Guangzhou Institute of Geochemistry
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From holocene to anthropogenic impact: Surpassing coral's pH up-regulation capacity under ocean acidification
No full textCorals' regulation of internal calcifying fluid (CF or cf) chemistry is crucial for their extraordinary calcification capacity, endowing them with a certain ability to cope with environmental changes such as anthropogenic ocean acidification (OA) and warming. However, it remains unclear whether the impacts of these changes on corals have substantially surpassed their regulation capacity, particularly in comparison to the CF chemistry responses to natural climate variability with minor or no human perturbation. In this study, we reconstructed the pH, dissolved inorganic carbon, and carbonate ion concentrations in coral CF (pH(cf), DICcf, and [CO32-](cf)) during the Mid- to Late-Holocene, by analyzing the skeletal delta B-11 and B/Ca of 80 Porites spp. from eastern Hainan Island in the South China Sea (SCS). Our records indicate considerable inter-colony variations in CF chemistry, with maximum disparities reaching 0.18 units for pH(cf) and 1664 mu mol/kg for DICcf. With this in mind, we found no clear responses of coral DICcf to the climate fluctuations during the past similar to 5500 years, nor evident differences in pH(cf) and [CO32-](cf) across pre-industrial natural epochs. However, pH(cf) and [CO32-](cf) of modern corals have significantly declined compared to fossil corals. Further analyzes compiling global data on Porites spp. also confirm this pronounced pH(cf) decrease in modern corals, suggesting the limitations of pantropical corals to counteract OA by up-regulating pH(cf). Importantly, these fossil and modern corals reveal a clear long-term pH(cf) descending trend parallel to atmospheric CO2 changes, supporting the reliability of coral delta B-11 in recording long-term changes in seawater pH (pH(sw))
Accumulation of lipophilic and proteinophilic halogenated organic pollutants (HOPs) in the different types of feathers of laying hens
No full textThis study investigated the bioaccumulation of halogenated organic pollutants (HOPs) in three types of feathers from laying hens through exposure experiments. The HOPs included lipophilic polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), as well as proteinophilic perfluoroalkyl carboxylic acids (PFCAs). Concentrations of PCBs, PBDEs, and short-chain PFCAs (8) showed no significant differences among primary, tail, and body feathers. The concentration order in the feathers was & sum;12PFCAs > & sum;7PBDEs > & sum;(13)PCBs, which was completely reversed by the exposure dose. The transfer rates (TRs) (concentration ratio of feather to serum) of PFCAs (0.11-6.8) were one order of magnitude higher than those (0.01-0.30) of PCBs and PBDEs. These results indicate that PFCAs preferentially accumulate in feathers compared to PBDEs and PCBs. TRs, regardless of whether they were lipophilic or proteinophilic HOPs, were significantly and positively correlated with the protein-water partition coefficient (log K-pw). Strong and significant correlations between feathers and inner tissues were primarily observed in body feathers. Egg-laying significantly affects PFCA accumulation in feathers and even distorts the actual exposure dose in hens; however, its impact on PCBs and PBDEs is limited. These findings provide crucial insights into HOP deposition in bird feathers
Stable Nd isotopic fractionation in REY-rich deep-sea sediments
No full textStable Nd isotope ratios are regarded as a potential tracer for marine rare earth elements (REEs) cycling. However, the fractionation behavior of Nd in marine geological processes has not yet been constrained. This study investigates the bulk and leachate compositions (phosphate, Fe-Mn oxides, and aluminosilicates) of a Ndenriched deep-sea sediment core in the western Pacific for both the stable and radiogenic Nd isotopes. The epsilon Nd values of the bulk sediments range from -6.2 to -5.1, indicating a basically consistent source material throughout the core. Compared to the Bulk Silicate Earth (BSE), the core shows enrichment in heavy Nd isotopes, suggesting that marine authigenic components play a key role in controlling the stable Nd isotope behavior. In the phosphate phase, Nd content correlates positively with P2O5 and CaO contents (R2 = 0.97 and R2 = 0.96, respectively), while the stable Nd isotopic compositions exhibit limited variability (0.076 %o +/- 0.055 %o), suggesting that phosphates have the potential to reconstruct the stable Nd isotope composition of paleo-seawater. For