Search

The Cryogenian Sturtian and Marinoan Snowball Earth glaciations bracket a nonglacial interval during which Demosponge and green-algal biomarkers first appear. To understand the relationships between environmental perturbations and early animal evolution, we measured sulfur and mercury isotopes from the Datangpo Formation from South China. Hg enrichment with positive Δ199Hg excursion suggests enhanced volcanism, potentially due to depressurization of terrestrial magma chambers during deglaciation. A thick stratigraphic interval of negative Δ33Spy indicates that the nonglacial interlude was characterized by low but rising sulfate levels. Model results reveal a mechanism to produce the Δ33S anomalies down to -0.284‰ through Rayleigh distillation. We propose that extreme temperatures and anoxia contributed to the apparent delay in green algal production in the aftermath of the Sturtian glaciation and the subsequent reoxygenation of the iron-rich and sulfate-depleted ocean paved the way for evolution of animals.

BACKGROUND Soil cadmium pollution has become one of the main factors that endanger human health. Rapid and effective remediation of Cd pollution soil requires a fundamental understanding of Cd sources and geochemical cycling. With the advancement of Cd isotope analysis technology and the in-depth understanding of its fractionation mechanism, Cd isotopes provide new perspectives for understanding the source and fate of Cd in the soil. OBJECTIVES To systematically summarize the cadmium isotope analysis method, and emphasize the research progress, problems, and potential application of Cd isotopes as tracers in soil. METHODS Sample digestion methods, such as high-temperature digestion bombs, microwave acid digestion, ashing, and acid extraction, are reviewed here with ion-exchange separation and multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). RESULTS Based on previous studies, this review systematically summarizes the fundamental principle and methodology of Cd isotopic analysis methods. For the soil samples, the high-temperature digestion bombs method and microwave acid digestion can meet its cadmium isotope analysis requirements. With sufficient recovery and complete removal of interfering elements, standard-sample bracketing, external normalization, and double-spike techniques can be used for mass bias correction to obtain accurate and reliable Cd isotope data. In addition, the theoretical basis of soil cadmium isotope tracing was reviewed. This review summarizes the cadmium isotopic composition of multiple potential cadmium sources in soil and the direction and extent of cadmium isotope fractionation in typical processes (weathering leaching, adsorption, precipitation/co-precipitation, complexation). Combined with the latest research results, the application of cadmium isotopes in tracing soil cadmium sources and their migration and transformation processes is summarized. CONCLUSIONS In the future, we should further develop and optimize the high-precision cadmium isotope analysis method, construct the fingerprint map of soil cadmium isotope, and reveal the cadmium isotope fractionation mechanisms in the processes of multi-component and multi-interface.

Rhenium (Re) and its isotopes offer valuable information for understanding various geological processes throughout Earth's history. However, Re isotope analysis remains quite challenging owing to its ultra-trace concentration in geological materials. Previous studies have developed column chemistry and analytical methods for Re isotope analysis, but issues such as tedious pretreatment and incomplete Re recovery still exist. Herein, we present a novel procedure integrating preconcentration and fast column chemistry for Re isotope analysis. Utilizing Na2S solution and activated carbon powder under acidified conditions, we achieved the quantitative recovery of Re from aqueous solutions via filtration while removing most matrices. Standard addition to diverse matrix solutions yielded complete Re recovery (99.6 ± 6.7%, n = 10, 2SD) and precise isotopic compositions (δ187Re = −0.49 ± 0.04‰, n = 10, 2SD), as determined using multi-collector inductively coupled plasma–mass spectrometry. Our method was applied to seawater (7.1 pg g−1 for Re) and solid reference materials (∼0.5–75 ng g−1 for Re), which resulted in stable and high recovery with isotopic results consistent with published data. Our method exhibits efficient matrix removal with stable and essentially quantitative Re recovery, which paves the way for wide applications of Re isotopes in the earth and planetary sciences. [ABSTRACT FROM AUTHOR]

Particle-bound mercury (PBM) records the oxidation of elemental mercury, of which the main oxidation pathways (Br∙/Cl∙/OH∙/O3) remain unclear, especially in the Southern Hemisphere. Here, we present latitudinal covariations of Hg and S-isotopic anomalies in cross-hemispheric marine aerosols that evidence an equator-to-poleward transition of Hg oxidants from OH∙/O3 in tropics to Br∙/Cl∙ in polar regions highlighting thus the presence of distinct oxidation processes producing PBM. The correlations between Hg, S and O-isotopic compositions measured in PBM, sulfates and nitrates respectively within the aerosols highlight the implication of common oxidants in their formations at different latitudes. Our results open a new window to better quantify the present-day atmospheric Hg, S and N budgets and to evaluate the influences of aerosols on climate and ecosystems once the isotopic fractionations associated with each process have been determined.