Determination of phospholipid fatty acid structures and stable carbon isotope compositions of deep-sea sediments of the Northwest Pacific, ODP site 1179

Sediment samples ranging from 0.05 to 278 m below sea floor (mbsf) at a Northwest Pacific deep-water (5564 mbsl) site (ODP Leg 191, Site 1179) were analyzed for phospholipid fatty acids (PLFAs). Total PLFA concentrations decreased by a factor of three over the first meter of sediment and then decreased at a slower rate to approximately 30 mbsf. The sharp decrease over the first meter corresponds to the depth of nitrate and Mn(IV) reduction as indicated by pore water chemistry. PLFA-based cell numbers at site 1179 had a similar depth profile as that for Acridine orange direct cell counts previously made on ODP site 1149 sediments which have a similar water depth and lithology. The mole percentage of straight chain saturated PLFAs increases with depth, with a large shift between the 0.95 and 3.95 mbsf samples. PLFA stable carbon isotope ratios were determined for sediments from 0.05 to 4.53 mbsf and showed a general trend toward more depleted δ¹³C values with depth. Both of these observations may indicate a shift in the bacterial community with depth across the different redox zones inferred from pore water chemistry data. The PLFA 10me16:0, which has been attributed to the bacterial genera Desulfobacter in many marine sediments, showed the greatest isotopic depletion, decreasing from − 20 to − 35‰ over the first meter of sediment. Pore water chemistry suggested that sulfate reduction was absent or minimal over this same sediment interval. However, 10me16:0 has been shown to be produced by recently discovered anaerobic ammonium oxidizing (anammox) bacteria which are known chemoautotrophs. The increasing depletion in δ¹³C of 10me16:0 with the unusually lower concentration of ammonium and linear decrease of nitrate concentration is consistent with a scenario of anammox bacteria mediating the oxidation of ammonium via nitrite, an intermediate of nitrate reduction.     

Shallow Water Bathymetry Derived from Green Wavelength Terrestrial Laser Scanner

Abstract

Shallow water bathymetry has proved to be a challenging task for remote sensing applications. In this work, Green-Wavelength Terrestrial Laser Scanning (GWTLS) is employed to survey nearshore bathymetry under clear atmospheric and water conditions. First, the obtained seabed points were corrected for refraction and then geo-registration, and filtering processes were exerted to obtain an accurate bathymetric surface. Terrain analysis was performed with respect to a reference surface derived from classical surveying techniques. The overall analysis has shown that the best results stem from 35° to 50° incident angles, whereas for angles higher than 65° measurements are not acceptable, although for the same angle in front and close to the instrument accuracy is considered acceptable due to the high laser power. Also, high resolution micro-topography, shallower than 1?m water depth, was managed to be captured. Systematic experimental approaches are expected to improve the GWTLS technique to detect bathymetry, which is anticipated to assist in mapping very shallow foreshore, tidal, and deltaic environments, to contribute conceptual into developing hybrid observation systems for coastal monitoring, and also to be applied in various maritime applications.     

Accuracy assessment of lidar-derived digital elevation models

Despite the relatively high cost of airborne lidar-derived digital elevation models (DEMs), such products are usually presented without a satisfactory associated estimate of accuracy. For the most part, DEM accuracy estimates are typically provided by comparing lidar heights against a finite sample of check point coordinates from an independent source of higher accuracy, supposing a normal distribution of the derived height differences or errors. This paper proposes a new methodology to assess the vertical accuracy of lidar DEMs using confidence intervals constructed from a finite sample of errors computed at check points. A non-parametric approach has been tested where no particular error distribution is assumed, making the proposed methodology especially applicable to non-normal error distributions of the type usually found in DEMs derived from lidar. The performance of the proposed model was experimentally validated using Monte Carlo simulation on 18 vertical error data-sets. Fifteen of these data-sets were computed from original lidar data provided by the International Society for Photogrammetry and Remote Sensing Working Group III/3, using their respective filtered reference data as ground truth. The three remaining data-sets were provided by the Natural Environment Research Council's Airborne Research and Survey Facility lidar system, together with check points acquired using high precision kinematic GPS. The results proved promising, the proposed models reproducing the statistical behaviour of vertical errors of lidar using a favourable number of check points, even in the cases of data-sets with non-normally distributed residuals. This research can therefore be considered as a potentially important step towards improving the quality control of lidar-derived DEMs.     

