Silicate alteration in marine sediments: kinetics, pathway, and dependency

Project Information

MadSilica

Grant agreement ID: 101087884

DOI

10.3030/101087884

EC signature date 27 February 2023

Start date 1 July 2023

End date 30 June 2028

Funded under

• European Research Council (ERC)

Total cost

€ 1 999 780,00

EU contribution

€ 1 999 780,00

Coordinated by

STOCKHOLMS UNIVERSITET
Sweden

Periodic Reporting for period 1 - MadSilica (Silicate alteration in marine sediments: kinetics, pathway, and dependency)

Reporting period: 2023-07-01 to 2025-12-31

Summary of the context and overall objectives of the project

Silicate, one of the most abundant mineral types on the Earth’s surface, has quietly regulated the concentration of atmospheric CO2 for millions of years through processes called silicate weathering and reverse weathering. Despite shifts between Greenhouse and Icehouse conditions, driven by fluctuations in atmospheric CO2 content and/or insolation strength, these processes have helped make Earth the only known habitable planet in the universe. Weathering of subaerial silicate minerals is believed to be the primary process absorbing CO2 from the atmosphere. In simple terms, silicate weathering acts as a vast natural thermostat: rainwater and carbon dioxide react with silicate rocks to form dissolved ions, which eventually lock carbon away in carbonate rocks over geological timescales.
Despite the large surface area—more than 70% of the Earth’s surface is now covered by ocean—silicate in marine environments is thought to contribute little to overall weathering, while most reverse weathering has been shown to occur in the ocean. In reverse weathering, marine minerals recombine with dissolved silica, releasing CO2 back into the atmosphere—a process that can offset the cooling effects of terrestrial weathering. This apparent “tug-of-war” between land and sea processes remains poorly quantified.
Such a contrast—terrestrial silicate weathering consuming CO2 while marine reverse weathering returns CO2 to the atmosphere—contradicts recent estimates suggesting that marine silicate weathering could be as important as its terrestrial counterpart. If this is true, we may have seriously underestimated the long-term strength of Earth’s natural carbon sink, with implications for both ancient climate reconstructions and modern climate change predictions.
The project MadSilica aims to resolve this conflict in our current understanding of the role of marine silicate in regulating CO2 and the Earth’s overall carbon cycle. The central question MadSilica seeks to answer is: can marine silicate weathering be as efficient as its terrestrial counterpart? By addressing this, the project will provide essential insights for climate models, carbon budget assessments, and potentially strategies for managing future CO2 levels.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Over the past two years, MadSilica has achieved several critical milestones by combining laboratory experiments, field observations, and numerical modelling to quantify the rates of silicate mineral decomposition and formation in marine sediments. A global dataset was compiled, including 48 sites where silicate alteration processes were documented in the literature. These sites span diverse environments with different silicate sources, providing a broad picture of global variability.
Analyses of the global database helped identify key environmental factors that govern the rate of marine silicate weathering. A numerical model constrained by this dataset was developed, and through it, the mica group silicate emerged as the most important phase for weathering. To validate the model, a laboratory method was created to chemically resolve different silicate phases in marine sediments. This method allows us to separate and analyse individual silicate phases directly, making it possible to track their specific alteration pathways.
Its applicability was successfully tested on sediments from varied environments and silicate sources. Chemical analyses confirmed the key role of mica group silicate, as suggested by the model. Studying different silicate phases in sediment archives revealed interactions between silicate and particulate carbon phases that further corroborated our modelling results.

A major achievement to date has been the integration of field observations with numerical modelling, creating a consistent framework for understanding marine silicate weathering at both local and global scales. In parallel, the project has developed a high-pressure, low-temperature incubation system capable of replicating deep-sea conditions—cold, dark, and hundreds of times atmospheric pressure. While incubation results are not yet incorporated into the integrated framework, a month-long trial has demonstrated stable system performance, with continuous sampling by an automated system to minimise disturbance. These incubations will be critical in the next project phase for testing model predictions under controlled laboratory conditions. Maintaining realistic conditions for marine silicate processes remains the highest priority for the rest of the project, enabling direct comparison between laboratory, field, and model results.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The successful prediction of field observations by numerical modelling has significant potential to advance our understanding of marine silicate alteration, bringing us closer to a mechanistic understanding of the process and its environmental dependency—the primary goal of MadSilica. This is the first time that marine silicate weathering has been linked quantitatively to specific mineral phase and sedimentary conditions, offering a predictive framework rather than descriptive correlations. Such a shift from observation-driven patterns to process-based prediction is a critical step toward integrating marine silicate weathering into global carbon cycle models with higher confidence.
Being able to associate marine silicate weathering with the burial conditions (time and temperature) of mica group silicate allows us to connect the process with specific sedimentary settings—a key step toward large-scale extrapolation. This link enables researchers to identify which parts of the seafloor act as long-term carbon sinks and which may release CO2, improving our ability to reconstruct past climate shifts and anticipate future carbon cycle feedbacks under a warming climate.
The next step is to examine the key controls of marine silicate alteration through laboratory incubation so these factors can be systematically tested under controlled conditions and understood from first principles. By adjusting parameters such as temperature, fluid composition, and sediment physical properties in isolation, MadSilica will be able to identify which factors exert the strongest influence and under what thresholds they change the direction of the process—from a CO2 sink to a source.
Reaching this level of detail is beyond the current state of the art because it requires long-term stability in high-pressure, low-temperature incubations—conditions notoriously difficult to sustain. The initial successes of our system show promise but also highlight the persistence needed to maintain such conditions for months or even years. Continued automation of incubation and sampling will reduce human error, enabling more reliable, continuous datasets. The approaches developed here could also be adapted to study other critical sedimentary processes, with potential applications in climate science, oceanography, and carbon sequestration research.