Methylhopane biomarker hydrocarbons in Hamersley Province sediments provide evidence for Neoarchean aerobiosis   总被引：1，自引：0，他引：1  

Jennifer L. Eigenbrode  Katherine H. Freeman  Roger E. Summons 《Earth and Planetary Science Letters》2008,273(3-4):323-331

Bacteriohopanepolyols with A-ring methyl substituents are bacterial lipid biomarkers that are presently known to originate from just a few specific taxa. When preserved in ancient rocks, the fossilized hydrocarbon skeletons of these molecules have the potential to provide biogeochemical records of those taxa and their respective physiologies. Considering both their occurrences in modern organisms, and their Proterozoic and Phanerozoic sedimentary distributions, hopanes carrying 2-methyl or 3-methyl substituents are proposed to be derived from cyanobacteria and oxygen-respiring methanotrophs, respectively. Here we report the distribution of methylhopanes in 2.72–2.56 billion-year-old, Neoarchean rocks from the Hamersley Province on the Pilbara Craton. The relative abundance of C₃₁-3β-methylhopane, but not that of C₃₁-2α-methylhopane, shows a strong correlation to the carbon isotopic composition of co-occurring kerogen (insoluble particulate organic matter). The unanticipated nature of this relationship provides evidence for a shallow-water locus of carbon cycling through aerobic oxidation of CH₄ and, coincidentally, a means to demonstrate biomarker syngenicity. 2α-Methylhopanes are most abundant in both shale and carbonate from shallow-water sediments, and a positive correlation to carbonate abundance, contrasts to variable, but generally lower, 2α-methylhopane abundances of deeper water facies. These observations are consistent with their origin from cyanobacteria which were likely the cornerstone of microbial communities in shallow-water ecosystems providing molecular oxygen, fixed carbon, and possibly fixed nitrogen.  相似文献   

Antioxidant responses to polycyclic aromatic hydrocarbons and organochlorine pesticides in green-lipped mussels (Perna viridis): do mussels "integrate" biomarker responses?   总被引：1，自引：0，他引：1  

Richardson BJ  Mak E  De Luca-Abbott SB  Martin M  McClellan K  Lam PK 《Marine pollution bulletin》2008,57(6-12):503-514

Polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCs) are generally present in the marine environment in complex mixtures. The ecotoxicological nature of contaminant interactions, however, is poorly understood, with most scientific observations derived from single contaminant exposure experiments. The objective of this experiment was to examine dose-response relationships between antioxidant parameters and body contaminant levels in mussels exposed to different exposure regimes under laboratory conditions. Accordingly, the green-lipped mussel, Perna viridis, was challenged with a mixture of PAHs (anthracene, fluoranthene, pyrene, benzo[a]pyrene) and OC pesticides (alpha-HCH, aldrin, dieldrin, p,p'-DDT) over a 4 week period. Contaminants were delivered under four different dosing regimes, with all treatments receiving the same total contaminant load by the end of the exposure period. Antioxidant biomarkers were measured after 1, 2, 3 and 4 weeks, including glutathione (GSH), gluathione-S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and lipid peroxidase (LPO). GST and CAT were induced in hepatic tissues in most of the exposure regimes, with the majority of significant induction occurring in a constant exposure regime and a two-step alternate exposure regime. Significant differences among exposure regimes were detected in the body burden of contaminants after 28 days. Hepatic CAT and GSH are proposed as potentially useful biomarkers as they showed good correlation with target contaminants and were not readily affected by different dosing patterns.  相似文献   

Antioxidant responses to polycyclic aromatic hydrocarbons and organochlorine pesticides in green-lipped mussels (Perna viridis): Do mussels “integrate” biomarker responses?     

Bruce J. Richardson  Eva Mak  Sharon B. De Luca-Abbott  Michael Martin  Katherine McClellan  Paul K.S. Lam 《Marine pollution bulletin》2008,57(6-12):503

Polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCs) are generally present in the marine environment in complex mixtures. The ecotoxicological nature of contaminant interactions, however, is poorly understood, with most scientific observations derived from single contaminant exposure experiments. The objective of this experiment was to examine dose-response relationships between antioxidant parameters and body contaminant levels in mussels exposed to different exposure regimes under laboratory conditions. Accordingly, the green-lipped mussel, Perna viridis, was challenged with a mixture of PAHs (anthracene, fluoranthene, pyrene, benzo[a]pyrene) and OC pesticides (α-HCH, aldrin, dieldrin, p,p′-DDT) over a 4 week period. Contaminants were delivered under four different dosing regimes, with all treatments receiving the same total contaminant load by the end of the exposure period. Antioxidant biomarkers were measured after 1, 2, 3 and 4 weeks, including glutathione (GSH), gluathione-S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and lipid peroxidase (LPO). GST and CAT were induced in hepatic tissues in most of the exposure regimes, with the majority of significant induction occurring in a constant exposure regime and a two-step alternate exposure regime. Significant differences among exposure regimes were detected in the body burden of contaminants after 28 days. Hepatic CAT and GSH are proposed as potentially useful biomarkers as they showed good correlation with target contaminants and were not readily affected by different dosing patterns.  相似文献   

