Total Inorganic Carbon Concentration Research Articles

Factors controlling long-term carbon sequestration in the paleo-Yellow River delta: Implications for future delta management

Factors controlling long-term carbon sequestration in the paleo-Yellow River delta: Implications for future delta management

Impact of wet-dry cycles on enhanced rock weathering of brucite, wollastonite, serpentinite and kimberlite: Implications for carbon verification

Enhanced rock weathering is a proposed CO2 removal strategy for mitigating climate change; its implementation can be facilitated by improving carbon verification methods. In this study, weathering experiments exposed brucite, wollastonite skarn, serpentinite, and kimberlite residues (Venetia Diamond Mine, South Africa), to wetting and drying cycles (4/day) for 1 yr to elucidate reaction pathways and rates while evaluating carbon verification tools, including mineral quantification, total inorganic carbon (TIC), and stable and radiogenic carbon isotopes. Two primary reaction pathways were identified: A) silicate and hydroxide dissolution leading to carbonate precipitation (desirable), and B) dissolution and reprecipitation of carbonates (undesirable). The kimberlite residues, containing serpentine (19–33 wt%) and calcite (4–5 wt%), experienced variable and minor changes in total inorganic carbon. The δ13C and δ18O values of the carbonate minerals approached those expected for atmospheric-derived CO2 and are best explained by the exchange of carbonate CO2 with atmospheric CO2 (pathway A) as opposed to net CO2 sequestration. In contrast, the reaction of brucite (1.22% to 5.98%) and wollastonite skarn (0.22% to 1.01%) with atmospheric CO2 was substantial, as indicated by the increases in TIC (pathway B) yet decreases in δ13C values were inconsistent with the incorporation of atmospheric CO2 as a result of kinetic isotope fractionation due to carbonation being CO2 supply limited. The pulverized serpentinite experience insufficient carbonation to be detected by TIC. Unweathered (blue ground) and naturally weathered (yellow ground) kimberlite from the Voorspoed Diamond Mine, South Africa were compared to kimberlite residues used in experiments. Yellow ground contained twice the TIC content compared to blue ground whereas quantitative scanning electron microscopy revealed calcite veinlets that are characteristic of secondary mineralization. While the blue and yellow ground samples were essentially radiocarbon dead (0.03 and 0.05 F14C, respectively), substantial modern carbon was incorporated into the kimberlite (up to +0.27 F14C; CO2 exchange), brucite (+0.55 F14C), and wollastonite skarn (+0.53 F14C; CO2 sequestration) powders during weathering experiments. Although stable and radiogenic carbon isotopes have been used to verify the mineralization of atmospheric CO2, these methods are affected by CO2 exchange and kinetic fractionation effects during weathering that can be misleading and, thus, should not be relied on as sole methods for carbon verification.

Demonstration of CO2 Capture Process Monitoring and Solvent Degradation Detection by Chemometrics at the Technology Centre Mongstad CO2 Capture Plant

Solvent management is one of the important current challenges in post combustion carbon capture (PCC) technology development. Using large-scale 1960 h test campaign data (Technology Centre Mongstad, Norway, 2015 MEA Test), we demonstrate a combination of multivariate methods (PLS-R, MSPC) and process analytical spectroscopy (FT-IR) as a tool to monitor and control PCC process performance. Two MEA solvent monitoring models, total inorganic carbon (TIC) content and total alkalinity (TA), were prepared. In long-term solvent monitoring, PLS-R model prediction uncertainty increased due to gradual solvent changes, e.g., solvent degradation and impurity accumulation. Hence, we show a specific model update methodology to keep the models updated, leading to good long-term monitoring ability of the TIC and TA models. In addition to reliable long-term solvent monitoring ability, a new principle for follow-up of thermal solvent reclaiming was demonstrated. This shows that the need for solvent reclaiming can be quantified. Furthermore, this methodology is an indicator to see the actual solvent deviation from the fresh solvent. This quantification may provide an input for “start” and “end of reclaiming operation” identification. Hence, we demonstrate that it is possible to extract information for process performance follow-up, solvent monitoring, and solvent reclaiming from a single spectroscopic instrument.

