Enhanced Rock Weathering for Carbon Removal-Monitoring and Mitigating Potential Environmental Impacts on Agricultural Land.

Terrestrial enhanced rock weathering (ERW) is the application of pulverized silicate rock to soils for the purposes of carbon removal and improved soil health. Although a geochemical modeling framework for ERW in soils is emerging, there is a scarcity of experimental and field trial data exploring potential environmental impacts, risks, and monitoring strategies associated with this practice. This paper identifies potential negative consequences and positive cobenefits of ERW scale-up and suggests mitigation and monitoring strategies.

Enhanced weathering in the US Corn Belt delivers carbon removal with agronomic benefits.

Terrestrial enhanced weathering (EW) of silicate rocks, such as crushed basalt, on farmlands is a promising scalable atmospheric carbon dioxide removal (CDR) strategy that urgently requires performance assessment with commercial farming practices. We report findings from a large-scale replicated EW field trial across a typical maize-soybean rotation on an experimental farm in the heart of the United Sates Corn Belt over 4 y (2016 to 2020). We show an average combined loss of major cations (Ca and Mg) from crushed basalt applied each fall over 4 y (50 t ha y) gave a conservative time-integrated cumulative CDR potential of 10.

Initial Validation of a Soil-Based Mass-Balance Approach for Empirical Monitoring of Enhanced Rock Weathering Rates.

Enhanced rock weathering (ERW) is a promising scalable and cost-effective carbon dioxide removal (CDR) strategy with significant environmental and agronomic co-benefits. A major barrier to large-scale implementation of ERW is a robust monitoring, reporting, and verification (MRV) framework. To successfully quantify the amount of carbon dioxide removed by ERW, MRV must be accurate, precise, and cost-effective.

New estimates of the storage permanence and ocean co-benefits of enhanced rock weathering.

Avoiding many of the most severe consequences of anthropogenic climate change in the coming century will very likely require the development of "negative emissions technologies"-practices that lead to net carbon dioxide removal (CDR) from Earth's atmosphere. However, feedbacks within the carbon cycle place intrinsic limits on the long-term impact of CDR on atmospheric CO that are likely to vary across CDR technologies in ways that are poorly constrained. Here, we use an ensemble of Earth system models to provide new insights into the efficiency of CDR through enhanced rock weathering (ERW) by explicitly quantifying long-term storage of carbon in the ocean during ERW relative to an equivalent modulated emissions scenario.

Technical comment on "Reexamination of 2.5-Ga 'whiff' of oxygen interval points to anoxic ocean before GOE".

Many lines of inorganic geochemical evidence suggest transient "whiffs" of environmental oxygenation before the Great Oxidation Event (GOE). Slotznick assert that analyses of paleoredox proxies in the Mount McRae Shale, Western Australia, were misinterpreted and hence that environmental O levels were persistently negligible before the GOE. We find these arguments logically flawed and factually incomplete.

A sedimentary record of the evolution of the global marine phosphorus cycle.

Phosphorus (P) is typically considered to be the ultimate limiting nutrient for Earth's biosphere on geologic timescales. As P is monoisotopic, its sedimentary enrichment can provide some insights into how the marine P cycle has changed through time. A previous compilation of shale P enrichments argued for a significant change in P cycling during the Ediacaran Period (635-541 Ma).

Strong evidence for a weakly oxygenated ocean-atmosphere system during the Proterozoic.

Earth's surface has undergone a protracted oxygenation, which is commonly assumed to have profoundly affected the biosphere. However, basic aspects of this history are still debated-foremost oxygen (O) levels in the oceans and atmosphere during the billion years leading up to the rise of algae and animals. Here we use isotope ratios of iron (Fe) in ironstones-Fe-rich sedimentary rocks deposited in nearshore marine settings-as a proxy for O levels in shallow seawater.

Triple oxygen isotope constraints on atmospheric O and biological productivity during the mid-Proterozoic.

Reconstructing the history of biological productivity and atmospheric oxygen partial pressure (O) is a fundamental goal of geobiology. Recently, the mass-independent fractionation of oxygen isotopes (O-MIF) has been used as a tool for estimating O and productivity during the Proterozoic. O-MIF, reported as Δ'O, is produced during the formation of ozone and destroyed by isotopic exchange with water by biological and chemical processes.

A largely invariant marine dissolved organic carbon reservoir across Earth's history.

Marine dissolved organic carbon (DOC), the largest pool of reduced carbon in the oceans, plays an important role in the global carbon cycle and contributes to the regulation of atmospheric oxygen and carbon dioxide abundances. Despite its importance in global biogeochemical cycles, the long-term history of the marine DOC reservoir is poorly constrained. Nonetheless, significant changes to the size of the oceanic DOC reservoir through Earth's history have been commonly invoked to explain changes to ocean chemistry, carbon cycling, and marine ecology.

Oxygenation, Life, and the Planetary System during Earth's Middle History: An Overview.

The long history of life on Earth has unfolded as a cause-and-effect relationship with the evolving amount of oxygen (O) in the oceans and atmosphere. Oxygen deficiency characterized our planet's first 2 billion years, yet evidence for biological O production and local enrichments in the surface ocean appear long before the first accumulations of O in the atmosphere roughly 2.4 to 2.

