Low Atmospheric Oxygen Research Articles

High-performance Multi-stage Baffled A2O Treatment Process for Domestic Sewage on Plateaus

At high altitudes, the low air pressure, low atmospheric oxygen content, and cryogenic environment during the cold season greatly limit the treatment efficiency of wastewater treatment plants (WWTPs). A novel pilot-plant configuration of the multi-stage baffled A2O wastewater treatment process was proposed and tested in Xizang. Different operational conditions involving at different influent loads and at low temperatures (10.0–11.0°C) were tested. When the influent flowrate increased to 4 m3∙d−1, the hydraulic retention time (HRT), internal and external reflux ratio, dissolved oxygen (DO), and aeration demands (gas to water ratio) all decreased to 34.2 h, 3.5/7, a stable 2.0–2.5 mg∙L−1, and 17.5, respectively. The effluent chemical oxygen demand (COD), total nitrogen (TN), ammonia nitrogen (NH+4−N), and total phosphorus (TP) all met the requirements of Class 1 Grade A of the China National Municipal Wastewater Discharge Standards (GB 18918-2002). The contribution of denitrifying phosphorus removal (DPR) to the removal of both nitrogen and phosphorus was over 50%. The alpha diversity and abundance of the top genera in the microbial community structure were both higher than the plateau WWTP. The reaction activity of the DPR process was significantly enhanced via the increased abundance of key functional genes within the metabolism pathway of ammonia-oxidizing bacteria (AOB) and nitrogen-oxidizing bacteria (NOB). The special multi-stage baffled structure featured a strategy of high sludge storage that improved the system tolerance for low temperatures and ensured favorable and stable performance for nitrogen and phosphorus removal at low temperatures. A short, periodic, and cyclically intermittent operation mode, with each cycle lasting only 20 minutes, effectively inhibited filamentous bacteria sludge bulking, resulting in a sludge volume index (SVI) that decreased to within 120 mL∙g−1 during the first 15 days of system start-up. A long sludge retention time (SRT) with no sludge discharging over 169 days and reduced aeration demands contributed to lower operation costs. The investigation revealed that the system had a high capacity for storing sludge phosphorus, possessing a TP content within a range of 23.45–28.99 mg∙g−1. This study provides a feasible solution for efficiently and economically treating wastewater in high-altitude areas.

Pulse of intense oxidative weathering during the latest Paleoproterozoic

The mid-Proterozoic (ca. 1.8−0.8 Ga) is broadly characterized by low atmospheric oxygen and pervasive oceanic anoxia punctuated by pulses of oxygenation. However, the causes underpinning these transient events remain elusive. Here, we report on 1.64 billion-year-old black shales and dolostone from the Chuanlinggou Formation in the North China Craton that represent sediment deposited during the break-up of the supercontinent Columbia. The rocks are characterized by high initial 187Os/188Os values, comparable to modern seawater values, alongside positive isotopic compositions of copper similar to those found in shales deposited during the Great Oxidation Event between 2.5 and 2.2 billion years ago. Additionally, we note high Th/U ratios and Chemical Index of Alteration values. Collectively, our data suggest a positive feedback initiated by continental fragmentation, with increased oxidative weathering on land, greater nutrient supply to the oceans, enhanced primary production of marine cyanobacteria, and ultimately, higher rates of oxygen production, perpetuating the feedback loop.

PSIV-24 Evaluation of different colostrum feeding volumes on serum immunoglobulin G concentration and metabolic profiles of calves in high altitude area

