Volcanic Sulfur Research Articles

Are Changes in Global Precipitation Constrained by the Tropospheric Energy Budget?

AbstractA tropospheric energy budget argument is used to analyze twentieth-century precipitation changes. It is found that global and ocean-mean general circulation model (GCM) precipitation changes can be understood as being due to the competing direct and surface-temperature-dependent effects of external climate forcings. In agreement with previous work, precipitation is found to respond more strongly to anthropogenic and volcanic sulfate aerosol and solar forcing than to greenhouse gas and black carbon aerosol forcing per unit temperature. This is due to the significant direct effects of greenhouse gas and black carbon forcing. Given that the relative importance of different forcings may change in the twenty-first century, the ratio of global precipitation change to global temperature change may be quite different. Differences in GCM twentieth- and twenty-first-century values are tractable via the energy budget framework in some, but not all, models. Changes in land-mean precipitation, on the other hand, cannot be understood at all with the method used here, even if land–ocean heat transfer is considered. In conclusion, the tropospheric energy budget is a useful concept for understanding the precipitation response to different forcings but it does not fully explain precipitation changes even in the global mean.

"Anything Can Be an Instrument": Misuse Value and Rugged Consumerism in Cormac McCarthy's No Country for Old Men

creative relationship between men and manmade objects that populate their worlds grounds aesthetic project of Cormac McCarthy's Western novels. Parham fashions from a paloverde tree and rope serves as material intermediary between Parham and she-wolf that he traps, enabling a communion of sorts between young boy and last vestiges of a disappearing wild. John Grady Cole, romantic hero of All Pretty Horses, recalls his grandfather's stories of Native Americans as he gazes upon telegraph poles early in novel. In their ongoing attempts to disrupt communication between white settlers, the Comanche would cut wires and splice them back with horse-hair (11), a symbolic triumph of improvisational over technological that colors Cole's subsequent journey through surveyed and fenced enclosures of Western desert. Along similar lines, in Blood Meridian, Judge Holden establishes his status as suzerain of nature (198) through his interactions with objects - chief example being his creation of gunpowder from urine and volcanic sulfur. Within McCarthy's nostalgic novels, these instances of material manipulation and creation resonate with older, mythic notions of American identity. Despite their clear differences, Parham, John Grady Cole, and Judge are all self-made and selfsustaining men who would feel quite at home in nineteenthcentury literary worlds of Natty Bumppo, Huck Finn, or Henry David Thoreau. Each character resists modern world of economic

Volcanic forcing of climate over the past 1500 years: An improved ice core‐based index for climate models

Understanding natural causes of climate change is vital to evaluate the relative impacts of human pollution and land surface modification on climate. We have investigated one of the most important natural causes of climate change, volcanic eruptions, by using 54 ice core records from both the Arctic and Antarctica. Our recently collected suite of ice core data, more than double the number of cores ever used before, reduces errors inherent in reconstructions based on a single or small number of cores, which enables us to obtain much higher accuracy in both detection of events and quantification of the radiative effects. We extracted volcanic deposition signals from each ice core record by applying a high‐pass loess filter to the time series and examining peaks that exceed twice the 31‐year running median absolute deviation. We then studied the spatial pattern of volcanic sulfate deposition on Greenland and Antarctica and combined this knowledge with a new understanding of stratospheric transport of volcanic aerosols to produce a forcing data set as a function of month, latitude, and altitude for the past 1500 years. We estimated the uncertainties associated with the choice of volcanic signal extraction criteria, ice core sulfate deposition to stratospheric loading calibration factor, and the season for the eruptions without a recorded month. We forced an energy balance climate model with this new volcanic forcing data set, together with solar and anthropogenic forcing, to simulate the large‐scale temperature response. The results agree well with instrumental observations for the past 150 years and with proxy records for the entire period. Through better characterization of the natural causes of climate change, this new data set will lead to improved prediction of anthropogenic impacts on climate. The new data set of stratospheric sulfate injections from volcanic eruptions for the past 1500 years, as a function of latitude, altitude, and month, is available for download in a format suitable for forcing general circulation models of the climate system.

