Search

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]

The Hangenberg mass extinction during the Devonian-Carboniferous (D-C) transition represents one of the largest biodiversity losses of the Phanerozoic, while the underlying cause remains controversial. An improved understanding of the contemporaneous sulfur cycle can provide insights into the latest Devonian environmental changes that potentially affected marine biotas. Here, we report on a high-resolution chemostratigraphic study of the sulfur isotopic composition of carbonate-associated sulfate (CAS) through the D-C transition in the Long'an and Qilinzhai sections of South China. The δ34S CAS profiles exhibit a long-term (i.e., >105 yr) negative excursion from +19.0‰ in the upper Lower Si. praesulcata Zone to +13.0‰ in the middle Upper Si. praesulcata Zone, and terminated with a recovery to 20.3‰ in the lower Si. sulcata – Si. duplicata zones, representing a depositional interval of ∼0.9 Myr. In addition, this long-term negative excursion is punctuated by episodic sharp negative shifts. The negative δ34S CAS excursion coincided with the end-Devonian biotic crisis, a positive shift in carbonate δ13C, and negative shifts in bulk-sediment δ15N values and I/Ca ratios. Increasing organic carbon burial indicated by the positive shift in δ13C precludes decreased pyrite burial as an explanation for the negative shift of δ34S CAS , supported by intensified marine anoxia revealed by the negative shifts in δ15N and I/Ca. We attribute the long-term negative shift in δ34S CAS to enhanced inputs of 34S-depleted riverine sulfate in conjunction with low seawater sulfate concentrations within the semi-restricted Yangtze Sea, whereas the transient negative spikes in δ34S CAS were possibly caused by episodic upwelling and oxidation of H 2 S in expanded oceanic oxygen-minimum zones. In conjunction with the positive shift in δ13C, the negative shift in δ34S CAS supports a significant role for enhanced subaerial weathering in intensifying marine anoxia and triggering the biotic crises that occurred during the latest Devonian, the most likely driver of which was the spread of vascular (especially seed-bearing) land plants. • First analysis of δ34S of carbonate-associated sulfate (CAS) in uppermost Devonian. • Long-term (>105 yr) negative δ34S CAS excursion is attributed to enhanced weathering. • Episodic transient negative δ34S shifts possibly caused by oxidation of rising H 2 S. • Ultimate driver was intensified chemical weathering linked to vascular plant spread. [ABSTRACT FROM AUTHOR]

Highlights a series of large-medium scale gold deposits in the Upper Triassic of Northwest Sichuan. Description of the Triassic Zagunao Formation; Fossils discovered in the Dongbeizhai-Chuanzhusi-Dabo Triassic.

[Display omitted] [ABSTRACT FROM AUTHOR]

Microorganisms and associated membrane lipids exhibit a remarkable sensitivity to ambient environmental fluctuations, rendering them invaluable for deciphering changes in the past environment. Among these lipids, 3-hydroxy fatty acids (3-OH-FAs), prevalent in the membrane of Gram-negative bacteria, have been recently developed as promising tools for palaeo-temperature and palaeo-pH reconstruction. Recent studies suggested that different mechanisms might cause the observed correlations of 3-OH-FAs with temperature or pH, and bacterial community variation is likely an important explanation for the pH-related correlation. Despite this, direct examinations of the role of the Gram-negative bacterial community in influencing the distribution of 3-OH-FAs and, consequently, impacting the 3-OH-FA-based pH proxies are notably absent in current literature. In this study, we collected acidic, neutral, and alkaline soil samples from Mt. Fanjing, Haozhuzi Cave's overlying soil, and Chenghai Lake's lakeside area in China, respectively, with pH ranging from 3.53 to 10.63. These sites display pronounced pH gradients while showing limited variation in other environmental parameters, such as mean annual air temperature (MAAT). We found that soil pH significantly influences the bacterial community and 3-OH-FA distribution. Furthermore, we observed that the Gram-negative bacterial community primarily comprises Proteobacteria, Acidobacteria, and Bacteroidetes, with each phylum exhibiting a distinct capacity for synthesising specific 3-OH-FAs. These findings suggest that fluctuations in soil pH drive shifts in the abundance of these phyla, thereby inducing alterations in soil 3-OH-FA distribution. Hierarchical partitioning further numerically emphasises the important role of community dynamics in shaping 3-OH-FA distribution. Therefore, in addition to membrane adaptation, changes in Gram-negative bacterial community under strong pH stress will significantly influence the distribution of 3-OH-FAs, consequently influencing the related pH proxies. • Both soil pH and MAAT show significant control on the 3-OH-FA distribution. • Soil pH is the primary determinant of the G− bacterial community composition. • Changes of G− bacterial community show a significant impact on 3-OH-FA distribution. [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]

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]

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]

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]

Arbuscular mycorrhizal fungi (AMF) is presumably to be associated with carbon sequestration and nutrient acquisition through mineral weathering in wetland ecosystems. However, information on AMF‐carbon‐weathering interactions is limited. Grain size, concentrations of nutrients, and the major components of 304 surface sediment samples and glomalin‐related soil protein (GRSP) in 133 surface sediment samples were analyzed in various environments, including the upper delta plain wetlands (UDPW) and its adjacent shallow sea wetlands (SSW), to evaluate the relationship among the GRSP, carbon content, nutrients, and chemical index of alteration (CIA) in the wetlands of the Liaohe Delta (LHD). The concentrations of GRSP in surface sediments ranged between ~ 0.11 and 11.31 mg g−1, with an average of 2.30 ± 0.17 mg g−1, and were significantly affected by the vegetation types. The ratios of organic carbon in GRSP (GRSP‐C) to soil organic carbon (SOC) varied from 0.71% to 25.34%, with an average of 10.34% ± 0.52%, indicating that the GRSP was an important carbon pool in sediments, and the carbon dynamics in these wetlands were closely related to human activities. Moreover, the CIA values ranged from ~ 18.97 to 68.75, and were significantly higher in the UDPW than in the SSW (p < 0.05), and were significantly correlated with the concentrations of GRSP (r2 = 0.22 [r = 0.43], p < 0.01). Meanwhile, both the CIA and GRSP were significantly correlated with SOC, Total Nitrogen, and Fe (r2 > 0.17 [r > 0.41], p < 0.01). The results indicate that AMF excursions in wetland ecosystems enhance carbon sequestration and mineral weathering, and in turn they alter retention of at least some nutrients. [ABSTRACT FROM AUTHOR]