Abstract Qinghai-Tibet Plateau is the highest plateau in the world, reputed as “the roof of the world” and “the world’s third pole”. Its ecological environment is characterized by low atmospheric oxygen pressure, cold, and limited feed supplies. This study aimed to investigate the serum immunoglobulin G (IgG) concentration and metabolic profiles of calves in high altitude area (3,650 m) fed different volumes of colostrum [8, 12, or 15% of birth body weight (BW)] using untargeted metabolomics strategies. Neonatal Holstein hybrid heifer calves (n = 44) were randomly divided into 1 of the 3 colostrum feeding amounts: 8% of birth BW (Low volume, L), 12% of birth BW (Middle volume, M), and 15% of birth BW (High volume, H) in colostrum. To safeguard the efficiency of colostrum intake, the colostrum was fed to calves within 0.5 h and 6 h after birth. The serum samples at 24 h after birth were collected for IgG concentration determination by indirect enzyme-linked immunosorbent assay (ELISA) and for LC-MS/MS metabonomic analysis. As the volumes of colostrum increased, there was a linearly increased in the serum IgG concentration (P < 0.01). Differential metabolites were selected according to the following 3 conditions: minimum fold change (FC) > 2, P-value < 0.01 in single-dimensional statistical analysis, and variable importance in projection (VIP) > 1 in the OPLS-DA model. Multivariate statistical analyses were performed to visualize differences among groups. Based on the screening criteria, a total of 3 differential metabolites (22 alpha-Hydroxy-campesterol, N-Myristoyl Histidine, and Calcitetrol) were detected between L and M, of which all differential metabolites were down-regulated. Six differential metabolites were detected between M and H, of which PC[P-18:1(11Z)/18:1(12Z)-2OH(9,10)] was up-regulated and 5 differential metabolites including 1-arachidonoyl-2-hydroxy-sn-glycero-3-phosphate, propanoyl phosphate, ascorbic acid 6-palmitate, 20-hydroxyecdysone, and 6’’’-deamino-6’’’-hydroxyparomomycin II were down-regulated. There were 28 differed metabolites (including leucyl-tryptophan, calcitetrol, 3’’-Oxoribostamycin) between L and H, of which 9 differential metabolites were up-regulated and 19 differential metabolites were down-regulated (Figure 1). Based on KEGG metabolic enrichment pathway analysis and pathway topology analysis, porphyrin metabolism was identified as the most impacted pathway between L and H (Figure 2). In conclusion, increasing colostrum volumes significantly increased serum IgG concentrations at 24 h after birth, favoring the success of the transfer of passive immunity. Alterations in serum metabolome of calves in the Qinghai-Tibet Plateau fed different volumes of colostrum were successfully revealed by untargeted metabolomics. The role of the identified differential metabolites and enriched pathway in the transfer of passive immunity in calves at high altitude deserves further investigation. Keywords: calf, colostrum volumes, high altitude area

Intense intrusion of low-oxygen waters into mid-Cambrian surface ocean carbonate factories

The Phanerozoic surface ocean is characterized by its high dissolved oxygen content owing to mixing with the atmosphere. However, atmospheric oxygen levels varied in the early Paleozoic and it remains unclear whether the surface ocean was susceptible to significant redox fluctuations in response to extreme environmental events. In this study, we probed the redox structures of shallow middle Cambrian marine depositional environments across the North China Platform, ranging from open tidal flats to relatively deep subtidal environments. We utilized a combination of least diagenetically altered carbonate materials (such as ooid cortices, calcimicrobes, and their fringing cements), as well as in situ element measurement and imaging techniques. By analyzing a set of redox-related elements (e.g., Ce anomaly, Zn/Fe molar ratio, Mn and Cr) and mineralogical proxies (hydrogenetic Fe oxides), we revealed a stratified redox structure in the Drumian surface oceans. Compared to earlier Drumian conditions, late Drumian surface oceans experienced significant intrusions of ferruginous waters, probably reaching into shallow subtidal environments with water depths less than 10 m. Furthermore, we identified shallow subtidal microbial O2-producing factories, characterized by dendritic Epiphyton thalli. These calcimicrobes exhibited more oxygenated signatures (negative Ce anomalies and enrichment of hydrogenetic Fe oxides) relative to contemporaneous less oxic shallower and deeper environments. This finding indicates that they produced oxygen oases or refuges during periods of both normal and poor dissolved O2 conditions. This study has the potential to broaden our understanding of redox conditions and microbial oxygen-producing mechanisms in the surface ocean, particularly during intervals characterized by low atmospheric oxygen levels or episodic anoxic events.

