Geomorphology,acoustic backscatter,and processes in Santa Monica Bay from multibeam mapping

Santa Monica Bay was mapped in 1996 using a high-resolution multibeam system, providing the first substantial update of the submarine geomorphology since the initial compilation by Shepard and Emery [(1941) Geol. Soc. Amer. Spec. Paper 31]. The multibeam mapping generated not only high-resolution bathymetry, but also coregistered, calibrated acoustic backscatter at 95 kHz. The geomorphology has been subdivided into six provinces; shelf, marginal plateau, submarine canyon, basin slope, apron, and basin. The dimensions, gradients, and backscatter characteristics of each province is described and related to a combination of tectonics, climate, sea level, and sediment supply. Fluctuations of eustatic sea level have had a profound effect on the area; by periodically eroding the surface of Santa Monica plateau, extending the mouth of the Los Angeles River to various locations along the shelf break, and by connecting submarine canyons to rivers. A wetter glacial climate undoubtedly generated more sediment to the rivers that then transported the increased sediment load to the low-stand coastline and canyon heads. The trends of Santa Monica Canyon and several bathymetric highs suggest a complex tectonic stress field that has controlled the various segments. There is no geomorphic evidence to suggest Redondo Canyon is fault controlled. The San Pedro fault can be extended more than 30 km to the northwest by the alignment of a series of bathymetric highs and abrupt changes in direction of channel thalwegs.     

Characterisation of the carbonate content of atmospheric aerosols

A programme of aerosol sampling by dichotomous sampler has been undertaken with analysis of soluble ions plus carbonate. The technique for carbonate involved release of CO₂ by HCl vapour and quantitative measurement of the CO₂ by FTIR spectroscopy. The method is suitable for amounts down to below 10g CO₃ ^2- per filter. The prevailing atmospheric levels in an urban area were found to be below 1g m^-3. Information on the particle size from the dichotomous sampler was supplemented by use of a cascade impactor. Although CaCO₃ is clearly the dominant species initial analyses demonstrated higher carbonate levels than could be accounted for on the basis of the concentrations of calcium and magnesium ions which are the most likely cations in mineral carbonates. Analysis with and without heating to 100°C in a vacuum oven demonstrates the presence of carbonate in volatile form. This could be due to carbon dioxide adsorbed onto particulate matter such as soot.     

Chemical and isotopic composition of the lower crust beneath the Meguma Lithotectonic Zone,Nova Scotia: evidence from granulite facies xenoliths

Granulite-facies xenoliths from an Upper Devonian lamprophyre dyke near Tangier, Nova Scotia, provide new information about the lower crust in the Meguma Zone. Two mineralogically and chemically distinet groups of xenoliths occur. Both groups contain quartz+feldspar+biotite+Fe–Ti oxides+sulfides. In addition, group A contains garnet+graphite±[aluminosilicates+spinel±sapphirine (hight Al₂O₃ subgroups A1 and A2)] or [clinopyroxene+sphene+apatite (high CaO sub-group A3)]. Group B has highly variable proportions of orthopyroxene (B1), clinopyroxene (B2), and amphibole (B3). Trace-element contents of the highly aluminous xenoliths compare closely with average to upper crustal model compositions and are similar in many aspects to other undepleted granulite-facies rocks. LowP-T sedimentary assemblages of quartz-chlorite-clay minerals-calcite-albite or paragonite can account for the compositions of group A xenoliths. Within group B, a high-MgO (MgO>13 wt%) subgroup with high transition-metal contents, and low-MgO (MgO<9 wt%) sub-groups with higher LIL (large-ion-lithophile) element contents exist. Although the rare-earth and high-field-strength elements indicate a tholeiitic or low-K calc-alkaline chemistry, the LIL elements are as high as those from high-K calc-alkaline volcanic are rocks. Isotopically, group A ranges from Nd_t=-2.56 to-0.80 and⁸⁷Sr/⁸⁶Sr _t =0.7046 to 0.7182 fort=370 Ma. For group B these values are +1.45 to +5.33 and 0.7028 to 0.7048, respectively. Model ages (T_CHUR) are correspondingly low and are tightly constrained (544±52 Ma). These young ages contrast with the middle Proterozoic Nd model ages of the overlying Meguma Zone low-grade flysch. This time-inverted stratigraphy appears to be the product of a tectonic break between a younger autochthonous Tangier lower crust (Avalon), and an older allochthonous Meguma Group upper crust.     