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial membrane lipids that have been widely used as tools for the quantitative reconstruction of past terrestrial temperatures in lakes. Two approaches, i.e., regional/global and site-specific calibrations, have been previously employed in the reconstruction. However, their strengths and weaknesses have not been properly evaluated yet, making it challenging to choose a suitable approach to paleoreconstruction. Here, we investigated the distribution of brGDGTs in surface sediments of 65 lakes along a mean annual lake water temperature (MLWT) transect in West China and developed a regional MBT' 5ME (methylation degree of 5-methylated brGDGTs) calibration for MLWT reconstruction. Meanwhile, a site-specific brGDGT calibration for Lake Yangzonghai (YZH), located within the West China transect, was generated based on the relationship between the instrumental temperature record over the past 100 years and individual brGDGT abundances in a short sediment core taken from the lake. These two calibrations were applied to global lake surface sediments, as well as a long sediment core spanning the Holocene from Lake YZH. The linear correlations between MBT' 5ME and temperature are highly consistent among lakes from different regions, indicating the near-universal response of brGDGTs in global lakes to temperature. However, MLWT inferred from the site-specific calibration shows a weak relationship with actual MLWT in global lakes, indicating that the site-specific calibration might be only a result of overfitting rather than reflecting the response of brGDGT distribution to ambient temperature. Applications to a Holocene sediment core in Lake YZH suggest that the regional MBT' 5ME calibration is more suitable for reconstructing paleotemperature than the site-specific calibration. The regional MBT' 5ME calibration derived temperature record shows a cold Younger Dryas (YD), followed by a rapid warming of ∼3 °C during the last deglaciation, and a long-term cooling of ∼1 °C from 9.9 to ∼0.2 cal ka BP. The principal component analysis shows that temperature is the dominant factor affecting brGDGT distributions in the long sediment core whereas the site-specific calibration is strongly affected by human activities rather than reflecting the ambient temperature. We highlight the importance of using appropriate approaches to developing calibrations for paleotemperature reconstruction and assessing the reliability of the temperature records. • Strong correlation between MBT '5ME and temperature for lakes in West China. • Systematic comparison regional calibration and site-specific calibration of brGDGTs. • Site-specific calibration fails to reflect the response of brGDGT distribution to temperature. • Regional MBT '5ME calibration is more suitable to reconstruct paleotemperature. • PCA can be used to verify the reliability of reconstructed temperature results. [ABSTRACT FROM AUTHOR]

Although the trajectory of the marine mass extinction at the ∼252-Ma Permian-Triassic (P-Tr) boundary has been well studied, details of the coeval collapse of terrestrial ecosystems remain murky. Here, we use hydrocarbon biomarker compositions and other geological records (i.e., organic carbon isotopes (δ 13 C org), charcoal abundance, and Hg content) from a tropical peatland succession in southwestern China to reconstruct in detail the history of terrestrial ecosystem collapse during the P-Tr crisis. Our high-resolution hydrocarbon biomarker records reveal that this collapse proceeded in a stepwise manner with increasing intensity as the crisis unfolded. We recognize three discrete crisis stages: Stage I within the uppermost Xuanwei Formation and Stages II and III within the lowermost Kayitou Formation. Stage I, the early crisis stage, is marked by a significant decline in terrestrial biomass (continuing into the later stages), as recorded by reduced C 29 steranes relative to total steranes and a concomitant reduction in the ratio of pristane to phytane (Pr/Ph). Stage II, the main crisis stage, records intensified soil erosion and sediment flux as revealed by rising dibenzofuran (DBF) content and high hopane/sterane ratios, the disappearance of coal seams, a sharp negative shift in δ 13 C org , and peak concentrations of charcoal reflecting increased wildfire incidence. Stage III, the late crisis stage characterized by enhanced soil erosion, corresponds to peak values of Hg and Hg/TOC but no charcoal peak, suggesting intensified volcanism and a return to a humid climate. These stages closely follow temperature records, which show a stepwise rise during the crisis interval, implying that the deforestation process was strongly influenced by punctuated rises in temperature and/or its attendant effects (e.g., climate aridification). This P-Tr transition scenario suggests that global warming can trigger deforestation and reduce terrestrial carbon storage, thus serving as a positive climate feedback, with important implications for present-day climate change. • Three stages of terrestrial crisis are recognized during P-Tr in South China. • Plant biomass was decreased and soil erosion was enhanced during P-Tr crisis. • The crisis of the terrestrial and marine ecosystems can be well correlated. • Rising temperature played a substantial role in the terrestrial crisis. [ABSTRACT FROM AUTHOR]

Abstract Lipids can survive long geological intervals within sediments and provide a unique tool that allows the reconstruction of past organismic diversity and environmental conditions. The lipids discussed in this review include all substances produced by organisms that are insoluble in water but extractable by organic solvents. Lipid biomarkers refer to both functionalized biolipids as well as their hydrocarbon derivatives in geological materials that contain diverse information about biotic sources and environmental conditions. In spite of diagenetic and catagenetic alteration, lipid biomarkers commonly preserve the hydrocarbon structure of their biotic counterparts and have been found in rocks up to 1.6 billion years in age. These features have promoted the use of lipid biomarkers in many fields, including petroleum geology, paleoclimatology, oceanography, meteorology, geobiology and environmental science. Here, we (i) review the use of lipid biomarker records for the reconstruction of environmental conditions in deep time, including climatic conditions (temperature), sedimentary environments (redox, salinity and chemical composition) as well as catastrophic terrestrial events (soil erosion and wildfire), and (ii) generate new insights into environmental perturbations during the Permian-Triassic transition based on investigation of lipid biomarkers. We further propose that the ratio of dibenzothiophene to phenanthrene (DBT/P) in marine carbonates may be a robust proxy for seawater sulfate concentrations in deep time. Our compiled DBT/P records show substantial variations in seawater sulfate levels through Earth history that are consistent with the results of other proxies. We discuss the future outlook for application of lipid biomarker records to deep-time environmental research. [ABSTRACT FROM AUTHOR]

Abstract Floral communities in terrestrial habitats such as steppes are highly sensitive to regional climate changes. Here, we generated carbon and nitrogen isotope profiles for soil organic matter (SOM) in the Weinan loess-paleosol section in order to investigate changes in floral communities on the Chinese Loess Plateau (CLP) and their relationship to climate variation since 75 ka. δ13C SOM at Weinan ranges from −23.6 to −18.0‰ and δ15N SOM ranges from +3.4 to +5.5‰. Modeling based on the δ13C SOM record suggests that the proportion of C4 plants (%C4) has varied from lower during cold intervals (with minima of 24–32% at 73.1 ka, 20.9 ka (LGM), and 0.6 ka) to higher during warm intervals (with maxima of 62–64% at 53.0 ka and 8.2 ka). The δ13C SOM and δ15N SOM profiles are strongly correlated (r = +0.82; p(α) <0.001), suggesting that the N-isotope composition of SOM was also largely controlled by inputs of C4 versus C3 plants, consistent with known patterns of N-isotope variation among modern plants. The %C4 profile exhibits significant covariation with reconstructed mean annual temperatures (MAT) (r = +0.42; p(α) <0.001), mean annual precipitation (MAP) (r = +0.42; p(α) <0.001), and summer monsoon intensity (r = +0.50; p(α) <0.001), suggesting that paleovegetation was controlled by each of these climate variables to a degree. Comparing the Weinan record to SOM profiles across the CLP region, we identified three zones of varying monsoonal influence, with the East Asian Summer Monsoon (EASM) exerting the strongest influence on the southeastern margin of the CLP, and the East Asian Winter Monsoon (EAWM) greater influence on its northwestern margin. This paper provides new insights into deciphering paleovegetation patterns and their links to paleoclimate change on the basis of paired C- and N-isotope records. Highlights • Analysis of δ13C and δ15N of soil organics in Weinan section, Chinese Loess Plateau • δ13C SOM and δ15N SOM profiles exhibit strong correspondence since 75 ka • Both C- and N-isotope compositions controlled mainly by inputs of C3 vs C4 plants • Paleovegetation type strongly influenced by summer monsoon intensity [ABSTRACT FROM AUTHOR]

