Composition Of N-alkanes Research Articles

Savanna in equatorial Borneo during the late Pleistocene

Equatorial Southeast Asia is a key region for global climate change. Here, the Indo-Pacific Warm Pool (IPWP) is a critical driver of atmospheric convection that plays a dominant role in global atmospheric circulation. However, fluctuating sea-levels during the Pleistocene produced the most drastic land-sea area changes on Earth, with the now-drowned continent of Sundaland being exposed as a contiguous landmass for most of the past 2 million years. How vegetation responded to changes in rainfall that resulted from changing shelf exposure and glacial boundary conditions in Sundaland remains poorly understood. Here we use the stable carbon isotope composition (δ13C) of bat guano and High Molecular Weight n-alkanes, from Saleh Cave in southern Borneo to demonstrate that open vegetation existed during much the past 40,000 yrs BP. This location is at the southern equatorial end of a hypothesized ‘savanna corridor’ and the results provide the strongest evidence yet for its existence. The corridor would have operated as a barrier to east-west dispersal of rainforest species, and a conduit for north-south dispersal of savanna species at times of lowered sea level, explaining many modern biogeographic patterns. The Saleh Cave record also exhibits a strong correspondence with insolation and sea surface temperatures of the IPWP, suggesting a strong sensitivity of vegetation to tropical climate change on glacial/interglacial timeframes.

Response of grassland ecosystem to monsoonal precipitation variability during the Mid-Late Holocene: Inferences based on molecular isotopic records from Banni grassland, western India

Banni, located in the arid western India, is one of the largest tropical grasslands of the Asian continent. The net primary production in this grassland ecosystem is currently mediated by precipitation during the Indian summer monsoon (ISM). However, timing of the grassland expansion and its link to the intensity of monsoonal precipitation remains enigmatic due to the paucity of datasets. The major objective of this study is to understand the changes in monsoonal precipitation and vegetation for the last 4600 cal yr BP using hydrogen and carbon isotopic composition of n-alkanes (δDn-alkane and δ13Cn-alkane) measured from two core sediments (Chachi and Luna) in Banni region. The δ13CC29 and δ13CC31 values for Chachi core sediments vary from −30.9 ‰ to −27.2 ‰ and −34.4 ‰ to −25 ‰ respectively. The δ13Cn-alkane values from the core sediments are converted into %C4 plants based on a binary mixing model using the end-member δ13Cn-alkane values derived from the dominant modern vegetation in the Banni region. The prominent feature of the paleovegetation curve is the marked increase in the δ13Cn-alkane values after 2500 cal yr BP, which suggests proliferation of C4 grasses in this region. Similar changes after 2500 cal yr BP have also been observed in the δDn-alkane values. The δDC29 values are used to calculate δD value of paleoprecipitation that varied from 10 ‰ to −60.2 ‰. A significant increase in the δD values of paleoprecipitation (ca. 25 ‰) indicates a weakened ISM precipitation after ca. 2500 cal yr BP. The regional aridification and frequent fire events may have helped the expansion of C4 plant dominated grassland ecosystem in Banni region. Correlation between paleoclimatic records suggests that the southward migration of intertropical convergence zone and more frequent warm phases of El-Nino Southern Oscillation have triggered the weakening of monsoonal precipitation in the tropical region.

