways during deglacial sea-level rise could generate a CO₂ flux significant enough to impact the global carbon cycle.

Methodology
The authors employ a 2D hydromechanical model to simulate fluid transport through a clay-rich sediment column beneath the Chatham Rise. The model treats the marine subsurface as a mixture of two incompressible phases: carbon-rich fluid and sedimentary rock, solving volume-averaged equations for mass and momentum conservation.

Key methodological components include:

Regime Comparison: The study contrasts a quasi-steady, fully drained regime (representing interglacial periods) with a disequilibrium, partially undrained regime driven by rapid surface loading (sea-level rise).
Parameterization: Sediment properties are constrained by IODP Expedition 372/375 data from the Hikurangi margin, specifically silty clay with permeabilities ranging from $3.0 \times 10^{-17}$ to $6.0 \times 10^{-14} \text{ m}^2$ . The model utilizes a porosity-dependent permeability relationship ( $k_\phi = k_0 (\phi/\phi_0)^{n_k}$ ) and poroviscous deformation to capture the asymmetry between compaction and decompaction.
Simulation Setup: The authors test initial permeability ( $k_0$ ) values between $5 \times 10^{-16}$ and $5 \times 10^{-15} \text{ m}^2$ , selecting $5 \times 10^{-15} \text{ m}^2$ as the best fit for observed pockmark sizes. The simulation tracks the emergence of localized fluid pathways (pockmarks) as the sediment matrix transitions to an undrained state.
Flux Estimation: Fluid volume flux is calculated by identifying peaks in vertical flux along the seafloor, approximating them as 2D Gaussian surfaces, and integrating the product of area and peak flux. The analysis focuses on the "first wave" of localized pathways, defined as the interval from the onset of localization to the first local minimum in total vertical flux.
Carbon Conversion: To estimate CO₂ mass flux, the authors apply conservative bounds: a CO₂ volume fraction of 1–5% (based on solubility limits in brine) and two phase densities (gas and liquid) corresponding to the water depths of the pockmarks (250–700 m).

Key Results

Localization Mechanism: The model demonstrates that rapid sea-level rise drives the sediment matrix into a partially undrained, viscously deforming state. This triggers the localization of flow, where vertical fluxes within emerging pathways exceed the distributed background flux of the quasi-steady regime by approximately three orders of magnitude ( $\sim 10^3$ ).
Fluid Volume Flux: For the 476 mapped small pockmarks (<1.45 km²) on the Chatham Rise, the integrated fluid volume flux during the first wave of localized release is estimated at approximately $1.8 \times 10^3 \text{ km}^3/\text{yr}$ .
CO₂ Mass Flux: Even under the most conservative assumptions (1% CO₂ by volume in gaseous form), the estimated release rate is approximately 2 Petagrams (Pg) of CO₂/yr.
Comparative Magnitude: This lower-bound estimate is roughly a factor of four greater than the median CO₂ release rate (0.6 Pg/yr) inferred for the onset of the Paleocene-Eocene Thermal Maximum (PETM).

Significance and Claims
The paper argues that geologic carbon release from pockmark fields may be a previously underappreciated component of the deglacial carbon cycle. The authors claim that the mechanism proposed—tapping into deep, ancient reservoirs of geologic carbon through clay-rich sediments via rapid loading—differs fundamentally from the shallow methane release mechanisms observed on glaciated margins.

The significance of the findings lies in the magnitude of the estimated flux. The authors state that a release rate of ~2 Pg CO₂/yr, sustained over a window short relative to the ocean carbon-cycle response (decades to centuries for South Pacific intermediate waters), is climatically relevant. They suggest that similar pulses from clay-rich continental margins worldwide could contribute to the "sawtooth-shaped" carbon cycle variations recorded in ice cores, though they emphasize that quantifying this contribution globally requires field-specific evidence currently lacking. The study does not claim to have modeled the thermodynamics or geochemistry directly but provides a hydromechanical framework to estimate the potential scale of such deep carbon release events.

Technical Summary: Carbon Release from Chatham Rise Pockmarks

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