Terrestrial organic carbon (OC) could be transported to marginal oceans by large rivers and deposited under different hydrological conditions. A mixture of the fresh & lithospheric OC, superimposed by the OC from different rivers, makes it challenging to distinguish sources and contributions of terrestrial OC. Here, we employed multiple geochemical proxies, including the hydrogen isotopic composition of leaf wax (δD wax), the carbon isotopic composition of total organic carbon (δ13C org), TOC/TN ratio, and major element distributions, to investigate the variability in sources of terrestrial OC in the Yangtze River Estuary (YRE) since 1270 CE. Our results revealed that the terrestrial OC deposition in the YRE was lower before 1950 CE and considerably increased after 1950 CE. The δD wax record in core A3 indicates that the OC deposition in the YRE was primarily modulated by the variability of El Niño-Southern Oscillation (ENSO) and East Asia Summer Monsoon. The strengthened El Niño-like state since 1600 CE resulted in increased precipitation in the middle and lower reaches of the Yangtze River basin and in turn, affected the terrestrial OC deposition in the YRE. Several episodes with lower carbon preference index (CPI) values of n -alkanes (CPI < 3) were identified. These episodes were concurrent with the streamflow shift of the ancient Yellow River during the transitions from wet to dry conditions, highlighting the potential contribution of the ancient Yellow River to the aged OC deposition in the YRE. • Geochemical proxies and lipid biomarkers were used to constrain the OC source. • ENSO regulates the organic matter deposition in the Yangtze River estuary. • Extreme lower CPI values reveal the aged OC from the ancient Huanghe River. [ABSTRACT FROM AUTHOR]

The patterns and mechanisms of Holocene temperature variability in China remain highly controversial, possibly due to the lack of sufficient high-resolution records and few systematic compilations and reviews of published records. Here, we used branched glycerol dialkyl glycerol tetraethers (brGDGTs) to generate a Holocene mean annual air temperature (MAAT) record from Lake Yangzonghai (YZH) in southwest (SW) China. Our record, largely ruling out the effect of seasonal bias, displays a long-term cooling of ∼1.5 °C since 10 cal ka BP, indicating that the discrepancy of Holocene temperature records (such as long-term cooling vs warming trends) in China cannot be attributed to the seasonal bias in temperature proxies. We compiled 67 published Holocene temperature records from China. These temperature records exhibit a mathematically consistent pattern with a relatively warmer mid-Holocene and colder late Holocene in the Asian summer monsoon (ASM) domain, whilst records show a relatively colder mid-Holocene and warmer late Holocene in the westerlies domain. This spatial heterogeneity of Holocene temperature variability is attributed to the modulation of monsoon systems, including the warming effect of ASM and the cooling effect of the East Asian winter monsoon (EAWM). In the ASM domain, the dominant pattern with the relatively warmer mid-Holocene and colder late Holocene is primarily controlled by the persistent weakening of the warming effect of the ASM and the concurrent strengthening of the cooling effect of the EAWM during the mid-to-late Holocene. In the westerlies domain, the warming effect of the ASM disappears, the cooling effect of the EAWM is confined to the north of the Tibetan Plateau due to the blocking effect of the Tibetan Plateau. This dominant pattern with the relatively colder mid-Holocene and warmer late Holocene is driven by the increases in atmospheric greenhouse gases (GHG) radiative forcing and Northern Hemisphere Annual Insolation (NHAI) forcing during the mid-to-late Holocene. • Long-term cooling of ∼1.5 °C since 10 cal ka BP recorded by brGDGT-based MAAT reconstruction. • Systematic compilation and review of 67 published Holocene temperature records from China. • Spatial heterogeneity of Holocene temperature variability between ASM and westerlies domains. • Monsoon systems control the trend of Holocene temperature variability in China. [ABSTRACT FROM AUTHOR]

Widespread oceanic anoxia marked by globally extensive deposition of organic-rich black shale during the Late Devonian was a major factor in the mass extinctions at the Frasnian-Famennian (FFB, ∼372 million years ago) and Devonian-Carboniferous boundaries (DCB, ∼359 million years ago), although the triggers for these deoxygenation events are still under debate. Here, we apply a novel paleoredox proxy, Hg isotopes, to investigate Late Devonian ocean redox variation and its causes. We found no Hg enrichments in North America across either the FFB or DCB, thus arguing against the hypothesis of global-scale volcanism as the trigger for Late Devonian environmental and biotic crises. Gradual negative shifts of both mass-independent fractionation (Δ 199 Hg) and mass-dependent fractionation (δ 202 Hg) occurred between the FFB and DCB, suggesting a progressive increase of Hg inputs associated with terrestrial organic matter. Moreover, multiple abrupt negative excursions of Δ 199 Hg (down to −0.19‰) along with concurrent positive shifts of δ 202 Hg occurred just above the FFB and across the DCB, providing strong evidence for recurrent photic-zone euxinia (PZE) that was preceded by increasing terrestrial inputs in the epicontinental seas of North America. We suggest that the increase of terrestrial inputs of nutrients, probably via expansion of vascular land plants, stimulated marine primary productivity and eventually PZE, which may have been a key kill mechanism for the Late Devonian mass extinction. • High-resolution Hg analysis of Frasnian-Famennian (FFB) and Devonian-Carboniferous (DCB) boundaries. • Lack of Hg enrichment does not support LIP eruptions during FFB and DCB biocrises. • Negative shifts of Δ 199 Hg (MIF) and δ 202 Hg (MDF) reflect rising terrigenous Hg inputs prior to the DCB. • Hg isotopes document photic zone euxinia (PZE) triggered by increased nutrient fluxes. • Hg isotopes are novel proxies of both PZE and terrestrial erosion. [ABSTRACT FROM AUTHOR]

The cause of the Triassic-Jurassic (Tr-J) boundary biotic crisis, one of the ‘Big Five’ mass extinctions of the Phanerozoic, remains controversial. In this study, we analyzed multiple sulfur-isotope compositions (δ 33 S, δ 34 S and δ 36 S) of pyrite and S py /TOC ratios in two Tr-J successions (Mariental, Mingolsheim) from the European Epicontinental Seaway (EES) in order to better document ocean-redox variations during the Tr-J transition. Our results show that upper Rhaetian strata are characterized by 34 S-enriched pyrite, low S py /TOC ratios, and values of Δ 33 S py (i.e., the deviation from the mass-dependent array) lower than that estimated for contemporaneous seawater sulfate, suggesting an oxic-suboxic depositional environment punctuated by brief anoxic events. The overlying Hettangian strata exhibit relatively 34 S-depleted pyrite, high Δ 33 S py , and S py /TOC values, and the presence of green sulfur bacterial biomarkers indicate a shift toward to euxinic conditions. The local development of intense marine anoxia thus postdated the Tr-J mass extinction, which does not provide support for the hypothesis that euxinia was the main killing agent at the Tr-J transition. Sulfur and organic carbon isotopic records that reveal a water-depth gradient (i.e., more 34 S-, 13 C-depleted with depth) in combination with S py /TOC data suggest that the earliest Jurassic EES was strongly stratified, with a chemocline located at shallow depths just below storm wave base. Shallow oceanic stratification may have been a factor for widespread deposition of black shales, a large positive shift in carbonate δ 13 C values, and a delay in the recovery of marine ecosystems following the Tr-J boundary crisis. [ABSTRACT FROM AUTHOR]

