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'Mass extinctions' have been a hot topic for several decades. What triggers a mass extinction? How does a mass extinction impact the evolution of life? How does our ecosystem recover after a mass extinction? These questions attracted the interest of both scientists and the public alike. NSR spoke to two renowned researchers in the field of mass extinctions: Prof. Douglas H. Erwin from the National Museum of Natural History of the USA, and Prof. Shuzhong Shen from Nanjing University, China. Prof. Erwin has been interested in the end-Permian mass extinction since graduate school. He has worked on a variety of problems, from Permian gastropod systematics to the origin of animals. Currently his work focuses on the nature of evolutionary novelty and innovation. Prof. Shen's research career is centered upon the end-Permian mass extinction, Permian stratigraphy and global correlations, with taxonomic expertise on brachiopods and conodonts. The International Commission on Stratigraphy recognizes his outstanding singular contribution to stratigraphy and awarded him the ICS Stratigraphy Medal in 2019. [ABSTRACT FROM AUTHOR]

This article discusses the topic of mass extinctions and their relevance to understanding the current biotic crisis. The article highlights that Earth has experienced at least five major mass extinctions, and significant progress has been made in documenting the patterns, processes, and causes of these events. The causes of mass extinctions can come from various sources, including the Earth's interior, exterior, and the biosphere itself. The article also emphasizes the importance of studying the resilience and recovery of ecosystems in response to climate change, using mass extinctions as natural experiments. The author concludes by expressing gratitude to all those who contributed to the Special Topic on mass extinction. [Extracted from the article]

Magnetotactic bacteria (MTB) may have been the earliest organisms to sense Earth's magnetic field and to form intracellular nanocrystals of magnetic minerals, so-called magnetotaxis and magnetosomes, respectively [[2]]. Considering the phylogenetic diversity of uncultured MTB and their diverse magnetic crystal morphologies and chain assemblies, a general model for gene networks that control or regulate magnetic particle biogenesis and chain assembly needs to be established on the basis of all available cultured and uncultured data. [Extracted from the article]

Global warming, the most severe faunal mass extinction and the shift of biogeochemical cycles were observed in the ocean across the Permian-Triassic boundary about 252 million years ago, providing an analog to understanding the modern oceans. Along with the progressive global warming, the biogeochemical cycle was documented to show a shift from the decoupled processes of carbon, nitrogen and sulfur prior to the mass extinction to the coupled biogeochemical processes during faunal mass extinction. The coupled biogeochemical cycle was further observed to shift from the coupled C-N processes during the first episode of the faunal mass extinction to the coupled C-N-S processes during the second episode, diagnostic of the progressive development of more deteriorated marine environmental conditions and the more severe biotic crisis across the Permian-Triassic boundary. The biogeochemical cycles could thus be an indication to the progressive collapse of marine ecosystems triggered by the global warming in Earth history. In modern oceans, the coupled C-N cycle triggered by the global warming was observed in some regions. If these local C-N processes develop and expand to the global oceans, the coupled C-N-S processes might be brought into existence and the marine ecosystems are inevitable to suffer from complete collapse as observed at 252 million years ago. [ABSTRACT FROM AUTHOR]

Microbial communities are known to expand as a result of environmental deterioration during mass extinctions, but differences in microbial community changes between extinction events and their underlying causes have received little study to date. Here, we present a systematic investigation of microbial lipid biomarkers spanning ∼20 Myr (Middle Permian to Early Triassic) at Shangsi, South China, to contrast microbial changes associated with the Guadalupian–Lopingian boundary (GLB) and Permian–Triassic boundary (PTB) mass extinctions. High-resolution analysis of the PTB crisis interval reveals a distinct succession of microbial communities based on secular variation in moretanes, 2-methylhopanes, aryl isoprenoids, steranes, n -alkyl cyclohexanes, and other biomarkers. The first episode of the PTB mass extinction (ME1) was associated with increases in red algae and nitrogen-fixing bacteria along with evidence for enhanced wildfires and elevated soil erosion, whereas the second episode was associated with expansions of green sulfur bacteria, nitrogen-fixing bacteria, and acritarchs coinciding with climatic hyperwarming, ocean stratification, and seawater acidification. This pattern of microbial community change suggests that marine environmental deterioration was greater during the second extinction episode (ME2). The GLB shows more limited changes in microbial community composition and more limited environmental deterioration than the PTB, consistent with differences in species-level extinction rates (∼71% vs. 90%, respectively). Microbial biomarker records have the potential to refine our understanding of the nature of these crises and to provide insights concerning possible outcomes of present-day anthropogenic stresses on Earth's ecosystems. [ABSTRACT FROM AUTHOR]

Microbes not only show sensitive responses to environmental changes but also play important roles in geochemical and geophysical systems. It is well known that microbes have caused major changes in surface environments and biogeochemical cycles through Earth history. Microbial processes can also induce the synthesis of certain minerals under Earth-surface conditions that previously were believed to form only under high temperatures and pressures in the deep Earth. For example, microbes can promote the conversion of smectite to illite, synthesis of authigenic plagioclase, precipitation of dolomite, and biotransformation of geolipids. These effects of microbes are due to their large surface/volume ratios, enzyme production, and abundant functional groups. Microbial catalyzation of chemical reactions proceeds through reaction-specific enzymes, a decrease in Gibbs's free energy, and/or break through the dynamics reaction thresholds via their metabolisms and physiology. Microbes can lower the surface free energy of mineral nuclei via biophysical adsorption due to their large surface/volume ratios and abundant functional groups. The mineral precipitation and transformation processes induced by microbes are functionally equivalent to geological processes operating at high temperatures and pressures in the deep Earth, suggesting that microbial processes can serve as analogs to deep abiotic processes that are difficult to observe. [ABSTRACT FROM AUTHOR]

