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1.
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2.
Leaf wax n-alkanes from barley (Hordeum vulgare) from a field in Switzerland exhibited changes in δD values on the order of 20‰ over a growing season, while source water (soil water) and leaf water varied by 40‰. Additionally the seasonal variability in δD values of leaf wax n-alkanes of different barley leaves can only be found across different leaf generations (i.e. leaves that were produced at different times during the growing season) while n-alkane δD values did not vary significantly within a leaf generation. Interestingly, δD values of n-alkanes correlated best with the δD values of leaf water at midday of the sampling day but showed no significant correlation with soil water (e.g. precipitation) δD values. These results provide empirical evidence that leaf wax δD values record leaf water enrichment, and therefore integrate the isotopic effects of precipitation and evapotranspiration. Our results show that leaf wax n-alkane δD values from grasses are ‘locked in’ early during leaf development and hence record the environmental drivers of leaf water enrichment, such as vapor pressure deficit (VPD). Our data have important implications for the interpretation of paleorecords of leaf wax δD. We suggest that leaf wax n-alkane δD values from sedimentary records could be used to estimate changes in the degree of leaf water enrichment and hence VPD.  相似文献   

3.
Soils in the McMurdo Dry Valleys, Antarctica contain ice and considerable amounts of salt. Ice often occurs at shallow depth throughout the Dry Valleys and other areas of hyperarid permafrost, notably on Mars. This common occurrence of shallow ice is enigmatic; however, since according to published sublimation models it should disappear relatively quickly (at rates of order 0.1 mm a−1) due to vapor loss to the atmosphere. This loss may be offset by recharge from snowmelt infiltrating and freezing in the soil. Herein, we present a first quantitative estimate of this recharge based on measured vertical profiles of δD and δ18O that reveal considerable detail about the sources and sinks of ice. We model these profiles, taking into account the salt content and a soil temperature record along a 1.6 m depth profile of ∼10 ka old ice-cemented soils in Victoria Valley, Antarctica. The stable isotopes of ice are enriched in heavy isotopes at the top of the ice cement (20 cm depth); both δD and δ18O values plotted against depth exhibit a concave upward curve. At depth, the isotope composition is similar to that of Lake Victoria and modern meteoric water. The concave shape of the isotope profile is suggestive of downward advection-dispersion of snowmelt water enriched in heavy isotopes into the ice cement. Our advection-dispersion model, coupled with field data, enables us to quantify the advective flux and dispersion of melt water into the ice. The advective velocity and dispersion coefficient depend on the time since advection began and the ice-to-brine ratio; they are, respectively, of the order of 10−11-10−10 m s−1 and 10−12-10−11 m2 s−1. These values suggest that over the ∼10 ka time period, a total of 190 mm water infiltrated into the ice-cemented ground. The isotope composition and deuterium excess values of the uppermost ice cement can be modeled from snowmelt water enriched in salts using open system-Rayleigh fractionation. To develop the isotopic signature of the upper ice cement requires evaporation of ∼95% of the snowmelt water. Based on 190 mm brine infiltrating into the soil requires an initial total of ∼4 m of snowmelt water. This corresponds to ∼0.4 mm a−1 suggesting that, under the current climate condition, water from snowmelt is sufficient to compensate modeled sublimation rates, and therefore conserve ground ice in Victoria Valley.  相似文献   

4.
Lithology and Mineral Resources - We studied the composition and isotopic characteristics (δ13C and δD) of hydrocarbon gases from the Kotelnikovsky, Zmeiny, and Goryachnisky hot springs...  相似文献   

