Natural concentrations of lead in ancient Arctic and Antarctic ice

Concentrations of Pb and K were determined in a series of veneer layers chiseled in sequence from the outside toward the center of each of the five 1500–5500yr old ice core sections that had been drilled in Greenland and Antarctic ice. They were analogs of very old ice samples analyzed earlier by Herronet al. (1977) and Craginet al. (1975), who reported high concentrations of Pb in them. Lead contamination, existing at exterior concentrations of about 10⁶ ng/kg ice, had intruded to the centers of the cores, establishing interior values of at least 1.4 ng/kg ice in three electromechanically drilled Camp Century core sections taken from fluid filled drill holes. Corresponding Pb concentration changes were 3 × 10⁴ ng/kg ice to 1.2 ng/kg ice in two thermally drilled New Byrd Station core sections taken from non-fluid filled drill holes. Contamination made the lowest center concentrations serve only as upper limits to the original concentrations of Pb in the ice.Potassium concentrations decreased from exterior values of about 5 × 10⁵ ng/kg ice to an interior value of 2 × 10³ ng/kg ice in the Camp Century core sections and from 8 × 10⁴ ng/kg ice to 9 × 10² ng/kg ice in New Byrd Station core sections. Potassium contamination effects were not large within the central portions of the cores.These data verify earlier findings by Murozumiet al. (1969) and extend to a broader geographical significance the general validity of their observation of a ~ 300-fold increase of Pb concentrations in the Greenland ice sheet during the past 3000 yr. Our findings refute claims by Herronet al. (1977) and Craguinet al. (1975) that 100-fold excesses of natural Pb exist in 800 yr old Greenland ice above levels contributed by silicate dusts. Our new data also show that average Pb concentrations of 26 ng Pb/kg ice, claimed by Boutron and Lorius (1979) to be natural and present for 60 yr in snow strata in Antarctica, did not exist in old Antarctic ice, and that Pb concentrations have increased at least 10-fold in that ice during the past century.Virtually all of the present day ~300-fold excess of Pb above natural levels in Greenland ice can be shown to be caused by industrial Pb emissions to the atmosphere on the basis of the following factors: (1) the historic increase of Pb in snow strata coincides with the historic increase of industrial Pb production and atmospheric emissions (2) mass inventories of industrial emissions can account for the excess Pb in polar snow (3) new quantitative measurements of Pb emissions from volcanic plumes by Buat-Menard and Arnold (1978), Pattersonet al. (1981), and Buat-Menardet al. (1981), and from sea spray by Ng and Patterson (1981) and Settle and Patterson (1981). show that these natural sources cannot account for 99% of the excess Pb above contributions by silicate dusts observed today in the atmosphere; and (4) the historic increase of Pb in snow strata is paralleled by analogous increases of excess Pb shown by isotopic tracers to be industrial in water-laid sediments in a remote continental region (Shirahataet al., 1980). It is now known, however, that snows display about a 10-fold greater excess of industrial Pb above crustal silicate concentrations than exists in the air above the snows.     

Glacial morphology and post-glacial contourites in northern Prince Gustav Channel (NW Weddell Sea,Antarctica)

We present the results of a marine geophysical investigation of the northern Prince Gustav Channel. By comparative analysis of multibeam bathymetric data, single channel seismic reflection profiles, underway chirp sonar data, ADCP current data and sediment coring, we define the main morphological elements of the area. In particular we define the glacial morphogenesis in relation to the excavation of inner shelf basins and troughs along structural discontinuities and lithologic boundaries. We identify streamlined surfaces that testify to the grounding of ice and past ice flow directions. These glacial forms are found only on glacial tills preserved in the deepest part of the basins, while net erosion to bedrock has occurred elsewhere. Since the Last Glacial Maximum (LGM), the relict glacial morphology has been draped by hemipelagic and diatomaceous mud, and bottom currents have played a major role in focusing sedimentation within small depocentres, that we define as contouritic drifts. Based on shallow sediment architecture and supported by direct measurements, we propose that the direction of bottom water flow is from the outer shelf into the Prince Gustav channel as a result of a combination of tidal currents and ice shelf-related thermohaline circulation.     

How can remote sensing contribute in groundwater modeling?

