Crassulacean acid metabolism influences D/H ratio of leaf wax in succulent plants

This study sought to characterize hydrogen isotopic fractionation during biosynthesis of leaf wax n-alkanes in succulent plants capable of crassulacean acid metabolism (CAM). The metabolic and physiological features of CAM represent crucial strategies for survival in hot and dry climates and have been hypothesized to impact hydrogen isotope fractionation. We measured the stable carbon and hydrogen isotopic compositions (δ¹³C and δD, respectively) of individual n-alkanes in 20 species of succulent plants from a global collection of the Huntington Botanical Gardens, San Marino, California. Greenhouse conditions and irrigation with water of constant δD value enabled determination of interspecies differences in net D/H fractionation between source water and leaf wax products. Carbon isotope ratios provide constraints on the extent of CAM vs. C₃ photosynthesis and indicate a wide range of CAM use, with δ¹³C values ranging from −33.01‰ to −18.54‰ (C₂₇–C₃₃ n-alkanes) and −26.66‰ to −17.64‰ (bulk tissue). Despite the controlled growth environment, we observed ca. 90‰ interspecies range in δD values from −193‰ to −107‰. A positive correlation between δ¹³C_bulk and δD_C31 values with R² = 0.60 (δ¹³C_C31 and δD_C31 values with R² = 0.41) implicates a metabolic isotope effect as the dominant cause of interspecies variation in the hydrogen isotopic composition of leaf wax n-alkanes in CAM-intermediate plants.     

The source and paleoclimatic implication of hydrogen isotopic composition of n-alkanes in sediments from the Yixian Formation,western Liaoning Province,NE China

Hydrogen isotopic composition of n-alkanes was measured in sediments from an excavated profile of the Early Cretaceous Yixian Formation in Liaoning Province, NE China, aiming to assess the significance of the δD value of n-alkanes in ancient lacustrine sediments as the indicator for determining the source inputs of organic matters and paleoclimatic conditions. The δD values of n-alkanes are in the range of − 250‰ to − 85‰ and display an obvious three-stage variation pattern through the profile, which is consistent with the distribution of the dominated n-alkanes and the profile of their δ¹³C values. The δD and δ¹³C values of n-alkanes suggest that short-chain n-alkanes are primarily derived from photosynthetic bacteria and algae; n-C₂₉ and n-C₃₁ are mainly originated from terrestrial higher plants; n-C₂₈ and n-C₃₀ may be derived from the same precursor but via the different biological mechanism of hydrogen isotopic fractionation; while the source inputs of medium-chain n-alkanes are more complicated, with n-C₂₃ being derived from some specific algae or biosynthesized by various aquatic organisms. The paleoclimatic conditions are reconstructed via two approaches. The reconstructed hydrogen isotopic values of lake water and meteoric water (expressed as δD_LW and δD_MW, respectively) were at the intervals of − 51.8‰ to 17.0‰ and − 118.1‰ to − 43.5‰, respectively, indicating a general climate transition from semi-arid to arid. The calculated ΔδD_LW-MW values vary from 37.0‰ to 89.1‰ and display a similar but a significant large-scale variation trend with the ΔδD_{C23 ‐ long} (− 28.8‰ to 85.0‰; long represents long-chain n-alkanes) and ΔδD_mid-long (− 15.4‰ to 43.4‰; mid represents medium-chain n-alkanes) values. The discrepancy may be attributed to the source input overlap for n-alkanes and the uncertainties of ε_water/lipid values. The coupling of ΔδD_{C23 ‐ long}, ΔδD_mid-long and ΔδD_LW-MW values with the paleoclimatic evidence indicates that the δD values of n-alkanes could be more sensitive to the change of paleoclimatic conditions.     

