N-alkane Ratios Research Articles

Investigation of aliphatic hydrocarbons in core sediments of Brunei Bay, East Malaysia

The distribution of aliphatic hydrocarbons in three sediment cores from Brunei Bay was investigated in order to understand their sources and the biogeochemical processes of these hydrocarbons. The total concentrations of C15 to C37n-alkanes ranged from 0.70 to 16.5 μg g−1. Traces of hopanes with C29–C31 carbon homologs were detected in the study area. The carbon preference index (CPI15–37) ranged from 1.23 to 3.42 coupled with the natural n-alkane ratio (NAR19–32) ratios (1.52 to 5.34), and the presence of unresolved complex mixtures and hopanes, suggested slight contamination by anthropogenic hydrocarbons, presumably derived from activities along the coasts. The presence of C27 trisnorhopene and diploptene, as well as their association with long-chain and short-chain n-alkanes, revealed a depositional environment of organic matter in the sediment cores.

Hydroclimate variation during the Mystery Interval in the East Asian Summer Monsoon area

The inconsistency of paleoclimate records between the mid-low and high latitudes during the Mystery Interval (MI, 17.5–14.5 ka BP) is not well resolved. To provide a mechanism analysis, this study conducts spatial comparisons of hydroclimate changes in the Asian Summer Monsoon (ASM) region during the MI by reconstructing the paleohydrology of the south of East Asian Summer Monsoon (EASM) region using the molecular distributions and carbon isotope ratio of n-alkanes, as well as elemental and isotopic composition of bulk organic matter, in a sedimentary core retrieved from Dingnan (DN) wetland. The multiple indices of the DN core confirmed the occurrence of dry-wet and wet-dry transitions at ca. 17.5 ka BP and 16.0 ka BP, respectively. Synchronous with the dry-wet transition in the DN records, the Indochina Peninsula at a slightly lower latitude became wetter. In contrast, the middle Yangtze region at a more northern latitude became slightly drier, and North China did not show a hydrological variation. Moreover, the wet-dry transition at the mid-MI was strong in the Indochina Peninsula (10–20°N, at about 16.5 ka BP) and the southern EASM region (23–27°N, at about 16.0 ka BP) but was nearly absent in the middle Yangtze region (28–32°N) and North China (35–40°N). The first hydrological transition possibly connects with the synchronous southward movement of the Intertropical Convergence Zone (ITCZ) and the westerly jet caused by the cooling of the Northern Hemisphere. The absence of the second hydrological transition is interpreted as a result of the decoupling of the ITCZ and the westerly jet caused by the delayed formation of the ITCZ due to the warming of the Southern Hemisphere. This study reveals spatial differences in the hydroclimate variations during the MI and highlights the potential influence of coupling between the westerly jet and the ITCZ on rainfall in the ASM region.

Characterization of sedimentary organic matter and depositional processes in the Mandovi estuary, western India: An integrated lipid biomarker, sedimentological and stable isotope approach

A multiproxy study involving bulk (TOC, δ13Corg, grain size) and molecular (n-alkane biomarkers) analyses is used to investigate surface sediments from the Mandovi estuary in Goa, west coast of India to determine the origin, distribution and composition of organic matter (OM). The δ13Corg and n-alkane based indices (terrigenous/aquatic ratio (TAR) and Paq) indicate higher terrigenous OM accumulation in the river dominated upper reaches of the estuary. The presence of unresolved complex mixture (UCM), n-alkane indices (carbon preference index (CPI), average chain length (ACL), natural n-alkanes ratio (NAR)) and diagnostic isoprenoid ratios (pristane/phytane (Pr/Ph), Pr/n-C17, Ph/n-C18) helped to characterise intense human activity in the lower estuary. This conclusion is further supported by relatively high concentration of hopanes indicating petroleum contamination in the lower estuary. Furthermore, the study also highlights the important role of grain size on the distribution of OM along coastal margins, and provides detailed understanding of the variations in OM distribution/accumulation forced by natural processes and anthropogenic activities. The results of this study have significant implications for identifying natural and anthropogenic OM sources in estuarine systems especially in the context of increasing anthropogenic activities.

