太湖富营养化湖区秋季水体和沉积物中硝化微生物分布特征及控制因素

微生物参与下的氮循环是富营养化湖泊十分重要的生物地球化学循环过程.采用基于amoA功能基因和16S rRNA基因的荧光定量PCR、PCR-DGGE与高通量测序等分子生物学技术,调查秋季太湖不同水体和表层沉积物中氨氧化古菌(AOA)、氨氧化细菌(AOB)和亚硝酸盐氧化菌(NOB)群落丰度和组成,探讨影响硝化微生物分布的关键环境因子.结果表明,中度富营养化的梅梁湾湖区水体表层、中层和底层水样和表层底泥中AOA amoA基因的丰度分别低于轻度富营养化的湖心区,而不同层水样中AOB amoA基因的丰度分别高于湖心区.梅梁湾湖区和湖心区水样中AOA群落组成基本相似,2个湖区表层沉积物样品中AOA群落组成亦基本相似,水体中AOA群落组成与表层沉积物中AOA群落组成有差异,AOA群落丰度显著受硝态氮、pH和DO影响;表层沉积物中AOB群落丰度有明显差异且显著受总氮含量影响,表层沉积物中NOB群落丰度也有明显差异且显著受亚硝态氮含量影响.太湖梅梁湾湖区和湖心区水体与表层沉积物AOA群落包括Nitrosopumilium和Nitrosotalea两大属;表层沉积物AOB群落主要包括亚硝化单胞菌(Nitrosomonas)和亚硝化螺菌(Nitrosospira)两大属,NOB群落主要包括硝化刺菌(Nitrospina)和硝化螺菌(Nitrospira)两大属,其中硝化螺菌属是淡水湖泊中比较少见的亚硝酸盐氧化菌.影响太湖水体和沉积物中AOA和AOB丰度的最主要环境因子为总氮、总磷与铵态氮.研究表明典型富营养指标(总氮、总磷、铵态氮、硝态氮和硝态氮等)是影响太湖梅梁湾和湖心区水体和沉积物中AOA或AOB丰度以及硝化微生物群落丰度的重要因素.     

Evaluation of Sludge Digester Effluent as Feeding Solution for the Enrichment of Anammox Bacteria

The aim of this study is to evaluate the feasibility of sludge digester effluent as feeding solution to enrich anaerobic ammonium oxidation (anammox) bacteria. The performance of the two parallel pilot scale‐upflow packed bed anammox reactors (UPBAn1 and UPBAn2) are examined in terms of the enrichment of anammox bacteria. The control experiment is set up conducting synthetic wastewater as feeding solution in the UPBAn1 reactor whereas, the sludge digester effluent is fed to the nitritation reactor and then the partially nitrated digester effluent to the UPBAn2 reactor. Anammox activities are evaluated by mass balances based on ammonium (NH₄⁺), nitrite (NO₂^?), and nitrate (NO₃^?) analysis and NRR. Microbial community of anammox bacteria is analyzed using real‐time polymerase chain reaction (PCR). The results demonstrate that UPBAn 1 and UPBAn2 reactors are successfully enriched on days 64 and 40 with NRRs of 19.54 and 19.43 g N m^?3 per day, respectively. This study reveals that both synthetic wastewater and digester effluent are suitable for the enrichment of anammox bacteria; however, digester effluent as feeding solution for enrichment of anammox bacteria based on the ease of process control and process stability is more advisable.     

Sulfur metabolism by marine heterotrophic bacteria involved in sulfur cycling in the ocean

Sulfur cycling in the biosphere is tightly interwoven with the cycling of carbon and nitrogen, through various biological and geochemical processes. Marine microorganisms, due to their high abundance, diverse metabolic activities, and tremendous adaptation potential, play an essential role in the functioning of global biogeochemical cycles and linking sulfur transformation to the cycling of carbon and nitrogen. Currently many coastal regions are severely stressed by hypoxic or anoxic conditions, leading to the accumulation of toxic sulfide. A number of recent studies have demonstrated that dissimilatory sulfur oxidation by heterotrophic bacteria can protect marine ecosystems from sulfide toxicity. Sulfur-oxidizing bacteria have evolved diverse phylogenetic and metabolic characteristics to fill an array of ecological niches in various marine habitats. Here, we review the recent findings on the microbial communities that are involved in the oxidation of inorganic sulfur compounds and address how the two elements of sulfur and carbon are interlinked and influence the ecology and biogeochemistry in the ocean. Delineating the metabolic enzymes and pathways of sulfur-oxidizing bacteria not only provides an insight into the microbial sulfur metabolism, but also helps us understand the effects of changing environmental conditions on marine sulfur cycling and reinforces the close connection between sulfur and carbon cycling in the ocean.     