FEATURES OF LIPID COMPOSITION OF SPHAGNUM AND TRUE MOSSES FROM VARIOUS NATURAL CLI-MATIC ZONES

A composition of 16 lipid samples of sphagnum and true mosses (Bryales) growing at an average annual temperature ranging from -9.1 °C to 1.5 °C is investigated by gas chromatography-mass spectrometry. The individual composition and content of n-alkanes, fatty n-acids and their esters, n-alkane-2-ones, aldehydes, farnesylfuranes, polycyclic aromatic hydrocarbons (PAHs), tocopherols, squalene, steroids, sesqui-, di- and triterpenoids of these mosses are determined. True mosses differ from sphagnum mosses in their lower content of n-alkanes, n-alkan-2-ones, n-aldehydes, tocopherols and cyclic terpenoids, and a higher content of PAHs. Campesterol prevails among steroids of true mosses, while stigmasterol and sitosterol dominate in sphagnum mosses. Sitosterol prevails in sphagnum mosses growing in areas with a negative average annual temperature. An increase in the temperature of the habitat results in a decrease in the relative content of n-alkanes with odd number of carbon atoms in the molecule in true mosses, and a slight decrease in their average chain length in sphagnum mosses. It is shown that terpenoids are the most dependent on natural habitat conditions of mosses. This is indicated by the content of squalene, sesqui- and diterpenoids, the ratio of hydrocarbons to oxygen-containing structures of cyclic triterpenoids, and that of compounds from series of perhydropicene and cyclopentapeperhydrochryzene. The increased humidity of habitat of a moss eliminates the effect of temperature. The stability of composition of n-alkanes and n-alkan-2-ones of sphagnum mosses developing under various conditions makes it possible to consider these compounds as potential chemotaxonomic markers of sphagnum mosses in peat deposits.

Multi-decadal atmospheric and marine climate variability in southern Iberia during the mid- to late-Holocene

Abstract. To assess the regional multi-decadal to multi-centennial climate variability along the southern Iberian Peninsula during the mid- to late-Holocene record of paleo-environmental indicators from marine sediments were established for two sites in the Alboran Sea (ODP-161-976A) and the Gulf of Cádiz (GeoB5901-2). High-resolution records of organic geochemical properties and planktic foraminiferal assemblages are used to decipher precipitation and vegetation changes as well as hydrological conditions with respect to sea surface temperature (SST) and marine primary productivity (MPP). As a proxy for precipitation change, records of plant-derived n-alkane composition suggest a series of five distinct dry episodes in southern Iberia at 5.4±0.3 ka cal BP, from 5.1 to 4.9±0.1 ka cal BP, from 4.8 to 4.7±0.1 ka cal BP, from 4.4 to 4.3±0.1 ka cal BP, and at 3.7±0.1 ka cal BP. During each dry episode the vegetation suffered from reduced water availability. Interestingly, the dry phase from 4.4 to 4.3±0.1 ka cal BP is followed by a rapid shift towards wetter conditions revealing a more complex pattern in terms of its timing and duration than was described for the 4.2 ka event in other regions. The series of dry episodes as well as closely connected hydrological variability in the Alboran Sea were probably driven by NAO-like (North Atlantic Oscillation) variability. In contrast, surface waters in the Gulf of Cádiz appear to have responded more directly to North Atlantic cooling associated with Bond events. In particular, during Bond events 3 and 4, a pronounced increase in seasonality with summer warming and winter cooling is found.

Molecular and Isotopic Characteristics of Mature Condensates from the East China Sea Shelf Basin Using GC×GC-TOFMS and GC-IRMS

In this study, biomarkers, together with stable carbon (δ13C) and hydrogen (δD) isotopic compositions of n-alkanes have been examined in a suite of condensates collected from the East China Sea Shelf Basin (ECSSB) in order to delineate their source organic matter input, depositional conditions and evaluate their thermal maturity. Previously, GC-MS analyses have shown that all the condensates are formed in oxidizing environment with terrestrial plants as their main source input. No significant differences were apparent for biomarker parameters, likely due to the low biomarker content and high maturity of these condensates. Conventional GC-MS analysis however, may provides limited information on the sources and thermal maturity of complex mixtures due to insufficient component resolution. In the current study, we used comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS) to increase the chromatographic resolution. Compounds such as alkyl cyclohexanes, alkyl cyclopentanes and diamondoids, which can be difficult to identify using conventional GC-MS analysis, were successfully identified using GC×GC-TOFMS. From our analyses we propose two possibly unreported indicators, including one maturity indicator (C5−-cyclohexane/5+-cyclohexane) and one oxidation-reduction environment indicator (alkyl-cyclohexane/alkyl-cyclopentane). Multiple petroleum charging events were proposed as an explanation for the maturity indicators indexes discrepancy between methyl-phenanthrene index (MPI) and methyl-adamantane index (MDI). In addition, the stable isotopic results show that condensates from the Paleogene have significantly higher positive δ13C values of individual n-alkanes than the Neogene samples. Based on δD values, the samples can be divided into two groups, the differences between which are likely to be attributed to different biosynthetic precursors. Variation within each group can likely be attributed to vaporization.