Geobiology is a new discipline on the crossing interface between earth science and life science, and aims to understand the interaction and co-evolution between organisms and environments. On the basis of the latest international achievements, the new data presented in the Beijing geobiology forum sponsored by Chinese Academy of Sciences in 2013, and the papers in this special issue, here we present an overview of the progress and perspectives on three important frontiers, including geobiology of the critical periods in Earth history, geomicrobes and their responses and feedbacks to global environmental changes, and geobiology in extreme environments. Knowledge is greatly improved about the close relationship of some significant biotic events such as origin, radiation, extinction, and recovery of organisms with the deep Earth processes and the resultant environmental processes among oceans, land, and atmosphere in the critical periods, although the specific dynamics of the co-evolution between ancient life and paleoenvironments is still largely unknown. A variety of geomicrobial functional groups were found to respond sensitively to paleoenvironmental changes, which enable the establishment of proxies for paleoenvironmental reconstruction, and to play active roles on the Earth environmental changes via elemental biogeochemical cycles and mineral bio-transformations, but to be deciphered are the mechanisms of these functional groups that change paleoenvironmental conditions. Microbes of potential geobiology significance were found and isolated from some extreme environments with their biological properties partly understood, but little is known about their geobiological functions to change Earth environments. The biotic processes to alter or modify the environments are thus proposed to be the very issue geobiology aims to decipher in the future. Geobiology will greatly extend the temporal and spatial scope of biotic research on Earth and beyond. It has great potential of application in the domains of resource exploration and global change. To achieve these aims needs coordinative multidisciplinary studies concerning geomicrobiology and related themes, database and modeling of biogeochemical cycles, typical geological environments, and coupling of biological, physical, and chemical processes. [ABSTRACT FROM AUTHOR]

The biosphere interacts and co-evolves with natural environments. Much is known about the biosphere's response to ancient environmental perturbations, but less about the biosphere's influences on environmental change through earth history. Here, we discuss the roles of microbes in environmental changes during the critical Permian-Triassic (P-Tr) transition and present a perspective on future geomicrobiological investigations. Lipid biomarkers, stable isotopic compositions of carbon, nitrogen and sulfur, and mineralogical investigations have shown that a series of microbial functional groups might have flourished during the P-Tr transition, including those capable of sulfate reduction, anaerobic HS oxidation, methanogenesis, aerobic CH oxidation, denitrification, and nitrogen fixation. These microbes may have served to both enhance and degrade the habitability of the Earth-surface environment during this crisis. The integrated microbial roles have enabled the Earth's exosphere to be a self-regulating system. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution stratigraphic records through the Permian–Triassic boundary (PTB) interval of the global stratotype section and point (GSSP) at Meishan, Zhejiang Province, China reveal that the PTB crisis was not a single, abrupt catastrophe. A bed-by-bed analysis of environmental and biotic changes makes clear that the crisis can be resolved into two discrete episodes, each consisting of three stages: A) unstably oscillating conditions, B) peak crisis conditions, and C) ameliorating conditions. The first crisis episode commenced in Bed 23, peaked in Beds 24e–26, and ameliorated in Beds 27 and 28, while the second crisis episode commenced in Bed 29, peaked in Beds 34–38, and ameliorated in Beds 39 and higher. The macroscopic mass extinctions happened not at the beginning, nor the end of each cycle, but at times when the crisis or perturbation of environments began. These extinction events do not show detectable feedbacks to concurrent environmental changes. In each episode, cyanobacteria proliferation postdated the macroscopic extinction while proliferation of green sulfur bacteria predated the environmental crisis. Causational analysis between environmental and microbial changes show that geomicrobial functional groups exercised pronounced effects on the marine C–N–S cycles and ocean redox conditions during the PTB crisis. It is possible thus that the microbial crises played an important role in strengthening or evening triggering the environmental crisis. [Copyright &y& Elsevier]

Microbes are well-known for their great diversity and abundance in modern natural environments. They also are believed to provide critical links among higher organisms and their associated environments. However, the low diversity of morphological features and structures of ancient microbes preserved in sediments and rocks make them difficult to identify and classify. This difficulty greatly hinders the investigation of geomicrobes throughout Earth history. Thus, most previous paleontological studies have focused on faunal and floral fossils. Here, geomicrobial functional groups (GFGs), or a collection of microbes featured in specific ecological, physiological or biogeochemical functions, are suggested to provide a way to overcome the difficulties of ancient microbe investigations. GFGs are known for their great diversity in ecological, physiological and biogeochemical functions. In addition, GFGs may be preserved as the biogeochemical, mineralogical and sedimentological records in sediments and rocks. We reviewed the functions, origins and identification diagnostics of some important GFGs involved in the elemental cycles of carbon, sulfur, nitrogen and iron. GFGs were further discussed with respect to their significant impacts on paleoclimate, sulfur chemistry of ancient seawater, nutritional status of geological environments, and the deposition of Precambrian banded iron formations. [ABSTRACT FROM AUTHOR]

Evaluating the pre-Jurassic marine source rocks in China has been difficult because these rocks are generally too high- or over-maturated for most traditional methods to work. As to the remaining parameter TOC (%), its lower limit for recognizing the carbonate source rocks in China has been in dispute. Nineteen Phanerozoic sections in the Middle-Upper Yangtze Platform and the Guizhou-Hunan-Guangxi Basin have been studied in search for a different approach to complementing the traditional evaluation method for these source rocks. We have applied a geobiological approach to tracing the organic carbon (OC) output and accumulation from the living stage (primary productivity) to the post-mortem deposited remains, and finally to the preserved burial organics. Four biological and geological parameters are employed to represent the OC of the three stages. A series of proxies of these parameters are discussed and integrated to establish a geobiological evaluation system independent of TOC and other traditional methods. Here we use the Guangyuan section in Sichuan as an example for the geobiological evaluation. Our results indicate that in the argillaceous rocks, the geobiological parameters show the qualified source rocks in accordance with high TOC values; but in the carbonates, the good source rocks delineated by the geobiological parameters have a wide range of TOC, from 0.03% to 1.59%, mostly <0.3%. We suggest that it is still premature to set TOC=0.3% or 0.5% as the lower limit for the pre-Jurassic carbonate source rocks in South China. [ABSTRACT FROM AUTHOR]

Testate amoebae from a large fen peatland of China were investigated in August 2009. Thirty-six testate amoebae species belonging to 16 genera and one rotifer were identified. Three relatively drier indicator species, Assulina muscorum, Assulina seminulum, and Trinema-corythion type, were the dominate species, comprising 54% of total amoebae shells. Non-metric multidimensional scaling (NMS) ordination divided the testate amoebae assemblages into two groups – a drier group including A. muscorum, A. seminulum, Euglypha rotunda type, Trinema-corythion type, and Plagiopyxis callida and a wetter group including Centropysis cassis, Cyphoderia ampulla, Difflugia oblonga, Difflugia lanceolata, Euglypha strigosa type, Nebela galeata, Nebela lageniformis, and Quadruella symmetrica. Pearson correlations showed that most testate amoebae species between the two groups are negatively correlated, reflecting the possible influence of a moisture gradient. However, the ubiquitous distributions of other testate amoebae in the two-dimensional NMS ordination map suggested that factors other than moisture are also influencing the testate amoebae community in the fen. [ABSTRACT FROM AUTHOR]