Climate tipping-point potential and paradoxical production of methane in a changing ocean

The global warming potential of methane (CH₄) is about 30 times stronger than that of carbon dioxide (CO₂) over a century timescale. Methane emission is hypothesized to have contributed to global climate change events and mass extinctions during Earth’s history. Therefore, the study of CH₄ production processes is critically important to the understanding of global climate change. It has been a dogma that biogenic CH₄ detectable in the oceans originates exclusively from the anaerobic metabolic activity of methanogenic archaea in hypoxic and anoxic environments, despite reports that many oxic surface and near-surface waters of the world’s oceans are CH₄-supersaturated, thereby rendering net sea-to-air emissions of CH₄. The phenomenon of CH₄ production in oxic marine waters is referred to as the “ocean methane paradox”. Although still not totally resolved, recent studies have generated several hypotheses regarding the sources of CH₄ production in oxic seawater. This review will summarize our current understanding of the importance of CH₄ in the global climate and analyze the biological processes and their underpinning mechanisms that lead to the production of CH₄ in oxic seawater environments. We will also tentatively explore the relationships of these microbial metabolic processes with global changes in climate and environment.     

Trace metal solubility in an anoxic fjord

Intermittent anoxia in the Saanich Inlet water column provides an easily accessible marine O₂/H₂S interface to study the response of metals to both a steep redox gradient and the availability of reactive reduced sulfur species. Our study indicates a strong anoxic zone sink for copper and cadmium and the characteristically enhanced solubility of manganese and iron. Thiosulfate and sulfite are below detection limits (1 μM and 0.1 μM, respectively) and thus not important in metal complexation. Elemental sulfur concentrations are high at the oxic/anoxic interface and throughout the anoxic zone, indicating the potential for metal complexation by polysulfides. A thermodynamic approach employing metal sulfide formation and class specific sulfidic ligand complexation to generate equilibrium profiles adequately describes the solubility of iron, copper, and cadmium. The extension of this scheme to other transition and class B metals in other marine environments with redox fronts is suggested.     

The biogeochemistry of a manganese-rich Scottish sea loch: Implications for the study of anoxic nitrification

The anoxic oxidation of ammonia by manganese oxides is a newly recognised pathway for the production of N₂ in sedimentary environments, potentially contributing a significant loss of nitrogen from the world's oceans. Due to the complex recycling of redox species in marine sediments this process is difficult to discern in the natural environment, and is consequently poorly understood. The potential for anoxic nitrification coupled to manganese reduction was investigated through field research and laboratory incubation experiments. Field data from Loch Fyne, a manganese-rich site, did not provide conclusive evidence for anoxic nitrification, although minor accumulation of nitrate was observed in anoxic pore-waters. Incubation of Loch Fyne sediments showed anoxic nitrification to occur, with accumulation of both nitrate and nitrite coincident with removal of ammonia under anoxia, although these observations were not reproduced in repeat experiments. The laboratory evidence for anoxic nitrification confirms the reaction is possible in marine sediments; however, the wider significance of anoxic nitrification remains uncertain. Contrary to previous assumptions about anoxic nitrification, results suggest the reaction may not be dependent on total manganese concentrations and may be inhibited by conventional heterotrophic manganese reduction in manganese-rich sediments.     