Fe-Mn oxide phases, Mn content initially correlates with Nd content and stable Nd isotope composition, and then exhibit a negative relationship, which suggests that Fe-Mn (hydr)oxides initially adsorb heavier 146Nd from seawater and subsequently release it into pore water. The bulk sediment illite abundance and Al2O3 content correlate with bulk Nd content (R2 = 0.55 and R2 = 0.62, respectively) in aluminosilicate phases, but not with stable Nd isotope composition, indicating that illite controls Nd distribution within this phase without causing stable isotope fractionation. These results elucidate the behavior of stable Nd isotope fractionation in REY-rich deep-sea sediments and provide a fundamental understanding of stable Nd isotopes as a tracer for marine REEs cycling
A prominent oxygenation event in the late Mesoproterozoic broke the calm of the second half of the "Boring Billion"
No full textThe redox conditions on Earth's surface during the so-called "Boring Billion" (ca. 1.8-0.8 Ga) were characterized by an overall low-oxygen background punctuated by pulsed oxygenation events. This viewpoint, however, is primarily based on the redox studies from the first half of the "Boring Billion". Therefore, it remains unclear whether this state continued into the second half. To address this issue, carbonate rocks from the ca. 1.25-1.22 Ga Taizi and Yemahe formations in the Shennongjia area, Yangtze Block, South China, were analyzed using integrated methods. The carbonate rocks in the upper Taizi Formation display persistent and significant negative Ce anomalies (0.50 +/- 0.05, n = 46) and relatively high I/(Ca + Mg) ratios (up to 1.28 mu mol/mol), whereas those from the Yemahe Formation show no negative Ce anomalies (0.99 +/- 0.21, n = 39) and low I/(Ca + Mg) ratios (0.03 +/- 0.04 mu mol/mol, n = 86). These data suggest the occurrence of a significant pulsed oxygenation event in shallow seawater during the deposition of the upper Taizi Formation. A model calculation shows that the shallow seawater oxygen concentrations may have reached up to 41 mu M, accompanied with a rise in atmospheric oxygen levels to 12% PAL (present atmospheric level). In contrast, the reconstructed seawater delta 98Mo value is +1.15 parts per thousand for this interval, lower than that of the modern seawater but similar to those of most mid-Proterozoic values, indicating the global seafloor largely remained anoxic. These findings indicate that the ocean redox state in the second half of the "Boring Billion" was more dynamic than previously thought
Terrestrial ecosystem response to Early Cretaceous global environmental change: A calibrated, high-resolution Aptian record from Northeast China
No full textExtensive studies of Aptian oceanic anoxic events and carbon cycle perturbations have significantly advanced our understanding of marine responses to global climate change. However, further exploration of possible volcanism-climate-environment linkages is hindered by the scarcity of continuous, well-documented terrestrial records. In an attempt to address this gap, the Yanshan Scientific Drilling Project extracted a 1497.5 m core from the shale-dominated, lacustrine, Jiufotang Formation in the Kazuo Basin of Northeast China. High-precision U-Pb geochronology of two interlayered tuffs yielded depositional ages of 121.05 +/- 0.32 Ma and 117.359 +/- 0.031 Ma, and a Bayesian age-depth model for the lower half of the formation. An astrochronological model based on delta 13Corg and major element chemostratigraphy has suggested a duration of 9.03-9.14 Ma for the entire core, from 121.05 to 121.30 to 111.91-112.20 Ma. A 75.2 m core interval with unequivocal correlation to the oceanic anoxic event (OAE) 1a was identified by carbon isotope stratigraphy, which has a calibrated onset at 120.2 Ma and a total duration of ca. 450 kyr. Our results highlight the potential of lacustrine strata in recording at highresolution the marine-correlated carbon cycle changes and in deciphering the drivers and mechanisms of climate change across the marine and terrestrial realms
Light iron isotopes in high-silica granites record fluid evolution in magmatic-hydrothermal systems