A 250 ka leaf-wax δD record from a loess section in Darai Kalon, Southern Tajikistan

The climate of SW Central Asia is influenced by strong precipitation seasonality with dry summers and winter-spring precipitation delivered by mid-latitude westerlies. Due to its geographic position, SW Central Asia is a key locality for identifying fluctuations of westerlies, Siberian High and SW monsoon. Yet, there is only limited information on the Pleistocene climate history in SW Central Asia. Here we use plant-wax biomarkers and their hydrogen isotope (δD) composition from a loess section in Darai Kalon, southern Tajikistan, to reconstruct environmental conditions of the past 250 thousand years (ka). We focus on the hydrogen isotope composition of long-chain n-alkanes (δDAlk) and long-chain n-carboxylic acids (δDCarb) to reconstruct changes in the hydrological system. Moreover, we infer information about past vegetation changes from proxies based on the relative abundance of these compounds. Results show that during glacials, grasses dominated whereas during interglacials arboreal species prevailed. These changes in vegetation follow the dominant glacial-interglacial variability visible in the loess stratigraphy. Our results are in line with decreased precipitation during glacials as a result of a more extensive Siberian High. Isotope measurements reveal a close relation of δDAlk and δDCarb with insolation, controlled by 20 ka cycles of orbital precession that is distinct from the glacial-interglacial variability of the loess stratigraphy. Depleted (enriched) δDAlk and δDCarb values coincide with low (high) winter-spring insolation. The precessional mode of our isotope records is likely influenced by variations in the precipitation seasonality between winter and spring precipitation caused by insolation-induced temperature changes. In comparison with speleothem records along the westerly path, our results further indicate that the winter westerly storm tracks did not extend to the east of the Tian Shan during the last two glacial cycles.

Pollution Characteristics and Source Analysis of n-alkanes and Saccharides in PM2.5 During the Winter in Liaocheng City

To investigate molecular composition, mass concentrations, and sources of n-alkanes and sugars which are adsorbed in ambient particulate matters in Liaocheng City during winter, PM2.5 samples were collected from January 17 to February 15, 2017 at Liaocheng University. 19 kinds (C18-C36) of n-alkanes and 10 kinds of sugars were determined using GC-MS. The identification of n-alkane and sugar sources were investigated using principal component analysis (PCA). The results showed that the mass concentrations of total n-alkanes in PM2.5 during the winter were (456.9±252.5) ng·m-3. During the haze period, the concentrations of n-alkanes were two times higher than those on clear days. Additionally, the concentrations of n-alkanes during fireworks event I and fireworks event Ⅱ were 0.9 times and 1.2 times higher than those on clear days. During the sampling period, the Carbon preference index (CPI) was 1.2±0.1, and the contribution from plant wax concentrations for n-alkanes (% Wax Cn) was between 3.1%~36.0%, indicating that fossil fuels were the major source of n-alkanes in Liaocheng City during the winter. The mass concentrations of saccharides in PM2.5 during the winter were (415.5±213.8) ng·m-3. Levoglucosan was the most abundant species, followed by galactosan and mannosan, which accounted for more than 91.6% of total saccharides, indicating that biomass burning was much more significant in Liaocheng City. PCA further suggested that n-alkane and saccharide compounds in atmospheric aerosol during the winter in Liaocheng City were primarily derived from fossil fuel and biomass burning.

