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1.
The global budget of N(2)O shows a significant imbalance between the known rate of destruction in the stratosphere and the estimated rates of natural and anthropogenic production in soils and the ocean. Measurements of the (15)N/(14)N and (18)O/(16)O ratios in two major tropospheric sources of N(2)O, tropical rain forest soils and fertilized soils, show that soil N(2)O from a tropical rain forest in Costa Rica and from sugar-cane fields in Maui is strongly depleted in both (15)N and (18)O relative to mean tropospheric N(2)O. A major source of heavy N(2)O, enriched in both (15)N and (18)O, must therefore be present to balance the light N(2)O from soils. One such source is the back-mixing flux of N(2)O from the stratosphere, which is enriched in (15)N and (18)O by photolysis and chemistry. However these return fluxes of (15)N and (18)O are so great that a large oceanic flux of N(2)O is required to balance the heavy isotope-enriched stratospheric flux. All these effects will be reflected in climatically related isotopic variations in trapped N(2)O in polar ice cores. 相似文献
2.
Carbon and oxygen isotope analysis through a 30-year (1944 to 1974) growth of Montastrea annularis from Hen and Chickens Reef (Florida Keys) shows a strong yearly variation in the abundances of both carbon-13 and oxygen-18 and a broad inverse relationship between the two isotopes. Normal annual dense bands are formed during the summer and are characterized by heavy carbon and light oxygen. "Stress bands" are formed during particularly severe winters and are characterized by heavy carbon and heavy oxygen. The isotopic effect of Zooxanthellae metabolism dominates the temperature effect on the oxygen-18/oxygen-16 ratio. The isotopic results on the deep-sea solitary coral Bathypsammia tintinnabulum, where Zooxanthellae are nonexistent, indicates that the abundance of the heavy isotopes carbon-13 and oxygen-18 is inversely related to the growth rate, with both carbon and oxygen approaching equilibrium values with increasing skeletal age. 相似文献
3.
Oxygen isotope composition of subglacially precipitated calcite: possible paleoclimatic implications
Isotopic analyses of subglacially precipitated calcite from near a modern temperate glacier show that the delta(18)O (= (18)O/(16)O relative to standard mean ocean water) of the calcite records the delta(18)O of the ice from that glacier. It may therefore be possible to determine the delta(18)O of Pleistocene ice sheets on the basis of isotopic analyses of calcite formed under that ancient ice. This, in turn, would allow estimation of the delta(18)O of Pleistocene oceans and correction of the paleotemperature scale based on foraminiferal oxygen isotopic analyses. 相似文献
4.
The ratios of oxygen-18 to oxygen-16 ( (18)O/(16)O) of cellulose purified from two sets of wheat plants grown under conditions similar in all respects except for a large difference in the (18)O/(16)O ratios of the carbon dioxide supplied to them differ by only a small amount. The difference in the (18)O/(16)O ratios of the cellulose is similar to that observed for the (18)O/(16)O ratios of the water present in the plants. These results indicate that the oxygen derived from carbon dioxide undergoes complete exchange with the oxygen of the water in the plant during the synthesis of cellulose and that the (18)O/(16)O ratio of the water inside the plant is the primary influence on the (18)O/(16)O ratio of cellulose in terrestrial plants. 相似文献
5.
The mean oxygen-18 content of continental ice sheets during the last glacial maximum is estimated to deltaO(18)=-30 per mille or less, and the consequent change in the isotopic composition of the oceans at that time to 1.2 per mille or more. This means that at least 70 percent of the oxygen-18 variations found in shells of planktonic foraminifera from deep-sea cores between times of glacial maximums and minimums are due to isotopic changes in ocean water, and at most 30 percent to changes in ocean surface temperature. Hence, Emiliani's "paleotemperature" curve rather depicts the amount of ice on the continents in excess of that present today. In this sense it may be renamed a "paleoglaciation" curve. 相似文献
6.
