Sulfur Isotopic Composition of Cenozoic Seawater Sulfate Paytan, Adina; Kastner, Miriam; Campbell, Douglas ...
Science (American Association for the Advancement of Science),
11/1998, Letnik:
282, Številka:
5393
Journal Article
Recenzirano
A continuous seawater sulfate sulfur isotope curve for the Cenozoic with a resolution of ∼1 million years was generated using marine barite. The sulfur isotopic composition decreased from 19 to 17 ...per mil between 65 and 55 million years ago, increased abruptly from 17 to 22 per mil between 55 and 45 million years ago, remained nearly constant from 35 to ∼2 million years ago, and has decreased by 0.8 per mil during the past 2 million years. A comparison between seawater sulfate and marine carbonate carbon isotope records reveals no clear systematic coupling between the sulfur and carbon cycles over one to several millions of years, indicating that changes in the burial rate of pyrite sulfur and organic carbon did not singularly control the atmospheric oxygen content over short time intervals in the Cenozoic. This finding has implications for the modeling of controls on atmospheric oxygen concentration.
Sulphur is abundant at the martian surface, yet its origin and evolution
over time remain poorly constrained. This sulphur is likely
to have originated in atmospheric chemical reactions, and so ...should provide
records of the evolution of the martian atmosphere, the cycling of sulphur
between the atmosphere and crust, and the mobility of sulphur in the martian
regolith. Moreover, the atmospheric deposition of
oxidized sulphur species could establish chemical potential gradients in the
martian near-surface environment, and so provide a potential energy source
for chemolithoautotrophic organisms. Here we present measurements
of sulphur isotopes in oxidized and reduced phases from the SNC meteorites-the
group of related achondrite meteorites believed to have originated on Mars-together
with the results of laboratory photolysis studies of two important martian
atmospheric sulphur species (SO2 and H2S). The photolysis
experiments can account for the observed sulphur-isotope compositions in the
SNC meteorites, and so identify a mechanism for producing large abiogenic
34S fractionations in the surface sulphur reservoirs. We conclude
that the sulphur data from the SNC meteorites reflects deposition of oxidized
sulphur species produced by atmospheric chemical reactions, followed by incorporation,
reaction and mobilization of the sulphur within the regolith.
The triple isotopic composition of oxygen in sulfate and nitrate, and the sulfur isotopic composition of the sulfate fine fraction, have been measured on size‐segregated aerosol samples collected at ...Trinidad Head, coastal California, alongside the ITCT‐2k2 campaign in April–May 2002. The isotopic anomaly Δ17O = δ17O − 0.52 × δ18O has been determined in both sulfate and nitrate and was used as a specific tracer of the formation pathways of these species. Coarse mode sulfate in all samples exhibited a small but significant Δ17O anomaly indicating either uptake or in situ formation of secondary sulfate on sea spray. Non‐sea‐salt sulfate Δ17O in the coarse fraction is consistent with (1) either primarily coagulation of finer sulfate particles, when Δ17O is low in all size fractions, or (2) ozone‐driven oxidation of SO2 within the sea spray, as observed in the relatively higher Δ17O in coarse particles compared to fine. It is proposed that triple‐isotope measurements of sulfate oxygen can be used to quantify the budget of in situ sea spray nss‐SO4 formation. The Δ17O measured in size‐resolved nitrate revealed, for the first time, differences in the nitrate formation budget as a function of particle size in a given air mass. The coarse particle nitrate possessed a higher Δ17O, suggesting a relatively larger N2O5 hydrolysis contribution to the nitrate formation budget compared to fine particles where homogeneous formation is more important. We conclude that the complete isotope ratio analysis may provide a basis for future modeling of the formation and transformation processes of the soluble aerosol, based on direct observation of the mechanisms.
Oxygen has three naturally occurring isotopes, of mass numbers 16, 17 and 18. Their ratio in atmospheric O2 depends primarily on the isotopic composition of photosynthetically produced O2 from ...terrestrial and aquatic plants, and on isotopic fractionation due to respiration. These processes fractionate isotopes in a mass-dependent way, such that 17O enrichment would be approximately half of the 18O enrichment relative to 16O. But some photochemical reactions in the stratosphere give rise to a mass-independent isotope fractionation, producing approximately equal 17O and 18O enrichments in stratospheric ozone and carbon dioxide,, and consequently driving an atmospheric O2 isotope anomaly. Here we present an experimentally based estimate of the size of the 17O/16O anomaly in tropospheric O2, and argue that it largely reflects the influences of biospheric cycling and stratospheric photochemical processes. We propose that because the biosphere removes the isotopically anomalous stratosphere-derived O2 by respiration, and replaces it with isotopically 'normal' oxygen by photosynthesis, the magnitude of the tropospheric 17O anomaly can be used as a tracer of global biosphere production. We use measurements of the triple-isotope composition of O2 trapped in bubbles in polar ice to estimate global biosphere productivity at various times over the past 82,000 years. In a second application, we use the isotopic signature of oxygen dissolved in aquatic systems to estimate gross primary production on broad time and space scales.
