Some comparative marine chemistries of rhenium, gold, silver and molybdenum

Four metals, Re, Au, Ag and Mo, whose dissolved forms in seawater can potentially be reduced to insoluble states, have been measured in a variety of solids depositing under anoxic conditions: hydrothermal sulfides; coastal sediments; and phosphorites. For comparative purposes these elements have also been determined in ferromanganese minerals and pelagic sediments which have accumulated under oxidizing conditions. Rhenium appears to be a unique sentinel for identifying reducing depositional environments, where enrichments of greater than three orders of magnitude above crustal concentrations are found. Molybdenum follows Re in these sediments but Mo is enriched also in those that accumulate under oxidizing conditions. The reported Mo crustal concentrations appear low in comparison to our measured sedimentary values. Gold and Ag are concentrated in hydrothermal deposits and sulfides appear to be involved in the precipitation of these elements. Coastal sediments adjacent to a domestic outfall of Los Angeles, California contain extraordinary high accumulations of anthropogenic Au, Ag and Pt. The study seeks an understanding of the mobilities and sinks of these metals in the marine environment during the major weathering cycle. Further, anthropogenic contributions to their sedimentary concentrations are identified.     

Occupation surfaces sealed by the Avellino eruption of Vesuvius at the Early Bronze Age village of Afragola in southern Italy: A micromorphological analysis

This paper reconstructs the use of space and defines activity areas within a single hut (Hut 8) at the Early Bronze Age village of Afragola (southern Italy). The village, consisting of a number of huts and other structures, was covered by approximately 1m of volcanic ash during the eruption of Vesuvius in 3550 ± 20BP. Thirteen samples were collected from inside the hut to analyze the spatial variability in sedimentary characteristics among three areas of Hut 8—the apsidal, central, and entrance areas. The micromorphological analysis revealed details about the occupation surface and its relationship to features and material remains in the hut not apparent in the field. The apsidal area was probably used for storage but not of solids, as no significant quantities of organic material were found. The central area contains a small oven, calcareous ash from fires, and organic material composed of charred remains and bone fragments and was likely used for small‐scale household tasks. A possible connection exists between the lithics and the microstratigraphic sequencing in the area west of the oven, suggesting that people congregated there to perform specific tasks. The entrance area contains highly compacted and heterogeneous sediments that were brought in from outside. Notable is the paucity of anthropogenic materials found inside the hut, especially given the remarkable preservation offered by the thick cover of volcanic ash. We hypothesize that Hut 8 was not occupied long enough to produce a large amount of debris or that it had limited indoor activities and was thoroughly cleaned. © 2010 Wiley Periodicals, Inc.     

Analytical Constraints on the Measurement of the Sulfur Isotopic Composition and Concentration of Trace Sulfate in Phosphorites: Implications for Sulfur Isotope Studies of Carbonate and Phosphate Rocks

The aim of this study was to evaluate the existing methods for extracting trace sulfate from francolite and measuring its concentration and sulfur isotope composition. Phosphatic rocks were chemically and thermally treated to remove non‐structural SO₄^2? in francolite, which would otherwise be inadvertently included in geochemical analyses of the structurally‐bound sulfate. Acetic acid (10% v/v) proved to be effective in removing calcite, dolomite and ankerite without affecting francolite. To remove all ‘easily’ soluble sulfates, such as Ca‐sulfates and adsorbed sulfate, rinsing with 10% v/v NaCl had to be repeated several times for most samples. For subsequent S isotope determination sample combustion at 600 °C was found to be an efficient way to remove non‐francolite S‐bearing phases. From a number of SO₄^2? detection methods tested, ICP‐AES proved to be the most accurate. For francolite‐sulfate recovery, our recommended protocol involved repeated rinsing of powdered phosphorites with 10% NaCl as well as NaOCl, and testing of the filtrate for SO₄^2? in each wash. If only S isotope compositions are needed, combustion at 600 °C with a subsequent de‐ionised water rinse could be undertaken instead of repeated NaOCl rinsing for studies of both francolite and carbonate. Re‐analysis of previously published data, using the new protocol, provided evidence that the use of this protocol considerably improves data quality.     

