Leaf Wax N-alkanes Research Articles

Decoupling Distribution of n-Alkanes in Aeolian Sand and Vegetation of the Northern Ulan Buh Desert, China: Insight into Organic Matter Preservation in Arid Regions.

Fallen leaves and their decomposition directly deposit leaf wax n-alkanes into sediments, which can be used to identify local flora. These n-alkanes are important for studying past vegetation and climate, but their distribution in sediments must be known. Aeolian sand n-alkanes are particularly important for understanding paleoclimates in arid regions, despite the challenges of extraction due to their extremely low abundance. To investigate the preservation of plant leaf wax n-alkanes in deserts, we analyzed n-alkanes in aeolian sands from the Northern Ulan Buh Desert (UBD), China, and compared them to the surrounding vegetation. We calculated the total n-alkane concentration (ΣALK), average chain length (ACL21-35), and carbon preference index (CPI21-35). In the Northern UBD, aeolian sand n-alkanes have lower ΣALK, indicating microbial degradation. The eastern aeolian sand has lower CPI21-35 and ACL21-35 than the adjacent vegetation, whereas the western sand values are consistent with the plants, likely due to the transport of plant-derived materials by wind and water from the nearby mountains. Our study shows that sedimentary n-alkane signatures are not only determined by local vegetation but also influenced by environmental factors like temperature and precipitation. Additionally, local deposition processes play a significant role in determining the properties of these n-alkanes.

Terrestrial response to the Early Cretaceous Weissert Event: Insights from carbon isotope records of organic matter and leaf wax n-alkanes in an inland East Asian lake

The Weissert Event (WE), a significant Early Cretaceous environmental disruption, is recognized globally in marine carbonate records for its positive carbon isotope excursion (CIE), organic matter (OM) enrichment, and widespread anoxia. However, records of its terrestrial impact are sparse. This study examines carbon isotope compositions (δ13C) from the lacustrine facies of North China's Dabeigou Formation (Yushuxia section, Luanping Basin). The synchronous positive CIEs of total organic carbon (TOC) and C27–C31n-alkanes within Members 2 to 3 of the Dabeigou Formation corroborate the Weissert Event, marking its first terrestrial observation in North China. Ratios of the isoprenoids pristane and phytane (Pr/Ph), Corg/P ratios and enrichment factors (EFs) of redox-sensitive trace metals (Mo and U) indicate transient anoxic conditions within a mainly oxic-suboxic setting from the late Valanginian to early Hauterivian, which were unfavorable for OM preservation. This highlights that although a global positive CIE occurred during the Weissert Event, anoxia and/or high TOC deposition in inland lakes were not inherent features.

Leaf wax n-alkane distribution and hydrogen isotopic fractionation in fen plant communities of two Mediterranean wetlands (Tenaghi Philippon, Nisí fen—Greece)

Many continental paleoclimate archives originate from wetland sedimentary sequences. While several studies have investigated biomarkers derived from peat-generating vegetation typical of temperate/boreal bogs (e.g., Sphagnum), only scant information is available on emergent plants predominant in temperate/subtropical coastal marshlands, peri-lacustrine and fen environments. Here, we address this gap, focusing on two wetlands in the Mediterranean (Nisí fen and Tenaghi Philippon, Greece). We examined the concentration, homologue distribution, and hydrogen stable isotopic composition (δ2H) of leaf wax n-alkanes in 13 fen plant species, their surrounding soil, and surface water during the wet growing season (spring) and the declining water table period (summer). Our findings indicate that local graminoid species primarily contribute to the soil n-alkane signal, with a lesser influence from forbs, likely owing to differences in morphology and vegetation structure. The δ2H values of surface and soil water align with local average annual precipitation δ2H, reflecting winter-spring precipitation. Consistently, the average δ2H of local surface, soil, and lower stem water showed negligible evaporative enrichment, confirming minimal 2H-fractionation during water uptake. We find that δ2H values of source water for wax compound synthesis in local fen plants accurately mirror local annual precipitation. Furthermore, despite differences between leaves and lower stems in n-alkane production rates, their δ2H values exhibit remarkable similarity, indicating a shared metabolic substrate, likely originating in leaves. Our net 2H-fractionation values (i.e., precipitation to leaf n-alkanes) align with those in Chinese highlands and other similar environments, suggesting consistency across diverse climatic zones. Notably, our data reveal a seasonal decrease in the carbon preference index (CPI) in plant samples, indicating wax lipid synthesis changes associated with increased aridity. Additionally, we introduce a new parity isotopic difference index (PID) based on the consistent δ2H difference between odd and even n-alkane homologues. The PID demonstrates a strong anticorrelation with plant CPI, suggesting a potential avenue to trace long-term aridity shifts through δ2H analysis of odd and even n-alkane homologues in sedimentary archives. While further development of the PID is necessary for broad application, these findings highlight the intricate interplay between plant physiology, environmental parameters, and sedimentary n-alkanes in unravelling past climatic conditions.