Solitary and cnoidal planetary waves

Abstract

A class of long planetary waves in a zonal channel analogous to the solitary and cnoidal waves of surface and internal gravity wave theory is discussed. On a mid-latitude β-plane, such waves exist as the result of divergence, non-uniform zonal velocity fields or bottom topography. In all cases studied the wave profile along the channel was found to satisfy the Korteweg-de Vries equation.     

Bonemapping: a LiDAR processing and visualization technique in support of archaeology under the canopy

For the past decade, archaeologists have been using LiDAR or Airborne Laser Scanning (ALS)-based methods to uncover trace signatures of human civilization in the landscape. A new technique called bonemapping involves processing the ALS data to create a map-like representation of the landscape, which aids in the detection and interpretation of traces of human settlement. The technique is a combination of two methods – the Simple Morphological Filter (SMRF) for ALS processing and the Perceptually Shaded Slope Map (PSSM) for ALS representation – and is used to represent subtle changes in the terrain that are often indicative of previous human settlement. The SMRF algorithm adds value by retaining more “feature” cells than comparable terrain-finding algorithms, and is easy to tune through the use of two intuitive parameters – a slope threshold and a window size. The PSSM visualization is then used to apply a vertical exaggeration-based slope shading, which has proven useful as an aid to rapid feature detection, identification, and interpretation. The findings of two years of field use of bonemapping by archaeologists at El Pilar demonstrate the ways in which the bonemap offers a value-added perspective to archaeology under the canopy.     

SWIFT: An adaptive optics assisted I/z band integral field spectrograph

SWIFT is an adaptive optics assisted integral field spectrograph covering the I and z astronomical bands (0.7–1.0 μm) at a spectral resolving power R  5000. At its heart is an all-glass image slicer with high throughput based on a novel de-magnifying design allowing a compact instrument. SWIFT profits from two recent developments: (i) the improved ability of second generation adaptive optics systems to correct for atmospheric turbulence in SWIFTS’s bandpass, and (ii) the availability of CCD array detectors with high quantum efficiency at very red wavelengths. It is a dedicated integral field spectrograph, specifically built to address a range of interesting astrophysical questions.     

Characterization of Asian Dust during ACE-Asia

ACE-Asia was a multi-national collaboration organized to investigate and understand the chemistry, radiative properties, and climatic effects of mineral dust and other aerosol particles in the East Asia/Northwest Pacific region. Studies conducted at the Gosan and Zhenbeitai surface supersites show striking variations in aerosol concentrations and properties that were affected by the occurrence and origins of the Asian dust storms, air mass pathways, and mixing during the transport. Investigations conducted on the R/V Ronald H. Brown (RHB) showed that dust had a pervasive influence on the chemical composition, size distribution, and optical properties of the aerosol. Analyses using an aerosol time-of-flight mass spectrometer on the RHB showed that most of the coarse-particle nitrate and sulfate in post-frontal air was associated with dust, and more remarkably, that competitive or exclusionary processes evidently are involved in the uptake or production of these substances. Studies conducted onboard the NCAR C-130 aircraft showed that coarse-mode dust was less absorbing and less hygroscopic than pollution aerosol and that there was little correlation in light scattering and absorption by the sub- vs. super-micrometer aerosol. Below 2 km, dust was commonly mixed with pollutants, and this had a stronger influence on the optical properties of the submicrometer particles than the coarse-mode dust; at higher altitudes, the dust was less affected by pollution. Single particle analyses of C-130 samples showed that the mixing of black carbon (BC) with dust was common, but only certain types of BC particles were aggregated. Models were used in the planning, execution and interpretative phases of ACE-Asia; and summaries of modeling results are presented to illustrate the progress being made in identifying new dust sources; in depicting the time-varying, three-dimensional structure of dust plumes; and in quantifying the production, transport, and deposition of Asian dust.     

Ecological consequences of dredged material disposal in the marine environment: a holistic assessment of activities around the England and Wales coastline

This study provides a holistic perspective on the ecological effects of dredged material disposal, both intertidally and subtidally. A number of numerical techniques (univariate, distributional, multivariate and meta-analysis) were used to assess impacts at 18 different disposal sites. The analyses revealed that ecological effects associated with dredged material disposal were dependent on the numerical techniques used, and that impacts were disposal-site specific. Disposal-site communities were generally faunistically impoverished to varying degrees, and impacts following intertidal placement were comparable to those of subtidal placement. We conclude that any assessment of the consequences of dredged material disposal to the coastal environment must take account of site-specific variation in prevailing hydrographic regimes and in ecological status, along with information on the disposal activity itself (mode, timing, quantity, frequency and type of material). As would be expected, variability in the latter presents a significant challenge in attempts to generalise about environmental and ecological impacts.