Morphological evolution of a complex drift-aligned prograded barrier

Prograded barriers are coastal landforms with a worldwide distribution that provide a paleoenvironmental record within a sequence of successive ridges and intervening swales. Most barriers with variable terrestrial morphologies, also known as complex barriers, have been poorly studied. At the main entrance of Western Port, a bay in southeastern Australia, a morphologically complex barrier was formed as a function of its somewhat sheltered position and orientation in relation to sporadic swells and tidal circulation. LiDAR-derived topography shows highly truncated and asymmetrical ridges both across and along the Somers–Sandy Point barrier plain. These uncommon morphologies are associated with an intricate hydrodynamic circulation subject to sporadic storms approaching at a sharp angle to the shoreline that eliminate a significant part of the sedimentary record but also redistribute vast quantities of sand to the downdrift shoreline, and a large and variable sandy bank that undergoes intense sediment movement. Optically stimulated luminescence (OSL) dating within a limited area on the western side revealed an age of ~2600 years for the innermost dated ridge, located about halfway across the plain. Significant erosion of the ridges' record occurred on the western side of the barrier between 2600 and 700 years ago and between 600 and 240 years ago, whereas undated ridges on the eastern side were preserved. This creates an opportunity for future research on past erosional events that would be of great value for coastal management and adaptation. Textural and elemental (XRF) sediment characteristics suggest that the type of material provided for barrier accretion remained the same throughout the late Holocene. Given the sustained growth of the barrier and other sandy parts of the bay, a net supply of marine sand from Bass Strait must have occurred. The proposed evolutionary model contributes to the understanding of the sediment budget for the bay as a whole.     

Synoptic interpretation of seismic reflection and refraction data

Summary. The structure of the upper lithosphere beneath southern Germany, northern Switzerland and west-central Utah (U.S.A.) has been investigated in detail by various geophysical methods. A synoptic interpretation of travel time and amplitude data obtained in seismic refraction and wide-angle reflection surveys, combined with near-normal incidence reflection observations, now permits the elucidation of the fine structure in a more quantitative and unified manner. With this scheme it is possible to unambiguously identify low-velocity zones and to deduce velocity gradients if reliable amplitude information is included in the inversion process.     

Anatomy of 1986 Augustine volcano eruptions as recorded by multispectral image processing of digital AVHRR weather satellite data

Eighteen digital AVHRR (advanced very high resolution radiometer) data sets from NOAA-6 and NOAA-9 polar-orbiting satellites recorded between 27 March and 7 April 1986 depict the eruptive activity of Augustine volcano, located 280 km SW of Anchorage, Alaska. The synoptic view (resolution of either 1.1 or 4.4 km), frequent coverage (often twice a day), and multispectral coverage (five bands: 0.58–0.68; 0.72–1.1; 3.55–3.93; 10.5–11.3; and 11.5–12.5 m) makes the AVHRR broadly applicable to analyzing explosive eruption clouds. The small scale of the Augustine activity (column heights of 2–13 km and eruption rates of 2x10⁶–8x10⁷ metric tonnes/day) facilitated intensive multispectral study because the plumes generally covered areas within the 550x550 km area of one easily manipulated image field. Hourly ground weather data and twice-daily radiosonde measurements from stations surrounding the volcano plus numerous volcanological observations were made throughout the eruption, providing important ground truth with which to calibrate the satellite data. The total erupted volume is estimated to be at least 0.102 km³. The pattern of changing eruption rates determined by satellite observations generally correlate with more detailed estimates of explosion magnitudes. Multispectral processing techniques were used to distinguish eruption clouds from meteorological clouds. Variable weather during the Augustine eruption offered an opportunity to test various trial algorithms. A ratio between thermal IR channels four and five, served to delineate the ashbearing eruption plumes from ordinary clouds. Future work is needed to determine whether the successful multispectral discrimination is caused by wavelength-dependent variable emission of silicate ash or reflects a spectral role of sulfuric acid aerosol in the plume.     