Duelling narratives of chironomids and pollen explain climate enigmas during The Last Glacial-Interglacial transition in North Island New Zealand

The Last Glacial-Interglacial Transition (LGIT) was a dynamic stage of Earth's history, and the difficulty of reconstructing this complex interval may be compounded by divergent proxy records, often collected from the same archive. To overcome this obstacle, we exploit the contrasting biological preferences of chironomids to both summer temperature and degree days (positive) and pollen to both the length of the growing season (positive) and winter duration (negative), recorded by a small lake in the central North Island of New Zealand. The climate proxy records are anchored to shifting zonal boundaries (e.g., southern westerly wind belt) via the hydrogen isotope ratios of leaf wax n-alkanes (δDwax). These results enable us to interrogate the structure of the LGIT and address two fundamental questions: 1) Is there evidence for Holocene-like temperatures during the early deglacial? and 2) Were early Holocene summers cool?Lake sediment δDwax values indicate a poleward retreat of the westerlies around 18,000 calibrated years before present (cal kyr BP), signalling the onset of climate amelioration for the region. Remarkably, the independently derived summer and mean annual temperature reconstructions are anti-phased. Chironomid-inferred summer temperatures surpass modern values by 17.5 cal kyr BP, whereas pollen-inferred mean annual temperatures remain supressed. Summers cool from 17.5 to 11 cal kyr BP, when they reach a minimum for the record, while winter and mean annual temperatures simultaneously warm to a maximum. The chironomid record generally traces regional insolation, although an Antarctic template imprints on this trend with declining summer temperatures during the Antarctic Cold Reversal (ACR) and warming during the Younger Dryas (YD). Forest development during the early LGIT, on the other hand, is supressed by cool, dry winters, punctuated by severe frosts, despite being set against a backdrop of overall warming; the successional pattern is best explained by a latitudinal retreat of the westerlies. Our findings underscore the complementarity of multiple bioproxy responses and reveal the importance of seasonal heat and energy distribution during the LGIT.

A multi-proxy reconstruction of the late Holocene climate evolution in the Kapsabet Swamp, Kenya (East Africa)

Multi-proxy high-resolution records relating to climate and dominant vegetation cover have been obtained from a peat deposit retrieved from the Kapsabet swamp in western Kenya. The 4-m long peat sequence provided a continuous sedimentation record spanning ca. 3023 cal yr BP to the present and is representative of the late Holocene changes in the relatively high-altitude part of the Lake Victoria catchment. Paleoenvironmental factors influencing peat formation and organic matter (OM) source inputs in Kapsabet were reconstructed based on total organic carbon, carbon accumulation rate, δ13C, δ15N, C/N ratio, and specific biomarker-based n-alkane ratios. The Kapsabet peat sequence was divided into five stages based on different climatic conditions: Stage 1 (3023–1670 cal yr BP) represents a progression from cool dry to wet conditions. Stage 2 (1670–1187 cal yr BP) is a relatively warm and wet period with increased productivity and high OM input. Stage 3 (1187–625 cal yr BP) represents gradual warming coeval to the late Holocene Medieval Warm Period. Stage 4 (625–188 cal yr BP) is a cool and wet period with high variability in precipitation and hydrological conditions representing the Little Ice Age. Stage 5 (188 cal yr BP to present) represents a relatively cool and wet period that coincides with the expansion of agriculture, particularly in the lowlands. The proxies indicate a progressive change from a forested landscape to an open woodland coeval to a decline in terrigenous inputs and the advent of more wet conditions. The climate on the highlands was less variable than in the lowlands, which underwent several periods of drought and intermittent wet conditions. The changes in the catchment coincided with the expansion of agriculture and land clearance marking increased human activities in the lowlands. Overall, the Kapsabet peat sequence tracks the regional climatic changes in East Africa and marks a promising sedimentary archive for palaeoclimate reconstruction from a region with a paucity of palaeoenvironmental and palaeovegetation histories.

