N-fatty Acids Research Articles

Seasonal Variability of Lipophilic Compounds in Oat (Avena sativa L.) Straw: A Comprehensive Chemical Study.

Oat straw, a residue of Avena sativa L., is recognized for its abundance in cellulose, hemicelluloses, and lignin. However, its potential as a source of lipophilic compounds within the framework of a biorefinery concept still remains unexplored. In this study, we conducted an extensive investigation into the content and chemical composition of the lipophilic compounds present in acetone extracts from oat straws of two distinct oat varieties, namely, Karen and Isaura. Furthermore, we examined their seasonal variability in content and composition in straw samples from oats planted in both spring and winter seasons. The extracted lipophilic compounds were predominantly composed of high molecular weight esters (26.0-38.1%), steroids (16.6-24.0%), n-fatty alcohols (10.9-20.7%), n-fatty acids (10.9-16.0%), and n-aldehydes (10.7-15.8%), with lower amounts of n-alkanes (1.1-3.0%), acylglycerides (2.3-3.8%), phytol and phytyl esters (0.6-2.9%), β-diketones (0.1-2.5%), triterpenoids (0.9-1.2%), tocopherols and tocopheryl esters (0.2-0.7%), 2-hydroxy fatty acids (0.1-0.2%), and n-alkylresorcinols (0.1%). Notably, these different classes of compounds exhibited variations in their contents depending on the oat variety and the specific planting season. Of particular interest was the Karen variety, which presented significant amounts of high molecular weight esters, free fatty acids, and acylglycerols, especially when it was cultivated during the winter season. These findings underline the potential of oat straw as a valuable resource for lipid extraction within a biorefinery context and emphasize the importance of selecting the appropriate variety and season for optimal lipid yield.

Compound-specific radiocarbon analysis of sedimentary fatty acids: Potential as a dating tool for lake sediments of Mt. Fuji volcanic region, Japan

Compound-specific radiocarbon analysis (CSRA) is a promising tool for dating sediment sequences where traditional dating methods are impractical. However, the applicability of CSRA of short-chain fatty acids as a dating tool remains poorly understood, especially in lacustrine settings. Accordingly, we determined the radiocarbon content (Δ14C) of individual fatty acids in sediments of Lake Yamanaka (central Japan), as well as their stable carbon and hydrogen isotope ratios, to evaluate the potential of CSRA as a dating tool in volcanic lake environments. We found that the Δ14C values of plant-derived (C24, C26, and C28) n-fatty acids (–99‰ to –149‰) were considerably lower than the Δ14C of charred plants (139‰) within the sediments and those of living aquatic plants (–52‰ to –58‰) in Lake Yamanaka, suggesting that contributions from pre-aged terrestrial and aquatic plant materials likely affect these acids. Similarly, the Δ14C of C16n-fatty acid (–95‰) in surface sediments was much lower than the Δ14C of modern aquatic plants (–52‰ to –58‰), as well as the Δ14C of dissolved organic carbon (DIC) in surface water (–48‰). Together with the stable isotope results, we conclude that in addition to autochthonous aquatic sources, contributions from pre-aged terrestrial carbon sources significantly affect the Δ14C of C16n-fatty acids. Comparing fatty acid Δ14C and concentration data across lakes within the Mt. Fuji region suggests that CSRA of the C16 acid provides valid chronological information only when the C16 originates exclusively from autochthonous aquatic sources, with minor allochthonous terrestrial input.

The preservation of photosynthetic and hydrological signals in the carbon and hydrogen isotope compositions of n-fatty acids in the seasonal wetland soils of the Okavango Delta (Botswana)

The Okavango wetland (Botswana) is the world’s largest inland delta. A strong seasonality in water input leads to the contraction and extension of wetlands in the floodplains. The extreme evapotranspiration and little precipitation lead to a difference in the hydrogen isotope signature of rain, soil and river water. Biomarkers, such as plant waxes, are stored in the soils and preserved on geological timescales. To understand which signal is preserved in the stable isotope signatures of plant waxes, soils along a 250 m-long transect spanning waterlogged to dry soils were collected over several seasons and three years. In addition, plants, and plant and soil water were collected along this transect. First, carbon isotope ratios (δ13C) of plant waxes (i.e, n-fatty acids) were used to classify their metabolism. δ13C of bulk organic matter and individual n-fatty acids analyzed in the soils show a strong dependance on the type of vegetation found along the transect (C3 versus C4 plants). Hydrogen isotope ratios (δ2H) of water present in soil showed that shallow-rooted C4 grasses use superficial soil water, whereas the xylem water δ2H content in trees growing near the flooded channel indicated the use of river water. In addition, plant hydrogen fractionation between lipids and rain showed a strong influence of carbon metabolisms with larger fractionation for C3 plants compared with C4 grasses. n-fatty acid δ2H ratios in surface soils followed the hydrological variation in the Delta with its floods and dry periods. Hence δ2H of long-chain fatty acids seems to track the river-level variation rather than precipitation.