Don’t mind the “charcoal gap”: A reassessment of Devonian wildfire

Little evidence of macrofossil charcoal, a wildfire proxy, is recorded from upper Lower to lowermost Upper Devonian rocks. Coals of this age are few, and petrographic data indicate low volumes (<10% mineral-matter free) of charcoal. This paucity of data forms the basis of the “charcoal gap,” which is used to suggest an extended interval of abnormally low atmospheric oxygen (pO2). We reassess the current evidence for this hiatus using Emsian−Eifelian charcoal from the Trout Valley and St. Froid Lake Formations, Maine (northeastern United States), and integrate the microscopic charcoal record of dispersed organic matter. We conclude there is ample evidence of fire in the Middle Devonian. This interval is not innately of low pO2. Rather, it is one in which under-interpretation of available data has led to a perceived paucity of charcoal. This reconciliation indicates the Phanerozoic record of wildfire was substantially uninterrupted. Hence, we propose that pO2 achieved levels >16% and remained at such levels from the Silurian through the floral and faunal colonization of land and, from our current estimates, stayed as such until the present.

Optimal design of a combined Power-Heating-Oxygen system for plateau hotel buildings

The Qinghai–Tibet Plateau of China is a region of low atmospheric pressure and oxygen deficiency, with a high heating demand in the winter; therefore, plateau hotel buildings have a demand for comprehensive power-heating-oxygen loads. Solar energy resources are particularly abundant in plateau areas, where a combined multi-energy system based on solar energy can be designed to meet the demand of plateau hotel buildings for multiple loads. However, currently, there is a relative lack of methods for the optimal design and performance evaluation of combined power-heating-oxygen (CPHO) systems. Thus, this study proposes a CPHO system model for plateau hotels, and provides two operation strategies, i.e., power priority and oxygen priority. Taking the minimum total annual cost of the combined system as the optimization objective, an optimized CPHO system model for plateau hotels has been proposed, followed by a case study of a hotel in Qilian County, Qinghai Province. Results showed that: 1) Compared with the conventional combined power-heating (CCPH) system, the CPHO system saw reductions of 0.8% and 1.3% in its total annual cost under the operation strategies of power priority and oxygen priority, respectively. 2) The energy self-consumption (SC) rates of the CCPH system and CPHO system under the operation strategies of power priority and oxygen priority were 84.8%, 64.2%, and 89.8%, respectively; with power self-sufficiency (PSS) rates of 8.3%, 49.9%, and 29.5%, and oxygen self-sufficiency (OSS) rates of 0.0%, 3.2%, and 4.7%, respectively. 3) The total annual cost of the CPHO system was affected slightly by the cost of photovoltaics (PVs) and energy storage devices, and significantly by the price of oxygen. When the price of oxygen was 8 yuan per normal cubic meter(Nm3) or above, the CPHO system was economically efficient under the operation strategy of oxygen priority. When the price of oxygen was 10yuan/Nm3 or above, the system was economically efficient under both operation strategies.

Embryos from Prepubertal Hyperglycemic Female Mice Respond Differentially to Oxygen Tension In Vitro.

Reduced oxygen during embryo culture in human ART prevents embryo oxidative stress. Oxidative stress is also the major mechanism by which maternal diabetes impairs embryonic development. This study employed induced hyperglycemia prepubertal mice to mimic childhood diabetes to understand the effects of varying oxygen tension during in vitro embryonic development. The oocytes were fertilized and cultured at low (≈5%) oxygen (LOT) or atmospheric (≈20%) oxygen tension (HOT) for up to 96 h. Embryo development, apoptosis in blastocysts, inner cell mass (ICM) outgrowth proliferation, and Hif1α expression were assessed. Though the oocyte quality and meiotic spindle were not affected, the fertilization rate (94.86 ± 1.18 vs. 85.17 ± 2.81), blastocyst rate (80.92 ± 2.92 vs. 69.32 ± 2.54), and ICM proliferation ability (51.04 ± 9.22 vs. 17.08 ± 3.05) of the hyperglycemic embryos were significantly higher in the LOT compared to the HOT group. On the other hand, blastocysts from the hyperglycemic group, cultured at HOT, had a 1.5-fold increase in apoptotic cells compared to the control and lower Hif1α transcripts in ICM outgrowths compared to the LOT. Increased susceptibility of embryos from hyperglycemic mice to higher oxygen tension warrants the need to individualize the conditions for embryo culture systems in ART clinics, particularly when an endogenous maternal pathology affects the ovarian environment.

