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Sediment diagenesis encompasses the suite of physical, chemical, and biological changes that convert freshly deposited sediments into more stable, lithified rocks within the first few meters of the seafloor. On continental margins, the interplay between rapid sediment supply, organic matter decay, and seawater intrusion creates a dynamic zone where minerals dissolve, precipitate, and re-form. The resulting porosity changes influence diffusion routes for nutrients and methane, while iron, manganese, and sulfate reductions alter redox conditions deeper in the substrate. Understanding these processes is essential because diagenetic pathways regulate how much carbon remains trapped as organic matter or gets re-released as carbon dioxide or methane to the ocean and atmosphere over millennial timescales.

Researchers approach this topic by integrating in situ sampling with laboratory incubations and advanced modeling. Core samples reveal porewater chemistry profiles, mineral assemblages, and textures that document diagenetic fronts shifting with age and local climate. Isotopic analyses trace carbon sources and turnover rates, while microelectrode measurements map redox gradients. High-resolution imaging isolates microfossil communities that influence sulfate reduction and carbonate precipitation. Coupled with process-based—and sometimes machine-learning—models, these data illuminate how sedimentary diagenesis modifies the efficiency of carbon burial, highlighting when buried carbon is protected by mineral phases and when it remains vulnerable to remineralization or methane generation in margins worldwide.

Continental margins experience high sedimentation rates driven by riverine input, coastal erosion, and climatic shifts. As organic material settles, microbial communities rapidly consume oxygen, initiating a cascade of anaerobic reactions. In this environment, dissolved inorganic carbon accumulates as remineralization proceeds, while iron and manganese oxides may dissolve and later re-precipitate, locking trace metals into sediments. The creation of authigenic carbonates can sequester carbon in stable mineral forms, extending the residence time of carbon in the sediment column. These processes collectively determine whether carbon is locked away for millennia or cycles back into the water column through porewater advection and diffusion.

The picture becomes more complex near tectonically active margins where uplift, subsidence, and fluid flow alter sediment characteristics. Gas hydrate stability zones, glacially derived debris, and volcanic inputs introduce heterogeneity that disrupts uniform diagenetic sequences. Fast burial can preserve organic matter efficiently by quickly limiting oxygen exposure, while slow accumulation permits deeper oxidation and greater carbon loss via dissolved inorganic carbon. Understanding these outcomes requires careful spatial mapping of sediment packages, dating of layers, and linking mineralogical changes to fluxes of organic matter. In turn, this knowledge informs models of regional carbon budgets and their sensitivity to climate-driven changes in sediment supply and ocean chemistry.

To predict burial efficiency across margins, scientists synthesize data on grain size distributions, porosity evolution, and mineral transformations through time. Fine-grained sediments often retain organic carbon more effectively due to lower permeability and slower water movement, whereas coarse layers can funnel porewaters rapidly, reducing residence times and enhancing remineralization. By combining laboratory measurements of reaction rates with field stratigraphy, researchers generate regional models of carbon burial efficiency that accommodate variable inputs, such as river discharge, sea-level rise, and storm-controlled sediment delivery. These models help explain why some margins appear to function as robust carbon sinks while others resemble transient repositories for short-lived carbon compounds.

Another critical dimension involves the role of microbial communities in diagenesis. Anaerobic bacteria drive sulfate reduction, methanogenesis, and iron reduction—processes that consume organic carbon and shape gas production and consumption in sediments. The balance among these pathways hinges on electron acceptor availability, temperature, and nutrient flux. When methane escapes through seafloor vents or is oxidized in situ, the net carbon burial efficiency shifts. By characterizing microbial community structure and metabolic pathways, researchers can forecast how microbial dynamics respond to changing environmental conditions and what that implies for long-term carbon storage in continental-margin basins.

Sediment diagenesis is not uniform; vertical and lateral variations create a mosaic of diagenetic regimes. Near-surface oxic zones yield rapid decomposition and release of nutrients, whereas deeper anoxic horizons favor durable mineral alterations and slower carbon turnover. Shallow cores often record sharp transitions between redox states, signaling interfaces where biological and chemical processes interact intensely. These interfaces can act as barriers or conduits for carbon transport, depending on the local mineralogy and pore-space geometry. Recognizing and mapping these microenvironments is essential to quantify how much carbon can be retained in sediments before burial halts further degradation.

Moreover, external forcing, including climate cycles and sea-level fluctuations, reshapes margin chemistry and sedimentation patterns. Glacial-interglacial periods periodically repackage margins with fresh material, delivering organic matter in pulses that saturate diagenetic pathways. This episodic input can temporarily boost burial efficiency, then gradually wane as diagenetic fronts migrate downward. Long-term trend analyses combining stratigraphy, radiometric dating, and geochemical proxies reveal how carbon burial responds to the cadence of natural cycles. Understanding these rhythms helps explain present-day carbon storage potential and informs projections under future climatic scenarios.

Quantifying the efficiency of carbon burial requires precise estimates of both sediment mass accumulation and the proportion of carbon that remains after diagenetic processing. Mass accumulation rates are derived from age models, tephra layers, and magnetostratigraphy, while carbon budgets emerge from organic carbon content surveys and inorganic carbon precipitation records. The interplay between burial and remineralization determines whether margins act as net sinks. In some cases, rapid burial may outpace decomposition, whereas in others, diagenetic reactions extensively recycle carbon back to the ocean. Deciphering these patterns across different margins builds a more reliable framework for evaluating global carbon storage potential.

Advances in remote sensing, borehole logging, and in situ micro-sensors empower new assessments of diagenetic states across vast margins. Integrated datasets reveal how pore-water chemistry shifts with depth, how mineral phases evolve, and how fluid flow pathways channel or hinder carbon transport. These tools enable high-resolution maps of burial efficiency and identify hotspots where diagenesis either safeguards carbon or accelerates its return to the ocean. By translating field observations into scalable models, scientists can reduce uncertainty in regional carbon cycle budgets and support policy-relevant forecasts for climate mitigation strategies.

The final objective of studying diagenesis on continental margins is to deliver robust, transferable insights about carbon cycling that hold across oceans and continents. An integrated approach combines sedimentology, geochemistry, microbiology, and numerical modeling to forecast how burial efficiency evolves with changing sediment supply and ocean chemistry. Collaborative efforts across institutions accelerate data sharing and methodological standardization, enabling comparisons among margins with diverse tectonics and climate histories. By building consensus on diagenetic controls, researchers can better predict the fate of coastal carbon reserves, inform coastal management, and refine estimates of the ocean’s ultimate capacity to sequester anthropogenic carbon.

In conclusion, sediment diagenesis in continental margins plays a pivotal role in shaping carbon burial efficiency. The dynamic interactions among mineral transformations, microbial metabolism, and physical sedimentation determine how much carbon is retained or released over long timescales. As climate and sea level continue to change, margins will respond with shifts in diagenetic pathways, altering the balance between burial and remineralization. Ongoing interdisciplinary research that couples field observations with laboratory experiments and process-based models will sharpen our understanding of carbon storage in marine sediments and improve projections for the global carbon cycle in a warming world.