Seasonal changes of organic matter origins and anammox activity in the Changjiang Estuary deduced from multi-biomarkers in suspended particulates

Human activity-induced eutrophication and harmful algal blooms are main causes of the expansion of the hypoxic zone in the Changjiang Estuary. Among the many changes in biogeochemical processes, anaerobic ammonium oxidation (anammox) is proposed to play an important role in the nitrogen cycle in hypoxic areas. Ladderane lipids have been used as biomarkers to indicate anammox activity in ecosystems, but the origins of anammox bacteria and ladderanes in suspended particulates are still unclear. In this study, we report the results of a suite of biomarker analyses of suspended particulates across a salinity gradient of the Changjiang Estuary in both the spring and summer to evaluate the origins of the ladderanes and their potential as proxies for anammox activity and hypoxia. The spatio-temporal variations in terrestrial biomarkers (n-alkanes and n-alkanols), marine biomarkers (brassicasterol and dinosterol), and the Terrestrial and Marine Biomarker Ratio and Branched and Isoprenoid Tetraether indices reveal that marine organic matter was dominant in the particulates in both the spring (55%) and summer (86%) seasons. Correlations with both marine and terrestrial biomarkers suggest that ladderanes were mainly produced in the water column, and therefore that ladderane concentrations in suspended particulates in the Changjiang Estuary mainly reflect anammox activity in the water column, although changes in anammox bacterial assemblages may also have played a role in ladderane concentrations. Overall, ladderane results suggest that anammox activity was widespread in the Changjiang Estuary; but higher ladderane concentrations in the summer (especially in the upwelling zone) were correlated with lower dissolved oxygen concentrations, which suggest that they are useful proxies for hypoxia.     

Spatiotemporal variability of ocean chemistry in the early Cambrian,South China

Following the Ediacaran metazoan radiation, the “Cambrian Explosion” set up the major framework of todays’ animal phyla as well as modern marine ecosystem. Here, we present a preliminary investigation on the temporal and spatial (from shallow to deep waters) variations of the early Cambrian ocean chemistry in South China through analyzing a Fe-S-C systematic dataset integrated from literature. Our investigation indicates that the early Cambrian deep ocean in South China was still anoxic and Fe²⁺-enriched (i.e., ferruginous) although its surface was oxic, and in between a metastable euxinic (anoxic and sulfidic) water zone may have dynamically developed in anoxic shelf waters with an increasing weathering sulfate supply. Furthermore, accompanying marine transgression and regression cycles in the early Cambrian, such a “sandwich” structure in ocean redox chemistry demonstrates five evolutional stages, which can be well correlated to the spatiotemporal patterns of fossil records in South China. The good correlation between metazoan fossil occurrences and water chemistry in South China suggests that early animals possibly possessed ability to inhabit anoxic but generally not euxinic environments as free H₂S was fatal to most eukaryotes. This view can well explain why those small shell fauna and sponges disappeared from shelf to slope areas where sulfidic Ni-Mo-rich shales were widely deposited. Thus, we conclude that the spatiotemporal variations of ocean chemistry and its biological effects probably played a key role in the phased animal radiations and “extinctions” in the early Cambrian.     

平原河网水体氮污染对氮循环菌的影响

采用最大可能数法对平原河网地区不同氮污染程度河道水体中浮游、颗粒附着及底泥中的氨化、亚硝化、硝化和反硝化菌进行测定,研究水体氮污染程度对氮循环菌不同种群的影响效应及其分布特征.结果表明,浮游、颗粒附着和底泥中亚硝化菌的丰度随着水体氮污染程度的增加而升高,但不同氮污染程度下氮循环菌种群结构组成之间差异不大,而浮游、颗粒附着及底泥生活类型之间的氮循环菌种群结构组成存在较大差异,其中浮游与底泥中氮循环菌种群组成结构之间差异最大.在氮污染水体中,浮游、颗粒附着和底泥氮循环菌中均以氨化菌为优势种群,显著高出其他氮循环菌种群多个数量级,而亚硝化菌和硝化菌丰度相对较低,反硝化菌在水体悬浮颗粒物上存在相对较高的丰度,不同氮循环菌种群组成比例存在失衡现象.     

Natural Attenuation of Perchlorate in Denitrified Groundwater

Monitoring of a well‐defined septic system groundwater plume and groundwater discharging to two urban streams located in southern Ontario, Canada, provided evidence of natural attenuation of background low level (ng/L) perchlorate (ClO₄^?) under denitrifying conditions in the field. The septic system site at Long Point contains ClO₄^? from a mix of waste water, atmospheric deposition, and periodic use of fireworks, while the nitrate plume indicates active denitrification. Plume nitrate (NO₃^?‐N) concentrations of up to 103 mg/L declined with depth and downgradient of the tile bed due to denitrification and anammox activity, and the plume was almost completely denitrified beyond 35 m from the tile bed. The ClO₄^? natural attenuation occurs at the site only when NO₃^?‐N concentrations are <0.3 mg/L, after which ClO₄^? concentrations decline abruptly from 187 ± 202 to 11 ± 15 ng/L. A similar pattern between NO₃^?‐N and ClO₄^? was found in groundwater discharging to the two urban streams. These findings suggest that natural attenuation (i.e., biodegradation) of ClO₄^? may be commonplace in denitrified aquifers with appropriate electron donors present, and thus, should be considered as a remediation option for ClO₄^? contaminated groundwater.     