Novel Intelligent System Based on Automated Machine Learning for Multiobjective Prediction and Early Warning Guidance of Biogas Performance in Industrial-Scale Garage Dry Fermentation

Industrial-scale garage dry fermentation systems are extremely nonlinear, and traditional machine learning algorithms have low prediction accuracy. Therefore, this study presents a novel intelligent system that employs two automated machine learning (AutoML) algorithms (AutoGluon and H2O) for biogas performance prediction and Shapley additive explanation (SHAP) for interpretable analysis, along with multiobjective particle swarm optimization (MOPSO) for early warning guidance of industrial-scale garage dry fermentation. The stacked ensemble models generated by AutoGluon have the highest prediction accuracy for digester and percolate tank biogas performances. Based on the interpretable analysis, the optimal parameter combinations for the digester and percolate tank were determined in order to maximize biogas production and CH4 content. The optimal conditions for the digester involve maintaining a temperature range of 35–38 °C, implementing a daily spray time of approximately 10 min and a pressure of 1000 Pa, and utilizing a feedstock with high total solids content. Additionally, the percolate tank should be maintained at a temperature range of 35–38 °C, with a liquid level of 1500 mm, a pH range of 8.0–8.1, and a total inorganic carbon concentration greater than 13.8 g/L. The software developed based on the intelligent system was successfully validated in production for prediction and early warning, and MOPSO-recommended guidance was provided. In conclusion, the novel intelligent system described in this study could accurately predict biogas performance in industrial-scale garage dry fermentation and guide operating condition optimization, paving the way for the next generation of intelligent industrial systems.

Biomass Fuel Production through Fermentation of Lysinibacillus sp. LC 556247 in Various Ratios of Palm Oil Mill Effluent and Empty Fruit Bunch

Biomass wastes originating from palm oil milling activities can be characterized by their high biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solid (TSS), and oil and grease content. The utilization of oil palm wastes such as palm oil mill effluent (POME) and empty fruit bunch (EFB) has great potential for a sustainable energy biomass pellet as it reduces the reliance on conventional materials for energy production. A mixture of POME and EFB in various ratios ranging between 7:3, 8:2, 9:1, and 10:0 was fermented in the presence of Lysinibacillus sp. LC 556247 for 120 h at 37 ± 2 °C and 180 rpm with the aim of elucidating the biodegradation of complex organic material in terms of BOD, COD, TSS, total organic carbon, inorganic carbon, and total carbon content. After fermentation, the mixtures were oven dried at 105 °C overnight and then subjected to calorific energy value (CEV) determination. The highest CEV of 20.26 MJ/kg was achieved for a ratio of 10:0 (slightly higher than the control experiment with the value of 18.67 MJ/kg), with maximum removal efficiencies of COD (12.19%), BOD (11.72%), TSS (93.94%), and oil reduction of 17.43%. The addition of EFB did not positively increase the CEV.

Quantification of the sources of sedimentary organic carbon at methane seeps: A case study from the South China Sea

