Guangzhou Institute of Geochemistry
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Millennial calcification trends in <i>Porites</i> corals: Resilient skeletal density and vulnerable linear extension in response to environmental change
No full textGlobal coral reefs are currently facing widespread declines in calcification rates, a trend that underscores the need to understand variations between calcification in contemporary and ancient corals. This study investigates the changes in coral calcification over the last millennium by analyzing 21 subfossil and 11 modern coral samples from a marginal reef in the northern South China Sea. Our results reveal that although coral skeletal density has remained relatively stable, significant differences are evident in linear extension rates between the Medieval Climate Anomaly (MCA, 900-1300 CE) and the Little Ice Age (LIA, 1550-1850 CE), as well as between the preand post-industrial periods. This finding suggests that inshore Porites corals have greater resilience in their skeletal density compared to linear extension rates when responding to environmental changes. Our analysis indicates that sea surface temperature (SST) is the primary environmental driver influencing coral calcification, with a positive correlation observed between SST and both modern coral linear extension and calcification rates. In contrast, factors such as seawater pH, salinity, and total solar irradiance appear to have minimal impact on coral skeletal growth. Therefore, the lower linear extension and calcification rates observed in the LIA corals, as compared to the MCA corals, are likely due to the cooler temperatures during the LIA. We also hypothesize that the extended period of cold SST from the LIA to the early 20th century may have led to the reduced linear extension and calcification rates in modern corals, with recent warming insufficient to facilitate a return to the optimal skeletal growth observed during the MCA
Sedimentary Organic Nitrogen Isotopic Constraints on the Mid-Holocene Transition in the Nitrogen Dynamics of the Northern South China Sea
No full textMillennial-scale nitrogen (N) cycling processes in marginal seas and their response to climate change have not been well understood. Here, we present high-resolution (ca. 110 years) organic nitrogen isotope (delta N-15(org)) data since the last deglaciation (16.1 ka) derived from a highly resolved sediment core in the northern South China Sea, aiming to explore millennial-scale N cycling processes in this area. Unlike most bulk nitrogen isotope (delta N-15(bulk)) records from the South China Sea, the delta N-15(org) records show a clear response to well-defined climatic episodes during the last deglaciation and early Holocene (EH, similar to 11.7 to 9 ka), but exhibit a gradually decreasing trend in mid-to-late Holocene (since ca. 9 ka). During the last deglaciation and EH, the upper water column N dynamics are controlled by the lateral transport of surface nitrate from eastern tropical Pacific (ETP) presumably via the North Pacific Intermediate Water (NPIW) and to some extent, influenced by the altered input of terrigenous matter driven by sea level change. The significant decrease in delta N-15(org) since the mid-Holocene (at ca. 9 ka) can be best explained by the increase in local N-2 fixation forced by enhanced El Ni & ntilde;o. This mechanism is consistent with modern observations. Overall, our results may reflect the main controlling factors of surface ocean N dynamics have shifted from zonal transport of nitrate from the ETP to El Ni & ntilde;o since the mid-Holocene. Plain Language Summary The South China Sea (SCS) is an ideal area in which to study past changes in the low-latitude oceanic nitrogen (N) pool using sedimentary N records. However, reconstructions of past oceanic N cycling in the SCS based on different delta N-15 proxies reveal distinct characteristics through the last deglaciation. Based on sedimentary organic nitrogen isotopic values, our results show that there is a clear response to well-defined climatic episodes over the last 16.1 ka. Global mean ocean nitrate delta N-15 change, mainly through the NPIW intrusion, is the primary control of upper water column N dynamics during climate episodes of the last deglaciation and EH, while the strengthened N-2 fixation (via the Kuroshio Intrusion into the SCS) forced by the El Ni & ntilde;o is proposed as the main cause for the significant decrease in delta N-15(org) since the mid-Holocene
Recent-year variations in O<sub>3</sub> pollution with high-temperature suppression over central China