1.44 Ga Oxygenation Event: Evidence From the Southern Margin of North China

AbstractPrevious studies suggest that the atmospheric and shallow seawater oxygen levels during the mid‐Proterozoic may have remained persistently unbalanced due to the low atmospheric oxygen levels and that, under these conditions, the oxygen concentrations of shallow seawater would largely reflect local oxygenation caused by primary productivity. As a result, in a microbialite‐rich setting, it may be difficult to differentiate oxygenation caused by local primary productivity from overall oxygenation of the surface environment. To address this issue, we conducted an integrative study of the ∼1.44 Ga stromatolitic carbonates of the Fengjiawan Formation in the Xiong’er Basin, southern North China, using techniques of sedimentology, mineralogy and geochemistry. The results show that the Fengjiawan Formation is dominated by water‐column precipitated carbonate mud (now dolomitized), pointing to moderately oxidized marine conditions. A significant and stable negative Cerium (Ce) anomaly (as low as 0.42) is identified in a long interval (>50 m in thickness) of this formation. This Ce anomaly is lower than the minimum values both recorded in the Great Oxidation Event (GOE; minimum 0.76) and in the Neoproterozoic Oxygenation Event (NOE; minimum 0.52), suggesting a significant oxygenation process rather than an oxygen oasis. Some intervals in this formation show I/(Ca + Mg) values higher than the Precambrian background value of 0.5 μmol/mol, providing a further support for shallow seawater oxygenation. This study, together with the enhanced oxygenation identified in the time‐equivalent Tieling Formation, indicates a multi‐basin oxygenation event in North China at ∼1.44 Ga.

Low Atmospheric Oxygen Attenuates Alpha Oscillations in the Primary Motor Cortex of Awake Rats.

Oxygen is pivotal for survival of animals. Their cellular activity and cognitive behavior are impaired when atmospheric oxygen is insufficient, called hypoxia. However, concurrent effects of hypoxia on physiological signals are poorly understood. To address this question, we simultaneously recorded local field potentials in the primary motor cortex, primary somatosensory, and anterior cingulate cortex, electrocardiograms, electroolfactograms, and electromyograms of rats under acute hypoxic conditions (i.e., 5.0% O2). Exposure to acute hypoxia significantly attenuated alpha oscillations alone in the primary motor cortex, while we failed to find any effects of acute hypoxia on the oscillatory power in the somatosensory cortex or anterior cingulate cortex. These area- and frequency-specific effects by hypoxia may be accounted for by neural innervation from the brainstem to each cortical area via thalamic relay nuclei. Moreover, we found that heart rate and respiratory rate were increased during acute hypoxia and high heart rate was maintained even after the oxygen level returned to the baseline. Altogether, our study characterizes a systemic effect of atmospheric hypoxia on neural and peripheral signals from physiological viewpoints, leading to bridging a gap between cellular and behavioral levels.

Phosphorous concentration in iron-rich rocks of the Chilpi Group, Bastar Craton, India: implications on late Palaeoproterozoic seawater palaeo-productivity