Anthropogenic emission controls organic aerosols at Gosan background site in the outflow from northeast Asia

Anthropogenic activities release substantial amounts of organic components into the atmosphere. In this study, eight groups of organic compounds such as polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes, n-alkanes, fatty acids, fatty alcohols, phthalate esters, and lignin and resin acids were identified in the ambient aerosol samples collected from a regional background site in the Korean Climate Observatory at Gosan (KCOG), South Korea. The total identified organics were most abundant in winter (220 ± 60.3 ng m−3), followed by spring, autumn, and summer, with the predominance of n-fatty acids. All classes of aliphatic lipid components showed a significant positive correlation with fossil fuel-derived organic carbon (OC-FF) and biomass burning-derived organic carbon (OC-BB), indicating that they were abundantly emitted from anthropogenic sources such as fossil fuel combustion and biomass burning. The composition profiles and diagnostic ratios of PAHs indicate that they were largely derived from coal and/or biomass combustion in the continent. In contrast, hopanes are predominantly emitted from gasoline or diesel engines, particularly in the summer, from commercial ships. The high concentration of phthalates in the summer suggested that plastic emissions from the open ocean substantially contributed to the Gosan aerosols. The low ratios of unsaturated/saturated fatty acids indicate that Gosan organic aerosols were photochemically aged during atmospheric transport. The temporal and seasonal variations of organic species over KCOG provide crucial information on the emission strengths of different contributing sources in the East Asian outflow. Positive Matrix Factorization (PMF) results and 14C-based source apportionment studies demonstrated that anthropogenically derived organic aerosols largely contributed to the aerosol mass over KCOG. Thus, the East Asian continent might be the major source region for organic aerosols over the western North Pacific, except in the summer.

Characteristics of n-alkyl lipids in cultivated Sphagnum and their preservation potential in the topsoil of Sphagnum farmlands in southwest China

Sphagnum, a crucial peat-forming plant, is essential for sustaining the ecosystem and counteracting climate change. In recent years, attempts have been made to cultivate Sphagnum commercially to reduce the environmental impacts of harvesting the natural Sphagnum. However, research on the distribution of lipids in cultivated Sphagnum and their potential for preservation potential in the underlying soil is still limited. This study examined the distribution of n-alkyl lipids and the carbon isotope composition of n-alkanes in both natural and cultivated Sphagnum, as well as the underlying topsoil in southwestern China. Results show that the distributions of n-alkyl lipids in the cultivated Sphagnum are similar to those of the natural Sphagnum in the same region. Additionally, the δ13C values of mid-chain n-alkanes (C23 and C25) in the cultivated Sphagnum are significantly negative compared to those of long-chain homologs (C29 and C31; one-way ANOVA, p < 0.05), indicating that symbiotic methanotrophs are relatively active in the cultivated Sphagnum. Furthermore, the n-fatty acids and n-alkan-2-ones in the topsoil are mainly imported from Sphagnum, while the n-alkanes in the topsoil may originate from both Sphagnum and vascular plants. These findings contribute to a better understanding of the ecological benefits of Sphagnum cultivation and the contribution and fate of Sphagnum-derived carbon in soil profiles.

Contrasting sources and fates of sedimentary organic carbon in subtropical estuary-marginal sea systems

