L. DeWayne Cecil

Chlorine-36, bromide, and the origin of spring water

Natural ratios of chlorine-36 (36Cl) to stable chlorine (i.e., 36Cl/Cl×10−15) vary in shallow groundwater of the United States from about 50 in coastal areas to about 1400 in the northern Rocky Mountains. Ratios lower than these indicate the presence of chloride (Cl−) that has been isolated from the atmosphere for hundreds of thousands of years, if not longer. Higher ratios, which can exceed 5000, usually originate from fallout from testing thermonuclear devices in the western Pacific in the 1950s. Natural mass ratios of chloride to bromide (Cl−/Br−) in precipitation vary in the United States from about 250 in coastal areas to about 50 in the north-central states. Lower ratios may suggest contamination from human sources. Higher ratios, which may exceed 2000, commonly reflect the dissolution of halite. Seawater has a Cl−/Br− ratio of 290. Both 36Cl and Cl−/Br− ratios have been measured in 21 samples of spring water collected from springs in 10 different states. Brackish water from Saratoga Springs area in New York has low values for both 36Cl and Cl−/Br− ratios. This indicates that a large component of the water has a very deep origin. Brackish water from Alexander Springs in Florida has a low 36Cl ratio but a high Cl−/Br− ratio similar to seawater. This suggests the addition of ancient seawater that may be trapped in the aquifer. Big Spring in Iowa discharges water with a very high Cl−/Br− ratio but a moderate 36Cl ratio. The high ratio of Cl−/Br− may be produced by dissolution of road salt or agricultural chemicals. Of the 21 springs sampled, only 10 appeared to have potable water not significantly affected by human activity. Chlorine-36 from testing of nuclear devices is still being flushed out of four of the spring systems that were sampled. Thus, more than 45 years have passed since 36Cl was introduced into the aquifers feeding the springs and the systems, as yet, have not been purged.

Oxygen isotopic and soluble ionic composition of a shallow firn core, Inilchek glacier, central Tien Shan

Oxygen isotopic and soluble ionic measurements made on snow-pit (2 m depth) and firn-core (12.4 m depth) samples recovered from the accumulation zone (5100 m) of Inilchek glacier (43° N, 79° E) provide information on recent (1992-98) climatic and environmental conditions in the central Tien Shan region of central Asia. The combined 14.4 m snow-pit/firn-core profile lies within the firn zone, and contains only one observed melt feature (10 m temperature = -12°C). Although some post-depositional attenuation of the sub-seasonal δ 18 O record is possible, annual cycles are apparent throughout the isotope profile. We therefore use the preserved δ 18 O record to establish a depth/age scale for the core. Mean δ 18 O values for the entire core and for summer periods are consistent with δ 18 /temperature observations, and suggest the δ 18 O record provides a means to reconstruct past changes in summer surface temperature at the site. Major-ion (Na + , K + , Mg 2+ , Ca 2+ , NH 4 + , Cl - , NO 3 - , SO 4 2- ) data from the core demonstrate the dominant influence of dust deposition on the soluble chemistry at the site, and indicate significant interannual variability in atmospheric-dust loading during the 1990s. Anthropogenic impacts on NH 4 + concentrations are observed at the site, and suggest a summer increase in atmospheric NH 4 + that may be related to regional agricultural (nitrogen-rich fertilizer use) activities.

Groundwater “fast paths” in the Snake River Plain aquifer: Radiogenic isotope ratios as natural groundwater tracers

Preferential flow paths are expected in many groundwater systems and must be located because they can greatly affect contaminant transport. The fundamental characteristics of radiogenic isotope ratios in chemically evolving waters make them highly effective as preferential flow path indicators. These ratios tend to be more easily interpreted than solute-concentration data because their response to water-rock interaction is less complex. We demonstrate this approach with groundwater {sup 87}Sr/{sup 86}Sr ratios in the Snake River Plain aquifer within and near the Idaho National Engineering and Environmental Laboratory. These data reveal slow-flow zones as lower {sup 87}Sr/{sup 86}Sr areas created by prolonged interaction with the host basalts and a relatively fast flowing zone as a high {sup 87}Sr/{sup 86}Sr area.

