Populations of sulfide inclusions in diamonds from the Orapa kimberlite pipe in the Kaapvaal-Zimbabwe craton, Botswana, preserve mass-independent sulfur isotope fractionations. The data indicate that ...material was transferred from the atmosphere to the mantle in the Archean. The data also imply that sulfur is not well mixed in the diamond source regions, allowing for reconstruction of the Archean sulfur cycle and possibly offering insight into the nature of mantle convection through time.
A class of isotope effects that alters isotope ratios on a mass-independent basis provides a tool for studying a wide range of processes in atmospheres of Earth and other planets as well as early ...processes in the solar nebula. The mechanism for the effect remains uncertain. Mass-independent isotopic compositions have been observed in O$_3$, CO$_2$, N$_2$O, and CO in Earth's atmosphere and in carbonate from a martian meteorite, which suggests a role for mass-independent processes in the atmosphere of Mars. Observed mass-independent meteoritic oxygen and sulfur isotopic compositions may derive from chemical processes in the presolar nebula, and their distributions could provide insight into early solar system evolution.
Sulfuric acid aerosols produced in the stratosphere following massive volcanic eruptions possess a mass‐independent sulfur isotopic signature, acquired when volcanic SO2 experiences UV ...photooxidation. The volcanic data are consistent with laboratory SO2 photooxidation experiments using UV light at 248 nm (maximum absorption of ozone), whereas sulfur isotopic anomalies previously observed in Archean samples are consistent with photodissociation at 190–220 nm. A mechanism of SO2 photooxidation, occurring in the early stage of a stratospheric volcanic plume, in the range of 220–320 nm (weak band absorption of SO2), is also proposed. Since mass‐independent sulfur isotope anomalies in stratospheric volcanic sulfate appear to depend on the exposure of SO2 to UV radiation, their measurements might therefore offer the possibility to determine the degree of UV penetration in the ozone‐absorption window for the present and past atmospheres. They can also be used to determine the stratospheric or tropospheric nature of volcanic eruptions preserved in glaciological records, offering the possibility to reassess the climatic impact of past volcanic eruptions.
We use observations of the mass‐independent oxygen isotopic composition (Δ17O) of sulfate in the marine boundary layer (MBL) to quantify the sulfate source from aqueous SO2 (S(IV)) oxidation by O3 in ...alkaline sea‐salt aerosols. Oxidation by O3 imparts a large Δ17O signature to the resulting sulfate (8.8‰) relative to oxidation by H2O2 (0.9‰) or by OH or O2 (0‰). Ship data from two Indian Ocean Experiment (INDOEX) cruises in the Indian Ocean indicate Δ17O values usually <1‰ in the submicron sulfate aerosol but considerable variability in the supermicron sulfate with frequent occurrences above 1‰ and up to 6.7‰. The large Δ17O values are associated with high concentrations of sea‐salt aerosols, providing evidence for the S(IV) + O3 pathway. We use a global chemical transport model (GEOS‐CHEM) to interpret quantitatively the INDOEX observations and to assess the global importance of sulfate production in sea‐salt aerosols. The model accounts for titration of sea‐salt alkalinity in the MBL by uptake of acid gases (SO2, H2SO4, and HNO3), shutting down the S(IV) + O3 pathway. We find that this titration occurs rapidly over much of the oceans except at high latitudes (strong sea‐salt emission) and is due to both the S(IV) + O3 reaction and HNO3 (g) condensation; that is, sulfate formation in sea‐salt aerosols is limited by the alkalinity flux from the ocean and by competition for this alkalinity supply from HNO3 (g). The model is consistent with the Δ17O magnitudes and patterns in the INDOEX data. Titration of alkalinity is critical for the success of the model simulation. Regeneration of sea‐salt aerosol alkalinity by OH uptake is inconsistent with the Δ17O observations in INDOEX. Model results indicate that sulfate production in sea‐salt aerosols decreases MBL SO2 concentrations and gas phase H2SO4 production rates by typically 10–30% (up to >70%) and increases MBL sulfate concentrations by typically >10% (up to 30%). Globally, this mechanism contributes 9% of atmospheric sulfate production and 1% of the sulfate burden. The impact on H2SO4 (g) formation and implications for the potential formation of new particles in the MBL warrants inclusion in models examining the radiative effects of sulfate aerosols.