Anomalous sulfur isotope compositions of volcanic sulfate over the last millennium in Antarctic ice cores

The reconstruction of past volcanism from glaciological archives is based on the measurement of sulfate concentrations in ice. This method does not allow a proper evaluation of the climatic impact of an eruption owing to the uncertainty in classifying an event between stratospheric or tropospheric. This work develops a new method, using anomalous sulfur isotope composition of volcanic sulfate in order to identify stratospheric eruptions over the last millennium. The advantages and limits of this new method are established with the examination of the 10 largest volcanic signals in ice cores from Dome C and South Pole, Antarctica. Of the 10, seven are identified as stratospheric eruptions. Among them, three have been known to be stratospheric (Tambora, Kuwae, the 1259 Unknown Event) and they exhibit anomalous sulfur isotope compositions. Three unknown events (circa 1277, 1230, 1170 A.D.) and the Serua eruption have been identified as stratospheric eruptions, which suggests for the first time that they could have had significant climatic impact. However, the Kuwae and the 1259 Unknown Event stratospheric eruptions exhibit different anomalous sulfur isotope compositions between South Pole and Dome C samples. Differences in sulfate deposition and preservation patterns between the two sites can help explain these discrepancies. This study shows that the presence of an anomalous sulfur isotope composition of volcanic sulfate in ice core indicates a stratospheric eruption, but the absence of such composition does not necessarily lead to the conclusion of a tropospheric process because of differences in the sulfate deposition on the ice sheet.

El Chichon: The genesis of volcanic sulfur dioxide monitoring from space

The 1982 eruption of El Chichon inspired a new technique for monitoring volcanic clouds. Data from the Total Ozone Mapping Spectrometer (TOMS) instrument on the Nimbus-7 satellite were used to measure sulfur dioxide in addition to ozone. For the first time precise data on the sulfur dioxide mass in even the largest explosive eruption plumes could be determined. The plumes could be tracked globally as they are carried by winds. Magmatic eruptions could be discriminated from phreatic eruptions. The data from El Chichon are reanalyzed in this paper using the latest version of the TOMS instrument calibration (V8). They show the shearing of the eruption cloud into a globe-circling band while still anchored over Mexico in three weeks. The measured sulfur dioxide mass in the initial March 28 eruption was 1.6 Tg; the April 3 eruption produced 0.3 Tg more, and the April 4 eruptions added 5.6 Tg, for a cumulative total of 7.5 Tg, in substantial agreement with estimates from prior data versions. TOMS Aerosol Index (absorbing aerosol) data show rapid fallout of dense ash east and south of the volcano in agreement with Advanced Very High Resolution Radiometer (AVHRR) ash cloud positions.

Archean Mass‐independent Fractionation of Sulfur Isotope: New Evidence of Bedded Sulfide Deposits in the Yanlingguan‐Shihezhuang area of Xintai, Shandong Province

Abstract: Multiple sulfur isotope ratios (34S/33S/32S) of Archean bedded sulfides deposits were measured in the Yanlingguan Formation of the Taishan Group in Xintai, Shandong Province, East of China; δ33S = −0.7%Δ to 3.8%, δ34S = 0.1%δ‐8.8%, Δ33S = −2.3% to −0.7%. The sulfur isotope compositions show obvious mass‐independent fractionation (MIF) signatures. The presence of MIF of sulfur isotope in Archean sulfides indicates that the sulfur was from products of photochemical reactions of volcanic SO2 induced by solar UV radiation, implying that the ozone shield was not formed in atmosphere at that time, and the oxygen level was less than 10−5 PAL (the present atmosphere level). The sulfate produced by photolysis of SO2 with negative Δ33S precipitated near the volcanic activity center; and the product of element S with positive Δ33S precipitated far away from the volcanic activity center. The lower Δ33S values of sulfide (‐2.30%Δ to −0.25%Δ) show that Shihezhuang was near the volcanic center, and sulfur was mostly from sulfate produced by photolysis. The higher Δ33S values (‐0.5%Δ to −2%Δ) indicate that Yanlingguan was far away from the volcanic center and that some of sulfur were from sulfate, another from element S produced by photolysis. The data points of sulfur isotope from Yanlingguan are in a line parallel to MFL (mass dependent fractionation line) on the plot of δ34S‐δ33S, showing that the volcanic sulfur species went through the atmospheric cycle into the ocean, and then mass dependent fractionation occurred during deposition of sulfide. The data points of sulfur isotope from Shihezhuang represent a mix of different sulfur source.

