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1.
The extensive vertical exposure (> 150 m) of terrestrial sediments on Axel Heiberg Island, which contain thick fossiliferous lignites, presents an exceptional opportunity to follow the establishment and re-establishment of Arctic Metasequoia forests during the middle Eocene. We compared δD values in n-alkanes of chain length 23, 25, 27 and 29 with δ18O values in phenylglucosazone (P-G) derived from α-cellulose; we also analyzed %-abundance of ferns, gymnosperms and angiosperms using pollen and spores isolated from each lignite. Our results showed that forest composition was altered upon uplift, as gymnosperms became more abundant within the relatively well-drained upland sediments. This was also reflected in the small (1‰), but significant, increase in the δ13C value of TOM from lowland to upland environments. However, neither the δD values of n-alkanes nor the δ18O in P-G were statistically different in the upland sediments, as compared to the lowland sediments; from this we inferred that the oxygen isotope signature of environmental water available to the forests for plant growth was relatively uniform throughout the time of the fossil forests. The δD value of environmental water implied by both n-alkanes and P-G ranged from ? 168 to ? 131% and was considerably enriched compared to all environmental water samples available from the modern Arctic region (< ? 180%). In addition to indicating a warmer Eocene Arctic, subject to meteoric transport patterns different from today's, these results argue against the presence of an Eocene polar ice cap.  相似文献   

2.
Even though the Cenozoic has been recognized as a period of important climate change, long-term climatic changes that took place in the continental domain are still questioned. For an area, southern Germany, for which other long-term palaeoclimatic records exist, analysis of oxygen isotope composition of small mammal teeth has been carried out for localities ranging in age from the late Eocene (c.36 Ma) to the middle Miocene (c.10 Ma). Comparison of this long-term continental δ18O record with the marine record reveals comparable trends. The major Cenozoic climatic events are thus recognized in the continental oxygen isotope record.Through comparison with other quantitative palaeoclimatic reconstructions available for the studied area, temperatures in southern Germany are broadly estimated to have fluctuated between 12 °C and 25 °C from late Eocene to early late Miocene. According to the different available chronological frameworks, either a ~ 2 °C (considering the classical biostratigraphy) or a ~ 6 °C (considering a revised biostratigraphy) decrease in mean air temperature is estimated for the Eocene/Oligocene boundary.  相似文献   

3.
The 13C/12C ratios of leaves of the conifer morphotype Frenelopsis were measured to decipher the influences of water and salt stress on stomatal density (SD), epidermal cell density (ECD) and stomatal index (SI). Three morphospecies were analyzed: F. ugnaensis from freshwater fluvio-lacustrine deposits (Upper Barremian), F. turolensis and alata from coastal deposits (Lower-Middle Albian and Upper Albian respectively). The cuticle δ13C values show a large variation from ? 28‰ to ? 21‰. Comparison with previously published marine carbonate δ13C records indicate that the difference in cuticle δ13C between the different deposits are mainly due to difference in CO2-plant isotope fractionation rather than to change in isotopic composition of inorganic carbon in the atmosphere and ocean. The less negative δ13C and wide range in δ13C of F. turolensis and alata (? 27.5 to ? 21‰), compared to F. ugnaensis, (? 28 to ? 25‰) are interpreted as a result of salt and/or water stress. The data as a whole yield a good relationship between the 13C/12C ratio and SD (r = 0.67, n = 42, p < 0.001), SI (r = 0.53, n = 41, p < 0.001), hence suggesting that the differences in SD and SI between the three morphospecies are related to freshwater/saline environment. Looking at single morphospecies, the SD of F. ugnaensis decreases with increasing δ13C value (r = ? 0.57, n = 15, p = 0.026) as well as a decrease of SI (r = ? 0.62, n = 15, p = 0.013), possibly reflecting warmer and drier conditions. Average SI of F. alata does not significantly change with δ13C and inferred soil salinity in contrast to SD (p < 0.01).  相似文献   