5.
The hydrogen isotope composition of terrestrial plant leaf wax in sediments is increasingly used as a paleoclimatic indicator. Modern calibration studies suggest that paleoclimatic interpretation of leaf wax δD values requires consideration of the differences in the apparent fractionation of hydrogen isotopes among different groups of plants. However, it is not common that paleoecological data are used to help interpret leaf wax δD profiles. Here we assess the relative importance of factors influencing millennial-scale shifts in δD values of n-alkanoic acids at Steel Lake (Minnesota, USA), an extensively studied site with independent records of vegetation composition, δD of input water to the lake, and evaporation. The δD values of the n-C28 alkanoic acid (δDC28) vary between −190 and −168‰, and do not correlate with δD of input water or the extent of evaporation. However, δDC28 is negatively correlated with the δ13C values of the n-C28 alkanoic acid (δ13CC28). The correlation, along with pollen assemblage and carbonate δ13C records, suggests that Holocene shifts between forest and grassland and/or in the water use efficiency of C3 plants influenced the stratigraphic variation in leaf wax δD. Thus, paleoecological information, such as that inferred from pollen assemblages and carbon isotopes of plant-derived compounds, may aid paleoclimatic interpretation of leaf wax δD profiles from lake sediments.  相似文献   

6.
《Applied Geochemistry》2001,16(9-10):1269-1284
Chemistry of major and minor elements, 87Sr/86Sr, δD, and δ18O of oilfield waters, and 87Sr/86Sr of whole rock were measured from Paleozoic strata in the Central Tarim basin, NW China. The aim is to elucidate the origin and migration of formation water and its relation to petroleum migration. High salinity oilfield waters in Carboniferous, Silurian and Ordovician reservoirs have maintained the same Na/Cl ratio as seawater, indicative of subaerially evaporated seawater. Two possible sources of evaporitic water are Carboniferous (CII) and Cambrian, both of which contain evaporitic sediments. Geographic and stratigraphic trends in water chemistry suggest that most of the high salinity water is from the Cambrian. Strontium, H and O isotopes as well as ion chemistry indicate at least 3 end member waters in the basin. High-salinity Cambrian evaporitic water was expelled upward into Ordovician, Silurian and Carboniferous reservoirs along faults and fractures during compaction and burial. Meteoric water has likely invaded the section throughout its history as uplift created subaerial unconformities. Meteoric water certainly infiltrated Silurian and older strata during development of the CIII unconformity and again in recent times. Modern meteoric water enters Carboniferous strata from the west and flows eastward, mixing with the high salinity Cambrian water and to a lesser degree with paleometeoric water. The third end member is highly radiogenic, shale-derived water which has migrated eastward from the Awati Depression to the west. Enrichment of Ca and Sr and depletion of K, Mg, and SO4 relative to the seawater evaporation trajectory suggest waters were affected by albitization of feldspars, dolomitization, illitization of smectite, and SO4 reduction. The mixing of meteoric water occurred subsequently to seawater evaporation, main water-rock interactions, and brine migration. The direction of brine migration is consistent with that of petroleum migration, suggesting water and petroleum have followed the same migration pathways.  相似文献   

7.
We analyzed the deuterium composition of individual plant-waxes in lake sediments from 28 watersheds that span a range of precipitation D/H, vegetation types and climates. The apparent isotopic fractionation (εa) between plant-wax n-alkanes and precipitation differs with watershed ecosystem type and structure, and decreases with increasing regional aridity as measured by enrichment of 2H and 18O associated with evaporation of lake waters. The most negative εa values represent signatures least affected by aridity; these values were −125 ± 5‰ for tropical evergreen and dry forests, −130‰ for a temperate broadleaf forest, −120 ± 9‰ for the high-altitude tropical páramo (herbs, shrubs and grasses), and −98 ± 6‰ for North American montane gymnosperm forests. Minimum εa values reflect ecosystem-dependent differences in leaf water enrichment and soil evaporation. Slopes of lipid/lake water isotopic enrichments differ slightly with ecosystem structure (i.e. open shrublands versus forests) and overall are quite small (slopes = 0-2), indicating low sensitivity of lipid δD variations to aridity compared with coexisting lake waters. This finding provides an approach for reconstructing ancient precipitation signatures based on plant-wax δD measurements and independent proxies for lake water changes with regional aridity. To illustrate this approach, we employ paired plant-wax δD and carbonate-δ18O measurements on lake sediments to estimate the isotopic composition of Miocene precipitation on the Tibetan plateau.  相似文献   