Amenability of nitrilotriacetic acid to biodegradation in a marine simulation

The behaviour of the detergent builder nitrilotriacetic acid (NTA) has been studied in the presence of a marine bacterial population potentially associated with a sewage discharge to coastal waters. Additions of 500 μg l^?1 NTA were made over a period of 80 days and 7500 μg l^?1 NTA over 40 days in both aerobic and anoxic environments. It was concluded that NTA was not degraded at either concentration under aerobic or anoxic conditions, despite the presence of a significant bacterial population under aerobic conditions. Possible effects of NTA recalcitrance and its accumulation in coastal marine waters are discussed.     

Biogeographical distribution and diversity of bacterial and archaeal communities within highly polluted anoxic marine sediments from the marmara sea

Physicochemical and microbiological characterization of anoxic sediments taken from seven highly polluted sites of the Marmara Sea was carried out. The 16S rRNA based microbial community structure analyses were performed using domain-specific PCR followed by denaturant gradient gel electrophoresis (DGGE) and sequencing of characteristic bands. The results showed that the microbial communities in these sediments were diverse and evenly distributed. Relating the prokaryotic and geochemical variables through statistical tools revealed that the microbial diversity in the sediments significantly related to depth, and S, Mn and Fe content of the sediments. Fermentative bacteria, denitrifying bacteria and hydrogenotrophic methanogens were dominant whereas sulfate reducing bacteria were absent in the DGGE patterns. This unusual microbial community structure implied that the newly discovered anaerobic methane oxidation coupled to denitrification process may occur in these subseafloor environments.     

Methane consumption in Cariaco Trench waters and sediments

Detailed measurements of CH₄ in the water column and sediments of the Cariaco Trench show that CH₄ is non-conservative in both environments. Concentration differences between the sediments and adjacent overlying water suggest that the sediments are the source of the water column CH₄. Co-metabolism of CH₄ by sulfate reducers appears to be the CH₄ sink in anoxic environments.     

Effects of Different Carbon Sources on Denitrification Efficiency Associated with Culture Adaptation and C/N Ratio

Stringent effluent limitations for nitrogen necessitate an accurate interpretation of the design and operation conditions of biological nitrogen removal systems. In this study, the effects of the nature of the organic substrate on biomass adaptation and response to different C/N ratios in terms of denitrification efficiency were investigated. A relatively high chemical oxygen demand (COD)_utilized/NO_x–N_reduced ratio of 8.1 was obtained when an excess amount of readily biodegradable carbon was supplied, which is suggested as the conversion of substrate surplus into storage polymers. An anoxic yield of 0.64 g cell COD/g COD for a four‐compound substrate mixture (acetate, propionate, ethanol and glucose), 0.63 g cell COD/g COD for a two‐compound substrate mixture (acetate and propionate), and 0.5 g cell COD/g COD for methanol were calculated. Fluorescence in situ hybridization analysis showed that the β‐subclass of proteobacteria was dominant in the seed and in cultures adapted to both the four‐compound and the two‐compound substrate mixture, whereas in the methanol‐adapted culture significant amounts of β‐proteobacteria were detected. The biocommunity composition, the type of organic compound and the COD/NO₃–N ratio strongly influence the nitrate reduction and carbon utilization profiles. Methanol has been shown to select for a denitrifying population consisting of Paracoccus and Hyphomicrobium vulgare genera, when used as only external carbon source.     