Biomarkers in the rock outcrop of the Kazusa Group reveal palaeoenvironments of the Kuroshio region

Long-chain alkenones and n-alkanes preserved in marine and lake sediment cores are widely used to reconstruct palaeoenvironments. However, applying this technique to exposed sedimentary rock sequences is relatively challenging due to the potential for the diagenetic alteration of organic biomarkers. Here, we extract long-chain alkenones and n-alkanes from an exposed outcrop of the Kazusa Group in central Japan, one of the most continuous sedimentary successions in the world, covering almost the entire Pleistocene. We find that the alkenone unsaturation ratio and average chain length of n-alkanes appears to reflect the glacial-interglacial changes in sea surface temperature and terrestrial climate, respectively. Alkenone-based sea surface temperatures between 1.1 and 1.0 million years ago concur with foraminiferal Mg/Ca-based temperature estimates and may reflect an intrusion of the Kuroshio Current. We suggest that the preservation of these biomarkers in the Kazusa Group demonstrates its potential to provide a detailed palaeoenvironmental record.

A long-term investigation of the variation in leaf wax n-alkanes responding to climate on Dongling Mountain, north China

Long chain n-alkanes of leaf waxes are widely used in paleoclimatic reconstructions. The application of these proxies depends on profound understandings gained from studies of the relationship between climatic factors and long chain n-alkanes in living plants. However, a lot of uncertainties still exist in the relationship due to the interactions among climatic factors, geographical and topographical factors, and phylogeny. In addition, unrealistic or inaccurate climatic data also introduce errors. To evaluate the effect of climate with minimized interfering factors, we conducted long-term measurements of leaf wax n-alkanes of the plants growing on Dongling Mountain, north China from 2004 to 2019, where a meterological observatory is located. On the whole, total n-alkane concentration (Σalk) was positively correlated mean annual precipitation (MAP); average chain length (ACL) was negatively related to MAP; carbon preference index (CPI) had poor correlations with all climate factors. Compared with Σalk, ACL is a better indicator that reflects annual precipitation. The coefficient of ACL vs. MAP is 0.0015/mm. However, MAP accounted for only 40% of the variability in the year-averaged ACL of all plants together due to the significant interspecific differences in the response of leaf wax n-alkane distribution to climatic parameters; thus, ACL should be employed in parallel with other proxies to quantitatively reconstruct paleoprecipitation. We conducted a sample reconstruction of paleoprecipitation using ACL records preserved in the annually laminated sediments of Maar Lake Twintaung, Myanmar. The results of reconstruction using ACL are completely consistent with the results of reconstruction using carbon isotope ratios of n-alkanes, and are highly consistent with historical documents.

A potential suite of climate markers of long-chain n-alkanes and alkenones preserved in the top sediments from the Pacific sector of the Southern Ocean

Investigating organic compounds in marine sediments can potentially unlock a wealth of new information in these climate archives. Here, we present pilot study results of organic geochemical features of long-chain n-alkanes and alkenones and individual carbon isotope ratios of long-chain n-alkanes from a newly collected, approximately 8 m long, located in the far reaches of the Pacific sector of the Southern Ocean. We analyzed a suite of organic compounds in the core. The results show abundant long-chain n-alkanes (C29–C35) with predominant odd-over-even carbon preference, suggesting an origin of terrestrial higher plant waxes via long-range transport of dust, possibly from Australia and New Zealand. The δ13C values of the C31n-alkane range from −29.4 to −24.8‰, in which the higher δ13C values suggest more contributions from C4 plant waxes. In the analysis, we found that the mid-chain n-alkanes (C23–C25) have a small odd-over-even carbon preference, indicating that they were derived from marine non-diatom pelagic phytoplankton and microalgae and terrestrial sources. Furthermore, the C26 and C28 with lower δ13C values (~−34‰) indicate an origin from marine chemoautotrophic bacteria. We found that the abundances of tetra-unsaturated alkenones (C37:4) in this Southern Ocean sediment core ranges from 11 to 37%, perhaps a marker of low sea surface temperature (SST). The results of this study strongly indicate that the δ13C values of long-chain n-alkanes and {U}_{37}^{mathrm{k}} index are potentially useful to reconstruct the detailed history of C3/C4 plants and SST change in the higher latitudes of the Southern Ocean.

