Formation and burial of pyrite (iron sulfide) in marine sediments exert a fundamental control on atmospheric oxygenation and seawater buffering over geological timescales. However, little is known about how the formation and delivery of its precursor, reactive iron (Fe) oxide minerals, have evolved throughout Earth history. Secular variability in reactive Fe (including Fe oxides and pyrite) preserved in marine sediments is commonly attributed solely to redox changes. Here, we develop an approach to distinguish redox-driven influences from other controls on sedimentary reactive Fe, including the intensity of continental silicate weathering and the transfer of terrigenous particles to the ocean. We apply this framework to a compilation of reactive Fe data spanning 1,200 My of Earth history. Our results reveal persistently low proportions of reactive Fe from the Mesoproterozoic through the Cambrian, followed by a pronounced mid- to late Paleozoic rise and a subsequent decline in the late Cenozoic. This temporal pattern is inconsistent with a purely redox-driven control. Comparison with independent proxies for continental weathering and land-ocean sediment and solute fluxes suggests a strong coupling between reactive Fe burial, oxidative silicate weathering, and tectonically driven erosion. Notably, the mid- to late Paleozoic rise in reactive Fe coincided with the proliferation of land plants and increasing atmospheric oxygen. We propose a positive feedback where Earth-surface Fe cycling was both amplified by atmospheric oxygenation and contributed to it through its influence on pyrite burial in marine sediments.
Enamel and enameloid are hypermineralized tissues that can be found on the surface of vertebrates' dental structures. Shared developmental features suggest that minor changes could have driven multiple transitions between dentine-enamel and dentine-enameloid structures. It has been hypothesized that delayed (H1) or prolonged epithelial cell activity (H2), as well as modifications in epithelial cell production rates (H3), could explain such transitions. To test these evo-devo hypotheses, we built a cell-based histogenetic model using simplified properties common to current vertebrates. By varying secreting cell parameters, the simulations can reproduce a wide range of dentine, enameloid, and enamel proportions, allowing exploration of their role in the enameloid-enamel transition. Our exploration of 12 cellular parameters showed that H1, and H3 to a lesser extent, could account for such a transition, whereas H2 likely needs to be associated with one other modification. Our results also suggest that changes in the position and timing of the mineralization front formation are key to constraining enamel-enameloid-dentine development. Thus, beyond the gain or loss of gene function, minor developmental modifications may also have played a key role in the emergence and evolution of dental tissues.
Chromium contamination in groundwater remains a significant environmental concern, primarily due to the toxicity and mobility of its hexavalent form (Cr(VI)). The effect of ZVI mass on Cr(VI) reduction and isotope fractionation was investigated under dynamic flow conditions. Flow-through cell (FTC) experiments were conducted to simulate permeable reactive barriers, with stable Cr isotope fractionation (δ53Cr) used to differentiate direct ZVI-mediated and indirect Fe(II)-mediated Cr(VI) reduction pathways. Results showed a dual-phase removal mechanism: an initial rapid surface-mediated reduction followed by a slower aqueous-phase reduction. Isotope fractionation increased as Cr(VI) concentrations declined. Cr(VI) removal efficiencies of 1.6 mg g-1 were observed in FTCs containing 2 g or 4 g of ZVI. A transition from a rapid surface-mediated mechanism to a slower aqueous-phase reduction occurred at 85% and 75% breakthrough in the 2 g and 4 g FTCs, respectively. Isotopic enrichment was greater with increased ZVI mass, with maximum δ53Cr values reaching 0.23‰ (2 g ZVI) and 0.30‰ (4 g ZVI), compared to 0.47‰ for 6 g systems observed in previous studies. An updated MIN3P reactive transport model, incorporating mineral passivation and refined kinetic parameters, captures these trends. The optimized model assigns an isotope fractionation factor (ε) of -0.07‰ for the rapid, surface-mediated reduction reaction and -3.5‰ for the slower Fe(II)-mediated reduction. These values align with fractionation factors reported for analogous geochemical processes. This study isolates the influence of reactive surface area on Cr(VI) removal efficiency and isotopic behavior, enhancing mechanistic understanding and model reliability.