Climate changes in the Eastern Mediterranean over the last 5000 years and their links to the high-latitude atmospheric patterns and Asian monsoons

Abstract This research aims to improve the knowledge of the mid to late Holocene climate changes and the underlying drivers in the eastern Mediterranean. We focus on the Peloponnese peninsula, SW Greece, characterized by a W-E rainfall/temperature gradient and a strong climate-sensitivity to shifts in the large-scale atmospheric patterns. A radiocarbon-dated sediment core, taken from the ancient Lake Lerna, a former lake in NE Peloponnese, was analyzed for distribution and hydrogen isotope (δD) composition of n-alkanes and bulk organic geochemistry (δ13C, TOC). The predominantly macrophyte (submerged/floating)-derived δD23 profile exhibits the largest long-term fluctuation in the record and co-varies with δD of long-chain n-alkanes providing evidence for precipitation and temperature changes over the last 5000 years. The Lerna δD23 signal is sometimes in agreement with other n-alkane δD records from SW Peloponnese indicating wetter conditions in the peninsula at ca 5000–4600, ca 4500–4100, ca 3000–2600 (more unstable in SW) and after ca 700 cal BP with drier periods at ca 4100–3900 and ca 1000–700 cal BP. Conversely, a NE-SW climate see-saw is revealed at ca 4600–4500, ca 3200, ca 2600–1800, and ca 1200–1000 cal BP when the δD23 Lerna exhibits more positive trends (drier in NE) with a reversal at ca 3900–3300, ca 3200–3000 and ca 1800–1300 cal BP. These opposing and sometimes similar signals between NE and SW Peloponnese can be explained by the relative dominance of high-latitude atmospheric patterns over the peninsula. A similar signal would be expected when the North Atlantic Oscillation (NAO) exerts the main control with NAO (+) creating conditions of reduced moisture. The dipole pattern is likely driven by shifts in North Sea–Caspian Atmospheric pattern (NCP), which account for the present-day regional climate variability with NCP (+) leading to wetter and colder conditions in NE Peloponnese. The Asian monsoonal system likely has an additional impact on the δD variabilities through influencing the summer temperatures. There is a consistency between the Peloponnesian δD signals and monsoonal records after ca 4000 cal BP confirming the actualistic models. Strong monsoonal periods coincide with cooler summers (lower δD values) in Lerna, due to the northerly winds, the Etesians. On the contrary, SW Peloponnese is dominated by warmer conditions during the same periods as the area is located on the lee side of the mountain and highly influenced by the adiabatic warming associated with the subsidence over the Eastern Mediterranean.

Sedimentary n-alkanes and n-alkanoic acids in a temperate bog are biased toward woody plants

Sedimentary plant waxes and their hydrogen and carbon (δ2H and δ13C) isotopes are important proxies for past hydrologic and vegetation change. However sedimentary waxes accumulate from diverse sources, integrating uncertainties from: (i) variable isotope fractionation among plant species, and (ii) unresolved processes controlling the transport of waxes from plants to sediments. We address these uncertainties by comparing the molecular and isotopic composition of n-alkanes and n-alkanoic acids in recent bog sediments with all major plant species growing in the catchment of Browns Lake Bog (BLB) in Ohio, USA. There are two distinct plant assemblages at BLB, including a forest dominated by trees and a bog shoreline composed of shrubs, woody groundcover, herbs and graminoids. n-Alkane concentrations in trees were 10–300 times higher than in shoreline plants, while n-alkanoic acid concentrations were generally lower and comparable across all species. The overall range of wax δ2H values among individual plants (77‰ for n-C29 alkane and 84‰ for n-C28 alkanoic acid) was likely driven by interspecies differences in biosynthetic δ2H fractionation as well as source water differences between forest and shoreline plants. A considerably smaller range of δ2Hwax values in the bog sediments (9‰ for n-C29 alkane and 11‰ for n-C28 alkanoic acid) suggests that sediments are either biased toward specific plants, or that signal averaging processes during or after deposition are constant. The combined δ2H and δ13C signatures of plant sources and sediments indicate a sediment bias mainly toward trees, with contributions from woody shrubs and groundcover growing in the bog shoreline. Within trees and woody shrubs, we observed δ2Hwax–δ13Cwax relationships of opposite sign for n-C29 alkane and n-C28 alkanoic acid, which we speculate may reflect contrasting seasonal timing of synthesis and plant metabolic status between compound classes. The net apparent δ2H fractionation between precipitation and wax (εapp) was approximately 30‰ larger for n-alkanes (−133‰) than for n-alkanoic acids (−103‰), both at the plant level and in sediments. These results demonstrate the sensitivity of sediments in a hydrologically closed basin to woody plants growing in the associated catchment and can guide εapp estimates for sedimentary records from similar depositional settings.