Bio-jet fuel range in biofuels derived from hydroconversion of palm olein over Ni/zeolite catalysts and freezing point of biofuels/Jet A-1 blends

According to the regulation announced by International Air Transport Association to reduce greenhouse gas emissions, there are many attempts to produce bio-jet fuels from natural oils to replace, at least in part, the fossil fuels. However, bio-jet fuels usually suffer from poor cold flow properties. Hence, this research aimed to convert palm olein to bio-jet fuel range with high content of iso-alkanes via hydroconversion over nickel (Ni)/zeolite-based catalysts. The levels of liquid biofuels classified as bio-gasoline, bio-jet and green diesel, including the selectivity for chemical compositions were evaluated. Under 40 bar initial H2 pressure at 360 °C for 4 h, the use of Ni/NH4-Beta catalysts (Ni content = 10 wt%) provided the maximum iso-/n-alkane ratio at 1.67 with a bio-jet yield of 20.8 wt%. The schematic reaction mechanism for this process was also proposed. The incorporation of platinum (Pt) into the Ni/NH4-Beta catalysts to a Pt/(Pt + Ni) wt ratio of 0.24 increased the bio-jet yield to 28.7 wt% with iso-/n-alkane ratio of 1.02. Differential scanning calorimetry thermograms indicated that the freezing temperature (Tf) of the biofuels decreased with increasing iso-/n-alkane ratio, where the Tf of the liquid biofuels with iso-/n-alkane ratio > 1.00 was not observed. For the biofuels/fossil jet fuel (Jet A-1) blends, the use of biofuels having iso-/n-alkane ratio of 1.67 could be blended with Jet A-1 up to 50/50 (v/v) and the Tf of the blended jet fuel was found at ca. −80 °C, which was lower than the limitation according to ASTM D1655-04a (−47 °C).

Evidence of terrestrial organic carbon inputs on Niger Delta Sea Shelf

The objective of this research is to determine the actual source of organic matter in the Niger Delta Sea Shelf (NDSS). Organic carbon (OC) and n-alkanes were investigated in the suspended matter (SM) and surfcial sediments of the Niger and Imo Rivers and the opposite Niger Delta Sea Shelf. Organic nitrogen and carbon isotope (δ13C) values were determined as additional parameters in the sediments. OC and n-alkane concentrations were highly variable. This variability was interpreted as the result of sources of materials from the inland basins and a complex sedimentation pattern involving the discharges of these two rivers. Using the constant ratio of high molecular weight odd n-alkanes to OC in both rivers, the estimated value of more than 70% of the OC preserved in shelf sediments were terrestrially-derived. This result was substantiated by the overall dominance of land-derived n-alkanes. A second approach using δ13C values and assuming binary dilution of riverine and marine OC led to the determined source of organic matter.
 Keywords: Organic carbon; δ13C; n-Alkanes; Niger River; Imo River; Niger Delta Sea Shelf.

Parent and methyl polycyclic aromatic hydrocarbons and n-alkanes emitted by construction machinery in China

Construction machinery emits considerable quantities of organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs) and n-alkanes, which significantly affect air quality, human health, and climate change. However, actions to reduce the pollution caused by these pollutants are insufficient due to a lack of comprehensive studies. Therefore, 16 United States Environmental Protection Agency (EPA) priority control PAHs (pPAHs), nine methyl PAHs (mPAHs), and 27 n-alkanes (C12-C38) in particulate matter (PM2.5) emitted by 20 construction machines of different types and emission standards, operated under three modes, were measured in this study. The results showed that (1) the total fuel-based emission factors of pPAHs, mPAHs, and n-alkanes for construction machinery were in the ranges 0.033–1.43, 0.027–1.37, and 1.32–87 mg/kg fuel, respectively. (2) The average emission factors of pPAHs, mPAHs, and n-alkanes in excavator and bulldozer emissions were higher than those in loader and forklift emissions, which can be attributed to machine type, operation mode, emission standards, and engine power. (3) Pry, Phe, C18-C22, 1-mNaP, and mFluo emissions were significantly dominant. Some diagnostic ratios of PAHs (e.g., Ant/(Ant + Phe), Flu/(Flu + Pry), BaA/(BaA + Chry), and IP/(IP + BghiP)) were consistent with those emitted by liquid fossil fuel combustion, whereas the ratios of low molecular weight n-alkanes (C ≤ 24) to high molecular weight (C > 24) n-alkanes from construction machines were higher than those for on-road gasoline vehicles, diesel vehicles, and vessels. (4) The benzo(a)pyrene equivalents (BaPeq) and lifetime cancer risk (LCR) values of PAHs from bulldozer and forklift emissions were higher than those from excavator and loader emissions, especially under working modes. Furthermore, the BaPeq and LCR values of PAHs from construction machineries were higher than that specified by GB3095-2012 and 10^−4, respectively, thereby indicating that PAHs emitted from construction machines pose high health risks.