Abstract: Palaeoenvironmental reconstruction based on phytolith analysis of late Holocene-aged soils in and around the Somapura Mahavihara archaeological monastery site in the Paharpur area, Badalgacchi Upazila of Naogaon District in northwestern Bangladesh was undertaken. Results indicate five climate zones marked by alternatively cool and temperate events. The phytolith assemblages of Zones 1, 3 and 5 are clearly characterized by a higher proportion of Pooideae phytoliths. The climate indices for these zones are all greater than 50, indicating cooler climatic conditions. In contrast, the phytolith assemblages of Zones 2 and 4 are typified by a higher proportion of Panicoideae phytoliths; their climate indices are 42 and 44, respectively, indicating the presence of a warmer, more temperate climate. In general, the dominance of grasses over broad- leaved trees throughout the sequences suggests that generally cool to temperate and dry conditions with some cyclical variability persisted around Paharpur and the surrounding region throughout the Pala Dynasty from AD 730 to 1080. The question of whether these shifts in vegetation might be linked with El Niño Southern Oscillation events, and whether these might in turn have cultural responses, is raised. [Copyright &y& Elsevier]

Abstract: Aliphatic des-A-triterpenoids have been tentatively assigned in samples taken from a 260cm thick peat sequence from the Dajiuhu Basin of southern China using gas chromatography–mass spectrometry (GC–MS). The compounds, possessing the carbon skeletons of oleanane, ursane or lupane, are generally considered as the microbial degradation products of plant triterpenoids under anoxic conditions. Abundant aliphatic des-A-triterpenoids were observed only in peat samples during the transitional period from the last glaciation to the early Holocene (9.5–11.6cal 14CkaBP). Among these, des-A-lupane is the only saturated ring A-degraded compound, whilst mono- and di-unsaturated des-A-triterpenes are dominated by oleanane and ursane derivatives. The mono- and di-unsaturated des-A-triterpenes show a strong correlation (R2 0.94) in abundance, indicating that they may be derived from the same source or process. Des-A-lupane shows no correlation in abundance with the mono- or di-unsaturated des-A-triterpenes (R2 <0.25) and may be derived from a different source or process in the catchment. The period with abundant aliphatic des-A-triterpenoids corresponds to the interval with relatively high sedimentation rate (> 0.3mm per year). These data indicate that the abundance of aliphatic des-A-triterpenoids in the Dajiuhu peat deposit in the early Holocene may result from the prevailing reducing conditions in the water table or surficial sediment and/or rapid preservation of the early diagenetic products. Our study highlights the potential application of des-A-triterpenes in the reconstruction of palaeoenvironments based on peat sequences. [Copyright &y& Elsevier]

Abstract: Lipid biomarker abundances and δ 13C values were determined across the Permian–Triassic (P–Tr) boundary at Meishan of southern China. The δ 13C values of n-alkanes showed large (∼9‰) fluctuations, which suggest major episodic changes in oceanographic conditions during faunal mass extinctions. Environment-related biomarker ratios, including pristane to phytane ratios (Pr/Ph), gammacerane to C31 homohopane ratios (γ/C31HP) and C27 18α(H)-22,29,30-trinorneohopane to C27 17α(H)-22,29,30-trinorhopane ratios (Ts/Tm), vary extensively throughout the section, with values typically associated with anoxic conditions coinciding with maximum δ 13C values. In particular, both faunal mass extinction horizons (beds 25 and 28) are characterised by biomarker ratios consistent with anoxic conditions and elevated n-alkane δ 13C values. The records of environment-related biomarkers and n-alkane δ 13C values clearly signify multiple environmental perturbations in association with faunal mass extinctions. [Copyright &y& Elsevier]

Abstract: We have carried out a multi-proxy analysis of a radiocarbon-dated peat core that records the history of paleoclimate change dating from 18ka in the Dingnan region of southern China. Fatty acid and hydrocarbon distributions, total organic carbon (TOC) concentrations, pollen assemblages and sediment lithology reveal a succession of three major paleoclimate intervals. Plant waxes are the predominant origin of the n-alkanoic acid and n-alkane compositions of this sedimentary sequence. Contributions of these geolipid components vary relative to TOC and with changes in lithology and help to refine a pollen-based reconstruction of local paleoclimate evolution. A period of cool and fairly wet climate (15,630–10,450calaBP) follows accumulation of coarse fluvial sediments under relatively dry deglacial conditions. The second period (10,450–6040calaBP) experienced the warmest climate and the highest precipitation, indicated by a minimum C18:1/C18:0 ratio, together with the low CPI values of n-alkanes and high ACL values. The third time interval (6040–3800calaBP) was a moderately dry and cool period. The climate record of the most recent period (&#60;3800calaBP) is obscured by agricultural disturbance. The Younger Dryas (12,900–11,600calaBP) appears in this record as a period of variable and very wet climate. During the interval 10,450–6040calaBP, both temperature and the precipitation/evaporation ratio maximized. Therefore, we consider this period to represent the Holocene Optimum which coincides with that of the northern hemisphere. Moreover, our results do not fit the spatially asynchronous pattern of the East Asian monsoon Holocene Optimum in China suggested by previous studies. They instead parallel the pattern of global paleoclimate change and consequently show that the evolution of Holocene paleoclimate in southern China is consistent with changes in northern hemisphere solar radiation. [Copyright &y& Elsevier]

Microbial expansion following faunal mass extinctions in Earth history can be studied by petrographic examination of microbialites (microbial crusts) or well-preserved organic-walled microbes. However, where preservation is poor, quantification of microbial communities can be problematic. We have circumvented this problem by adopting a lipid biomarker-based approach to evaluate microbial community changes across the Permo/Triassic (P/Tr) boundary at Meishan in South China. We present here a biomarker stratigraphic record showing episodic microbial changes coupled with a high-resolution record of invertebrate mass extinction. Variation in the microbial community structure is characterized by the 2-methylhopane (2-MHP) index (a ratio of the abundance of cyanobacterial biomarkers to more general bacterial biomarkers). Two episodes of faunal mass extinction were each preceded by minima in the 2-MHP index, followed by strong maxima, likely reflecting microbial responses to the catastrophic events that caused the extinction and initiated ecosystem changes. Hence, both cyanobacterial biomarker and invertebrate fossil records provide evidence for two episodes of biotic crisis across the P/Tr boundary. [ABSTRACT FROM AUTHOR]