Biomarkers of novel ecosystem development in boreal forest soils

Novel ecosystem development is occurring within the western boreal forest of Canada due to land reclamation following oil sand surface mining. Sphagnum peat is the primary organic amendment used to reconstruct soil in these novel ecosystems. We hypothesised that ecosystem recovery would be indicated by an increasing similarity in the biomolecular characteristics of novel soil organic matter (SOM) derived from peat to those of natural boreal ecosystems. We evaluated the use of the homologous series of long chain (⩾ C₂₁) n-alkanes with odd/even predominance to monitor the re-establishment of boreal forest on these anthropogenic soils. The lipids were extracted from dominant vegetation inputs and SOM from a series of natural and novel ecosystem reference plots. Twice the concentration of n-alkanes was extracted from natural than from novel ecosystem SOM (p < 0.01). We observed unique n-alkane signatures for the source vegetation, e.g. peat material was dominated by C₃₁, and aspen (Populus tremuloides Michx.) leaves by C₂₅. The n-alkane distribution differed between the two systems (p < 0.001) and reflected the dominant vegetation input, i.e. peat or tree species. Our results indicate that further research is required to clarify the influence of vegetation or disturbance on the signature of n-alkanes in SOM; however, the use of n-alkanes as biomarkers of novel ecosystem development is a promising application.     

Source characterization using molecular distribution and stable carbon isotopic composition of n-alkanes in sediment cores from the tropical Mundaú–Manguaba estuarine–lagoon system,Brazil

The Mundaú–Manguaba estuarine–lagoon system (MMELS) constitutes one of the most representative ecosystems in the state of Alagoas, NE Brazil. Approximately 30% or 60,000 ha of the lower surrounding drainage basin of the MMELS are covered by sugar cane and a total of 250,000 inhabitants contribute untreated effluent to the system. Short sediment cores from MMELS were collected in 2007 at three sites: Manguaba Lagoon (C03), Mundaú Lagoon (C07) and Mundaú River (C08) in order to characterize the delivery and deposition of n-alkanes over the past 40 yr. The n-alkanes ranged from C₁₅ to C₃₅, with total aliphatic hydrocarbon (TAH) concentration in the range 27.8–139.5 μg g⁻¹. An unresolved complex mixture (UCM) was observed in all sediments. The terrigenous/aquatic ratio (TAR), carbon preference index (CPI) and average chain length (ACL) showed that the terrigenous input dominated. The (δ¹³C) values of individual n-alkanes (C₁₆–C₃₃) varied between −22.6‰ and −34.2‰, suggesting a dominance of ¹²C-enriched n-alkanes that originated from C₃ plants and lacustrine algae. The data reflect how anthropogenic input (via sewage, industrial pollution and agriculture) has influenced the organic content of the system through time.     

n-Alkan-2-one distributions in a northeastern China peat core spanning the last 16 kyr

Most research on long chain methyl ketones has focused on their origins and distributions. Their application in paleoclimate studies is less common than that of other n-alkyl lipids. The goal of this research was to explore this potential by studying n-alkan-2-ones from the Hani peat sequence in northeastern China. They were identified using gas chromatography-mass spectrometry (GC-MS) and showed a distribution ranging from C₁₉ to C₃₁ with a strong odd/even predominance. This type of distribution is considered to derive from Sphagum and microbial oxidation of n-alkanes. Comparison with climate sensitive indicators and macrofossil analysis shows that microbial oxidation of n-alkanes derived from higher plants was enhanced during the warm early Holocene period. This led us to develop three n-alkan-2-one proxies - C₂₇/ΣC_23-31 (C₂₇/HMW-KET), carbon preference index (CPI_H-KET) and average chain length (ACL_(27-31)-KET) - as possible indicators of paleoclimate in the peat-forming environment. These proxies, in combination with C₂₇n-alkane δD values and peat cellulose δ¹⁸O records, might allow examination of paleo-ecosystem behavior during climatic evolution in northeastern China over the past 16,000 yr.     

Environmental significance of mid- to late Holocene sapropels in Old Man Lake,Coorong coastal plain,South Australia: An isotopic,biomarker and palaeoecological perspective