Signals indicative of paleo-seawater rare earth element (REE) composition and microbial activity were identified in marine ooids from the Lower Triassic of South China using in situ laser ablation–inductively coupled plasma-mass spectroscopy (LA-ICP-MS) together with petrographic and isotope geochemical techniques. Quantitative trace element profiles were generated across successive growth laminae in the cortices of selected ooids. The shale-normalized REE and yttrium (Y) data of these layers show 1) light rare earth element depletion (mean La SN /Yb SN = 0.36 ± 0.14), 2) positive La anomalies (mean (La/La*) SN = 2.02 ± 1.25), and 3) high ratios of Y/Ho (mean 53 ± 12), which are similar to modern seawater compositions and Bahamian ooids. These findings imply that ooids in the study samples faithfully record Early Triassic paleo-seawater chemical signals such as REE + Y distributions. Petrographic observations revealed dark-colored layers with intense fluorescence containing structures that resemble microbial filaments or extracellular polymeric substances. These layers also possess more enriched REE compositions and higher concentrations of nutrient-like elements (e.g., Zn and Ba) than adjacent recrystallized light-colored laminae. Most ooid laminae contain negative Ce anomalies indicative of a well-oxygenated environment of formation, but some laminae have minimal negative anomalies suggesting the influence of suboxic porewater conditions. The present study provides a new perspective on the role of microbes in ooid genesis and on the utility of ooids as proxies for paleo-seawater chemistry. [ABSTRACT FROM AUTHOR]

The incursion of euxinic waters into the ocean-surface layer is hypothesized to have been an important killing agent during the end-Permian mass extinction. However, both the causes and extent of oceanic euxinia during this crisis remain poorly known, making assessment of its role in the mass extinction difficult. Here, we document the distribution of aryl isoprenoids (AIs), which are biomarkers of obligate anaerobic green sulfur bacteria (Chlorobiaceae) that are indicative of photic-zone euxinia, in 12 Permian-Triassic Boundary (PTB) sections with a wide distribution globally. Profiles of AI abundance for the 12 study sections show significant spatio-temporal variation. No AIs were identified in the shallowest sections, but AIs are present both prior to and following the mass extinction in intermediate-depth sections and following the mass extinction in deep-water sections. This pattern suggests a combination of upward and oceanward expansion of photic-zone euxinia during the PTB crisis, possibly fueled by elevated riverine nutrient fluxes as a consequence of climatic warming, terrestrial ecosystem destruction, and enhanced erosion. This hypothesis is supported by the close association of AIs with elevated abundances of moretanes and dibenzofuran (DBF), which are biomarkers for terrestrial erosion. Expansion of oceanic euxinia at intermediate water depths may have established a long-term reservoir that fed episodic incursions of H 2 S-bearing waters into shallow-marine environments, delaying the recovery of marine ecosystems during the Early Triassic. The biomarker records of the present study thus provide significant evidence of terrestrial-marine linkage during the PTB crisis. [ABSTRACT FROM AUTHOR]

• Branched relative to normal C 15 alkanols (BNA 15) was tested as a temperature proxy. • BNA 15 was evaluated with 129 samples from 18 globally distributed peatlands. • BNA 15 in surface peats correlates with temperature, with a minor influence from pH. • Branched alkan-1-ols are enriched at the acro/catotelm boundary. • BNA 15 in catotelm correlates with MAAT. The BNA 15 biomarker proxy, which reflects the relative abundance of the branched over the normal C 15 alkan-1-ols, was recently proposed as a novel terrestrial paleothermometer and applied to ancient peat deposits to reconstruct past temperature variations across the Holocene. However, to date, a peat-specific calibration for this novel temperature proxy does not exist. Here we analyzed a set of surface and downcore peat samples from Chinese peatlands with a broad range in mean annual air temperature (MAAT) (–3.2 °C to 18.5 °C) and pH (4.7 to 8) to understand the relationship between the BNA 15 proxy and temperature in peat deposits. Downcore samples from three peatlands outside China were also obtained to test its wider applicability. Our results show that the variations in BNA 15 across multiple surface samples from a single peatland are relatively large, suggesting that we must be careful with the application of BNA 15 to reconstruct small amplitude temperature variations. In addition, the BNA 15 changes significantly with depth, with higher values in the anoxic catotelm in mid/low latitude peatlands and slightly higher values in the oxic acrotelm in high latitude/altitude peatlands. Combined with concentrations of alkan-1-ols in a subtropical peat core retrieved from central China, we propose that branched alkan-1-ols are predominantly produced at the acrotelm-catotelm boundary. BNA 15 has a moderate correlation with the growth temperature (including the months that the daily temperature is over 0 °C) in surface peat samples. In contrast, a strong positive correlation exists between BNA 15 and MAAT using catotelm samples from Chinese peatlands (MAAT = 2.03 × BNA 15 – 2.33; R2 = 0.95, p < 0.01, RMSE = 2.3 °C). We find no clear correlation between BNA 15 and pH in the surface peat samples. The application of the BNA 15 index to two forest/woody wetlands from outside of China highlights that care should be taken when applying this index in these environments. [ABSTRACT FROM AUTHOR]

Droughts and floods caused by extreme hydroclimatic events in East Asian monsoon area often have serious effects on human society. The Poyang Lake region has always been one of the most severe floods and droughts in East China. In order to explore the relationship between monsoon climate change and occurrence of drought/flood, this study rebuilt a high-resolution (~ 10 yr) of temperature and aridity change history of the past 1000 years. Phytolith assemblages together with the climatic indices revealed 3 phases of paleoenvironmental changes over the last millennium: (1) Medieval Warm Period (MWP) during 900–1370 AD witnessed increased monsoon precipitation and frequent floods corresponding to strong El Niño–like state; (2) Little Ice Age (LIA) during 1370–1800 AD experienced severe droughts coupling with decreased monsoon precipitation and intensive La Niña–like state; (3) Current Warm Period (CWP) during 1800–2003 AD encountered highly frequent floods related to the increased monsoon precipitation modulated by strong El Niño–like state. Our results confirmed that there is a connection between solar irradiance, ENSO activity and monsoon precipitation in the subtropical East China. On interannual-decadal timescales, due to the modulation of ENSO on the location of the Western Pacific Subtropical High (WPSH) and Meiyu Belt, the occurrences of droughts and floods affected by ENSO-related monsoon precipitation has significantly affected not only the sedimentary environment, but also human activities, which is significant for the prediction of future prevention of droughts and floods in the East Asian monsoon region against the background of global warming. • Medieval Warm Period witnessed increased monsoon precipitation and frequent floods. • Little Ice Age experienced severe droughts and decreased monsoon precipitation. • Drought and flood occurrences were modulated by ENSO-related monsoon precipitation. [ABSTRACT FROM AUTHOR]