Molecular stratigraphic analyses using gas chromatograph-mass spectrometry have been performed in the upper section (S0, L1, S1) of the Yuanbo loess–paleosol sequences in northwest China, with a record extending from the last interglaciation through the present interglaciation. The CPI (Carbon Preference Index) values of both n-alkanols and n-alkan-2-ones display variations between loess deposits and paleosols, showing a correlation with the magnetic susceptibility record, an indicator of the East Asian summer monsoon. The observed variations in the indexes in relation to changes in lithology/paleoclimate are proposed to result from microbial degradation of higher plant lipids in the paleosols. The CPI values of n-alkanes, n-alkanols, and n-alkan-2-ones are negatively correlated with δ13C of bulk organic matter. The correlations suggest that the observed glacial–interglacial variations of δ13C data in the loess stratigraphy reflect the relative importance of the contribution of paleovegetation compared with microorganisms (including both the degradation and the addition of organic matter) and allochthonous loess/soil parent materials. It is thus necessary to evaluate the contributions of the latter two before the paleovegetation can be reconstructed based on the δ13C analysis of bulk organic matter in some loess–paleosol sequences of the Chinese Loess Plateau. [Copyright &y& Elsevier]

A 40 cm deep Sphagnum-dominated peat monolith from Bolton Fell Moss in Northern England was systematically investigated by lipid molecular stratigraphy and compound-specific δ13C and δD analysis using gas chromatography (GC), GC-mass spectrometry (GC-MS), GC-combustion-isotope ratio-MS (GC-C-IRMS) and GC-thermal conversion-IRMS (GC-TC-IRMS) techniques. 210Pb dating showed the monolith accumulated during the last ca. 220 yr, a period encompassing the second part of Little Ice Age. While the distributions of lipids, including n-alkan-1-ols, n-alkan-2-ones, wax esters, sterols, n-alkanoic acids, α,ω-alkandioic acids and ω-hydroxy acids, display relatively minor changes with depth, the cooler climate event was recorded in the concentrations of n-alkanes and organic carbon, CPI values of n-alkanes and n-alkanoic acids, and the ratio of 5-n-alkylresorcinols/sterols. Superimposed on the fossil fuel effect, the relatively cooler climate event was also recorded by δ13C values of individual hydrocarbons, especially the C23 n-alkane, a major compound in certain Sphagnum spp. The δD values of the C29 and C33 n-alkanes correlated mainly with plant composition and were relatively insensitive to climatic change. In contrast the C23 n-alkane displayed variation that correlated strongly with recorded temperature for the period represented by the monolith, agreeing with previously reported deuterium records in tree ring cellulose spanning the same period in Scotland, Germany and the USA, with more negative values occurring during the second part of Little Ice Age. These biomarker characteristics, including the compound-specific δ13C and δD records, provide a new set of proxies of climatic change, potentially independent of preserved macrofossils which will be of value in deeper sections of the bog where the documentary records of climate are unavailable and humification is well advanced. [Copyright &y& Elsevier]

Lipid extracts from a 61.7-cm-long subtropical stalagmite in southern China, spanning the period of ca. 10,000–21,000 yr ago as constrained by U–Th dating, were analyzed using gas chromatography–mass spectrometry. The higher plants and microorganisms in the overlying soils contribute a proportion of n-alkanes identified in the stalagmite. The occurrence of LMW (lower molecular weight) n-alkanols and n-alkan-2-ones in the stalagmite was mainly related to the soil microorganisms. We suggest that HMW (higher molecular weight) n-alkanols and n-alkan-2-ones identified in the stalagmite originate from soil organics and reflect input from contemporary vegetation. Shifts in the ratio of LMW to HMW n-alkanols or n-alkan-2-ones indicative of the variation of soil ecosystems (e.g., microbial degradation of organic matter and/or the relative abundance of soil microorganisms to higher plants) are comparable with the subtropical alkenone-SST (sea surface temperature) record of the same period. The similar trends seen in the δ13C data and the lipid parameters in this stalagmite imply that the overlying soil ecosystem response to climate might be responsible for the variation of δ13C values. [Copyright &y& Elsevier]

Molecular stratigraphic analyses using GC/MS have been performed on the top section of the Jiuzhoutai loess-paleosol sequences near Lanzhou in northwest China, with a record extending from the second-last interglacial through the present interglacial. The various molecular fossils identified from the second-order loess and paleosol layers include C14–C35 n-alkanes, C8–C30 n-alkanoic acids, C12–C30 n-alkanols and C23–C33 n-alkan-2-ones. The CPI (carbon preference index) values and the ratio of C29/C31 n-alkan-2-ones display alternations between loess deposits and paleosols. They show a significant correlation with the loess magnetic susceptibility, an indicator of the East Asian summer monsoon. The observed variations of the ketone indices in relation to the change of lithology are proposed to result from microbial re-working of higher plant inputs in the paleosols. [Copyright &y& Elsevier]

The red paleosols (Oxisols) in southern China provide a record of global climate oscillation during at least the last 0.80 Ma. Here we present a correlation between the marine oxygen isotope record (stage 11–21) and the paleosol molecular fossil signature in the fourth Xiushui river terrace in southern China. Temporal variations seen in two molecular ratios—C15–21/C22–33 n-alkanes and pristane to phytane (Pr/Ph)—down the paleosol profile are postulated to have arisen from variations in biological input and subsequent pedogenesis in response to the changing strength of the East Asian summer monsoon climate. The preliminary findings suggest strong couplings among the soil, vegetation and climate, and provide a basis for a correlation between the terrestrial and oceanic records. [Copyright &y& Elsevier]

Presents a study which examined the link of the occurrence of the dominant peat normal alkane derived from bryophyte to cold climate. Discussion on the paleo-organism replacement recorded by molecular fossils; Analysis of the peat core record; Results.

Presents a study which evaluates the gold emigration from algae to organic matter and organic fluid under the geologic processes. Role of organic matter and crude oil in gold geochemistry processes; Formation of an organism-organic matter-fluid system; Results of the study.

Presents information on a study which involved the identification of a series of biomarkers in hydrocarbon inclusions through gas chromatography-mass spectrometry (GC-MS). Methodology used in study; Optical and spectral characteristics of the individual hydrocarbon inclusions; Extractable organic matter (EOM) and biomarkers in hydrocarbon inclusions; Concluding remarks.

The article explores the use of the geobiological approach in the assessment of Chinese carbonate source rocks. A series of paleoecological and biogeochemical parameters were employed to represented organic carbon (OC). It notes that clastic rocks based on geobiological parameters are qualified source rocks, while good source rocks from carbonates have low total organic carbon (TOC) values. It also notes the broad range of habitat types for carbonate source rocks in the Yangtze platform.

