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To address the low priority given to university-level outreach, the authors created an outreach program that makes it easy for scientists to connect with the public, while at the same time providing effective transfer of scientific research results to the public and the K-12 community. The result is a program called the Hot Science--Cool Talks Outreach Lecture Series, a regular event at the University of Texas at Austin (UT Austin) overseen by the university's Environmental Science Institute (ESI). The program combines lectures by scientists with hands-on activities, webcasts, and workshops for teachers, students, and the public. This paper describes the concept for this lecture series, its operation, and its unique outcomes for K-12 outreach. (Contains 4 tables and 2 figures.)

The application of stable isotopes in speleothem records requires an understanding of the extent to which speleothem calcite isotopic compositions reflect the compositions of the cave waters from which they precipitate. To test for equilibrium precipitation, modern speleothem calcite was grown on glass plates, so that the carbon and oxygen isotope composition of the calcite and the water from which it precipitated could be directly compared. The plates were placed on the tops of three actively growing stalagmites that occupy a 1 [m.sup.2] area in Harrison's Cave, Barbados, West Indies. Only some of the plate [delta][sup.13]C values and none of the plate [delta][sup.18]O values correspond to equilibrium values, indicating significant kinetic isotope effects during speleothem calcite growth. We investigate herein mechanisms that may account for the kinetic isotope effects. On each plate, speleothem calcite was deposited with distinct [delta][sup.18]O and [delta][sup.13]C compositions that increase progressively away from the growth axis, with up to 6.6 [per thousand] [sup.13]C and 1.7 [per thousand] [sup.18]O enrichments. The positive [delta][sup.13]C versus [delta][sup.18]O trends are likely a result of [sup.18]O and [sup.13]C Rayleigh-distillation enrichment in the HC[O.sup.-.sub.3] reservoir owing to progressive C[O.sub.2] degassing and CaC[O.sub.3] precipitation. The magnitude of the [delta][sup.13]C versus [delta][sup.18]O slope is likely controlled by the extent to which C[O.sub.2] hydration-hydroxylation reactions buffer the oxygen isotope composition of the HC[O.sup.-.sub.3] reservoir during calcite precipitation. Complete oxygen isotopic buffering of the HC[O.sup.-.sub.3] reservoir by C[O.sub.2] hydration-hydroxylation reactions will produce a vertical [delta][sup.13]C versus [delta][sup.18]O slope in calcite sampled along a growth layer. As oxygen isotope buffering of the HC[O.sup.-.sub.3] reservoir decreases to no buffering, the [delta][sup.13]C versus [delta][sup.18]O slope in calcite sampled along a growth layer will decrease from vertical to 0.52 at the cave temperature. In this study, modern speleothem calcite sampled along the growth layer produced a [delta][sup.13]C versus [delta][sup.18]O slope of 3.9, indicating incomplete oxygen isotope buffering of the HC[O.sup.-.sub.3] reservoir during calcite precipitation. Both modern and Holocene speleothem calcite from Barbados, sampled temporally along the growth axis, shows similar positive [delta][sup.13]C versus [delta][sup.18]O slopes. These results, along with the spatial variations in glass plate calcite carbon and oxygen isotope compositions, suggest that the isotopic composition of the Holocene speleothems is in part controlled by non-equilibrium isotope effects. In addition, there is a correlation between stalactite length and oxygen and carbon isotope ratios of calcite precipitated on the corresponding stalagmite and glass plate, which may be due to [sup.13]C and [sup.18]O enrichment of the HC[O.sup.-.sub.3] reservoir during C[O.sub.2] degassing--calcite precipitation along the overhanging stalactite. We compiled 165 published speleothem stable isotope records with a global distribution and found that most of these records show a positive covariation between [delta][sup.13]C and [delta][sup.18]O values. Speleothem stable isotope records may be influenced by kinetic isotope effects such that temperature-controlled equilibrium fractionation models alone cannot directly explain the significance of the variations in these records. Advancing the interpretation of these records requires the calibration of cave environmental conditions with the non-equilibrium isotope effects that cause [delta][sup.13]C and [delta][sup.18]O covariations in speleothems. Keywords: kinetic isotope effects, speleothems, oxygen isotopes, carbon isotopes, non-equilibrium, Barbados.

A critical review of the stable isotope paleoaltimetry is presented. Stable isotope studies of authigenic minerals can help useful inferences on paleotopography, with uncertainties that critically depend on a detailed understanding of local-to global-scale paleoclimate during the time interval of interest.