8.
Geochemical characterisation of 18 crude oils from the Potwar Basin (Upper Indus), Pakistan is carried out in this study. Their relative thermal maturities, environment of deposition, source of organic matter (OM) and the extent of biodegradation based on the hydrocarbon (HC) distributions are investigated. A detailed oil-oil correlation of the area is established. Gas chromatography-mass spectrometry (GC-MS) analyses and bulk stable carbon and hydrogen isotopic compositions of saturated and aromatic HC fractions reveals three compositional groups of oils. Most of the oils from the basin are typically generated from shallow marine source rocks. However, group A contains terrigenous OM deposited under highly oxic/fluvio-deltaic conditions reflected by high pristane/phytane (Pr/Ph), C30 diahopane/C29Ts, diahopane/hopane and diasterane/sterane ratios and low dibenzothiophene (DBT)/phenanthrene (P) ratios. The abundance of C19-tricyclic and C24-tetracyclic terpanes are consistent with a predominant terrigenous OM source for group A. Saturated HC biomarker parameters from the rest of the oils show a predominant marine origin, however groups B and C are clearly separated by bulk δ13C and δD and the distributions of the saturated HC fractions supporting variations in source and environment of deposition of their respective source rocks. Moreover, various saturated HC biomarker ratios such as steranes/hopanes, diasteranes/steranes, C23-tricyclic/C30 hopane, C28-tricyclic/C30 hopane, total tricyclic terpanes/hopanes and C31(R + S)/C30 hopane show that two different groups are present. These biomarker ratios show that group B oils are generated from clastic-rich source rocks deposited under more suboxic depositional environments compared to group C oils. Group C oils show a relatively higher input of algal mixed with terrigenous OM, supported by the abundance of extended tricyclic terpanes (up to C41+) and steranes.Biomarker thermal maturity parameters mostly reached to their equilibrium values indicating that the source rocks for Potwar Basin oils must have reached the early to peak oil generation window, while aromatic HC parameters suggest up to late oil window thermal maturity. The extent of biodegradation of the Potwar Basin oils is determined using various saturated HC parameters and variations in bulk properties such as API gravity. Groups A and C oils are not biodegraded and show mature HC profiles, while some of the oils from group B show minor levels of biodegradation consistent with high Pr/n-C17, Ph/n-C18 and low API gravities.  相似文献   

9.
《International Geology Review》2012,54(13):1443-1463
Fluid inclusions hosted by quartz veins in high-pressure to ultrahigh-pressure (HP-UHP) metamorphic rocks from the Chinese Continental Scientific Drilling (CCSD) Project main drillhole have low, varied hydrogen isotopic compositions (δD?=??97‰ to??69‰). Quartz δ18O values range from??2.5‰ to 9.6‰; fluid inclusions hosted in quartz have correspondingly low δ18O values of??11.66‰ to 0.93‰ (T h?=?171.2～318.8°C). The low δD and δ18O isotopic data indicate that protoliths of some CCSD HP-UHP metamorphic rocks reacted with meteoric water at high latitude near the surface before being subducted to great depth. In addition, the δ18O of the quartz veins and fluid inclusions vary greatly with the drillhole depth. Lower δ18O values occur at depths of ～900–1000 m and ～2700 m, whereas higher values characterize rocks at depths of about 1770 m and 4000 m, correlating roughly with those of wall-rock minerals. Given that the peak metamorphic temperature of the Dabie-Sulu UHP metamorphic rocks was about 800°C or higher, much higher than the closure temperature of oxygen isotopes in quartz under wet conditions, such synchronous variations can be explained by re-equilibration. In contrast, δD values of fluid inclusions show a different relationship with depth. This is probably because oxygen is a major element of both fluids and silicates and is much more abundant in the quartz veins and silicate minerals than is hydrogen. The oxygen isotope composition of fluid inclusions is evidently more susceptible to late-stage re-equilibration with silicate minerals than is the hydrogen isotope composition. Therefore, different δD and δ18O patterns imply that dramatic fluid migration occurred, whereas the co-variation of oxygen isotopes in fluid inclusions, quartz veins, and wall-rock minerals can be better interpreted by re-equilibration during exhumation.

