Interference Testing for Atmospheric HOx Measurements by Laser-induced Fluorescence

Accurate OH and HO₂ (collectively called HO_x) measurements by laser-induced fluorescence (LIF) may be contaminated by spurious signals from interfering atmospheric chemicals or from the instrument itself. Interference tests must be conducted to ensure that observed OH signal originates solely from ambient OH and is not due to instrument artifacts. Several tests were performed on the Penn State LIF HO_x instrument, both in the laboratory and in the field. Theseincluded measurements of the instrument's zero signal by using either zero air or perfluoropropylene to remove OH, examination of spectral interferences from naphthalene, sulfur dioxide, and formaldehyde, and tests of interferences by addition of suspected interfering atmospheric chemicals, including ozone, hydrogen peroxide, nitrous acid, formaldehyde, nitric acid, acetone, and organic peroxy radicals (RO₂). All tests lacked evidence ofsignificant interferences for measurements in the atmosphere, including highly polluted urban environments.     

PCBs and organochlorine pesticides in Hector’s (Cephalorhynchus hectori hectori) and Maui’s (Cephalorhynchus hectori maui) dolphins

Polychlorinated biphenyls (PCBs) and organochlorine (OC) pesticide levels were determined in blubber samples collected from stranded and incidentally by-caught Hector’s (Cephalorhynchus hectori hectori) and Maui’s (Cephalorhynchus hectori maui) dolphins from New Zealand waters between 1997 and 2009. PCBs (45 congeners) and a range of OC pesticides including dieldrin, hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT), along with its metabolites DDE and DDD were determined. OC pesticides dieldrin, p,p′-DDE, p,p′-DDD and p,p′-DDT were present at the highest concentrations. Sum DDT concentrations ranged from 93.7 to 8210 (Mean = 1358, S.D = 1974) and 252.4 to 57,390 (Mean = 12,389, S.D = 18,161) μg/kg wet weight in females and males, respectively. Similarly, Σ45CB concentrations ranged from 45.5 to 981.3 (Mean = 333.2, S.D = 265.8) and 60.5 to 5574 (Mean = 1833, S.D = 1659) μg/kg wet weight in females and males, respectively. The transfer of ΣDDTs and summed PCBs (both as ΣICES7CBs and Σ45CBs) between a pregnant female and her unborn fetus was calculated at 5.7% and 4.3%, respectively. As the fetus was close to term, this likely represents the degree of placental transfer. Concentrations of OC pesticides determined in the present study are higher than those previously reported for Hector’s dolphins. Sum DDT and DDE/ΣDDT levels calculated reveal New Zealand’s legacy of DDT usage, particularly off the east coast of the South Island.     

Weathering of Oil in a Surficial Aquifer

The composition of crude oil in a surficial aquifer was determined in two locations at the Bemidji, MN, spill site. The abundances of 71 individual hydrocarbons varied within 16 locations sampled. Little depletion of these hydrocarbons (relative to the pipeline oil) occurred in the first 10 years after the spill, whereas losses of 25% to 85% of the total measured hydrocarbons occurred after 30 years. The C_6‐30 n‐alkanes, toluene, and o‐xylene were the most depleted hydrocarbons. Some hydrocarbons, such as the n‐C_10–24 cyclohexanes, tri‐ and tetra‐ methylbenzenes, acyclic isoprenoids, and naphthalenes were the least depleted. Benzene was detected at every sampling location 30 years after the spill. Degradation of the oil led to increases in the percent organic carbon and in the δ ¹³C of the oil. Another method of determining hydrocarbon loss was by normalizing the total measured hydrocarbon concentrations to that of the most conservative analytes. This method indicated that the total measured hydrocarbons were depleted by 47% to 77% and loss of the oil mass over 30 years was 18% to 31%. Differences in hydrocarbon depletion were related to the depth of the oil in the aquifer, local topography, amount of recharge reaching the oil, availability of electron acceptors, and the presence of less permeable soils above the oil. The results from this study indicate that once crude oil has been in the subsurface for a number of years there is no longer a “starting oil concentration” that can be used to understand processes that affect its fate and the transport of hydrocarbons in groundwater.     

Comparison of catchment and network delineation approaches in complex suburban environments: application to the Chaudanne catchment,France

Suburban areas are subject to strong anthropogenic modifications, which can influence hydrological processes. Sewer systems, ditches, sewer overflow devices and retention basins are introduced and large surface areas are sealed off. The knowledge of accurate flow paths and watershed boundaries in these suburban areas is important for storm water management, hydrological modelling and hydrological data analysis. This study proposes a new method for the determination of the drainage network based on time efficient field investigations and integration of sewer system maps into the drainage network for small catchments of up to 10 km². A new method is also proposed for the delineation of subcatchments and thus the catchment area. The subcatchments are delineated using a combination of an object‐oriented approach in the urban zone and geographical information system–based terrain analysis with flow direction forcing in the rural zone. The method is applied to the Chaudanne catchment, which belongs to the Yzeron river network and is located in the suburban area of Lyon, France. The resulting subcatchment map gives information about subcatchment response and contribution. The method is compared with six other automatic catchment delineation methods based on stream burning, flow direction forcing and calculation of subcatchments for inlet points. None of the automatic methods could correctly represent the catchment area and flow paths observed in the field. The watershed area calculated with these methods differs by as much as 25% from the area computed with the new method. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental and theoretical determination of concentration profiles and influence of particle characteristics in blowing snow