Groundwater resources assessment, modeling and management are hampered considerably by a lack of data, especially in semi-arid and arid environments with a weak observation infrastructure. Usually, only a limited number of point measurements are available, while groundwater models need spatial and temporal distributions of input and calibration data. If such data are not available, models cannot play their proper role in decision support as they are notoriously underdetermined and uncertain. Recent developments in remote sensing have opened new sources for distributed spatial data. As the relevant entities such as water fluxes, heads or transmissivities cannot be observed directly by remote sensing, ways have to be found to link the observable quantities to input data required by the model. An overview of the possibilities for employing remote-sensing observations in groundwater modeling is given, supported by examples in Botswana and China. The main possibilities are: (1) use of remote-sensing data to create some of the spatially distributed input parameter sets for a model, and (2) constraining of models during calibration by spatially distributed data derived from remote sensing. In both, models can be improved conceptually and quantitatively.     

The modern distribution of chironomid sub-fossils (Insecta: Diptera) in the Sierra Nevada, California: Potential for paleoclimatic reconstructions

Surface lake sediment was recovered from 57 lakes along an elevation gradient in the central, eastern Sierra Nevada of California. The surface sediment was analysed for subfossil chironomid remains in order to assess the modern distribution of chironomids in the region. The lakes sampled for the calibration dataset were between 2.0 and 40.0 m in depth, spanned an altitudinal gradient of 1360 m and a surface water temperature gradient of approximately 14 °C. Redundancy analysis (RDA) identified that five of the measured environmental variables – surface water temperature, elevation, depth, strontium, particulate organic carbon – accounted for a statistically significant amount of the variance in chironomid community composition. Quantitative transfer functions, based on weighted-averaging (WA), partial least squares (PLS) and weighted-averaging partial least squares (WA-PLS), were developed to estimate surface water temperature from the chironomid assemblages. The best model was a WA model with classical deshrinking, which had a relatively high coefficient of determination (r² = 0.73), low root mean square error of prediction (RMSEP = 1.2 °C) and a low maximum bias (0.90 °C). The results from this study suggest that robust quantitative estimates of past surface water temperature can be derived from the application of these models to fossil chironomid assemblages preserved in late-Quaternary lake sediment in this region.     

Application of sedimentary and chronological analyses to refine the depositional context of a Late Pleistocene vertebrate deposit,Naracoorte, South Australia

Cave deposits of infill sediments and associated vertebrate fossils provide a valuable source of information on terrestrial palaeoenvironments, climatic conditions and palaeocommunities. In the deposits of the Naracoorte Caves World Heritage Area, such records span the last 500 ka and are renowned for their rich, diverse vertebrate assemblages. Previous research into the Grant Hall deposit of Victoria Fossil Cave suggested that it may preserve the only peak last interglacial (ca. 125 ka) faunal community within the World Heritage Area. The current work tested this existing model for the age of faunal remains from Grant Hall using multiple techniques. Physical and geochemical properties of the visually homogeneous sediments were analysed at regular intervals through the sequence to establish meaningful stratigraphic divisions and sediment provenance. Optically stimulated luminescence dating of individual quartz grains indicates that sediments accumulated in Grant Hall from 93 ± 8 to 70 ± 5 ka. Minimum ages provided by U/Th dating of fossil teeth (72.3 ± 2.2 to 38.2 ± 0.8 ka) are consistent with the luminescence chronology, and show that the deposit represents a more recent faunal accumulation than previously modelled for the site. U/Th ages on calcite straws within the deposit are significantly older than the sediments and fossil teeth (>500 to 186.4 ± 1 ka). As such they provide no further constraint on the chronology of the deposit but do indicate that speleothem deposition was active over much of the Middle Pleistocene. Sedimentary analyses resulted in the identification of five depositional units, contrasting with previous divisions which were based only on visual observation of the sedimentary sequence. Sediments within each unit are broadly classified as sandy silts with soil structures and may be indirectly derived from the lunettes of nearby Bool Lagoon, although their ultimate provenance is unknown. As a result of this work, palaeoenvironmental reconstruction based on fossil remains in the deposit may be more accurately related to prevailing climatic and environmental conditions at the time of accumulation. It also contributes to an understanding of the temporal occurrence of regional vertebrate faunas through the Late Pleistocene, reinforcing the value of developing stratigraphically constrained chronologies for cave deposits based on multiple techniques.     

