In the vast and dynamic theater of Earth’s oceans, subtle chemical interactions play outsized roles in shaping the planet’s climate and biosphere over geological timescales. A recent breakthrough study led by Fakhraee, Bauer, Planavsky, and their colleagues has shed new light on an often-overlooked process in ocean chemistry: the formation and burial of pyrite in anoxic marine environments. This mechanism, as their research reveals, is not merely a geological curiosity but a globally significant driver of ocean alkalinity and a hitherto unrecognized moderator of Earth’s long-term carbon cycle and climate stability.
Pyrite, commonly known as “fool’s gold,” forms under oxygen-depleted conditions when sulfur combines with iron in seawater sediments. This process predominantly occurs in anoxic environments—zones within the ocean where oxygen is absent and reduced chemical species like sulfide dominate. Historically, pyrite burial was understood mainly as a pathway for sulfur removal from the ocean, influencing oceanic sulfur budgets and sediment geochemistry. However, until now, its role in regulating the ocean’s acid–base balance and broader climate feedback mechanisms had languished in relative obscurity.
The researchers employed an innovative coupled carbon–sulfur cycle model to quantify the impact of pyrite burial on ocean alkalinity over the expansive Phanerozoic eon, spanning the last 541 million years. Their results are nothing short of staggering: pyrite burial could contribute between 5 and 46 teramoles per year (Tmol yr⁻¹) of alkalinity production. To contextualize these numbers, this flux might be up to six times greater than the modern background volcanic carbon flux, an influential driver in the global carbon budget. Such a magnitude suggests that pyrite burial has been a powerful agent modulating ocean chemistry and atmospheric CO₂ levels through deep time.
Of particular interest in the study are intervals known as Oceanic Anoxic Events (OAEs), transient periods characterized by widespread depletion of dissolved oxygen across vast swathes of the ocean. These events, often triggered by immense volcanic outpourings associated with Large Igneous Provinces (LIPs), are notorious for their profound impacts on marine ecosystems and global climate. Fakhraee and colleagues reveal that during OAEs, the production of alkalinity through pyrite burial is drastically amplified, effectively acting as a negative feedback mechanism that tempers the severity of CO₂-induced greenhouse warming.
This anoxia-driven alkalinity feedback emerges as a heretofore underappreciated stabilizer within Earth’s climate system, offsetting the substantial carbon emissions unleashed during massive volcanic episodes. The enhanced burial of pyrite during these intervals helps to neutralize excess carbonic acid in seawater, thereby maintaining ocean pH and buffering atmospheric CO₂ concentrations. Consequently, this stabilizing role softens the climatic and ecological shocks that might otherwise have been more catastrophic.
Mechanistically, the coupling of sulfur and carbon cycles is pivotal for this feedback. When pyrite precipitates and is sequestered in sediments, it essentially removes sulfur and associated acidity from the marine system. This removal leads to an increase in ocean alkalinity—the capacity of seawater to neutralize acids—which in turn facilitates enhanced uptake of atmospheric CO₂ by the ocean. The intricate interplay between sedimentary pyrite formation and carbon sequestration thus forms a crucial biogeochemical link that has been underappreciated until now.
The implications of this research are broad and profound. By highlighting the importance of pyrite burial in regulating ocean alkalinity and climate, the study reframes long-held conceptions of how the Earth system maintains equilibrium amidst episodic carbon perturbations. It suggests that natural processes associated with ocean deoxygenation do not invariably exacerbate climate change but may, paradoxically, activate powerful feedbacks that mitigate greenhouse warming and its biospheric consequences.
Furthermore, tracing the feedback’s influence over the last 300 million years, the authors document its involvement in multiple significant OAEs linked to LIP volcanism. Each of these events, despite injecting vast quantities of CO₂ and other volatiles into the atmosphere, was partially moderated by enhanced anoxic alkalinity production via pyrite burial. This insight underscores the resilience of Earth’s biogeochemical systems and their capacity to self-regulate through complex feedback loops, even under extreme environmental stress.