Large amounts of methane are stored along continental margins in the form of methane hydrate. Methane hydrate is sensitive to environmental change, resulting in the release of substantial quantities of methane upon its destabilization. In the marine subsurface, microorganisms consume most of the methane in the sulfate-methane transition zone and convert a certain amount of methane into organic matter. Burial of such organic matter deriving from methane oxidation represents a long-term carbon sink, therefore mitigating the effect of a prominent greenhouse gas on global warming. However, the controls on the formation and consumption of sedimentary organic matter at marine seeps remain poorly constrained, impeding accurate quantification of carbon burial at seeps and its role in the marine carbon cycle. To gain new insight on the effect of seeps on carbon burial, sediments from two seep sites of the South China Sea (Site F, Haiyang 4) and a nearby reference site (Jiulong canyon) were analyzed for total organic carbon contents (TOC), δ13CTOC and Δ14C values, total inorganic carbon contents (TIC) and δ13CTIC values, as well as organic nitrogen (N) contents. Depth distributions reveal that the TOC at seeps (Site F, 0.55% ± 0.08%, Haiyang 4, 0.67% ± 0.11%) is higher than in sediments not affected by seepage (Jiulong canyon, 0.50% ± 0.10%). The enrichment of total sulfur, high TIC, and negative δ13CTIC values in sediments from Site F and Haiyang 4 agrees with locally prominent sulfate-driven anaerobic oxidation of methane (AOM) and resultant precipitation of authigenic carbonate. At the two seep sites, the sediments are characterized by more negative δ13CTOC and Δ14C values and a lower TOC/N ratio, indicating a contribution of the microbial fixation of 13C-depleted methane to the local pool of sedimentary organic matter. A linear increase in 14C ages of organic carbon with sediment depth at the reference site indicates steady depositional conditions, whereas the 14C age of organic carbon at seeps is typified by contributions of methanotrophy-derived carbon. A Δ14C mass balance approach shows that carbon derived from fossil methane accounts for at least 10 to 20% of the organic carbon preserved in the sediments. By comparing seeps, hydrate-bearing sediments, modern coastal sediments, and Archaean rocks, it becomes apparent that the carbon stable isotope composition of organic carbon in seep sediments is mainly controlled by the rate of methane oxidation and marine primary productivity.

Content and Spatial Distribution of Carbon in Shuangtaizi Estuary, China

Contents of total organic carbon (TOC), total inorganic carbon (TIC) and total carbon (TC) in water and sediment in Shuangtaizi estuary in China were studied. The results showed that the TIC and TC contents in water were high, and the TOC content was very low. In sediment, the TOC and TC contents were high, while the TIC was very low. TOC, TIC and TC had obvious spatial distribution characteristics in water and sediment in the area. The distribution of TOC and TC in sediment was similar, which was increase along with the distance to the mouth. The distribution of TIC and TC in water was similar. The TIC was mainly distributed at the outer mouth in surface water, while at the inner in deep water was little. The terrigenous input was the main source of carbon in the area. Carbon sequestration in the long range would convert the inorganic carbon to organic carbon.

Changes in Bacterial Communities and Their Effects on Soil Carbon Storage in Spartina alterniflora Invasion Areas, Coastal Wetland Bare Flats, and Sueada salsa Areas.

Spartina alterniflora is considered an invasive species that has affected the biogeochemical circle of carbon in coastal wetlands around the world. Nevertheless, it is still unclear how S. alternation invasion affects the carbon storage capacity of coastal wetlands as carbon pools through bacterial changes. Herein, bacterial communities and soil carbon content in coastal wetland native areas and S. alterniflora invasion areas were detected. It was found that an S. alterniflora invasion brought more organic carbon and resulted in the increase in Proteobacteria in bare flats and Sueada salsa areas. When decomposition capacity was not sufficient, large amounts of organic carbon may be stored in specific chemical forms, such as monosaccharides, carboxylic acids, alcohols, etc. The results have also shown that soil bacterial communities were highly similar between the bare flat and S. alterniflora invasion area, which is extremely conducive to the rapid growth of S. alterniflora. However, an S. alterniflora invasion would decrease total carbon contents and inorganic carbon contents in the Sueada salsa area. This is not conducive to the stability of the soil carbon pool and soil health. These findings may complement, to some extent, the shortcomings of the interaction between S. alterniflora and bacterial communities, and their joint effect on soil carbon storage.