4.
Planktic and epibenthic foraminiferal δ13C records at Site PS62/015-3 (southwestern Greenland Sea) reveal a series of transient events of extreme 13C depletion down to − 6‰ during the period 90–40 ka. Scanning electron microscope studies of the ultrastructures of foraminiferal tests suggest that 13C depleted specimens are affected by some 10–20% overgrowth by authigenic calcite contributing to the light δ13C signal. Incremental-leaching experiments and census counts of pristine versus overgrowth-affected specimens show that the 13C depleted foraminiferal tests incorporate a primary δ13C signature most likely ranging from + 1‰ to − 1.7‰ and a post-depositional δ13C signature around − 17‰ to − 19.5‰. Extremely low values of productivity and organic carbon in Late Quaternary sediments along the east Greenland margin preclude organic matter as potential source of the isotopically light carbon. In contrast, thermal instability of clathrates and subsequent aerobic oxidation of (highly 12C enriched) methane in pore and ocean water provide a compelling mechanism to account for the negative δ13C excursions of both primary and post-depositional carbonates. Here, pore water methane may have led to a supersaturation of 13C depleted bicarbonate and precipitation of isotopically light authigenic calcite on and in foraminiferal tests, a feature that may serve as a tracer to former sites of clathrate destabilization.  相似文献   

5.
Stable isotopes (δ15N and δ13C) are being widely applied in ecological research but there has been a call for ecologists to determine species- and tissue-specific diet discrimination factors (?13C and ?15N) for their study animals. For large sharks stable isotopes may provide an important tool to elucidate aspects of their ecological roles in marine systems, but laboratory based controlled feeding experiments are impractical. By utilizing commercial aquaria, we estimated ?15N and ?13C of muscle, liver, vertebral cartilage and a number of organs of three large sand tiger (Carcharias taurus) and one large lemon shark (Negaprion brevirostris) under a controlled feeding regime. For all sharks mean ± SD for ?15N and ?13C in lipid extracted muscle using lipid extracted prey data were 2.29‰ ± 0.22 and 0.90‰ ± 0.33, respectively. The use of non-lipid extracted muscle and prey resulted in very similar ?15N and ?13C values but mixing of lipid and non-lipid extracted data produced variable estimates. Values of ?15N and ?13C in lipid extracted liver and prey were 1.50‰ ± 0.54 and 0.22‰ ± 1.18, respectively. Non-lipid extracted diet discrimination factors in liver were highly influenced by lipid content and studies that examine stable isotopes in shark liver, and likely any high lipid tissue, should strive to remove lipid effects through standardising C:N ratios, prior to isotope analysis. Mean vertebral cartilage ?15N and ?13C values were 1.45‰ ± 0.61 and 3.75‰ ± 0.44, respectively. Organ ?15N and ?13C values were more variable among individual sharks but heart tissue was consistently enriched by ~ 1–2.5‰. Minimal variability in muscle and liver δ15N and δ13C sampled at different intervals along the length of individual sharks and between liver lobes suggests that stable isotope values are consistent within tissues of individual animals. To our knowledge, these are the first reported diet–tissue discrimination factors for large sharks under semi-controlled conditions, and are lower than those reported for teleost fish.  相似文献   

6.
A globally recorded negative carbon isotope excursion characterizes the transition from Cambrian Series 2 to Cambrian Series 3. This transition is also well exposed in sedimentary successions on the Yangtze Platform, and the Wuliu–Zengjiayan section, Guizhou Province, South China has been proposed as a potential Global Stratotype Section and Point (GSSP) for this boundary. Here, we report δ13Ccarb values for the Jianshan and the Wuliu–Zengjiayan sections. Both sections display a progressive decrease in δ13C from values around + 3‰ upwards in stratigraphy to a pronounced δ13C minimum with values as low as ? 6.9‰ at the proposed boundary level, and a return to δ13C values between 0 and + 1‰ in the upper part of the sections. The δ13C minimum is thought to be caused by a transgressive event, flooding the shelf area with 13C depleted basinal anoxic bottom water. Our δ13C data are in good agreement with carbon isotope profiles recorded elsewhere. These define the so called ROECE event (Redlichiid–Oleneliid Extinction Carbon Isotope Excursion, cf. Zhu et al., 2006, 2007) and may reflect the perturbation of the global carbon cycle during the Cambrian Series 2 to Cambrian Series 3 transition.  相似文献   