AbstractThe concentration of the bio-limiting nutrient element, phosphorus (P), in seawater is important for primary marine productivity and the evolution of life on geological time scales. The molar percentage of P/Fe in banded iron formations (BIF) and iron oxide-rich chemical sediments is a good proxy for the first-order approximation of seawater P concentration. Bio-available concentration of phosphorus in Precambrian, especially during the late Palaeoproterozoic Era (2.0–1.8 Ga), is poorly constrained. We evaluated the P/Fe ratios of iron-rich rocks from the late Palaeoproterozoic Chilpi Group, Bastar Craton, Central India. The bulk rock molar percentage of P/Fe ratios of the Chilpi rocks vary between 0.11 and 1.17 (average 0.51 ± 0.3), and the average of EPMA spot analysis P/Fe molar ratio is 0.32 ± 0.4; both have values similar to Archaean BIFs of the world. The observed low molar ratio is not an artefact of contamination from terrestrial sources, diagenetic alterations or high-temperature hydrothermal inputs; it indicates the deposition from phosphorus-lean seawater. The modelled P/Fe molar ratio in the Chilpi Group suggests that the concentration of phosphorus in the shallow marine environment was less than 0.12 μM. The low level of phosphorus concentration in seawater during the late Palaeoproterozoic Era is interpreted to be a consequence of the low primary production during a period of low atmospheric oxygen content, which might have impeded the evolution of eukaryotes.

Evaluation of childhood developing via optical coherence tomography-angiography in Qamdo, Tibet, China: A prospective cross-sectional, school-based study.

Optical coherence tomography angiography (OCTA) is a new and reliable machine used to evaluate retinal structure and macular perfusion in children. The use of OCTA under bad condition such as high altitude, low atmospheric oxygen, and low humidity, in children is rarely. To quantify the macular micro-vasculature in healthy children of various ages using OCTA in Qamdo. Design: Prospective cross-sectional, school-based study. Three hundred and forty-seven normal students from 9 schools in 4 different areas in Qamdo were included. OCTA was performed on a 3 mm × 3 mm area centered on the macular region and macular cube 512 × 128 showed details in macular. Early treatment of diabetic retinopathy study Vessel Flow Density (VD) of the macular central vascular plexus density (CVD), inner vascular plexus density (IVD), full vascular plexus density (FVD), and the size of the foveal avascular zone (FAZ) were measured. All these results corrected by t/s = 3.382 × 0.01306 × (axial length-1.82). The differences were compared among various ages, sexes and living environments. The mean FAZ area in all eyes was 0.27 mm2 ± 0.12 mm2. The mean foveal thickness (MFT) in the macular cube was 227.64 μm ± 23.51 μm. Compared with girls, boys had a lager FAZ (P = 0.0029). Among the different age groups, MFT (P < 0.001) and FVD (P < 0.0001), IVD (P < 0.0001), and CVD (P = 0.0050) increased with age. FAZ areas were not correlated with age (P = 0.8853) or others (MFT, area). OCTA can use to evaluate macular perfusion in children. Our data bridge the gap between structural OCT and perfusion density in children in high altitude. Even though these were not a longitudinal study, it may provide us with hints about retina development during puberty and clinical implications of OCTA in children.

Extreme climate changes influenced early life evolution at ∼ 1.4 Ga: Implications from shales of the Xiamaling Formation, northern North China Craton

The Mesoproterozoic Era (ca.1.6–1.0 Ga) witnessed a long-term evolution stasis of eukaryote, which is usually ascribed to the persistent low atmospheric oxygen levels. However, several oxygenation processes were identified on different continents during the Mesoproterozoic Era, implying that the oxygen levels may not be the only factor influencing the evolution of early-life during the early Mesoproterozoic Era. Here, we report the molybdenum isotopes, redox sensitive elements, nutrient elements and total organic carbon (TOC) content of black and green shales from the ∼ 1.4 Ga Xiamaling Formation in the northern part of the North China Craton (NCC), which has been affected by Milankovitch-style cycle, orbital forcing of extreme change of climate ∼ 1.4 billion years ago. The highest δ98Mo of the green shale reaches 1.56 ± 0.04 ‰ (modern ocean: 2.34 ‰), which may also confirm that it was in an oxygenation state at that time. In contrast, the black shale has lower δ98Mo values (1.02 ± 0.07 ‰) than that of green shale, indicating a less oxidized environment. Moreover, the TOC and nutrient elements (e.g., P, Cu, Ni) contents of the black shale are higher than those of green shale, which results from an increased nutrient input caused by stronger weathering and river runoff during a wet period. We conclude that the marine environment was persistently oxidative during the deposition of the black and green shales, while the TOC contents of the black and green shales are mainly controlled by the concentration of the nutrient elements that are constrained by the climatic conditions. Even though in oxic aquatic environment, the unstable nutrient supply would hinder the early life evolution, our findings imply vice versa. Hence, these results imply that the extreme climate change leading to unsustainable supply of nutrients, may have largely influenced emergence and diversification of animals in the Mesoproterozoic Era.