The marine carbonate system variability in high meltwater season (Spitsbergen Fjords, Svalbard)

The spatial variability in hydrography (salinity and temperature) and carbonate chemistry (alkalinity - AT, total inorganic carbon concentration - CT, pH, CO2 partial pressure - pCO2, and the saturation state of aragonite - ΩAr) in high meltwater season (summer) was investigated in four Spitsbergen fjords - Krossfjorden, Kongsfjorden, Isfjorden, and Hornsund. It was found that the differences in hydrology entail spatial changes in the CO2 system structure. AT decline with decreasing salinity was evident, hence it is clear that freshwater input generally has a diluting effect and lowers AT in the surface waters of the Spitsbergen fjords. Significant surface water AT variability (1889–2261 µmol kg−1) reveals the complexity of the fjords’ systems with multiple freshwater sources having different alkalinity end-member characteristics and identifies the mean AT freshwater end-member of 595 ± 84 µmol kg−1 for the entire region. The effect of AT fluxes from sediments on the bottom water was rather insignificant, despite high AT values (2288–2666 μmol kg−1) observed in the pore waters. Low pCO2 results in surface water (200–295 μatm) points to intensive biological production, which can strongly affect the CT values, however, is less important for shaping alkalinity. It has also been shown that the freshening of the surface water in the fjords reduces significantly ΩAr (an increase in freshwater fraction contribution by 1% causes a decrease in ΩAr by 0.022). Although during the polar day, due to low pCO2, ΩAr values are still rather far from 1 (they ranged from 1.4 to 2.5), during polar night, when pCO2 values are much higher, ΩAr may drop markedly. This study highlights that the use of salinity to estimate the potential alkalinity can carry a high uncertainty, while good recognition of the surface water AT variability and its freshwater end-members is key to predict marine CO2 system changes along with the ongoing freshening of fjords waters due to climate warming.

Distinct lake sedimentary imprints of earthquakes, floods and human activities in the Xiaojiang Fault zone: Towards a quantitative paleoseismograph in the southeastern Tibetan Plateau

Lake sediments that widely distributed in the active and complicated fault zones have been recently showing great potential for paleoseismic reconstruction. However, flood events and human activities may make the seismic signal unrecognizable. In this study, high-resolution analyses of sedimentary structure, physical and chemical proxies, as well as absolutely radioactive dating were conducted on seven representative sediment cores from the depocenter, nearshore and inlet areas of Yangzong Lake, a typical fault lake in the Xiaojiang Fault zone, southeastern Tibetan Plateau (TP). These new data were calibrated by historical documents, suggesting that seismically induced mass-transport deposits (MTDs, i.e., turbidites) were massive and/or amalgamated (earthquake doublet), became fining and thickening towards the lake center (without changing lake morphology), and occasionally exhibited soft sediment deformation structures (SSDs, i.e., microfaults). These sediments were relatively poorly sorted and instantaneously deposited from slope failures within the lake. An extremely strong earthquake could cause coseismic subsidence of the lake basin and destruct the local hydrological system, resulting in exceptionally high Mn and total inorganic carbon (TIC) contents in the lake center. In contrast, flood deposits were thinner with horizontal beddings, had higher terrestrial organic matter (higher C/N ratios), and distributed locally in the lake inlet area. Human activities-induced sediments were inversely graded, poorly sorted and gradually deposited, had horizontal beddings and no erosive base, and exhibited high carbon, Pb and Zn contents and low C/N ratios. In addition, macroseismic investigations and statistical results from intensity prediction equations (IPEs) provided a conservative threshold of ∼8 Modified Mercalli Intensities (MMI) for triggering turbidites, and a ∼ 10 MMI for inducing coseismic subsidence and hydrological destruction. This study was among the first attempts to establish a quantitative lacustrine paleoseismograph in the southeastern TP, and the new results would greatly improve the valid assessment of geohazard risks.

Basic techniques of mound construction of the Yamnaya culture in the Southern Urals