The most important quest in Mars exploration is the search for biosignatures. We adopt a Mars System Science approach, calling on information from the atmosphere, hydrosphere, cryosphere, lithosphere, and geologic history for an integrated organizational framework of inquiry. We "follow the water" by focusing on the characteristics of the hydrological system/cycle, their individual component water reservoirs, and their relationships and interconnectedness through time. We examine the ancillary hydrological cycle environments/processes (fluvial, lacustrine, glacial, cryospheric, groundwater) required for a robust, vertically integrated hydrological cycle to support long-duration northern lowlands oceans, arguably the largest proposed water reservoirs in Mars' history. We find that northern lowlands marine environments are likely to be low volume, transient, and short lived, prior to freezing and sublimation. Temporally associated hydrological system components (e.g., valley networks, lakes) are generally poorly integrated and characterized by intermittent, short-duration wet periods. This highly abbreviated hydrological cycle is likely to be not vertically integrated but instead horizontally stratified and thus potentially characterized by a global cryosphere separating the surface from a deeper, subsurface geothermally warmed groundwater system. Evidence for a horizontally stratified hydrological system can be traced back in time to the Late Noachian. The observed high erosion rates and the presence of phyllosilicates in the Early/Middle Noachian may have been predominantly due to the effects of the three most recent large impact basins, Hellas, Isidis, and Argyre, and their accompanying transient global deluges of hot, torrential rainfall. Sub-cryospheric, long-duration (over 4 billion years), warm subsurface groundwater systems and related chemical reactions provide an environment favorable to troglodytic chemotrophic biota in a globally connected martian "deep biosphere." If life developed on Mars, catastrophic release and dispersal of subsurface groundwater and impact excavation mean that biosignatures are likely to have been introduced and preserved globally. Samples of sedimentary environments returned to Earth may therefore offer a robust test of whether Mars ever possessed life.
Changes in Arctic tundra vegetation, driven by climate change, may be inducing major shifts in ecosystem services and the Arctic carbon budget, and altering high latitude feedbacks to the climate system. Field-based studies have documented warming-induced shrub expansion, and remote sensing has revealed heterogeneous, but primarily positive, trends in peak summer greenness across the Arctic. However, efforts to move beyond remotely sensed measures of spectral greening to quantify the spatial extent and rate of shrub expansion have been constrained by spectral similarities among tundra vegetation types, limited ground truth data, low revisit frequency of satellite observations, and sub-pixel heterogeneity of land cover at medium spatial resolution (30 m). To address these challenges, we developed a methodology that integrates high spatial resolution (2 m) commercial satellite imagery with Harmonized Landsat and Sentinel-2 observations in a machine learning framework, and used it to produce annual maps for 2016 to 2023 of sub-pixel land cover fractions at 30-m spatial resolution across three Arctic tundra ecoregions spanning 3.35 × 105 km2 between the Seward and Tuktoyaktuk Peninsulas. Uncertainty was quantified at each pixel via Monte Carlo resampling. Independent accuracy assessments yielded good accuracies (mean squared errors of 15.98% and 11.89% for low-stature vegetation and erect shrub cover, respectively), that were comparable to or exceeded previous mapping efforts. Further, repeat commercial satellite image pairs enabled the first assessment of mapped fractional cover change in Arctic tundra (R2 of 0.46 and 0.55, change direction accuracies of 77% and 78% for low-stature vegetation and erect shrub cover, respectively). This novel, scalable, multi-sensor approach to fractional land cover mapping produced the first annual maps of land cover fractions in the Arctic tundra, which support more accurate representation of vegetation dynamics and their linkages to climate change and disturbance processes.
The third longest Yangtze River plays an important role in transporting organic matter from the land to the global oceans, but the impacts of hydrological conditions remain unclear. Based on weekly measurements during 2020-2023, this study demonstrated the regulating effects of hydrological conditions on the transport of dissolved organic matter (DOM) in the Yangtze River. The results showed that DOM concentration and composition seasonally fluctuated along with the hydrological addition-dilution effects. Weekly DOC concentration at the Datong station had a variation range of 0.45-6.58 mg/L. In the rainy summer, high water discharge flushed humic substance output from the land and phytoplankton also produced protein-like DOM; water discharge was positively correlated with DOC concentration (p < 0.01). However, extremely high water discharge diluted DOC concentration when water volume increase exceeded DOM supply. By constructing a piecewise concentration-discharge quantitative model, we identified a water discharge threshold of 25,000 m3/s for the transition of addition (b = 0.23) and dilution (b = -0.45) effects. Additionally, potential hydrological regulation and watershed-scale human activities may further modify downstream DOM transport, although their individual contributions require further research. In sum, this study reveals the synergistic regulation effects of hydrological conditions on DOM transport in the Yangtze River, which are of great significance for managing river water quality and optimizing carbon cycle models.