7.
Geochemical proxy records of sea surface temperature (SST) or sea surface salinity (SSS) variability on intra- and interannual time-scales in corals from geological periods older than Pleistocene are extremely rare due to pervasive diagenetic alteration of coralline aragonite. Very recently, however, stable isotope data (δ18O, δ13C) from specimens of Porites of Late Miocene age (10 Ma) have been shown to preserve original environmental signatures. In this paper we describe new finds of the zooxanthellate corals Porites and Tarbellastraea in exceptional aragonite preservation from the island of Crete in sediments of Tortonian (~ 9 Ma) and Early Messinian (~ 7 Ma) age. Systematic, comparative stable isotope analysis of massive Tarbellastraea and Porites sampled from the same beds and localities reveal identical stable isotope fractionation patterns in both genera. Therefore, extinct Tarbellastraea represents an additional environmental archive fully compatible and mutually exchangeable with Porites. Provided that seasonal variations in δ18O reflect SST changes only, seasonal SST contrasts of 7.3 °C for the Tortonian and 4.8 °C for the Early Messinian are inferred, implying warmer summer and cooler winter SSTs during the Tortonian than during the Messinian. However, reduced δ18O seasonality (1.1‰ in the Tortonian and 0.7‰ in the Messinian) and slightly less negative mean δ18O in Messinian corals (? 2.4‰) compared to Tortonian specimens (? 2.7‰) may not necessarily indicate a long-term fall in SSTs, but changes in surface water δ18O, i.e. global ice build-up or enhanced evaporation during summer or increased precipitation/river discharge during winter and changes in insolation. On the other hand, coral communities of Tortonian and Messinian age in central Crete are identical, and compatible annual extension rates indicate similar average SSTs during the two investigated time periods. In addition, lithological and paleobotanical data from Central Crete document a change from humid to dry climatic conditions during the Late Miocene. Therefore, a likely explanation for the observed shift in coral mean δ18O and reduced δ18O seasonality from the Tortonian to the Early Messinian is a change in ambient seawater δ18O caused by a change in the hydrological balance towards high evaporation/high salinity during summer.  相似文献   

8.
Three megalodontoid bivalves from the Upper Triassic Cassian Formation (N Italy, Dolomites) were sampled for δ13C and δ18O sclerochronology (n = 270). With more than 1000 described invertebrate species, the Cassian Formation has one of the best records of an Early Mesozoic tropical fauna. In addition, the Cassian Formation is one of the very few Triassic occurrences with original aragonite preservation, with all studied shells consisting of pristine aragonite. The presence of aragonite and crossed lamellar as well as fibrous prismatic shell microstructures shown for the first time for Triassic megalodontoids suggests absence or minimal impact of diagenetic alteration. The δ13C values range from 3.6 to 5.8‰ and show a distinct cyclicity in two studied shells whereas a third shell shows no obvious cyclicity. In one bivalve specimen, the cycles are somewhat offset from δ18O cycles and in the other specimen δ18O and δ13C curves are inversely correlated. Seasonal variation in freshwater runoff including nutrient input and subsequent changes in plankton productivity during dry and wet seasons may explain δ13C cyclicity. δ18O values show a pronounced cyclicity within each of the studied shells varying from ? 3.6 to ? 1.4‰. The variations in δ18O suggest a pronounced seasonality in Late Triassic tropical shallow waters of the western Tethys, with inferred seasonal temperature changes ranging from 24 to 32 °C. Influx of fresh water during the rainy seasons (mega-monsoon) or upwelling might also explain part of the variation in δ18O. The presented data suggest that the diverse Cassian fauna lived under conditions characterized by warm sea-surface waters with a pronounced seasonality. Similar conditions are reported for some modern tropical settings.  相似文献   