The mineral protection of microbial necromass is critical for soil carbon stabilization. The water impact on the interactions between minerals and microbial necromass, however, remains unclear due to a lack of proper methods to quantify the mineral-protected microbial necromass. Here, we used offline hydrous pyrolysis to release the archaeal necromass—isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) bound to clay minerals by heating samples at increasing temperatures (150, 200, 250, 300, and 350 °C) under argon atmosphere. The content of extractable isoGDGTs in soils reached the maximum at 200–250 °C, indicating the release of bound isoGDGTs. By investigating the free and bound isoGDGTs along a soil transect with increasing soil water content (SWC), we found that the portion of bound isoGDGTs reached up to 97% of total isoGDGTs in dry soils, and decreased with increased SWC, suggesting that SWC controls isoGDGT stabilization on clay minerals. This relationship was confirmed in the soils from the Northeast China Transect, where the proportion of bound isoGDGTs decreased with increased mean annual precipitation from 160 to 814 mm. Such a connection was further supported by the water-saturated samples of the lake and marine sediments, which have a much lower proportion of bound lipids than the soils. The decrease of bound lipid portion with increasing water content is related to the lower attachment of microbial cells to minerals in wetter soils. Microbial cells are more strongly attached to the mineral phase under drier conditions due to the thin water film on the mineral surfaces. In addition, microorganisms secrete more extracellular polymeric substances under drier conditions, which reinforces the interactions between microbial-derived organic matter and minerals. The increased microbe-mineral interactions under drier conditions offer more stable microbial legacies and stabilize organic matter in the (semi)arid regions. • Mineral-bound archaeal lipids were released using offline pyrolysis. • Bound archaeal lipids could account for 97% of total archaeal lipids in soils. • The proportion of bound archaeal lipids negatively correlated with soil water content. • Aridity favors the preservation of archaeal necromass in soils. [ABSTRACT FROM AUTHOR]

The Late Ordovician was a critical interval in geologic history, during which both the biosphere and marine environments underwent severe perturbations, including one of the ‘Big Five’ Phanerozoic mass extinctions and the massive but short-term (~ 0.5-Myr) Hirnantian glaciation. The onset and termination of the Hirnantian glaciation have been widely accepted as the triggers for the two extinction pulses that comprise the Late Ordovician biocrisis, but the mechanisms that caused the Hirnantian glaciation itself remain poorly known. Here, we analyze the nitrogen isotope composition (δ 15 N) of two sections in South China (Wangjiawan and Nanbazi) in order to better understand nitrogen cycle perturbations in the Late Ordovician ocean and their relationship to contemporaneous climatic and biogeochemical changes. Low δ 15 N (~ 1‰) in the upper Katian and lower Rhuddanian of both sections suggests intensive (i.e., near-quantitative) denitrification and, thus, nitrogen fixation as the main source of biologically available nitrogen for primary producers. A positive δ 15 N excursion in both sections during the Hirnantian indicates weaker (i.e., non-quantitative) denitrification, possibly as a result of more vigorous thermohaline circulation and improved ocean ventilation. Weaker denitrification would have reduced the flux of N 2 O, an intermediate product of denitrification, to the atmosphere. N 2 O is a potent greenhouse gas, and a major decline in its production would have led to cooler climatic conditions and, ultimately, the Hirnantian glaciation. A global survey of published nitrogen isotope records suggests that similar processes operated broadly within the Late Ordovician global ocean. [ABSTRACT FROM AUTHOR]

• Modern carbon dynamics of peatland were tracked. • A critical water table depth level was proposed using the nonlinear models. • The mechanism of critical WTD level for ecological function shifts was analyzed. • Paleoecological records supported the critical WTD level. Peatlands, one of the largest biosphere carbon reservoirs, are facing climate change induced water-table drawdown and carbon loss. To provide insights into peatland protection and carbon–water cycle under the background of global change, the detailed relationship between peatland ecology and water table depth (WTD) should be considered. In this study, we focused on carbon flux and synthesized datasets on WTD, carbon dynamics, vegetation and microbiologic activities in the Dajiuhu Peatland to better understand the ecological response to the hydrological variations. Based on modern monitoring, the daily CH 4 emission decreased and CO 2 emission increased with the fall of the WTD. When the WTD was deeper than 30 cm, daily carbon sequestration reduced until it approached 0 according to nonlinear models. By comparisons with previous spatial soil TOC, vegetation and microbiologic surveys, we proposed that approximately 30 cm is a critical WTD level (turning point or zone) affecting the structure and function of peatland ecosystems. Prolonged and severe droughts might trigger an ecological shift of peatland because increase in oxygen availability and decrease in water availability are not able to meet the physiological needs of living organisms, which further decreases CH 4 emission due to limited methanogenesis and enhanced methanotrophy and weakens carbon sequestration through enhanced litter decomposition. This was also confirmed by palaeo-ecological records. In particular, precipitation-induced declines of WTD (WTD > 30 cm) during 9,500–9,200 cal yr BP, 6,000–4,000 cal yr BP and 3,600–3,200 cal yr BP caused a series of ecological changes, including the decreases in wet-preferred Sphagnum and herbs, enhanced aerobic bacteria activities and ecosystem respiration, and changed soil carbon sequestration. Drought during 6,000–4,000 cal yr BP induced low carbon sequestration. However, rapid vegetation succession and peat accumulation caused by the abrupt hydrological variations during 9,500–9,200 cal yr BP and 3,600–3,200 cal yr BP might have resulted in temporary increases in carbon sequestration. Our results demonstrate that WTD is crucial to the regulation of peatland ecological functions. This finding offers references for peatland carbon–water cycles and management. [ABSTRACT FROM AUTHOR]

• Peatland degradation caused a significant loss of testate amoeba (TA) biodiversity. • Unexpectedly, this loss was accompanied by an increase in TA biosilicification. • TA biodiversity was not coupled to protozoic biogeochemical silicon (Si) cycling. • New insights into microbial biogeochemical Si cycling on a continental scale. Anthropogenic peatland degradation is a global threat. As peatlands store large amounts of carbon (C) their potential for mitigation of climate change has been emphasized recently. Global C cycling is linked to silicon (Si) fluxes from the continents into the oceans. These fluxes in turn are driven by biosilicification, the incorporation of inorganic Si into living organisms, in terrestrial ecosystems. Biosilicification by testate amoeba (TA) communities and its potential for Si cycling has been highlighted since the beginning of the 21st century. However, the effects of peatland degradation on TA biodiversity and corresponding protozoic biosilicification on a continental scale remained unresolved so far. We show that TA biodiversity in Asian peatlands is strongly affected by the grade of human impact. This biodiversity decline was accompanied by an unexpected increase in protozoic biosilicification. Our findings provide new insights into the interactions between the biodiversity of soil microorganisms and biogeochemical Si cycling. [ABSTRACT FROM AUTHOR]

Char and polycyclic aromatic hydrocarbons (PAHs), which can serve as proxies for wildfire frequency and/or intensity, are widely present in Permian-Triassic boundary (PTB) strata, providing information on volcanism or on climatic control of fuel availability (linked to vegetation type and density) or combustibility (linked to aridity). Here, we present evidence to separate temporal from geographic signals of climate impact on wildfire during the Permian-Triassic (P-Tr) transition. Geographically, char and pyrolytic PAHs for wildfire are concentrated in temperate and tropical regions and show a connection with forest distribution as reflected by occurrences of Upper Permian coals. Temporally, the subtropical terrestrial Dalongkou section of northwestern China provides evidence of two intervals of increased pyrolytic PAHs of combustion origin. The first interval was linked to climatic hyperwarming during the latest Permian, whereas the second interval was associated with rapid climatic drying, as recorded by spore-to-pollen ratios (S/P), during the P-Tr transition. This record suggests that rapid climate change during the P-Tr transition increased wildfire frequency. A climate link is also shown by turnovers of ostracods, conchostracans, and charophytes in conjunction with greater wildfire frequency. The trigger for enhanced wildfires and biotic changes is inferred to have been volcanically induced climatic warming and aridification. Our data thus document important links between wildfires, climate change, volcanism, and mass extinction during the P-Tr transition. • Pyrolitic PAHs document increased wildfire frequency during the P-Tr transition. • Wildfire distribution strongly correlated to tropical/temperate forested regions. • Two intervals of enhanced wildfire frequency coincided with end-Permian biocrisis. • Increased wildfire linked to volcanically induced climate warming and aridification. • Rapid climate change during end-Permian contributed to increase wildfire frequency. [ABSTRACT FROM AUTHOR]