Prediction of severe pancreatitis in a population with low atmospheric oxygen pressure

To establish the severity of pancreatitis, there are many scoring systems, the most used are the Marshall and APACHE II systems, each one has advantages and disadvantages; but with good relation regarding mortality and prediction of complications. In populations with low barometric pressures produced by a decrease in atmospheric pressure, there is a decrease in partial pressure of oxygen, in these cases scores which take arterial oxygen partial pressure as one of their variables, may be overestimated. A diagnostic trial study was designed to evaluate the performance of APACHE II, Marshall and BISAP in a city 2640 m above sea level. A ROC analysis was performed to estimate the AUC of each of the scores, to evaluate the performance in predicting unfavorable outcomes (defined as the need for percutaneous drainage, surgery, or mortality) and a non-parametric comparison was made between the AUC of each of the scores with the DeLong test. From January 2018 to December 2019, data from 424 patients living in Bogota, with a diagnosis of gallstone pancreatitis was collected consecutively in a hospital in Bogota, Colombia. The ROC analysis showed AUC for predicting adverse outcomes for APACHE II in 0.738 (95% CI 0.647–0.829), Marshall in 0.650 (95% CI 0.554–0.746), and BISAP in 0.744 (95% CI 0.654–0.835). The non-parametric comparison to assess whether there were differences between the different AUC of the different scores showed that there is a statistically significant difference between Marshall and BISAP AUC to predict unfavorable outcomes (p=0.032). The mortality in the group of patients studied was 5.8%. We suggest the use of BISAP to predict clinical outcomes in patients with a diagnosis of biliary pancreatitis in populations with decreased atmospheric pressure because it is an easy-to-use tool and does not require arterial oxygen partial pressure for its calculation.

Reactive Oxygen and Sulfur Species: Partners in Crime

The emergence of complexity requires cooperation, yet selection typically favors defectors that do not cooperate. Such evolutionary conflict can be alleviated by a variety of mechanisms, allowing complexity to emerge. Chemiosmosis is one such mechanism. In syntrophic relationships, the chemiosmotic partner benefits simply from exporting products. Failure to do this can result in highly reduced electron carriers and detrimental amounts of reactive oxygen species. Nevertheless, the role of this mechanism in the history of life (e.g., the origin of eukaryotes from prokaryotes) seems questionable because of much lower atmospheric levels of oxygen and a largely anaerobic ocean. In this context, the role of sulfur should be considered. The last eukaryotic common ancestor (LECA) was a facultative aerobe. Under anaerobic conditions, LECA likely carried out various forms of anaerobic metabolism. For instance, malate dismutation, in which malate is both oxidized and reduced, allows re-oxidizing NADH. The terminal electron acceptor, fumarate, forms succinate when reduced. When oxygen is present, an excess of succinate can lead to reverse electron flow, forming high levels of reactive oxygen species. Under anaerobic conditions, reactive sulfur species may have formed. Eliminating end products may thus have had a selective advantage even under the low atmospheric oxygen levels of the Proterozoic eon.

Mesoproterozoic surface oxygenation accompanied major sedimentary manganese deposition at 1.4 and 1.1Ga.