No full textHigh-silica (SiO2 > 70 wt%) granites in continental collisional zones are crucial for understanding formation and evolution of the upper continental crust. Fluids released from felsic magmas can help drive the transition from magmatic to magmatic-hydrothermal systems in shallow magma chambers. However, the influence of these fluids on compositional variations and Fe isotope fractionation during the later stages of evolution of felsic magmas are unclear. In this contribution, we report stable Fe-Mg isotope compositions for the Paleocene Zhengga leucogranite pluton, part of the Gangdese batholith in southern Tibet. The pluton consists of both biotite granite and garnet-bearing two-mica granite, the latter of which contains zoned plagioclase and patchy K-feldspar that show fluid-mediated partial replacement textures, recording complicated magmatic and hydrothermal processes. Compared to high-silica granites worldwide (delta Fe-57 = +0.10 parts per thousand to +0.74 parts per thousand), all rocks from the Zhengga leucogranite pluton have light and variable delta Fe-57 values (+0.03 parts per thousand to +0.28 parts per thousand relative to IRMM-014), which display wave-shaped variations with progressive magmatic differentiation. However, their delta Mg-26 values (relative to DSM-3) decrease from -0.12 parts per thousand to -0.72 parts per thousand with increasing SiO2. The variable Fe and Mg isotope signatures of the Zhengga pluton can be best explained by a three-stage process, comprising initial fractional crystallization of biotite and magnetite, followed by deuteric fluid exsolution with decreasing temperatures and pressures, and final interaction between trapped fluids and residual melts in the highly crystalline magma mush. In combination with previously published Sr-Nd-Mo isotopes on the same samples, our new results suggest that fluid exsolution is required to elevate the delta Fe-57 of the felsic melts by up to 0.15 permil, but subsequent fluid-melt reaction reduces the Fe isotopes and leads to similar light-Fe isotope compositions of final residual melts to their primary magma. Therefore, the high-silica granites can be enriched in light Fe isotopes due to the effects of magmatic fluids, which make a significant contribution to the formation and evolution of upper continental crust
Atomic Insights into the Heterogeneous Crystallization of Manganese (Oxyhydr)oxides on Typical Iron (Oxyhydr)oxides: from Adsorption to Oxidation to Crystallization
No full textHeterogeneous crystallization of manganese (oxyhydr)oxides (MnO x ) on iron (oxyhydr)oxides (FeO x ) is crucial for the biogeochemical cycling of Mn, yet atomic-level insights into this process are important but relatively limited. Herein, we revealed the distinct adsorption, oxidation, and crystallization mechanisms of Mn on hematite (Hem), ferrihydrite (Fhy), and goethite (Gth). Gth exhibited highest ability in Mn(II) removal and oxidation, followed by Hem and Fhy. Manganite and hausmannite were the main MnO x products with distinct proportions, and morphologies cross the systems. MnO x growth mechanisms involve surface-induced nucleation, crystallization by particle attachment (CPA), and self-catalyzed growth. On Fhy, self-catalyzed growth was dominant; for Gth, surface-induced nucleation was prevalent, supplemented by CPA; and Hem combined all three mechanisms. These distinct mechanisms led to nanoparticles primarily of hausmannite on Gth and nanowires of manganite and hausmannite on Hem and Fhy, with those on Hem displaying lower aspect ratios. Differences in MnO x structure and morphology were attributed to Mn(II)-FeO x complexation, FeO x electronic band structure, and crystal structure mismatch between MnO x and FeO x , which respectively influenced the direct and indirect electron transfer and heterogeneous nucleation efficiency. This work advances our understanding of MnO x crystallization on FeO x at the nanoscale, explaining the diverse morphology and structure of MnO x in different environments
From bedrock to life activity and atmospheric deposition: Drivers of soil element coupling across horizons
No full textUnraveling the intricate coupling of multiple elements and their underlying drivers in natural soils is crucial for comprehending ecosystem functions, yet this knowledge has remained elusive. Using a comprehensive dataset of 900 soil samples collected from 116 sites across 26 mountains, this study dissected the coupling relationship of 23 elements within three soil development horizons, spanning five climate zones in China. Our findings revealed a robust continental-scale coupling of soil elements, influenced by plants and environmental factors including spatial distance, climate, soil properties, and atmospheric nitrogen deposition, accounting for 36% of the observed variance in element coupling. Notably, our study unveiled the horizon-specific nature of element coupling mechanisms. In the parent horizon, rock type exerted the primary control on the dynamics of element coupling. However, as soil developed, life activities