Molybdenum as a Paleoredox Proxy

Abstract

Molybdenum (Mo) is a widely used trace metal for investigating redox conditions. However, unanswered questions remain that concentration and bulk isotopic analysis cannot specially answer. Improvements can be made by combining new geochemical techniques to traditional methods of Mo analysis. In this Element, we propose a refinement of Mo geochemistry within aquatic systems, ancient rocks, and modern sediments through molecular geochemistry (systematically combining concentration, isotope ratio, elemental mapping, and speciation analyses). Specifically, to intermediate sulfide concentrations governing Mo behavior below the "switch-point" and dominant sequestration pathways in low-oxygen conditions. The aim of this work is to (1) aid and improve the breadth of Mo paleoproxy interpretations by considering Mo speciation and (2) address outstanding research gaps concerning Mo systematics (cycling, partitioning, sequestration, etc.). The Mo paleoproxy has potential to solve ever-complex research questions. By using molecular geochemical recommendations, improved Mo paleoproxy interpretations and reconstruction can be achieved.

Molybdenum Release Triggered by Dolomite Dissolution: Experimental Evidence and Conceptual Model

“…Similar results at different filter sizes during step 1 of sequential extraction indicated that Mo is not linked to nanoparticles > 0.015 μm (Figure ). However, studies on Suwannee River fulvic and humic acid showed organic components with hydrodynamic diameters below 15 nm. − Because mechanisms linking Mo to OM are still debated, mainly due to the complexity of OM, , further investigations will be necessary to elucidate how the release and association of Mo and sulfurized OM operate at the molecular level.…”

Volcanism and carbon cycle perturbations in the High Arctic during the Late Jurassic – Early Cretaceous

“…High Mo concentrations (>20 ppm) in sedimentary rocks may reflect anoxic conditions (e.g. Tribovillard et al, 2006;Lyons et al, 2009;Hlohowskyj et al, 2021). However, whilst there is a weak correlation between Hg and Mo at both Axel Heiberg sites and the lowest part of the Festningen section (Table 3), the Mo concentrations are consistently low (< 10 ppm excepting one outlier of c. 20 ppm; Figs.…”

Improving Mercury Systematics With Molybdenum and Vanadium Enrichments: New Insights From the Cambrian‐Ordovician Boundary

“…The residence time of Hg is less than ∼2 years in the atmosphere and can be used to represent the transient variation of Hg flux in Earth's history (Mason & Sheu, 2002;Selin, 2009), whereas Mo displays a long residence time in the ocean water (∼400 kyr; Miller et al, 2011). Provided that Hg and Mo are preferentially buried with organic matter and iron sulfide phases (Chappaz et al, 2018;Hlohowskyj et al, 2021;Shen et al, 2020), we propose to use the Hg-Mo relationship as a tool to refine our understanding of Hg sequestration under reducing Not accounting for the samples showing anomalies (n = 15, Figure 3c; n = 11, Figure 3d), Hg displays a high correlation with Mo (r s = 0.86, p < 0.05, n = 73, Figure 3c; r s = 0.86, p < 0.05, n = 20, Figure 3d). For the DBH 15/73 core deposited under a deeper water column, Hg is positively correlated with Mo during the Miaolingian, but shows a negative relationship with Mo during the Stage 10 (Figure 3c).…”