Hydroxylated isoprenoid GDGTs (OH‐GDGTs) have emerged as a novel tool for reconstructing sea surface temperatures. However, when using marine OH‐GDGT calibration in lacustrine settings, it leads to a significant overestimation of temperatures, emphasizing the necessity for a thorough examination of OH‐GDGTs in lakes. Here, we investigated OH‐GDGT distributions in surface sediments from 65 lakes in West China and compiled published Asian lake and global marine OH‐GDGT data sets. Among all GDGT‐based indices, RI‐OH showed the strongest correlation with temperature across Asian lakes. The RI‐OH value was higher in lakes than in marine sediments, likely due to differences in the composition of Group 1.1a thaumarchaeotal species between the two settings. The first RI‐OH temperature calibration for lakes was developed and it addressed the issue of temperature overestimation when applied to both water column and sediment core, highlighting the potential of OH‐GDGTs as a new terrestrial paleothermometer. Plain Language Summary: Reconstruction of past terrestrial temperatures plays a crucial role in understanding modern global warming and projecting future climate patterns, yet reliable terrestrial temperature proxies remain limited. In this study, we present compelling evidence that the ring index of OH‐GDGTs, expressed as RI‐OH, is predominantly influenced by temperature in lacustrine settings, regardless of the wide range of physical and chemical characteristics of the lakes. We developed the first lacustrine RI‐OH‐temperature calibration and successfully applied it to a water column and a sediment core. These findings suggest that RI‐OH can be used as a novel paleothermometer in lacustrine settings. Key Points: OH‐GDGTs were first investigated in lacustrine settings along a wide temperature gradientTemperature was the most important factor affecting OH‐GDGT distributions in lacustrine settingsThe first calibration in lacustrine settings was established and successfully applied to a water column and a sediment core [ABSTRACT FROM AUTHOR]

The compound-specific stable carbon (δ13C) and hydrogen (δ2H) isotopic compositions of microbial fatty acids have been widely used to trace microbial metabolism across a range of mesophilic environments. However, few studies have combined the δ13C and δ2H values of microbial fatty acids. So far none have determined the δ2H of microbial phospholipid fatty acids (PLFAs) in soils or peats, even though these stable isotope combinations could provide new insights into soil microbial metabolism. Here, we measured the δ13C and δ2H values of microbial PLFAs in top soils from peatlands, meadows, and woodlands in the Dajiuhu basin, central China. We observed a significant (p < 0.05) positive correlation between the δ13C and δ2H of microbial PLFAs across the three habitats studied here, indicating that central metabolic pathways affect both carbon and hydrogen isotopic compositions of microbial PLFAs. Moreover, our stable isotope data consistently indicate a relatively conservative metabolic state, which is dominated by expected heterotrophic metabolism. The exception to these observations is PLFAs associated with methanotrophs, as these appear to have decoupled carbon and hydrogen isotopes, providing an additional tool for tracing methanotrophic signals. Our results suggest that the carbon and hydrogen dual isotopic composition of microbial PLFAs can not only provide cross-validation for microbial metabolism in natural environments, but as a combined tool can also provide new insights into the perturbation of soil microbial community metabolism. [ABSTRACT FROM AUTHOR]

Aims: Coastal salt marshes are productive ecosystems that are highly efficient carbon sinks, but there is uncertainty regarding the interactions among climate warming, plant species, and tidal restriction on C cycling. Methods: Open-top chambers (OTCs) were deployed at two coastal wetlands in Yancheng, China, where native Phragmites australis (Phragmites) and invasive Spartina alterniflora (Spartina) were dominant, respectively. Two study locations were set up in each area based on difference in tidal action. The OTCs achieved an increase of average daytime air temperature of ~ 1.11–1.55 °C. Net ecosystem CO2 exchange (NEE), ecosystem respiration (Reco), CH4 fluxes, aboveground biomass and other abiotic factors were monitored over three years. Results: Warming reduced the magnitude of the radiative balance of native Phragmites, which was determined to still be a consistent C sink. In contrast, warming or tidal flooding presumably transform the Spartina into a weak C source, because either warming-induced high salinity reduced the magnitude of NEE by 19% or flooding increased CH4 emissions by 789%. Remarkably, native Phragmites affected by tidal restrictions appeared to be a consistent C source with the radiative balance of 7.11–9.64 kg CO2-eq m–2 yr–1 because of a reduction in the magnitude of NEE and increase of CH4 fluxes. Conclusions: Tidal restrictions that disconnect the tidal hydrologic connection between the ocean and land may transform coastal wetlands from C sinks to C sources. This transformation may potentially be an even greater threat to coastal carbon sequestration than climate warming or invasive plant species in isolation. [ABSTRACT FROM AUTHOR]

The Holocene hydroclimate evolution and underlying mechanisms modulating the East Asian summer monsoon (EASM) remains controversial, especially in south eastern China. Here we present a multiproxy peat record of monsoon evolution from southeastern China covering the last 14 ka. Our new records show a relatively weaker EASM but wetter hydroclimate during the early (10 to 8 ka) and late Holocene (after 5.4 ka), while a stronger EASM and overall drier climate during the mid-Holocene (8 to 5.4 ka). In line with nearby speleothem records, our results reveal a dominant control of the northern-latitude ice-sheet meltwater forcing on millennial-scale East Asian hydroclimate variability during the last deglaciation and early Holocene. This dominant influence, however, likely waned once the global sea level had stabilized during the mid-to-late Holocene, giving way to other drivers of the monsoon and hydroclimate, including a combination of summer insolation and teleconnection patterns associated with vegetation-dust feedbacks. [ABSTRACT FROM AUTHOR]

[Display omitted] The goal of achieving carbon neutrality in the next 30–40 years is approaching worldwide consensus and requires coordinated efforts to combat the increasing threat of climate change. Two main sets of actions have been proposed to address this grand goal. One is to reduce anthropogenic CO 2 emissions to the atmosphere, and the other is to increase carbon sinks or negative emissions, i.e., removing CO 2 from the atmosphere. Here we advocate eco-engineering approaches for ocean negative carbon emission (ONCE), aiming to enhance carbon sinks in the marine environment. An international program is being established to promote coordinated efforts in developing ONCE-relevant strategies and methodologies, taking into consideration ecological/biogeochemical processes and mechanisms related to different forms of carbon (inorganic/organic, biotic/abiotic, particulate/dissolved) for sequestration. We focus on marine ecosystem-based approaches and pay special attention to mechanisms that require transformative research, including those elucidating interactions between the biological pump (BP), the microbial carbon pump (MCP), and microbially induced carbonate precipitation (MICP). Eutrophic estuaries, hypoxic and anoxic waters, coral reef ecosystems, as well as aquaculture areas are particularly considered in the context of efforts to increase their capacity as carbon sinks. ONCE approaches are thus expected to be beneficial for both carbon sequestration and alleviation of environmental stresses. [ABSTRACT FROM AUTHOR]