9.
Sediment trap samples collected over a seven-year period (February 1991–October 1997) from Guaymas Basin in the Gulf of California were used to study the oxygen isotope composition of five species of planktonic foraminifera, Globigerinoides ruber (white), Globigerina bulloides, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globorotalia menardii. The δ18O data were analyzed for temporal and interspecies variability and were compared to local hydrography to evaluate the use of each species in reconstructing past oceanographic applications. The two surface dwelling species, G. ruber and G. bulloides displayed the lowest δ18O values (~ 0.0 to ? 5.0‰), while δ18O values for the thermocline dwelling N. dutertrei, P. obliquiloculata, and G. menardii were higher (~ 0.0 to ? 2.0‰). The δ18O of G. ruber most accurately records measured sea surface temperatures (SSTs) throughout the year. G. bulloides δ18O tracks SSTs during the winter–spring upwelling period but for the remainder of the year records slightly colder, subsurface temperatures. The difference between the δ18O of the surface dwelling species, G. ruber and G. bulloides, and that of the thermocline dwelling species, N. dutertrei, P. obliquiloculata, and G. menardii, was used to estimate the surface to thermocline temperature gradient. During the winter these δ18O differences are small (~ 0.50‰) reflecting a well-mixed water column. These interspecies δ18O differences increase during the summer (~ 1.90‰) in response to the strong thermal stratification that exists at this time of year.  相似文献   

10.
Estrogens were prohibited in the food producing animals by European Union (96/22/EC directive) and added to the Report on Carcinogens in United States since 2002. Due to very low concentration in serum or urine (~pg/mL), the method of control its abuse had not been fully developed.The endogenous estrogens were separated from urines of 18 adult men and women. The exogenous estrogens were chemical reference standards and over the counter preparations. Two patients of dysfunctional uterine bleeding (DUB) administered exogenous estradiol and the urines were collected for 72 h. The urinary estrogens were separated by high-performance liquid chromatography (HPLC) and confirmed. The exogenous and exogenous estrogens were analyzed by gas chromatography combustion isotope ratio mass spectrometry (GC–C–IRMS) to determine the 13C/12C ratio (δ13C‰).The δ13C‰ values of reference standard of E1, E2, and E3 were ?29.36 ± 0.72, ?27.98 ± 0.35, ?27.62 ± 0.51, respectively. The δ13C‰ values of the endogenous E1, E2, and E3 were ?21.62 ± 1.07, ?22.14 ± 0.98, and ?21.88 ± 1.16, with P < 0.01 (t-test). Two DUB patients’ urinary estradiol δ13C‰ values was depleted to ?28.02 ± 0.33 after the administration. The progesterone, 17α-hydroxyprogesterone, pregnanediol, as well as desogestrel and ethinylestradiol from contraceptives were also determined.Stable carbon isotope analysis can distinguish the endogenous and exogenous urinary estrogen in human.  相似文献   

11.
《Marine Micropaleontology》2007,62(4):196-208
Oxygen and carbon isotopes of foraminifera were analyzed in core PC4, water depth 1366 m, off northern Japan, near the east side of the Tsugaru Strait (130 m depth) between the open northwestern Pacific Ocean and the Japan Sea. At present, the site is at the confluence of the Tsugaru Warm Current which flows eastwards out of the Sea of Japan through the Tsugaru Strait, the subarctic Oyashio Current and the subtropic Kuroshio Current. During the Last Glacial Maximum (LGM), the Oyashio Current penetrated further to the South and outflow from the Japan Sea was restricted by glacio-eustatic sea level lowering.The isotopic values of the planktic foraminifer Neogloboquadrina pachyderma (sinistral) and the benthic foraminifer Uvigerina akitaensis reflect rapid millennial-scale paleoceanographic changes between 34 and 6 ka. Hydrographic changes during deglaciation were related to events at high northern latitudes, but Holocene hydrographic changes were dominated by local effects, such as the development of the outflow of the Tsugaru Warm Current. High values of planktic δ18O during the LGM reflect the southward advance of the Oyashio Current. These values decreased by 0.3‰ from 19.4 to 18.9 ka, then increased by 0.5‰ at 18 ka, with highest values between 17.5 and 15 ka. The δ18O oscillations between 19.4 and 15 ka may reflect millennial-scale warm–cold oscillations during Heinrich event 1. Planktic microfossil data indicate that cold Oyashio waters flowed from the northwestern Pacific into the Japan Sea via the Tsugaru Strait between 17 and 16 ka, consistent with the occurrence of the highest planktic δ18O values in core PC4. Planktic δ18O values rapidly decreased by 0.9‰ at 15 ka, possibly reflecting the effects of both a rapid increase in fresh water flux and rising temperatures in the subarctic North Pacific. During the Younger Dryas, cold event planktic δ18O values increased by 0.5‰, followed by a gradual decrease by 1‰ from the early to middle Holocene, reflecting a gradual increase in eastward outflow via the Tsugaru Strait with sea level rise. Both planktic and benthic foraminiferal δ13C values oscillated between 34 and 10 ka, at relatively large amplitudes (about 0.5‰), then remained relatively stable during the last 10 kyr. Several negative planktic and benthic (∼  0.7‰) δ13C excursions were present in sediment dated between the precipitation of secondary carbonates during episodic methane release possibly associated with methane release from continental margin sediments.  相似文献   