Late-orogenic basins in the Archaean Superior Province, Canada: characteristics and inferences

The late-orogenic Archaean Duparquet, Kirkland and Stormy basins of the Canadian Superior Province are characterized by bounding crustal-scale faults and abundant porphyry stock emplacement. Lava flows and pyroclastic deposits are restricted to the Kirkland and Stormy basins, and coarse clastic detritus characterizes the Duparquet basin. Seven distinct lithofacies are identified: (1) mafic volcanic, (2) felsic volcanic, (3) pyroclastic, (4) volcaniclastic, (5) conglomerate-sandstone, (6) sandstone-argillite  conglomerate), and (7) argillite-sandstone  tuffaceous sandstone). The mafic and felsic volcanic lithofacies represent effusive lava flows, the pyroclastic lithofacies is formed of subaerial surge and airfall deposits and the volcaniclastic lithofacies is composed of reworked volcanic debris. The conglomerate-sandstone lithofacies is interpreted as alluvial fan, fan delta or proximal braided stream deposits, whereas the sandstone-argillite lithofacies is consistent with sandy-dominated flood- or braidplain deposits. A dominantly shallow-water lacustrine setting is inferred for the argillite-sandstone lithofacies. These different lithofacies record the basin history and can be used to identify basin-forming processes. Lithofacies stacking and rapid lateral changes of lithological units in conjunction with interformational unconformities and basin margin faults suggest tectonically induced sedimentation. Volcanism can also influence basin evolution and the delicate balance between erosion, sedimentation, and prevalent transport processes is affected by volcanic input. Catastrophic influx of pyroclastic material facilitated mass-wasting processes and formation of non-confined hyperconcentrated flood flow deposits account for local congestion of alluvial or fluvial dispersal patterns. Confined stream flow processes govern sedimentation during intravolcanic phases or prominent tectonic uplift. In addition, climate which controls the weathering processes, and vegetation which stabilizes unconsolidated material, affects the transport and depositional process. A CO₂-rich aggressive weathering, humid Archaean atmosphere favours traction current deposits and an absence of vegetation promotes rapid denudation. Although tectonism is the prevalent long-term controlling factor in restricted basins, the effects of volcanism, climate and lack of vegetation can also be detected.     

Impact of Air Pollution on Genetic Material of Shallot (Allium cepa L. var. ascalonicum) Exposed at Differently Polluted Sites in Slovenia

Test shallot plants Allium cepa L. var. ascalonicum were exposed to field conditions at six research plots in the most polluted areas in Slovenia in the vegetation seasons in 1999 and 2000. The intention of this research was to evaluate the influence of air pollution on mitotic activity and frequency of chromosomal aberrations in meristematic tissues of root tips of bioindication plants. Significant differences in the mitotic index and in frequency of chromosomal aberrations at different sampling plots in pot experiments were found and the correlation between the ozone concentration and the mitotic index was determined. The results showed the presence of cytotoxic substances at chosen sampling sites, which caused the decrease of mitotic cell division and the presence of genotoxic substances, which resulted in the increase of frequency of chromosomal aberrations.     

Influence of diet on growth, condition and reproductive capacity in Newfoundland and Labrador cod (Gadus morhua): Insights from stable carbon isotopes (δC)

Cod populations in Newfoundland and Labrador waters have shown differing growth, condition and recruitment since near-universal declines in these properties during the cold period of the late 1980s and early 1990s. To assess the influence of variable prey communities on these parameters, we compared cod energetics and diet in populations off Labrador and the northeast and south coasts of Newfoundland. Many properties were highest in the southern group(s) and lowest in the northern group(s), including growth, somatic condition, liver index and age-at-maturity. Most differences could be explained by variations in diet, as measured by stomach contents and stable carbon isotopes (δ¹³C). The diet of Labrador cod consisted almost entirely of northern shrimp (Pandalus borealis), and these cod displayed the most benthic δ¹³C signatures. Northeast cod had a more varied diet that included capelin and other fish, but still had mostly benthic δ¹³C signatures, suggesting the importance of benthic prey like shrimp in this population. South coast cod exhibited the most varied diet, including capelin (Mallotus villosus), zooplankton, crabs and other fish, and had the most pelagic δ¹³C signatures. Among and within populations, the benefits of a more pelagic diet in medium-sized (30–69 cm) cod included higher somatic condition, higher liver index (lipid stores) and greater spawning potential (decreased incidence of atresia). It is hypothesized that major rebuilding of Newfoundland and Labrador cod stocks will require a return to a system that supports mostly pelagic feeding (i.e. capelin) in cod.     