Sediments deposited in subtropical deltas and continental shelves are the “recorders” of sources, transport processes, and accumulation of organic carbon (OC) at the land-ocean interface, but their role in the global carbon cycle remains poorly constrained. In this study, we determined the abundance and carbon isotopic composition (δ13C and Δ14C) of bulk OC, as well as characteristics of specific biomarker compounds (plant wax n-alkanes, n-fatty acids, and phytoplankton sterols) in surface sediments from the Pearl River estuary (PRE) and adjacent continental shelf of the northern South China Sea (SCS) in order to examine the sources and fates of OC delivered to a large subtropical river-marginal sea system. We observed marked spatial variability in the sources, hydrodynamic processes and accumulation of sedimentary OC in PRE and northern SCS shelf, with the emergence of two distinct regimes reflected in the bulk OC isotopic characteristics of surface sediments. In Pearl River impacted regions, relatively fresh terrestrial OC (OCterr) was subject to substantial degradation and aging during transport within the estuary and from the estuary to the shelf. In contrast, sedimentary OC in the Taiwanese river impacted region comprised a mixture of fluvially-derived refractory OCterr from the Choshui River and modern marine OC. Burial efficiencies of OCterr are also spatially heterogeneous as a result of these different OC sources and hydrodynamic processes. The overall OCterr burial efficiencies are relatively low in the Pearl River influenced region, with an average value of 27 ± 10% in the PRE and an average value of 17 ± 6% in the western shelf, in contrast to the higher values in the region impacted by Taiwanese rivers (55% ± 39%).These findings suggest both sources and hydrodynamic processes during transport exert strong influence on the fate of OC, with important implications for the role of river-dominated marginal seas in the global carbon cycle.

Effects of paddy irrigation-drainage system on water quality and productivity of small rivers in the Himi region of Toyama, Central Japan

The aim of this study was to clarify the impact of differences between historical and recently introduced irrigation and drainage management systems on water quality in the rivers around paddy fields. We investigated the seasonal variation in nutrients concentration and dissolved organic carbon (DOC) components in single- (used for intake only) and dual-purpose (used for both intake and drainage) channels during a 4-year period in the Himi region of Toyama, Central Japan. The system of dual-purpose channel has traditionally been used in the region of this study. A total of 197 three-dimensional excitation-emission matrix (3DEEM) fluorescence spectra of DOM in waters were applied for the parallel factor analysis (PARAFAC) modeling. Based on the 3DEEM and PARAFAC, the abundance of terrestrial humic-like components in the dual-purpose channel was significantly higher than that in the single-purpose channel. The even long-chain n-fatty acids derived associated with rice cropping in sediments of the dual-purpose channels were 22−30-fold higher than that of the single-purpose channel. In addition, the turbidity values of the river waters had significantly positive linear correlations with concentrations of K+, DOC, and humic-like components. These observations indicate that the dissolved nutrient concentrations in the river water were higher in the dual-purpose channel compared to those of the single-purpose channel, which may be supplied by leaching from the inflow of soil particles from the paddy fields. During the mid-irrigation period, the quantity of epiphytic chlorophyll a on artificial substrate tiles in the dual-purpose channel were 3.1–4.1-fold higher than that in the single-purpose channel. This study clear that the input of paddy drainage during the irrigation season significantly changes the DOC components in river waters and irrigation management is strongly linked to the primary production in agricultural channels. Therefore, it is important to consider the impact of the introduction of different irrigation and drainage management systems on water quality and productivity in order to maintain the riverine ecosystems around rice paddies, which are based on historical water use systems.

A New Unsaturated Aliphatic Anhydride from Aspergillus candidus T1219W1, an Endophytic Fungus, from Pittosporum mannii Hook f.

A new unsaturated aliphatic anhydride derivative (Z)-(12Z)-heptadec-12-enoic-2′-hydroxypropanoic anhydride (1) and ten known compounds, three flavonoids (2–4), two terphenyllins (5-6), four triterpenoids (7-8, 10-11), and one n-fatty acid (9), were isolated from the EtOAc extract of Aspergillus candidus T1219W1, an endophytic fungus, inhabiting Pittosporum mannii. All the isolated compounds were characterized using 1D- and 2D-NMR and HR-EI experiments together with the reported literature. p-terphenyls are suggested to be the chemophenetic marker of the genus Aspergillus. The ethyl acetate crude extract as well as some isolated compounds of A. candidus was assayed for antibiofilm activity, anti-inflammatory (ROS) activity, and cytotoxicity on brine shrimps and the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cytotoxicity assay on 3T3 cell lines. The tested sample showed good antibiofilm activity with the lowest MBEC50 obtained at 64 μg/mL. Compounds showed low anti-inflammatory activity even at high concentration (250 μg·mL−1 with an IC50 of 59.6 ± 0.1 μg·mL−1) with moderate cytotoxicity on brine shrimps at high concentration (1000 μg·mL−1, with 46.67% mortality). However, no cytotoxic activity was observed against 3T3 cell lines.