Variability of leaf wax n-alkanes across gradients of environment and plant functional type in China

The abundance and distribution of long-chain n-alkanes in sedimentary archives have been proposed as plant-derived paleoenvironmental proxies. The reliable application of these proxies hinges on comprehensive understandings drawn from investigations of living plants. However, previous studies have predominantly relied on narrow environmental gradients and limited datasets sourced from local and regional sampling. As a result, our comprehension of how n-alkanes in living plants respond to climate factors on larger spatial scales remains unclear, especially across different plant functional types (PFTs). In this study, we analyzed the abundance and distribution of n-alkanes in the leaves of 552 plant samples from diverse regions in China and explored the variability of leaf wax n-alkanes across gradients of climate and PFTs. Average chain length (ACL) and carbon preference index (CPI) exhibit statistically significant differences between various PFTs, and the ratio of C33/(C31 + C33) holds the potential to distinguish between C3 and C4 vegetation types. The n-alkane concentration (Σalk) is primarily controlled by precipitation, with a notable negative correlation between Σalk and mean annual precipitation (MAP) that is independent of PFTs. Overall, ACL is negatively related to MAP and positively to mean annual temperature (MAT), but the relationship varies across PFTs. MAT is a stronger driver of ACL for C4 herbs and woody plants, while MAP exerts a more pronounced influence on C3 herbs. CPI in most PFTs shows no correlation with environmental variables. These findings indicate Σalk is a good indicator of precipitation, and ACL is indicative of precipitation or temperature depending on the specific PFT; CPI appears unsuitable as a climate indicator and great caution should be exercised in using CPI records in paleoclimate research.

Insights into the provenance implication of leaf wax n-alkanes along the lower Yellow River

Insights into the provenance implication of leaf wax n-alkanes along the lower Yellow River

Behaviourally modern humans in coastal southern Africa experienced an increasingly continental climate during the transition from Marine Isotope Stage 5 to 4

Linking human technological and behavioural advances to environmental changes is challenging, as it requires a robust understanding of past climate at local scales. Here, we present results from regional high-resolution numerical simulations along with climate data directly from the archaeological sequence of Blombos Cave (BBC), a well-studied site in coastal southern Africa. The model simulations cover two distinct periods centred at 82 and 70 thousand years (ka) ago (Marine Isotope Stage [MIS] 5 and the onset of MIS 4, respectively), when orbital parameters and global sea level were markedly different from one another. Climatic changes from 82 to 70 ka are determined through four simulations that use past and present-day coastline configurations. The hydrogen isotopic composition of leaf waxes (δ2Hwax) and n-alkane distributions and abundances are used to reconstruct hydroclimate around BBC. The leaf wax n-alkane record, one of the first produced in an archaeological setting in this region to date, can be interpreted as a drying signal from MIS 5c to 4. This agrees with our modelling results, which indicate a drier and more continental climate over coastal southern Africa at 70 ka, compared to 82 ka. The simulated aridification is most evident from the reduced precipitation amounts in both summer (∼20%) and winter (∼30%). The annual number of summer days (Tmax ≥ 25 °C) and cold nights (Tmin < 5 °C) in the vicinity of BBC increases more than 5 and 3-fold, respectively, under the more continental climate at 70 ka. Weaker westerly winds in winter, a cooler Agulhas Current, and a land surface expansion associated with the coastline shift due to lower sea levels at 70 ka all contribute to the simulated climate shift. Our approach highlights the importance of multiple lines of evidence for achieving robust results, while demonstrating how both large-scale forcing and local influences worked together in shaping the local climate that early humans lived in. Adaptation to a drier climate and increased continentality around BBC might have induced greater mobility, which led to increased population interactions, cultural transmission rates, skill exchange, and material complexity during the so-called Still Bay period.

