Jie Li

The lead-up to the Great Oxidation Event (GOE; between 2.5 and 2.2 Ga) was arguably as consequential as the event itself, yet substantial uncertainties remain regarding the timing and magnitude of oxygen rise in early Earth’s oceans. Heavy molybdenum isotope compositions (δ ⁹⁸ Mo) in Neoarchean marine sediments have traditionally been interpreted as evidence for adsorption of dissolved Mo onto iron oxyhydroxides [e.g., ferrihydrite; Fe(OH) ₃ ] and manganese oxides (MnO ₂ ) formed in oxygenated marine environments, implying at least regional surface oxygen accumulation immediately prior to the GOE. Here, we propose an alternate explanation in which these isotopic signatures arose in a largely anoxic ocean. Analyses of Neoarchean banded iron formations (BIFs) deposited at 2.57 to 2.51 Ga reveal a broad range of δ ⁹⁸ Mo values, which are best explained by the combined effects of Mo adsorption onto primary ferrihydrite, followed by its diagenetic incorporation into Fe(II)-Mo(IV)-sulfides. After accounting for isotopic fractionation during adsorption, we estimate that Neoarchean seawater δ ⁹⁸ Mo maintained a relatively stable composition between 1.5‰ and 1.6‰. A newly developed Mo isotope mass balance model further indicates that only a minor MnO ₂ sink was required to generate these heavy δ ⁹⁸ Mo values. Instead, the dominant control was likely removal of isotopically light Mo via adsorption to settling ferrihydrite particles in ferruginous seawater. Given the lack of oxygen indicators for cyanobacterial photosynthesis, we posit that anoxygenic photosynthetic bacteria (photoferrotrophs) were the primary drivers of ferrihydrite precipitation during BIF deposition. Together, these findings imply that the Neoarchean Mo isotope record reflects anaerobic biological oxidation of Fe(II) rather than pervasive surface seawater oxygenation preceding the GOE.

Determination of PGEs in Chang'e-6 agglutinate glass by LA-ICP-MS.

Coral skeletal trace‐metal compositions are commonly assumed to derive from seawater, yet the extent to which biological processes contribute remains poorly constrained. Here we present the first paired Mo isotope measurements of coral tissue, symbiotic zooxanthellae, and skeleton. All three compartments are depleted in δ ⁹⁸ Mo relative to seawater, with zooxanthellae significantly lighter than host tissue. A strong negative correlation between zooxanthellae and skeletal δ ⁹⁸ Mo, together with a negative power‐law relationship between skeletal Mo concentration and δ ⁹⁸ Mo across species and reef environments, indicates a symbiont‐mediated control on Mo partitioning. Fossil corals further show systematic variability in skeletal δ ⁹⁸ Mo associated with climate variability over the past millennium, suggesting that environmental changes modulate symbiont‐driven biological processes recorded in coral skeletons. These observations suggest that biologically processed Mo contributes substantially to skeletal composition and that coral δ ⁹⁸ Mo may serve as a novel proxy for symbiont metabolic activity and its response to environmental change.

A single-column N235 protocol enables efficient Cu purification from diverse matrices through acid-dependent retention, providing a simple procedure for high-precision Cu isotope analysis.

A simple, low-blank, and effective Zn purification method with a self-made trialkyl amine extraction resin is developed to separate Zn from biological materials for high precision determination of Zn isotopic composition by double spike MC-ICP-MS.

Fluids released from subducting slabs play an important role in arc magmatism and global volatile cycles, yet resolving their lithological origins and spatial distribution remains a major challenge. Here, we integrate molybdenum (Mo) isotope systematics with improved P-wave tomography across the Kamchatka arc to trace the origins and transport pathways of slab-derived fluids. Arc lavas exhibit δ ^98/95 Mo values systematically higher than the depleted mantle and correlate positively with fluid-mobile element enrichment. We identify a distinctive “dumbbell-shaped” isotopic pattern cospatial with prominent low-velocity zones in the mantle wedge. The anomalies further align with regions of marked velocity reductions in the incoming Pacific Plate, indicating that the fluid budget of the volcanic front is directly inherited from heterogeneous serpentinization of the subducting lithospheric mantle prior to subduction. Our results demonstrate that preexisting slab hydration exerts first-order control on subduction zone chemical architecture, providing a predictive framework for understanding global volatile cycling.

Single-column Zr separation with TOPO resin (rinsed/eluted with 3 M HNO ₃ /1 M HCl and 3 M HNO ₃ + 0.1 M HF) and MC-ICP-MS with Sr normalization (C-SSBIN) yields ±0.061‰ (2SD) for geological reference.