Source localization in shallow water in the presence of sensorlocation uncertainty

The problem of source localization in shallow water in the presence of sensor location uncertainty is considered. The Cramer-Rao Bound is used to carry out a feasibility study for the joint source and sensor location problem when the multipath propagation channel is modeled as a known, deterministic waveguide. Unlike the free-space propagation channel, the boundedness of the shallow-water waveguide along its vertical axis provides the key to joint determination of the source and sensor location parameters. It is seen that, when a set of intuitive identifiability conditions are satisfied, numerical examples indicate that, for the scenarios considered, the resulting loss in accuracy with which the source location can be estimated due to sensor location uncertainty may be tolerable     

Temporal dynamics of dissolved combined neutral sugars and the quality of dissolved organic matter in the Northwestern Sargasso Sea

The dynamics of dissolved combined neutral sugars (DCNS) were assessed in the upper 250 m at the Bermuda Atlantic Time-series Study (BATS) site between 2001 and 2004. Our results reveal a regular annual pattern of DCNS accumulation with concentrations increasing at a rate of 0.009–0.012 μmol C L^?1 d^?1 in the surface 40 m from March to July and reaching maximum mean concentrations of 2.2–3.3 μmol C L^?1. Winter convective mixing (between January and March) annually exported surface-accumulated DCNS to the upper mesopelagic zone (100–250 m), as concentrations increased there by 0.3–0.6 μmol C L^?1. The exported DCNS was subsequently removed over a period of weeks following restratification of the water column. Vertical and temporal trends in DCNS yield (% of DOC) supported its use as a diagenetic indicator of DOM quality. Higher DCNS yields in surface waters suggested a portion of the DOM accumulated relatively recently compared to the more recalcitrant material of the upper mesopelagic that had comparably lower yields. DCNS yields and mol% neutral sugar content, together, indicated differences in the diagenetic state of the surface-accumulated and deep pools of DOM. Seasonally accumulated, recently produced DOM with higher DCNS yields was characterized by elevated mol% of galactose and mannose+xylose levels. Conversely, more recalcitrant DOM from depths >100 m had lower DCNS yields but higher mol% of glucose. Lower DCNS yields and elevated mol% glucose were also observed in the surface waters during winter convective mixing, indicating an entrainment of a diagenetically altered DOM pool into the upper 100 m. A multivariate statistical analysis confirms the use of DCNS as an index of shifts in DOM quality at this site.     

Venus gravity west of Beta Regio

Doppler tracking data from the Pioneer Venus Orbiter (PVO) have been used to estimate the anomalous gravity field in the region of Venus west of Beta Regio. The analysis invokes a Kalman filter-smoother to solve the nonlinear spacecraft state estimation problem and a linear Bayesian estimator to perform the geophysical inversion. The topographic map for this region, derived from the PVO radar, has been filtered to have the same distortions and degree of smoothing as the gravity map. The undulations of the gravity are about 0.2 times as large as expected from the topography on the assumption that the latter is uncompensated. A comparison of the gravity and topography by means of the spectral admittance is consistent with Airy compensation at a depth of 50 km if the surface material has a density of 2.6 g/cm³. However, this is not a unique interpretation.     

Coronal electron density maps for 7 March, 1970, derived from Mgx λ625 spectroheliograms

We have analyzed daily Mgx 625 spectroheliograms acquired by the Harvard College Observatory experiment on OSO-6 for a 28-day period centered on 7 March, 1970, the date of a well-observed total solar eclipse. These data are used to construct maps of the variation across the solar disk of the electron density at the base of the corona. The correspondence of high and low density regions with regions of enhanced and reduced emission in white light and Mgx pictures made during or near the time of the eclipse are described.