Hydroclimate variations over the last 17,000 years as estimated by leaf waxes in rodent middens from the south-central Atacama Desert, Chile

Leaf cuticular waxes are one of the most important environment-plant interaction structural systems that enable desert plants to withstand extreme climatic conditions. We present a long chain n-alkyl lipids study in fresh plant leaves and rodent palaeomiddens collected along an elevational gradient in the south-central Atacama Desert of Chile, covering six different vegetation belts: Steppe (4500-4000 m asl), Puna (4000-3300 m asl), pre-Puna (3300-2400 m asl), Absolute Desert (2400-1000 m asl) and Coastal Desert (1000-0 m asl). The 28 rodent palaeomiddens analyzed from Quebrada Incahuasi (25.6 °S, 3600 m asl) span the last 17,000 years. Modern-day distribution of long-chain n-alkanes and n-alkanoic acids varies among the dominant plant associations of the Atacama Desert. These plants show a species-specific chemotaxonomy linked to the climatic conditions. Furthermore, differences in average chain length (ACL) and carbon preference index (CPI) suggest that these plant communities are highly adapted to extreme environmental conditions. The sum of leaf wax n-alkanes was highest under wet conditions, while n-alkanoic acids (between n-C24 and n-C28) increased with hyperaridity. Similarly, analysis of n-alkane time series from palaeomiddens showed that the greatest changes in leaf wax n-alkane distributions (ACL and CPI) corresponded to the greatest increases in moisture during the Central Andean Pluvial Event (CAPE; between 18 and 9 ka cal BP) and the Late Holocene. The shift in the palaeomidden n-alkane distributions is corroborated by the relative abundance of rainfall-dependent extra-local taxa. This is the first study to report leaf wax content obtained from ancient rodent middens, and shows promising results as a robust hydroclimate proxy for the Atacama Desert region.

Controls on the hydrogen isotope composition of tetraether lipids in an autotrophic ammonia-oxidizing marine archaeon