Compositional characteristics and indication of n-fatty acids in alpine meadow plants and soils

AimTo explore the distributions and indication of n-fatty acids in the plants and soils from alpine meadow, and how n-fatty acids in plants and soils are associated. MethodsThe plant (grass, herb, and shrub) and soil samples were collected from alpine meadow in the Qinghai-Tibet Plateau, and the compositional characteristics of n-fatty acids were analyzed using GC-MS. Results and conclusionn-Fatty acids ranging from C6 to C28 were identified, C16 was the most abundant fatty acid in most plants, which contributed between 39.1% and 74.2% to total n-fatty acids; the most abundant fatty acid in soils was C15, which contributed between 72.1% and 89.1% to total n-fatty acid. The total n-fatty acid content of Artemisia hedinii and the long chain n-fatty acid content of Ajuga lupulina were the highest, while the total and long chain n-fatty acid content of Saxifraga tangutica were the lowest. The contents of C20, C22, C24 and C26 in indicative plants of degradation and typical dominant plants (Festuca sinensis, Elymus nutans, Poa crymophila, Kobresia humulis, Kobresia pygmaea) were higher than other long chain n-fatty acids (C ≥ 20). The n-fatty acids content of the plants in degraded alpine meadow were higher than that in non-degraded alpine meadow except C6, C23, C25 and C27. The total n-fatty acids content of plants and soils in degraded alpine meadow were higher than that of non-degraded meadow. The n-fatty acids content in soils were decreased with the increasing depth of sampling except C15. The positive correlation of long chain n-fatty acids content in soils and plants was strongly significant (p < 0.001, R2 = 0.926). The compositional characteristics of n-fatty acids in plants and soils were similar. Therefore, the source of the long chain n-fatty acids in the soil might be deduced from native vegetation.

Domestication of Wild Edible Species: The Response of Scolymus hispanicus Plants to Different Fertigation Regimes

Scolymus hispanicus L. is a wild edible species with wide distribution in the Mediterranean area. Recent research has focused on the domestication of wild edible greens, which is essential for the preservation of agroecosystems and the increase in biodiversity, especially under the adversely changing climate conditions. In the present work, the aim was to evaluate the response of S. hispanicus plants to different fertilization regimes that varied in the amounts of nitrogen, phosphorus and potassium in regard to plant growth and chemical composition of leaves. For this purpose, plants were grown in pots within an unheated greenhouse. Seven experimental treatments were used, including six fertigation regimes (SH1-SH6) and the control treatment (SHC), where no fertilizers were added. Fresh yield was beneficially affected by the treatments that included a high content of P and K (e.g., SH3 and SH5), while lesser amounts of these macronutrients (e.g., SH1 and SH4) resulted in higher chlorophyll content (SPAD index) and leaf area. In terms of mineral profile, high amounts of P and K improved dietary fiber and carbohydrates content, whereas the untreated plants had the highest content of ash, fat and crude protein. Oxalic and quinic acid were the major organic acids detected, with fertigation regimes significantly reducing their content compared to the control treatment. α-tocopherol was the only isoform of vitamin E detected in all the samples, while glucose and fructose were the most abundant sugars, with their highest content detected in control and SH4 treatments, respectively. Scolymus hispanicus leaves were rich in macro and micro minerals, while their contents varied depending on the fertigation regime. Finally, α-linolenic, palmitic, and linoleic acid were the major fatty acids detected, while their contents were beneficially affected by low nutrient inputs (e.g., untreated plants and SH1 and SH2 treatments). In conclusion, the regulation of nutrient solution seems to be an effective practice to increase fresh yield in S. hispanicus without compromising the nutritional profile of the edible product, while low inputs of macronutrients such as P and K may improve the chemical composition of the species, especially in terms of n-fatty acids.

Chemical composition of the lipophilic compounds from the rind and pith of papyrus (Cyperus papyrus L.) stems.