Impact of drill core contamination on compound-specific carbon and hydrogen isotopic signatures

Compound-specific carbon and hydrogen isotope ratios are routinely measured on extractable organic matter to decipher biogeochemical processes and events in Earth history. To deliver accurate interpretations, it is paramount that isotopic values are derived from indigenous compounds and are not the result of contamination. However, distinguishing between compounds from these different provenances can be difficult, especially if a degree of mixing occurred. In this study, we assess the impact of hydrocarbon contamination on the carbon and hydrogen isotopic composition of n-alkanes from ∼820 Ma Precambrian evaporitic drill core samples through exterior/interior (E/I) rock extraction experiments. In these experiments, exterior and interior portions of the same rock samples were separately crushed to powder, extracted and processed. Compound-specific isotope values of n-alkanes from the different rock portions were subsequently measured and compared. In most cases, n-alkanes from exterior rock portions had consistently more depleted δ13C and δ2H values than their interior counterparts with an E/I isotopic offset averaging 0.1–6.9‰ for δ13C and 2–33‰ for δ2H. These diverging isotope patterns tend to correspond to E/I concentration differences of n-alkanes and are the result of contaminants overprinting on indigenous isotopic signals. Through the application of E/I experiments, the degree of isotopic overprinting can be investigated and mixed indigenous/contaminant signals identified.

Distribution Characteristics and Implication of n-alkanes in Soils and Plants in Alpine Meadow

The present study was conducted to investigate the n-alkane composition of typical alpine meadows. Plant and soil samples were collected and analyzed to characterize the n-alkane components. The results show that the n-alkane with maximum concentration (Cmax) was C22 in Ligularia virgaurea and Aconitum pendulum, C29 in Elsholtzia densa, Pedicularis kansuensis and Oxytropis kansuensis, and C31 in Potentilla anserine and Leontopodium nanum. Furthermore, the C29 and C31 concentrations in the surface soil from typical alpine meadow were higher than that in sub-layer soil; however, the opposite relationship was seen in soil from degraded alpine meadow. In addition, the correlation between the long chain n-alkanes in soils and plants was strongly significant (p < 0.01, r = 0.816). The change of the C29 and C31 concentration with soil depth could be related to the plant succession of the alpine meadow.

Identifying the ‘savanna’ signature in lacustrine sediments in northern Australia

This study reports palynological and geochemical results for modern and ancient sediments from 19 lakes on a rainfall gradient (784–1880 mm), across a range of savannas in Northern Australia. All proxies varied significantly across the range of sites examined, providing a robust envelope of values that can reliably be employed to identify a savanna signature in the sedimentary record. While the results indicate it is possible to identify a savanna, we found only three statistically significant relationships between any proxy measured in surface sediments and the major climate driver of savanna vegetation composition (rainfall amount). This is because edaphic factors play a dominant role in determining vegetation composition and also potentially because of the impact of land use change.Measures of fire determined by charcoal counting were positively correlated with geochemical measures of pyrogenic carbon abundance, suggesting both record a similar signal. While measures of fire incidence were not correlated with rainfall, there was a significant positive correlation between charcoal abundance and number of fires early in the dry season, suggesting that charcoal abundance is controlled more by the number/timing of fires than climate. There was also a significant correlation between the δ13C-value of pyrogenic carbon and tree:grass ratio derived from palynological indicators, indicating that the δ13C-value of PyC is a reliable indicator of savanna ‘woodiness’. Comparison of the carbon isotope composition of total organic carbon, PyC and n-alkanes between modern and Holocene sediments suggest that the savannas of the region have remained either similar in ‘woodiness’ or have thickened over the last millennia.