Tracking volcanic sulfur dioxide clouds for aviation hazard mitigation

Satellite measurements of volcanic sulfur dioxide (SO2) emissions can provide critical information for aviation hazard mitigation, particularly when ash detection techniques fail. Recent developments in space-based SO2 monitoring are discussed, focusing on daily, global ultraviolet (UV) measurements by the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite. OMI’s high sensitivity to SO2 permits long-range tracking of volcanic clouds in the upper troposphere and lower stratosphere (UTLS) and accurate mapping of their perimeters to facilitate avoidance. Examples from 2006 to 2007 include eruptions of Soufriere Hills (Montserrat), Rabaul (Papua New Guinea), Nyamuragira (DR Congo), and Jebel at Tair (Yemen). A tendency for some volcanic clouds to occupy the jet stream suggests an increased threat to aircraft that exploit this phenomenon. Synergy between NASA A-Train sensors such as OMI and the Atmospheric Infrared Sounder (AIRS) on the Aqua satellite can provide critical information on volcanic cloud altitude. OMI and AIRS SO2 data products are being produced in near real-time for distribution to Volcanic Ash Advisory Centers (VAACs) via a NOAA website. Operational issues arising from these improved SO2 measurements include the reliability of SO2 as proxy for co-erupted ash, the duration of VAAC advisories for long-lived volcanic clouds, and the potential effects of elevated concentrations of SO2 and sulfate aerosol in ash-poor clouds on aircraft and avionics (including cumulative effects after multiple inadvertent transits through dilute clouds). Further research is required in these areas. Aviation community assistance is sought through continued reporting of sulfurous odors or other indications of diffuse volcanic cloud encounters, in order to validate the satellite retrievals.

Investigation of the use of filter packs to measure the sulphur isotopic composition of volcanic sulphur dioxide and the sulphur and oxygen isotopic composition of volcanic sulphate aerosol

Filter packs have been used to collect sulphur and oxygen from air for isotope analysis from many areas of the world. Here we discuss their use to determine the sulphur isotope systematics of SO 2 and the sulphur and oxygen systematics of sulphate particles from volcanic vents. Our field data suggest that fractionation of sulphur isotopes occurs during the collection of SO 2 from concentrated volcanic gas plumes on alkali-impregnated filter papers. The collection of volcanogenic HCl on the same filters may play a role in this fractionation. Comparison with previous studies, which sampled areas of cleaner atmosphere, suggests that isotopic fractionation only becomes significant where elevated filter loadings occur (e.g., when sampling gas streams with SO 2 concentrations greater than ∼1 μmol m −3), although this requires further investigation. Previous studies also suggest that for volcanic sulphate particle samples collected at the same time, oxygen isotopes are fractionated while sulphur isotopes are not. Minimising the filter loading reduces these effects, but there is a trade-off with the amount of SO 2 or SO 4 2 - required for isotopic measurements. Despite the convenience of the filter pack technique these fractionation effects limit the use of filter packs for determining δ 34S for SO 2 in volcanic gases and δ 18O and δ 17O for the sulphate in volcanic particles, and they will certainly not be useful for determining small variations in the source isotopic signature of the sulphur in the SO 2 or the oxygen in the SO 4 2 - being measured. This highlights the importance of collecting SO 2 quantitatively for isotopic analysis. These effects may also have implications if using similar methods to collect SO 2 in other environments, especially where concentrations are high.

Satellite-based detection of volcanic sulphur dioxide from recent eruptions in Central and South America

Abstract. Volcanic eruptions can emit large amounts of rock fragments and fine particles (ash) into the atmosphere, as well as several gases, including sulphur dioxide (SO2). These ejecta and emissions are a major natural hazard, not only to the local population, but also to the infrastructure in the vicinity of volcanoes and to aviation. Here, we describe a methodology to retrieve quantitative information about volcanic SO2 plumes from satellite-borne measurements in the UV/Visible spectral range. The combination of a satellite-based SO2 detection scheme and a state-of-the-art 3D trajectory model enables us to confirm the volcanic origin of trace gas signals and to estimate the plume height and the effective emission height. This is demonstrated by case-studies for four selected volcanic eruptions in South and Central America, using the GOME, SCIAMACHY and GOME-2 instruments.