Papyrus (Cyperus papyrus L.) is a sedge plant with a high rate of biomass productivity that represents an interesting raw material to produce chemicals, materials and fuels, which are currently still obtained from fossil resources, in the context of a lignocellulosic biorefinery. In this work, the content and chemical composition of the lipids present in papyrus stems were thoroughly studied. For this, the papyrus stems were separated into the rind and the pith. The lipid content accounted for 4.1% in the rind and 4.9% in the pith (based on dry matter). The main compounds identified in both parts of the papyrus stem were hydrocarbons, n-fatty acids, 2-hydroxyfatty acids, alcohols, alkylamides, mono- and diglycerides, steroids (sterols, ketones, hydrocarbons, esters and glycosides), tocopherols, tocopherol esters, phytol, phytol esters, alkyl ferulates, ω-carboxyalkyl ferulates (and their monoglycerides), and acylglycerol glycosides. The rind presented a predominance of n-fatty acids (6790 mg/kg; that represented 28.6% of all identified compounds), steroid compounds (6255 mg/kg; 26.3%), phytol and phytol esters (4985 mg/kg; 21.0%), and isoprenoid hydrocarbons, namely phytadiene and squalene (2660 mg/kg; 11.2%), while the most abundant lipids in the pith were steroids (8600 mg/kg; 44.4% of all identified compounds) and fatty acids (6245 mg/kg; 32.2%). Due to the great diversity and significant abundance of the compounds identified in papyrus, it can be considered as a potential raw material for biorefineries to obtain valuable phytochemicals of interest to various industrial sectors.

Organic molecules based palaeoenvironmental inferences and U mineralization in Palaeoproterozoic Bijawar basins of Central India

Palaeoproterozoic, siliclastic, intracratonic rocks of the Bijawar and Sonrai basins contain anomalous U concentration and abundant Organic Matter (OM), although, earlier studies documented rare data on commonality between high U content and closely associated OM. Moreover, OM contains several biomolecules of complex carbonaceous compounds with macro-molecular structures, but insignificant information is available on the origin and associated palaeoenvironmental conditions. Thus, present study on organo-uranyl-complexes is relevant and carried out to understand palaeoenvironmental reasons accountable for U mineralization. For this purpose, OM (isolated from each bulk sample) was analyzed for Total Organic Carbon (TOC), n-alkanes, n-fatty acids and Polycyclic Aromatic Hydrocarbon compounds (PAHs). Obtained TOC values range between 0.02 and 0.23 wt%. Mostly, calculated [(C/S)/12] and [(C/N)/12] values are low; indicate algal source and anoxic depositional conditions, but, Rohini carbonate, Bandai sandstone and Chloritic shale high values signify sub-oxic conditions. Also, low (<1.25) U/Th and high authigenic U data of mineralized Chloritic shale imply anoxic conditions and post-depositional enrichment of U ions (mostly as organo-uranyl-complexes), respectively.GC-MS data show high concentration of n-alkane, fatty acid methyl ester (FAME) and PAH molecules in the OM associated with the rocks signifying high U values. The predominance of Short Chain (SC) n-alkanes together with the SC n-fatty acids revealed derivation of OM from marine algae and bacteria. The Rohini carbonate and Chloritic shale show low isoprenoids, Pristane (Pr)/Phytane (Ph), CPI, OEP, Pr/n-C-17, Ph/n-C18, but high TC-/(Pr/Ph), TC/(Pr + Ph), MP, MPI, MPR and VR values, suggest biodegraded and thermally matured OM which has undergone hydrothermal alteration under anoxic to sub-anoxic conditions. Considerably, high degree of OM oxidization occurred synchronously with the reduction of U6+ to U4+ by sulfate-reducing bacteria. The consistent loss of diaromatic PAHs is also noticed from older to younger rock-units. Further, scanty appearance of PAHs in the lower Gorakalan shale and their disappearance in the upper Chloritic and black shale units, indicate progressive maturation of sediments. The Low Molecular Weight (LMW)-PAHs predominate over the High Molecular Weight (HMW)-PAHs. Comparatively, high phenanthrene abundance is also noticed in the Rohini carbonate, Chloritic shale and -black shale (with high U content). The high proportion of LMW-PAHs and absence of HMW-PAHs (>6 rings) is pointing towards the presence of hydrothermally derived bitumen. Moreover, partial combustion of OM (pyrogenic) contributed to the formation of PAHs. The Chloritic shale and Rohini carbonate are coeval with the Bijawars of the Sonrai basin, representing almost similar organo-molecular records. Organo-molecular abundance and their structural attributes when plotted across the stratigraphic successions, revealed alternate humid conditions facilitated U4+oxidation and formation of U6+ rich solutions, although arid/semiarid climatic conditions assisted precipitation, sorption and absorption of U4+. Almost, similar clay mineral attributes for both the basins lend support to cyclic humid to arid/semiarid palaeoenvironmental conditions. Moreover, majority of the OM derived from the algal mats has played critical role in U mineralization by trapping and adsorption of tiny uraninite grains as well as U ions onto the OM.

Ectopic Overexpression of CsECR From Navel Orange Increases Cuticular Wax Accumulation in Tomato and Enhances Its Tolerance to Drought Stress.