Amorphous phases usually possess dense active sites and abundant dangling bonds, while crystalline counterparts provide better electronic conductivity and structural stability. Herein an amorphous/crystalline@amorphous core-shell heterostructure (a/c-CoNiP300@a-NiFe LDH/NF) is synthesized to combine the amorphous high active-site density and crystalline superior conductivity & stability. The crystallinity of the core is optimized by regulating the phosphorization temperature, as deviations from the optimal range degrade electrochemical performance. The constructed heterostructure effectively facilitates electron transfer and local charge redistribution. Its unique small-sized morphology, combined with superhydrophilic and gas-repellent surface properties, synergistically enhances electrode behavior. The material demonstrates outstanding multifunctional performance. In supercapacitors, it delivers an ultrahigh specific capacitance of 3071.64 F g-1 at 5 mA cm-2, with an assembled hybrid device achieving 56.41 Wh kg-1 energy density. DFT calculations demonstrate enhanced interfacial charge transfer from NiFe LDH to CoNiP, improved Fermi-level density of states, and boosted OH- adsorption across the heterointerface. Furthermore, a/c-CoNiP300@a-NiFe LDH/NF requires low potentials of only 1.31 V (vs. RHE) for the urea oxidation reaction and 160 mV (vs. RHE) for the hydrogen evolution reaction to reach 100 mA cm-2. Its practical potential is validated in a flexible supercapacitor and a urea-containing wastewater treatment system.
This study presents a novel galvanic deposition method to create antimony sulfide thin films on FTO glass. The presence of palladium as a top layer on the surface of Sb2S3 (designated as Sb2S3:Pd) promotes hydrogen production and dye degradation. Four differently treated Sb2S3 films were studied. In neutral buffer medium, maximum efficiency related to water splitting for hydrogen evolution was observed for the annealed Sb2S3:Pd films, displaying a low onset potential of -116 mV and a Tafel slope of 64 mV/decade. The inclusion of Pd boosts the HER performance, which exhibits a current density of 10 mAcm-2 at a comparatively lower overpotential of -204 mV with significant stability. Sb2S3:Pd films also demonstrated improved dye degradation capability in comparison to Sb2S3 films without Pd.
Isidoidae Heestand Saucier, France & Watling, 2021 is a rare octocoral family currently represented by a single genus and species, Isidoides armataNutting, 1910 recorded in the western Pacific Ocean. The taxonomic status and diversity of Isidoides is unclear, due to the lack of diagnostic taxonomic features and limited taxon sampling. Based on 23 Isidoides specimens obtained from the northwestern to southwestern Pacific, we carried out morphological and phylogenetic analyses to reveal the taxonomic status of new species and develop reliable features for species identification. The 23 specimens could be classified into four well-supported clades by the phylogenomic analysis of ultraconserved elements (UCEs), four groups by 28S rDNA, and two groups by mtMutS-cox1. Integrating morphology and molecular data, we uncovered unexpected diversity of Isidoides composed of the known species Isidoides armata and three new species, viz., I. elegans sp. nov., I. gracilis sp. nov. and I. pseudarmata sp. nov. The morphological analysis showed high intraspecific morphological variation in colony color and the size, shape and arrangement of polyps. By contrast, sclerite forms with their surface sculpturing are more diagnostic features for species identification. Our phylogenetic and species delimitation analyses indicate that UCEs have higher resolution than the nuclear 28S rDNA and the mitochondrial genes mtMutS and cox1 for species discrimination within Isidoidae. ZooBank: urn:lsid:zoobank.org:pub:392485F5-502E-4383-B153-45B167571190.
Sulfur plays a critical role in modulating redox cycling on Earth. Yet, sulfur's behavior during subduction and in mantle redox reactions is debated. We analyzed 34S/32S in mafic arc melt inclusions from contrasting subduction zones and modeled slab-mantle interaction to investigate the subduction zone sulfur cycle. We find that degassing may enrich or deplete the melt strongly in 34S as a function of melt redox state. After correction for this effect, arc magmas have a substantially narrow range of δ34S values (+3 ± 2‰), higher than the ambient upper mantle (-1‰). Slab-derived sulfur is oxidized, evidenced by a concurrent increase in mantle Fe3+ and sulfur contents, and contributes up to 86% of the mantle wedge's sulfur budget. Arc magma δ34S values reflect a common slab source for sulfur: the oceanic crust. Subduction zones act as a "filter" for oxidative power and 34S, effectively returning these to the surface over geological timescales.