Quartz veins in the Dabie-Sulu UHP metamorphic terrane are the product of high-Si fluids. Given that channelized fluid migration is much faster than pervasive flow, and that the veins formed through precipitation of quartz from high-Si fluids, the abundant veins indicate significant fluid mobilization and migration within this subducted continental slab. Many mineral reactions can produce high-Si fluids. For UHP metamorphic rocks, major dehydration during subduction occurred when pressure–temperature conditions exceeded the stability of lawsonite. In contrast, for low-temperature eclogites and other HP metamorphic rocks with peak metamorphic P–T conditions within the stability field of lawsonite, dehydration and associated high-Si fluid release may have occurred as hydrous minerals were destabilized at lower pressure during exhumation. Because subduction is a continuous process whereas only a minor fraction of the subducted slabs returns to the surface, dehydration during underflow is more prevalent than exhumation even in subducted continental crust, which is considerably drier than altered oceanic crust.  相似文献   

10.
Vicia villosa is an annual legume plant,and is mainly used for green manure by farmers in southwest China.Field growth experiments were performed on six plots.The concentrations of mineral nutrients and soluble sugar,and the changes of carbon and nitrogen isotopic composition within and among organs of Vicia were deter- mined.Significant differences in legume growth were found in response to soil type and its moisture conditions.The Vicia villosa was relatively well adapted to growth in limestone soils than sandstone soils.The distribution of sugar concentrations andδ1 3C-differences between roots and leaves indicate that the translocation of sugars from leaves to roots may be restricted by soil drought.Therefore,there was an inhibition of Pi distribution from roots to leaves, resulting in over optimum threshold of N/P ratio.Those may originate from the feedback regulation in the legume, where soluble sugar could not be distributed from leaves to roots.The results ofδ1 5N values in tissues suggest that there should be different preferential use of nitrogen resource by legume during the formation of nodules:before nodule formation the legume preferentially utilizes inorganic nitrogen from soils,but afterwards the nitrogen should be mainly from N2-fixation.Our results indicate that the lack of nodulation development,except for S2,should be ascribed to the factor controlling bi-direction nutrient transfer,which should be efficiency of establishment symbiosis with arbuscular mycorrhiza before nodulation formation.It is predicted that the species of Vicia villosa should be a legume associated with dual symbiosis with rhizobia and mycorrhiza.  相似文献   

11.
Two multi-year oxygen isotope (δ18O) records were obtained from archaeological Ostrea angasi shells, confirming the potential of this species to provide valuable environmental records for the late Holocene period in southeastern Australia. High-resolution δ18Oshell samples from the O. angasi clearly display a seasonal variability, offering insight into past climate conditions in a region where such information is presently limited.

The oxygen isotope record in O. angasi reflects a combined temperature–salinity signal. Observations of δ18Oshell data from modern specimens are used as a point of reference to assist in decoupling these two influences, with the two archaeological samples compared with the δ18Oshell profile of four modern O. angasi. Assuming similar paleo- δ18Owater values at the collection sites, data from these archaeological shells present a record of temperatures during the period of their growth that are consistently lower than modern day, with mean annual temperatures ～2°C cooler.  相似文献   


12.
《Applied Geochemistry》2005,20(4):691-700
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13.
A 30 ka paleo-climate record of the Boise area, Idaho, USA has been delineated using groundwater stable isotopic compositions. Groundwater ages are modern (cold batholith), 5-15 ka (thermal batholith) , 10-20 ka (frontal fault) , and 20-30 ka (Snake River plain thermal). The stable isotopic composition of groundwaters have been used as a surrogate for the stable isotopic composition of precipitation. Using δ2H and δ18O compositions, local groundwater lines (LGWL's) were defined for each system. Each LGWL has been evaluated with defined slopes of 6.94 and 8, respectively, and resulting deuterium excess values (d) were found for each groundwater system for each slope. Time dependent changes in moisture source humidity and temperature, and Boise area recharge temperatures, calculated from stable isotopic data and the deuterium excess factors, agree with previous paleo-climate studies. Results indicate that from the last glacial maximum to the present time the humidity over the ocean moisture source increased by 9%, sea surface temperature at the moisture source increased 6-7°C, and local Boise temperature increased by 4-5°C. A greater increase of temperature at the moisture source as compared to the Boise area may impart be due to a shift in the moisture source area.  相似文献   