From a contemporary perspective, this research offers critical lessons. Modern oceans are experiencing unprecedented deoxygenation due to anthropogenic climate change and nutrient loading. While the long-term effects of rising anoxia on ocean chemistry and climate remain uncertain, the study by Fakhraee et al. posits that similar alkalinity feedbacks could be engaged in the near future. This potential feedback could provide a natural, albeit limited, buffer against accelerating atmospheric CO₂ increases, offering a glimmer of hope amid ongoing environmental upheavals.
Nevertheless, the study emphasizes caution. While pyrite burial contributes to alkalinity production and climate stabilization on geologic timescales, the rates and magnitudes of contemporary ocean deoxygenation occur on much shorter timescales. The efficacy of this feedback as a counterbalance to human-driven carbon emissions remains subject to further investigation, particularly given the multifaceted challenges threatening marine ecosystems and ocean chemistry.
Technically, the coupled carbon–sulfur model used by the researchers integrates comprehensive geochemical parameters derived from sediment records, volcanic flux estimates, and sulfur isotope data. This robust methodological framework lends strong support to their conclusions by reconciling sedimentary pyrite burial rates with changes in ocean alkalinity and atmospheric CO₂ across multiple temporal scales. Their approach exemplifies interdisciplinary geochemical modeling that bridges the gaps between Earth surface processes, marine chemistry, and climate dynamics.
One of the most compelling outcomes of the study is its demonstration that pyrite burial-driven alkalinity feedbacks have not been constant but fluctuate significantly in response to changes in ocean oxygenation. This variability aligns well with geological evidence for periods of enhanced ocean anoxia and reveals the dynamic nature of Earth’s biogeochemical regulation mechanisms. It challenges researchers to incorporate sulfur cycle processes alongside the more traditionally studied carbon cycle interactions to achieve a fuller understanding of Earth system stability.
Moreover, the research invites renewed scrutiny of past mass extinction events and climatic anomalies. Many of these upheavals are contemporaneous with OAEs and LIP eruptions, classic scenarios where carbon emissions and ocean redox states are tightly interwoven. Understanding how pyrite burial modulates alkalinity provides a new lens to interpret the nuances of these episodes, potentially explaining why certain events, though intense, did not cause irreversible damage to the global climate system.
This study also opens avenues for future investigations into the biotic factors influencing pyrite formation, including microbial sulfur metabolism, sedimentation patterns, and organic matter availability. These biological and sedimentological drivers are essential components dictating the rate of pyrite burial and thus the strength of the alkalinity feedback. Continued exploration in this domain will enrich models of how Earth’s surface environment has evolved in response to shifting ocean chemistry.
In the grand tapestry of Earth’s climate evolution, pyrite burial emerges as a subtle yet potent thread woven deeply into the regulation of carbon and sulfur cycles. The work by Fakhraee and collaborators significantly advances our understanding of Earth’s natural buffering systems and underscores the importance of integrating chemical feedbacks in predicting future climate trajectories. Their findings remind the scientific community that the ocean’s chemical complexity offers both vulnerabilities and resilience, with processes like anoxic alkalinity production serving as crucial bulwarks against climatic extremes.
As the Earth faces an era of rapid environmental transformation driven by anthropogenic forces, elucidating natural geochemical feedbacks like those stemming from pyrite burial is paramount. Such knowledge equips scientists and policymakers with a richer conceptual toolkit to anticipate how the planet might respond to escalating greenhouse gas emissions. While no single mechanism can fully offset the scale and speed of human impacts, the ocean’s ancient chemistry contains invaluable clues for sustaining Earth’s habitability in the turbulent centuries ahead.
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Subject of Research: Climate stabilization through alkalinity production induced by pyrite burial in anoxic ocean environments.
Article Title: Climate stabilization by alkalinity production from pyrite burial during oceanic anoxia.
Article References:
Fakhraee, M., Bauer, K.W., Planavsky, N.J. et al. Climate stabilization by alkalinity production from pyrite burial during oceanic anoxia.
Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01698-0
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