High-performance gas sensors with extreme sensitivity and rapid response kinetics are fundamental to sub-ppm H2S detection, which is crucial for environmental monitoring and industrial safety. However, most conventional rare-earth ferrites have relatively sluggish responses at low concentrations because of thermodynamic and kinetic constraints and inherently high surface reaction barriers. Herein, a high-entropy perovskite oxide with the composition (Gd0.2Tb0.2Dy0.2Ho0.2Er0.2)FeO3 was designed and synthesized using a wet-chemical method. The incorporation of multiple principal elements induced strong local lattice distortion and generated abundant chemically heterogeneous active sites. Furthermore, the application of an external magnetic field significantly optimized electron transfer pathways and accelerated the surface redox reaction kinetics. Our results reveal that the synergistic coupling between high-entropy-induced structural distortion and weak magnetic field modulation breaks the traditional response-recovery trade-off, yielding a 6-fold sensitivity enhancement over conventional counterparts, an ultrafast 1.72 s recovery time, and an H2S detection limit of 0.5 ppm. This strategy, which integrates local coordination reconstruction with spin-state intervention, is expected to be widely applicable to the development of next-generation intelligent sensing systems.
Mine water geothermal (MWG) heating offers a low-carbon solution for space heating, helping to reduce greenhouse gas emissions. To assess the feasibility of an MWG scheme, an estimate of extractable heat is required to size the system, to determine if it meets surface demand, and evaluate economic viability. In early project stages, where data are limited, static methods, such as geothermal heat flow, mine water volume, rock volume, and flow rate, are commonly used. However, these methods do not account for mine geometry. GEMSToolbox is a streamlined dynamic model, purpose built for MWG, that operates with the same limited data as static methods but also incorporates digitised mine plans. It allows rapid modelling of scenarios such as roadway collapse and shaft treatments, and helps identify optimal injection and abstraction points. We apply GEMSToolbox to a digitised two-seam coal mine and to a simplified synthetic grid model of similar size. The resulting dynamic heat estimates are compared with those from static methods, revealing order of magnitude differences, from 4,200 MWh to 210,000 MWh over 40 years. Using dynamic modelling early in project development improves targeting of exploration wells, enables site-specific mitigation planning, and reduces uncertainty. GEMSToolbox offers a practical alternative to static methods, enhancing both technical confidence and investment readiness in MWG projects.
Arctic and boreal regions are experiencing rapid environmental changes that include thawing permafrost and increasing disturbances. The NASA Arctic-Boreal Vulnerability Experiment (ABoVE) sought to better understand these changes through field, airborne, and remote sensing measurements. One key airborne instrument was the Land, Vegetation, and Ice Sensor (LVIS), a wide-swath imaging laser altimeter system. LVIS conducted 32 flights during June-August periods of 2017 and 2019, capturing data across more than 91,000 km² of diverse Arctic and boreal ecosystems. The surface topography and vegetation structure data collected throughout Alaska and Northwestern Canada spans boreal forests to Arctic tundra, crossing 12 distinct ecoregions. This airborne collection enables direct comparison with coincident NASA Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) data, extends research beyond the ~52° N limit of NASA's Global Ecosystem Dynamics Investigation (GEDI) sensor, and provides precursor data for future satellite missions, such as NASA's recently selected Earth Dynamics Geodetic Explorer (EDGE). We summarize detailed information on LVIS data records from ABoVE deployments, including access and visualization using custom open source tools.
Glacier albedo controls surface energy balance and mass balance but remains poorly observed in remote sub-Antarctic regions. We present a glacier albedo dataset for Heard Island (53°06'S, 73°31'E) derived from NASA VIIRS VNP43 BRDF/albedo parameters for January 2012 to May 2024. The dataset includes a glacier-wide area-mean time series (4,466 daily albedo records) and annual albedo rasters at 375-500 m resolution. White-sky albedo (WSA) was computed from BRDF parameters with quality filtering (mandatory quality ≤ 1). Processing used Google Earth Engine with glacier masking and interior buffering (1 pixel, 375 m). Temporal data availability is 98.9%; spatial coverage is 44.04% of the glacier area due to cloud cover. The dataset is suitable for glacier surface energy balance studies, trend analysis, and integration with climate reanalysis. Data are provided in CSV and GeoTIFF formats with accompanying quality metadata.