Retrieval of volcanic SO2 column abundance from Atmospheric Infrared Sounder data

The concentrations of volcanic sulphur dioxide (SO2) in the upper troposphere and lower stratosphere are inferred using new infrared measurements made by the Atmospheric Infrared Sounder (AIRS). Column abundance of SO2 is derived using the strong SO2 absorption feature near 1362 cm−1 (ν3‐band). The retrieval takes into account interference from water vapor across the band. Examples from several recent volcanic eruptions are given to illustrate the technique and the retrievals are compared to contemporaneous SO2 ultraviolet measurements from the Ozone Monitoring Instrument (OMI), Global Ozone Monitoring Experiment (GOME) and Total Ozone Mapping Spectrometer (TOMS).

Synchronisation of the EDML and EDC ice cores for the last 52 kyr by volcanic signature matching

Abstract. A common time scale for the EPICA ice cores from Dome C (EDC) and Dronning Maud Land (EDML) has been established. Since the EDML core was not drilled on a dome, the development of the EDML1 time scale for the EPICA ice core drilled in Dronning Maud Land was based on the creation of a detailed stratigraphic link between EDML and EDC, which was dated by a simpler 1D ice-flow model. The synchronisation between the two EPICA ice cores was done through the identification of several common volcanic signatures. This paper describes the rigorous method, using the signature of volcanic sulfate, which was employed for the last 52 kyr of the record. We estimated the discrepancies between the modelled EDC and EDML glaciological age scales during the studied period, by evaluating the ratio R of the apparent duration of temporal intervals between pairs of isochrones. On average R ranges between 0.8 and 1.2 corresponding to an uncertainty of up to 20% in the estimate of the time duration in at least one of the two ice cores. Significant deviations of R up to 1.4–1.5 are observed between 18 and 28 kyr before present (BP), where present is defined as 1950. At this stage our approach does not allow us unequivocally to find out which of the models is affected by errors, but assuming that the thinning function at both sites and accumulation history at Dome C (which was drilled on a dome) are correct, this anomaly can be ascribed to a complex spatial accumulation variability (which may be different in the past compared to the present day) upstream of the EDML core.

Volcanic emissions and the early Earth atmosphere

Despite uncertainties in our understanding of early Earth volcanism and atmospheric composition, thermodynamic modelling is able to offer estimates of the global production of reactive trace species (NO, OH, SO 3, Cl, Br and I) from early Earth volcanism, and thereby to shed light on processes which may have been different in Earth’s early atmosphere. Model results show that thermal decomposition of magmatic H 2O, CO 2 and SO 2 in high- T mixtures of magmatic and atmospheric gases (at T > 1400 °C) generate high levels of reactive trace gas species. Production of these reactive trace species is insensitive to atmospheric CO 2 in mixtures where the atmospheric gas is the minor component and will hence continue during periods of low atmospheric CO 2. Fluxes of NO, OH, Cl, Br and I from early Earth volcanism are predicted to exceed those from modern Earth volcanism as the higher temperature of early Earth emissions compensates for lower levels of O 2 in the atmosphere, compared to the modern Earth. Under certain conditions, the volcanic NO flux from early Earth volcanism is found to be comparable to other sources of reactive N such as lightning NO and photochemical HCN. This is one possible source of fixed nitrogen which may alleviate any postulated Archean nitrogen crisis. Our thermodynamic model reveals that production of SO 3 (a potential precursor for near-source volcanic sulphate and hence ‘primary’ volcanic aerosol) is likely to be significantly lower from early Earth volcanism. Uncertainty in the pathway to near-source sulphate in modern volcanism (i.e., the reaction of SO 3 with water or direct emission) introduces a large uncertainty into the production rate of near-source volcanic sulphate on the early Earth.

Atmospheric volcanic loading derived from bipolar ice cores: Accounting for the spatial distribution of volcanic deposition