14.
Karst rocks from the Huanglong Formation exposed at the margin of the Eastern Sichuan Basin can be divided into four types:slightly corroded, moderately corroded porous, intensely corroded brecciated and intensely corroded and replaced secondary calcic karstic rocks. The carbon, oxygen and strontium isotope compositions of the various karst rocks are analyzed systematically and compared to rocks without karst corrosion. The results indicate that(1) the Huanglong Formation in the eastern Sichuan Basin was a restricted bay supplied and controlled by freshwater in which mudmicrite and mud-dolomicrite exhibit low δ13C and δ18O values and high 87Sr/86 Sr ratios;(2) all types of karstic rocks in the paleokarst reservoirs of the Huanglong Formation in the research area are affected by atmospheric freshwater with the δ13C and δ18O values and 87Sr/86 Sr ratios in the original formation approaching those of atmospheric freshwater, which reflects ancient hydrological conditions, fluid properties, isotopic source and the fractionation effect;(3) the intensely corroded and replaced secondary limestone is affected by a variety of diagenetic fluids, often reflected by δ13C and δ18O values, while the 87Sr/86 Sr ratios exhibit the strong degree of the corrosion;(4) after comparing the 87Sr/86 Sr ratios of each type of karst rock, the diagenetic fluids are determined to be mainly atmospheric freshwater, and depending on the strength of corrosion, and the low 87Sr/86 Sr ratio fluids in the layer will participate in the karst process. The carbon, oxygen, and strontium isotopes of different karstic reservoirs can provide meaningful geochemical information for forecasting and evaluating the development and distribution rules of the Huanglong Formation at the margin of the eastern Sichuan Basin in time and space.  相似文献   

15.
The stable carbon isotope (δ13C) and elemental C/N ratios in Total Organic Carbon (TOC) extracted from radiometrically dated cores from two Midwestern USA lakes were determined to investigate the factors that control these values in temperate lakes. The range of δ13C values (-26 to -32%) and C/N ratios (mean value ∼10.8) are typical of values reported for other temperate lake organic matter in this region. In the core from Lake Winnebago, Wisconsin, a negative correlation was seen between the TOC and δ13C, which can be interpreted in terms of a re-mixing and consumption of sedimented organic carbon along with rapid equilibration throughout the water column. No correlation was seen between the TOC and δ13C in the record from Ladd Lake, Ohio, implying that in this latter lake productivity alone was not a singular process controlling the isotope ratio. Here, it is suggested that equilibrium conditions are maintained such that the DIC of the water is never depleted of aqueous CO2 during high organic production and the resulting δ13C of the organic carbon lacks correlation with the TOC. Further, in this lake a fine resolution analysis was carried out which indicated a possible anthropogenic influence on the isotope ratio around times when human settlement (∼300 yrs ago) and enhanced agricultural practices (∼80 yrs ago) were significant. The study shows that carbon isotope studies are useful in paleolimnologic investigations.  相似文献   

16.
The middle Paleolithic stratigraphic sequence of Les Pradelles (Charente, France) spans from the end of Marine Isotope Stage (MIS) 4 until the middle of MIS 3. Micromammal remains are present in all the stratigraphic levels, offering a rare opportunity to address the questions of both environmental and climatic fluctuations throughout this period. Climate modes were studied through the taphonomy, biodiversity and oxygen isotope compositions of phosphate (δ18Op) from 66 samples of rodent tooth enamel. The δ18Op values from the lower sedimentary levels provide summer mean air temperatures of 19 ± 2°C (level 2/1) and of 16 ± 2°C (levels 2A, 2B and 4A). Within the middle of sequence (level 4B), a paleobiodiversity change can be identified with an increase of Dicrostonyx torquatus, which is associated with the largest amplitude in δ18Op values and the highest maximal δ18Op values. At the top of the sequence (level 5-2), a biodiversity change is observed with the increase of Microtus arvalis, but without any change in δ18Op values. The association of cold rodent species with unexpected high and large amplitudes in the δ18Op values of their teeth, possibly indicative of aridity, suggests their deposition during a Heinrich event.  相似文献   