Fingerprint of plant life in the Atacama Desert – Insights from n-alkane analyses

Although the Atacama is the oldest and most continuous dry desert on Earth, organic matter (OM) is ubiquitous in its surface sediments. Today, vegetation growth is restricted to the Coastal Cordillera and the Andean foothills, which are predominantly supplied by fog or rainfall. The sources of OM in topsoils of hyperarid regions and deep sediments remain an open question; therefore, we hypothesized that desert plants exhibit specific n-alkane compositions that can be traced in adjacent topsoils and assessed possible OM sources and formation processes in hyperarid regions and soil depths of desert. We determined the n-alkane signatures of plants (n = 28), of soil OM in their vicinity, of hyperarid surface sediments (n = 82), and of four depth profiles (up to 200 cm).We found that n-alkane distributions in fog-fed plants were dominated in order by nC31, nC29, nC33, and nC27 alkanes, while rain-fed plants were dominated by nC29 and nC31 alkanes. When the ratio of nC27+nC33/nC29+nC31 was applied as a “fog-to-rain n-alkane ratio”, the data in surface soils and sediments below 1200 m a.s.l. (in the west of the desert) indicated fog-influenced formation of organics, while all soils and sediments formed higher than 1200 m a.s.l. (in the center and east of the desert) archived n-alkanes from plants fed by rain. Surprisingly, 75–98% of the desert’s OM was found in deep sediments, even under recent vegetation cover. Hence, our findings indicate that currently vegetation-free hyperarid regions of the Atacama Desert once varied in size depending on climate change.

Leaf wax n-alkanes in leaves, litter, and surface soil in a low diversity, temperate deciduous angiosperm forest, Central Missouri, USA

ABSTRACT The leaf wax n-alkanes in modern ecosystems serve as proxies for assessing the ecologic and climatic conditions in soils, sediments and other geologic archives, and potentially as baselines for future ecological changes. In this study, the concentrations and distributions of long-chain (C25-C35) n-alkanes in fresh mature leaves, leaf litter fall, and surface soil (0-5 cm) from 0.4 ha, low diversity (oak-hickory-maple), deciduous angiosperm forest are quantified. Owing to degradation and dilution, leaf litter (350 ± 227 μg/g dw) and soil (13 ± 13 μg/g dw) each contain significantly lower concentrations of long-chain n-alkanes than fresh mature leaves (574 ± 291 μg/g dw). The average chain length and odd-even predominance (OEP) of fresh mature leaves increased and decreased, respectively, in leaf litter and soil indicating preferential and progressive degradation of the more abundant C27 and C29 homologues relative to less abundant C31 and C33 homologues. A poor relationship between OEP and a normalised n-alkane ratio(s) demonstrates the large potential effects of inter- and inner-species variability and/or varying effects of degradation on leaf wax n-alkanes, and highlights the potential limitations of the endmember modelling in paleo reconstructions.