12.
《Aquatic Botany》2007,87(4):292-298
The effect of salinity on leaf area and the relative accumulation of Na+ and K+ in leaves of the mangrove associate Hibiscus tiliaceus were investigated. Photosynthetic gas exchange characteristics were also examined under arid and non-arid leaf conditions at 0, 10, 20 and 30‰ substrate salinity. At salinities  40‰, plants showed complete defoliation followed by 100% mortality within 1 week. Salinities  30‰ were negatively correlated with the total leaf area per plant (r2 = 0.94). The reduction in the total plant leaf area is attributed to the reduction in the area of individual leaves (r2 = 0.94). Selective uptake of K+ over Na+ declined sharply with increasing salinity, where K+/Na+ ratio was reduced from 6.37 to 0.69 in plants treated with 0 and 30‰, respectively. Under non-arid leaf condition, increasing salinity from 0 to 30‰ has significantly reduced the values of the intrinsic components of photosynthesis Vc,max (from 50.4 to 18.4 μmol m−2 s-1), Jmax (from 118.0 to 33.8 μmol photons m−2 s−1), and VTPU (from 6.90 to 2.30 μmol m−2 s−1), while stomatal limitation to gas phase conductance (SL) increased from 14.6 to 38.4%. Water use efficiency (WUE) has subsequently doubled from 3.20 for the control plants to 8.93 for 30‰ treatment. Under arid leaf conditions, the stomatal factor (SL) was more limiting to photosynthesis than its biochemical components (73.4 to 26.6%, respectively, at 30‰). It is concluded that salinity causes a drastic decline in photosynthetic gas exchange in H. tiliaceus leaves through its intrinsic and stomatal components, and that the apparent phenotypic plasticity represented by the leaf area modulation is unlikely to be the mechanism by which H. tiliaceus avoids salt stress.  相似文献   

13.
《Aquatic Botany》2008,88(4):292-298
The effect of salinity on leaf area and the relative accumulation of Na+ and K+ in leaves of the mangrove associate Hibiscus tiliaceus were investigated. Photosynthetic gas exchange characteristics were also examined under arid and non-arid leaf conditions at 0, 10, 20 and 30‰ substrate salinity. At salinities  40‰, plants showed complete defoliation followed by 100% mortality within 1 week. Salinities  30‰ were negatively correlated with the total leaf area per plant (r2 = 0.94). The reduction in the total plant leaf area is attributed to the reduction in the area of individual leaves (r2 = 0.94). Selective uptake of K+ over Na+ declined sharply with increasing salinity, where K+/Na+ ratio was reduced from 6.37 to 0.69 in plants treated with 0 and 30‰, respectively. Under non-arid leaf condition, increasing salinity from 0 to 30‰ has significantly reduced the values of the intrinsic components of photosynthesis Vc,max (from 50.4 to 18.4 μmol m−2 s-1), Jmax (from 118.0 to 33.8 μmol photons m−2 s−1), and VTPU (from 6.90 to 2.30 μmol m−2 s−1), while stomatal limitation to gas phase conductance (SL) increased from 14.6 to 38.4%. Water use efficiency (WUE) has subsequently doubled from 3.20 for the control plants to 8.93 for 30‰ treatment. Under arid leaf conditions, the stomatal factor (SL) was more limiting to photosynthesis than its biochemical components (73.4 to 26.6%, respectively, at 30‰). It is concluded that salinity causes a drastic decline in photosynthetic gas exchange in H. tiliaceus leaves through its intrinsic and stomatal components, and that the apparent phenotypic plasticity represented by the leaf area modulation is unlikely to be the mechanism by which H. tiliaceus avoids salt stress.  相似文献   