The aim of the study. To determine the material and basic techniques for constructing burial mounds (kurgans) of the Yamnaya culture of the Bronze Age in the Southern Urals based on a comprehensive analysis with an emphasis on meso- and micromorphological analysis. Location and time of the study. The research objects are located in the Orenburg region within the East European Plain. Security excavations were carried out in 2019-2022 at three burial mounds located in the Tashlinsky (mound burial grounds Boldyrevo IV and Tashla IV) and Grachevsky districts (kurgan burial ground Kalikino II) of the Orenburg region. Mound 1 in the Boldyrevo IV burial mound, due to its significant size of 4.2 m in height and 60 m in diameter was chosen as a key object for which a full survey was carried out. Additionally, the smaller in size mounds of the 1st burial mound Tashla IV, as well as 1, 4 and 5 of the Kalikino II burial mound were studied. Methods. To determine the source of building materials and the basic techniques of soil and ground subsoil substrates for mound construction, a comprehensive analysis was carried out with an emphasis on macro-, meso- and micromorphological properties of the substrates. For the analytical study, which was carried out only for the Boldyrevo IV mound 1, total carbon content, organic and inorganic (carbonates) carbon content, loss on ignition, particle size distribution, magnetic susceptibility and pH were determinied. Results. The structure and materials of five burial mounds of the Yamnaya culture of the Bronze Age (5500 - 4300 years ago) were studied. The kurgans were proven to have been built from the local soils with the addition of anthropogenic material (silt, bones, shells). Representatives of the Yamnaya culture created variegated flowers using the construction techniques such as kneading, ramming, and the inclusion of anthropogenic material. At the micromorphological level, these techniques produces patterns of light loose and more compacted dark microzones in construction materials. Conclusions. Based on meso- and micromorphological analysis of the studied mound structures, we conclude that the representatives of the Yamnaya culture had knowledge of construction technologies and used them appropriately. The main method of mound constructing was creating a variegated mixed soil from humus or carbonate horizons with admixtures of anthropogenic and carbonate material. When building small mounds, people used rough kneading and tamping, but for larger mounds, either more complex construction was used, or more thorough kneading and tamping, as well as longer exposure to water.

Geochemical record of methane seepage in carbon cycling and possible correlation with climate events in the Qiongdongnan basin, South China Sea

At cold seeps, sulfate-driven anaerobic oxidation of methane (SD-AOM) is the dominant biogeochemical process, which can significantly affect the marine carbon-sulfur cycle. In this paper, multiple sedimentary indicators in core QS-1 were reported for methane seepage from Haima seep of the South China Sea (SCS). By combining total carbon (TC), total organic carbon (TOC), total sulfur (TS), total inorganic carbon (TIC), as well as the carbon and oxygen isotope compositions of benthic foraminifera Uvigerina spp. In sediments, our aim was to explore the geochemical evidence on methane seepage activities in this area. We identified three methane release events (MREs) with different intensities and timescales during MIS 1–2, characterized by particular anomalies of negative δ13CTIC (as low as −41.42‰) and δ13CU.spp (as low as −5.50‰), high contents of TS and high S/C ratios, simultaneously. High S/C ratios and negative values of δ13CTIC effectively indicate the intense SD-AOM and SD-AOM-related process in core QS-1. Three MREs, occurred at high or low sea level, may due to the climate-driven increase of hydrostatic pressure and seafloor temperature. The insights for sediment carbon-sulfur trace element, carbon isotopes of TIC contents and benthic foraminifera have obvious implications for tracing past methane seepages and its possible link with climate changes.

Mineral Carbonation of Basic Oxygen Furnace Slags

Mineral carbonation is a method in carbon capture and utilization (CCU) in which carbon dioxide reacts with natural or synthetic mineral phases to form carbonates. In this study, BOF slag consisting of alite, Ca3SiO5, belite, Ca2SiO4, melilite, (Ca,Na)2(Mg,Al)[4][Si2O7], brownmillerite, Ca(Fe,Al)2O5, calcium ferrite, Ca2FeO4 and Ca-, Mg- and Mn-bearing wuestite, (Mg,Ca,Mn,Fe)O, was crushed into different particle size fractions and exposed over various durations (1 d, 3 d, 9 d, 14 d, 24 d) at a grate to 120 °C hot off-gas with a CO2 content of 25%. However, the total inorganic carbon (TIC) content never increases above the detection limit of 0.5% throughout the experimental duration. The determination of the carbonation depth using phenolphthalein does not reveal a homogeneous carbonation front, but an irregular carbonation. This observation was confirmed by microprobe analyses using elemental mapping. The solubility of the slag increases with increasing carbonation, e.g., the leachability of sulfate increases from 7.8 to 8270 mg/kg dry matter (DM), and of calcium from 940 to 3860 mg/kg DM. The leaching of environmentally relevant element varies: the leachable concentration of molybdenum increases from 0.017 mg/kg DM to 0.089 mg/kg DM, that of chromium remains constant (ca. 0.05 mg/kg DM) whereas that of vanadium decreases from 1.1 to 0.45 mg/kg. In summary, the chosen carbonation technology must be improved to enhance carbonate yield.