No full textBy analyzing environmental and meteorological monitoring data over recent years of 2015 - 2022, the Twain -Hu Basin (THB) in central China was identified as a regional O-3 pollution center over China with the highest increasing trend at 1.10 %center dot yr(-1) in interannual variations of O-3 concentrations with deteriorating O-3 pollution over recent years. We explored the spatiotemporal variations in O-3 pollution in the THB with ozone suppression (OS) under high air temperature over metropolitan, small urban, and mountainous areas. The bipolarized interannual trends in interannual O-3 variations in urban and mountainous areas over central China were characterized with the increasing and decreasing 90th percentiles of the daily maximum 8-h (MDA8-90) O-3 concentrations respectively in polluted urban areas and clean mountainous areas over recent eight years. The changes of the near -surface O-3 concentrations with air temperature exhibited the inflection points of OS from increasing to decreasing O-3 at air temperature of 30.5 C-degrees in mountainous areas, 32.5 C-degrees in small urban areas, and 34.5 C-degrees in metropolitan areas, and the intensity of OS was estimated in the ranking with mountainous areas (-2.30 mu g center dot m(-3) center dot C-degrees(-1) ) > small urban areas (-1.96 mu g center dot m(-3) center dot C-degrees(-1)) > metropolitan areas (-1.54 mu g center dot m(-3) center dot C-degrees(-1)), indicating that the OS was more significant over the lower -O-3 mountainous areas. This study has implications for understanding O-3 pollution variations with the meteorological drivers
Young KREEP-like mare volcanism from Oceanus Procellarum
No full textThe Moon's mare volcanism predominantly occurs within the Procellarum KREEP Terrane (PKT), which is widely thought to be associated with KREEP components within the lunar interior. The Chang'e-5 (CE-5) mission sampled a young (2 Ga) mare basalt Em4/P58 unit of northern Oceanus Procellarum. The geochemistry of the CE-5 mare basalt enables assessment of mantle source compositions which are essential to understand the thermo-chemical mechanism for prolonged volcanism during secular cooling of the Moon. Geochemical compositions of the CE-5 bulk soil, breccias, and basalt clasts from various depths within the drill core consistently display high concentrations of incompatible trace elements (ITE: similar to 0.3 x high-K KREEP; similar to 5 mu g/g Th) with KREEP-like inter-element ratios, for example for La/Sm, Nb/Ta, and Zr/Y. Exotic impact ejecta, extensive magma differentiation ( 30-60 % augite, and little or no ilmenite), with a small amount of late-stage interstitial melt that resembles KREEP (similar to 1-1.5 modal %, equivalent to 0.2-0.3 mu g/g Th in the mantle source). The voluminous mare basalts making up the Em4/P58 unit (>1500 km(3)) provide compelling evidence for large-scale, ITE enriched young mare magmatism within Oceanus Procellarum. In combination with remote sensing data and with the unique Th-rich Apollo 12 basalt fragment 12032,366-18 (impact ejecta likely from Oceanus Procellarum), this implies that significant portions of the FeO- and Th-rich mare regions of the western PKT may also have formed in a similar way
Ozone Chemistry on Greasy Glass Surfaces Affects the Levels of Volatile Organic Compounds in Indoor Environments
No full textThe chemistry of ozone (O-3) on indoor surfaces leads to secondary pollution, aggravating the air quality in indoor environments. Here, we assess the heterogeneous chemistry of gaseous O-3 with glass plates after being 1 month in two different kitchens where Chinese and Western styles of cooking were applied, respectively. The uptake coefficients of O-3 on the authentic glass plates were measured in the dark and under UV light irradiation typical for indoor environments (320 nm < lambda < 400 nm) at different relative humidities. The gas-phase product compounds formed upon reactions of O-3 with the glass plates were evaluated in real time by a proton-transfer-reaction quadrupole-interface time-of-flight mass spectrometer. We observed typical aldehydes formed by the O-3 reactions with the unsaturated fatty acid constituents of cooking oils. The formation of decanal, 6-methyl-5-hepten-2-one (6-MHO), and 4-oxopentanal (4-OPA) was also observed. The employed dynamic mass balance model shows that the estimated mixing ratios of hexanal, octanal, nonanal, decanal, undecanal, 6-MHO, and 4-OPA due to O-3 chemistry with authentic grime-coated kitchen glass surfaces are higher in the kitchen where Chinese food was cooked compared to that where Western food was cooked. These results show that O-3 chemistry on greasy glass surfaces leads to enhanced VOC levels in indoor environments
Prioritizing Organic Pollutants for Shale Gas Exploitation: Life Cycle Environmental Risk Assessments in China and the US
No full textEnvironmental impacts associated with shale gas exploitation have been historically underestimated due to neglecting to account for the production or the release of end-of-pipe organic pollutants. Here, we assessed the environmental impacts of shale gas production in China and the United States using life cycle assessment. Through data mining, we compiled literature information on organic pollutants in flowback and produced water (FPW), followed by assessments using USEtox to evaluate end-of-pipe risks. Results were incorporated to reveal the life cycle risks associated with shale gas exploitation in both countries. China exhibited higher environmental impacts than the US during the production phase. Substantially different types of organic compounds were observed in the FPW between two countries. Human carcinogenic and ecological toxicity attributed to organics in FPW was 3 orders of magnitude higher than that during the production phase in the US. Conversely, in China, end-of-pipe organics accounted for approximately 52%, 1%, and 47% of the overall human carcinogenic, noncarcinogenic, and ecological impacts, respectively. This may be partially limited by the quantitative data available. While uncertainties exist associated with data availability, our study highlights the significance of integrating impacts from shale gas production to end-of-pipe pollution for comprehensive environmental risk assessments