Influence of Vegetation Characteristics on Soil Denitrification in Shoreline Wetlands of the Danjiangkou Reservoir in China

Soil denitrification in reservoir shoreline wetlands is an important process for removing excess inorganic nitrogen from upland runoff and controlling eutrophication in aquatic ecosystems. As yet, little is known about the influence of vegetation characteristics on the soil denitrification potential in reservoir shoreline wetlands, although vegetation can affect both denitrifying bacteria and soil properties. In this study, we measured the spatial variability of denitrification enzyme activity (DEA) using acetylene block method in shoreline wetlands of the Danjiangkou Reservoir, a water source of the South‐to‐North Water Transfer Project in China. Results indicated that DEA ranged from 0.001 to 2.449 µg N (N₂O) g^?1 h^?1, with a mean of 0.384 µg N (N₂O) g^?1 h^?1. DEA varied significantly among five representative plant communities and the highest DEA (0.248–2.449 µg N (N₂O) g^?1 h^?1) was observed in the Polygonum hydropiper community. Plant biomass and vegetation cover were significantly and positively related to DEA and together explained 44.2% of the total variance. These results suggest that vegetation characteristics should also be considered in assessing soil denitrification capacity and restoring shoreline wetlands for nitrogen pollution removal in the Danjiangkou Reservoir after dam heightening.     

Stable isotopic characterisation of francolite formation

Stable isotopic data are presented for 112 samples of francolite from 18 separate phosphate deposits. Values ofδ¹³C andδ³⁴S in most offshore deposits suggest formation within oxic or suboxic environments either by carbonate replacement or direct precipitation of francolite from water of normal marine compositions. The exceptions are concretionary francolite from Namibia, which has an isotopic composition in keeping with its formation within organic-rich sediments, and that from offshore Morocco, which has an isotopic signature of the anoxic/suboxic interface. Onshore deposits from Jordan, Mexico, South Africa and, possibly, the Permian Phosphoria Formation in the western U.S.A., are substantially depleted in¹⁸O: they appear to be too altered for deductions to be made about their environments of formation. In other onshore deposits which are unaltered, or minimally altered, the isotopic composition suggests that some formed within sulphate-reducing sediments (Sedhura, Morocco) whilst francolite from the Georgina Basin of Australia formed at the oxic/anoxic boundary, where oxidation of biogenic H₂S decreases theδ³⁴S of pore water. In general, pelletal samples show non-oxic isotopic signatures, whilst non-pelletal samples show oxic isotopic signatures, but samples from Namibia, Peru (Ica Plateau) and the Californian and Moroccan margins are exceptions to this rule. Morphology may therefore be a misleading indicator of francolite genesis as no definitive relation exists between phosphorite type and isotopic signature.     

N/N variations in Cretaceous Atlantic sedimentary sequences: implication for past changes in marine nitrogen biogeochemistry

At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds (“black shales”) were found to have significantly lower δ¹⁵N values (lower¹⁵N/¹⁴N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have °¹⁵N values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools. In contrast, black, organic-carbon-rich beds at a third site (DSDP Site 603) contain predominantly terrestrial organic matter and have C- and N-isotopic compositions similar to organic matter of modern terrestrial origin.The recurring¹⁵N depletion in the marine-derived Cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry. Existing isotopic and other data indicate that the low¹⁵N relative abundance is the consequence of pelagic rather than post-depositional processes. Reduced ocean circulation, increased denitrification, and, hence, reduced euphotic zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by N₂-fixing blue-green algae, a possible source of this sediment¹⁵N-depletion. Lack of parallel isotopic shifts in Cretaceous terrestrially-derived nitrogen (Site 603) argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment.     

Two episodes of C-depletion in organic carbon in the latest Permian: Evidence from the terrestrial sequences in northern Xinjiang, China

New analyses reveal two intervals of distinctly lower δ¹³C values in the terrestrial organic matter of Permian–Triassic sequences in northern Xinjiang, China. The younger negative δ¹³C_org spike can be correlated to the conspicuous and sharp δ¹³C drops both in carbonate carbon and organic carbon near the Permian–Triassic event boundary (PTEB) in the marine section at Meishan. The geochemical correlation criteria are accompanied by a magnetic susceptibility pulse and higher abundances of distinctive, chain-like organic fossil remains of Reduviasporonites.The older negative δ¹³C_org spike originates within a latest Permian regression. Significant changes in organic geochemical proxies are recorded in the equivalent interval of the marine section at Meishan. These include relatively higher concentrations of total organic carbon, isorenieratane, C₁₄–C₃₀ aryl isoprenoids and lower ratios of pristane/phytane that, together, indicate the onset of anoxic, euxinic and restricted environments within the photic zone. The massive and widespread oxidation of buried organic matter that induced these euxinic conditions in the ocean would also result in increased concentrations of ¹³C-depleted atmospheric CO₂. The latest Permian environmental stress marked by the older negative δ¹³C_org episode can be correlated with the distinct changeover of ostracod assemblages and the occurrences of morphological abnormalities of pollen grains. These observations imply that biogeochemical disturbance was manifested on the land at the end of the Permian and that terrestrial organisms responded to it before the main extinction of the marine fauna.     