Spectrophotometric analysis of the CO2 system in aqueous solutions: A freshwater example from the Snake River, Idaho, USA

AbstractThis work describes a new, generally applicable method to comprehensively characterize the inorganic carbon system of aqueous solutions. The method requires only simple spectrophotometric measurements and is appropriate for not only open‐ocean seawater (where convenient assumptions and approximations may be made) but also the more challenging case of freshwaters. The overall approach is to (1) measure pH in the field at the time of sample collection and (2) measure sample pH, carbonate alkalinity (AC), and total alkalinity (AT) later in the laboratory. All required equipment is inexpensive and portable. The paired laboratory measurements of pH and AC can be used to obtain the concentration of total inorganic carbon (CT). This CT can in turn be paired with the field pH measurements to comprehensively characterize carbon‐system parameters in the sampled water body at in situ conditions. To our knowledge, this method is the first to spectrophotometrically measure AC and thus the first to completely characterize CT and the carbon system of freshwaters using spectrophotometric measurements only. The concurrent measurements of AC and AT can also be used to partition alkalinity into its carbonate and noncarbonate components. This work additionally describes how to quantitatively correct for artifacts that may arise (especially in freshwater samples) from using HgCl2 to halt respiration in sample bottles. The use of these methods is illustrated using samples collected from the Snake River (Idaho, USA) before and during the 2020 spring flow.

Millennial‐ to centennial‐scale anti‐phase relationship between the Westerlies and the East Asian summer monsoon and its cultural response along the Silk Roads after a great earthquake in southern Altay ~ 3500 cal a BP

AbstractIt is strongly debated whether the Westerlies and the East Asian summer monsoon (EASM) are in‐phase, anti‐phase or out‐of‐phase, and how hydroclimatic changes in the above two climate systems affected trans‐Eurasian cultural exchanges during the late Holocene. In this study, we establish a 3500‐a‐long paleoclimatic sequence based on high‐resolution analyses of sedimentological and geochemical data of a well‐dated sediment core from Yileimu Lake in southern Altay. High percentages of the >63‐µm fraction and high values of Zr/Rb and Rb/Sr ratios indicate strong transport of weakly weathered, coarse sediments into the depocenter of the lake caused by enhanced surface runoff and catchment erosion associated with a wet climate, and vice versa. High values of Ca and total inorganic carbon (TIC) contents imply increased precipitation of endogenic carbonates in the lake water under intense evaporation associated with a dry climate, and vice versa. This new record indicates two wet intervals at 3500–2300 and 600–100 cal a bp, interrupted by a severe and prolonged dry interval from 2300 to 1000 cal a bp, and a mild dry interval with occasionally wet conditions from 1000 to 600 cal a bp. These results are broadly consistent with other paleoclimatic records in Westerlies‐dominated Asia and are generally anti‐phase with those in the EASM region. We suggest that a strengthening/weakening and southward/northward migration of the Westerlies during a negative/positive phase of the North Atlantic Oscillation (NAO) transported more/less water vapor into arid Asia. Meanwhile, a decreasing/increasing El Niño‐Southern Oscillation (ENSO) superimposed on a southward/northward shift of the Intertropical Convergence Zone (ITCZ) triggered a weakening/strengthening and southward/northward movement of the West‐Pacific subtropical high (WPSH), resulting in decreasing/increasing EASM intensity. In addition, the wet climate from 3500 to 2300 cal a bp may have contributed to the development of nomadic herding in the eastern Eurasian Steppe and Altay region, and to the opening of the proto‐Silk Roads. Potentially, intense seismic activities in the Altay Mountains ~3500 cal a bp may have also promoted the opening of the proto‐Silk Roads by forcing the herdsmen to move to the inter‐mountainous basins. The strong EASM intensity from 2300 to 1000 cal a bp in eastern China may have contributed to the creation of the ancient Silk Roads by the Han Dynasty.