14.
Minor and trace elements in foraminiferal carbonates are potential paleo-proxies of climate, nutrient and seawater composition. There are very few reports of trace element composition of symbiont-bearing, larger foraminifera that are known to be important constituents of shallow-marine, modern and ancient carbonates. In this paper we examine the range of variation in Mg and Sr content of Recent species of these foraminifera from a lagoon of Lakshadweep Atoll (Indian Ocean) and Akajima Islands, Japan. Two hyaline species, Amphistegina lessonii and Neorotalia calcar,and two porcellaneous species, Amphisorus hemprichii and Marginopora vertebralis were collected live from Lakshadweep islands. Mg / Ca in these foraminifera is of an order of magnitude higher than the values reported for planktonic and symbiont-free benthic foraminifera. The Sr / Ca values are, however, comparable with the reported values in other foraminiferal taxa and they are found to vary within a narrow range. Electron-probe micro-analysis of three symbiont-bearing benthic species indicates spatial heterogeneity of high orders in Mg / Ca composition in all the species. The annual variation in temperature and pH of the lagoon water cannot explain the observed amplitude of the compositional variation. The photosynthesis and respiration of the symbionts and host foraminifera are possibly the major cause of compositional heterogeneity in individual tests, as has also been recently postulated for symbiont-bearing planktonic foraminiferal species. It highlights the need to isolate biological factors and necessitates species-specific paleotemperature scale in paleoclimatic analysis. We also analyzed δ18O, δ13C, Ca, Mg and Sr in carefully dissected chambers of a reef-dwelling, porcellaneous benthic foraminifer, Marginopora kudakajimaensis, collected live in four seasons. A moderate positive correlation is observed between Mg / Ca and temperature. However, large inter- and intra-test variation in Mg limits the precision of Mg / Ca as palaeotemperature proxy. The Sr / Ca of the test calcite is unrelated to temperature of the sea water. The δ13C of M. kudakajimaensis does not correlate with δ18O, Mg / Ca or Sr / Ca.  相似文献   

15.
《Aquatic Botany》2004,78(4):349-360
The effects of salinity on water relations and ion concentrations were investigated in seedlings of the mangroves Avicennia alba, Bruguiera gymnorrhiza, Heritiera littoralis and Xylocarpus granatum grown at salinities of 0, 10, 20, 30, 40 and 60‰. All four species survived and grew at salinities ranging from 0 to 40‰, but none survived at a salinity of 60‰. The concentration of sodium and chloride in the xylem sap increased with increasing salinity in both A. alba and B. gymnorrhiza. Sodium and chloride concentrations in the xylem sap of A. alba grown at 40‰ salinity both reached 114 mol m−3, about 15% of the external concentration around the roots. The xylem sap of B. gymnorrhiza grown at 40‰ salinity, by contrast, contained only 7.0 mol m−3 sodium and 4.1 mol m−3 chloride, about 1% of their concentrations in the external solution around the roots. The results indicated that B. gymnorrhiza, which does not have salt-secreting glands, was more effective at excluding salt than A. alba, which has salt-secreting glands.Analysis of pressure–volume curves showed that the bulk modulus of elasticity increased with increasing salinity. This was accompanied by a decrease in shoot water potential, mainly associated with a reduction in shoot osmotic potentials with increasing salinity. The decrease in osmotic potential was attributed to increasing solute concentrations, particularly sodium and chloride, in the leaves of all species except H. littoralis, which had little sodium and chloride in the leaves.  相似文献   

