The influence of weathering and soil organic matter on Zn isotopes in soils

Zinc is an essential micronutrient that is ultimately released during mineral weathering. In soils, organic matter plays a key role in influencing Zn partitioning and therefore on Zn biogeochemical cycling. Soil organic matter is partitioned between carbon that is more readily available for decomposition by microorganisms, and more stable carbon transiently preserved from decomposition. The role of the stable pool of soil organic matter on Zn biogeochemical cycling remains poorly understood. The pool of stable carbon is controlled by combination with mineral constituents or is material that is intrinsically resistant to decomposition. The Zn stable isotopes are fractionated by interactions between Zn and soil mineral and organic constituents. This study reports the Zn isotope composition of five Icelandic soil profiles derived from the same parent basalt and characterized by contrasting degrees of weathering and organic matter content (δ66Zn = + 0.10 ± 0.05 to + 0.35 ± 0.02‰), the distribution of reactive mineral constituents available to form associations with soil organic matter, and the amount of stable organic carbon. Throughout these soils, the δ66Zn isotope variations are little influenced by mineral constituents, but rather by soil organic matter content. These data suggest that a combination of organic matter accumulation and Zn loss by leaching is required to explain the observed decrease in Zn concentration in soils and lighter soil δ66Zn with increasing organic carbon content. These results suggest that the presence of stable organic carbon in soils provides a pool of light Zn, attributed to the Zn isotope signature of organic matter partially preserved from decomposition. Crucially, this stable organic carbon pool may also contribute to the formation of the light Zn isotope sink reported in organic-rich marine sediments, a key output required to explain the oceanic mass balance of Zn isotopes

Osmium uptake, distribution, and 187Os/188Os and 187Re/188Os compositions in Phaeophyceae macroalgae, Fucus vesiculosus: Implications for determining the 187Os/188Os composition of seawater

The osmium isotopic composition (187Os/188Os) of seawater reflects the balance of input from mantle-, continental- and anthropogenic-derived sources. This study utilizes the Phaeophyceae, Fucus vesiculosus, to analyse its Os abundance and uptake, as well as to assess if macroalgae records the Os isotope composition of the seawater in which it lives. The data demonstrates that Os is not located in one specific biological structure within macroalgae, but is found throughout the organism. Osmium uptake was measured by culturing F. vesiculosus non-fertile tips with different concentrations of Os with a known 187Os/188Os composition (∼0.16), which is significantly different from the background isotopic composition of local seawater (∼0.94). The Os abundance of cultured non-fertile tips show a positive correlation to the concentration of the Os doped seawater. Moreover, the 187Os/188Os composition of the seaweed equaled that of the culture medium, stongly confirming the possible use of macroalgae as a biological proxy for the Os isotopic composition of the seawater

Unravelling the controls on the molybdenum isotopic composition of rivers

Formation and crystallisation of the Lunar Magma Ocean (LMO) was one of the most incisive events during the early evolution of the Moon. Lunar Magma Ocean solidification concluded with the coeval formation of K-, REE- and P-rich components (KREEP) and an ilmenite-bearing cumulate (IBC) layer. Gravitational overturn of the lunar mantle generated eruptions of basaltic rocks with variable Ti contents, of which their δ49Ti variations may now reflect variable mixtures of ambient lunar mantle and the IBC. To better understand the processes generating the spectrum of lunar low-Ti and high-Ti basalts and the role of Ti-rich phases such as ilmenite, we determined the mass dependent Ti isotope composition of four KREEP-rich samples, 12 low-Ti, and eight high-Ti mare basalts by using a 47Ti-49Ti double spike. Our data reveal significant variations in δ49Ti for KREEP-rich samples (+0.117 to +0.296 ‰) and intra-group variations in the mare basalts (-0.030 to +0.055 ‰ for low-Ti and +0.009 to +0.115 ‰ for high-Ti basalts). We modelled the δ49Ti of KREEP using previously published HFSE data as well as the δ49Ti evolution during fractional crystallisation of the LMO. Both approaches yield δ49TiKREEP similar to measured values and are in excellent agreement with previous studies. The involvement of ilmenite in the petrogenesis of the lunar mare basalts is further evaluated by combining our results with element ratios of HFSE, U and Th, revealing that partial melting in an overturned lunar mantle and fractional crystallisation of ilmenite must be the main processes accounting for mass dependent Ti isotope variations in lunar basalts. Based on our results we can also exclude formation of high-Ti basalts by simple assimilation of ilmenite by ascending melts from the depleted lunar mantle. Rather, our data are in accord with melting of these basalts from a hybrid mantle source formed in the aftermath of gravitational lunar mantle overturn, which is in good agreement with previous Fe isotope data

Unravelling the controls on the molybdenum isotope ratios of river waters

The molybdenum (Mo) isotope ratios (δ98/95Mo) of river waters control the δ98/95Mo values of seawater and impact on the use of Mo isotope ratios as a proxy of past redox conditions. The δ98/95Mo values of river waters vary by more than 2 ‰, yet the relative roles of lithology versus fractionation during weathering remain contested. Here, we combine measurements from river waters (δ98/95Modiss), river bed materials (δ98/95MoBM) and soils from locations with contrasting lithology. The δ98/95Mo values of river bed materials (δ98/95MoBM), set by rock type, vary by ~1 ‰ between rivers in New Zealand, the Mackenzie Basin, and Iceland. However, the difference between dissolved and solid phase Mo isotopes (Δ98/95Modiss-BM) varies from +0.3 ‰ to +1.0 ‰. We estimate Mo removal from solution using the mobile trace element rhenium and find that it correlates with Δ98/95Modiss-BM across the sample set. The adsorption of Mo to Fe-Mn-(oxyhydr)oxides can explain the observed fractionation. Together, the amount of Mo released through dissolution and taken up by (oxyhydr)oxide formation on land may cause changes in the δ98/95Mo values of rivers, driving long term changes in the Mo isotope ratios of seawater

