A microcontroller‐based data‐logger design for seasonal hydrochemical studies

Detailed studies of seasonal patterns of karst processes are rare in remote regions with limited winter access. An important aspect of erosional and environmental processes is how these change over time, and how they relate to annual cycles of temperature, precipitation and runoff. Such measurements have consistently proved difficult in remote alpine areas, resulting in a paucity of continuous data from these environments. An automated data‐logger installation designed to perform under difficult conditions, including limited sunlight for solar recharge, heavy snowfall and disturbance by bears, has provided four years of data at a 2‐hour sampling interval of electrical conductivity (used to predict solute concentration), water level (used to predict discharge) and temperature, at the Marble Mountains karst resurgence, California, USA. Copyright © 2001 John Wiley & Sons, Ltd.     

Application of electromagnetic techniques in survey of contaminated groundwater at an abandoned mine complex in southwestern Indiana,U.S.A.

In part of a large abandoned mining complex, electromagnetic geophysical surveys were used along with data derived from cores and monitoring wells to infer sources of contamination and subsurface hydrologic connections between acidic refuse deposits and adjacent undisturbed geologic materials.Electrical resistivity increases sharply along the boundary of an elevated deposit of pyritic coarse refuse, which is highly contaminated and electrically conductive, indicating poor subsurface hydrologic connections with surrounding deposits of fine refuse and undisturbed glacial material. Groundwater chemistry, as reflected in values of specific conductance, also differs markedly across the deposit's boundary, indicating that a widespread contaminant plume has not developed around the coarse refuse in more than 40 yr since the deposit was created. Most acidic drainage from the coarse refuse is by surface runoff and is concentrated around stream channels.Although most of the contaminated groundwater within the study area is concentrated within the surficial refuse deposits, transects of apparent resistivity and phase angle indicate the existence of an anomalous conductive layer at depth (>4 m) in thick alluvial sediments along the northern boundary of the mining complex. Based on knowledge of local geology, the anomaly is interpreted to represent a subsurface connection between the alluvium and a flooded abandoned underground mine.     

The Antarctic achondrite ALHA 76005: a polymict eucrite

ALHA 76005 is a basaltic achondrite containing few. if any, orthopyroxenes. Its bulk major and trace element composition is like that of a non-cumulate eucrite, and unlike that of a howardite. It contains a variety of igneous clasts which differ in their textures, pyroxene/plagioclase ratios and pyroxene and plagioclase compositions. One clast, No. 4, was found to have the REE pattern of a cumulate eucrite and an oxygen isotopic composition different from that of the bulk meteorite. Both the chemical and oxygen isotopic composition of clast No. 4 suggest that it was derived from a source different from its host. These observations lead to the conclusion that ALHA 76005 is a polymict eucrite.     

The Kenna ureilite: an ultramafic rock with evidence for igneous,metamorphic, and shock origin

The Kenna ureilite was found in February, 1972 near the town of Kenna, Roosevelt County, New Mexico U.S.A., weighed 10.9 kg, and measured 26.7 × 14.7 × 14.2 cm; it is the seventh known ureilite. The meteorite is composed of xenoblastic olivine (Fo_79.2), commonly rimmed by forsterite (Fo₉₉), and pigeonite (En₇₃Wo₉Fs₁₈), in a volumetric ratio of 3:1, set in a matrix of three carbon polymorphs (graphite, lonsdaleite, and diamond) plus nickel-iron metal and troilite. Some thin metalliferous veins penetrating silicate grains contain secondary inclusions of melt with high-calcium clinopyroxene (high-Ca, Mg-rich augite to augite), andesine, K-feldspar, chromite, and siliceous CaO- and alkali-rich glasses of variable compositions.Textural, mineralogical and fabric information suggest a complex history for Kenna, involving igneous, metamorphic and shock processes. The rock appears to have originated as an ultramafic cumulate whose texture and structure was modified by adcumulus processes and by solution and redeposition in a weak deviatoric stress field. A strong mineral elongation lineation was produced during this high-temperature phase accompanied by mild plastic deformation of olivine on the system 0kl[100]. Superimposed on this original texture and fabric are processes resulting from light to moderate (50–250 kbar) shock deformation, as manifested by fracturing of the silicates, slip parallel to (001) in olivine, and twin and translation gliding parallel to (100) in the clinopyroxene. Lonsdaleite and diamond probably formed during this shock phase, which may be associated with the break-up of the parent body, but the relative time of introduction of the carbon-rich matrix is still unresolved.     