Impact of monsoon, vegetation, and landscape on pedogenesis: A case study using organic and inorganic tracers from the Himalayan foreland sediments

The physical and chemical properties of paleosols are widely used to explain their genesis. However, the physical attributes of paleosols subjected to burial cannot be used for paleoenvironmental reconstructions. In contrast, selective pedogenic tracers such as rare earth (REE) and trace elements, and organic proxies such as pristane/phytane (Pr/Ph) ratios, and D/H and 13C/12C ratios of n-alkanes that are resistant to post-depositional processes can provide insight into pedogenic conditions. Although the upper Miocene Siwalik paleosols from the Himalayan Foreland Basin (HFB) have been used for past vegetation and climate reconstructions, little emphasis has been given to understand their formation. In this regard, the Jabbarkhad Siwaliks of the Kangra sub-basin, identified as distal alluvial fan deposits with records of temporal variability in rainfall and vegetation composition, have been used to investigate the combined impact of depositional environment, topography, climate and vegetation composition on paleosol formation.Prominent negative Eu-anomalies in CI-normalised REE patterns along with uniform ratios of refractory elements suggest a dominant and consistent source of sediments from K-rich granitic upper continental crust. A wide variation in the abundance of REE indicates the modification of sediments by pedogenetic processes. In the Jabbarkhad region, oxic (higher Pr/Ph) and well-drained soils favoured the proliferation of grasses. The high root density and organic turnover of grasses facilitated the development of a mature, strongly leached soil (high Ba/Sr) under high rainfall and humid conditions (lower δ2Η values). Less mature (lower Ba/Sr) paleosols were developed in low-lying anoxic (Pr/Ph <1) floodplain areas dominated by C3 trees near the active channel. Comparison of soil maturity from the Gangetic floodplain, a modern analogue of the Siwalik sediments, suggests that the spatial variability of paleosol maturity was controlled by the landscape mosaic of the Siwalik floodplain. Since pedogenesis and vegetation distribution are controlled by floodplain morphology, sampling of paleosols with similar pedogenic and geomorphic characteristics is essential for evaluation of vegetation distribution in temporally separated paleosols.

Distribution of n-alkanes and their δ2H and δ13C values in typical plants along a terrestrial-coastal-oceanic gradient

Reconstructing past responses of coastal wetlands to climate change contextualizes ongoing and future developments in these globally important ecosystems. The molecular distributions and stable isotope ratios (δ2H and δ13C) of sedimentary plant wax n-alkanes are frequently used to infer past vegetation and hydroclimate changes in wetland systems. However, there is limited modern information available about these compounds in subtropical wetlands. Here we analyzed mature leaves from 30 typical plant species and roots from 6 plant species collected in the Florida Everglades, including tree island plants, freshwater wetland plants, mangroves, and seagrass. The n-alkane abundance (2 to 884 µg/g dry weight), percent of aquatic plants ratio (Paq, 0 to 1), average chain length (ACL23-33, 24.0–30.7), concentration weighted average (CWA) δ2H (−231 to −78‰) and δ13C values (−38.9 to −14.4‰) spanned wide ranges with plant growth habit. Significant differences in n-alkane abundances, Paq, ACL23-33, CWA δ2H and δ13C values were found to exist between the leaves and roots of some emergent aquatic plants. Simple mass balance calculations of wetland aquatic plants suggest that long chain n-alkanes (e.g., C29n-alkanes) are predominantly derived from leaves rather than roots in wetland surface sediments/soils. However, the contribution from mid-chain n-alkanes (e.g., C23n-alkane) from roots may be equal to or greater than those from leaves. This implies that the differences in the isotopic compositions between root and leaf derived material need to be taken into account when interpreting down core changes in mid-chain n-alkane δ2H and δ13C values, which may be derived from variable contributions from leaves and roots rather than a change in hydroclimate or vegetation. Considering the large variation in both n-alkane distribution proxies and isotopic composition, no single molecular index or stable isotope ratio can capture multivariate changes of wetland ecosystems in the past. Nevertheless, principal component analysis shows promising potential to resolve different plant functional types. Paleo-reconstruction of subtropical aquatic ecosystems using n-alkanes will be most useful if the full molecular and isotopic distribution information of plant waxes are used.