Mass-independent isotopic signatures for δ33S, δ34S, and δ36S from sulfide and sulfate in Precambrian rocks indicate that a change occurred in the sulfur cycle between 2090 and 2450 million years ago ...(Ma). Before 2450 Ma, the cycle was influenced by gas-phase atmospheric reactions. These atmospheric reactions also played a role in determining the oxidation state of sulfur, implying that atmospheric oxygen partial pressures were low and that the roles of oxidative weathering and of microbial oxidation and reduction of sulfur were minimal. Atmospheric fractionation processes should be considered in the use of sulfur isotopes to study the onset and consequences of microbial fractionation processes in Earth's early history.
Seawater Sulfur Isotope Fluctuations in the Cretaceous Paytan, Adina; Kastner, Miriam; Campbell, Douglas ...
Science (American Association for the Advancement of Science),
06/2004, Letnik:
304, Številka:
5677
Journal Article
Recenzirano
The exogenic sulfur cycle is tightly coupled with the carbon and oxygen cycles, and therefore a central component of Earth's biogeochemistry. Here we present a high-resolution record of the sulfur ...isotopic composition of seawater sulfate for the Cretaceous. The general enrichment of isotopically light sulfur that prevailed during the Cretaceous may have been due to increased volcanic and hydrothermal activity. Two excursions toward isotopically lighter sulfur represent periods of lower rates of pyrite burial, implying a shift in the location of organic carbon burial to terrestrial or open-ocean settings. The concurrent changes in seawater sulfur and inorganic carbon isotopic compositions imply short-term variability in atmospheric oxygen partial pressure.
The sulfur and oxygen isotopic composition of sulfate in polar ice cores provides information about atmospheric sulfate sources and formation pathways, which have been impacted regionally by human ...activity over the past several centuries. We present decadal scale mean ice core measurements of Δ17O, δ34S, Δ33S, and Δ36S of sulfate over the past 230 years from the West Antarctic Ice Sheet (WAIS) Divide deep ice core drill site (WDC05‐A). The low mean δ34S of non–sea‐salt sulfate at WAIS Divide (6.0 ± 0.2‰) relative to East Antarctic coastal and plateau sites may reflect a combination of stronger influence of volcanogenic and/or stratospheric sulfate with low δ34S and the influence of frost flowers on the sea‐salt sulfate‐to‐sodium ratio. Δ33S and Δ36S measurements are all within analytical uncertainty of zero but do not contradict a contribution of stratospheric sources to background sulfate deposition at WAIS Divide. Δ17O of non–sea‐salt sulfate shows a small but significant increase between the late 1700s (1.8‰ ± 0.2‰) and late 1800s (2.6‰ ± 0.2‰), but the influence of stratospheric scale volcanic events on Δ17O in the early 1800s remains uncertain. An isotope mass balance model shows that the lack of change in Δ17O of non–sea‐salt sulfate from the mid‐1800s to early 2000s (2.4‰–2.6‰ ± 0.2‰) is consistent with previous atmospheric chemistry model estimates indicating preindustrial to industrial increases in O3 as high as 50% and decreases in OH of 20% in the southern polar troposphere, as long as H2O2 concentrations also increase by over 50%.
Ship emissions contribute significantly to gaseous and particulate pollution worldwide. To better understand the impact of ship emissions on air quality, measurements of the size-resolved chemistry ...of individual particles in ship emissions were made at the Port of Los Angeles using real-time, single-particle mass spectrometry. Ship plumes were identified through a combination of ship position information and measurements of gases and aerosol particles at a site 500 m from the center of the main shipping channel at the Port of Los Angeles. Single particles containing mixtures of organic carbon, vanadium, and sulfate (OC-V-sulfate) resulted from residual fuel combustion (i.e., bunker fuel), whereas high quantities of fresh soot particles (when OC-V-sulfate particles were not present) represented distinct markers for plumes from distillate fuel combustion (i.e., diesel fuel) from ships as well as trucks in the port area. DC-V-sulfate particles from residual fuel combustion contained significantly higher levels of sulfate and sulfuric acid than plume particles containing no vanadium. These associations may be due to vanadium (or other metals such as iron) in the fuel catalyzing the oxidation of S0(2) to produce sulfate and sulfuric acid on these particles. Enhanced sulfate production on OC-V-sulfate ship emission particles would help explain some of the higher than expected sulfate levels measured in California compared to models based on emissions inventories and typical sulfate production pathways. Understanding the overall impact of ships emissions is critical for controlling regional air quality in the many populated coastal regions of the world.
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