Multiple-sulfur isotope compositions ( 32 S, 33 S, 34 S and 36 S) were analyzed for paired carbonate-associated sulfate (CAS) and disseminated pyrite (PY) from the ∼1.6-Ga Gaoyuzhuang Formation of the North China Craton to reconstruct the history of sulfate levels in Proterozoic oceans. The 200-m-thick study interval yielded relatively constant values for δ 34 S CAS (13.0 ± 1.8‰), δ 34 S PY (8.0 ± 2.3‰), and Δ 34 S CAS-PY (∼5‰), as well as relatively constant Δ 33 S (0 ± 0.05‰) and Δ 36 S (0.35 ± 0.15‰) for both CAS and pyrite. Limited variation in δ 34 S PY and slightly lower Δ 33 S of pyrite relative to CAS suggest water-column precipitation of pyrite. Limited fractionation of sulfur during microbial sulfate reduction (as documented by Δ 34 S CAS-PY ) implies low seawater sulfate concentrations in the early Mesoproterozoic ocean. We quantitatively constrained paleo-seawater [SO 4 2− ] using a novel modeling approach based on measured values of Δ 34 S CAS-PY and ∂ δ 34 S CAS /∂ t (max). For the study unit, Δ 34 S CAS-PY is 5.4 ± 1.4‰ ( n = 17), and ∂ δ 34 S CAS /∂ t (max) is 6.8–34‰ Myr −1 based on sedimentation rates of 30–150 m Myr −1 . These data indicate early Mesoproterozoic seawater [SO 4 2− ] of ∼<0.1 to 0.35 mM (with a maximum possible concentration of 1.8 mM), a range that is lower and more tightly constrained than earlier estimates for the Mesoproterozoic. Compilation of published data suggests that low seawater sulfate concentrations began about ∼1.7 Ga and persisted until at least the mid-Mesoproterozoic (∼1.4 Ga), documenting a distinct early Mesoproterozoic perturbation in ocean chemistry that may have been related to a decline in atmospheric p O 2 after Great Oxidation Event I. [ABSTRACT FROM AUTHOR]

Changes in marine productivity and redox conditions during the end-Ordovician (Hirnantian) glaciation and Ordovician–Silurian transition were investigated through Mo-isotope and major- and trace-element analyses of the Wangjiawan (Hubei Province) and Nanbazi (Guizhou Province) sections from the Yangtze Platform of South China. Katian shales of the Wufeng Formation, which yield the graptolites Dicellograptus complanatus , Dicellograptus complexus , and Paraorthograptus pacificus , were deposited under euxinic conditions at both localities, as shown by high Mo EF , U EF , and δ 98 Mo values. A major sea-level regression during the Hirnantian glaciation resulted in shallowing and a shift toward better-oxygenated conditions within the Yangtze Sea, as well as deposition of thin-bedded siliceous sediments, calcirudite debris flows, and limestone turbidites of the Kuanyinchiao Formation, the base of which correlates with the first phase of the end-Ordovician mass extinction. The termination of the Hirnantian glaciation at the top of the Kuanyinchiao Formation was associated with a major sea-level transgression, a rapid expansion of euxinia in the Yangtze Sea (as documented by a return of high Mo EF , U EF , and δ 98 Mo values), and the second phase of the mass extinction, during which the cool-adapted Hirnantian Fauna went extinct. The long-term cooling trend of the Middle and Late Ordovician, which culminated in the Hirnantian glaciation, was driven by enhanced burial of organic carbon, as documented by δ 13 C carb , δ 13 C org , and δ 34 S py records. Increased organic carbon burial was linked to high rates of marine productivity, as shown by high TOC and biogenic Ba concentrations especially at the deeper, less-restricted Wangjiawan locale, producing the HICE (Hirnantian Isotopic Curve Excursion) δ 13 C carb excursion. The locus of organic carbon burial during the Hirnantian crisis shifted to deeper-water environments that were located outside the study region. The relatively rapid onset and termination of the Hirnantian glaciation were probably due to crossing of tipping points in the Late Ordovician climatic–oceanic system. [ABSTRACT FROM AUTHOR]

Organic matter preserved in speleothems has the potential to reflect the changes of the overlying vegetation and soil ecosystem. Here we report the first near 50-yr-resolution acid-soluble organic matter (ASOM) carbon isotope (δ 13 C ASOM ) sequence derived from a laminated stalagmite (HS-4) spanning the last 9 ky in Heshang Cave, central China. The δ 13 C ASOM values vary between − 25.8‰ and − 22.0‰, with lower values from 9 to 4 ka BP and less negative values from 4 to 0 ka BP. We postulate that the δ 13 C ASOM sequence is mainly controlled by temperature and water balance. Temperature could affect both vegetation physiology and microbial degradation in soil horizons. The influence of temperature on the δ 13 C ASOM is supported by the negative correlation ( r = − 0.48, p < 0.001) between the δ 13 C ASOM record and the paleotemperature record in the nearby Dajiuhu peatland. The water balance can affect the retention time of organic matter in soils. Under drier conditions, the soil organic matter will be retained longer and is more likely to be biologically degraded, resulting in more negative δ 13 C ASOM values. Our results reveal that δ 13 C ASOM in speleothems has the potential to reflect the response of vegetation and/or soil processes to paleoclimate changes. [ABSTRACT FROM AUTHOR]

Abstract: The global carbon cycle experienced a major perturbation during the Permian–Triassic transition, reflected inter alia in a large increase in the vertical (shallow-to-deep) gradient of carbonate δ13C (Δ13Ccarb) in Early Triassic seas. However, the effect of this perturbation on the vertical gradient of organic matter δ13C in seawater (Δ13Corg) is less known to date. Here, we examine geographic and secular variations in Δ13Corg in Late Permian–Early Triassic seas of the South China craton and their implications for contemporaneous changes in microbial community composition and paleoredox conditions. Vertical δ13Corg gradients document the existence of a narrow and relatively shallow oxygen-minimum zone (OMZ) within the open-ocean Northern Deepwater Basin (NDW) and a deeper and thicker OMZ within the semi-restricted Nanpanjiang Basin (NPJB). For the pre-extinction interval, Δ13Corg gradients between the shallow and intermediate watermasses of the NDB and between the shallow and deep watermasses of the NPJB record contributions to the sediment of organic matter from bacteria living below the ocean-surface layer. These bacteria were mainly anaerobic chemoautotrophs that inhabited suboxic to anoxic waters of an OMZ and that produced more strongly 13C-depleted organic matter than surface-water eukaryotic algae, thus increasing Δ13Corg. For the post-extinction interval, a reversed Δ13Corg in the NDB is attributed to blooms of green sulfur bacteria or other anaerobic photoautotrophic bacteria that were resident in a deep chlorophyll maximum layer and that had smaller carbon isotopic fractionation than surface-water algae. Although quantitatively important in intermediate- to deep-water areas during the Early Triassic, such bacteria were absent in coeval shallow-water sections, reflecting water-depth controls on microbial community composition. A concurrent flatting of the Δ13Corg gradient in the NPJB was caused by a return of oxic conditions and/or a decline of primary productivity in the surface ocean. [Copyright &y& Elsevier]

