Distribution of bacterial 3-OH-FAs in Chinese saline lakes and its implication for paleoclimate reconstruction

Microbial communities in saline lakes are sensitive to environmental changes and showed promise for paleoclimate reconstruction. However, how the Gram-negative bacterial communities and their related membrane lipids, 3-hydroxy fatty acid (3-OH-FA), adapt to salinity change is still unclear. Here, we report the potential impacts of salinity and pH on 3-OH-FA distributions, based on saline lake samples, including lacustrine sediments and surrounding soils, collected from the Balikun Lake of the Xinjiang Province and 12 shallow lakes of the Inner Mongolia Province, China. Our results revealed that 3-OH-FAs in saline lakes are mainly derived from in situ production. The 3-OH-FA distributions are sensitive to salinity and pH variations. Specifically, in brackish lakes (< 30 parts per thousand), salinity and pH dominated the distribution of 3-OH-FAs. However, in hypersaline lakes, salinity predominated the 3-OH-FA distributions. Moreover, multiple linear regression has been used to explore the potential salinity proxies based on 3-OH-FAs. The result revealed the promising potential of using 3-OH-FAs for paleoenvironment reconstruction, which provides alternative tools for investigating the paleoclimate changes in saline environments

Fractionation of radiogenic Pb isotopes in meteorites and their components induced by acid leaching

In 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

A new calcite reference material for <i>in situ</i> oxygen isotope analysis using secondary ion mass spectrometry: development and application constraints

The oxygen isotopic microanalysis of calcite is essential for obtaining high spatial resolution data linked to microstructures, a challenge for conventional techniques. This analysis, however, relies heavily on matrix-matched reference materials, of which only a few calcite standards are available. In this study, an inorganically precipitated calcite vein sample (WS-1) was evaluated through 225 SIMS oxygen isotope analyses and was found to have a homogeneous isotopic composition, with an external reproducibility <= 0.21 parts per thousand (1 sigma), suggesting its potential as a SIMS reference material. The precise delta 18OVPDB value, determined via traditional gas-source IRMS, was -16.52 +/- 0.13 parts per thousand (1SD). Matrix effects were assessed using various carbonates, including abiotic aragonite (VS001/1-A), three abiotic calcites (NBS18, Cal-1, WS-1), and a high-Mg calcite (gorgonian coral). The results revealed negligible matrix effects between abiotic aragonite and calcites but significant differences between calcites and high-Mg calcite, likely due to Mg content or differences in biogenic crystal morphology and trace organic composition. This study demonstrates the utility of in situ oxygen isotopic microanalysis for calcite but emphasizes the need for caution when analyzing high-Mg calcitic skeletons

P-wave attenuation variations beneath the central and western Tien Shan from teleseismic waves

The seismic attenuation plays an important role in understanding the subsurface structure and provides complementary information on the mantle dynamic together with seismic velocity information. Here we explore the attenuation structure beneath the central and western Tien Shan using teleseismic P-wave data. Firstly, we map the spatial distribution of relative attenuation parameter using the spectral ratio technique in the frequency band between 0.1 and 1.5 Hz. Our results reveal strong lateral attenuation variations in the lithosphere and asthenosphere underneath the study area. Then we invert for the Qp values using a linear inversion approach. Two high-attenuation regions are observed beneath the middle Tien Shan and western Tarim Basin that could be associated with upwelling hot materials and/or a small plume. Moreover, low-attenuation regions are found beneath the Kazakh Shield and western Tien Shan, which can be attributed to the underthrusted/subducted lithospheric fragments

A preliminary investigation of pore development mechanisms in highly matured solid bitumen: Implications from the Ediacaran Dengying Formation solid bitumen in the central Sichuan Basin, Southwest China

Although pores in solid bitumen are crucial for shale reservoirs, their development mechanisms have not been fully understood partly due to the small size of solid bitumen in shales and the difficulty in its discrimination from residual kerogen. However, solid bitumen in conventional reservoirs generally has a larger size and definite origin, and therefore the examination of their pores can provide some insights into the mechanisms of pore formation in shale solid bitumen. In this study, solid bitumen samples from conventional reservoirs of the Ediacaran Dengying Formation in the central Sichuan Basin were collected for petrographic and geochemical analyses to investigate their pore characteristics and formation mechanisms. The results indicate that pores are commonly identified in solid bitumen grains that are derived from the cracking of tar pads and in solid bitumen grains that have experienced gravity-driven component separation during their formation. The development of pores in solid bitumen is controlled by the combined effect of gas expulsion and the viscosity of solid bitumen during its movable stage. The gas expulsion from movable bitumen creates pores, and they can be preserved or healed depending on the component-controlled viscosity of movable bitumen. The enrichment of sulfur- and oxygen-containing compounds and heavy components such as asphaltenes in movable bitumen can enhance its viscosity and thus inhibit the healing of pores, ultimately facilitating pore development in the present overmature solid bitumen grains