Measurements of magnetic fluxes and field strengths in the photospheric network

We present digital pictures of an active region network cell in five quantities, measured simultaneously: continuum intensity, line-center intensity, equivalent width, magnetogram signal, and magnetic field strength. These maps are derived from computer analysis of circularly polarized line profiles of FeI 5250.2; spectral and spatial resolution are 1/40 Å and 1.5, respectively. Measured Zeeman splittings show the existence of strong magnetic fields (1000–1800 G) at nearly all points with a magnetogram signal exceeding 125 G. The mean and rms deviation of the field strengths change by less than 20% over a factor-of-four range of fluxes. From the significant disparity between measured fluxes and field strengths, we conclude that large flux patches (up to 4 across) consist of closely-packed unresolved filaments. The smallest filaments must be less than 0.7 in diameter. We also observe the dark component of the photospheric network, which appears to contain sizable transverse fields.     

The role of prokaryotes in subsurface weathering of hydrothermal sediments: A combined geochemical and microbiological investigation

A detailed geochemical and microbiological study of a ∼2 m sediment core from the inactive Alvin mounds within the TAG hydrothermal field was conducted to examine, for the first time, the role of prokaryotes in subsurface weathering of hydrothermal sediments. Results show that there has been substantial post-depositional remobilisation of metal species and diagenetic overprinting of the original high-temperature hydrothermal minerals, and aspects have involved prokaryotic processes. Prokaryotic enumeration demonstrates the presence of a population smaller than the average for deep sea sediments, probably due to the low organic carbon content, but not inhibited by (and hence adapted to) the metal rich environment. There was a small but significant increase in population size associated with the active redox boundary in an upper metal sulphide layer (50-70 cm) around which active metal remobilisation was concentrated (Cu, Au, Cd, Ag, U, Zn and Zn). Hence, subsurface prokaryotes were potentially obtaining energy from metal metabolism in this near surface zone. Close association of numbers of culturable Mn and Fe reducing prokaryotes with subsurface Fe²⁺ and Mn²⁺ pore water profiles suggested active prokaryotic metal reduction at depth in core CD102/43 (to ∼175 cm). In addition, a prokaryotic mechanism, which is associated with bacterial sulphate reduction, is invoked to explain the U enrichment on pyrite surfaces and Zn and Pb remobilisation in the upper sediment. Although prokaryotic populations are present throughout this metalliferous sediment, thermodynamic calculations indicated that the inferred low pH of pore waters and the suboxic/anoxic conditions limits the potential energy available from Fe(II) oxidation, which may restrict prokaryotic chemolithotrophic biomass. This suggests that intense prokaryotic Fe oxidation and weathering of seafloor massive sulphide deposits may be restricted to the upper portion of the deposit that is influenced by near neutral pH and oxic seawater unless there is significant subsurface fluid flow.     

Inferring erosional resistance of bedrock units in the east Tennessee mountains from digital elevation data

Measures of local relief, regional relief, and slope were calculated from digital elevation models (DEMs) for 50 bedrock units in the Ridge and Valley and Blue Ridge provinces of Tennessee. Each of these measures was normalized and the three were then averaged to produce the erosional resistance index (ERI). Bedrock units with higher ERI values include coarse clastics, intermediate clastics, and metaplutonics. Units with lower values include shales, limestones, limestones plus dolostones, and carbonates plus fine clastics. Dolostones tend to have intermediate values. The calculated ERI values were compared with subjective ratings by a geologist with decades of field experience in east Tennessee. Generally, the agreement between the two ratings was good, the most glaring exception being several shales with improbably high ERI values. These turned out to be thin units cropping out beneath very hard sandstones, allowing them to stand higher and steeper than would otherwise be possible. A systematic method for detecting such erroneously high ERI values is suggested. Inspection of a drainage map superimposed on the geology map shows that in a given area, streams tend to flow on rock units with the lowest ERI values. In addition, statistical analysis shows that bedrock units with the lowest ERI values are, on average, almost three times closer to the nearest stream and six times as likely to have streams flowing on them than are units with highest values. Further, the effect of ERI on stream location is strongest for streams with drainage areas between 1 and 30 km². Thus, small streams appear to be subject to greater lithologic control than are larger streams.     

