Detailed mineralogy and petrology of highly shocked poikilitic shergottite Northwest Africa 6342

Northwest Africa (NWA) 6342 is an intermediate, poikilitic shergottite, found in Algeria in 2010. It is comprised of two distinct petrographic areas; poikilitic domains with rounded Mg‐rich olivine chadacrysts enclosed by large low‐Ca pyroxene oikocrysts, and a nonpoikilitic domain mainly comprised of subhedral olivine and vesicular recrystallized plagioclase. Oxygen fugacity conditions become more oxidizing during crystallization from the poikilitic to the nonpoikilitic domain (QFM?3.0 to QFM?2.2). As such, it is likely that NWA 6342 experienced a two‐stage (polybaric) crystallization history similar to that of the enriched poikilitic shergottites. NWA 6342 also experienced relatively high levels of shock metamorphism in comparison to most other poikilitic shergottites as evidenced by the fine‐grained recrystallization texture in olivine, as well as melting and subsequent crystallization of plagioclase. The recrystallization of plagioclase requires an extended period of postshock thermal metamorphism for NWA 6342 and similarly shocked intermediate poikilitic shergottites NWA 4797 and Grove Mountains 99027 most likely due to launch from Mars. The similarities in petrology, chemistry, and shock features between these three meteorites indicate that they have similar crystallization and shock histories; possibly originating from the same source area on Mars.     

PCB exposure in sea otters and harlequin ducks in relation to history of contamination by the Exxon Valdez oil spill

Exposure to contaminants other than petroleum hydrocarbons could confound interpretation of Exxon Valdez oil spill effects on biota at Prince William Sound, Alaska. Hence, we investigated polychlorinated biphenyls (PCBs) in blood of sea otters and harlequin ducks sampled during 1998. PCB concentrations characterized by lower chlorinated congeners were highest in sea otters from the unoiled area, whereas concentrations were similar among harlequin ducks from the oiled and unoiled area. Blood enzymes often elevated by xenobiotics were not related to PCB concentrations in sea otters. Only sea otters from the unoiled area had estimated risk from PCBs, and PCB composition or concentrations did not correspond to reported lower measures of population performance in sea otters or harlequin ducks from the oiled area. PCBs probably did not influence limited sea otter or harlequin duck recovery in the oiled area a decade after the spill.     

Fluoride in Nebraska's Ground Water

Fluoride concentrations in ground water are generally low but play an important role in dental health. This study evaluates the vertical and spatial distribution of fluoride in Nebraska's ground water and examines the geological and geochemical processes that control its concentration. Data from 1794 domestic wells sampled by the Nebraska Department of Health and Human Services. Regulation, and Licensure (NDOH) had a range of fluoride concentrations from <0.1 to 2.6 mg/L. and a median concentration of 0.3 mg/L. The median fluoride concentrations for Nebraska's 13 ground water regions varied from 0.2 to 0.7 mg/L. In each of these regions, individual wells may have either insufficient or overabundant F concentrations; we recommend that individual private water systems be tested for fluoride. Based on these data, system-specific recommendations can be made regarding the necessity for fluoridation.
Geochemical data indicated that the majority of fluoride occurs as F. Dissolution of F-bearing minerals controls fluoride occurrence. Apatite plus minor amounts of fluorite along with significant ground water residence times are the primary factors controlling F in the water from the Dakota Formation in Knox County, as well as in other parts of northeastern Nebraska. In western and southwestern Nebraska, dissolution of volcanic glass is the most probable source of F Long residence times plus fluorite also may contribute to the F concentrations in the Chadron Formation.     

Controls on carbonate platform architecture and reef recovery across the Palaeozoic to Mesozoic transition: A high-resolution analysis of the Great Bank of Guizhou

Carbonate platforms spanning intervals of global change provide an opportunity to identify causal links between the evolution of marine environment and depositional architecture. This study investigates the controls on platform geometry across the Palaeozoic to Mesozoic transition and yields new stratigraphic and palaeoenvironmental constraints on the Great Bank of Guizhou, a latest Permian to earliest Late Triassic isolated carbonate platform in the Nanpanjiang Basin of south China. Reconstruction of platform architecture was achieved by integrating field mapping, petrography, biostratigraphy, satellite imagery analysis and δ¹³C chemostratigraphy. In contrast to previous interpretations, this study indicates that: (i) the Great Bank of Guizhou transitioned during Early Triassic time from a low-relief bank to a platform with high relief above the basin floor (up to 600 m) and steep slope angles (preserved up to 50°); and (ii) the oldest-known platform-margin reef of the Mesozoic Era grew along steep, prograding clinoforms in an outer-margin to lower-slope environment. Increasing platform relief during Early Triassic time was caused by limited sediment delivery to the basin margin and a high rate of accommodation creation driven by Indosinian convergence. The steep upper Olenekian (upper Lower Triassic) slope is dominated by well-cemented grainstone, suggesting that high carbonate saturation states led to syndepositional or rapid post-depositional sediment stabilization. Latest Spathian reef initiation coincided with global cooling following Early Triassic global warmth. The first Triassic framework-building metazoans on the Great Bank of Guizhou were small calcareous sponges restricted to deeper water settings, but early Mesozoic reef builders were volumetrically dominated by Tubiphytes, a fossil genus of uncertain taxonomic affinity. In aggregate, the stratigraphic architecture of the Great Bank of Guizhou records sedimentary response to long-term environmental and biological recovery from the end-Permian mass extinction, highlighting the close connections among marine chemistry, marine ecosystems and carbonate depositional systems.     