Titanium stable isotope investigation of magmatic processes on the Earth and Moon

We present titanium stable isotope measurements of terrestrial magmatic samples and lunar mare basalts with the aims of constraining the composition of the lunar and terrestrial mantles and evaluating the potential of Ti stable isotopes for understanding magmatic processes. Relative to the OL–Ti isotope standard, the δ49Ti values of terrestrial samples vary from −0.05 to +0.55‰, whereas those of lunar mare basalts vary from −0.01 to +0.03‰ (the precisions of the double spike Ti isotope measurements are ca. ±0.02‰ at 95% confidence). The Ti stable isotope compositions of differentiated terrestrial magmas define a well-defined positive correlation with SiO2 content, which appears to result from the fractional crystallisation of Ti-bearing oxides with an inferred isotope fractionation factor of View the MathML source. Primitive terrestrial basalts show no resolvable Ti isotope variations and display similar values to mantle-derived samples (peridotite and serpentinites), indicating that partial melting does not fractionate Ti stable isotopes and that the Earth's mantle has a homogeneous δ49Ti composition of +0.005 ± 0.005 (95% c.i., n=29). Eclogites also display similar Ti stable isotope compositions, suggesting that Ti is immobile during dehydration of subducted oceanic lithosphere. Lunar basalts have variable δ49Ti values; low-Ti mare basalts have δ49Ti values similar to that of the bulk silicate Earth (BSE) while high-Ti lunar basalts display small enrichment in the heavy Ti isotopes. This is best interpreted in terms of source heterogeneity resulting from Ti stable isotope fractionation associated with ilmenite–melt equilibrium during the generation of the mantle source of high-Ti lunar mare basalts. The similarity in δ49Ti between terrestrial samples and low-Ti lunar basalts provides strong evidence that the Earth and Moon have identical stable Ti isotope compositions

No V-Fe-Zn isotopic variation in basalts from the 2021 Fagradalsfjall eruption

The Earth’s mantle is chemically heterogeneous in space and time, which is often reflected by variable isotopic compositions of mantle derived basalts. Basalts from the first 40 days of the 2021 Fagradalsfjall eruption, Reykjanes Peninsula, Iceland, display systematic temporal variations in the ratios of incompatible elements alongside resolvable variations in Sr, Nd and Pb radiogenic isotopes. These variations reflect progressive influx of magma derived from melting of a deeper, more enriched and potentially lithologically distinct source. We use this eruptive time series to conduct the first combined V-Fe-Zn isotope study, exploring the sensitivity of the combined isotopic approach, with particular focus on fingerprinting source lithological heterogeneity. We find no analytically resolvable change in V (δ51VAA between −0.95 ± 0.09 ‰ 2 s.d. and −0.86 ± 0.07 ‰ 2 s.d.), Fe (δ56FeIRMM-524 between +0.047 ± 0.042 ‰ 2 s.d. and +0.094 ± 0.049 ‰ 2 s.d.) and Zn (δ66ZnAA-ETH between −0.042 ± 0.003 ‰ 2 s.d. and +0.013 ± 0.027 ‰ 2 s.d.) isotopic compositions. The lack of variability in V-Fe-Zn isotopes, despite the evolving trace element and radiogenic isotope ratios, suggests there is no significant contribution of melts from a lithologically distinct (pyroxenite) mantle component under the Reykjanes Peninsula

Unravelling the controls on the molybdenum isotope ratios of river waters

The molybdenum (Mo) isotope ratios (δ98/95Mo) of river waters control the δ98/95Mo values of seawater and impact on the use of Mo isotope ratios as a proxy of past redox conditions. The δ98/95Mo values of river waters vary by more than 2 ‰, yet the relative roles of lithology versus fractionation during weathering remain contested. Here, we combine measurements from river waters (δ98/95Modiss), river bed materials (δ98/95MoBM) and soils from locations with contrasting lithology. The δ98/95Mo values of river bed materials (δ98/95MoBM), set by rock type, vary by ~1 ‰ between rivers in New Zealand, the Mackenzie Basin, and Iceland. However, the difference between dissolved and solid phase Mo isotopes (Δ98/95Modiss-BM) varies from +0.3 ‰ to +1.0 ‰. We estimate Mo removal from solution using the mobile trace element rhenium and find that it correlates with Δ98/95Modiss-BM across the sample set. The adsorption of Mo to Fe-Mn-(oxyhydr)oxides can explain the observed fractionation. Together, the amount of Mo released through dissolution and taken up by (oxyhydr)oxide formation on land may cause changes in the δ98/95Mo values of rivers, driving long term changes in the Mo isotope ratios of seawater

Expansion and further delineation of the SETD5 phenotype leading to global developmental delay, variable dysmorphic features, and reduced penetrance

Diagnostic exome sequencing (DES) has aided delineation of the phenotypic spectrum of rare genetic etiologies of intellectual disability (ID). A SET domain containing 5 gene (SETD5) phenotype of ID and dysmorphic features has been previously described in relation to patients with 3p25.3 deletions and in a few individuals with de novo sequence alterations. Herein, we present additional patients with pathogenic SETD5 sequence alterations. The majority of patients in this cohort and previously reported have developmental delay, behavioral/psychiatric issues, and variable hand and skeletal abnormalities. We also present an apparently unaffected carrier mother of an affected individual and a carrier mother with normal intelligence and affected twin sons. We suggest that the phenotype of SETD5 is more complex and variable than previously presented. Therefore, many features and presentations need to be considered when evaluating a patient for SETD5 alterations through DES