October 2003     

Katherine Stone  Orville Magoon  Billy Edge  Lesley Ewing 《Environmental Geology》2003,44(7):876-875

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Identifying when microbes biosilicify: The interconnected requirements of acidic pH, colloidal SiO₂ and exposed microbial surface     

Derek R. Amores  Lesley A. Warren   《Chemical Geology》2007,240(3-4):298-312

This study demonstrates discernible biosilicification of natural microbial mats through batch laboratory experiments. Identification of the geochemical requirements for this process to occur includes thermodynamically favorable, but sluggish silica reaction kinetics associated with acidic conditions, and the necessity for colloidal silica rather than dissolved silicic acid species. This study provides the first results to bridge the apparent literature discrepancy between widespread, in-situ observations of microbial silicification, and the inability to demonstrate a detectable microbial impact in this process under well-constrained laboratory conditions. We compared the silica scavenging abilities of three natural microbial mats collected from Yellowstone National Park (YNP) hotsprings, relative to those of both abiotic particle (TiO₂) and solution controls at constant, near-saturated aqueous silica concentrations, while experimental pH and temperature conditions were varied, using both dissolved and colloidal SiO₂ forms. We specifically evaluated three microbial mats sampled from YNP sites all exhibiting saturation with respect to amorphous SiO₂, but possessing variable pH and temperature conditions that should reflect differential kinetics (and therefore biological opportunity) relative to silica polymerization: (1) most biologically favorable, acidic-mesophile (AM: pH 3, T = 35 °C); (2) biologically possible, but less opportune, alkaline, mesophile (ALK-M: pH 8, T = 35 °C) and (3) unlikely to be biologically favorable, alkaline-thermophile (ALK-T: pH 8, T = 80 °C). Comparison of field and laboratory results substantiates the requirements for thermodynamically favorable, but kinetically slower SiO₂ polymerization conditions. Results show that acidic moderate temperature conditions were required for an observable biosilicification impact. Moreover, they also identified for the first time, the necessity specifically for colloidal silica forms which are surface bound under acidic pH conditions, to distinguish discernible biosilicification compared to mineral particle controls. Results also highlight the important influence of mat surface characteristics in this process, specifically the extent of live, non-mineralized, exposed biological mat surface. Greater colloidal SiO₂ scavenging abilities are associated with non-mineralized microbial mat surfaces than with mineral particle surfaces or microbial mat surfaces encrusted with authigenic silica. These results are the first to demonstrate that biosilicification can be a microbially mediated, discernible geobiological process, shedding new light on the longstanding argument in the literature, and opening the door for more sensitive evaluation of this phenomenon in natural systems.  相似文献   

Diffusion of osmium in pyrrhotite and pyrite: implications for closure of the Re–Os isotopic system     

James M. Brenan  Daniele J. Cherniak  Lesley A. Rose 《Earth and Planetary Science Letters》2000,180(3-4):399-413