Microbial glycerol dialkyl glycerol tetraethers (GDGTs) in lacustrine sediments are widely used to reconstruct terrestrial paleoenvironments. However, lipids of diverse origin in lakes make it difficult to decipher environmental information, appealing for the necessity to evaluate the impact of terrigenous input on the distribution of GDGTs through long-term monitoring. In this study, we conducted two-year monitoring of GDGTs along the river, estuary, near shore, to the center of Lake Liangzi in central China. By comparing the spatiotemporal changes of GDGT distribution in suspended particulate matter (SPM) and surface sediments, we found that the archaeal isoprenoid GDGTs (isoGDGTs) were mainly produced in situ in the river-lake systems, and not affected by the soil input. In contrast, the bacterial branched GDGTs (brGDGTs) were affected, to some extent, by soil input, depending on the distance to the lakeshore. The soil input of brGDGTs was enhanced during an episode of abnormal rainfall (flood). Moreover, the large variation of isoGDGTs indicates the in situ production under the anoxic condition in lake water. The paired increase in the GDGT-0/Cren ratio and GDGT concentration might be diagnostic of flooding events in ancient times. [ABSTRACT FROM AUTHOR]

[Display omitted] [ABSTRACT FROM AUTHOR]

The composition of microbial communities and their relationship to ocean redox structure in the Precambrian are topics of continuing interest in geobiology. Our knowledge of organismic diversity and environmental conditions during this time are mostly based on fragmentary paleontological and geochemical records and might be skewed accordingly. In North China the Xiamaling Formation (∼1.37 Ga) is characterized by black shales of relatively low thermal maturity ( T max is ∼445 °C) and has been identified as a potential petroleum source rock. To date, however, the biological sources of the organic matter and the environmental conditions prevalent during the deposition of these sediments remain unclear. In this study we analyzed the hydrocarbon biomarker compositions of the Xiamaling Formation shales and a superjacent stromatolitic carbonate in order to shed light on the microbial diversity in the sedimentary environments they represent. The hydrocarbons extracted from both sediments are dominated by low-molecular-weight n -alkanes with a maximum at C 15–18 , suggesting that bacteria and/or algae were primary biotic precursors. Our inability to detect steranes in bitumen I, and only traces of rearranged steranes in bitumen II of black shales, indicates that modern eukaryotic algae were either ecologically insignificant or not preserved due to a taphonomic bias. The high relative concentration of hopanes and diahopanes ranging from C 27 to C 35 , as well as monomethylalkanes, suggests that cyanobacteria may have been the dominant primary producers and could have contributed to the biologically available nitrogen pool through N 2 -fixation. This observation is supported by the low nitrogen isotopic composition of the kerogens. Even though all facies zones appear to have been anoxic but not sulfidic on the basis of biomarker ratios and trace metals, subtle but distinct molecular differences are observed between the stromatolite and the black shales, which can be attributed to both, lithologically-controlled diagenetic rearrangements and differential biotic input. The discrepancy between the presence of a large UCM and high abundances of alkyl lipids on one hand, yet the absence of a stable carbon isotopic offset between lipids and kerogen, on the other, suggests that strong heterotrophic reworking might not be the sole source of the biodegraded fingerprint that is so typical for Proterozoic bitumens, and demands alternative explanations. [ABSTRACT FROM AUTHOR]

The temperature gradient along the altitude transect of Mt. Jianfengling provides a good opportunity to establish and evaluate the microbial lipid-based environmental proxies. The soils collected from 14 different altitudes of Mt. Jianfengling contain abundant microbial fatty acids and fatty alcohols, including iso/ anteiso fatty acids ( i/ aC- i/ aC), 10-Me-C fatty acid, iso/ anteiso fatty alcohols ( i/ aC- iC), 10-Me-C fatty alcohol and unsaturated fatty alcohols, which can indicate a strong microbial activity in the Jianfengling soils. The branched and unsaturated fatty alcohols can be only detected when saponification is performed, implying that these lipids are present as the constituents of bacterial wax esters in the soils. The ratio of aC/ iC fatty acids is positively correlated with altitude, suggesting that the decrease in temperature can induce the increase in the relative abundance of anteiso C fatty acid. In contrast, the ratio of aC/ iC fatty alcohols and of aC/ nC fatty alcohols both decrease with increased altitude or decreased temperature. Similarly, the ratio of nC/ nC fatty alcohols also decreases with decreased temperature, which is opposite to the previous observation that unsaturation of fatty acids in microorganism increases in response to decreased temperature. Besides, the average chain length (ACL) of long chain fatty alcohols (C-C) from leaf waxes and carbon preference index (CPI) of all n-fatty alcohols are also significantly correlated with altitude or mean annual temperature, demonstrating their potential for paleoclimate reconstruction. The correlation of microbial fatty acids and alcohols as well as ACL and CPI of plant wax-derived fatty alcohols with altitude may provide novel ways to reconstruct paleotemperature and paleoaltimetry. [ABSTRACT FROM AUTHOR]

Moisture transportation to (semi-)arid Central Asia is influenced by the interplay of multiple atmospheric circulation patterns. The mechanism underlying the hydroclimate evolution in CA has recently received increasing attention. In northeastern CA, most of the precipitation falls in summer, counter to other westerly-dominated regions of CA where precipitation maximizes in boreal winter. The marine isotope stage (MIS) 3 offers a unique opportunity to examine the mechanisms driving hydroclimate variations during warm periods of the ice age in the CA. However, due in part to reliable proxies for reconstruction, the hydroclimate and vegetation change during MIS3 in northeastern CA have not been well studied. Here, we use grain size and magnetic susceptibility data from the Zeketai loess profile to reconstruct historical shifts in precipitation patterns during MIS3 in the Ili Basin from arid Central Asia (ACA). Notably, abrupt changes around 35 ka are evident in the grain size and magnetic susceptibility records, reflecting a transition to reduced wind intensity and increased aridity. Subsequent analysis of plant leaf waxes (n -alkanes), hydrogen isotopic composition of n -alkanes (δD n -alkane), and stable carbon isotope ratios of total organic carbon (δ13C org) within the loess profile indicates a concurrent shift towards more shrubs, aligning with reduced moisture availability. The δ13C org record further elucidates that during MIS3, the Ili Basin predominantly harbored C 3 vegetation. However, the alteration in δ13C org and δD n -alkane to more positive values at approximately 35 ka substantiates the transition to more drought-resistant vegetation. Furthermore, we link the paleo-hydroclimate variations to the decrease in solar radiation and the strengthening of the Atlantic Meridional Overturning Circulation (AMOC) and Siberian High during late MIS3. This joint influence weakens the Westerly winds and subsequently diminishes the conveyance of moisture to CA. • Loess proxies indicate increased aridity in Central Asia during late MIS3. • Reduced moisture transport to Central Asia linked to stronger AMOC. • Aridification caused an abrupt shift towards more woody vegetation. [ABSTRACT FROM AUTHOR]