Rare earth elements (REEs) are essential for modern electronics and are increasingly entering electronic waste (e-waste) streams. Informal recycling can release REEs into the environment, but their sources, transfer pathways, and retained inventories remain poorly quantified. Here, we combine microscopic particle characterization, neodymium (Nd) isotopes, Bayesian source apportionment, and a Level III steady-state multimedia aquivalence (SMA) model to characterize REE sources, cross-media transport, and retained inventories in Guiyu, China. Spatial clustering of REE concentrations near historical recycling sites, together with spherical and angular particles, supported anthropogenic inputs from thermal treatment and mechanical fragmentation. Isotopic mixing models estimated that geogenic contributions remained dominant, whereas e-waste contributions accounted for 21.4%, 16.4%, and 33.6% of REEs loading in soil, road dust, and sediment, respectively. Fly ash and wastewater sludge were the main anthropogenic end-members, pointing to combustion and acid-leaching pathways. Multimedia modeling identified land-to-river export as the dominant cross-media pathway, with soil runoff and surface wash-off serving as major vectors to aquatic systems. The retained inventory within the modeled solid compartments, including soil, road dust, and sediment, was estimated at 1.68 × 103 t ΣREE, with an uncertainty range of 0.555 × 103 to 4.74 × 103 t. Scenario extrapolations to 2030 projected annual REE releases of 3.98 × 103 t under historical recycling intensities and 1.32 × 103 t under regulated management. These findings suggest that informal e-waste recycling can shift recoverable REEs into persistent environmental reservoirs, making secondary remobilization an additional concern beyond direct emissions.
Achieving a sustainable energy system for space missions remains challenging due to the continued reliance on Earth-supplied materials. This underscores the importance of in situ resource utilization (ISRU) strategies that convert planetary resources into functional electronic components. In this work, we harness the dielectric characteristics of Martian regolith (MR) simulant to create an MR/polydimethylsiloxane (PDMS) composite film with enhanced triboelectric properties. Structural and morphological analyses of the MR reveal multiple oxide-rich phases, which improve both the dielectric properties and the surface microstructure of the MR/PDMS composite film. The resultant MR/PDMS composite film-based triboelectric nanogenerator (TENG) delivers an approximately two-fold increase in open-circuit voltage compared to the pristine PDMS-based TENG. The real-world use of the MR/PDMS TENG is further demonstrated by proof-of-concept applications: a glove-mounted tactile surface sensor with wireless signal transmission and a wearable triboelectric keypad. This work not only showcases advances in MR-based TENG performance but also marks the first demonstration of triboelectric applications using MR simulants as functional triboelectric material. Additionally, we have demonstrated foundational work toward ISRU-oriented tactile interfaces incorporating MR-simulant-derived functional materials for future controlled habitats and robotic platforms relevant to future space exploration.
While the rich diversity of surface sites on high-entropy alloys (HEAs) is essential for tuning electrocatalytic activity, the coverage-dependent lateral interactions that shape reactive interfaces are often neglected in theoretical studies. Here, we develop a machine learning interatomic potential (MLIP)-enabled framework to model the oxygen reduction reaction (ORR) within an Ag-Ir-Ru-Pd-Pt-Cu-Rh-Re alloy composition space. By tracking the binding strengths of O* and OH* intermediates during competitive coadsorption on crowded surfaces, this framework highlights the key role of lateral interactions, including attractive hydrogen-bond networks and electrostatic repulsion, in evaluating electrocatalytic activity. Incorporating these coverage-induced effects improves agreement with reported PtIr and AgPd composition-activity trends relative to an isolated-site baseline. We further show that increasing compositional complexity within the studied alloy space can amplify lateral repulsion under finite-coverage conditions, broadening binding strength distributions and reducing the population of optimal active sites. The competition between local electronic optimization and coverage-dependent lateral interactions gives rise to a volcano-shaped activity-entropy relationship, offering guidance for the rational design of HEA-based ORR electrocatalysts.
