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  1. Abstract

    Hydrogen (δD) and oxygen (δ18O) isotopic ratios are strongly correlated in precipitation over time and space, defining the meteoric water line, and the slope of this δD‐δ18O relationship reflects covariations of deuterium excess (d‐excess) with δD or δ18O. This δD‐δ18O line provides a tool for inferring hydrologic processes from the evaporation source to condensation site. Here, we present δD‐δ18O relationships on seasonal and annual timescales for daily precipitation, snow pits, and a 15‐m ice core (Owen) at Summit, Greenland. Seasonally, precipitation δD‐δ18O slopes are less than 8 (summer = 7.70; winter = 7.77), while the annual slope is greater than 8 (8.27). We suggest that intra‐season slopes result primarily from Rayleigh distillation, which, under prevailing conditions, produces slopes less than 8. The summer line has a greater intercept (higher d‐excess) than the winter line. This separation causes annual slopes to be greater than seasonal ones. We attribute high summer d‐excess primarily to contributions of vapor sublimated from the Greenland Ice Sheet and other terrestrial sources. High sublimated moisture proportions result in a large separation between seasonal δD‐δ18O lines, and thus high annual slopes. Inter‐seasonal weighting of precipitation amount also influences annual slopes because slopes are weighed by the number of storms each season. Using snow pit measurements, we demonstrate that precipitation isotopic signals translate to the snowpack. We generate indices to determine Sublimation Proportion Index and Precipitation Weighting Index, and find that annual Owen core δD‐δ18O line slopes are significantly related to these indices, demonstrating that these factors are recorded in ice cores.

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  2. Cambrian–Devonian sedimentary rocks of the northern Canadian Cordillera record both the establishment and demise of the Great American Carbonate Bank, a widespread carbonate platform system that fringed the ancestral continental margins of North America (Laurentia). Here, we present a new examination of the deep-water Road River Group of the Richardson Mountains, Yukon, Canada, which was deposited in an intra-platformal embayment or seaway within the Great American Carbonate Bank called the Richardson trough. Eleven detailed stratigraphic sections through the Road River Group along the upper canyon of the Peel River are compiled and integrated with geological mapping, facies analysis, carbonate and organic carbon isotope chemostratigraphy, and new biostratigraphic results to formalize four new formations within the type area of the Richardson Mountains (Cronin, Mount Hare, Tetlit, and Vittrekwa). We recognize nine mixed carbonate and siliciclastic deep-water facies associations in the Road River Group and propose these strata were deposited in basin-floor to slope environments. New biostratigraphic data suggest the Road River Group spans the late Cambrian (Furongian) – Middle Devonian (Eifelian), and new chemostratigraphic data record multiple global carbon isotopic events, including the late Cambrian Steptoean positive carbon isotope excursion, the Late Ordovician Guttenberg excursion, the Silurian Aeronian, Valgu, Mulde (mid-Homerian), Ireviken (early Sheinwoodian), and Lau excursions, and the Early Devonian Klonk excursion. Together, these new data not only help clarify nomenclatural debate centered around the Road River Group, but also provide critical new sedimentological, biostratigraphic, and isotopic data for these widely distributed rocks of the northern Canadian Cordillera. 
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  3. High concentrations of barium (Ba), strontium (Sr) and radium (Ra) are present in both the liquid and suspended solid portions of wastewater produced from hydraulic fracturing. These high concentrations often require special treatment in which the solid and liquid portions are separated and then independently treated prior to disposal. The solids are typically disposed in landfills while the liquids are further treated, recycled for future hydraulic fracturing, or disposed via injection wells. Finding optimal treatment methods of both the solid and the liquid fractions requires a thorough understanding of potential Ra mobility from both the raw suspended solids and mineral precipitates formed during treatment. Using a sequential extraction procedure, we found that, without treatment, more than 50% of Ra-226 in the suspended solids was associated with soluble salts and readily exchangeable fractions. When the liquid portion of the wastewater was treated by mixing with acid mine drainage (AMD), which contained high sulfate concentrations, approximately 80–97% of the total Ra-226 in the mixture solution is found in the insoluble sulfate fraction of the precipitate. The activity of Ra-226 sequestered in the precipitated solid sulfate fractions is positively correlated with the Sr/Ba ratio of the wastewater-AMD solution. We discuss implications of these findings for effective long-term management of elevated radium in both solid and liquid wastes. 
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  4. During the last deglaciation temperatures over midcontinental North America warmed dramatically through the Bølling-Allerød, underwent a cool period associated with the Younger-Dryas and then reverted to warmer, near modern temperatures during the early Holocene. However, paleo proxy records of the hydroclimate of this period have presented divergent evidence. We reconstruct summer relative humidity (RH) across the last deglacial period using a mechanistic model of cellulose and leaf water δ 18 O and δD combined with a pollen-based temperature proxy to interpret stable isotopes of sub-fossil wood. Midcontinental RH was similar to modern conditions during the Last Glacial Maximum, progressively increased during the Bølling-Allerød, peaked during the Younger-Dryas, and declined sharply during the early Holocene. This RH record suggests deglacial summers were cooler and characterized by greater advection of moisture-laden air-masses from the Gulf of Mexico and subsequent entrainment over the mid-continent by a high-pressure system over the Laurentide ice sheet. These patterns help explain the formation of dark-colored cumulic horizons in many Great Plains paleosol sequences and the development of no-analog vegetation types common to the Midwest during the last deglacial period. Likewise, reduced early Holocene RH and precipitation correspond with a diminished glacial high-pressure system during the latter stages of ice-sheet collapse. 
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