In order to better constrain the extent to which common sulfide minerals will retain their osmium isotopic composition subsequent to crystallization, we have conducted experiments to quantify the diffusion behavior of osmium in pyrite and pyrrhotite. Experiments consisted of either (1) isothermal soaking of diffusion couples consisting of natural pyrite or pyrrhotite crystals packed against powdered Os-bearing Fe-sulfide or (2) ‘relaxation’ of initially high near-surface osmium concentrations produced in the latter experiments (pyrite only). Osmium penetration into samples was characterized by depth profiling using Rutherford backscattering spectroscopy (RBS) (pyrite) or electron microprobe analyses across sectioned run products (pyrrhotite). Results of the first type of diffusion experiment involving pyrite show only limited osmium penetration into sample surfaces, with the extent of penetration uncorrelated with run duration. Images of pyrite samples using atomic force microscopy show roughening of initially smooth surfaces as a consequence of step formation and suggest that osmium incorporation into the near-surface occurred by solute uptake during step growth and not by volume diffusion. Prolonged (1000⁺ h) ‘relaxation’ experiments revealed no additional osmium penetration into pyrite surfaces and based on the depth resolution for RBS, a maximum diffusion coefficient of 2.5×10⁻²³ m²/s at 500°C was calculated. Experiments involving pyrrhotite over the temperature range of 950–1100°C showed extensive osmium uptake and osmium concentration gradients that conform with Fickian diffusion behavior. We found that pyrrhotite Fe/S could be varied by changes in the composition of the starting material and osmium source and over the range of Fe/S produced in experiments (molar Fe/S=0.83–0.90), we observed no systematic variation in the osmium diffusion coefficient. Diffusion coefficients measured parallel to the a crystallographic axis were on average 1.4× higher than values measured parallel to c and regression of the c-axis data yielded the Arrhenius relation:The application of these diffusion data to simple models of diffusive exchange during static or polythermal time–temperature histories is used to assess the conditions under which radiogenic osmium will be retained. During isothermal annealing, calculations indicate that the cores of millimeter-sized spherical pyrrhotite crystals undergoing diffusive exchange with an external osmium reservoir will have their initial compositions perturbed in ≤0.5 Ma at temperatures exceeding 400°C. Pyrite undergoing the same process at 500°C requires in excess of 10 Ma before crystal cores are affected. The relatively short ‘core retention’ time-scales for pyrrhotite indicates that this mineral may be prone to isotopic resetting following relatively brief crustal thermal events, thus possibly accounting for the scatter that commonly occurs in Re–Os isochrons generated from massive sulfide samples. Calculated closure temperatures (T_c) for osmium exchange in pyrrhotite yielded values of 300–400°C for grain sizes ranging from 10 to 1000 μm. These values of T_c are similar to those calculated for Ar retention in biotite, and considerably lower than for Sr in apatite and plagioclase, for example. Such low closure temperatures for pyrrhotite suggest this mineral will date the final stage in the cooling of a magmatic system and possibly be susceptible to open system osmium exchange in the presence of late-stage hydrothermal fluids. This latter result infers that caution be applied when interpreting elevated initial osmium isotopic ratios as a product of crustal assimilation at the magmatic stage.  相似文献   

Climate change risks to US infrastructure: impacts on roads,bridges, coastal development,and urban drainage     

James E. Neumann  Jason Price  Paul Chinowsky  Leonard Wright  Lindsay Ludwig  Richard Streeter  Russell Jones  Joel B. Smith  William Perkins  Lesley Jantarasami  Jeremy Martinich 《Climatic change》2015,131(1):97-109

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A checklist of the benthic and epiphytic marine dinoflagellates of New Zealand,including Rangitāhua/Kermadec Islands     

Lesley Rhodes  Kirsty F. Smith 《新西兰海洋与淡水研究杂志》2019,53(2):258-277

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The three dimensional structure of the atmospheric energy budget: methodology and evaluation   总被引：1，自引：0，他引：1  

Kevin E. Trenberth  Lesley Smith 《Climate Dynamics》2009,32(7-8):1065-1079

Studies of the vertically-integrated energy and moisture budgets of the atmosphere are expanded to three dimensions. The vertical integrals of the moisture, energy and heat budget equations computed analytically act as a very strong constraint on any local computational results of the vertical structure. This paper focuses on the methodology and difficulties in closing the budgets and satisfying constraints, given the need to use a pressure coordinate because model coordinates all differ. Vertical interpolation destroys delicate mass balances and can lead to inconsistencies, such as from how geopotential or vertical motion is computed. Using the advective rather than flux form of the equations greatly reduces the contamination from these effects. Results are documented for January 1989 using European Centre for Medium Range Weather Forecasts reanalysis (ERA-40) data. The moistening, diabatic heating and total energy forcing of the atmosphere are computed as a residual from the analyses using the moisture, dry energy (dry static energy plus kinetic energy) and total atmospheric (moist static plus kinetic) energy equations. The components from the monthly averaged flow and transients, as a function of layer in the atmosphere, and as quasi-horizontal and vertical fluxes of dry static, latent and kinetic energy are examined. Results show the moistening of the atmosphere at the surface, its release as latent heat in precipitation and transformation into dry static energy, and thus net radiative cooling as a function of height and location. The vertically integrated forcings computed from the model parameterizations are compared with available observations and budget-derived values, and large ERA-40 model biases are revealed in radiation and precipitation. The energy and moisture budget-derived quantities are more realistic, although results depend on the quality of the analyses which are not constructed to conserve mass, moisture or energy, owing to analysis increments.  相似文献   