The stable hydrogen isotope composition of persistent biomolecules is used as a palaeohydrological proxy. While much previous work has focused on plant leaf wax-derived n-alkanes, the potential of prokaryotic lipid biomarkers as carriers of H isotope signatures remains underexplored, particularly in the Archaea. Here we investigated H isotope distributions in the membrane lipids of the ammonia-oxidizing chemoautotroph Nitrosopumilus maritimus strain SCM1. Hydrogen isotope ratios were measured on the cleaved biphytane chains of tetraether membrane lipids extracted from steady-state continuous cultures cultivated at slow, medium, and fast growth rates. In contrast to recent work on bacterial fatty acids, where the direction and magnitude of isotopic fractionation varies widely (ca. 600‰ range) as a function of central C and energy metabolism, archaeal biphytane data in the present work are relatively invariant. The weighted average 2H/1H fractionation values relative to growth water (2εL/W) ranged from –272 to –260‰, despite a three-fold difference in doubling times (30.8–92.5 hr), yielding an average growth-rate effect <0.2‰ hr−1. These 2εL/W values are more negative than most heterotrophic microbial lipid H isotope measurements in the literature, and are on par with those from other autotrophic archaea, as well as with phytol from photoautotrophic algae. N. maritimus values of 2εL/W also varied systematically with the number of internal rings (cyclopentyl + cyclohexyl), increasing for each additional ring by 6.4 ± 2.7‰. Using an isotope flux-balance model in tandem with a comprehensive analysis of the sources of H in archaeal lipid biosynthesis, we use this observation to estimate the kinetic isotope effects (KIEs) of H incorporation from water; from reducing cofactors such as flavins and NADPH, and for the transhydrogenation reaction(s) that convert the electron-donor derived NADH into these cofactors. Consistent with prior studies on bacteria and plants, our results indicate the KIEs of reducing cofactors in archaea are highly fractionating, while those involving exchange of water protons are less so. When combined with the observation of minimal growth-rate sensitivity, our results suggest biphytanes of autotrophic 3HP/4HB utilizing Nitrososphaerota (a.k.a. Thaumarchaeota) may be offset from their growth waters by a nearly constant 2εL/W value. Together with the ring effect, this implies that all biphytanes originating from a common source should have a predictable ordering of their isotope ratios with respect to biphytane ring number, allowing precise reconstruction of the original δ2H value of the environmental water. Collectively, these patterns indicate archaeal biphytanes have potential as paleo-hydrological proxies, either as a complement or an alternative to leaf wax n-alkanes.

Rainshadow effect on hydrogen isotopes in leaf wax n-Alkanes across the Cascade Mountains of Washington, USA

Rainshadow effect on hydrogen isotopes in leaf wax n-Alkanes across the Cascade Mountains of Washington, USA

Paleoaltimetry performance of coupled δ2Hwax-[formula omitted] proxy in semiarid conditions

The multi-proxy approach is becoming an effective means to reduce uncertainties and errors compared to the single proxy approach. In this study, we investigated leaf wax biomarker and brGDGTs in topsoils along a semiarid elevation transect on the Chinese Loess Plateau. We found that both leaf wax n-alkane δ2Hwax values and brGDGTs-derived MBT5ME′ decreased significantly with elevation, and thus the coupled δ2Hwax-MBT5ME′ proxy can improve correlation coefficients (R2 = 0.96) compared to a single proxy (R2 = 0.82 and 0.90 for δ2Hwax and MBT5ME′, respectively) and reduce the uncertainty (RMSE = 230 m) relative to a single proxy (RMSE = 275 m and 360 m for δ2Hwax and MBT5ME′, respectively) in elevation estimates. Then we tested the effectiveness and advantages of coupled δ2Hwax-MBT5ME′ proxy from surface soils on the Tibetan Plateau compared to a single proxy. Collectively, the coupled δ2Hwax-MBT5ME′ proxy can be used as a potentially advantageous proxy for reconstructing paleoelevation in semiarid conditions.

Apparent fractionation of hydrogen isotope from precipitation to leaf wax n-alkanes from natural environments and manipulation experiments

Knowledge of hydrogen isotopic fractionation (ε) of plant leaf waxes is the foundation for applying hydrogen isotope values (δ2H) in environmental reconstructions. In this work, we systematically investigated plant ε values (εalk/precipitation, εalk/soil water, εalk/leaf water and εalk/lake water, representing the isotopic fractionation between plant n-alkane δ2H and precipitation δ2H, soil water δ2H, leaf water δ2H and lake water δ2H) from the natural environments and manipulation experiments. The results show that the εalk/precipitation values of terrestrial plants have large variations (from −190 ‰ to −20 ‰) and become more negative with increasing aridity index. This phenomenon is possibly caused by the δ2H changes in source water (from precipitation to soil water and then to leaf water) during plant leaf wax synthesis under various evapotranspiration conditions in different climatic zones. The rainfall manipulation experiments show that leaf water δ2H values are generally higher than soil water δ2H values, and the latter are higher than precipitation δ2H values. This finding further demonstrates that the evapotranspiration effect on source water δ2H affects the quantification of the leaf wax apparent ε values (εalk/leaf water < εalk/soil water < εalk/precipitation). The εalk/lake water values of submerged plants display a smaller range (−153 ± 5 ‰) than the εalk/precipitation values of terrestrial plants, which is close to the terrestrial εalk/precipitation values in humid areas. Therefore, the biosynthetic ε value of terrestrial plant leaf waxes is relatively constant (ca. –153 ± 5 ‰), and the observed variable apparent εalk/precipitation values are possibly caused by the varied degree of evapotranspiration effect on the water that plants used in different climatic conditions. This effect should be considered when applying δ2H values of leaf waxes to trace environmental changes.