Previous studies have used small numbers of ice core records of past volcanism to represent hemispheric or global radiative forcing from volcanic stratospheric aerosols. With the largest‐ever assembly of volcanic ice core records and state‐of‐the‐art climate model simulations of volcanic deposition, we now have a unique opportunity to investigate the effects of spatial variations on sulfate deposition and on estimates of atmospheric loading. We have combined 44 ice core records, 25 from the Arctic and 19 from Antarctica, and Goddard Institute for Space Studies ModelE simulations to study the spatial distribution of volcanic sulfate aerosols in the polar ice sheets. We extracted volcanic deposition signals by applying a high‐pass loess filter to the time series and examining peaks that exceed twice the 31‐year running median absolute deviation. Our results suggest that the distribution of volcanic sulfate aerosol follows the general precipitation pattern in both regions, indicating the important role precipitation has played in affecting the deposition pattern of volcanic aerosols. We found a similar distribution pattern for sulfate aerosols from the 1783–1784 Laki and 1815 Tambora eruptions, as well as for the total β activity after the 1952–1954 low‐latitude Northern Hemisphere and 1961–1962 high‐latitude Northern Hemisphere atmospheric nuclear weapon tests. This confirms the previous assumption that the transport and deposition of nuclear bomb test debris resemble those of volcanic aerosols. We compare three techniques for estimating stratospheric aerosol loading from ice core data: radioactive deposition from nuclear bomb tests, Pinatubo sulfate deposition in eight Antarctic ice cores, and climate model simulations of volcanic sulfate transport and deposition following the 1783 Laki, 1815 Tambora, 1912 Katmai, and 1991 Pinatubo eruptions. By applying the above calibration factors to the 44 ice core records, we have estimated the stratospheric sulfate aerosol loadings for the largest volcanic eruptions during the last millennium. These loadings agree fairly well with estimates based on radiation, petrology, and model simulations. We also estimate the relative magnitude of sulfate deposition compared with the mean for Greenland and Antarctica for each ice core record, which provides a guideline to evaluate the stratospheric volcanic sulfate aerosol loading calculated from a single or a few ice core records.

Correction to “Oxygen and sulphur isotope composition of volcanic sulphate aerosol at the point of emission”

Correction to “Oxygen and sulphur isotope composition of volcanic sulphate aerosol at the point of emission”

Ice core paleovolcanic records from the St. Elias Mountains, Yukon, Canada

We previously reported a record of regionally significant volcanic eruptions in the North Pacific using an ice core from Eclipse Icefield (St. Elias Mountains, Yukon, Canada). The acquisition of two new ice cores from Eclipse Icefield, along with the previously available Eclipse Icefield and Mount Logan Northwest Col ice cores, allows us to extend our record of North Pacific volcanism to 550 years before present using a suite of four ice cores spanning an elevation range of 3–5 km. Comparison of volcanic sulfate flux records demonstrates that the results are highly reproducible, especially for the largest eruptions such as Katmai (A.D. 1912). Correlation of volcanic sulfate signals with historically documented eruptions indicates that at least one‐third of the eruptions recorded in St. Elias ice cores are from Alaskan and Kamchatkan volcanoes. Although there are several moderately large (volcanic explosivity index (VEI) ≥ 4) eruptions recorded in only one core from Eclipse Icefield, the use of multiple cores provides signals in at least one core from all known VEI ≥ 4 eruptions in Alaska and Kamchatka since A.D. 1829. Tephrochronological evidence from the Eclipse ice cores documents eruptions in Alaska (Westdahl, Redoubt, Trident, and Katmai), Kamchatka (Avachinsky, Kliuchevoskoi, and Ksudach), and Iceland (Hekla). Several unidentified tephra‐bearing horizons, with available geochemical evidence suggesting Alaskan and Kamchatkan sources, were also found. We present a reconstruction of annual volcanic sulfate loading for the North Pacific troposphere based on our ice core data, and we provide a detailed assessment of the atmospheric and climatic effects of the Katmai eruption.

Measurement of volcanic SO 2 fluxes with differential optical absorption spectroscopy

Measurements of volcanic sulphur dioxide fluxes are important indicators of volcanic activity and are crucial to understanding the impacts of volcanic emissions upon the environment and climate. For more than thirty years correlation spectrometers (COSPECs) have provided valuable service in this respect. However, given the vintage and operational costs of these devices, research groups and volcano observatories have recently begun using state of the art, lightweight, compact and inexpensive USB2000 ultraviolet spectrometers as a replacement technology, with differential absorption spectroscopy SO 2 concentration retrievals. In order to widen the dissemination of the latter approach, an overview of this methodology is given here, covering hardware protocols and the use of freely available software, written for this purpose.

Mass-Independent Sulfur Isotopic Compositions in Stratospheric Volcanic Eruptions

The observed mass-independent sulfur isotopic composition (Delta33S) of volcanic sulfate from the Agung (March 1963) and Pinatubo (June 1991) eruptions recorded in the Antarctic snow provides a mechanism for documenting stratospheric events. The sign of Delta33S changes over time from an initial positive component to a negative value. Delta33S is created during photochemical oxidation of sulfur dioxide to sulfuric acid on a monthly time scale, which indicates a fast process. The reproducibility of the results reveals that Delta33S is a reliable tracer to chemically identify atmospheric processes involved during stratospheric volcanism.