Manganese (Mn) oxidation in marine environments requires oxygen (O2 ) or other reactive oxygen species in the water column, and widespread Mn oxide deposition in ancient sedimentary rocks has long been used as a proxy for oxidation. The oxygenation of Earth's atmosphere and oceans across the Archean-Proterozoic boundary are associated with massive Mn deposits, whereas the interval from 1.8-1.0Ga is generally believed to be a time of low atmospheric oxygen with an apparent hiatus in sedimentary Mn deposition. Here, we report geochemical and mineralogical analyses from 1.1Ga manganiferous marine-shelf siltstones from the Bangemall Supergroup, Western Australia, which underlie recently discovered economically significant manganese deposits. Layers bearing Mn carbonate microspheres, comparable with major global Mn deposits, reveal that intense periods of sedimentary Mn deposition occurred in the late Mesoproterozoic. Iron geochemical data suggest anoxic-ferruginous seafloor conditions at the onset of Mn deposition, followed by oxic conditions in the water column as Mn deposition persisted and eventually ceased. These data imply there was spatially widespread surface oxygenation ~1.1Ga with sufficiently oxic conditions in shelf environments to oxidize marine Mn(II). Comparable large stratiform Mn carbonate deposits also occur in ~1.4Ga marine siltstones hosted in underlying sedimentary units. These deposits are greater or at least commensurate in scale (tonnage) to those that followed the major oxygenation transitions from the Neoproterozoic. Such a period of sedimentary manganogenesis is inconsistent with a model of persistently low O2 throughout the entirety of the Mesoproterozoic and provides robust evidence for dynamic redox changes in the mid to late Mesoproterozoic.

Enhanced Weathering Triggered the Transient Oxygenation Event at ∼1.57 Ga

AbstractThe mid‐Proterozoic (∼1.8–0.8 Ga) is characterized by low atmospheric oxygen and pervasive oceanic anoxia, with transient oxygenation events. One of the oxygenation events happened at ∼1.57 Ga, during which atmospheric O2 may have reached ≥4% present atmospheric level (PAL) and thus promoted the evolution of multi‐cellular eukaryotes. The cause of this oxygenation event, however, remained unknown. Here, we report δ202Hg, ∆199Hg, P concentration, Rb/Al, and εNd(t) data across the ∼1.57 Ga oxygenation event in the Gaoyuzhuang Formation of North China. The positive δ202Hg, εNd(t), and negative Δ199Hg shifts, plus the accompanied peaks in Rb/Al, P, and I/(Ca + Mg), suggest that this oxygenation event was likely resulted from enhanced weathering of intermediate to mafic rocks, which may have promoted primary production via increasing P influx to the ocean and led to the rise in oxygen levels. The data indicate that enhanced weathering input could trigger transient oxygenation events during the mid‐Proterozoic.

Mesoproterozoic oxygenation event: From shallow marine to atmosphere

AbstractOxygen availability is crucial for the evolution of eukaryotes in geological history, but the redox conditions of the mid-Proterozoic atmospheric-oceanic system remain vigorously debated. Previous geochemical studies suggested a very low mid-Proterozoic atmospheric oxygen level of probably below 0.1%–1% of the present atmospheric level (PAL) with weakly oxygenated surface ocean, which may have suppressed the early evolution of eukaryotes in the ocean. A recent study, however, revealed a pulsed oxygenation event that was recorded in shallow marine carbonate of the middle Gaoyuzhuang Formation (at ca. 1.57 Ga, North China) with atmospheric pO2 of up to ≥4% PAL based on iodine speciation. This event is associated with the earliest known multi-cellular eukaryotic fossils. To elucidate whether this pulsed oxygenation was limited to shallow local seawaters or could also reflect an increase in atmospheric oxygen, chromium (Cr), and carbonate-associated sulfate (CAS), sulfur isotopes in the middle Gaoyuzhuang Formation were studied in two sections of the North China Platform. The results show a positive shift in authigenic Cr isotope from −0.18‰ to +0.66‰, which was followed by a decline to −0.16‰. This suggests a rise in atmospheric oxygen sufficient to initiate oxic Cr cycling and isotope fractionation (pO2 &amp;gt; 0.1%–1% PAL). This positive Cr isotope excursion was associated with a transient positive shift in δ34SCAS from ~20‰ to ~50‰ and a subsequent decline to ~10‰, which provides independent evidence of atmospheric oxygenation. This oxygenation may have enhanced oxidative terrestrial weathering and increased sulfate input to the ocean, thus stimulating bacterial sulfate reduction and pyrite burial in deep anoxic seawaters. This is broadly consistent with previous results of carbonate I/(Ca + Mg) and Ce anomaly but also reveals a lag between shallow seawater and atmospheric oxygenation. Fluctuated redox conditions and decoupled oxygenation between shallow seawater and atmosphere during the mid-Proterozoic may help to account for the current debate.