Drought stress often occurred in citrus to limit its growth, distribution, and fruit quality. Cuticular waxes play an important role in regulating plant tolerance to drought stress. Plant enoyl-CoA reductase (ECR) is involved in the biosynthesis of cuticular waxes and catalyzes the last step of very long-chain fatty acids (VLCFAs) elongation. In this study, a putative ECR gene, named CsECR, was cloned from “Newhall” navel orange. CsECR protein has high identities with other plant ECR proteins and contained a conserved NADP/NAD-binding motif and three conserved functional sites. The highest expression of CsECR was observed in leaves, followed by stems, flavedos, ovaries, juice sacs, stigmas, stamens, albedos, and petals. Besides, the expression of CsECR was significantly induced by PEG6000 and ABA treatments. Ectopic overexpression of CsECR increased the contents of total waxes and aliphatic wax fractions (n-fatty acids, unsaturated fatty acids, n-alkanes, alkenes, iso-, and anteiso-alkanes) in the leaves and fruits of the transgenic tomato. Furthermore, ectopic overexpression of CsECR reduced the cuticle permeability in the leaves and fruits of the transgenic tomato and increased its tolerance to drought stress. Taken together, our results revealed that CsECR plays an important role in plant response to drought stresses by regulating cuticular wax biosynthesis.

Induction of water repellency by leaves of contrasting Australian native species: effects of composition and heating

AimsThis study identifies the contribution of leaf matter from individual plant species on water repellency with a focus on the composition of organic compounds and the role of heat in releasing these compounds to soil.MethodsLeaf powder from four plant species (Banksia menziesii, Eucalyptus marginata, Allocasuarina fraseriana, Xanthorrhoea preissii) was mixed with acid-washed sand (AWS) under a range of temperatures and WR measured. Plant chemical composition was characterized by extraction of leaf powder and GC/MS analysis.ResultsIncreasing concentrations of plant powder mixed with AWS increased WR for three species; whereas for X. preissii there was no WR at any concentration. Heating increased WR for all species over the range of 30 to 120 °C. B. menziesii had the greatest WR, which was associated with the largest diversity of fatty acids and n-alcohols and highest concentration of alkanes, whereas X. preissii with the smallest WR had only C16 alcohol and C16 fatty acids at relatively low concentration.ConclusionsPhysically mixing leaf powder with AWS allows the contribution of different plant species on WR to be directly examined. WR appears to be related to differences in the concentrations and diversity of n-alcohols, n-fatty acids, and high n-alkanes in the leaves. The observed temperature effects on WR provide insights into the kinetics of release and dispersal of organic compounds from interstitial material.

Production of short-chain n-fatty acids in coral reefs in the southern South China Sea since the Late Miocene

The monsoon system modulates surface production in the South China Sea (SCS). The winter monsoon has long been recognized as the primary factor regulating surface production in the northern SCS; however, the role of monsoon remains in debate in the southern SCS. Here, we present a long record of short-chain n -fatty acids ( n -FAs) in reefal carbonates from one deep well (NK1) on an isolated coral atoll (Meiji) in order to provide new insights into the change of surface production in the southern SCS since the Late Miocene (ca. 10.5 Ma). Short-chain n -FAs indicative of total marine organic matter input are rather feasible to reflect the total production associated with mixotrophic reef-building corals that feed on various marine biotas (i.e., phytoplankton, zooplankton and bacteria). By ruling out the significant influence of diagenetic and degradation processes, short-chain n -FAs can be further applied to reconstruct paleo-production in Well NK1 coral reefs. The temporal distribution of short-chain n -FAs changes similarly with many other independent paleo-production records (i.e., Ln(Ba/Ti) and opal) in Well NK1 and adjacent ODP Site 1143, demonstrating the close coupling between coral reef production and surface water production. This occurs through the common factor of nutrients in modulating production of symbiotic autotrophic coralgae and asymbiotic phytoplankton and/or the large heterotrophic dependence of corals on phytoplankton-governed food webs in surface waters. Short-chain n -FAs inferred surface production displays a progressively decreased trend from the Late Miocene to Pliocene (ca. 10.5–2.6 Ma) followed by a substantial increase since the Pleistocene on million-year timescales, which follows the variation of terrigenous supply to the coral atoll and responds almost inversely to the sea-level change. Accordingly, we propose that long-term paleo-production in the southern SCS was associated with terrestrial nutrient input which was controlled by relative sea-level change since the Late Miocene. This study highlights the feasibility of short-chain n -FAs as appropriate production recorders in shallow-water coral reefs which are widespread in tropical-subtropical oceans, providing valuable perspectives on long-term paleo-production evolution in surface waters. • A long coral reef well (NK1) in the southern SCS was studied. • OM-poor coral reef carbonates were decalcified and extracted for biomarkers. • Short-chain n -FAs reflect paleo-production in coral reefs since the Late Miocene. • Long-term production was governed by terrestrial nutrient related to sea level.