Helsen MM van den Broeke MR van de Wal RS van de Berg WJ van Meijgaard E Davis CH Li Y Goodwin I 《Science (New York, N.Y.)》2008,320(5883):1626-1629
Antarctic Ice Sheet elevation changes, which are used to estimate changes in the mass of the interior regions, are caused by variations in the depth of the firn layer. We quantified the effects of temperature and accumulation variability on firn layer thickness by simulating the 1980-2004 Antarctic firn depth variability. For most of Antarctica, the magnitudes of firn depth changes were comparable to those of observed ice sheet elevation changes. The current satellite observational period ( approximately 15 years) is too short to neglect these fluctuations in firn depth when computing recent ice sheet mass changes. The amount of surface lowering in the Amundsen Sea Embayment revealed by satellite radar altimetry (1995-2003) was increased by including firn depth fluctuations, while a large area of the East Antarctic Ice Sheet slowly grew as a result of increased accumulation. 相似文献
7.
Stable isotope enrichment in paleowaters of the southeast atlantic coastal plain, United States 总被引：1，自引：0，他引：1
Plummer LN 《Science (New York, N.Y.)》1993,262(5142):2016-2020
Paleowaters from the Floridan aquifer system in the southeastern Atlantic coastal plain have higher D/H and (18)O/(16)O ratios than local Holocene ground water. Maximum delta(18)O enrichments in ground water having adjusted radiocarbon ages of 20,000 to 26,000 years are 0.7 to 2.3 per mil. The trend in isotopic enrichment in paleowaters is the reverse of that normally observed in continental glacial age ground water. Dissolved nitrogen and argon concentrations indicate, however, that the average recharge temperature was 5.3 degrees C cooler than that today. The data indicate cool conditions in the southeast Atlantic coastal plain during the last glacial maximum, with recharge limited primarily to late summer tropical cyclones and hurricanes. 相似文献
8.
Shackleton NJ 《Science (New York, N.Y.)》2000,289(5486):1897-1902
The deep-sea sediment oxygen isotopic composition (delta(18)O) record is dominated by a 100,000-year cyclicity that is universally interpreted as the main ice-age rhythm. Here, the ice volume component of this delta(18)O signal was extracted by using the record of delta(18)O in atmospheric oxygen trapped in Antarctic ice at Vostok, precisely orbitally tuned. The benthic marine delta(18)O record is heavily contaminated by the effect of deep-water temperature variability, but by using the Vostok record, the delta(18)O signals of ice volume, deep-water temperature, and additional processes affecting air delta(18)O (that is, a varying Dole effect) were separated. At the 100,000-year period, atmospheric carbon dioxide, Vostok air temperature, and deep-water temperature are in phase with orbital eccentricity, whereas ice volume lags these three variables. Hence, the 100,000-year cycle does not arise from ice sheet dynamics; instead, it is probably the response of the global carbon cycle that generates the eccentricity signal by causing changes in atmospheric carbon dioxide concentration. 相似文献
9.
The oxygen-18/oxygen-16 ratio of molecular oxygen trapped in ice cores provides a time-stratigraphic marker for transferring the absolute chronology for the Greenland Ice Sheet Project (GISP) II ice core to the Vostok and Byrd ice cores in Antarctica. Comparison of the climate records from these cores suggests that, near the beginning of the last deglaciation, warming in Antarctica began approximately 3000 years before the onset of the warm B?lling period in Greenland. Atmospheric carbon dioxide and methane concentrations began to rise 2000 to 3000 years before the warming began in Greenland and must have contributed to deglaciation and warming of temperate and boreal regions in the Northern Hemisphere. 相似文献
10.
A study has been made of carbon-13 and oxygen-18 variations in Greek marbles from the ancient quarry localities of Naxos, Paros, Mount Hymettus, and Mount Pentelikon. Parian, Hymettian, and Pentelic marbles can be clearly distinguished by the isotopic relationships; Naxian marbles fall into two groups characterized by different oxygen-18/oxygen-16 ratios. Ten archeological samples were also analyzed; the isotopic data indicate that the "Theseion" is made of Pentelic marble and a block in the Treasury of Siphnos at Delphi is probably Parian marble. 相似文献
11.