The Holocene successions of numerous shallow lakes located along the Coorong coastal plain in South Australia attest to the impact of rising sea level and changing climate on their depositional environment. Old Man Lake is one of the smallest perennial alkaline lakes in the region. Its succession comprises a basal lagoonal sand rich in humic organic matter (OM) overlain by a 3.7 m thick upward shoaling lacustrine mudstone. The latter features three discrete sapropel units deposited between 3270 and 4910 cal yr BP, a time of increasing aridity throughout southeastern Australia. A core taken from the lake’s eastern margin yielded sedimentological, mineralogical, geochronological and micropaleontological data. Coring at five other sites across the lake provided sections of the humic and sapropelic facies (n = 20) for total organic carbon and Rock–Eval analysis; isotopic characterization of their micritic carbonate (δ¹³C_carb, δ¹⁸O_carb) and co-existing OM (δ¹³C_org); and GC–MS and GC–irMS analysis of their free aliphatic hydrocarbons. For each ‘sapropel event’ high productivity of diatoms and green algae was the principal driver of the accumulation and preservation of OM in such high concentrations. The precursor algal blooms were likely triggered by the influx of fresh water following winter rainfall. The combination of kerogen hydrogen index and δ¹³C_carb–δ¹³C_org, previously employed to track secular changes in algal productivity and organic preservation, proved useful in identifying synchronous geographic differences in these processes across the lake. Highly branched isoprenoids (HBI: C_25:1 ≫ C_20:0) are prominent components of the aliphatic hydrocarbons in the sapropels, confirming the significant contribution of diatoms to their OM. The C isotopic signatures of the principal C_25:1 HBI isomer and the co-occurring C₂₃–C₃₁ odd carbon numbered n-alkanes further document the non-uniformity of biomass preservation within and between the three sapropel units. The evidence from this study suggests that seasonal algal blooms and meromixis, although not necessarily an anoxic hypoliminion, were required for sapropel formation in the Holocene lakes of the Coorong region. Higher resolution sampling, dating and comparative analysis (microfossil, biomarker and isotopic) of these sapropels is required to clarify their potential significance as palaeoclimate proxies.     

Different source of n-alkanes and n-alkan-2-ones in a 6000 cal. yr BP Sphagnum-rich temperate peat bog (Roñanzas,N Spain)

The most widely accepted origin of n-alkan-2-ones in peats is the microbial oxidation of the related n-alkanes and/or oxidative decarboxylation of fatty acids derived from plant input. The distributions of n-alkanes and n-alkan-2-ones in 48 samples from the Roñanzas 6000 cal. yr BP peat bog profile (N Spain) do not justify a single source. The n-alkan-2-ones typically dominate the n-alkanes, maximizing at C₁₉ or C₂₅/C_27, whereas the n-alkanes maximized either at C₂₃ or at C₃₁/C₃₃. The averaged δ¹³C values of the n-alkanes ranged from −32.3‰ to −33.1‰, but those of the n-alkan-2-ones were consistently higher (−29.2‰ to −29.9‰), suggesting a different, probably bacterial, source for the ketones.     

A ∼25 ka Indian Ocean monsoon variability record from the Andaman Sea

Recent paleoclimatic work on terrestrial and marine deposits from Asia and the Indian Ocean has indicated abrupt changes in the strength of the Asian monsoon during the last deglaciation. Comparison of marine paleoclimate records that track salinity changes from Asian rivers can help evaluate the coherence of the Indian Ocean monsoon (IOM) with the larger Asian monsoon. Here we present paired Mg/Ca and δ¹⁸O data on the planktic foraminifer Globigerinoides ruber (white) from Andaman Sea core RC12-344 that provide records of sea-surface temperature (SST) and δ¹⁸O of seawater (δ¹⁸O_sw) over the past 25,000 years (ka) before present (BP). Age control is based on nine accelerator mass spectrometry (AMS) dates on mixed planktic foraminifera. Mg/Ca-SST data indicate that SST was ∼3 °C cooler during the last glacial maximum (LGM) than the late Holocene. Andaman Sea δ¹⁸O_sw exhibited higher than present values during the Lateglacial interval ca 19–15 ka BP and briefly during the Younger Dryas ca 12 ka BP. Lower than present δ¹⁸O_sw values during the BØlling/AllerØd ca 14.5–12.6 ka BP and during the early Holocene ca 10.8–5.5 ka BP are interpreted to indicate lower salinity, reflect some combination of decreased evaporation–precipitation (E–P) over the Andaman Sea and increased Irrawaddy River outflow. Our results are consistent with the suggestion that IOM intensity was stronger than present during the BØlling/AllerØd and early Holocene, and weaker during the late glaciation, Younger Dryas, and the late Holocene. These findings support the hypothesis that rapid climate change during the last deglaciation and Holocene included substantial hydrologic changes in the IOM system that were coherent with the larger Asian monsoon.     