N-Alkanes as indicators of climate and vegetation variations since the last glacial period recorded in a sediment core from the northeastern South China Sea (SCS)

Variations in n-alkanes proxies (L/H, C31/C27 and ACL), molecular abundances of n-alkanes and stable carbon isotopic compositions of n-alkanes (δ13Calk) from the core STD235 (20°21.15′N, 118°22.56′E) have been used to trace characterize the climatic changes that occurred in the northern South China Sea (SCS) during the last glacial period. The ratio of low to high molecular-weight n-alkanes (L/H) and the concentration of n-alkanes indicated that organic matters in the sediments were derived from the mixture of both marine and terrestrial sources, but dominated by marine autochthonous input over the past 20 ka. Total n-alkanes were higher during the last glacial stage relative to the interglacial stage, implying the low sea level and the strengthened East Asian winter monsoon (EAWM) during the glacial time. The δ13Calk data indicated that the terrestrial plants on the adjacent continent of the present study area were dominated by C3 plants during the Holocene and experienced the expansion of C4 plants during the last glacial period. This similar result can be proved by the chain length parameter of n-alkanes (C31/C27, ACL) and the content of the herb pollen. In addition, n-alkanes distributions and C4 vegetation proportion calculated by δ13C of long-chain n-alkanes in the core STD235 recorded a short arid duration paralleled by the Heinrich event 1. Thereby we deduced that the occurrence of the dry event and the variation of regional vegetation community at the adjacent lands of the northern SCS were likely under the influence of the climate change emanated from the boreal high-latitudes.

Paleoclimate changes of the past 30 cal ka BP inferred from lipid biomarkers and geochemical records from Qionghai Lake, southwest China

Multi-proxy records of paleoclimate changes spanning the past 30 cal ka BP were obtained from Qionghai Lake sediment core, Sichuan Province, southwest China, where southwest summer monsoon prevails. The core was studied for molecular compositions of n-alkanes, stable carbon isotope ratios (δ13C) of organic matter (OM), total organic carbon (TOC), total nitrogen (TN) and trace elements. Evidence from n-alkanes, cross chart of C/N-δ13C values and trace elements indicated the organic matter derived from a mixed source composed of autochthonous aquatic organisms and allochthonous terrestrial plants, and the sediments mainly deposited in reducing conditions, which is in favor of preservation and accumulation of OM. Variations of n-alkanes biomarker proxies, δ13C of organic matter and Mo concentrations reflected three stages of paleoclimate evolution during the past 30 cal ka BP: a relatively warm and humid climate between 29.1 and 22.9 cal ka BP, corresponding to a strong southwest summer monsoon; climate shifted towards cold and dry condition during the period of 22.9–15.7 cal ka BP, in response to the reduced insolation and weakened southwest summer monsoon; temperature and humidity gradually increased in the Holocene with fluctuations, broadly track the strengthening trend of southwest summer monsoon. Our findings further confirm that variations in solar activity may primarily affect the strength of southwest summer monsoon, resulting in the shifts of paleoclimate conditions. Further studies are needed to better constrain the detailed forcing drivers which may amplify the intensity of southwest summer monsoon particularly in the Holocene period.

Dual isotope evidence for sedimentary integration of plant wax biomarkers across an Andes-Amazon elevation transect

Tropical montane regions tend to have high rates of precipitation, biological production, erosion, and sediment export, which together move material off the landscape and toward sedimentary deposits downstream. Plant wax biomarkers can be used to investigate sourcing of organic matter and are often used as proxies to reconstruct past climate and environment in sedimentary deposits. To understand how plant waxes are sourced within a wet, tropical montane catchment, we measure the stable C and H isotope composition (δ13C and δD) of n-alkanes and n-alkanoic acids in soils along an elevation transect and from sediments within the Madre de Dios River network along the eastern flank of the Peruvian Andes, draining an area of 75,400 km2 and 6 km of elevation. Soils yield systematic trends in plant wax δ13C (+1.75 and +1.31‰ km−1, for the C29n-alkanes and C30n-alkanoic acids respectively in the mineral horizon) and δD values (−10 and −12‰ km−1, respectively) across a 3.5 km elevation transect, which approximates trends previously reported from canopy leaves, though we find offsets between δ13C values in plants and soils. River suspended sediments generally follow soil isotopic gradients defined by catchment elevations (δ13C: +1.03 and +0.99‰ km−1 and δD: −10 to −7‰ km−1, for the C29n-alkanes and C30n-alkanoic acids respectively) in the wet season, with a lowering in the dry season that is less well-constrained. In a few river suspended sediments, petrogenic contributions and depth-sorting influence the n-alkane δ13C signal. Our dual isotope, dual compound class and seasonal sampling approach reveals no Andean-dominance in plant wax export, and instead that the sourcing of plant waxes in this very wet, forested catchment approximates that expected for spatial integration of the upstream catchment, thus with a lowland dominance on areal basis, guiding paleoenvironmental reconstructions in tropical montane regions. The dual isotope approach provides a cross-check on the altitudinal signals and can resolve ambiguity such as might be associated with vegetation change or aridity in paleoclimate records. Further, the altitude effect encoded within plant waxes presents a novel dual-isotope biomarker approach to paleoaltimetry.