Accumulation of lipophilic and proteinophilic halogenated organic pollutants (HOPs) in the different types of feathers of laying hens

This 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

Acidity of Atmospheric Waters Induces Enhanced H₂O₂ Production through Photosensitized Chemistry of Phenolic Substances

Hydrogen peroxide (H2O2) is known to convert SO2 to sulfuric acid and acts as a dominant reservoir of highly reactive hydroxyl radical (OH) in atmospheric waters (cloud, fog, rain, and aerosol liquid water). Here, we conclusively demonstrate that photosensitized oxidation of phenolic substances (catechol, o-cresol, and guaiacol) by the excited triplet state of nonphenolic compound (3,4-dimethoxybenzaldehyde, DMB) represents an unrecognized significant source of H2O2. Intriguingly, the highest H2O2 formation rate, (3.43 +/- 0.14) x 10-9 M s-1, and H2O2 yield (Phi H2O2 ), (7.68 +/- 0.08) x 10-1, were observed by photosensitized chemistry of catechol at low pH values (2.50) typical of cloud and aerosol water. The quantum chemical calculations revealed that the fraction of the protonated triplet state of DMB increases with a pH decrease, resulting in a faster formation of H2O2. A detailed mechanism was proposed describing the formation of H2O2 from the photosensitized reaction

Organosulfur Compounds: A Non-Negligible Component Affecting the Light Absorption of Brown Carbon During North China Haze Events

The roles of organosulfur compounds (OSCs), an important component in organic matter, in brown carbon (BrC) aerosol absorption is often overlooked. Here, the molecular composition of OSCs and its associations with methanol-soluble BrC (MS-BrC) absorption during a haze event in North China were revealed using a Fourier transform ion cyclotron resonance mass spectrometry analysis. By combining aggregated boosted tree model and partial least squares regression estimation, our results suggested that OSCs were mainly composed of potential aromatic structures, and the MS-BrC absorption was closely related to OSCs. Specifically, OSCs contribute a notable 26% of the total potential BrC molecular number and an upper limit of 10.4% of total MS-BrC absorption. Furthermore, we found that OSCs were mainly influenced by coal combustion, and the potential desulfurization reactions showed associations with the variations of MS-BrC absorption. Since the residential coal combustion (an important primary source of OSs) was the major energy in North China, our research underscores the potential of aromatic OSCs as tracers for assessing the impact of fossil fuel combustion on BrC and highlights the important atmospheric influences of OSCs (e.g., light absorption and health), which need more works to uncover the origins, fates, and environmental effects of OSCs

Magnesium Isotope Fractionation During Basalt Weathering: An Index of Weathering Fluxes and CO₂ Consumption

The weathering of silicate rocks exerts a significant control on the weathering fluxes of metals and atmospheric CO2 consumption. In this study, we present new magnesium (Mg) isotope data from a basalt weathering profile in Hainan Island, South China, to investigate Mg isotope fractionation and calculate weathering fluxes and CO2 consumption. The Mg mobility (tau(Mg,Ti)) in saprolites decreases from -34.1% to -95.7%. The delta Mg-26 values in saprolites vary from -0.25 +/- 0.07 parts per thousand to 0.43 +/- 0.07 parts per thousand, higher than those of the parent rock (-0.25 +/- 0.07 parts per thousand). The significant Mg loss during the formation and decomposition of clay minerals influences Mg isotope fractionation, particularly with changes in kaolinite structure under different pH conditions, which prefer heavy Mg isotopes. By applying a mass balance model, we have developed a novel method to calculate weathering fluxes based on the weathering profile, yielding Mg elemental fluxes (Mg-Flux) of 2.45-5.85 mol/cm(2)/Myr, Mg isotopic fluxes (delta Mg-26(Flux)) of -0.44 to -0.04 parts per thousand/mol/cm(2)/Myr, and CO2 consumption of 2.3 x 10(12) mol/yr for the weathering outputs of basaltic rocks. This highlights the crucial role of basalt weathering in global carbon sequestration. Our findings improve the understanding of Mg cycling and isotope fractionation in epigenetic environments and facilitate the quantification of weathering fluxes and atmospheric CO2 consumption during basalt weathering