16.
We investigated the ability of the ichthyotoxic haptophyte Prymnesium parvum to use sewage-originated nutrients applying stable carbon (C) and nitrogen (N) isotope techniques. P. parvum was cultured under N and phosphorus (P) sufficient and deficient conditions in either sewage effluent-based medium or in a nitrate- and phosphate-based control. Cell densities and toxicities were monitored and stable carbon N isotopes signatures (δ13C and δ15N) of P. parvum and the sewage effluent analysed. Nitrogen and P sufficient cultures achieved the highest biomass followed by P and N deficient cultures, regardless of sewage effluent additions. The P deficient cultures with sewage effluent had higher toxicity, estimated as haemolytic activity (9.4 ± 0 × 10?5 mg Saponin equiv. cell?1) compared to the P deficient control and to all N deficient and NP sufficient cultures. Nutrient deficient conditions had no effect on the cell δ15N, but a decreasing effect on δ13C in the inorganic N deficient treatment. Growth in sewage-based media was followed by a substantial increase in the cell δ15N (10.4–16.1‰) compared to the control treatments (2.4–4.9‰), showing that P. parvum is capable of direct use of sewage-originated N, inorganic as well as organic. Uptake of terrestrial derived C in the sewage treatments was confirmed by a decrease in cell δ13C, implying that P. parvum is able to utilize organic nutrients in sewage effluent.  相似文献   

17.
We combine cyclo- and sequence stratigraphy along with whole rock δ13C and conodont apatite δ18O analysis to document high-frequency (104–105 yr) and My-scale sea-level changes for the Middle Pennsylvanian (Desmoinesian or Moscovian) Gray Mesa Formation of central New Mexico. Approximately 75 subtidal cycles (1–8 m) are grouped into 4 1/2 My-scale depositional sequences (40–80 m). About 50% of the cycles show evidence of prolonged subaerial exposure at cycle tops with the development of calcretes, diagenetic mottling, and regolith intraclasts. High-resolution δ13C analysis of whole rock limestones across nine of the cycles indicates that the cycle tops were diagenetically altered by isotopically light, meteoric fluids during sea-level fall and lowstand. These δ13C trends support the interpretation that high-frequency sea-level changes were responsible for cycle development.Conodont apatite δ18O values from sampled cycles indicate that the high-frequency sea-level changes were driven by glacio-eustasy combined with changes in surface seawater temperature (SST). δ18O values from conodont apatite, spanning parts of three depositional sequences indicate that My-scale glacio-eustasy and/or SST changes controlled sequence development. δ18O shifts indicate that the magnitudes of 104–105 yr glacio-eustasy were between ~ 55 and 170+ m combined with tropical SST changes of ~ 1.5°–6 °C. Calculated My-scale glacio-eustatic oscillations were between ~ 60 and 140 m with SST changes of < 3.5 °C. The most plausible driver for the My-scale paleoclimate changes is long-period obliquity (~ 1.2 My) variations. These calculated high-frequency, glacio-eustatic values are similar or greater than Pleistocene values, and lie within the range estimated for other Middle Pennsylvanian successions using a variety of independent eustatic proxies. The similarity in range of magnitudes between high-frequency and My-scale sea-level changes combined with the large differences in magnitudes between individual high-frequency sea-level oscillations helps explain the lack of systematic cycle-stacking patterns within these Pennsylvanian icehouse sequences.  相似文献   