Low level of phosphorous concentration in terminal Paleoproterozoic shallow seawater: Evidence from Chuanlinggou ironstone on North China Platform

Phosphorus (P) is a bio-limiting nutrient element, which through modulating marine primary productivity can influence ocean redox conditions. Precambrian, especially the mid-Proterozoic (1.8–0.8 Ga), seawater phosphorous concentrations have been poorly constrained. The well-preserved ∼1.65 Ga ironstones in North China provide a nice opportunity to explore the phosphorous concentrations of shallow seawater at that time. To avoid potential contamination we performed fabric-specific analysis of dense laminasets in ooid cortices without cracks, and in stromatolitic columns. These data revealed a low P/Fe molar ratio of 0.0007 ± 0.0003 (n = 12), pointing to an extremely low phosphorus concentration (<0.002–0.016 μM) in ∼1.65 Ga shallow seawater. If such a low phosphorus concentration is an universal phenomenon during terminal Paleoproterozoic, this is likely the significant reason for limited primary productivity and therefore a low atmospheric oxygen level during that time.

A New Depositional Framework for Massive Iron Formations After the Great Oxidation Event

AbstractThe oldest recognized proxies for low atmospheric oxygen are massive iron‐rich deposits. Following the rise of oxygen ∼2.4 billion years ago (Ga), massive iron formations (IFs) largely disappear from the geologic record, only to reappear in a pulse ∼1.88 Ga, which has been attributed to sea‐level transgressions, changing ocean chemistry triggered by intense volcanism, or lowered atmospheric oxygen levels. The North American Gogebic Range is one of the rare records of this pulse and even more uniquely has exposures of both volcanics and IF, providing an ideal field locality to investigate triggers for this pulse of IF. To determine the environmental context and key factors driving IF deposition after the initial rise in oxygen, we made detailed observations of the stratigraphy and facies relationships and present updated mapping relationships of the Gogebic Range Ironwood Iron Formation and the Emperor Volcanics. This work expands existing mine datasets and logs to constrain variations in stratigraphy. Our results are the first to quantitatively constrain thickness variations along the entire Gogebic Range and tie them to syn‐sedimentary faulting along listric normal faults and half grabens. Furthermore, our dataset suggests that initiation of intense syn‐basinal volcanism linked to a large igneous province does not coincide with initial iron deposition, thus cannot be invoked as a causal trigger. Finally, the possibility of iron deposition in a shallow‐water environment suggests that the post‐GOE IF pulse may not reflect global marine transgressions, but instead a chemocline shallowing due to changing global atmospheric oxygen.

Wildfires in the Early Triassic of northeastern Pangaea: Evidence from fossil charcoal in the Bogda Mountains, northwestern China

Fires are an integral part of modern and ancient ecosystems, serving as friends for renewal or foes for complete destruction and extinction. Indicators of palaeowildfire were so far absent from the Lower Triassic. Lack of plants in the Early Triassic due to the end-Permian mass extinction event and low atmospheric oxygen levels were proposed as the major reasons for the scarcity of wildfires. We present macroscopic charcoals from the Olenekian (Lower Triassic) in northwestern China, indicating probable ground/smoldering fires occurred on landscapes in mid-latitudes of northeastern Pangaea. Atmospheric oxygen concentration during the Olenekian would have been above 18.5%. These findings demonstrate that wildfires continued to be a source of disturbance of terrestrial ecosystems in Bogda Mountains after the end-Permian marine biotic crisis. There were adequate supplies of fuels and oxygen during this critical time period in the Earth history.