Occurrence and composition of solid bitumens from the Bulonggoer Devonian paleo-oil reservoir,North Xinjiang,China

The Bulonggoer paleo-oil reservoir (BPR) on the northwest Junggar Basin is the first Devonian paleo-oil reservoir discovered in North Xinjiang, China. Solid bitumens occur within sandstone pores and as veins filling fractures. Samples of both types were analyzed using stable carbon isotope and reflectance measurements, as well as molecular biomarker parameters.The extremely positive δ¹³C values and biomarker indicators of depositional environment/lithology, such as pristane/phytane (Pr/Ph), C₂₉/C₃₀ hopane, diasteranes/regular steranes and dibenzothiophene/phenanthrene ratios, indicate a siliciclastic source for the BPR and their deposition in a highly reducing hypersaline environment. The presence of long chain n-alkanes and abundant tetracyclic diterpanes, C₂₀–C₂₁ tricyclic terpanes and perylene are indicators of higher plant organic matter input. Moreover, the bimodal distribution of C₂₇ > C₂₈ < C₂₉ regular steranes and abundant methyltriaromatic steroids also support a contribution of microalgae as well as higher plants organic matter. The similar molecular composition and thermal maturity parameters indicate that the reservoir and veined solid bitumens were altered from a common paleo-petroleum, which originated from peak oil window matured source rocks.All solid bitumens from the BPR are characterized by relatively low bitumen reflectance values (Rb% < 0.7), suggesting that they were generated from low temperature processes rather than oil thermal cracking. Comparatively, the Rb% values for veined bitumens are higher than reservoir bitumens, indicating that the veined bitumens occurred earlier and experienced higher thermal conditions.     

Precise indices based on n-alkane distribution for quantifying sources of sedimentary organic matter in coastal systems

Precise indices based on n-alkane signatures were developed in order to determine the sources and composition of sedimentary organic matter (SOM) in coastal systems. The Arcachon Bay (France), a well-studied temperate lagoon, was used as an example of a complex coastal system sheltering a wide diversity of OM sources. Three main groups of sources were well discriminated from their n-alkane signatures: seagrass (Zostera sp.) produced mainly n-C₁₇, n-C₁₉, n-C₂₁, n-C₂₃ and n-C₂₅ alkanes, algae (Rhodophyta, Chlorophyta) produced n-C₁₅ and n-C₁₇ and the terrigenous input [Quercus sp., Spartina sp. and river suspended particulate OM (SPOM)] was characterized by n-C₂₅, n-C₂₇, n-C₂₉, n-C₃₁ and n-C₃₃. From the above and literature n-alkane fingerprints, we developed a set of indices (n-alkane ratios) to quantify the contribution of these three major sources of the SOM. At the Arcachon Bay scale, they indicated that SOM was composed mainly of seagrass (ca. 53 ± 19%) and terrestrial (ca. 41 ± 17%) material, followed by algae (ca. 6 ± 9%). Moreover, the new n-alkane indices exhibited more relevant spatial patterns than classical ones – the TAR (C₂₇ + C₂₉ + C₃₁/C₁₅ + C₁₇ + C₁₉; terrestrial to aquatic ratio) and the P_aq (C₂₃ + C₂₅/C₂₃ + C₂₅ + C₂₉ + C₃₁; aquatic plant %) – with a greater contribution from marine sources in the central part of the lagoon where a high density of Zostera seagrass was observed. Therefore, the development of precise indices adapted to the local diversity of OM sources is needed when using n-alkanes for quantifying the source composition of SOM in complex coastal systems.     

Compound specific δD values of long chain n-alkanes derived from terrestrial higher plants are indicative of the δD of meteoric waters: Evidence from surface soils in eastern China

The stable carbon and hydrogen isotope composition of higher plant-derived long chain n-alkanes (δ¹³C_n-alkanes and δD_n-alkanes) from 45 surface soil samples (within well characterized vegetation zones) from eastern China (18°N–50°N) are reported. The weighted average δD_n-alkanes value for n-C₂₇, n-C₂₉ and n-C₃₁ in the samples and the annual average δD of meteoric water recorded at 12 weather stations proximal to the sampling sites show similar spatial variations. The δD of n-alkanes shows a gradual depletion in value with increasing latitude. The results demonstrate that, on a large spatial scale, the δD values of long chain n-alkanes derived from higher plants have the potential to record the δD of meteoric water, although many other factors can also influence the isotope values. There appears to be no apparent relationship between the δD of the n-alkanes extracted from the surface soil and the overlying vegetation type (i.e. forest/grassland or C₃/C₄ composition). Therefore, palaeoenvironmental studies utilizing δD_n-alkanes from higher plant-derived material in geological samples have the potential to provide additional information with regard to the past hydrological cycle.     