Oxygen suppression of macroscopic multicellularity.

Atmospheric oxygen is thought to have played a vital role in the evolution of large, complex multicellular organisms. Challenging the prevailing theory, we show that the transition from an anaerobic to an aerobic world can strongly suppress the evolution of macroscopic multicellularity. Here we select for increased size in multicellular 'snowflake' yeast across a range of metabolically-available O levels.

Microbial helpers allow cyanobacteria to thrive in ferruginous waters.

The Great Oxidation Event (GOE) was a rapid accumulation of oxygen in the atmosphere as a result of the photosynthetic activity of cyanobacteria. This accumulation reflected the pervasiveness of O on the planet's surface, indicating that cyanobacteria had become ecologically successful in Archean oceans. Micromolar concentrations of Fe in Archean oceans would have reacted with hydrogen peroxide, a byproduct of oxygenic photosynthesis, to produce hydroxyl radicals, which cause cellular damage.

Bistability in the redox chemistry of sediments and oceans.

For most of Earth's history, the ocean's interior was pervasively anoxic and showed occasional shifts in ocean redox chemistry between iron-buffered and sulfide-buffered states. These redox transitions are most often explained by large changes in external inputs, such as a strongly altered delivery of iron and sulfate to the ocean, or major shifts in marine productivity. Here, we propose that redox shifts can also arise from small perturbations that are amplified by nonlinear positive feedbacks within the internal iron and sulfur cycling of the ocean.

Novel insights into the taxonomic diversity and molecular mechanisms of bacterial Mn(III) reduction.

Soluble ligand-bound Mn(III) can support anaerobic microbial respiration in diverse aquatic environments. Thus far, Mn(III) reduction has only been associated with certain Gammaproteobacteria. Here, we characterized microbial communities enriched from Mn-replete sediments of Lake Matano, Indonesia.

Publisher Correction: The role of calcium in regulating marine phosphorus burial and atmospheric oxygenation.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The role of calcium in regulating marine phosphorus burial and atmospheric oxygenation.

The marine phosphorus cycle plays a critical role in controlling the extent of global primary productivity and thus atmospheric pO on geologic time scales. However, previous attempts to model carbon-phosphorus-oxygen feedbacks have neglected key parameters that could shape the global P cycle. Here we present new diagenetic models to fully parameterize marine P burial.

Large Mass-Independent Oxygen Isotope Fractionations in Mid-Proterozoic Sediments: Evidence for a Low-Oxygen Atmosphere?

Earth's ocean-atmosphere system has undergone a dramatic but protracted increase in oxygen (O) abundance. This environmental transition ultimately paved the way for the rise of multicellular life and provides a blueprint for how a biosphere can transform a planetary surface. However, estimates of atmospheric oxygen levels for large intervals of Earth's history still vary by orders of magnitude-foremost for Earth's middle history.

On the co-evolution of surface oxygen levels and animals.

Few topics in geobiology have been as extensively debated as the role of Earth's oxygenation in controlling when and why animals emerged and diversified. All currently described animals require oxygen for at least a portion of their life cycle. Therefore, the transition to an oxygenated planet was a prerequisite for the emergence of animals.

The impact of marine nutrient abundance on early eukaryotic ecosystems.

The rise of eukaryotes to ecological prominence represents one of the most dramatic shifts in the history of Earth's biosphere. However, there is an enigmatic temporal lag between the emergence of eukaryotic organisms in the fossil record and their much later ecological expansion. In parallel, there is evidence for a secular increase in the availability of the key macronutrient phosphorus (P) in Earth's oceans.

Photoferrotrophy, deposition of banded iron formations, and methane production in Archean oceans.

Banded iron formation (BIF) deposition was the likely result of oxidation of ferrous iron in seawater by either oxygenic photosynthesis or iron-dependent anoxygenic photosynthesis-photoferrotrophy. BIF deposition, however, remains enigmatic because the photosynthetic biomass produced during iron oxidation is conspicuously absent from BIFs. We have addressed this enigma through experiments with photosynthetic bacteria and modeling of biogeochemical cycling in the Archean oceans.

Ecosystem-bedrock interaction changes nutrient compartmentalization during early oxidative weathering.

Ecosystem-bedrock interactions power the biogeochemical cycles of Earth's shallow crust, supporting life, stimulating substrate transformation, and spurring evolutionary innovation. While oxidative processes have dominated half of terrestrial history, the relative contribution of the biosphere and its chemical fingerprints on Earth's developing regolith are still poorly constrained. Here, we report results from a two-year incipient weathering experiment.

A paleosol record of the evolution of Cr redox cycling and evidence for an increase in atmospheric oxygen during the Neoproterozoic.

Atmospheric oxygen levels control the oxidative side of key biogeochemical cycles and place limits on the development of high-energy metabolisms. Understanding Earth's oxygenation is thus critical to developing a clearer picture of Earth's long-term evolution. However, there is currently vigorous debate about even basic aspects of the timing and pattern of the rise of oxygen.