Constraints on Ore Genesis from Trace Ore Mineralogy: A New Occurrence of Kupcikite and Paděraite from the Zhibula Cu Skarn Deposit, Southern Tibet
No full textMineral assemblages containing Cu-Bi sulfosalts, Bi chalcogenides, and Ag-(Au) tellurides have been identified in the mid-Miocene Zhibula Cu skarn deposit, Gangdese Belt, southern Tibet. Different mineral assemblages from three locations in the deposit, including proximal massive garnet skarn, proximal retrogressed pyroxene-dominant skarn in contact with marble, and distal banded garnet-pyroxene skarn hosted in marble, are studied to constrain the evolution of the mineralization. Hypogene bornite contains elevated Bi (mean 6.73 wt.%) and co-exists in proximal andradite skarn with a second bornite with far lower Bi content, carrollite, Au-Ag tellurides (hessite, petzite), and wittichenite. This assemblage indicates formation at relatively high temperatures (>400 degrees C) and high f(S2) and f(Te2) during prograde-stage mineralization. Assemblages of Bi sulfosalts (wittichenite, aikinite, kupc & iacute;kite, and paderaite) and bismuth chalcogenides (e.g., tetradymite) in proximal pyroxene skarn are also indicative of formation at relatively high temperatures, but at relatively lower f(Te2) and f(S2) conditions. Within the reduced distal skarn (chalcopyrite-pyrrhotite-bearing) in marble, cobalt, and nickel occur as discrete minerals: cobaltite, melonite and cobaltic pentlandite. The trace ore mineral signature of the Zhibula skarn and the distributions of precious and critical trace elements such as Ag, Au, Co, Te, Se, and Bi support an evolving magmatic-hydrothermal system in which different parts of the deposit each define ore formation at distinct local physicochemical conditions. This is the first report of kupc & iacute;kite and paderaite from a Chinese location. Their compositions are comparable to other occurrences, but conspicuously, they do not form nanoscale intergrowths with one another
Recent advances made by reaction experiments on melting of heavily metasomatized hydrous mantle
No full textMantle-derived magmas are traditionally assumed to originate by melting of an upper mantle consisting of uniform spinel- or garnet peridotite dominated by olivine. However, extensive studies of mantle-derived basalts suggest that the mantle is more mineralogically heterogeneous, so that the genesis of even the most common magmas requires consideration of mixed source regions within the mantle involving pyroxenites and hydrous minerals. We refer to these with the group term metasomes. However, most experimental studies on mantle melting have assumed a homogeneous source composition, presenting a challenge in quantifying the impact of these heterogeneities. This paper provides a comprehensive review of recent advances in reaction experiments that depart from traditional approaches assuming a homogeneous mantle. We begin by assembling evidence for the existence of metasomes, discussing their formation and integration into basaltic melts. Further, we introduce the reaction experiments combining peridotite with hydrous assemblages, such as phlogopite, amphiboles, and apatite, leading to more accurate simulations of natural magmatic processes. These experiments reveal that the melting of hydrous metasomes and subsequent melt-peridotite interactions are key to producing the high alkali contents observed in natural lavas. The melting of hydrous metasomes occurs at lower temperatures than peridotite, resulting in diverse melt compositions. The interaction between metasome-derived melts and peridotite further modifies these melts, influenced by the pressure-dependent melting behaviors of minerals like orthopyroxene and olivine. This dynamic process leads to the generation of K- and Na-alkaline melts with varying silica and alkali contents, reflecting the complex interplay of melting and reaction mechanisms in the mantle. Formation of hydrous metasomes have also been studied by reaction experiments. Experimental studies have predominantly focused on potassium-rich systems due to the geochemical signatures of potassic igneous rocks suggesting sedimentary rock contributions to their sources. These studies simulate interactions between melts and mantle peridotite, particularly in sub-arc regions, leading to potassium-rich metasomes. More experimental studies are needed on sodium-rich alkaline systems to understand the formation of amphibole-rich metasomes and bridge knowledge gaps. Future studies should emphasize the detailed compositional variability of melts from metasomes, their reactions with peridotites, and comparisons with surface lavas. Understanding the kinetics of these reactions and the melting mechanisms of metasome-derived melts is essential. However, the considerable mineralogical diversity of hydrous metasomes poses a primary challenge facing experimental studies. It underscores the need for more experiments on additional melt source rocks and their reaction with peridotites, as the story about the reaction of melts from hydrous metasomes with mantle peridotites has only just begun