Identifying eroded organic matter sources in sediments at fluvial system using multiple tracers on the Loess Plateau of China

Erosion is a fundamental phenomenon that governs the biogeochemical cycle of carbon (C) in the Earth system. Understanding the fate of eroded C at the watershed scale thus provides essential guidance for balancing the C budget and evaluating soil management strategies. In this study, we collected a total of 229 topsoils of source materials [land use types (forests, grassland, cropland, orchard, and fallow) and gully bank] and a total of 56 surface sediment samples [main river channel (18) and three tributaries (38) with different erosion intensity]. Multiple tracers (C and nitrogen (N) isotopes, molecular n-alkane biomarker, and spectroscopic indices) applied widely were then analyzed to determine relative source contributions to eroded organic matter (OM) (including bulk OM and water-extractable OM) in sediments at a broader watershed on the Loess Plateau of China. The results from an isotopic mixing model analysis showed that gully bank was the primary contributor of bulk OM in sediments, accounting for mean probability estimate (MPE) 55.3%, followed by “grassland” (MPE 21.0%), “cropland” (MPE 14.4%), and “forests” (MPE 9.3%). The contributions of grassland and cropland showed an increasing trend from upstream to downstream sections of the studied watershed. The contribution of forests was found higher in upstream than those of midstream and downstream. Along with previous evidences, our results show that erosion intensity mainly affects the proportion of C source, where gully bank was found as the highest contributor in three associated catchments, especially in region with light erosion intensity. We further demonstrated that the sediment bulk OM deposited was mainly derived from the region with light erosion intensity at the broader watershed scale. Moreover, results of n-alkane ratios and spectroscopic indices also implied that biological production of OM other than terrestrial sources (i.e., soil OM) might play a critical role in source contribution of water-extractable OM in sediments of main river channel.

Environmental fluctuation impacted the evolution of Early Pleistocene non-human primates: Biomarker and geochemical evidence from Mohui Cave (Bubing, Guangxi, southern China)

Quaternary climate variability, profoundly impacting the evolution and distribution of plants and animals across the globe, has been reconstructed by many sediment archives. Here, we track past changes of temperature, rainfall and plant type by using the n-alkane and glycerol dialkyl glycerol tetraethers (GDGTs), as well as weathering and pedogenesis by mineralogical and geochemical proxies from a 250 cm deep soil sediment profile from the Early Pleistocene deposits in Mohui Cave, southern China. Indices for weathering intensity such as mineral composition (quartz, feldspar and calcite), major element proxies (Ti/Na, Al/Na, Al/Mg, Ti/Mg, CIW, PIA, CPA, CIA), trace element proxies (Ba/Sr and Rb/Sr), and biomarker proxies (OEP, LSR and CPI) show similar secular trends, revealing a three-stage historical accumulation. The high long-chain n-alkane ratios (C31/C29 and (C31+C33)/(C27+C29)) indicate that the vegetation in the region had increases in percentage of woody plants and decreases in herbs during periods of relatively lower temperature and less precipitation, which evidenced from GDGTs, consistent with a weak weathering process influenced by summer monsoon strength. Further, we compared the distribution of these plant types with the taxonomic variation in the vertebrate paleontological fossils excavated from the same profile in Mohui Cave. The distribution of Lufengpithecus appears in only one interval but Gigantopithecus blacki appears throughout the profile, despite an environment that experienced transitional stages from grassland to woodland in relatively cooler and drier conditions. We infer that in face of these climatic changes Lufengpithecus may have preferred to emigrate from the region, while Gigantopithecus blacki may have stayed given that it was limited to staying in its core area.

A comparison of methods for estimating forage intake, digestibility, and fecal output in red deer (Cervus elaphus).

The objective of this experiment was to determine appropriate methods for estimating fecal output, digestibility, and intake in red deer (Cervus elaphus). Dry matter intake (DMI), digestibility, and fecal output were estimated using the dual-marker (titanium dioxide; TiO2 and indigestible acid detergent fiber) technique, double n-alkane ratio technique (ALK) and the pulse dose (Yttrium; Y) technique to determine a suitable method to estimate DMI, fecal output, and digestibility measurements. Four male and four female deer were stratified by sex and randomly assigned either fresh-cut perennial ryegrass (Lolium perenne L.) or fresh-cut plantain (Plantago lanceolata) ad libitum in a cross-over design experiment. Actual DMI (mean ± SD: 1.5 ± 0.36 kg DM/d), digestibility (0.70 ± 0.06), and fecal output (0.45 ± 0.1 kg DM/d) were measured daily over the collection periods, and the average of each period was used for methods' comparison. The ALK method adequately estimated digestibility and fecal output of plantain; however, overestimated digestibility (P < 0.05) and DMI of ryegrass, so that there was no statistical agreement (P > 0.10) in DMI when diets were pooled. The overestimated DMI of the ryegrass diet led to ALK predicting greater intake when deer consumed ryegrass than plantain, which was the opposite of actual measurements. The pulse dosed Y overestimated (P < 0.05) fecal output and consequently DMI for both plantain and ryegrass, however, indicated similar trends to actual values. The dual-marker technique using TiO2 was able to detect the statistical differences between plantain and ryegrass as the actual measurements, had moderate to strong precision (r = 0.50 to 0.66) and statistical agreement (P < 0.05) with the pooled diet data. Therefore, the dual-marker technique provided the best alternative estimation method to actual measurements of forage DMI of grazing red deer.