Mass‐independent isotopic signatures for δ33S, δ34S, and δ36S produced in the photolysis of sulfur dioxide exhibit a strong wavelength dependence. Photolysis experiments with three light sources (ArF ...excimer laser (193 nm), mercury resonance lamp (184.9 and 253.7 nm), and KrF excimer laser (248 nm)) are presented. Products of sulfur dioxide photolysis undertaken with 193‐nm radiation exhibit characteristics that are similar to sulfur multiple‐isotope data for terrestrial sedimentary rock samples older than 2450 Ma (reported by Farquhar et al. 2000a), while photolysis experiments undertaken with radiation at other wavelengths (longer than 220 nm and at 184.9 nm) exhibit different characteristics. The spectral window between 190 and 220 nm falls between the Schumann‐Runge bands of oxygen and the Hartley bands of ozone, and its absorption is therefore more sensitive to changes in altitude and atmospheric oxygen content than neighboring wavelengths. These two observations are used to suggest a link between sulfur dioxide photolysis at 193 nm and sulfur isotope anomalies in Archean rocks. This hypothesis includes the suggestion that UV wavelengths shorter than 200 nm penetrated deep in the Earth's atmosphere during the Archean. Potential implications of this hypothesis for the chemistry, composition, and UV absorption of the atmosphere are explored. We also explore the implications of these observations for documentation of bacterial sulfur metabolisms early in Earth's history.
High-precision measurements of the oxygen isotopic compositions of carbonates (calcite and dolomite) from five CM2 chondrites are presented and put into context of the previously determined ...mineralogic alteration index (MAI), which places these meteorites into an alteration sequence. The carbonate oxygen isotopic compositions range from +20.0 to +35.7‰ for δ
18O, +8.0 to +17.7‰ for δ
17O, and −0.7 to −2.7‰ for Δ
17O. Carbonate Δ
17O values are inversely correlated with MAI and track the evolution of fluid composition from higher to lower Δ
17O values with increasing alteration on the CM parent body. Similar Δ
17O values for calcite and dolomite fractions from the same splits of the same meteorites indicate that calcite and dolomite in each split precipitated from a single fluid reservoir. However, reversed calcite dolomite fractionations (δ
18O
dol − δ
18O
cc) indicate that the fluid was subject to processes, such as freeze–thaw or evaporation, that fractionated isotopes in a mass-dependent way. Consideration of the carbonate isotopic data in the context of previously proposed models for aqueous alteration of carbonaceous chondrites has provided important insights into both the evolving alteration conditions and the utility of the models themselves. The data as a whole indicate that the isotopic evolution of the fluid was similar to that predicted by the closed-system, two-reservoir models, but that a slightly larger matrix–water fractionation factor may apply. In the context of this model, more altered samples largely reflect greater reaction progress and thus probably indicate more extended times of fluid exposure. Petrographic observations of carbonates reveal a trend of variable carbonate morphology correlated with alteration that is also consistent with changes in the duration of fluid–rock interaction. The data can also be reconciled with fluid-flow models in a restricted region of the parent body, which is consistent with assertions that the different types of carbonaceous chondrites derive from different regions of their parent bodies. In this case, the model results for a 9-km-radius body, and our data place the location of the CM chondrite formation in a 100-m-thick zone 1 km from the surface. The size of this zone could be increased if the model parameters were adjusted.
Ice core measurements (H2O2 and CH4/HCHO) and modeling studies indicate a change in the oxidation capacity of the atmosphere since the onset of the Industrial Revolution due to increases in fossil ...fuel burning emissions e.g., Lelieveld et al., 2002; Hauglustaine and Brasseur, 2001; Wang and Jacob, 1998; Staffelbach et al., 1991. The mass‐independent fractionation (MIF) in the oxygen isotopes of sulfate and nitrate from a Greenland ice core reveal that biomass‐burning events in North America just prior to the Industrial Revolution significantly impacted the oxidation pathways of sulfur and nitrogen species deposited in Greenland ice. This finding highlights the importance of biomass‐burning emissions for atmospheric chemistry in preindustrial North America and warrants the inclusion of this impact in modeling studies estimating changes in atmospheric oxidant chemistry since the Industrial Revolution, particularly when using paleo‐oxidant data as a reference for model evaluation.
van der Waals heterostructures assembled from atomically thin crystalline layers of diverse two-dimensional solids are emerging as a new paradigm in the physics of materials. We used infrared ...nanoimaging to study the properties of surface phonon polaritons in a representative van der Waals crystal, hexagonal boron nitride. We launched, detected, and imaged the polaritonic waves in real space and altered their wavelength by varying the number of crystal layers in our specimens. The measured dispersion of polaritonic waves was shown to be governed by the crystal thickness according to a scaling law that persists down to a few atomic layers. Our results are likely to hold true in other polar van der Waals crystals and may lead to new functionalities.
Ground‐level ozone (O3) has been sampled from three environments: La Jolla and Pasadena, California, and White Sands Missile Range, New Mexico, using recently developed techniques for cryogenically ...collecting and isotopically analyzing samples of atmospheric O3. Significant isotopic variability is observed at each location, in addition to potentially important differences between the sampling locations. The isotopic composition of O3 is a sensitive indicator for the formation and decomposition processes which have influenced the O3 reservoir Thus the isotopic characterization of ground‐level O3 could provide a new source of information regarding atmospheric transformation mechanisms. To date, the measured isotopic variability in ground‐level O3 shows no correlation with O3 or NOx mixing ratios, meteorological parameters, or time of day. However, preliminary results show a correlation between the pattern of isotopic fractionation and degree of photochemical control over the local O3 budget at each sampling location. It should be noted that the conclusions presented are preliminary because of the relatively small data sets, particularly at the Pasadena and New Mexico locations. However, we believe that the results of this research indicate that the isotopic composition of tropospheric O3 is variable and contains information which could be useful in the effort to understand the tropospheric O3 budget.
PDF