Extending the dataset of fluid geochemistry of the Menez Gwen, Lucky Strike, Rainbow, TAG and Snake Pit hydrothermal vent fields: Investigation of temporal stability and organic contribution

The Menez Gwen, Lucky Strike, Rainbow, TAG (Transatlantic Geotraverse) and Snake Pit hydrothermal vent fields on the Mid-Atlantic Ridge were revisited and resampled for geochemical investigation during the BIOBAZ 2013 and BICOSE 2014 research cruises. Geochemical analysis of the major and minor elements of the hydrothermal fluid and concentrations of gases extends and complements the existing dataset. Our results are consistent with values previously reported and fall within the range of the analytical error. This indicates that the hydrothermal vent field system has remained relatively stable over the last few decades. However, some differences were observed and (i) suggested a recent eruption at Menez Gwen, (ii) supported the occurrence of low-temperature serpentinisation in this same site, (iii) supported a change in the reaction zone or axial magma chamber (AMC) depth at Lucky Strike, (iv) an increase of the temperature at depth at Snake Pit and (v) supported the hypothesis of large seawater entrainment through the TAG hydrothermal mound. Besides, it is possible that small temporal and spatial scale processes may control a significant part of the geochemistry, owing to the fact that some variations in the data could not be interpreted. However, our investigation of the organic geochemistry represents a pioneering addition to research for Menez Gwen, Snake Pit and TAG and a much more comprehensive study for Lucky Strike and Rainbow. Concentrations for a wide variety of semi volatile organic compounds (SVOCs) were obtained for the first time at all sites. Our results showed that a great part of the total organic carbon (TOC) could not be allocated by the total SVOCs studied here, suggesting that other processes/sources of organic carbon remain to be identified. The TAG organic geochemistry seemed entirely based on thermogenic processes whereas mixed processes may occur at the other vent field. The presence of n-alkanes suggested the contribution of a low-temperature fluid at all sites. An additional high-temperature organic matter degradation component was likely present at Menez Gwen and Lucky Strike. Our results also indicated that both abiogenic and biogenic processes produced organic compounds. Therefore, we suggest that a portion of the fatty acids at Menez Gwen and polyaromatic hydrocarbons (PAHs) at Rainbow may be derived from abiogenic processes, whereas biogenic processes could be responsible for the presence of n-fatty acids (n-FAs) at Lucky Strike and Rainbow. Moreover, organic geochemistry data appeared to be helpful in understanding some inorganic processes.

Environmental evolution and fire history of Rebun Island (Northern Japan) during the past 17,000 years based on biomarkers and pyrogenic compound records from Lake Kushu

Rebun is a small island located northwest of Hokkaido Island where hunter-fisher-gatherer cultural traditions continued until the 19th century CE. In this study, we quantified polycyclic aromatic hydrocarbons (PAHs), pentacyclic triterpene methyl ethers (PTMEs), n-fatty acids, and glycerol dialkyl glycerol tetraethers (GDGTs) in sediments from Lake Kushu in northern Rebun Island to reconstruct changes in limnology, the local environment and local to regional fire activities during the past 17,000 years (i.e., 17 ka). The PAH concentration increased from 11 to 10 cal ka BP. PAH and PTME compositions indicate that this change was associated with an increase of fire activity at proximal locations (i.e., the vicinity of Lake Kushu) and a change in the composition of grasses growing around the lake. A peak in PAH concentrations at 6.6–6.0 cal ka BP likely indicates intensive fire activity on Rebun Island. The PAH composition after 6 cal ka BP mainly reflected the combustion of conifers near the lake. The GDGTs, n-fatty acids, perylene, and PTME concentrations were higher around 10 cal ka BP and after 6 cal ka BP compared to the remaining periods, suggesting better preservation of those compounds under lake conditions marked by lower oxygen concentrations.