Salinity variations in the northern Coorong Lagoon,South Australia: Significant changes in the ecosystem following human alteration to the natural water regime

European settlement and drought have significantly impacted the hydrology of the Coorong, a shallow coastal lagoon complex in South Australia, which is part of a terminal wetland at the mouth of the River Murray. An increased salinity associated with lower water levels and progressive isolation from ocean flushes contributed to a severe decline in ecological diversity over the past decades. Here we have conducted a molecular and stable isotopic study of a sedimentary core from the northern Coorong Lagoon spanning more than 5000 years to investigate the recent palaeoenvironmental history of the ecosystem. Major alterations were evident in many biogeochemical parameters in sediments deposited after the 1950s coinciding with the beginning of intensified water regulations. The most prominent shift occurred in δ¹³C profiles of C₂₁–C₃₃ n-alkanes from average values of −23.5‰ to an average of −28.2‰. Further changes included decreases in carbon preference index (CPI) and average chain length (ACL) of the n-alkane series as well as significant increases in algal (e.g. C₂₀ HBI, long chain alkenes and C₂₉-alkadiene) and bacterial (e.g. ¹³C depleted short chain n-alkanes and hopanoids, δ¹³C: −35.9‰ to −30.1‰) derived hydrocarbons. Long chain n-alkanes with a strong odd/even predominance as observed here are typically attributed to terrigenous plants. In the Coorong however, terrigenous input to sedimentary OM is only minor. Therefore changes in the before mentioned parameters were attributed to a source transition from a major contribution of macrophytes towards predominantly microalgae and bacteria.δD values of C₂₁–C₃₃ n-alkanes showed a general trend towards more enriched values in younger sediments, indicating an overall rising salinity. However, the most pronounced positive shift in these profiles again occurred after the 1950s. Altogether this study demonstrates that the recent human induced changes of the Coorong hydrology, compounded by a severe drought led to an increase in salinity and alterations of primary production which have been much more significant than natural variations occurring throughout the Holocene over several thousands of years.     

Synchronous climate anomalies in the western North Pacific and North Atlantic regions during the last 14,000 years

A peat cellulose δ¹⁸O record spanning around 14,000 years from the Hani peat mire in northeastern China reveals several abrupt temperature anomalies in the period from the last deglaciation through the Holocene. The timing of these anomalies coincides well with the notable cooling events recorded respectively using the GISP2 ice core and ice-rafted sediment of the North Atlantic Ocean, such as the Older Dryas, Inter-Allerød, Younger Dryas, and the nine ice-rafted debris events. The results demonstrate that this repeating pattern of abrupt temperature deterioration is not limited to the North Atlantic area at high latitude but also exists in the western North Pacific region at middle latitude. The synchronous temperature anomalies possibly are resulted from the joint effects of meltwater discharge into the North Atlantic Ocean and reduced solar activity. In the period from around 8600 to 8200 cal. yrs BP the Hani peat record shows a broad δ¹⁸O peak that may reflect compound climate signals resulting from the two kinds of forcing factors: the temperature drop related to reduced solar activity at around 8600–8250 cal. yrs BP, and the temperature anomaly attributed to the meltwater effect at around 8220 ± 70 cal. yrs BP. This result may provide palaeo-temperature evidence for existence of the sharp “8.2 k” event in the western North Pacific region. In addition, our results have revealed that in the period from the last deglaciation through the Holocene the synchronous temperature anomalies before and after the “8.2 k” event seem to be related to meltwater outflow and reduced solar activity, respectively. It is important that the all temperature anomalies—whether because of reduced solar activity in the late Holocene or from meltwater discharge in the early Holocene—are accompanied by an abrupt decline in the Indian Ocean summer monsoon and abrupt strengthening of the East Asian summer monsoon. It is likely that reduced solar activity and meltwater outflow appear to modulate Earth system changes in the same direction. The influences could be compounded. Reduced solar activity and meltwater outburst both appear to act as triggers for occurrence of the El Niño phenomenon in the equatorial Pacific Ocean, which may result in broad teleconnections between the temperature anomaly in the Northern Hemisphere and abrupt variation of the Asian monsoon.     