Weak precipitation δ2H response to large Holocene hydroclimate changes in eastern North America

In eastern North America, annual precipitation increased by >40% over the Holocene, largely in response to melting of the Laurentide Ice Sheet. The change substantially raised lake levels and transformed conifer-dominated ecosystems into mesic deciduous forests. δ2H values of terrestrially derived leaf-wax n-alkanes can facilitate diagnoses of the climate dynamics involved by reconstructing δ2H values of mean annual precipitation (δ2HMAP). However, competing influences on δ2HMAP values in the mid-latitudes, such as changes in moisture sources and in the seasonal distribution of precipitation, can generate confounding effects. To test δ2HMAP sensitivity to potential changes associated with the final Holocene phases of deglaciation in eastern North America, we used 14 fossil-pollen records to reconstruct monthly precipitation changes and to model δ2HMAP values during the Holocene. The pollen-inferred precipitation increased by 100–200 mm during both cold and warm seasons, but modeled δ2HMAP values changed by only ∼10‰, because isotopically-heavy summer precipitation increased by nearly as much as the cold-season isotopically-light winter precipitation. Three new leaf wax n-C29-alkane (δ2HC29) records spanning the Holocene from Vermont, Pennsylvania, and Massachusetts closely follow modeled δ2HMAP trends and confirm only a small decline in δ2HMAP values over the Holocene. Because the shifts in precipitation seasonality accurately predict the n-alkane records, changes in moisture sources or pathways appear to play only a minor role in the regional δ2HMAP history despite the effects of deglaciation on atmospheric circulation. Soil evaporation also did not significantly alter δ2HC29 values from the values predicted using the pollen-derived reconstructions. The results affirm that δ2HC29 values faithfully detected anticipated isotopic changes in δ2HMAP values, but that important paleoclimate events may not always yield strong changes in δ2HMAP values.

Leaf wax biomarkers of a high-mountain lake area in western iberia—Implications for environmental reconstructions

Leaf wax n-alkane biomarkers are widely used to infer past vegetation dynamics and hydroclimate changes. The use of these compounds strongly relies on the characterization of modern plants. However, few studies have explored leaf waxes of modern plants and their application to reconstructing climate and environmental changes in the Iberian Peninsula, a region known for its high vulnerability to climate change. In this study, we characterize the distributions and compound-specific isotopic compositions of the leaf waxes of dominant plants in the vegetation cover, soil, and surface sediment of the Lake Peixão area, a high-mountain glacial lake in Serra da Estrela (central Portugal). Our results show that the modern oro-Mediterranean (subalpine) vegetation of the study area is dominated by C3 grasses/herbs and shrubs that preferentially produce long-chain leaf waxes (≥C27). The C31n-alkane display the overall highest concentration, produced by some grasses and shrubs, but especially Erica sp (heather), which is highlighted as a major source for the total n-alkane pool in the lake sediments. C29 is the second-most abundant and the most equally produced n-alkane of the vegetation cover; C25 and C27 homologs are mainly associated with aquatic-related grasses/herbs, while C33 and C35 are particularly linked to cold-drought tolerant Juniperus sp. shrubs. Shrubs show higher but proportional values than grasses/herbs in the isotopic space, suggesting a directly proportional physiological adaptation of the two ecological forms to the prevailing climatic and environmental factors of the study area. C29 is pointed as the most representative (or less plant-biased) leaf wax n-alkane in the lake sediments. Thus, δD of C29n-alkane is interpreted as a robust terrestrial hydrological indicator (δDterr), which signal is believed to be strongly influenced by the mean air temperature and/or precipitation amount. Despite the sparse vegetation and small catchment area, the apparent hydrogen fractionation factor, determined from δDterr of the lake surface sediment, is in line with the modeled global mean values for the latitude of the study area. The different molecular and compound-specific signatures of the studied oro-Mediterranean species have the potential to support future interpretations of leaf wax biomarkers in the Iberian Peninsula.