Geochemical and tectonic implications of igneous rocks from ODP leg 114, sub-antarctic South Atlantic

Igneous rocks recovered from three major tectonic features of the sub-antarctic South Atlantic Ocean during ODP Leg 114 have a range of compositions: Northeast Georgia Rise, basalt to andesite; Meteor Rise, basalt to trachyte; spreading center in the West South Atlantic Basin, MORB-like basalt. Major and trace element as well as Sr and Nd isotopic data clearly indicate that all rocks share the enriched elemental and isotopic signatures typical of both hotspot and mid-ocean ridge volcanism in the southern ocean basins. Data for the Northeast Georgia and Meteor Rises also suggest the influence of older, continental lithosphere.     

Strategies for waveform processing in sparker data

A sparker is a marine seismic impulsive source used for high-resolution seismic surveys. Sparker sources were very popular during the late 1960s and 1970s before being supplanted by small volume airguns. However, in the last 10 years there has been renewed interest in sparker technology because (1) it can be easily deployed at relatively low costs and (2) in certain areas the use of small airguns is restricted for environmental purposes. In this study a sparker source was used to assess the seismic stratigraphy of Quaternary deposits and to image the sediment/bedrock interface. Three different inverse filtering methods were tested (i.e., spiking deconvolution, match-filtering and vertical seismic profile (VSP) deconvolution) to correct the poor shot-to-shot repeatability of the source and to compress its reverberations. Results show that the matched-filter and VSP deconvolution methods, which design and apply one operator for each shot, produced comparable results, whereas the spiking deconvolution that used the same operator on all traces failed to compress the source signature properly.     

Silicon control of strontium and cesium partitioning in hydroxide-weathered sediments

Cation partitioning and speciation in an aqueous soil suspension may depend on the coupling of reaction time, sorbate amount and mineral weathering reactions. These factors were varied in sediment suspension experiments to identify geochemical processes that affect migration of Sr²⁺ and Cs⁺ introduced to the subsurface by caustic high level radioactive waste (HLRW). Three glacio-fluvial and lacustrine sediments from the Hanford Site (WA, USA) were subjected to hyperalkaline (pH > 13), Na-Al-NO₃-OH solution conditions within a gradient field of (i) sorptive concentration (10⁻⁵-10⁻³ m) and (ii) reaction time (0-365 d). Strontium uptake (q_Sr) exceeded that of cesium at nearly all reaction times. Sorbent affinity for both Cs⁺ and Sr²⁺ increased with clay plus silt content at early times, but a prolonged slow uptake process was observed over the course of sediment weathering that erased the texture effect for Sr²⁺; all sediments showed similar mass normalized uptake after several months of reaction time. Strontium became progressively recalcitrant to desorption after 92 d, with accumulation and aging of neoformed aluminosilicates. Formation of Cs⁺ and Sr²⁺-containing cancrinite and sodalite was observed after 183 d by SEM and synchrotron μ-XRF and μ-XRD. EXAFS data for q_Sr ≈ 40 mmol kg⁻¹ showed incorporation of Sr²⁺ into both feldspathoid and SrCO₃(s) coordination environments after one year. Adsorption was predominant at early times and low sorbate amount, whereas precipitation, controlled largely by sediment Si release, became increasingly important at longer times and higher sorbate amount. Kinetics of contaminant desorption at pH 8 from one year-weathered sediments showed significant dependence on background cation (Ca²⁺ versus K⁺) composition. Results of this study indicate that co-precipitation and ion exchange in neoformed aluminosilicates may be an important mechanism controlling Sr²⁺ and Cs⁺ mobility in siliceous sediments impacted by hyperalkaline HLRW.