The sulfuric acid speleogenesis (SAS) model was introduced in the early 1970s from observations of Lower Kane Cave, Wyoming, and was proposed as a cave-enlargement process due to primarily [H.sub.2]S autoxidation to sulfuric acid and subaerial replacement of carbonate by gypsum. Here we present a reexamination of the SAS type locality in which we make use of uniquely applied geochemical and microbiological methods. Little [H.sub.2]S escapes to the cave atmosphere, or is lost by abiotic autoxidation, and instead the primary [H.sub.2]S loss mechanism is by subaqueons sulfur-oxidizing bacterial communities that consume [H.sub.2]S. Filamentous 'Epsilonproteobacteria' and Gammaproteobacteria, characterized by fluorescence in situ hybridization, colonize carbonate surfaces and generate sulfuric acid as a metabolic byproduct. The bacteria focus carbonate dissolution by locally depressing pH, compared to bulk cave waters near equilibrium or slightly supersaturated with calcite. These findings show that SAS occurs in subaqueons environments and potentially at much greater phreatic depths in carbonate aquifers, thereby offering new insights into the microbial roles in subsurface karstification. Keywords: cave, hydrogen sulfide, geomicrobiology, sulfur-oxidizing bacteria, fluorescence in situ hybridization, carbonate dissolution.

Strontium isotopes are a unique tool to study soil-erosion dynamics. Changes in Sr isotope ratios ([87.sup]Sr/[.sup.86]Sr) provide a record of late Quaternary landscape denudation of the Edwards Plateau of central Texas, United States. The use of Sr isotopes as a tracer for soil erosion is based on the observation that, in central Texas, the [sup.87]Sr/[sup.86]Sr ratio of soil correlates with soil thickness. Plants and animals express the [sup.87]Sr/[sup.86]Sr ratio of exchangeable Sr in the soil. Therefore, we use changes in Sr isotope ratios through a well-dated stratigraphic sequence of fossil plants and animals in Hall's Cave, Kerr County, Texas, as a proxy for temporal changes in soil thickness. By using this record we are able to characterize late Quaternary climate-driven soil-erosion dynamics on the Edwards Plateau. We find that continuous erosion removed at least 180 cm of soil at a constant minimum rate of 11 cm/k.y.; this continuous phase of erosion ended ca. 5 ka. The Sr isotope record of soil erosion is consistent with late Quaternary environmental change in central Texas that has been independently modeled by using local and regional climate records. However, the rate of this climate-driven soil-erosion event was an order of magnitude slower than recent soil erosion caused by human land use. These results link erosion to century- to millennial-scale climate change and are cautionary evidence that even greater landscape degradation may result from coincident climatic variability and anthropogenic influences. Keywords: soil erosion, strontium, isotopes, Edwards Plateau, Quaternary.

A >10-m.y.-long sequence of ratite (e.g., ostrich) eggshells from Siwalik Group sedimentary deposits of northern Pakistan and India shows a dramatic (approximately 8 per thousand) increase in the Delta13C in biomineralogic calcite by approximately 4 Ma. Values of Delta13C from ratite eggshell carbonate older than 7 Ma are about the same as those from carbonate from contemporaneous fossil mammal tooth enamel and paleosols. However, after 4 Ma, the ratite eggshell carbonate Delta13C values are approximately 5 per thousand less than these coexisting materials. These findings are evidence of the development of a C3-C4 vegetative mosaic probably mirroring the sedimentologic-edaphic mosaic of the aggrading alluvial plain of the Siwalik depositional system.

Color determination of soil evidence is often done by visual comparison to soil color charts. A handheld spectrophotometer was tested with representative materials for its suitability for forensic soil characterization. Instrumental colorimetry provides accurate colorimetry with ~10‐fold better precision than a soil color chart. The minimum sample size for accurate color determination was between 0.02 and 0.04 mg of fine soil for the specific instrument tested. Reporting colors in the L*a*b* space permits quantification of ΔE00, a measure of perceptible color difference, could enable objective quantification of small color differences and thresholds for forensic soil comparisons. A ΔE00 greater than ~ 3.5 to 6 likely indicates disparate soil sources in a forensic comparison, in the absence of confounding factors like sample alteration. Despite the superior precision of instrumental colorimetry, this approach is inappropriate for samples which are mottled at an inseparable scale, attached to a substrate, or too small for instrumental measurement. [ABSTRACT FROM AUTHOR]

The authors have investigated bacterial communities from filamentous microbial mats from sulfidic cave springs. They have identified distinct epsilonproteobacterial filament groups within the microbial mats in the cave via the use of the full-cycle rRNA approach including quantitative fluorescence in situ hybridization.