Fischer TP Hilton DR Zimmer MM Shaw AM Sharp ZD Walker JA 《Science (New York, N.Y.)》2002,297(5584):1154-1157
We report N and He isotopic and relative abundance characteristics of volatiles emitted from two segments of the Central American volcanic arc. In Guatemala, delta15N values are positive (i.e., greater than air) and N2/He ratios are high (up to 25,000). In contrast, Costa Rican N2/He ratios are low (maximum 1483) and delta15N values are negative (minimum -3.0 per mil). The results identify shallow hemipelagic sediments, subducted into the Guatemalan mantle, as the transport medium for the heavy N. Mass balance arguments indicate that the subducted N is efficiently cycled to the atmosphere by arc volcanism. Therefore, the subduction zone acts as a "barrier" to input of sedimentary N to the deeper mantle. 相似文献
12.
Loye HC Leary KJ Keller SW Ham WK Faltens TA Michaels JN Stacy AM 《Science (New York, N.Y.)》1987,238(4833):1558-1560
The effect of oxygen isotope substitution on the superconducting transition temperature, T(c), has been measured for BaBi(0.25)Pb(0.75)O(3) (T(c), approximately 11 K) and Lal(1.85) Ca(0.15)CuO(4) (T(c) approximately 20 K), and is compared to the shifts observed for La(1.85)Sr(0.15)CuO(4) (T(c) approximately 37 K) and YBa(2)Cu(3)O(7) (T(c) approximately 92 K). For all four materials, the transition temperature is shifted to lower temperature upon substitution of oxygen-18 for oxygen-16. The observed shifts demonstrate that phonons are involved in the electron-pairing mechanism in these oxide superconductors. 相似文献
13.
The oxygen isotope compositions (delta(18)O) of eclogitic xenoliths from the Roberts Victor kimberlite range from 2 to 8 per mil relative to SMOW (standard mean ocean water). This surprising variation appears to be due to fractional crystallization: the eclogites rich in oxygen-18 represent early crystal accumulates; the eclogites poor in oxygen-18 represent residual liquids. Crystal-melt partitioning probably exceeded 3 per mil and is interpreted to be pressure-dependent. Anomalous enrichment of oxygen-18 in cumulate eclogites relative to ultramafic xenoliths suggests that crystal-melt partitioning increased after melt-formation but prior to crystallization. 相似文献
14.
We propose an isotopic fractionation mechanism, based on photolytic destruction, to explain the 15N/14N and 18O/16O fractionation of stratospheric nitrous oxide (N2O) and reconcile laboratory experiments with atmospheric observations. The theory predicts that (i) the isotopomers 15N14N16O and 14N15N16O have very different isotopic fractionations in the stratosphere, and (ii) laboratory photolysis experiments conducted at 205 nanometers should better simulate the observed isotopic fractionation of stratospheric N2O. Modeling results indicate that there is no compelling reason to invoke a significant chemical source of N2O in the middle atmosphere and that individual N2O isotopomers might be useful tracers of stratospheric air parcel motion. 相似文献
15.
Cellulose from plants having crassulacean acid metabolism was enriched in deuterium but not in oxygen-18 in relation to cellulose from C(3) and C(4) plants growing in the same area, indicating that the deuterium enrichment is due to isotopic fractionation during biochemical reactions rather than during evapotranspiration. Hydrogen and oxygen stable isotope ratios of cellulose from the plants in this restricted area showed more variability than that observed in samples collected across an entire continent. Biological factors appear to be as important as environmental factors in determining the isotope ratios of plant cellulose. 相似文献
16.