A sediment record of terrestrial organic matter inputs to Dongting Lake and its environmental significance from 1855 to 2019

The extensive anthropogenic activities and their potential impacts on lakes during the Anthropocene could be recorded in the sediments. In this study, the composition of biomarkers (i.e., n-alkanes and n-fatty acids), total organic carbon (TOC), and particle size in 210Pb-dated sediment cores from West Dongting Lake were investigated to trace the historical trend of anthropogenic inputs and their environmental significance. The TOC content was in the range of 3.15–27.32 mg g−1. The n-alkanes and n-fatty acids were distributed from C11–C33 and C12:0–C34:0, respectively. The short- and long-chain biomarkers accounted for a significant proportion of the total. Aquatic plants and algae living in West Dongting Lake were the main source (short-chain) followed by leaf waxes derived from terrestrial C3 plants (long-chain), as demonstrated by their concentrations. The variations of the key indicators i.e., the carbon preference index (CPI), aquatic plant n-alkane proxy (Paq), vascular plant n-alkane proxy (Pwax), and the ratio of unit short- to long-chain n-alkanes (L/H) also indicated that the aliphatic hydrocarbon fractions were mainly composed of short- and long-chain biomarkers. The sedimentary biomarkers had a significant temporal heterogeneity, which was controlled by different factors and sedimentary processes. Fine particles (<16 µm) were the dominant particle size (66.91%–78.52%) in the sediment. Both values of the dry/wet climate proxy (Kd) and average particle size were consistent over time. The dominance of terrestrial C3 plant-derived long-chain molecules gradually changed, with algae-derived short-chain molecules then becoming dominant. The hot and drought climate conditions and enhanced agricultural inputs from 1855 to 2019 in the watershed resulted in a decrease of terrestrial C3 plants and rapid growth of algae in the lake water.

A Lacustrine Biomarker Record From Rebun Island Reveals a Warm Summer Climate in Northern Japan During the Early Middle Holocene Due to a Stronger North Pacific High

The summer climate of northern Japan since the last glacial period has likely been determined by atmospheric and oceanic dynamics, such as changes in the North Pacific High, the position of the westerlies, the Kuroshio Current, the Tsushima Warm Current (TWC), and the East Asian summer monsoon. However, it is unclear which factor has been most important. In this study, we analyzed leaf wax δ13C and δD and glycerol dialkyl glycerol tetraethers (GDGTs) in sediments from Lake Kushu, Rebun Island, northern Japan, and discuss changes in climate over the past 17,000 years. The GDGT-based temperature, the averaged chain length, δ13C and δD of long-chain n-fatty acids indicated that the climate was cold during the Oldest Dryas period ∼16 ka and warm in the early Middle Holocene from ∼9 to 6 ka. This climate change is consistent with the sea surface temperature in the Kuroshio–Oyashio transition, but inconsistent with changes in the TWC in the Sea of Japan. The results imply that the summer climate of northern Japan was controlled mainly by changes in the development of the North Pacific Highviachanges in the position of the westerly jet and East Asian summer monsoon rainfall, whereas the influence of the TWC was limited over a millennial timescale.

Geochemical Characteristics of Hydrocarbons in Core Sediments From the Southwest Sub-Basin of the South China Sea and Its Implications for the Sedimentary Environment

Marine sediments are found to record various information for example the evolution of ocean and the exchange of matter and energy between the surrounding continents and oceans. The Southwest Sub-basin is one of the most important tectonic unit in the South China Sea Basin. The geochemical information of the sediments provides potential to understand the sedimentary history of the Southwest Sub-basin of South China Sea. In this paper, the aliphatic hydrocarbon compounds in two core sediments from the Southwest sub-basin were analyzed using lipid biomarker analysis. The average concentration of the total organic carbon (TOC) and the total nitrogen (TN) for both core sediment A and sediment B are similar, falling in the range of 0.64% ± 0.18 and 0.10% ± 0.02%, respectively. The C/N ratios vary from 3.2 to 11.1, reflecting that the organic carbon was a mixture of terrestrial and marine sources with more contributions from marine sources in core sediment B than sediment A. The long-chain n-alkanes of both core sediments show an even-odd predominance, reflecting the contributions of terrestrial higher plants and short-chain n-alkanes from marine plankton or bacteria. The Pr/Ph of core sediments A and B are 0.3–0.5 and 0.2–0.4, respectively, both of which are far less than 1, indicating that the sedimentary environment was dominated by strong reduction and long-term stability. The odd-even distribution of medium-chain n-alkanes (n-C14–20) in the core sediments A and B is due to the reduction of n-fatty acids with an odd carbon dominance in a strongly reductive depositional environment.