Oxygen and sulfur isotopic composition of volcanic sulfate aerosol at the point of emission

Volcanic sulfate aerosol is emitted from the vents of many active volcanoes, but its origin has not yet been explained. We report the first measurements of the isotopic compositions of near‐vent volcanic aerosol sulfate and use the combined sulfur and oxygen isotope systematics of the aerosol and magma at Masaya volcano, Nicaragua, to draw preliminary conclusions about the production mechanism of near‐source volcanic sulfate. The sulfate aerosol does not display a significant mass‐independent oxygen or sulfur isotopic signature, which suggests that primary volcanic aerosol does not contribute to the larger mass‐independent anomalies found in some ambient atmospheric aerosols and as preserved in ice cores. The oxygen isotope composition of the sulfate appeared to become heavier on the particle filters with increasing amount of sample collected and suggests that the δ18O value of the sulfate aerosol is <8‰. The sulfur isotopic composition of the sulfate did not vary with sample loading on the filters and had a mean δ34S value of 7.7 ± 0.8‰, similar to that of the magma (6.6 ± 0.2‰). The low Δ17O value, the δ18O value of the magma (6.6 ± 0.3‰) and the high δ18O value of atmospheric oxygen (23.5‰) suggest that known atmospheric oxidation pathways at ambient temperatures are not the major routes of production for this sulfate. Instead, the isotopic systematics of aerosol and magma are consistent with sulfate production either by high‐temperature equilibration of the magmatic gas mixture with small amounts of atmospheric oxygen or by direct emission of SO42− from the magma.

Chronic exposure to volcanic environments and chronic bronchitis incidence in the Azores, Portugal

The village of Furnas, like other active volcanic areas in the world, exhibits high levels of hazardous gases. We aimed to investigate the existence of a possible association between chronic exposure to volcanic sulfur gases and chronic bronchitis. To investigate this, we used two populations, one exposed to active manifestations of volcanism (Furnas) and another from an area where no volcanic activity took place for over three million years (Santa Maria), both in the Azores. We used data on the incidence of chronic bronchitis among both populations (1991–2001), obtained from the records of each local health center, and population denominators from censuses carried out in 1991 and 2001, using five age-groups. We also estimated relative risks and mean annual age-standardized rates of chronic bronchitis incidence. Incidence rates were extremely higher in the volcanically active area for both sexes, and especially in the youngest groups. Accordingly, the risk of chronic bronchitis for the people living in the volcanically active area was extremely higher (males RR=3.99; females RR=10.74) when compared to those living in the volcanically inactive area. Comparison of chronic bronchitis incidence rates between both populations suggests an association between this disease and the chronic exposure to the volcanically active environment, with all its hazardous gases like hydrogen sulfide and sulfur dioxide. These findings may help health officials to better advice people inhabiting volcanic areas, or others with high levels of sulfur gases, on how to prevent and minimize the risks of chronic bronchitis.

Sulphur isotope evidence for an oxic Archaean atmosphere

The presence of mass-independently fractionated sulphur isotopes (MIF-S) in many sedimentary rocks older than approximately 2.4 billion years (Gyr), and the absence of MIF-S in younger rocks, has been considered the best evidence for a dramatic change from an anoxic to oxic atmosphere around 2.4 Gyr ago. This is because the only mechanism known to produce MIF-S has been ultraviolet photolysis of volcanic sulphur dioxide gas in an oxygen-poor atmosphere. Here we report the absence of MIF-S throughout approximately 100-m sections of 2.76-Gyr-old lake sediments and 2.92-Gyr-old marine shales in the Pilbara Craton, Western Australia. We propose three possible interpretations of the MIF-S geologic record: (1) the level of atmospheric oxygen fluctuated greatly during the Archaean era; (2) the atmosphere has remained oxic since approximately 3.8 Gyr ago, and MIF-S in sedimentary rocks represents times and regions of violent volcanic eruptions that ejected large volumes of sulphur dioxide into the stratosphere; or (3) MIF-S in rocks was mostly created by non-photochemical reactions during sediment diagenesis, and thus is not linked to atmospheric chemistry.