Wetlands play a crucial role in the carbon cycle as they are the largest natural source of methane, a potent greenhouse gas. Changes in wetland hydrology can alter the rate of greenhouse gas release from wetlands and have the potential to alter Earth's carbon budget. However, the microbial dynamics underpinning these observations are poorly constrained. Here we combine monitoring of environmental parameters and greenhouse gas fluxes with monthly records of microbial phospholipid fatty acid (PLFAs) δ13C values to probe changes in microbial community and biogeochemistry in response to hydrological changes in a monsoon influenced subtropical wetland from central China. Our results show that water table depth is a key factor controlling the microbial community structure, with Gram-negative bacteria and actinobacteria increasing and fungi decreasing during dry and low water table periods. Meanwhile, the δ13C values of specific PLFAs decreased up to 12‰ during dry compared to wet periods. The extent of depletion varied, but PLFAs from Gram-negative bacteria were most depleted in 13C, indicative for a rapid increase in methanotrophy (methane consumption) during these dry periods. Furthermore, the methane emission of the wetland was drastically reduced and even had negative flux values during dry periods, suggesting that the increased methanotrophy led to a reduced methane flux and a temporary shift of the wetland from a methane source to a methane sink. Our results indicate that short-term hydrological variations lead to a rapid response in microbial community and carbon metabolic activity that directly influences wetland carbon dynamics and greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Abstract: Suspended particulate matter (SPM) was collected above and below the Three Gorges Dam (TGD) on the Yangtze River in May, July and December 2009, respectively, for a study of the spatial and temporal variation in glycerol dialkyl glycerol tetraethers (GDGTs) in the riverine system. The branched GDGTs (bGDGTs) were > 0.6ng/l and isoprenoid GDGTs (iGDGTs) > 0.3ng/l in most SPM samples in May and July, whereas, iGDGTs were on average about 10× more abundant than bGDGTs in December. The results suggest that the abundance of bGDGTs and iGDGTs in the Yangtze River at the TGD varied seasonally, which might be affected by soil runoff and in situ production. Despite these effects, the TEX86-inferred temperature derived from SPM reflected the measured river surface water temperature in the sampling months, suggesting that planktonic Thaumarchaeota might actively make iGDGTs in the river water near the TGD throughout the year. The bGDGT-derived CBT/MBT temperature from the SPM was not significantly different among the three seasons and the values together averaged 15.2±0.7°C, close to the annual mean air temperature (16.9°C) in the region near the TGD. However, the bGDGT-derived pHCBT values were close to the water pH and slightly higher than the pH of the local soil. These results suggest that the sources of bGDGTs in the river water are complicated and that bGDGTs may not solely derive from the local soil runoff. Nevertheless, our study highlights the potential of using TEX86 and MBT/CBT proxies for a better understanding of the source and mechanism of GDGT production in riverine systems increasingly affected by the construction of dams. [Copyright &y& Elsevier]

The article focuses on a study which examined the biodiversity and hydro-ecological selection of testate amoebae from Dajiuhu peatland in Shennongjia, Central China. Samples were collected from microsites within the peatland. Results of the study showed high variations in the morphology of testate amoebae in 136 Sphagnum samples. The study observed that variations in shell morphology can be attributed to different moisture conditions in their habitat.

Abstract: By using gas chromatograph (GC) and GC–mass spectrometry, a series of biomarkers were identified in the aliphatic fractions of extracts from microbialites following the end-Permian faunal mass extinction in Chongyang section, Hubei Province, South China. The dominance of lower-molecular-weight n-alkanes in the samples from the section suggests that algae and bacteria were the dominant contributors to the organic fraction preserved in this marine section, with bacteria particularly enhanced within the stromatolite. The end-Permian biotic crisis coincided with a short-term suppression of autotrophs, indicated by the ratio of pristane (Pr) and phytane (Ph) to C17 and C18 n-alkanes, and proliferation of heterotrophs, shown by the ratio of branched-to-normal C17 alkanes. The biotic crisis also may have been associated with a transient oxygenation event in the shallow marine, indicated by elevated Pr/Ph ratios and lowered C27 18α(H)-22,29,30-Trisnorneohopane (Ts) to C27 17α(H)-22,29,30-Trisnorhopane (Tm) and gammacerane (γ) to C31 homohopane (C31HP) ratios. Subsequently, three short-term episodes of intensified anoxia or enhanced salinity at Chongyang are recorded by decreases in Pr/Ph ratios in conjunction with lithological boundaries in the section. [Copyright &y& Elsevier]

Abstract: A variety of phytoliths, together with prolific microcharcoal particles, sponge spicules and diatoms were extracted and identified in four cultural layers from an archeological site at Jinluojia, Macheng, Hubei Province, Central China. The warmth (Iw) and aridity (Iph) indices calculated from grass phytoliths reveal warm and wet periods during the West Zhou, early East Zhou, Tang and Song Dynasties whilst cool and dry periods occurred during the late East Zhou, Ming and Qing Dynasties. The paleoclimate conditions reconstructed on the basis of grass phytoliths extracted from archeological sediments are in agreement with those from natural sediments in the Middle Yangtze region. In contrast, the woody phytoliths show a positive correlation with microcharcoal particles, suggesting an anthropogenic contribution to the woody phytoliths from the use of woody plants for fuel during cooking and heating. Two episodes of the enhanced abundance of woody phytoliths and microcharcoal particles were found to occur at East Zhou Dynasty and from Ming and Qing Dynasties to the Present, proposed to be a consequence of the population expansion and/or the frequent wars. [Copyright &y& Elsevier]

We report the results of a comparative study of n-alkane biomarkers and pollens in lacustrine and peat deposits at Dingnan, Jiangxi Province in southern China, and discuss the likely causes for the discrepancy in the interpretations of the n-alkane biomarker and pollen records in terms of climate and vegetation change. The results show that past changes in climate and vegetation revealed by the n-alkane record are not always consistent with the pollen assemblage record in the whole section. Biomarkers do not permit direct identification of the plant family and/or genus and mainly record compositions of local plant remains, while pollens mainly reflect the regional vegetation change. Bio-markers and pollen records complement each other, providing a better picture of local and regional environments. Furthermore, biomarkers are more sensitive than pollen to climatic and vegetational change. Several climatic events are clearly identified by the n-alkane biomarker proxies, such as C31/(C27+C29+C 31) ratio and can be correlated to the North Atlantic Heinrich event, B/A, YD and two dry-cool events during the early Holocene such as the periods of 9850 to 9585 cal a B.P. and 8590 to 7920 cal a B.P. These events are consistent with those found in the surrounding regions, suggesting that the regional climate was coupled with global-scale abrupt climatic events. Our results suggest that biomarker and pollen data can record the more detailed climate and vegetation information, thus improving the resolution and precision of vegetation and climate reconstruction. [ABSTRACT FROM AUTHOR]