18.
The impact of chronic air pollution such as increased CO2 and NOx emissions on forest ecosystems in the Athabasca oil sands region in Alberta, Canada, was investigated in Pinus banksiana (jack pine) and Populus tremuloides (trembling aspen, aspen) stands in two watersheds (NE7 and SM8) located at different distances from the main emission sources of oil sands mining and upgrading facilities, using δ13C, δ15N, and Ca/Al of soil and tree ring samples as indicators. Watershed NE7 was exposed to greater amounts of acid deposition due to its closeness to the mining and upgrading area. The δ15N in the forest floor was lower (p < 0.05) in NE7 (ranged from −1.42 to −0.87‰) than in SM8 (−0.54 to 1.43‰), implying a greater amount of recent deposition of 15N-depleted N in NE7. Tree ring δ13C gradually decreased over time for both tree species/watersheds, indicating the influence of 13C-depleted CO2 emitted from industrial sources. Tree ring N concentration and δ15N were not different between watersheds and did not significantly change with time. Interestingly, however, the difference between watersheds (NE7–SM8) that is expressed as Diff_N (for N) increased with concomitant decreases in Diff_δ15N over time, implying greater increases in 15N-depleted N input in NE7 than in SM8. Such trends were stronger in aspen stands (R2 = 0.64 and p < 0.001 for Diff_N and R2 = 0.44 and p < 0.01 for Diff_δ15N between 1964 and 2009) than in jack pine stands. We conclude that δ15N in the forest floor and differences in N and δ15N of tree rings between watersheds are useful indicators reflecting the impact of spatial variations of air pollution on forest stands in the Athabasca oil sands region in western Canada.  相似文献   

19.
The diversity and metal tolerance of endophytic fungi from six dominant plant species in a Pb–Zn mine wasteland in Yunnan, China were investigated. Four hundred and ninety-five endophytic fungi were isolated from 690 tissue segments. The endophytic fungal colonization extent and isolation extent ranged from 59 % to 75 %, and 0.42–0.93, respectively, and a positive correlation was detected between them. Stems harboured more endophytic fungi than leaves in each plant species, and the average colonization extent of stems was 82 %, being significantly higher than that of leaves (47 %) (P  0.001, chi-square test). The fungi were identified to 20 taxa in which Phoma, Alternaria and Peyronellaea were the dominant genera and the relative frequencies of them were 39.6 %, 19.0 % and 20.4 %, respectively. Metal tolerance test showed that 3.6 mM Pb2+ or 11.5 mM Zn2+ exhibited the greatest toxicity to some isolates and they did not grow on the metal-amended media. In contrast, some isolates were growth stimulated in the presence of tested metals. The isolates of Phoma were more sensitive to Zn2+ than the isolates of Alternaria and Peyronellaea. However, the sensitivity of isolates to Pb2+ was not significantly different among Phoma, Alternaria, Peyronellaea and other taxa (P > 0.05, chi-square test). Our results suggested that fungal endophyte colonization in Pb–Zn polluted plants is moderately abundant and some isolates have a marked adaptation to Pb2+ and Zn2+ metals, which has a potential application in phytoremediation in this area.  相似文献   

20.
The intensification of agricultural land use and urbanisation has increased nutrient loads in aquatic ecosystems. Nitrogen loads can alter ecosystem structure and functioning, resulting in increased algal productivity, algal blooms and eutrophication. The principal aim of the present paper is to extend the use of epilithic δ15N signatures to a lake ecosystem in order to evaluate the potential impact of anthropogenic nitrogen discharges (organic and inorganic) that can also reach coastal waters.Epilithic associations were collected from volcanic rocks in different seasons in shallow water along the entire perimeter of Lake Bracciano and analysed for their nitrogen stable isotope signatures. Furthermore, some stones were moved from an unpolluted site to a polluted one in order to verify the effect on the nitrogen signature of the epilithic association. The epilithon’s δ15N signatures provided strong evidence of the space-time variability of N inputs. The differing quality of nitrogen loads was reflected in high isotopic variation within the lake, especially at the beginning of summer (1.7‰  δ15N  13.3‰), while in winter, when anthropogenic pressure was lowest, the δ15N signature variation was less accentuated (3.1‰  δ15N  7.6‰). At all sampling times, spatial variability was found to be related to the various human activities along the lake shore (especially tourism and agriculture), while seasonal variation at all sampling sites was related to the intensity of anthropogenic pressures (higher in summer and lower in winter).Our results showed that epilithic algal associations and the physicochemical properties of the water did not influence the δ15N signature, which in contrast was strongly related to the site-specific effect of human activities around the lake. Thus, the distribution of δ15N across space and time can be used to direct nutrient reduction strategies in the region and can assist in monitoring the effectiveness of environmental protection measures.  相似文献   

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