• 3D spectral model developed to fingerprint loess soils using principal component analysis. • Sensor fusion improves the performance of machine-learning-based models. • Spectral modeling provides alternative to mineral/geochemical pedogenic proxies. • Loess deposits from various climatic zones were influenced by the Asian monsoons. • Spectral modeling facilitates large-scale investigation of environmental changes. Loess deposits are important records of the evolution of the soil environment and pedogenic weathering. Changes in pedogenic weathering conditions through space and time, as well as discrimination/sourcing of loess-derived soils, are important scientific issues in the soil (paleosol) community. Here, 502 soil samples from four loess chronosequences representing different climatic zones of China were investigated using portable X-ray fluorescence (PXRF) and visible to near-infrared reflectance (VNIR) in combination with previously published mineralogic and magnetic datasets. A spectral modeling approach was employed to discriminate loess-derived soils from different regions of China. We developed a three-dimensional model to fingerprint loess-derived soils using principal component analysis (PCA), showing that soils accumulating under varying climatic conditions were effectively discriminated with sensor fusion data. Six key soil mineralogic and magnetic attributes serving as pedogenic-weathering proxies were analyzed and predicted with conventional methods and chemometric models. Predictive models were constructed with machine learning methods, including partial least squares regression (PLSR), random forest (RF), and Cubist algorithms. The results indicate that the Cubist algorithm works better than PLSR and RF in predicting pedogenic-weathering proxies. The cross-validation results indicate that, although models derived from single sensors (i.e., PXRF or VNIR) work well in predicting pedogenic-weathering proxies, the sensor fusion approach is superior with regard to accuracy and robustness of results in most cases. We suggest that the combined elemental and secondary-mineral information provided by the fused PXRF-VNIR datasets can yield high-accuracy models in soil (paleosol) investigations. The sensor fusion models reveal that pedogenic processes in the loess chronosequences are diversified both spatially and temporally in different climate zones of China. Our results suggest that spectral modeling can be an alternative to geochemical, mineralogic and magnetic pedogenic-weathering proxies, and that it has great potential for investigating soil-forming conditions and pedogenic-weathering evolution, especially when large-area and/or high-resolution analysis is required. [ABSTRACT FROM AUTHOR]

Abstract: Sinojackia is a Chinese endemic genus of Styracaceae, containing eight species. The taxonomy of one species, Sinojackia dolichocarpa (≡Changiostyrax dolichocarpa), is controversial. Here we investigate the distribution of leaf wax n-alkanes to clarify the chemotaxonomic position of S. dolichocarpa. Leaf samples of six Sinojackia species from Wuhan Botanical Garden in central China were collected during April, July, and December in 2010 to capture different developmental stages of the epicuticular waxes. Our results show that the waxes of S. dolichocarpa differ from the other five species by having a lower abundance of nC31 but a higher abundance of nC33. Although developmental variations of n-alkane distributions were observed during the sampling periods, cluster analysis based on the percentages of n-alkanes from C27 to C33 separates S. dolichocarpa from the other Sinojackia species. Based on these finding, we suggest S. dolichocarpa is a species independent of the Sinojackia genus. [Copyright &y& Elsevier]

Abstract: Microbialites flourished globally immediately following the latest Permian mass extinction. In this study, lipid biomarker records were analyzed in the Cili section (Hunan Province, South China) in order to determine the types of microbes involved in microbialite formation and their response to contemporaneous environmental changes. Various biomarkers were identified in the aliphatic and aromatic fractions using gas chromatography (GC) and GC–mass spectrometry (GC–MS). Low abundance of steranes in the microbialite layer suggests that it did not contain large amounts of algae, in striking contrast to the abundant algal fossils and algal-derived steranes present in the underlying (pre-crisis) skeletal limestone. Although pristine/phytane (Pr/Ph) ratios increased in the microbialite layer, covariation of Pr/Ph with the ratio of low- to high-molecular-weight n-alkanes (C20−/C20+) suggests that the former proxy was controlled by microbial (particularly cyanobacterial) inputs rather than by redox conditions. The microbialite also yielded low ratios of hopanes to short-chain n-alkanes (HP/Lalk) and high abundances of C21 n-alkylcyclohexane, indicating that, in addition to cyanobacteria, anaerobic bacteria, archaea, and possibly acritarchs flourished in the aftermath of the marine extinction event. The upper part of the thinly bedded micritic limestone overlying the microbialite exhibits a bimodal distribution of n-alkanes as well as increased abundances of extended tricyclic terpanes and steranes, suggesting a return of habitable shallow-marine conditions for eukaryotic algae several hundred thousand years after the latest Permian mass extinction. Increases in the dibenzofuran ratio (i.e., DBF/(DBF+DBT+F)) and in the coronene to phenanthrene ratio (Cor/P) in the skeletal limestone immediately below the microbialite are evidence of enhanced soil erosion rates and wildfire intensity, marking the collapse of terrestrial ecosystems. The terrestrial crisis thus slightly preceded the marine biotic crisis in the South China region, to which it may have been a major contributing factor. [Copyright &y& Elsevier]

Abstract: When used in conjunction with trace metal redox proxies, the use of U/Mo ratios and δ95/95Mo values can considerably enhance the interpretation of ocean oxygenation trends both locally and globally. This is illustrated with studies from two, biogenic-chert dominated records of mass extinction: the Ordovician–Silurian boundary and the Late Permian in sections from the Yangtze Block in South China. The latest Ordovician mass extinction is well known to coincide with oxygenation episode in the Hirnantian Stage here revealed by trace metal proxies (V/V+Ni, V/Cr, Ni/Co) that show it sandwiched between anoxic/euxinic black shales. The predominantly anoxic/euxinic Ordovician–Silurian strata provide a record of seawater δ95/95Mo values that are seen to gradually rise during the interval from 0.5 to 1.0‰. The exception to the δ98/95 Mo stability is the datum of the slight negatively δ98/95Mo, associated with decreasing of V/Cr and V/(V+Ni) ratio suggesting the Hirnantian oxygenation event. The Upper Permian chert succession at Shangsi reveals an overall better ventilated record in which the best oxygenated strata show the highest U/Mo values that is interpreted as relative enrichment of U in suboxic conditions. At a few levels anoxic/euxinic conditions show the δ95/95Mo values to be ~2‰, close to modern values, implying that latest Permian oceans were as well ventilated as those today. The well-known end-Permian oceanic anoxic event is therefore suggested to only develop at the end of this period. [Copyright &y& Elsevier]