Pump‐and‐Treat Groundwater Remediation Using Chlorine/Ultraviolet Advanced Oxidation Processes

Comparative studies of the use of chlorine/ultraviolet (Cl₂/UV) and hydrogen peroxide/ultraviolet (H₂O₂/UV) Advanced oxidation processes (AOPs) to remove trichloroethylene (TCE) from groundwater in a pump‐and‐treat application were conducted for the first time at the full‐scale operational level at two water treatment facilities in Northern California. In these studies, aqueous chlorine replaced hydrogen peroxide in the AOP treatment step, where the oxidant is exposed to UV light to produce highly reactive radical species that degrade groundwater contaminants. TCE removal rates as a function of initial chlorine dose and pH were then determined. At the site where the natural pH of the water was 7.1, TCE was removed (to a concentration of less than 0.5 µg/L) for nearly every chlorine dose point tested, and pH adjustment slightly enhanced the treatment process at this facility. The second site had a high natural pH of 7.7, and here, TCE was not completely removed for any chlorine dose up to 5.7 mg/L, although TCE removal did increase when the chlorine dose increased between 0.9 and 3.6 mg/L. Residual TCE remaining in the water post‐Cl₂/UV was readily removed using active carbon filtration, which is part of the overall treatment train at this facility. These studies also verified that Cl₂/UV AOP did not interfere with the photolysis of N‐nitrosodimethylamine or result in an effluent acutely toxic toward Ceriodaphnia dubia. Comparative economic analysis revealed that the chemical costs associated with Cl₂/UV AOP were 25 to 50% of the costs associated with in place H₂O₂/UV AOP treatment.     

Microbial sources of intact polar diacylglycerolipids in the Western North Atlantic Ocean

Intact polar membrane lipids are essential components of microbial membranes and recent work has uncovered a diversity of them occurring in the ocean. While it has long been understood that lipid composition varies across microbial groups, the microbial origins of the intact polar lipids in the surface ocean remain to be fully explained. This study focused on identifying the microbial sources of intact polar diacylglycerolipids (IP-DAGs) in the surface waters of the western North Atlantic Ocean. We used three approaches to define these microbial sources: (i) ¹³C tracing to identify photoautotrophic and heterotrophic production of the major classes of IP-DAGs, (ii) cell sorting flow cytometry of Prochlorococcus, Synechococcus and heterotrophic bacteria to determine IP-DAG composition and (iii) regrowth incubations targeting IP-DAG production by heterotrophic bacteria. Stable isotope tracing indicated that sulfoquinovosyldiacylglycerol (SQDG) and diacylglyceryl-trimethyl-homoserine (DGTS) were produced predominantly by photoautotrophs, while phosphatidylglycerol (PG) production was dominated by heterotrophic bacteria. Of the cells sorted with flow cytometry, Prochlorococcus and Synechococcus were found to have abundant glycolipids, while heterotrophic bacteria were dominated by phospholipids. The regrowth incubations showed that the growth of heterotrophic bacteria correlated with an increase in the concentration of PG, phosphatidylethanolamine (PE) and monoglycosyldiacylglycerol (MGDG). The finding of MGDG in heterotrophic bacteria differs from previous work, which had asserted that the membranes of heterotrophic bacteria in this environment were composed entirely of phospholipids. Overall, our findings indicate that phytoplankton are the primary source of SQDG and DGTS, while heterotrophic bacteria are the dominant source of PG, making these three compounds promising biomarkers for the study of microbes in the surface ocean.     

Trends and Variability in Total Ozone from a Mid-Latitude Southern Hemisphere Site: The Melbourne Dobson Record 1978–2012

Abstract

The Australian Bureau of Meteorology maintains a number of long-running Dobson measurement programs, among the few in southern hemisphere mid-latitudes. Data from the Melbourne site (the Melbourne/Airport World Ozone and Ultraviolet Radiation Data Centre (WOUDC) station was originally located at Aspendale, then moved to the city centre, and finally to Melbourne Airport) from 1978 to 2012 have recently been reviewed and re-evaluated. These data are analyzed using multi-linear regression and also by application of an 11-year running mean. Satellite data from the Merged Ozone Dataset are also used for comparison with the Dobson results. We show that the Quasi-Biennial Oscillation (QBO) plays a major role in winter and spring once phase is taken into account by month. We also show that the three so-called “classical” proxies (QBO, solar cycle, and Equivalent Effective Stratospheric Chlorine (EESC)) alone are able to give a good fit to ozone for Melbourne and, more generally, the southern mid-latitudes for most months of the year, in contrast with the case in the northern hemisphere where dynamical variation plays a much more important role. Correspondingly, the smoothed Melbourne Dobson time series shows a high correlation to EESC.