Quantitative reconstruction of the relative humidity by a coupled δ18O-δ2H approach during the Younger Dryas in central China

Paleoclimate records in central China reveal asynchronous hydroclimate changes to those from both northern and southern China during the Holocene. Whether such a spatial mode works for the Younger Dryas event (YD), a prominent abrupt climate change during the transition from the last glacial to the Holocene, is poorly constrained by quantitative records. In this study, we apply the novel coupled hydrogen isotope composition of leaf wax n-alkanes and oxygen isotope of hemicellulose (δ2Hn-alkane-δ18Osugar) paleohygrometer approach to reconstruct the paleo relative humidity (RH) on a peat layer spanning 13.1–10.0 cal ka BP in the Dajiuhu peatland, central China. The coupled δ2Hn-alkane-δ18Osugar approach reveals that the RH was relatively low in the period of 12.7–12.1 cal ka BP (RH avg. 79%, 1σ 4.9%) and then turned to relatively high values during 12.1–11.7 cal ka BP (RH avg. 88.6%, 1σ 3.9%). A dry interval happened from the end of the YD to 11.3 cal ka BP (RH< 80%). A general wetting trend during the YD period in central China contrasts with the prevailing drying in northern China and maybe also in southern China. The occurrence of a wetting trend during the YD period in central China probably results from the interplay between the westerlies and the East Asian summer monsoon under a context with weak summer monsoon intensity.

Mid- and long-chain leaf wax δ2H values in modern plants and lake sediments from mid-latitude North America

Compound-specific δ2H values of leaf wax n-alkanes are increasingly being used to infer past hydroclimates. However, differences in n-alkane production and apparent fractionation factors (εapp) among different plant groups complicate the relationships between n-alkane δ2H values and those of environmental water. Mid- and long-chain n-alkanes in sedimentary archives (i.e., n-C23 and n-C29) are thought to derive from aquatic and terrestrial plants, respectively, and track the isotopic composition of either lake water or precipitation. Yet, the relationship between n-C23 δ2H values and lake water δ2H values is not well constrained. Moreover, recent studies show that n-alkane production is greater in terrestrial plants than in aquatic plants, which has the potential to obscure n-alkane aquatic inputs to sedimentary archives. Here, we investigated n-alkane contributions to sedimentary archives from both aquatic and terrestrial plants by analyzing n-alkane δ2H values in plants and lake sediments at 29 sites across mid-latitude North America. We find that both aquatic and terrestrial plants synthesize n-C23 and that sedimentary n-C23 δ2H values parallel those of terrestrial plants and differ from those of aquatic plants. Our results indicate that across mid-latitude North America, both mid- and long-chain n-alkanes in lake sediments commonly derive from terrestrial higher plants challenging the assumption that submerged aquatic plants produce the n-C23-alkane preserved in lake sediments. Moreover, angiosperm and gymnosperm plants exhibit similar εapp values between n-C29 and mean annual precipitation (MAP) δ2H values across North America. Therefore, vegetation shifts between angiosperm and gymnosperm plants do not strongly affect εapp values between n-C29 and MAP. Our results show that both mid- and long-chain n-alkanes track the isotopic composition of MAP in temperate North America.