Leaf wax &amp;lt;i&amp;gt;n&amp;lt;/i&amp;gt;-alkane patterns and compound-specific &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C of plants and topsoils from semi-arid and arid Mongolia

Abstract. Leaf wax n-alkane patterns and their compound-specific δ13C signatures are valuable proxies for paleoenvironmental reconstructions. So far, their potential has not been investigated in semi-arid to arid Mongolia. We have therefore analysed the leaf wax n-alkanes and their compound-specific δ13C signature of five plant species (Poaceae, Cyperaceae, Artemisia spp., Caragana spp. and Larix sp.) and topsoils (0–5 cm) along two transects in central and southern Mongolia. Grasses show a distinct dominance of the n-C31 homologue, whereas the shrubs Caragana spp. and Artemisia spp. are dominated by n-C29. Larix sp. is characterised by the mid-chain n-alkanes n-C23 and n-C25. From plant to topsoil, n-alkane patterns show the potential to differentiate between grass-covered sites from those covered by Caragana spp. n-Alkane concentrations and odd-over-even predominance (OEP) of the topsoils are distinctly influenced by mean annual temperature, mean annual precipitation and aridity, likely reflecting the degree of n-alkane degradation and biomass production. In contrast, the average chain length (ACL) and the n-alkane ratio (n-C31∕n-C29+n-C31) are not affected by climatic parameters and, thus, are not biased by climate. The compound-specific δ13C signatures are strongly correlated to climate, showing a significant enrichment with increasing aridity, indicating the effect of water use efficiency. Our calibration results suggest that long-chain n-alkanes and their compound-specific δ13C signatures have great potential to reconstruct paleoenvironmental and paleoclimatic conditions when used in sediment archives from Mongolia.

Paleoenvironmental implications of molecular and carbon isotopic distributions of n-alkanes in the hominoid-bearing upper Miocene sediments from the Zhaotong Basin, southwestern China

It is crucial to understand the relationship between hominoid primates and their living environment. Located at the southeastern margin of the Tibetan Plateau, the Shuitangba (STB) outcrop from the Zhaotong Basin is famous for bearing the remains of the youngest known ape fossil in the terminal Miocene (~6.2 Ma). In this study, the molecular and carbon isotope compositions of n-alkanes, together with the loss on ignition and the bulk carbon isotope composition of total organic matter, were investigated in the STB outcrop to infer the paleoenvironmental conditions in this uppermost Miocene sedimentary sequence, with the emphasis on the habitat of the STB hominoid. In the hominoid-bearing peaty clay layer and the surrounding lignite layers, the n-alkane molecular and carbon isotope compositions support a primary contribution from terrestrial higher plants. In contrast, n-alkanes in the upper shallow lake sediments are derived from multiple origins, mainly from aquatic plants and bacteria. Both carbon preference index (CPI) and average chain length (ACL) vary closely with the lithology, but the CPI record shows the larger amplitude of change than the ACL and varies sharply during the lithological boundary. It is notable that the changes of the molecular and carbon isotope compositions of long-chain n-alkanes do not parallel with the abrupt increase of Poaceae pollen percentage during the STB hominoid appearing stage. Such an inconsistency between herb pollen percentage and n-alkane ratios may result from the different sources. Our results clearly support that these organic matter-based ratios have the potential to record the paleoenvironmental changes in ancient lacustrine sediments.