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The lakes surrounding the iron ore mining region of Schefferville, Quebec, Canada, sit within a landscape of historical disturbances, two of which have been relatively well documented over time: metal contamination and nutrient loading. Based on the analysis of sediment cores, we used cladoceran zooplankton subfossil assemblages from two lakes located in Schefferville to track both alpha and beta diversity over the last 100+ years. We showed that high metal concentrations were correlated with decreased cladoceran diversity, and that the site that experienced both direct wastewater input and atmospheric metal loading (Lake Dauriat) had the greatest declines in cladoceran richness. In both lakes, turnover in cladoceran assemblages was highest in the mining period. During the period of mine closures and improvement of wastewater treatment, some decreases in metal enrichment in the sediments and increases in cladoceran richness were observed in Lake Dauriat. Overall, a combined use of species richness and beta diversity metrics showed alpha and beta diversity are not always congruent, and that there are various ways to interpret scenarios of temporal beta diversity in northern freshwater systems. Les lacs entourant la region miniere ferrifere de Schefferville (Quebec, Canada) se trouvent dans un paysage marque par des perturbations passees, dont deux sont relativement bien documentees dans le temps, a savoir la contamination par les metaux et l'apport de nutriments. A la lumiere de l'analyse de carottes de sediments, nous avons utilise des assemblages de cladoceres zooplanctoniques subfossiles provenant de deux lacs situes a Schefferville pour caracteriser les diversites alpha et beta au cours des 100 dernieres annees et plus. Nous demontrons que de fortes concentrations de metaux sont correlees a une diversite de cladoceres reduite et que le site ayant recu des apports directs d'eaux usees et des apports atmospheriques de metaux (lac Dauriat) presente les plus fortes baisses de richesse des cladoceres. Dans les deux lacs, le renouvellement des assemblages de cladoceres etait a son plus fort durant la periode d'exploitation miniere. Durant la periode des fermetures de mines et de l'amelioration du traitement des eaux usees, certaines baisses de l'enrichissement en metaux dans les sediments et augmentations de la richesse des cladoceres ont ete observees dans le lac Dauriat. Dans l'ensemble, l'utilisation combinee de mesures de la richesse specifique et de la diversite beta a permis de demontrer que les diversites alpha et beta ne concordent pas toujours et qu'il y a differentes manieres d'interpreter les scenarios de diversite beta dans le temps dans les systemes d'eau douce nordiques. [Traduit par la Redaction], Introduction Perturbation of freshwater systems is of broad concern because of their importance in providing ecosystem services (Limburg 2009), their role as biodiversity hotspots (Strayer and Dudgeon 2010), and the [...]

The Archean-Proterozoic transition is characterized by the widespread deposition of organic-rich shale, sedimentary iron formation, glacial diamictite, and marine carbonates recording profound carbon isotope anomalies, but notably lacks bedded evaporites. All deposits reflect environmental changes in oceanic and atmospheric redox states, in part associated with Earth's earliest ice ages. Time-series data for multiple sulfur isotopes from carbonate-associated sulfate as well as sulfides in sediments of the Transvaal Supergroup, South Africa, capture the concomitant buildup of sulfate in the ocean and the loss of atmospheric mass-independent sulfur isotope fractionation. In phase with sulfur is the earliest recorded positive carbon isotope anomaly, convincingly linking these environmental perturbations to the Great Oxidation Event (ca. 2.3 Ga).