Weather as a Chronic Hazard for Road Transportation in Canadian Cities

Inclement weather creates a chronic hazard for Canadian travellers. Past studies indicate that road collision rates increase during precipitation, although the magnitude of theincrease varies from study to study, partly as a result of variations in weather and driving conditions,but also because of differences in methods. The goal of the current study is to improve ourunderstanding of the links between weather and travel risk in mid-sized Canadian cities by using astandardized method for analyzing data from six cities with different climates: Halifax-Dartmouth,Ottawa, Québec, Hamilton, Waterloo Region, and Regina. The study has four interrelated objectives: (1) Toconduct a sensitivity analysis to determine the extent to which risk estimates vary depending onthe criteria used to define precipitation events and `normal' conditions; (2) To compare therelative risk of collision and injury during precipitation relative to `normal' conditions; (3) Todetermine the extent to which weather-related risks vary fordifferent Canadian cities; and (4) To explore any differences in collision characteristics between events and controls, especially as theyvary from city to city. Results are based on a matched-pair analysis, using six-hour time blocks over afour-year period, 1995 to 1998. Results indicate only modest sensitivity to the criteria used to define precipitation events and `normal' conditions. On average, precipitation is associated with a 75 percentincrease in traffic collisions and a 45 percent increase in related injuries, as compared to `normal'seasonal conditions, but risk levels vary depending on the characteristics of the weather event.Both sensitivity to specific weather conditions and weather-related accident profiles vary from city tocity in ways that are not easily explained.     

Contrasting stable isotope behavior between calcite and dolomite marbles,Lone Mountain,Nevada

 Late Proterozoic to Cambrian carbonate rocks from Lone Mountain, west central Nevada, record multiple post-depositional events including: (1) diagenesis, (2) Mesozoic regional metamorphism, (3) Late Cretaceous contact metamorphism, related to the emplacement of the Lone Mountain granitic pluton and (4) Tertiary hydrothermal alteration associated with extension, uplift and intrusion of silicic porphyry and lamprophyre dikes. Essentially pure calcite and dolomite marbles have stable isotopic compositions that can be divided into two groups, one with positive δ¹³C values from+3.1 to +1.4 ‰ (PDB) and high δ¹⁸O values from +21.5 to +15.8 ‰ (SMOW), and the other with negative δ¹³C values from –3.3 to –3.6‰ and low δ¹⁸O values from +16.9 to +11.1‰. Marbles also contain minor amounts of quartz, muscovite and phlogopite. Brown and blue luminescent, clear, smooth textured quartz grains from orange luminescent calcite marbles have high δ¹⁸O values from +23.9 to +18.1‰, while brown luminescent, opaque, rough textured quartz grains from red luminescent dolomite marbles typically have low δ¹⁸O values from +2.0 to +9.3‰. The δ¹⁸O values of muscovite and phlogopite from marbles are typical of micas in metamorphic rocks, with values between +10.4 and +14.4‰, whereas mica δD values are very depleted, varying from −102 to −156‰. No significant lowering of the δ¹⁸O values of Lone Mountain carbonates is inferred to have occurred during metamorphism as a result of devolatilization reactions because of the essentially pure nature of the marbles. Bright luminescence along the edges of fractures, quartz cements and quartz overgrowths in dolomite marbles, low δD values of micas, negative δ¹³C values and low δ¹⁸O values of calcite and dolomite, and depleted δ¹⁸O values of quartz from dolomite marbles all indicate that meteoric fluids interacted with Lone Mountain marbles during the Tertiary. Partial oxygen isotopic exchange between calcite and low ¹⁸O meteoric fluids lowered the δ¹⁸O values of calcite, resulting in uniform quartz-calcite fractionations that define an apparent pseudoisotherm. These quartz-calcite fractionations significantly underestimate both the temperature of metamorphism and the temperature of post-metamorphic alteration. Partial oxygen isotopic exchange between quartz and meteoric fluids also resulted in ¹⁸O depletion of quartz from dolomite marbles. This partial exchange was facilitated by an increase in the surface area of the quartz as a result of its dissolution by meteoric fluids. The negative δ¹³C values in carbonates result from the oxidation of organic material by meteoric fluids following metamorphism. Stable isotopic data from Lone Mountain marbles are consistent with the extensive circulation of meteoric hydrothermal fluids throughout western Nevada in Tertiary time. Received: 1 February 1994/Accepted: 12 September 1995