17.
Please refer to the attachment(s) for more details.  相似文献   

18.
We have determined the position of deuterium atoms in δ-AlOOD by neutron powder diffraction at ambient pressure. As previously reported by theoretical and experimental studies, the deuterium atoms are located in the tunnel formed by the chains of AlO6 octahedra. The data are best fit with the P21 nm structure, producing bond lengths of D–O1 of 1.552(2) Å, O2–D of 1.020(2) Å and O1–O2 of 2.571(2). This study confirms that the hydrogen bond is asymmetric at ambient conditions in agreement with recent single-crystal synchrotron study for δ-AlOOH.  相似文献   

19.
This paper investigates the stable isotopic composition from late Pleistocene–Holocene (~ 13 to ~ 10.5 cal ka BP) shells of the land snail Helix figulina, from Franchthi Cave (Greece). It explores the palaeoclimatic and palaeoenvironmental implications of the isotope palaeoecology of archaeological shells at the time of human occupation of the cave. Modern shells from around the cave were also analysed and their isotopic signatures compared with those of the archaeological shells. The carbon isotope composition of modern shells depicts the consumption of C3 vegetation. Shell oxygen isotopic values are consistent with other Mediterranean snail shells from coastal areas. Combining empirical linear regression and an evaporative model, the δ18Os suggest that modern snails in the study area are active during periods of higher relative humidity and lower rainfall δ18O, probably at night. Late glacial and early Holocene δ18Os show lower values compared to modern ones. Early Holocene δ18Os values likely track enhanced moisture and isotopic changes in the precipitation source. By contrast, lower late glacial δ18O could reflect lower temperatures and δ18Op, compared to the present day. Shell carbon isotope values indicate the presence of C3 vegetation as main source of carbon to late glacial and early Holocene snails.  相似文献   

20.
Natural variations in the ratios of nitrogen isotopes in biomass reflect variations in nutrient sources utilized for growth. In order to use δ15N values of chloropigments of photosynthetic organisms to determine the corresponding δ15N values of biomass - and by extension, surface waters - the isotopic offset between chlorophyll and biomass must be constrained. Here we examine this offset in various geologically-relevant taxa, grown using nutrient sources that may approximate ocean conditions at different times in Earth’s history. Phytoplankton in this study include cyanobacteria (diazotrophic and non-diazotrophic), eukaryotic algae (red and green), and anoxygenic photosynthetic bacteria (Proteobacteria), as well as environmental samples from sulfidic lake water. Cultures were grown using N2, NO3−, and NH4+ as nitrogen sources, and were examined under different light regimes and growth conditions. We find surprisingly high variability in the isotopic difference (δ15Nbiomass − δ15Nchloropigment) for prokaryotes, with average values for species ranging from −12.2‰ to +11.7‰. We define this difference as εpor, a term that encompasses diagenetic porphyrins and chlorins, as well as chlorophyll. Negative values of εpor reflect chloropigments that are 15N-enriched relative to biomass. Notably, this enrichment appears to occur only in cyanobacteria. The average value of εpor for freshwater cyanobacterial species is −9.8 ± 1.8‰, while for marine cyanobacteria it is −0.9 ± 1.3‰. These isotopic effects group environmentally but not phylogenetically, e.g., εpor values for freshwater Chroococcales resemble those of freshwater Nostocales but differ from those of marine Chroococcales. Our measured values of εpor for eukaryotic algae (range = 4.7-8.7‰) are similar to previous reports for pure cultures. For all taxa studied, values of εpor do not depend on the type of nitrogen substrate used for growth. The observed environmental control of εpor suggests that values of εpor could be useful for determining the fractional burial of eukaryotic vs. cyanobacterial organic matter in the sedimentary record.  相似文献   

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