Organic haze and sulfur gases are ubiquitous in planetary atmospheres and were likely present in Earth's Archean atmosphere. Currently, there are few experiments investigating how H2S influences organic haze chemistry on Archean Earth. Here, we present results from laboratory haze‐analog experiments probing the role of H2S in the composition and total mass of aerosol produced from precursor mixtures of Archean‐like gas fluxes (e.g., pCO2 ∼3–50xPAL). We show that trace H2S enhances organic aerosol production at all carbon dioxide mixing ratios studied, and we observe both organic and inorganic sulfur aerosol products. Our finding challenges predictions that H2SO4 and S8 were the primary sulfur reservoirs in Earth's Archean atmosphere, and these results suggest that inorganic sulfur and organic haze chemistry are tightly coupled during the formation of organic hazes in the atmospheres of the Archean Earth and likely Archean‐like exoplanets. Plain Language Summary: The Archean Eon (4.0–2.5 billion years ago) atmosphere was much different from the modern one, with very little oxygen and higher amounts of carbon dioxide (CO2) and methane (CH4). Light from the sun would have jump‐started chemical reactions leading to a mixture of organic molecules and particles ("organic haze"). Gases in smaller amounts (trace gases) can greatly influence "haze" chemistry. One common trace gas is hydrogen sulfide (H2S). We conducted laboratory experiments that attempted to reproduce this "haze" chemistry with gas mixtures of CO2, CH4, and H2S in a nitrogen background. When H2S was added to the gas mixture, organosulfur molecules were formed, and the mass of organic particles greatly increased. These results challenge two current assumptions about Archean organic haze and sulfur chemistry. The first is that the production of organic particles in a CO2/CH4 haze should decrease when CO2 is increased; we show that organic particle mass is essentially independent of CO2 when trace H2S is present. The second is that sulfur particles would be composed of inorganic sulfur; we show that organosulfur accounts for a significant portion of the sulfur. Our results may affect the current understanding of the history and evolution of Earth's atmosphere. Key Points: In haze‐analog experiments with carbon dioxide (CO2)/methane (CH4)/N2 precursors, addition of trace H2S increases aerosol production by at least a factor of ∼3.8In CO2/CH4/N2 gas mixtures, high CO2 inhibits organic aerosol formation. With trace H2S, organic aerosol formation is independent of CO2Inorganic and organic sulfate aerosol forms when trace H2S is present, suggesting that organic sulfur is an important sulfur reservoir [ABSTRACT FROM AUTHOR]

The Platreef ore horizon of the Bushveld Complex, South Africa, is the third largest platinum group element ore deposit in the world, but the origin of its ore remains enigmatic. A complex contact relationship between the igneous and footwall rocks of the Bushveld Complex, coupled with evidence for widespread late-stage hydrothermal processing, obscures the original mineralization history of the Platreef. We constrain the parental magmatic origin of the Platreef by exploiting multiple sulfur isotope contrasts across Bushveld Complex contact zones in order to see through the effects of postmineralization hydrothermal activity. We report S isotope measurements made on samples collected along two profiles through the Platreef into underlying metapelitic and metacarbonate footwall rocks. In both profiles, igneous rocks far from the contact have low [[DELTA].sup.33]S values (average [[DELTA].sup.33]S = 0.15%o), whereas metasedimentary rocks far from the contact have high [[DELTA].sup.33]S values ([[DELTA].sup.33]S to 5.04%o) with a smoothly varying profile between the two end members. The midpoint in both isotope profiles is displaced into the footwall, defining a classic advective-dispersive tracer geometry. This geometry is not present in the associated [[DELTA].sup.34]S values. The displacement of the [[DELTA].sup.33]S front suggests fluid transport and advection of S into the country rocks; this was accompanied by back diffusion of the S isotope tracer into the Platreef. The Platreef magma was apparently S saturated prior to emplacement and, counterintuitively, lost S during the formation of the present Platreef ore horizon.

Inverse calculations reveal the three-dimensional geometry of time-integrated fluid flux over a 120 [km.sup.2] area during peak Barrovian regional metamorphism in southeastern Vermont. Prograde changes in whole-rock C[O.sub.2], [sup.18]O, and [sup.13]C and calculated fluid compositions at the peak of metamorphism were inverted assuming tracer mass balance to obtain the time-integrated fluid flux in three dimensions. Peak metamorphic fluid flow was spatially nonuniform with flux magnitudes ranging from ~0 to 3*[10.sup.5] mol fluid/[cm.sup.2] rock and flux directions ranging from vertical (upward and downward) to horizontal. Averaged over the entire study area, the magnitude of the time-integrated metamorphic fluid flux vector is ~3.4*[10.sup.4] mol fluid/[cm.sup.2] rock. The average flux vector trends 45[degrees] to the southwest and points upward at 36[degrees] from the present horizontal, parallel to formation boundaries on a regional scale. Fluids in the terrain carried ~3*[10.sup.3] mol C[O.sup.2]/[cm.sup.2] rock toward Earth's surface during the peak of metamorphism. Results suggest that local cross-layer transport processes are secondary to terrain-scale metamorphic fluid flow in driving prograde decarbonation reactions. Regional structure exerts a first-order control on the gross geometry of peak metamorphic fluid flow. Keywords: metamorphism, fluid flow, inverse problem, C[O.sup.2], [[delta].sup.18]O, [[delta].sup.13]C.