Characteristics of Alkanes in Ferromanganese Nodules of the Clarion–Clipperton Fracture Zone

This work presents the first results of a comparative study on the composition and distribution of organic matter (OM) (TOC, n-alkanes, pristane, phytane) in ferromanganese nodules and underlying sediments (0–1 cm) from three sites within the Clarion–Clipperton Fracture Zone, Pacific Ocean. Samples were collected during Cruise 120 of the RSS James Cook in 2015. The studied nodules differ in size, shape, and morphology. The TOC content in the nodules is 0.15% on average with insignificant variations which is less than in the sediments. The molecular composition of n-alkanes in the nodules is mainly determined by modern bacterial activity with high preservation of terrigenous n-alkanes in the environment of the ore deposit formation.

Variations in Composition of Alkanes and Free Fatty Acids in Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) on Exposure to Monocrotophos

Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) is an important herbivore pest of cucurbitaceae, which is currently controlled by insecticides in southeast Asia. The insect cuticle is the first line of defence against insecticides. So, we investigated the variations in the composition of n-alkanes and free fatty acids (FFAs) in cuticular and internal lipids of A. foveicollis males and females exposed to monocrotophos compared to untreated adults. Both sexes of A. foveicollis adults were dipped in petroleum ether for 1 min at room temperature for extraction of surface waxes, and the insects were further kept in dichloromethane for 15 days for extraction of internal lipids. n-Alkanes and FFAs of cuticular and internal lipids were identified and quantified by GC–MS and GC–FID analyses. Higher quantities of cuticular lipids were observed in males and females exposed to monocrotophos than untreated males and females. Twenty n-alkanes were identified between n-C15 and n-C36 in cuticular lipids of untreated A. foveicollis adults; whereas 21 n-alkanes were detected in cuticular lipids of treated adults. Nineteen FFAs were recorded between C10:0 and C22:0 in cuticular lipids of untreated adults; whereas 21 and 19 FFAs were recorded in cuticular lipids of treated males and females, respectively. Hentriacontane and palmitoleic acid were the predominant n-alkane and FFA in the cuticular lipids of treated males and females, respectively. This study revealed that change of alkanes and FFAs in cuticular lipids of A. foveicollis males and females are linked to exposure to monocrtophos, which might result in increasing resistance of A. foveicollis.

Effect of continuous light on leaf wax isotope ratios in Betula nana and Eriophorum vaginatum: implications for Arctic paleoclimate reconstructions

Reconstructions of climate using leaf wax D/H ratios (δDwax) require accounting for the apparent isotopic fractionation (εapp) between plant source water and waxes. There have been conflicting publications on whether plants in the Arctic growing under 24-hour continuous light, fractionate less than temperate and tropical plants. In this study, we examine the effect of diurnal light (DL) versus 24-hour continuous light (CL) on the isotopic composition of leaf n-alkanes and n-acids in greenhouse experiments using two common Arctic plants (Eriophorum vaginatum, or tussock cottongrass and Betula nana, or dwarf birch). For E. vaginatum, the δDwax values of various wax homologues were 5–11‰ more positive for CL plants relative to their DL counterparts, whereas for B. nana, CL waxes were 3–24‰ more negative, suggesting that daylight length is not a unifying control on leaf wax D/H ratios of Arctic plants. The δ13Cwax of B. nana was more negative for plants grown in continuous light compared to diurnal light, reflecting lower water-use efficiency, associated with prolonged stomatal opening in the CL treatment. We modeled the impact of increasing stomatal conductance and effective flow path lengths (mimicking variable leaf morphologies) on the isotopic composition of leaf waters (δDlw) and find that variations in leaf-water enrichment may explain the variable δDwax responses seen between E. vaginatum and B. nana. We suggest that between-species differences in the δDlw response to light, and differences in the utilization of stored carbohydrates, were important for governing δDwax. Our greenhouse results suggest that Arctic plant leaf waxes do not consistently display reduced εapp values as a result of 24-hour day light, providing additional support for field observations.