Inverse relationships between salinity and hydrogen isotope fractionation of n-alkanes in the Aegiceras corniculatum leaves and surface sediments from Zhanjiang mangrove estuary of China

Hydrogen isotope ratios of mangrove lipids have recently gained increasing interest because of their potential for reconstructing past water salinity and paleohydrology conditions. Although it has been suggested that the deuterium fractionation in mangrove leaf lipids appears to be primarily affected by water salinity, it remains an important research topic if this inverse relationship between salinity and hydrogen fractionation in leaf wax can be universally applied. In this regard, we have investigated the hydrogen isotopic composition of n-alkanes in leaves of Aegiceras corniculatum and surface sediments and the environmental water (surface water; αn-alkane-Water), collected along a 30 ppt salinity gradient in the Zhanjiang mangrove estuary of China, aiming to evaluate the impact of water salinity on the hydrogen isotopic fractionation of leaf wax derived n-alkanes. δ2H values of A. corniculatum leaf wax n-alkanes were between −183‰ and − 127‰ for C27, C29, and C31n-alkanes, and their αn-alkane-Water values range from 0.823 to 0.887. Sedimentary δ2H values range from −171‰ to −132‰ for C27, C29, and C31n-alkanes, and their αn-alkane-Water values were between 0.832 and 0.887. Inverse relationships between αn-alkane-Water and salinity were observed in mangrove A. corniculatum and surface sediment. This relationship for mangrove A. corniculatum may result from the selective utilization of freshwater during the rain event, changes in biosynthetic fractionation, and the relatively high humidity and/or larger changes in water vapour isotopic composition. For surface sediment, the inverse relationship could be mainly attributed to the mangrove-derived organic matter input, as the principal component analysis (PCA) results demonstrated a strong connection between the studied mangrove tree and the surface sediment. The consistent negative correlations between αn-alkane-Water and salinity for mangrove leaf waxes and surface sediments provide encouraging evidence for applying the hydrogen isotopic composition of mangrove leaf wax for paleohydrological reconstruction.

N-Alkanes and their carbon isotopes (δ13C) reveal seasonal foddering and long-term corralling of pastoralist livestock in eastern Mongolia

The compound-specific δ13C values of n-alkanes from pastoralist winter campsites in Mongolia have great potential to reconstruct dietary seasonality of livestock and local vegetation. We analysed leaf wax n-alkanes and their carbon isotope ratios in common fodder plants (Artemisia mongolica, Chenopodium album, Elymus dahuricus, Elymus sibiricus and Stipa sibirica) fed to domesticates during the winter months, and also in topsoils (0–8 cm) from four livestock corrals in northern and southern Mongolia. n-Alkanes identified in fresh plant parts reflect signatures with mean δ13C stable isotope values of individual n-alkanes typical for C3 plants (−34.1‰). Plants from forest- and desert-steppe exhibit similar mean n-alkane δ13C values but significantly wider isotopic variation in the desert steppe flora. The non-anthropogenic control samples exhibit δ13C mean values significantly higher from that of dung deposits and fresh plants for the same regions. Our data support previous research that n-alkanes profiles and their carbon isotopic values vary depending on the local vegetation and environment, while simultaneously demonstrating how anthropogenic activity, such as corralling of livestock, is recorded in the n-alkane of domesticates dung validating the use of biomarker studies in pastoralist archaeological contexts for distinguishing seasonal foddering, local environmental data and to an extent grazing habitats.

Early onset of summer monsoon during the Mystery Interval (17.5–14.5 ka BP) in the East Asian Summer Monsoon area: Evidence from leaf alkane δ2H

Exploring the seasonal atmospheric processes involved with hydroclimate changes of the East Asian Summer Monsoon (EASM) during the Mystery Interval (MI, 17.5–14.5 ka BP) will enhance understanding of the EASM climate system. Here we report on the δ2H values of leaf wax n-alkanes (δ2Halk) in a wetland core retrieved from southern China. These values are relatively negative during the MI, contrasting to positive excursion recorded by stalagmite δ18O in nearby caves during the same period. Considering the overlap of the primary synthesis time of leaf waxes in deciduous woody plants and periods of precipitation δ2H alteration in the EASM (late spring to early summer), we interpret the relatively negative signal of δ2Halk in the wetland core as the early onset of summer rainfall during the MI. The early onset of summer rainfall was likely due to the early northeastward shifting of the Western Pacific subtropical high due to the low land-sea thermogradient between the Qinghai-Tibet Plateau and the West Pacific Ocean.