Chemical Fractionation Modeling of Plumes Indicates a Gas-rich, Moderately Alkaline Enceladus Ocean

Enceladus harbors an ocean beneath its ice crust that erupts spectacular plumes from fissures at the south pole. The plume composition was measured by the Cassini spacecraft, and provides evidence for the ocean’s gas content, salinity, pH, and potential for life. Understanding the ocean’s composition is complicated by physicochemical processes that alter the plume composition during eruption, such as water vapor condensation in the icy fissures and gas exsolution from the ocean surface. We developed a model that includes key fractionation processes, in particular fractionation during gas exsolution, which has not been previously considered. Our model predicts a moderately alkaline (pH 7.95–9.05), gas-rich ocean (∼10−5–10−3 molal) with high concentrations of ammonium ions (10−2–10−1 molal). Our derived dissolved gas concentrations are higher than in recent studies because we account for gas exsolution, which depletes gases in the plume compared to the ocean, and because our model conserves mass flow rates between gas exsolution from the ocean and eruption from the tiger stripe fissures. We find carbon dioxide and hydrogen concentrations that could provide sufficient chemical energy for oceanic life in the form of hydrogenotrophic methanogens. Carbon dioxide concentrations of 10−5–10−3 molal indicate a more Earth-like pH than the pH ∼8.5–13.5 in previous studies. The inferred bulk ammonium and total inorganic carbon concentrations are consistent with cometary levels. This corroborates evidence from cometary deuterium-hydrogen (D/H) ratios that Enceladus formed from comet-like planetesimals. Our results suggest a gas-rich ocean that inherited its high volatile concentrations from comet-like building blocks.

Identification of the sources and influencing factors of the spatial variation of heavy metals in surface sediments along the northern Jiangsu coast

Determining the sources and factors influencing the spatial variation of heavy metals in the surface sediments of tidal flats is important for controlling and reducing heavy metal pollution. We used principal component analysis and partial least square regression to analyse the distribution characteristics, sources, and factors influencing the spatial variation of nine heavy metals (As, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn) in the surface sediments of tidal flats along four sites located on the northern Jiangsu coast. Our results indicate that the northern three sampling areas had a high heavy metal content, whereas the southern sampling area had a low heavy metal content. The heavy metals Mn and Pb are related to both natural and anthropogenic sources, whereas V and Cr are primarily derivatives of human activities, and As, Co, Cu, Ni, and Zn are primarily a result of natural processes. The spatial variation of Mn and Pb was primarily affected by the total inorganic carbon and clay content (positive affect) as well as the sand and silt content (negative affect). The spatial variation of V and Cr was primarily related to silt, clay, and total phosphorus content (positive influence) as well as sand (negative influence). In addition, the spatial variation of As, Co, Cu, Ni, and Zn was primarily influenced by the total organic carbon and clay content (positive effect) as well as sand and pH (negative effect). The grain size of sediments plays an important role in the spatial variation of heavy metals in the surface sediments of tidal flats, with fine-grained clay materials being related to the enrichment of heavy metals. The results of our study are important for the control and reduction of heavy metal pollution in coastal sediments, protecting both the ecological environment and human health.