氧化亚氮(N2O)是主要的温室气体之一,并且对平流层臭氧层分解起到重要作用。土壤中N2O的产生和排放过程复杂多样,对其进行精准溯源与过程区分有助于制定减排策略。稳定同位素自然丰度技术利用N2O的同位素值δ15Nbulk(N2O中15N在整体水平上的同位素特征值)、δ18O(N2O中18O在整体水平上的同位素特征值)以及δ15Nsp(N2O分子内15N的位点特异性同位素值),可以示踪N2O来源、指示N2O产生的微生物作用途径,在N2O转化过程溯源中已取得重要进展。而同位素分馏效应是稳定同位素自然丰度技术应用的理论基础,其中微生物过程及其导致的同位素分馏是需要重点关注的问题。本研究概述了同位素分馏效应在N2O的产生、排放过程中的研究进展及其主要影响因素,梳理了同位素特征值δ15Nbulk、δ18O和δ15Nsp在分析N2O来源的研究进展,并且提出了影响准确区分过程的因素。因素包括单一产生路径的同位素特征值范围广、不同产生路径的同位素特征值范围的重叠、反应底物同位素组成的变化以及与N2O还原相关的分馏因子的可变性等问题。明确了今后需加强δ15Nsp等N2O同位素特征值分馏效应的测定,利用组合同位素特征值及先进手段进行全面的N2O溯源研究。图2参80 相似文献
17.
The oxygen-18 (18O) content of atmospheric carbon dioxide (CO2) is an important indicator of CO2 uptake on land. It has generally been assumed that during photosynthesis, oxygen in CO2 reaches isotopic equilibrium with oxygen in 18O-enriched water in leaves. We show, however, large differences in the activity of carbonic anhydrase (which catalyzes CO2 hydration and 18O exchange in leaves) among major plant groups that cause variations in the extent of 18O equilibrium (theta(eq)). A clear distinction in theta(eq) between C3 trees and shrubs, and C4 grasses makes atmospheric C18OO a potentially sensitive indicator to changes in C3 and C4 productivity. We estimate a global mean theta(eq) value of approximately 0.8, which reasonably reconciles inconsistencies between 18O budgets of atmospheric O2 (Dole effect) and CO2. 相似文献
18.
Gases trapped in Miocene to Upper Cretaceous amber were released by gently crushing the amber under vacuum and were analyzed by quadrupole mass spectrometry. After discounting the possibility that the major gases N(2), O(2), and CO(2) underwent appreciable diffusion and diagenetic exchange with their surroundings or reaction with the amber, it has been concluded that in primary bubbles (gas released during initial breakage) these gases represent mainly original ancient air modified by the aerobic respiration of microorganisms. Values of N(2)/(CO(2) + O(2)) for each time period give consistent results despite varying O(2)/CO(2) ratios that presumably were due to varying degrees of respiration. This allows calculation of original oxygen concentrations, which, on the basis of these preliminary results, appear to have changed from greater than 30 percent O(2) during one part of the Late Cretaceous (between 75 and 95 million years ago) to 21 percent during the Eocene-Oligocene and for present-day samples, with possibly lower values during the Oligocene-Early Miocene. Variable O(2) levels over time in general confirm theoretical isotope-mass balance calculations and suggest that the atmosphere has evolved over Phanerozoic time. 相似文献
19.
The relative amounts of primary and secondary sulfates in atmospheric aerosols and precipitation can be estimated from measurements of the stable oxygen isotope ratios. The oxygen-18 content of sulfates formed in power plant stack gases before emission into the atmosphere is significantly higher than that of sulfates formed from sulfur dioxide after emission. Results show that 20 to 30 percent of the sulfates in rain and snow at Argonne, Illinois, are of primary origin. 相似文献
20.
The ocean is an important global source of nitrous oxide (N(2)O), a greenhouse gas that contributes to stratospheric ozone destruction. Bacterial nitrification and denitrification are thought to be the primary sources of marine N(2)O, but the isotopic signatures of N(2)O produced by these processes are not consistent with the marine contribution to the global N(2)O budget. Based on enrichment cultures, we report that archaeal ammonia oxidation also produces N(2)O. Natural-abundance stable isotope measurements indicate that the produced N(2)O had bulk δ(15)N and δ(18)O values higher than observed for ammonia-oxidizing bacteria but similar to the δ(15)N and δ(18)O values attributed to the oceanic N(2)O source to the atmosphere. Our results suggest that ammonia-oxidizing archaea may be largely responsible for the oceanic N(2)O source. 相似文献