Snow drift transport may cause avalanches on the roads during the periods of snowfall and strong wind. To better understand the factors influencing transport we have developed a theoretical model. This model is based on the boundary layer theory, where the particle mass conservation is considered. Assuming that the saturation is reached, the concentration profile can be represented by a negative exponential law. By means of this analysis, the influence of particle characteristics is explored through the roles of threshold friction velocity and fall velocity. Using fluid mechanics laws, an analysis of the concentration profile resulting from the effect of the wind on a particle bed was also developed. For several velocities of flow and for different kinds of particles an experimental determination of the concentration profile was achieved. We used a laser visualisation and image processing technique to carry out these experiments. The obtained results fit with the values predicted by the theoretical model.     

Microstructural analysis and P–T conditions of the Azul megashear zone, Tandilia, Buenos Aires province, Argentina

A microstructural analysis was carried out on mylonitic rocks of the Azul megashear zone (AMSZ), Tandilia, which were formed in a range of metamorphic conditions from lower greenschist to amphibolite facies. Tailed porphyroclasts are common and mostly symmetric. Scarce asymmetric rotated porphyroclasts show both sinistral and dextral senses of shear. In sections parallel to the mylonitic foliation, porphyroclasts are round. The AMSZ is probably related to the late Transamazonian orogenic cycle and may be due to NNE–SSW-directed convergence. In weakly deformed protolith and protomylonites, quartz deforms by dynamic recrystallization, mainly subgrain rotation in dislocation creep Regime 2. K-feldspar porphyroclasts and plagioclase show scarce fracturation and deform by dynamic recrystallization along grain boundaries. Quartz microstructures in mylonites indicate predominantly Regime 3 grain boundary migration recrystallization. Feldspar structures indicate recrystallization through the nucleation and growth of new grains at grain boundaries. The temperatures of deformation from mineral assemblages in the CNKFMASH system in four bulk compositions are in the range of 400–450 °C, and the pressures are more than 6 kb.     

The composition of back-arc basin lower crust and upper mantle in the Mariana Trough: A first report

Abstract The Mariana Trough is an active back-arc basin, with the rift propagating northward ahead of spreading. The northern part of the Trough is now rifting, with extension accommodated by combined stretching and igneous intrusion. Deep structural graben are found in a region of low heat flow, and we interpret these to manifest a low-angle normal fault system that defines the extension axis between 19°45' and 21°10'N. A single dredge haul from the deepest (∼5.5 km deep) of these graben recovered a heterogeneous suite of volcanic and plutonic crustal rocks and upper mantle peridotites, providing the first report of the deeper levels of back-arc basin lithosphere. Several lines of evidence indicate that these rocks are similar to typical back-arc basin lithosphere and are not fragments of rifted older arc lithosphere. Hornblende yielded an ⁴⁰Ar/³⁹Ar age of 1.8 ± 0.6 Ma, which is interpreted to approximate the time of crust formation. Harzburgite spinels have moderate Cr# (<40) and coexisting compositions of clinopyroxene (CPX) and plagioclase (PLAB) fall in the field of mid-ocean ridge basalt (MORB) gabbros. Crustal rocks include felsic rocks (70-80% SiO₂) and plutonic rocks that are rich in amphibole. Chemical compositions of crustal rocks show little evidence for a 'subduction component', and radiogenic isotopic compositions correspond to that expected for back-arc basin crust of the Mariana Trough. These data indicate that mechanical extension in this part of the Mariana Trough involves lithosphere that originally formed magmatically. These unique exposures of back-arc basin lithosphere call for careful study using ROVs and manned submersibles, and consideration as an ocean drilling program (ODP) drilling site.     

Fault throw determination using 4 component VSP: Aigion fault (Greece) case study

The present paper presents the results of a technique based on Vertical Seismic Profiling (VSP) to quantify the offset of a fault in a context where seismic reflection profiles do not image any reflectors. The case study is located in Greece, in the Aigion area, on the south border of the Corinth Gulf. The Aigion fault, oriented East–West, and dipping at 60°N, has been intersected by the scientific well Aig-10 at 760 m in depth, but some uncertainty remained concerning its exact offset since the depth of the pre-rift sequence is open to debate due to the lack of subsurface data. The pre-rift consists of a Mesozoic low-porosity series (carbonates and radiolarite), while the syn-rift consists of poorly compacted conglomerates and turbidites.

Seismic diffractions on fault edges are expected to be present along the fault surface. We find that a few diffracted events are effectively recorded in P and S wave mode by the 4 components of the VSP survey, and critically refracted arrivals along the Aigion fault plane. These singular events have been used in order to refine the fault geometry and to determine its throw. Additionally, results from a 2D finite difference elastic seismic model of a single fault step geometry have been closely examined in order to illustrate the generation of the singular seismic events observed on the field data, such as P-wave and S-wave refracted and diffracted events, and support their interpretation with higher confidence. As a result, the seismic arrival patterns from full waveform seismic modelling confirm the characterisation of the main fault geometry (mainly its throw: about 200 m) in the well vicinity derived from the actual analysis of the 4 Component Aigion VSP data.