On the basis of GC and GC-MS analyses, the seasonal variation of leaf lipids is observed in five plant species in Qingjiang in Hubei Province. The CPI values (carbon preference index) of n-alkanes decrease gradually from May to November, though the carbon number distributions and the predominant carbon number in an individual species keep unchanged. The declined CPI values might be caused by the leaf fading, which is further supported by a comparison of the defoliated leaves with the fresh leaves. This observation infers the CPI values of n-alkanes in Quaternary sediments can be used as a tool to index the humification, and thus the climatic and the environmental conditions. The plants analyzed here show a remarkable difference in n-alkanes abundance, suggesting their differential contribution to the n-alkanes identified in sediments. The abundance and the compound species of the n-alkenes detected in the plant leaves change greatly with the seasons due to the influence of temperature, with the least compounds being identified in August. [ABSTRACT FROM AUTHOR]

The policy and practice of ecological restoration and conservation in China obtained some remarkable results. For example, Sphagnum moss growing on abandoned farmland, which was peatland before agricultural use, has rapidly expanded the wetland area in SW China. Microorganisms such as testate amoebae are sensitive to environmental change and thus have been widely used as ecological indicators in various habitats. We analyzed differently aged Sphagnum growing plots on a Sphagnum growing farmland and natural Sphagnum plots in SW China to examine how Sphagnum-dwelling testate amoeba communities and corresponding protozoic silicon (Si) pools respond to ecological restoration practice. We found that abundance, taxon richness, and diversity of testate amoebae were higher in Sphagnum growing farmland plots compared to natural Sphagnum plots. Protozoic Si pools showed an increase with Sphagnum growing time representing increased Si accumulation by idiosomic testate amoeba shells. However, protozoic Si pools were negatively correlated with taxon richness and diversity of testate amoebae. Our results showed that (i) natural Sphagnum plots were not characterized by the expected higher biodiversity of testate amoebae compared to Sphagnum growing plots and (ii) consequently protozoic Si pool quantity in natural Sphagnum plots was less driven by biodiversity of testate amoebae than expected. We concluded our results to underline the value of (i) environmental restoration policy in general and (ii) testate amoeba communities and corresponding protozoic Si pools for Si cycling in restoration areas of peatlands in particular. Based on our results, we recommend a sustainable cultivation of Sphagnum moss and an additional establishment of protected areas, where no Sphagnum harvesting occurs. These protected Sphagnum areas might represent hot spots of undisturbed testate amoeba communities and corresponding protozoic Si pools and thus of microbial Si cycling. [ABSTRACT FROM AUTHOR]

5-n-Alkylresorcinols with alkyl chain lengths varying from C19 to C25 were identified solely in bog-forming plant species classified as sedges (Eriophorum vaginatum, E. angustifolium, Trichophorum cespitosum and Rhynchospora alba). These compounds were then identified throughout the peat deposit on which these plants grow. Total abundances of 5-n-alkylresorcinols were found to reflect macrofossil abundances of sedges in a 40 cm peat profile from Bolton Fell Moss, Cumbria, UK, thereby complementing macrofossil data in palaeoclimate studies. [Copyright &y& Elsevier]

3-Hydroxy fatty acids (3-OH-FAs), derived from Gram-negative bacterial outer membranes, have received recent attention for their potential as new terrestrial pH and temperature proxies for palaeoclimate studies. Initial studies from altitudinal transects of contemporary soils – correlating bacterial 3-OH-FA compositions to air temperature and pH – have shown promising results. But the geographical extent of recent calibrations is limited. In this study, we analyse 3-OH-FA lipid distributions in 186 globally distributed soil samples to study the environmental factors controlling the relative distribution of the 3-OH-FA isomers. Our sample-set covers a wide range of temperatures (−0.4 to 27 °C) and pH (3.6–9.2). For the global compilation we find that the ratio of anteiso to normal 3-OH-FAs of the C 15 or C 17 homologues (RAN 15 or RAN 17) shows a strong linear relationship with mean annual air temperature (MAAT) (R2 = 0.48, p < 0.001 and R2 = 0.41, p < 0.001, respectively). Additionally, the negative logarithm of the ratio of the summed iso and anteiso to the total amount of normal 3-OH-FAs (RIAN) is also strongly anticorrelated with the soil pH (R2 = 0.66, p < 0.001). However, we find that for our 3-OH-FA based proxies there are significant differences in slope and intercept of the linear corrections at regional scales. Thus local or regional calibrations are likely preferable (at this stage of 3-OH-FA proxy development) for application to specific palaeoclimate archives. We also explore the relationship of 3-OH-FA isomer fractional abundances to environmental parameters using machine learning tool (a Gaussian Process (GP) emulator). This confirms the first order relationships to environmental parameters highlighted by the empirical equations and also derives several alternative GP emulator models for reconstructing MAAT and pH which give higher R2 values (0.66 for MAAT; 0.63 for pH) and lower RSME values (3.5 °C for MAAT; 0.76 for pH) compared to simple linear regressions at the global scale. We compare our 3-OH-FA based indices with bacterial branched glycerol dialkyl glycerol tetraethers (brGDGTs) based indices from the same soil samples. At a global scale RAN 15 and RAN 17 show negative correlations with the MBT′ 5ME -MAAT (MBT′ 5ME , methylation index of 5-methyl branched tetraethers) (r = −0.59, p < 0.001 and r = −0.42, p < 0.001, respectively), whilst RIAN shows strong linear correlations with the cyclisation ratio of branched tetraethers (CBT) (r = 0.77, p < 0.001). Similar to 3-OH-FA based temperature proxies, GDGT based temperature proxy MBT′ 5ME also showed different regional calibrations. Our new field-based correlations demonstrate the broad physiological response of Gram-negative bacterial cell membranes to external environmental changes on a global scale. We suggest that 3-OH-FA based proxies have widespread potential for palaeoenvironmental studies to estimate past MAAT and soil pH, but that regional/local and context specific calibrations may need to be applied. [ABSTRACT FROM AUTHOR]