Chemotaxonomic Considerations of the n-Alkane Composition in Pinus heldreichii, P.nigra, and P.peuce.

The n-alkane composition in the leaf cuticular waxes of natural populations of Bosnian pine (Pinus heldreichii), Austrian pine (P.nigra), and Macedonian pine (P.peuce) was compared for the first time. The range of n-alkanes was wider in P.nigra (C16 -C33 ) than in P.heldreichii and P.peuce (C18 -C33 ). Species also diverged in abundance and range of dominant n-alkanes (P. heldreichii: C23 , C27 , and C25 ; P.nigra: C25 , C27 , C29 , and C23 ; P.peuce: C29 , C25 , C27 , and C23 ). Multivariate statistical analyses (PCA, DA, and CA) generally pointed out separation of populations of P.nigra from populations of P.heldreichii and P.peuce (which were, to a greater or lesser extent, separated too). However, position of these species on the basis of n-alkane composition was in accordance neither with infrageneric classification nor with recent molecular and terpene investigations.

Eastern Mediterranean hydroclimate reconstruction over the last 3600 years based on sedimentary n-alkanes, their carbon and hydrogen isotope composition and XRF data from the Gialova Lagoon, SW Greece

Understanding past hydroclimate variability and related drivers is essential to improve climate forecasting capabilities especially in areas with high climatic sensitivity, such as the Mediterranean. This can be achieved by using a broad spectrum of high resolution, multiple proxy records which can also allow us to assess linkages between regional hydroclimate variability and shifts in the large-scale atmospheric patterns. Here, we present a multiproxy reconstruction of the central-eastern Mediterranean hydroclimate changes over the last 3600 years based on a sediment core from the Gialova Lagoon, a shallow coastal ecosystem in SW Peloponnese, Greece. Our combined dataset consists of the distribution and compound-specific carbon and hydrogen isotope (δ13C and δD) composition of n-alkanes, bulk organic matter properties and X-ray fluorescence (XRF) core scanning data. This approach was complemented with a semi-quantitative analysis of plant remains in the core. The results indicate a high contribution of local aquatic vegetation to organic matter. Large δ13C variations in predominantly aquatic plant-derived mid-chain alkanes (C23-25) mainly reflect changes in the aquatic plant abundance and their carbon source. Our data suggest that higher δ13C23-25 values (up to −19‰) largely correspond to expansion of aquatic vegetation during wet and/or cold periods causing carbon-limiting conditions in the water and assimilation of isotopically-enriched bicarbonate by the plants. The δD records of the individual n-alkanes (C17 to C31) exhibit a nearly identical pattern to each other, which implies that they all reflect changes in the source water isotope composition, driven by hydroclimate variability. In addition, the δD profiles are consistent with the XRF data with both proxies being driven by a common hydroclimate signal. We observe two major shifts from dry and/or warm periods at ca 3600-3000 cal BP and ca 1700-1300 cal BP to wet and/or cold episodes at ca 3000-2700 cal BP and ca 1300-900 cal BP. The period ca 700-200 cal BP is the wettest and/or coldest in our record and coeval with the Little Ice Age. The climatic fluctuation reported in this study can be explained by the relative dominance of high-latitude (e.g. North Atlantic Oscillation during winters) and the low-latitude atmospheric patterns (Intertropical convergence zone, Subtropical High and the effects of Asian monsoons during summers) which suggests an Atlantic-Mediterranean-Monsoon climate link in this area for the late Holocene.