A sediment trap intercomparison study in the Santa Barbara Basin

Four sediment traps of radically different design were deployed in the Santa Barbara Basin for approximately 45 days. The measured fluxes ranged from 370 to 774 g m^?2 yr^?1 for the different designs. These values lie within flux measurements previously determined for the basin. Compared to the 25-year record (920 g m^?2 yr^?1), however, all fluxes determined in this experiment are somewhat low. Because this experiment was conducted during a general period of high storm activity and runoff, measurement of greater than average flux was expected. It is probable that the higher flux recorded by the sediments results from a significant input of detritus into the basin by near bottom transport.The chemical composition of trapped material was nearly identical in all four trap designs. The deep cone design, however, had a significantly lower Mn content. Since this trap was the only one in which reducing conditions were produced in the sample container, reduction and mobilization of manganese after collection is believed to have occurred.In spite of the very different designs tested, the factor of two agreement in flux determination and the compositional similarity of the material collected is encouraging for future attempts to directly measure the flux of particulates in the ocean.     

Pu in coastal marine environments

Analysis of water samples from the New York Bight area and Narragansett Bay reveals that a small fraction of the total Pu (probably Pu (III + IV) species) is continuously removed to the sediments at a rate similar to that of the particle-reactive isotope²²⁸Th. A more “soluble” Pu species appears to be released at times from the sediments to the water column in these nearshore regions. Sediments in shallow areas of the New York Bight south of Rhode Island and Narragansett Bay have high Pu inventories and relatively deep penetration of this element, although the net sediment accumulation rate is generally low (<0.03 g/cm² yr). The high Pu inventories can be explained if both sediment resuspension and sediment mixing are assumed to be the major controlling factors for the effective transfer of Pu from the water column to the sediments. By simultaneous modelling of the depth distribution of three tracers which operate on vastly different time scales:²³⁴Th (half-life 24 days),²¹⁰Pb (half-life 22 years) and^239,240Pu (introduced into the environment during the past 30 years), bioturbation rates ranging from 4 to 32 cm²/yr in the surface mixed layer (5–10 cm thick) and from 0.3 to 2.5 cm²/yr in the layer below (up to 40 cm thick) and net sediment accumulation rates of approximately zero to 0.14 g/cm² yr were calculated for these areas.     

A Synthetic Haematite Reference Material for LA‐ICP‐MS U‐Pb Geochronology and Application to Iron Oxide‐Cu‐Au Systems

In both nature and synthetic experiments, the common iron oxide haematite (α‐Fe₂O₃) can incorporate significant amounts of U into its crystal structure and retain radiogenic Pb over geological time. Haematite is a ubiquitous component of many ore deposit types and, therefore, represents a valuable hydrothermal mineral geochronometer, allowing direct constraints to be placed on the timing of ore formation and upgrading. However, to date, no suitable natural haematite reference material has been identified. Here, a synthetic haematite U‐Pb reference material (MR‐HFO) is characterised using LA‐ICP‐MS and ID‐TIMS. Centimetre‐scale ‘chips’ of synthesised α‐Fe₂O₃ were randomly microsampled via laser ablation‐extraction and analysed using ID‐TIMS. Reproducible U/Pb and Pb/Pb measurements were obtained across four separate chips (n = 13). Subsequently, an evaluation of the suitability MR‐HFO in constraining U‐Pb data via LA‐ICP‐MS is presented using a selection of natural samples ranging from Cenozoic to Proterozoic in age. The MR‐HFO normalised U‐Pb ratios are more concordant and ages more accurate versus the same LA‐ICP‐MS spot analyses normalised to zircon reference material, when compared with independently acquired ID‐TIMS data from the same natural haematite grains. Results establish MR‐HFO as a suitable reference material for LA‐ICP‐MS haematite U‐Pb geochronology.     

Privatised Communities: the use of owners corporations in master planned estates in Melbourne

This paper contributes to the growing body of work on master planned estates in Australia by addressing the issue of the privatisation of assets and facilities, which in more conventional residential developments are in the public realm, owned and managed by local councils or other public bodies. The paper addresses the trend to place assets presented as lifestyle features, such as community and recreational facilities, open space or landscaping features, in a form of collective private ownership, known in Victoria as owners corporations. The provision of these facilities and assets for residents, however, has a number of implications relating to exclusivity, separation from the wider community, and potential conflicts within the master planned community itself. These issues are examined with reference to data gathered through an investigation of recently established master planned communities in the growth areas of Melbourne.     