Measurement report: Impact of emission control measures on environmental persistent free radicals and reactive oxygen species - a short-term case study in Beijing
No full textA series of emission control measures implemented by the Chinese government have effectively reduced air pollution by multiple pollutants in many regions of the country in recent decades. However, the impacts of these control measures on environmental persistent free radicals (EPFRs) and reactive oxygen species (ROSs), the two groups of chemical species that are known to be linked with adverse human health effects, are still not clear. In this study, we investigated the levels, patterns, and sources of EPFRs and gas- and particle-phase ROSs (referred to as G-ROSs and P-ROSs, respectively) in Beijing during the 2015 China Victory Day Parade period when short-term air quality control measures were imposed. EPFRs in the non-control period (NCP) tended to be radicals centered on a mixture of carbon and oxygen, while those in the control period (CP) were mainly oxygen-centered free radicals. The contribution of G-ROSs to the atmospheric oxidizing capacity increased, and that of P-ROSs decreased during the CP compared to the NCP. The strict control measures reduced ambient EPFRs, G-ROSs, and P-ROSs by 18.3 %, 24.1 %, and 46.9 %, respectively; these amounts were smaller than the decreases in most other measured pollutants. Although particle-matter-based air quality control measures have performed well in achieving "Parade Blue", it is difficult to simultaneously reduce the negative impacts of the atmosphere on human health. The Parade Blue days were largely attributed to the dramatic reduction in secondary aerosols, which were also largely responsible for EPFR and ROS reductions. Compared to the cases during the NCP, the source-sector-based concentrations of PM2.5, EPFRs, G-ROSs, and P-ROSs during the CP were reduced by 78.7 %-80.8 % when coming from secondary aerosols, by 59.3 %-65.0 % when coming from dust sources, by 65.3 %-67.0 % when coming from industrial emissions, and by 32.6 %-43.8 % when coming from vehicle emissions, while concentrations from other sources increased by 1.61 %-71.5 %. Vehicle emissions and other sources may play complex roles in air quality and public health. This insight will prompt policymakers to reevaluate current air quality management strategies to more effectively address the challenges posed by pollutants such as EPFRs and ROSs
Anaerobic oxidation of methane and greigite formation: Evidence of isotopically heavy pyrite in Pleistocene coastal sediments from the South Yellow Sea
No full textDiagenetic alteration of magnetic minerals, driven by closely linked C-S-Fe cycles, is highly likely to complicate the paleomagnetic record. In addition to the anomalous diagenetic paleomagnetic signatures caused by ferromagnetic greigite growth, pyrite sulfur isotope compositions are often "heavy" (i.e., delta(34)Spyr > 0). However, the dependencies and mechanistic origins of these signatures remain controversial. This study presents a highresolution delta(34)Spyr record of a long sediment core collected from the South Yellow Sea, China. Ferromagnetic greigite is prominently identified in two coastal deposits within this core. The delta(34)Spyr values of these coastal deposits are isotopically (super) heavy, ranging from -10.6 to 22.8%o and from -14.5 to 26.5%o, with mean and 1 sigma values of 5.9 +/- 10.3%o (n = 15) and 12.2 +/- 9.8%o (n = 33), respectively. Additionally, magnetic parameters show positive trends with delta(34)Spyr values throughout the sediment core. These positive trends, along with the enrichment of ferrous iron and sedimentary microtextural evidence of the authigenic growth sequence of framboidal pyrite, siderite, euhedral pyrite, and greigite, indicate that anaerobic oxidation of methane (AOM) is a fundamental factor for ferromagnetic greigite formation in coastal sediments with sulfate limitation. We estimate the delay time of greigite formation relative to the depositional age of surrounding sediments to be a few hundred years due to the rapid sedimentation rates and shallow burial depths of the sulfate-methane transition zone (SMTZ) in coastal deposits. Conversely, the deep burial of SMTZ likely suggests that a longer delay time is prevailing for greigite formation in hemipelagic sediments. This study highlights the role of AOM in controlling the formations of greigite and coeval (super) heavy pyrite