Space weathering causes physical and spectral changes on the surfaces of airless bodies. However, our understanding of how space weathering operates in the presence of volatile ices is in its early stages. Electron irradiation of ice-coated surfaces is expected in astrophysical environments including the early solar system, volatile ice-rich permanently shadowed regions of the Moon and Mercury, and other airless bodies like asteroids. A recent study suggests that anomalous oxygen isotope exchange occurs between water-ice and underlying surfaces when exposed to electron irradiation at extremely low temperatures (10 K). To delve deeper into the physical processes underlying isotopic exchange, we employ nanoscale atomic force microscopy-based infrared (AFM-IR) spectroscopy to identify Si-O bond formation resulting from the electron irradiation of H2O ice coated silicon targets. Experimental variables include electron energy, amount and timing of water-ice deposition, and surface area exposed to the electron beam. AFM-IR point spectra, surface topography and IR absorption mapping reveal that the degree of surface oxidation is dependent upon experimental conditions. Scanning electron microscopy and (scanning) transmission electron microscope imaging confirm the formation of thicker SiO x in regions of enhanced interaction between electron irradiation, water-ice, and the silicon substrate. In summary, we find that electron irradiation with energies as low as 1 keV/electron can break the chemical bonds of refractory solids like Si under these simulated cold astrophysical conditions. These results suggest that cosmic rays may play a more significant role than previously thought in the chemical evolution of dust grains in cold astrophysical and protoplanetary environments.
Fulvic acid (FA), a highly reactive and soluble fraction of dissolved organic matter in cultivated soils, facilitates the formation of stable colloids through complexation with iron (Fe), thereby significantly modulating the environmental mobility of arsenic (As). However, the migration behavior of As associated with FA-Fe colloids in porous media remains insufficiently characterized, particularly regarding the integration of coupled migration processes with quantitative modeling. This study investigated colloid-mediated As(III) migration in saturated porous media using column experiments and a time-fractional advection-dispersion equation (fADE). Increasing FA concentration enhanced As mobility, as evidenced by elevated breakthrough ratios and an increase in the fractional order α from 0.475 to 0.881, signifying the attenuation of memory effects and a transition toward Fickian migration. Conversely, elevated Fe concentrations promoted colloidal aggregation and suppressed As migration, with α decreasing to 0.437, capturing non-Fickian behavior associated with particle retention and deposition. Mechanistically, FA stabilizes FA-Fe colloids through electrostatic repulsion and steric hinderance while competing for adsorption sites, whereas Fe induces aggregation and enhances pore-scale interception, leading to As sequestration via inner-sphere complexation with Fe-OH groups. Under alkaline conditions, surface charge effects strengthened electrostatic repulsion and promoted migration, while elevated ionic strength compressed the electrical double layer, facilitated deposition. These results demonstrate that As migration is governed by the coupling between colloidal stability and interfacial interactions, which is effectively quantified by fADE. These findings provide a theoretical framework for understanding As mobility in subsurface environments and offer critical insights for groundwater remediation strategies involving colloid-facilitated migration.
Efficient stabilization of heavy-metal co-contaminated wastewater remains limited by poor material selectivity, secondary sludge, and unclear immobilization mechanisms. In this study, Bacillus licheniformis ys isolated from groundwater was used to construct mineralization systems with Mg/Ca molar ratios of 1, 3, 6, and 12, producing microbially derived CaCO3 with distinct polymorphs for Cu2+, Cd2+, and Pb2+ immobilization. With increasing Mg/Ca ratio, the mineral phase shifted from magnesian calcite (Ca1-xMgxCO3) to monohydrocalcite (CaCO3·H2O) and then to an aragonite (CaCO3)-monohydrocalcite mixed phase. In single-metal systems, the mixed phase favored Cu2+ removal, while monohydrocalcite showed relatively stable high-capacity immobilization of Cd2+ and Pb2+. In ternary systems, the priority was Pb2+>Cu2+>Cd2+. Monohydrocalcite showed the highest Pb2+ removal, whereas the aragonite-monohydrocalcite mixed phase was more favorable for competitive Cu2+ immobilization; in contrast, Cd2+ immobilization was strongly hindered by ionic competition and mainly occurred as surface-bound, poorly crystalline, or X-ray amorphous species rather than distinct crystalline Cd-bearing phases. Overall, Pb2+ showed the highest removal efficiency and fastest reaction rate, whereas Cu2+ and Cd2+ were more polymorph-sensitive. Carbonate polymorphs controlled both capacity and immobilization pathways, including surface precipitation, localized new-phase formation, poorly crystalline sequestration, and phase transformation. The kinetic data were best described by the pseudo-second-order model, suggesting that surface chemical reactions were important during immobilization. This study clarifies how Mg/Ca-regulated carbonate polymorphism differentially controls heavy-metal immobilization, providing a basis for designing microbially derived CaCO3 materials for multi-metal remediation and understanding microbial mineralization functions under different Mg/Ca conditions.