Distribution and carbon isotopic composition of long-chain leaf wax n-alkanes from Holocene lake sediments in the Altai Mountains

The Altai Mountains are located at the junction of Asia and Europe and pathways linking East Asian climate with the Arctic and North Atlantic. Here, we report a record of n-alkanes from the sediments of Shuanghu Lake in the Altai Mountains. In this forested region, the vegetation is dominated by C3 plants and the long-chain n-alkanes (C29–C31) in the lake sediments are predominantly derived from leaf wax lipids. The compound-specific carbon isotopic values of the long-chain n-alkanes are sensitive to regional moisture. Both the δ13C29–31 value and the Paq index show a decreasing trend since ∼9.0 kyr BP, implying an increase in moisture. This trend is punctuated by abrupt decreases in isotopic values centered at 8.2, 7.4, 5.6, 3.0, 2.0 and 0.2 kyr BP, which may indicate cold and wet events on decadal–centennial timescales. The Holocene hydrological patterns recorded at Shuanghu Lake are different from those from monsoonal Asia and they may reflect a response to decreasing Arctic sea ice cover that provided an enhanced moisture source and promoted increased heavy snowfall in the study region, or an increase in the temperature gradient and strength of the jet stream and extratropical cyclones at mid-latitudes, as proposed previously.

Local differences in paleohydrology have stronger influence on plant biomarkers than regional climate change across two Paleogene Laramide Basins, Wyoming, USA

Plant biomarkers in the geologic record are commonly used to reconstruct paleovegetation and paleoclimate. Yet the representativeness of these biomarker-based reconstructions is not entirely straightforward because both local and regional climatic influences are convolved in the recovered biomarker composition. Furthermore, geomorphic processes including sedimentation, deposition, burial rates, and surface and groundwater levels can also influence biomarker preservation and taphonomy. The combination of leaf compression fossils with the biomarker record provides a robust framework in which ecological reconstructions can be made. Herein we present a case study examining the biomarker responses to a major regional climatic signal, the Paleocene Eocene Thermal Maximum (PETM), from local effects in two basins with different paleohydrology: the Hanna Basin (HB) and Bighorn Basin (BHB), in Wyoming (USA). Data collected include (1) leaf wax n-alkanes and plant-derived non-steroidal di- and triterpenoids, (2) pristane/phytane vs. terrestrial to aquatic ratio (Pr/Ph:TAR), plant material source proxy (Paq), hopanes, and bacteria which provide constraints on organic matter sourcing, redox conditions, and bacterial inputs, and (3) carbon (δ13Cn-alk) and hydrogen (δ2Hn-alk) isotopic compositions of plant wax n-alkanes. We find the two basins differed significantly in weight % total organic carbon (TOC), alkane and terpenoid concentrations, and δ13Cn-alk and δ2Hn-alk values. We examined the effects of δ13Catm on δ13Cn-alk values by assuming comparable regional climate in the two basins. Differences in paleohydrology and paleovegetation were assessed using the above proxies and previously published paleobotanical data. Local paleohydrologic conditions, an abiotic factor, likely drove variability in plant biomarker preservation and paleovegetation structure. Notably, an abundance of water in the HB during the PETM created a conifer refugium while drying within the BHB caused a local extirpation. This study highlights the importance of considering the influence of local environment, specifically paleohydrology, on the local fossil record and the need to compare multiple sites to disentangle regional climate effects on terrestrial plant communities. Distinguishing local from regional differences is imperative if we are to understand how ecosystems respond to future climate change.