and atmospheric deposition of anthropogenic trace metals concurrently reshaped the element coupling patterns, particularly in the organic and surficial mineral horizons. Elements were divided into two distinct elemental groups, exhibiting opposite fitting trends with atomic mass and crustal abundance, and the effect of these properties on coupling diminished with soil depth. Heavy metals enriched by human activity deviated from property-based predictions with lower coupling. This study represents the first continental-scale quantification of multi-element coupling across soil horizons, underscoring the paramount importance of life activity and atmospheric deposition in modulating the initial lithological-mediated multi-element coupling. Our insights advance understanding of terrestrial ecosystem biogeochemistry and urge further research on the impacts of anthropogenic activities and environmental changes on these delicate elemental interactions
Fractionation of radiogenic Pb isotopes in meteorites and their components induced by acid leaching
No full textIn this study we test the possibility that radiogenic 207Pb/206Pb ratios (207Pb*/206Pb*) in meteorites can be fractionated during partial dissolution, and explore the consequences of this fractionation for Pb-isotope chronology of meteorites. We report the results of experiments tailored to detect Pb-isotope fractionation, induced by partial dissolution through acid leaching, in plutonic angrite Northwest Africa (NWA) 4801 and ungrouped achondrites NWA 10132 and Erg Chech (EC) 002. We also re-examine previously published U-Pb data for other achondrites and for Ca-Al-rich refractory inclusions (CAIs), to seek evidence of such fractionation. We observe that, in primitive achondrite NWA 10132, differences in 207Pb*/206Pb* ratios, corresponding to the age bias of ca. 1-2 Ma, exist between the 0.5 M hydrofluoric acid leachates of pyroxene or crushed rock, and the residues after such leaching. In angrite NWA 4801, similar acid treatment of pyroxene separates did not cause a resolvable age bias. In EC 002, three steps of partial dissolution in 0.2 M - 5 M HF caused irregular 207Pb*/206Pb* fractionation between leaching steps, and generally higher 207Pb*/206Pb* ratios in the residues than in HF leachates. These age biases were observed in leaching pairs with highly radiogenic Pb, and cannot be explained by mixing between radiogenic Pb, primordial Pb, and Pb introduced by terrestrial contamination. Instead, the observed isotope fractionation is attributed to the combined effects of the size difference between alpha-recoil tracks in the decay chains of 238U and 235U, and exsolution of primary pigeonite, leading to the formation of a lamellar structure consisting of augite and low-Ca pyroxene by either slow-cooling or subsequent metamorphic reactions. Where extensive acid leaching intended for removal of non-radiogenic Pb causes fractionation of radiogenic Pb isotopes, its detrimental effect can be reversed by performing a numeric recombination of partial leachate and residue data. Currently, it is unclear how common leaching-induced isotopic fractionation is in Pb-isotopic chronology to meteoritic materials. Acid leaching is an essential step for removal of non-radiogenic Pb in the precise Pb-isotopic dating of meteorites, which currently does not have viable alternatives. However, it is important to be aware of its possible side effects, and to continue search for new non-radiogenic Pb removal techniques that do not cause radiogenic 207Pb* and 206Pb* fractionation
Pegmatite lithium deposits formed within low-temperature country rocks
No full textThe global climate crisis is likely to lead to a potential supply risk of lithium (Li) over the coming decades. More than half of the world's production of Li is derived from Li-bearing pegmatites. Although pegmatites are widespread, only a small fraction host economically relevant Li mineralization. Revealing which factors cause some pegmatites to be enriched in Li and others to be barren is critical for understanding Li pegmatite formation and for guiding exploration for new Li resources. In this study, we used an approach involving the analysis of natural samples from the Jiajika pegmatite deposit (China), combined with thermal and diffusion modeling. Here we show that Li contents in pegmatites are controlled not only by the initial Li contents in pegmatite melts but also by the temperature of the surrounding country rocks at the time of pegmatite emplacement. Lithium-mineralized pegmatites form preferentially when Li-rich pegmatite melts intrude low-temperature country rocks