Metabolic patterning of biosilicification     

Derek R. Amores  Lesley A. Warren   《Chemical Geology》2009,268(1-2):81-88

Here we show a discernibly unique biosilicification pattern for live, metabolically active Synechococcus cyanobacterial cell surfaces compared to dead Synechococcus cells under identical experimental conditions. The live cell treatments showed signs of cell division and the growth of fimbriae indicating metabolic activity during the 5-day silicification experiment. Live treatment cells were also recultivable after the experiments confirming their continued viability. The metabolically active live cyanobacteria treatment bound twice the amount of colloidal SiO₂ and held it more tightly compared to the dead cell treatment. Further, biosilicification of the live, actively metabolizing bacteria was unipolar, leaving the core surface largely unencrusted. In contrast, biosilicification of the dead cells was heterogeneous, occurring across the entire cell surface with no observable localized pattern. The directed biosilicification localization of live cell surfaces is likely a bacterial strategy to protect the cell functionality against the potentially inhibitory effects of mineral encrustation. Localization of silica biominerals to the polar end of the cell is also consistent with reported bacteria regulated cell polarity, which, under the experimental pH of 3, would enable localized differential attraction between the charged colloidal silica (+) particles and the bacterial cell polar surface (−). Our results show a novel metabolically-linked distinct colloidal SiO₂ biomineralization fingerprint, suggesting a putative biomineralization signature.  相似文献   

Sustainable Household Capability: which households are doing the work of environmental sustainability?   总被引：2，自引：2，他引：0  

Gordon Waitt  Peter Caputi  Chris Gibson  Carol Farbotko  Lesley Head  Nick Gill 《The Australian geographer》2012,43(1):51-74

This paper presents a framework for analysing which households are doing ‘their bit’ for sustainability in an era of climate change, using a two-stage cluster analysis of sustainable household capabilities. The framework segments households by their reported level of commitment to ‘pro-sustainability’ practices common to conventional government policies. Results are presented from a large-scale survey of Wollongong households, New South Wales, Australia. Results illustrate the importance of approaching household sustainability through everyday practices. Attention is drawn to the wide variation in participation in specific household sustainability practices. Investigation into sustainable household capability by household segments shows the limits of even the most committed households. Results show the importance of socio-cultural contexts in differentiating sustainable household capabilities—with women, suburban-detached households and lower income segments of the population ultimately doing most of the work of being sustainable.  相似文献   

Assembling Birrarung Wilam: a case study of Indigenous public artwork in the city     

Julia Flaster  Lesley Head 《The Australian geographer》2020,51(1):19-34

ABSTRACT

Indigenous public artworks in Australian urban spaces have challenged assumptions of Indigenous absence from the city. This paper examines the construction of Birrarung Wilam, in central Melbourne, in the period 2005–2008. We use archival documents and semi-structured interviews to analyse the collaborations between Indigenous and non-Indigenous participants in a project sponsored by the city. We show the particular mediating contribution of ‘fabricators’: a group of commissioned workers and tradespeople with material-specific expertise. Person to person encounters occurred through the modules of project management, with limited scope for long-term engagement. Despite being embedded in formal state-based recognition, Birrarung Wilam asserts Indigenous self-recognition through the renewal and adaptation of Indigenous material practices and traditions and the refusal to provide straightforward interpretive materials at the site. The study provides support for arguments that challenge a simple binary of co-option and resistance in interpreting such public art practice.  相似文献   

A special issue dedicated to microbial geochemistry     

Lesley A Warren 《Geochimica et cosmochimica acta》2004,68(15):3139

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