Error analysis of multi-wavelength sun photometry

The error terms involved in precision multi-wavelength sun photometry, as used to study atmospheric aerosols, are analyzed. The error terms treated include instrumental errors, calibration errors, and errors imposed by the atmosphere. It is shown that in order to derive accurate aerosol parameters, one must exercise great care in the photometer calibration. A procedure for accurate calibration is described, based on an intercalibration between extrapolations of the extraterrestrial solar spectral irradiance and irradiance of a standard lamp. Methods are described to assess, and reduce, uncertainties brought about by diffuse radiation in the photometer's field of view, temporal variations in aerosol optical depth, and gaseous absorption features at the operating wavelength. It is shown that if care is taken sun photometry can be used to derive monochromatic aerosol optical depth to an accuracy of several thousandths.     

Simultaneous measurement and inversion of surface wave dispersion and attenuation curves

Surface wave tests are non-invasive seismic techniques that have traditionally been used to determine the shear wave velocity (i.e. shear modulus) profile of soil deposits and pavement systems. Recently, Rix et al. [J. Geotech. Geoenviron. Engng 126 (2000) 472] developed a procedure to obtain near-surface values of material damping ratio from measurements of the spatial attenuation of Rayleigh waves. To date, however, the shear wave velocity and shear damping ratio profiles have been determined separately. This practice neglects the coupling between surface wave phase velocity and attenuation that arises from material dispersion in dissipative media. This paper presents a procedure to measure and invert surface wave dispersion and attenuation data simultaneously and, thus, account for the close coupling between the two quantities. The methodology also introduces consistency between phase velocity and attenuation measurements by using the same experimental configuration for both. The new approach has been applied at a site in Memphis, TN and the results obtained are compared with independent measurements.     

Stable carbon and oxygen isotopic variations in modern Rabdotus land snail shells in the southern Great Plains, USA, and their relation to environment

Variations of stable isotopic ratios of carbon (¹³C/¹²C) and oxygen (¹⁸O/¹⁶O) were investigated in modern shells of two species of Rabdotus land snails (R. dealbatus and R. alternatus) in the southern Great Plains. Geographic variation in relation to climate and vegetation, microgeographic variation, variability among individuals, and detailed records of seasonal variations within individual shells were studied. Stable carbon isotopic ratios in shell carbonate are primarily a function of the isotopic composition of the diet of the snails, as represented by the isotopic composition of shell organic matter. This in turn reflects the presence or absence of CAM (Crassulacean Acid Metabolism) or C₄ plants. Vegetation density may have a small effect on the carbon isotope ratios. Microgeographic variation (samples within 25 to 300 m) is greater than that seen across different climatic regions and points to very local control of isotopic variations, predominantly related to vegetation. Seasonal variations, as assessed through serial analysis of individual shells (up to 35 samples per shell), may provide a means for distinguishing between isotopic influences of perennial CAM vs. annual C₄ plants. Carbon isotopic variations in time-series of shells from a site provide a means of reconstructing temporal changes in environment and climate.Oxygen isotopic values of shell carbonate are uniform across the region and also show no significant microgeographic variation. The oxygen isotopic composition appears to be mainly a function of the rainwater isotopic composition, with no direct influence of rainfall amount or evaporative effects. The δ¹⁸O values are only 2‰ enriched relative to estimated equilibrium with rainwater. Variability is low (SD of 0.8‰ among sites), so the isotopic composition of fossil Rabdotus shells can provide a precise record of changes in the isotopic composition of rain over time.     

Reconstruction of Summer Temperatures in Interior Alaska from Tree-Ring Proxies: Evidence for Changing Synoptic Climate Regimes

Maximum latewood density and δ ¹³C discrimination of Interior Alaska white spruce were used to reconstruct summer (May through August) temperature at Fairbanks for the period 1800–1996, one of the first high-resolution reconstructions for this region. This combination of latewood density and δ ¹³C discrimination explains 59.9% of the variance in summer temperature during the period of record 1906–1996. The 200-yr. reconstruction is characterized by 7 decadal-scale regimes. Regime changes are indicated at 1816, 1834, 1879, 1916, 1937, and 1974, are abrupt, and appear to be the result of synoptic scale climate changes. The mean of summer temperature for the period of reconstruction (1800–1996) was 13.49 °C. During the period of instrument record (1903–1996) the mean of summer temperature was 13.31 °C for both the reconstruction and the recorded data. The coldest interval was 1916–1937 (12.62 ° C) and the warmest was 1974–1996 (14.23 °C) for the recorded data. The reconstruction differs from records of northern hemisphere temperatures over this period, especially because of Interior Alaska warm periods reconstructed from 1834 to 1851 (14.24 °C) and from 1862 to 1879 (14.19 °C) and because of the cool period in the early part of the 20th century (1917–1974). We show additional tree ring data that support our reconstruction of these warm periods. Alternate hypotheses involving autogenic effect of tree growth on the site, altered tree sensitivity, or novel combinations of temperature and precipitation were explored and while they cannot be ruled out as contributors to the anomalously warm 19th century reconstruction, they were not supported by available data. White spruce radial growth is highly correlated with reconstructed summer temperature, and temperature appears to be a reliable index of carbon uptake in this system.