Activation of Persulfate by Surfactants under Acidic and Basic Conditions

Activated persulfate is a commonly used oxidant source used for in situ chemical oxidation (ISCO) for remediation of subsurface contamination. Surfactants are sometimes used in ISCO to desorb contaminants and dissolve nonaqueous phase liquids (NAPLs). The potential activation of persulfate by such surfactants was investigated, and the reactive oxygen species generated by persulfate in the presence of anionic, nonionic, and cationic surfactants were determined. Twenty surfactants were screened; most activated persulfate to generate reductants + nucleophiles at acidic and basic pH. The most reactive anionic, nonionic, and cationic surfactants (Lankropol 4500, polyethylene glycol 400, and Ethoduomeen T/25) were investigated in more detail. All three surfactants activated persulfate; however, the cationic surfactant showed the most potential for persulfate activation with high fluxes of hydroxyl radical and reductants + nucleophiles. The results of this research demonstrate that surfactants added to ISCO systems often activate persulfate to generate reductants at both acidic and basic pH, and hydroxyl radical at basic pH. These findings provide a new paradigm for persulfate activation in surfactant in situ chemical oxidation (SISCO) systems; pH regimes >11 may not be necessary for persulfate activation resulting in cost savings and potentially more effective activation of persulfate.     

Observations of asteroids with ALMA

Thermal observations of large asteroids at millimeter wavelengths have revealed high amplitude rotational lightcurves. Such lightcurves are important constraints on thermophysical models of asteroids, and provide unique insight into the nature of their surface and subsurface composition. A better understanding of asteroid surfaces provides insight into the composition, physical structures, and processing history of these surviving remnants from the formation of our solar system. In addition, detailed observations of the larger asteroids, accompanied by thermophysical models with appropriate temporal and spatial resolution, promise to decrease uncertainties in their flux predictions. Of particular interest are the near-Earth objects, which can be observed at large phase angles, permitting better assessment of the thermal response of their unilluminated surfaces. The high sensitivity of ALMA will enable us to detect many small bodies in all the major groups, to obtain lightcurves for a large sample of main-belt and near-Earth objects, to resolve the surfaces of some large objects, and to separate the emission from primary and secondary objects in binary pairs. In addition to the science goals of asteroid studies, these bodies may also prove useful operationally because those with known shapes and well-characterized lightcurves could be employed for flux calibration by ALMA and other high frequency instruments.     

Systematic Errors Induced by the Elliptical Power-law model in Galaxy-Galaxy Strong Lens Modeling

The elliptical power-law model of the mass in a galaxy is widely used in strong gravitational lensing analyses.However,the distribution of mass in real galaxies...     

The geography of mercury and PCBs in North Carolina's local seafood

Mercury and PCBs are used by non-governmental organizations and federal agencies to inform seafood safety recommendations. Pollution dynamics suggest recommendations on the national scale may be too large to be accurate. We tested softshell and hardshell blue crab, white and pink shrimp, oysters, clams, spot, and mullet from fishers in each of the three North Carolina fishery districts. We measured mercury using EPA method 7473 and PCBs using a commercially available ELISA kit. Over 97% of samples were below the Environmental Protection Agency levels of concern for both mercury and PCBs. Mercury and PCBs have different spatial dynamics, but both differ significantly by water body, suggesting that seafood safety recommendations should occur by water body instead of at the national scale. This finding supports previous research suggesting that differences in water chemistry, terrestrial influence, and flushing time in a particular water body control the contaminant load in locally resident species.     

Population Structure of Adult Blue Crabs, <Emphasis Type="Italic">Callinectes sapidus</Emphasis>, in Relation to Physical Characteristics in Barnegat Bay,New Jersey

Blue crabs (Callinectes sapidus) are an important species in coastal or lagoonal estuaries where adult population characteristics may differ as compared to drowned-river estuaries. Barnegat Bay, in southern New Jersey, is composed of two large embayments: one without and one with a salinity gradient. We tested the influence of physical characteristics on the abundance, sex ratio, and size of adult blue crabs and examined variation in measures of reproductive potential (e.g., sperm stores) in both sexes in Barnegat Bay from June to September, 2008–2009. Population structure was distinct between the embayments due to sex-specific responses to salinity: male abundance was negatively correlated with salinity whereas adult females were more abundant in high salinity because of proximity to Barnegat Inlet. This produced high sex ratios in low salinity areas and low sex ratios in high salinity areas. Summer was a growing season for adult males while in late summer-early fall, juvenile males recruited to the adult size class. The spawning season lasted from May to August and ovigerous females were concentrated near the inlets. Information on female sperm stores and ovarian development identified two cohorts of adult females: females that will spawn in the current summer and females that will not spawn until the following summer. Thus, not all adult females near the spawning grounds were members of the current spawning stock. This suggests that annual estimates of spawning stock size which overlook the proximity of females to spawning are overestimating the current spawning stock in Barnegat Bay and other estuaries.