Earth paleoenvironments : records preserved in mid- and low-latitude glaciers

Part I: Introduction And Methods 1. High-Altitude, Mid and Low-Latitude Ice Core Records: Implications for our Future by L.G. Thompson 2. Methods of Mid- and Low-Latitude Glacial Record Collection, Analysis, and Interpretation by J.R. Green, L.D. Cecil and S.K. Frape Part II: The Climate And Environmental Change Record Over The Last 200 Years 3. The Influence of Post-Depositional Effects on Ice Core Studies: Examples from the Alps, Andes, and Altai by U. Schotterer, W. Stichler and P. Ginot 4. Event to Decadal-Scale Glaciochemical Variability on the Inilchek Glacier, Central Tien Shan by K. Kreutz, C.P. Wake, V.B. Aizen, L.D. Cecil, J.R. Green and H.A. Synal 5. Climatic Interpretation of the Gradient in Glaciochemical Signals Across the Crest of the Himalaya by C.P. Wake, P.A. Mayewski and S. Kang 6. Reconstruction of European Air Pollution from Alpine Ice Cores by M. Schwikowski 7. Glacier Research in Mainland Scandinavia by W.B. Whalley Part III: The Climate And Environmental Change Record Over The Last 200 - 500 Years 8. Four Centuries of Climatic Variation Across the Tibetan Plateau from Ice-Core Accumulation and d18O Records by M.E. Davis and L.G. Thompson 9. Climatic Changes over the Last 400 Years Recorded in Ice Collected from the Guliya Ice Cap, Tibetan Plateau by Y. Tandong and Y. Meixue 10. Evidence of Abrupt Climate Change and the Development of an Historic Mercury Deposition Record Using Chronological Refinement of Ice Cores at Upper Fremont Glacier by P.F. Schuster, D.L. Naftz, L.D. Cecil and J.R. Green 11. Variations between d18O in Recently Deposited Snow and On-Site Air Temperature, Upper Fremont Glacier, Wyoming by Naftz, D.D. Susong, L.D. Cecil and P.L. Schuster

Isotopes as Indicators of Environmental Change

Publisher Summary In addition to providing an understanding of processes within a catchment system, isotopic techniques have been instrumental in providing reconstructions of catchment climate and other environmental indicators at various time scales. Many recent changes are a direct consequence of anthropogenic activities. Isotopic analysis serves as a valuable tool for distinguishing between natural variations in long-term climatic patterns and anthropogenic effects, yielding improved understanding of natural feedback mechanisms and the development of realistic remediation strategies. This chapter discusses the examples of isotopic techniques that have been applied to understand several types of ongoing and recent environmental changes, and in paleo-environmental studies. It discusses isotope geochemistry, hydrology, and climatology to look at new ways of applying isotopic tracing techniques to provide information on environmental change. It also gives an overview on how isotopic indicators are being applied in investigations of environmental change in continental settings.

Identification of bomb-produced chlorine-36 in mid-latitude glacial ice of North America

Abstract In 1991, the U.S. Geological Survey collected a 160-meter (m) ice core from the Upper Fremont Glacier (43°07′N, 109°36′W) in the Wind River Mountain Range of Wyoming in the western United States [1]. In 1994–1995, ice from this core was processed at the National Ice Core Laboratory in Denver, Colorado, and analyzed for chlorine-36 (36Cl) by accelerator mass spectrometry at PRIME Laboratory, Purdue University. A tritium bomb peak identified in the work by [1] was used as a marker to estimate the depth of bomb-produced 36Cl. Tritium concentrations ranged from 0 tritium units (TU) for older ice to more than 300 TU at 29 m below the surface of the glacier, a depth that includes ice that was deposited as snow during nuclear-weapons tests through the early 1960s. Maximum 36Cl production during nuclear-weapons tests was in the late 1950s; therefore, the analyses were performed on ice from a depth of 29.8 to 32 m. Calculated flux for 36Cl in ice deposited in the late 1950s ranged from 1.2 ± 0.1 × 10−1 atoms/cm2 s for ice from 29.8 to 30.4 m, to 2.9 ± 0.1 × 10−1 atoms/cm2 s for ice from 31.5 to 32.0 m. Ice samples from a depth of 104.7 to 106.3 m were selected to represent pre-weapons tests 36Cl flux. Calculated flux for 36Cl in this deeper ice was 4.6 ± 0.8 × 10−3 atoms/cm2 s for ice from 104.7 to 105.5 m and 2.0 ± 0.2 × 10−2 atoms/cm2 s for ice from 105.5 to 106.3 m. These flux calculations from the Upper Fremont Glacier analyses are the first for bomb-produced 36Cl in ice from a mid-latitude glacier in North America. It may now be possible to fully quantify the flux of 36Cl from nuclear-weapons tests archived in mid-latitude glacial ice and to gain a better understanding of the distribution of 36Cl and other cosmogenic nuclides.