Abstract: Large perturbations to the global carbon cycle occurred during the Permian–Triassic boundary mass extinction, the largest extinction event of the Phanerozoic Eon (542Ma to present). Controversy concerning the pattern and mechanism of variations in the marine carbonate carbon isotope record of the Permian–Triassic crisis interval (PTCI) and their relationship to the marine mass extinction has not been resolved to date. Herein, high-resolution carbonate carbon isotope profiles (δ13Ccarb), accompanied by lithofacies, were generated for four sections with microbialite (Taiping, Zuodeng, Cili, and Chongyang) in South China to better constrain patterns and controls on δ13Ccarb variation in the PTCI and to test hypotheses about the temporal relationship between perturbations to the global carbon cycle and the marine mass extinction event. All four study sections exhibit a stepwise negative shift in δ13Ccarb during the Late Permian–Early Triassic, with the shift preceding the end-Permian crisis being larger (>3‰) than that following it (1–2‰). The pre-crisis shifts in δ13Ccarb are widely correlatable and, hence, represent perturbations to the global carbon cycle. The comparatively smaller shifts following the crisis demonstrate that the marine mass extinction event itself had at most limited influence on the global carbon cycle, and that both Late Permian δ13Ccarb shifts and the mass extinction must be attributed to some other cause. Their origin cannot be uniquely determined from C-isotopic data alone but appears to be most compatible with a mechanism based on episodic volcanism in combination with collapse of terrestrial ecosystems and soil erosion. [ABSTRACT FROM AUTHOR]

• Distinct distributions of 3-OH-FAs are found in soils, marine- and lake sediments. • First systematic investigation of 3-OH-FAs in lake environments. • We propose a novel temperature proxy based on 3-OH-FAs for lake environments. Bacterial 3-hydroxy fatty acids (3-OH-FAs) show potential for terrestrial paleoclimate reconstruction; however, the possibility of using 3-OH-FAs as proxies in lacustrine environments remains to be investigated. We analysed the composition and distribution of 3-OH-FAs in surface sediments from 20 Chinese alkaline lakes and investigated the development of climate proxies based on 3-OH-FAs in these lacustrine environments. The results show that lake sediments contain higher relative abundances of anteiso 3-OH-FAs compared to soils. Analysis of the gene community composition from Lake Liangzi reveals that Gram-negative bacterial communities in that lake environment are distinct from marine sediments from the South China Sea but share many characteristics with soils from Mt. Yujia at the phylum level. At the class level, the Lake Liangzi samples yield distinctly higher proportions of Deltaproteobacteria (23%), Betaproteobacteria (13%), Gammaproteobacteria (14%), and Bacterioidia (10%). pH proxies based on 3-OH-FAs (Branching Ratio, Branched index, RIN and RIAN) yield weak linear relationships with lake water pH, while RAN 13 (previously proposed as a sea surface temperature proxy) shows a linear relationship with mean annual air temperatures (MAAT; ranging from 5 °C to 17 °C). The soil temperature proxies RAN 15 (previously applied to a stalagmite) and RAN 17 do not appear to be suitable for temperature calibration in lacustrine environments. We propose a novel temperature proxy (RIN 17 , ratio of iso to normal C 17 3-OH-FA) for lake environments. These field-based correlations demonstrate that the physiological response of Gram-negative bacterial cell membranes to external environmental changes are recorded in lake sediments on a large regional scale. This further highlights the potential use of bacterial 3-OH-FAs as proxies for paleoclimate reconstruction in both aquatic and terrestrial environments. [ABSTRACT FROM AUTHOR]

Glycerol dialkyl glycerol tetraethers (GDGTs) are widespread but unique membrane-spanning lipids of many Archaea and some Bacteria. However, their specific biological sources and the associated environmental controls on their distribution remain unclear, especially in lacustrine settings, hindering our understanding of these compounds and their application as environmental proxies. Here we investigated the GDGT distributions across a large bottom water dissolved oxygen (DO) gradient (0.10–7.20 mg/L) using surface sediments of Lake Yangzonghai, a warm monomictic lake in southwestern China. We show that the distributions of both branched (br) and isoprenoidal (iso) GDGTs co-vary significantly with bottom water DO concentration. The relative abundances of tetramethylated brGDGTs, 5-methyl penta- and hexamethylated brGDGTs and isoGDGT-0 show a stepwise increase as bottom water DO concentration decreases. On the other hand, the relative abundances of 6-methyl penta- and hexamethylated brGDGTs and crenarchaeol exhibit a stepwise decline with a decrease in bottom water DO concentration. Genetic data indicate these DO-induced changes in GDGT parameters are related to changes in the bacterial and archaeal communities across the oxycline in the lake. For example, the high abundance of isoGDGT-0 in low DO samples coincides with a high abundance of methanogenic archaea and Bathyarchaeota. We propose that brGDGT-producing bacteria might include a diversity of other phyla in addition to the proposed source organism acidobacteria; different groups of anaerobic and aerobic bacteria are likely to contribute to the increased abundance of 5-methyl brGDGTs and 6-methyl brGDGTs in low and high DO zones, respectively. Consequently, the MBT′ and MBT′ 6ME brGDGT indices display strong correlations with DO concentration. Importantly, the MBT′ 5ME index is not significantly influenced by changes in DO concentration, suggesting that this index might be more resilient to these impacts and more suitable to reconstruct temperature in lake systems. • One of the most systematic investigation on DO impact on all the GDGT compounds and the related paleoclimate proxies • A new ternary diagram was used to identity the sources of lacustrine brGDGTs • Anaerobic and aerobic bacteria contribute to the increased abundance of 5-methyl and 6-methyl brGDGTs, respectively • MBT′ 5ME might be more suitable to reconstruct temperature in lake systems than MBT′ and MBT′ 6ME [ABSTRACT FROM AUTHOR]

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial membrane lipids that have been extensively used as tools for paleoclimate reconstruction. Temperature and pH were thought to be two major factors affecting the distributions of brGDGTs; however, the effects of other factors on the distribution of brGDGTs and related temperature and pH proxies in soil environments remain unclear. Here, we investigated iso- and br-GDGT distributions in three soil profiles (SPs) developed on bedrocks consisting of hornfels (HP), granite (GP), and basalt (BP), respectively. The downward environmental factors in these SPs differ, thus providing a chance to evaluate their effects on the distribution of brGDGTs. In the three SPs, the methylation degree for 5-methyl and total brGDGTs (MBT′ 5ME and MBT′), respectively, varied significantly downwards despite minor changes in soil temperature, highlighting a non-temperature effect. The depth-dependence of these proxies appears to be caused by the oxygen level. The MBT′ for 5- or 6-methyl brGDGTs (MBT′ 5ME and MBT′ 6ME), or total brGDGTs (MBT′), increased as the oxygen level decreased, suggesting tetramethylated brGDGTs (Ia, Ib, and Ic) would increase in abundance with decreased oxygen level. The two pH proxies, CBT and IR 6ME , both decreased at lower oxygen levels. Such regulation of brGDGT compositions in response to oxygen availability could be explained by the changing bacterial communities that have different oxygen preferences. The possible oxygen level impact on the distribution of GDGTs could result in brGDGT-inferred temperature skewed towards higher values and pH towards lower values with decreased oxygen level. This finding may also have implications for the mechanism of soil aridity impact on the brGDGT-based proxies in semi-arid and arid regions, which is of profound importance for paleotemperature and hydroclimate reconstruction in loess-paleosol sequences. Increasing soil aridity could lead to changes in brGDGT-based proxies similar to that observed at the higher oxygen level, i.e., lower MBT′, higher CBT, and higher IR 6ME. As soil aridity is generally associated with better aeration and higher oxygen level, we argue that changes in oxygen level might be the real cause of the bias in brGDGT-based proxies in soils from semi-arid and arid regions. • GDGTs in three soil profiles with varying environmental factors investigated. • Oxygen level could be a factor influencing the distribution of GDGTs in soil environments. • Lower oxygen levels led to higher MBT', lower CBT and IR 6ME. [ABSTRACT FROM AUTHOR]