The research of typical microbial functional group reveals a new oceanic carbon sequestration mechanism——A case of innovative method promoting scientific discovery

Marine microbes are major drivers of marine biogeochemical cycles and play critical roles in the ecosystems. Aerobic anoxygenic phototrophic bacteria(AAPB) are an important bacterial functional group with capability of harvesting light energy and wide distribution, and appear to have a particular role in the ocean's carbon cycling. Yet the global pattern of AAPB distribution was controversial at the beginning of the 21 st century due to the defects of the AAPB enumeration methods. An advanced time-series observation-based infrared epifluorescence microscopy(TIREM) approach was established to amend the existing AAPB quantitative deviation and led to the accurate enumeration of AAPB in marine environments. The abundance of AAPB and AAPB% were higher in coastal and continental shelf waters than in oceanic waters, which does not support the idea that AAPB are specifically adapted to oligotrophic conditions due to photosynthesis in AAPB acting a supplement to their organic carbon respiration. Further investigation revealed that dependence of AAPB on dissolved organic carbon produced by phytoplankton(PDOC) may limit their competition and control AAPB distribution. So, the selection of carbon sources by AAPB indicated that they can effectively fractionate the carbon flow in the sea. Enlightened by these findings, the following studies on the interactions between marine microbes and DOC led to the discovery of a new mechanism of marine carbon sequestration—the Microbial Carbon Pump(MCP). The conceptual framework of MCP addresses the sources and mechanism of the vast DOC reservoir in the ocean and represents a breakthrough in the theory of ocean carbon sequestration.     

Depositional environments and maturity evaluated by biomarker analyses of sediments deposited across the Cenomanian–Turonian boundary in the Yezo Group,Tomamae area,Hokkaido, Japan

Biomarker analyses for evaluating maturity of organic matter and depositional environments such as redox conditions, were performed in sediments across the Cenomanian–Turonian boundary (CTB) in the Saku Formation of the Yezo Group distributed along the Shumarinai‐gawa River and the Omagari‐zawa River, both in the Tomamae area, Hokkaido, Japan. Maturity indicators using steranes and hopanes, show that organic matter in sediments from the Shumarinai‐gawa and Omagari‐zawa sections are of lower maturity than those from the Hakkin‐gawa section (Oyubari area). Moreover, the ββ hopane ratios clearly show that the maturity of the Shumarinai‐gawa samples is lower than that of the Omagari‐zawa samples. These variations in the maturity of organic matter presumably reflect the difference in their burial histories. The results for the pristane/phytane (Pr/Ph) ratios suggest that the Shumarinai‐gawa samples were deposited under dysoxic to anoxic environments across the CTB, while the depositional environments of the Omagari‐zawa samples were relatively oxic. By another paleoredox indicator using C₃₅ homohopanoids including a homohopene index (HHenI), higher values are observed in the Shumarinai‐gawa section, particularly in the horizons of the preceding period and an early stage of the first negative shift phase and the latest oceanic anoxic event 2 (OAE2) interval. These results suggest that the Shumarinai‐gawa samples record dysoxic to anoxic environments across the CTB. In contrast, the signals for the C₃₅ homohopanoid index values show a relatively oxic condition in the Omagari‐zawa section. The trends of stratigraphic variations in redox conditions are different from those in the OAE2 interval in the proto‐Atlantic and Tethys regions as reported previously. Hence, the redox variations in the Tomamae area were basically related to a local environmental setting rather than global anoxia. However, the prominent anoxic emphasis observed in the HHenI profile of the Shumarinai‐gawa section can be a distinctive, and possibly global, event in the North‐West Pacific just before the OAE2.