Effect of climate change on delivery and degradation of lipid biomarkers in a Holocene peat sequence in the Eastern European Russian Arctic

Lipid biomarkers from a peat plateau profile from the Northeast European Russian Arctic were analyzed. The peat originated as a wet fen ca. 9 ka BP and developed into a peat bog after the onset of permafrost ca. 2.5 ka BP. The distributions and abundances of n-alkanols, n-alkanoic acids, n-alkanes, n-alkan-2-ones and sterols were determined to study the effect of degradation on their paleoclimate proxy information. Plant macrofossil analysis was also used in combination with the lipid distributions. The n-alkanol and n-alkanoic acid distributions in the upper part of the sequence generally correspond to compositions expected from plant macrofossil assemblages. Their carbon preference index (CPI) values increase with depth and age, whereas those of the n-alkanes decrease. The different CPI patterns suggest that n-alkanoic acids and n-alkanols deeper in the sequence may be produced during humification through alteration of other lipids. Excursions in the n-alkanoic acid content also suggest an important contribution of invasive roots to the lipid biomarker composition. The CPIs associated with these compounds show that under permafrost conditions organic material from Sphagnum is better preserved than material from vascular plants. Increasing stanol/stenol ratio values and decreasing n-alkane CPI values indicate progressive degradation of organic matter (OM) with depth. The n-alkan-2-one/n-alkane and n-alkan-2-one/n-alkanoic acid ratios were shown to be useful proxies that can reflect the degree of OM preservation and suggest that both microbial oxidation of n-alkanes and decarboxylation of n-alkanoic acids produce n-alkan-2-ones in this peat sequence.     

Thermal degradation of rye and maize straw: Lipid pattern changes as a function of temperature

Future climatic conditions may coincide with an increased potential for wildfires in grassland and forest ecosystems, whereby charred biomass would be incorporated into soils. Molecular changes in biomass upon charring have been frequently analysed with a focus on black carbon. Aliphatic and aromatic hydrocarbons, known to be liberated during incomplete combustion of biomass have been preferentially analysed in soot particles, whereas determinations of these compounds in charred biomass residues are scarce. We discuss the influence of increasing charring temperature on the aliphatic and aromatic hydrocarbon composition of crop grass combustion residues. Straw from rye, representing C₃ grasses and maize, representing C₄ grasses, was charred in the presence of limited oxygen at 300, 400 and 500 °C. Typical n-alkane distribution patterns with a strong predominance of long chain odd-numbered n-alkanes maximising at C₃₁ were observed in raw straw. Upon combustion at 300 °C aliphatic hydrocarbons in char were dominated by sterenes, whereas at 400 °C sterenes disappeared and medium chain length n-alkanes, maximising around n-C₂₀, with a balanced odd/even distribution were present. At a charring temperature of 500 °C n-alkane chain length shifted to short chain homologues, maximising at C₁₈ with a pronounced predominance of even homologues. Even numbered, short chain n-alkanes in soils may thus serve as a marker for residues of charred biomass. Aromatic hydrocarbons indicate an onset of aromatization of biomass already at 300 °C, followed by severe aromatization upon incomplete combustion at 400–500 °C. The diagnostic composition of aliphatic and aromatic hydrocarbons from charred biomass affords potential for identifying residues from burned vegetation in recent and fossil soils and sediments.     

Intermediate sulfidation epithermal gold-base metal deposits in Tertiary subaerial volcanic rocks,Sahinli/Tespih Dere (Lapseki/Western Turkey)