Intermobility of barium,strontium, and lead in chloride and sulfate leach solutions

Iron(III)-precipitates formed by the oxidation of dissolved Fe(II) are important sorbents for major and trace elements in aquatic and terrestrial systems. Their reductive dissolution in turn may result in the release of associated elements. We examined the reductive dissolution kinetics of an environmentally relevant set of Fe(II)-derived arsenate-containing Fe(III)-precipitates whose structure as function of phosphate (P) and silicate (Si) content varied between poorly-crystalline lepidocrocite, amorphous Fe(III)-phosphate, and Si-containing ferrihydrite. The experiments were performed with 0.2–0.5 mM precipitate-Fe(III) using 10 mM Na-ascorbate as reductant, 5 mM bipyridine as Fe(II)-complexing ligand, and 10 mM MOPS/5 mM NaOH as pH 7.0 buffer. Times required for the dissolution of half of the precipitate (t_50%) ranged from 1.5 to 39 h; spanning a factor 25 range. At loadings up to ~ 0.2 P/Fe (molar ratio), phosphate decreased the t_50% of Si-free precipitates, probably by reducing the crystallinity of lepidocrocite. The reductive dissolution of Fe(III)-phosphates formed at higher P/Fe ratios was again slower, possibly due to P-inhibited ascorbate binding to precipitate-Fe(III). The slowest reductive dissolution was observed for P-free Si-ferrihydrite with ~ 0.1 Si/Fe, suggesting that silicate binding and polymerization may reduce surface accessibility. The inhibiting effect of Si was reduced by phosphate. Dried-resuspended precipitates dissolved 1.0 to 1.8-times more slowly than precipitates that were kept wet after synthesis, most probably because drying enhanced nanoparticle aggregation. Variations in the reductive dissolution kinetics of Fe(II) oxidation products as reported from this study should be taken into account when addressing the impact of such precipitates on the environmental cycling of co-transformed nutrients and contaminants.

     

Metals in sediments and fish from Sea Lots and Point Lisas Harbors, Trinidad and Tobago

Concentrations of heavy metals were determined in nearshore marine sediments and fish tissue from Sea Lots area on the west coast, at Caroni Lagoon National Park, and in the Point Lisas harbor, Trinidad. The most dominant metals found in sediments were Al, Fe and Zn with mean concentrations highest at Sea Lots (Al-39420 μg/g; Fe-45640 μg/g; Zn-245 μg/g), when compared to sediments from Point Lisas (Al-11936 μg/g; Fe-30171 μg/g; Zn-69 μg/g) and Caroni (Al-0400 μg/g; Fe-19000 μg/g; Zn-32 μg/g), High concentration of Cu, Al, Fe and Zn were also detected in fish tissue from Point Lisas and Caroni. Metal concentrations in fish tissue showed significant correlation with sediment metals concentration, which suggests that tissue levels are influenced by sediment concentration. Of the metals, only Zn, Hg and Cu had a bioaccumulation factor (BAF) greater than one, which suggests a high bioaccumulation potential for these metals.     

Geoarchaeological analysis of an acheulean site at Kalambo Falls,Zambia

Acheulean sites are commonly recovered from sandy channel contexts, particularly in Africa. These sites frequently contain impressive concentrations of artifacts dominated by typical Acheulean large bifacial artifacts (‘handaxes,’ etc.). Possible influences of fluvial sedimentary processes in Acheulean site formation are explored through consideration of sedimentary context and detailed analysis of relevant artifact assemblage characteristics in part of a major Acheulean ‘Floor’ at Kalambo Falls, Zambia. The Kalambo Falls patterns are analyzed here with regard to influences of behavioral and natural processes in their formation, and are compared to those observed in Acheulean horizons at Montagu Cave, South Africa. Spatial concentration of bifaces and paucity of debitage at many Acheulean sites may be due largely to fluvial disturbance and winnowing, although a hominid preoccupation with large bifacial tools may be a bona fide behavior pattern at some sites. Better control over sedimentary context is necessary to elucidate the range of behaviorally-produced patterns at Acheulean sites.     

Preferential groundwater flow through a sorted net landscape,Arctic Canada

Preferential suprapermafrost groundwater flow was observed in deepened channels lying between raised frost mounds. Here, saturated hydraulic conductivity, k, ranged from 90 to 1000 m/day but was only 0·1–1·0 m/day in the mound centres. A high proportion of fines occurs in the frost mound centre due to particle sorting, while channels contain gravels. Three approaches of areal weighting of k and groundwater flow, Q _s, across a wetland–upland boundary were explored. When percentage area covered by channels, mounds or gravel was considered, estimates of water flow on a daily and seasonal basis fell by 30 to 50 per cent. This study is of relevance to northern scientists who require reliable estimates of groundwater flow across patterned ground landscapes. Copyright © 2001 John Wiley & Sons, Ltd.