Use of chlorine-36 to determine regional-scale aquifer dispersivity, eastern Snake River Plain aquifer, Idaho/USA

Abstract Chlorine-36 ( 36 Cl) derived from processed nuclear waste that was disposed at the US Department of Energy’s Idaho National Engineering and Environmental Laboratory (INEEL) through a deep injection well in 1958, was detected 24–28 yr later in groundwater monitoring wells approximately 26 km downgradient from the source. Groundwater samples covering the period 1966–1995 were selected from the US Geological Survey’s archived-sample library at the INEEL and analyzed for 36 Cl by accelerator mass spectrometry (AMS). The smaller 36 Cl peak concentrations in water from the far-field monitoring wells relative to the input suggest that aquifer dispersivity may be large. However, the sharpness of the 1958 disposal peak of 36 Cl is matched by the measured 36 Cl concentrations in water from these wells. This implies that a small aquifer dispersivity may be attributed to preferential groundwater flowpaths. Assuming that tracer arrival times at monitoring wells are controlled by preferential flow, a 1-D system-response model was used to estimate dispersivity by comparing the shape of predicted 36 Cl-concentration curves to the shape of 36 Cl-concentration curves measured in water from these observation wells. The comparisons suggest that a 1-D dispersivity of 5 m provides the best fit to the tracer data. Previous work using a 2-D equivalent porous-media model concluded that longitudinal dispersivity (equivalent to 1-D dispersivity in our model) was 90 m (Ackerman, US). A 90 m dispersivity value eliminates the 1958 disposal peak in our model output curves. The implications of the arrival of 36 Cl at downgradient monitoring wells are important for three reasons: (1) the arrival times and associated 36 Cl concentrations provide quantitative constraints on residence times, velocities, and dispersivities in the aquifer; (2) they help to refine our working hypotheses of groundwater flow in this aquifer and (3) they may suggest a means of estimating the distribution of preferential flowpaths in the aquifer.

Sampling and analysis for radon-222 dissolved in ground water and surface water

Radon-222 is a naturally occurring radioactive gas in the uranium-238 decay series that has traditionally been called, simply, radon. The lung cancer risks associated with the inhalation of radon decay products have been well documented by epidemiological studies on populations of uranium miners.The realization that radon is a public health hazard has raised the need for sampling and analytical guidelines for field personnel. Several sampling and analytical methods are being used to document radon concentrations in ground water and surface water worldwide but no convenient, single set of guidelines is available. Three different sampling and analytical methods-bubbler, liquid scintillation, and field screening-are discussed in this paper. The bubbler and liquid scintillation methods have high accuracy and precision, and small analytical method detection limits of 0.2 and 10 pCi/l (picocuries per liter), respectively. The field screening method generally is used as a qualitative reconnaissance tool.

Comparison of the effects of filtration and preservation methods on analyses for strontium-90 in ground water

From 1952 to 1988, about 140 curies of strontium-90 were discharged in liquid waste to disposal ponds and wells at the INEL (Idaho National Engineering Laboratory). Water from four wells was sampled as part of the U.S. Geological Surveys quality-assurance program to evaluate the effects of filtration and preservation methods on strontium-90 concentrations in ground water at the INEL. Water from each well was filtered through either a 0.45- or a 0.1-micrometer membrane filter; unfiltered samples also were collected. Two sets of filtered and two sets of unfiltered water samples were collected at each well. One of the two sets of water samples was field acidified.Strontium-90 concentrations ranged from below the reporting level to 52±4 picocuries per liter. Descriptive statistics were used to determine reproducibility of the analytical results for strontium-90 concentrations in water from each well. Comparisons were made with unfiltered, acidified samples at each well. Analytical results for strontium-90 concentrations in water from well 88 were not in statistical agreement between the unfiltered, acidified sample and the filtered (0.45 micrometer), acidified sample. The strontium-90 concentration for water from well 88 was less than the reporting level.For water from wells with strontium-90 concentrations at or above the reporting level, 94 percent or more of the strontium-90 is in true solution or in colloidal particles smaller than 0.1 micrometer. These results suggest that changes in filtration and preservation methods used for sample collection do not significantly affect reproducibility of strontium-90 analyses in ground water at the INEL.

Optimizing societal benefit using a systems engineering approach for implementation of the GEOSS space segment

The Group on Earth Observations (GEO) is driving a paradigm shift in the Earth Observation community, refocusing Earth observing systems on GEO Societal Benefit Areas (SBA). Over the short history of space-based Earth observing systems most decisions have been made based on improving our scientific understanding of the Earth with the implicit assumption that this would serve society well in the long run. The space agencies responsible for developing the satellites used for global Earth observations are typically science driven. The innovation of GEO is the call for investments by space agencies to be driven by global societal needs. This paper presents the preliminary findings of an analysis focused on the observational requirements of the GEO Energy SBA. The analysis was performed by the Committee on Earth Observation Satellites (CEOS) Systems Engineering Office (SEO) which is responsible for facilitating the development of implementation plans that have the maximum potential for success while optimizing the benefit to society. The analysis utilizes a new taxonomy for organizing requirements, assesses the current gaps in spacebased measurements and missions, assesses the impact of the current and planned space-based missions, and presents a set of recommendations.