Provenance of Inorganic Carbon Sinks in Closed Basins

AbstractMuch dissolved inorganic carbon (DIC) may exist in lacustrine carbonates in the terminal lakes of closed basins in arid areas, and inorganic carbon sinks in arid regions are an important hypothesis of global carbon cycle research in recent years. Previous studies have made significant progress in estimating the inorganic carbon content. However, the source of inorganic carbon sinks remains unclear. Here, we choose four typical arid closed basins in North China to investigate the provenance of inorganic carbon sinks. The results show that CO2 absorbed by saline‐alkaline soil is the main source of groundwater DIC in the study area, with a contribution rate of approximately 50%. Forty‐three groundwater radiocarbon ages from arid closed basins indicate that the DIC in groundwater is transported along the direction of water flow and deposited in terminal lakes, forming inorganic carbon sinks. Our study suggests that the total inorganic carbon contents of Zhuye Lake, Yanchi Lake, Huahai Lake, and Qinghai Lake in the Holocene are 0.318 Pg, 0.003 Pg, 0.160 Pg, and 3.289 Pg, respectively. The results demonstrate that inorganic carbon sinks are much larger than lake organic carbon storage, thereby serving as an important carbon cycle factor in arid regions.

Increasing sulfate concentration and sedimentary decaying cyanobacteria co-affect organic carbon mineralization in eutrophic lake sediments

Sulfate (SO42−) concentrations in eutrophic lakes are continuously increasing; however, the effect of increasing SO42− concentrations on organic carbon mineralization, especially the greenhouse gas emissions of sediments, remains unclear. Here, we constructed a series of microcosms with initial SO42− concentrations of 0, 30, 60, 90, 120, 150, and 180 mg/L to study the effects of increased SO42− concentrations, coupled with cyanobacterial blooms, on organic carbon mineralization in Lake Taihu. Cyanobacterial blooms promoted sulfate reduction and released a large amount of inorganic carbon. The SO42− concentrations in cyanobacteria treatments significantly decreased and eventually reached close to 0. As the initial SO42− concentration increased, the sulfate reduction rates significantly increased, with maximum values of 9.39, 9.44, 28.02, 30.89, 39.68, and 54.28 mg/L∙d for 30, 60, 90, 120, 150, and 180 mg/L SO42−, respectively. The total organic carbon content in sediments (51.16–52.70 g/kg) decreased with the initial SO42− concentration (R2 = 0.97), and the total inorganic carbon content in overlying water (159.97–182.73 mg/L) showed the opposite pattern (R2 = 0.91). The initial SO42− concentration was positively correlated with carbon dioxide (CO2) emissions (R2 = 0.68) and negatively correlated with methane (CH4) emissions (R2 = 0.96). The highest CO2 concentration and lowest CH4 concentration in the 180 mg/L SO42− treatment were 1688.78 and 1903 μmol/L, respectively. These biogeochemical processes were related to competition for organic carbon sources between sulfate reduction bacteria (SRB) and methane production archaea (MPA) in sediments. The abundance of SRB was positively correlated with the initial SO42− concentration and ranged from 6.65 × 107 to 2.98 × 108 copies/g; the abundance of MPA showed the opposite pattern and ranged from 1.99 × 108 to 3.35 × 108copies/g. These findings enhance our understanding of the effect of increasing SO42− concentrations on organic carbon mineralization and could enhance the accuracy of assessments of greenhouse gas emissions in eutrophic lakes.

Carbon dioxide delivery and resulting biomass separation in microalgae cultivation using triethanolamine

ABSTRACT This study investigates a novel use of triethanolamine (TEA), a well-known carbon dioxide (CO2) – capturing chemical, to simultaneously deliver CO2 and separate microalgae biomass from the growth media in microalgae cultivation processes. For this purpose, the growth and nutrient utilization rates of Chlorella sp., were monitored at different concentrations of TEA saturated with 15% of CO2 in a gas mixture. In addition, the total inorganic carbon content in the growth media was followed in order to estimate the CO2 delivery rates. The highest growth and nutrient utilization rates occurred at 20 and 30 mM TEA concentrations, which results in 2.5-fold increase in biomass production rate at these TEA concentrations. More than 85% of the produced biomass was successfully separated from the medium by flotation facilitated by the release of oxygen and CO2 gases to the air from the oversaturated growth media, as well as the surfactant characteristics of TEA.