RATIONALE High-temperature, conversion-reduction (HTC) systems convert hydrogen and oxygen in materials into H2 and CO for δ2H and δ18O measurements by isotope ratio mass spectrometry. HTC of nitrogen- and sulfur-bearing materials produces unintended byproduct gases that could affect isotope analyses by: (1) allowing isotope exchange reactions downstream of the HTC reactor, (2) creating isobaric or co-elution interferences, and (3) causing deterioration of the chromatography. This study characterizes these HTC byproducts. METHODS A HTC system (ThermoFinnigan TC/EA) was directly connected to a gas chromatograph/quadrupole mass spectrometer in scan mode ( m/z 8 to 88) to identify the volatile products generated by HTC at conversion temperatures of 1350 °C and 1450 °C for a range of nitrogen- and sulfur-bearing solids [keratin powder, horse hair, caffeine, ammonium nitrate, potassium nitrate, ammonium sulfate, urea, and three nitrated organic explosives (PETN, RDX, and TNT)]. RESULTS The prominent HTC byproduct gases include carbon dioxide, hydrogen cyanide, methane, acetylene, and water for all nitrogen-bearing compounds, as well as carbon disulfide, carbonyl sulfide, and hydrogen sulfide for sulfur-bearing compounds. The 1450 °C reactor temperature reduced the abundance of most byproduct gases, but increased the significant byproduct, hydrogen cyanide. Inclusion of a post-reactor chemical trap containing Ascarite II and Sicapent, in series, eliminated the majority of byproducts. CONCLUSIONS This study identified numerous gaseous HTC byproducts. The potential adverse effects of these gases on isotope ratio analyses are unknown but may be mitigated by higher HTC reactor temperatures and purifying the products with a purge-and-trap system or with chemical traps. Published in 2013. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Microbial mats in sulfidic cave streams offer unique opportunities to study redox-based biogeochemical nutrient cycles. Previous work from Lower Kane Cave, Wyoming, USA, focused on the aerobic portion of microbial mats, dominated by putative chemolithoautotrophic, sulfur-oxidizing groups within the Epsilonproteobacteria and Gammaproteobacteria. To evaluate nutrient cycling and turnover within the whole mat system, a multidisciplinary strategy was used to characterize the anaerobic portion of the mats, including application of the full-cycle rRNA approach, the most probable number method, and geochemical and isotopic analyses. Seventeen major taxonomic bacterial groups and one archaeal group were retrieved from the anaerobic portions of the mats, dominated by Deltaproteobacteria and uncultured members of the Chloroflexi phylum. A nutrient spiraling model was applied to evaluate upstream to downstream changes in microbial diversity based on carbon and sulfur nutrient concentrations. Variability in dissolved sulfide concentrations was attributed to changes in the abundance of sulfide-oxidizing microbial groups and shifts in the occurrence and abundance of sulfate-reducing microbes. Gradients in carbon and sulfur isotopic composition indicated that released and recycled byproduct compounds from upstream microbial activities were incorporated by downstream communities. On the basis of the type of available chemical energy, the variability of nutrient species in a spiraling model may explain observed differences in microbial taxonomic affiliations and metabolic functions, thereby spatially linking microbial diversity to nutrient spiraling in the cave stream ecosystem. [ABSTRACT FROM AUTHOR]

To date, little effort has been devoted to understanding the nature of streamfiow from dryland catchments where springs are found, and little is known about how changes in vegetation may alter that streamfiow. But where they do occur in drylands, springs are important—ecologically as well as hydrologically. Areas that naturally support spring flow, such as those having an underlying karst geology, hold the most promise for increasing streamfiow through control of woody plants. For rangelands, this possibility is a particularly appealing one. However, few studies have documented that such a method is effective (except in Mediterranean climates). For this reason, we studied runoff generation for a site on the Edwards Plateau of Texas: a first-order (19-ha) rangeland catchment supplied with intermittent streamfiow from a spring at its base. Using hydrometric as well as isotopic characterization, we evaluated the extent to which runoff changed following removal of most of the woody plant cover (predominantly Ashe juniper). After monitoring streamfiow for 4 years (two before plant removal and two following removal), we found that (1) streamfiow increased following removal of juniper, by about 46 mm annually, except during the summer; (2) for the 4 years of observation, runoff made up about 22% of the water budget, with baseflow from the spring accounting for about half the total flow; and (3) hydrograph separation analysis conducted for two events following juniper removal indicated that pre-event water made up 25% and 50% of the runoff (these numbers represent lower bounds for the percentage of water derived from the spring during storm events). These findings are important, not only because they add to our understanding of runoff generation from spring-fed catchments, but also in particular because they demonstrate that where springs are present, decreasing woody plant cover may augment runoff. [ABSTRACT FROM AUTHOR]