Gold in the Sahinli and Tespih Dere intermediate sulfidation gold-base metal deposits in Western Turkey occurs in relatively deep epithermal quartz veins along with base metal minerals which have epithermal textures, including plumose quartz, vug infills, comb and cockade textures and matrix-supported milled breccias. The total sulfide content of the veins in the area is variable ranging from < 1% to 60% and is dominated by pyrite, galena, sphalerite and chalcopyrite. Sphalerite is Fe-poor (0.6 to 1.4 mol% FeS). Minor amounts of Ag-rich tetrahedrite are present. Primary hydrothermal alteration minerals include illite/muscovite, mixed-layer illite/smectite (11.6 Å) and clinochlore towards the east and, alunite, dickite/nacrite and pyrophyllite towards the west at Sahinli; major illite/muscovite and dickite occur at Tespih Dere and Sarioluk, respectively.Fluid inclusions in main-stage quartz at Sahinli are only liquid-rich, with homogenization temperatures ranging from 220 to 322 °C and the majority of T_h values between 250 and 300 °C. Salinity ranges from 4.3 to 6.9 wt.% NaCl equiv. First ice-melting temperatures (T_mf) between ?24.5 and ?19.0 °C indicate that the fluids were dominated by NaCl – H₂O during mineralization. The relatively higher average T_h at the Tespih Dere deposit (295 °C) is attributed to a relatively deeper level of exposure.Calculated δ¹⁸O values indicate that ore-forming hydrothermal fluids in the study area had δ¹⁸O_H2O ranging from + 1.1 to + 9.7‰ (average = 3.8‰), strongly ¹⁸O-enriched compared with present-day hydrothermal meteoric water in the area (δ¹⁸O = ?8.5‰). δD values of fluid inclusions in quartz range from ?58 to ?93‰ and δD values of clay minerals and alunite from ?40 to ?119‰. δD values from intermediate argillic alteration (average = ?68‰) in the study area are very similar to δD values of the present-day local geothermal system (average δD = ?54‰) whereas δD values from advanced-argillic alteration (average δD = ?33‰) are very different from the present-day local geothermal system.The δ³⁴S values in samples from the Sahinli and Tespih Dere deposits average ?2.9‰ for pyrite; ?3.3‰ for chalcopyrite; ?5.4‰ for sphalerite and ?7.6‰ for galena. These data are consistent with derivation of the sulfur from either igneous rocks or possibly from local wallrock.     

The <Emphasis Type="Italic">n</Emphasis>-alkanol paleoclimate records in two peat deposits: a comparative study of the northeastern margin of the Tibetan Plateau and Northeast China

A number of studies have revealed that the climate in the eastern margin of the Tibetan Plateau and Northeast China is sensitive to postglacial changes. Unfortunately, the link of the past climate evolution between the two regions is not well understood. In this study, two cores are analyzed to determine this link directly. The high-resolution n-alkanol distribution patterns from two typical peat sequences covering the past 16,000 cal years in the northeastern margin of the Tibetan Plateau and Northeast China, respectively, are closely examined by gas chromatograph–mass spectrometry analysis. In combination with other palaeoclimatic proxies, it is proposed that the n-alkanol average chain length and (C₂₂ + C₂₄)/(C₂₆ + C₂₈) ratio could reflect past climate changes in the two peat sequences. The n-alkanol proxies reveal several climatic intervals in the period from the last deglaciation through the Holocene. A comparison of n-alkanol records between the northeastern margin of the Tibetan Plateau and Northeast China indicates that the start and end of the warm Holocene Optimum differed at the two locations. The spatially asynchronous pattern of climatic change is possibly a result of different responses to change in solar radiation. The evolution of the Holocene paleoclimate is more consistent with changes in Northern Hemisphere solar radiation in Northeast China than on the Tibetan Plateau. The Holocene Optimum began and terminated earlier in Northeast China than in the northeastern margin of the Tibetan Plateau. Thus, the two n-alkanol proxies provide valuable insights into the regional Holocene climate and local environmental conditions.     

Cold climate during the closest Stage 11 analog to recent Millennia

The early part of marine isotopic Stage 11 near 400,000 years ago provides the closest analog to Holocene insolation levels of any interglaciation during the era of strong 100,000-year climatic cycles. The CH₄ concentration measured in Vostok ice fell to ∼450 ppb, and CO₂ values to ∼250 ppm. These natural decreases contrast with the increases in recent millennia and support the early anthropogenic hypothesis of major gas emissions from late-Holocene farming. During the same interval, δD values fell from typical interglacial to nearly glacial values, indicating a major cooling in Antarctica early in Stage 11. Other evidence suggests that new ice was accumulating during the closest insolation analog to the present day: a major increase in δ¹⁸O_atm at Vostok, a similar increase in marine δ¹⁸O values, and re-initiation of ice rafting in the Nordic Sea. The evidence permits extended (>20,000 year) intervals of Stage 11 interglacial warmth in the Antarctic and North Atlantic, yet it also requires that this warmth ended and a new glacial era began when insolation was most similar to recent millennia. The Holocene CO₂ anomaly was produced only in part by direct anthropogenic emissions; over half of the anomaly resulted from the failure of CO₂ values to fall as they had during previous interglaciations because of natural responses, including a sea-ice advance in the Antarctic and ice-sheet growth in the northern hemisphere.     

The applicability of accelerated solvent extraction (ASE) to extract lipid biomarkers from soils

We investigated the ability of accelerated solvent extraction (ASE) to extract selected lipid biomarkers (C₁₉–C₃₄ n-alkanes, n-alcohols and n-fatty acids as well as dehydroabietic acid and β-sitosterol) from a sandy soil profile under Corsican pine. Two organic layers (moss and F1) as well as two mineral soil horizons (EA and C1) were sampled and extracted with DCM/MeOH (93:7 v/v) by ASE at 75 °C and a pressure of 6.9 × 10⁶ Pa or 17 × 10⁶ Pa. Soxhlet extractions were used as the established reference method. After clean-up and derivatization with BSTFA, the extracts were analyzed on GC/MS.Using Soxhlet as a reference, we found ASE to extract all compounds adequately. The n-alkanes, especially, were found to be extracted very efficiently from all horizons studied. Only the n-fatty acids and β-sitosterol from the organic layers seemed to be extracted at a slightly lower efficiency by ASE. In all but two instances the relative abundance of extracted lipids within a component class was the same regardless of the extraction method used.Using a higher pressure in the ASE extractions significantly increased the extraction efficiency for all component classes in the moss layer, except β-sitosterol. The effect was most pronounced for the n-alkanes. In the EA horizon, a higher pressure slightly reduced the extraction efficiency for dehydroabietic acid. The observed differences between ASE and Soxhlet extractions as well as the pressure effect can be explained by a decrease in polarity of the extractant due to the elevated pressure and temperature applied during ASE extractions as compared to Soxhlet extractions. This would mainly increase the extraction efficiency of the least polar biomarkers: the n-alkanes as was observed. In addition, a better penetration of still partially water-filled micro pores under elevated pressure and temperature may have played a role.     

Geochemical assessment of hydrocarbon migration phenomena: Case studies from the south-western margin of the Dead Sea Basin

Calcite veins with fluid and solid bitumen inclusions have been discovered in the south-western shoulder of the Dead Sea rift within the Masada-Zohar block, where hydrocarbons exist in small commercial gas fields and non-commercial fields of heavy and light oils. The gas–liquid inclusions in calcite are dominated either by methane or CO₂, and aqueous inclusions sometimes bear minor dissolved hydrocarbons. The enclosed flake-like solid bitumen matter is a residue of degraded oil, which may be interpreted as “dead carbon”. About 2/3 of this matter is soot-like amorphous carbon and 1/3 consists of n-C₈C₁₈ carboxylic acids and traces of n-alkanes, light dicarboxylic acids, and higher molecular weight (>C₂₀) branched and/or cyclic carboxylic acids. Both bitumen and the host calcites show genetic relationship with mature Maastrichtian chalky source rocks (MCSRs) evident in isotopic compositions (δ¹³C, δ³⁴S, and δ¹⁸O) and in REE + Y patterns. The bitumen precursor may have been heavy sulfur-rich oil which was generated during the burial compaction of the MCSR strata within the subsided blocks of the Dead Sea graben. The δ¹⁸O and δ¹³C values and REE + Y signatures in calcites indicate mixing of deep buried fluids equilibrated with post-mature sediments and meteoric waters. The temperatures of fluid generation according to Mg–Li-geothermometer data range from 55 °С to 90 °С corresponding to the 2.5–4.0 km depths, and largely overlap with the oil window range (60–90 °С) in the Dead Sea rift (Hunt, 1996; Gvirtzman and Stanislavsky, 2000; Buryakovsky et al., 2005). The bitumen-rich vein calcites originated in the course of Late Cenozoic rifting and related deformation, when tectonic stress triggers damaged small hydrocarbon reservoirs in the area, produced pathways, and caused hydrocarbon-bearing fluids to rise to the subsurface; the fluids filled open fractures and crystallized to calcite with entrapped bitumen. The reported results are in good agreement with the existing views of maturation, migration, and accumulation of hydrocarbons, as well as basin fluid transport processes in the Dead Sea area.