The Winchcombe fireball—That lucky survivor     

Sarah McMullan  Denis Vida  Hadrien A. R. Devillepoix  Jim Rowe  Luke Daly  Ashley J. King  Martin Cupák  Robert M. Howie  Eleanor K. Sansom  Patrick Shober  Martin C. Towner  Seamus Anderson  Luke McFadden  Jana Horák  Andrew R. D. Smedley  Katherine H. Joy  Alan Shuttleworth  Francois Colas  Brigitte Zanda  Áine C. O'Brien  Ian McMullan  Clive Shaw  Adam Suttle  Martin D. Suttle  John S. Young  Peter Campbell-Burns  Richard Kacerek  Richard Bassom  Steve Bosley  Richard Fleet  Dave Jones  Mark McIntyre  Nick James  Derek Robson  Paul Dickinson  Philip A. Bland  Gareth S. Collins 《Meteoritics & planetary science》2024,59(5):927-947

On February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behavior, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s⁻¹). A near-catastrophic fragmentation at ∼0.07 MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures.  相似文献   

A high-resolution radio survey of Class I protostars     

P. W. Lucas  Katherine M. Blundell  P. F. Roche 《Monthly notices of the Royal Astronomical Society》2000,318(2):526-534

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The quasar fraction in low-frequency-selected complete samples and implications for unified schemes     

Chris J. Willott  Steve Rawlings  Katherine M. Blundell  Mark Lacy 《Monthly notices of the Royal Astronomical Society》2000,316(3):449-458

Low-frequency radio surveys are ideal for selecting orientation-independent samples of extragalactic sources because the sample members are selected by virtue of their isotropic steep-spectrum extended emission. We use the new 7C Redshift Survey along with the brighter 3CRR and 6C samples to investigate the fraction of objects with observed broad emission lines – the 'quasar fraction'– as a function of redshift and of radio and narrow-emission-line luminosity. We find that the quasar fraction is more strongly dependent upon luminosity (both narrow-line and radio) than it is on redshift. Above a narrow [O  ii ] emission-line luminosity of log₁₀( L _{[O  ii ]}/W)≳35 [or radio luminosity log₁₀( L ₁₅₁/W Hz⁻¹ sr⁻¹)≳ 26.5], the quasar fraction is virtually independent of redshift and luminosity; this is consistent with a simple unified scheme with an obscuring torus with a half-opening angle θ _trans≈53°. For objects with less luminous narrow lines, the quasar fraction is lower. We show that this is not due to the difficulty of detecting lower luminosity broad emission lines in a less luminous, but otherwise similar, quasar population. We discuss evidence which supports at least two probable physical causes for the drop in quasar fraction at low luminosity: (i) a gradual decrease in θ _trans and/or a gradual increase in the fraction of lightly reddened (0≲ A _V ≲5) lines of sight with decreasing quasar luminosity; and (ii) the emergence of a distinct second population of low-luminosity radio sources which, like M87, lack a well-fed quasar nucleus and may well lack a thick obscuring torus.  相似文献   

How geomorphic context governs the influence of wildfire on floodplain organic carbon in fire-prone environments of the western United States     

Ellen Wohl  Katherine B. Lininger  Sara L. Rathburn  Nicholas A. Sutfin 《地球表面变化过程与地形》2020,45(1):38-55

We draw on published studies of floodplain organic carbon storage, wildfire-related effects on floodplains in temperate and high latitudes, and case studies to propose a conceptual model of the effects of wildfire on floodplain organic carbon storage in relation to climate and valley geometry. Soil organic carbon typically constitutes the largest carbon stock in floodplains in fire-prone regions, although downed wood can contain significant organic carbon. We focus on the influence of wildfire on soil organic carbon and downed wood as opposed to standing vegetation to emphasize the geomorphic influences resulting from wildfire on floodplain organic carbon stocks. The net effect of wildfire varies depending on site-specific characteristics including climate and valley geometry. Wildfire is likely to reduce carbon stock in steep, confined valley segments because increased water and sediment yields following fire create net floodplain erosion. The net effect of fire in partly confined valleys depends on site-specific interactions among floodplain aggradation and erosion, and, in high-latitude regions, permafrost degradation. In unconfined valleys in temperate latitudes, wildfire is likely to slightly increase floodplain organic carbon stock as a result of floodplain aggradation and wood deposition. In unconfined valleys in high latitudes underlain by permafrost, wildfire is likely in the short-term to significantly decrease floodplain organic carbon via permafrost degradation and reduce organic-layer thickness. Permafrost degradation reduces floodplain erosional resistance, leading to enhanced stream bank erosion and greater carbon fluxes into channels. The implications of warming climate and increased wildfires for floodplain organic carbon stock thus vary. Increasing wildfire extent, frequency, and severity may result in significant redistribution of organic carbon from floodplains to the atmosphere via combustion in all environments examined here, as well as redistribution from upper to lower portions of watersheds in the temperate zone and from floodplains to the oceans via riverine transport in the high-latitudes. © 2019 John Wiley & Sons, Ltd.  相似文献   

Floodplain downed wood volumes: a comparison across three biomes          下载免费PDF全文

Katherine B. Lininger  Ellen Wohl  Nicholas A. Sutfin  Joshua R. Rose 《地球表面变化过程与地形》2017,42(8):1248-1261

Downed large wood (LW) in floodplains provides habitat and nutrients for diverse organisms, influences hydraulics and sedimentation during overbank flows, and affects channel form and lateral migration. Very few studies, however, have quantified LW volumes in floodplains that are unaltered by human disturbance. We compare LW volumes in relatively unaltered floodplains of semiarid boreal lowland, subtropical lowland, and semiarid temperate mountain rivers in the United States. Average volumes of downed LW are 42.3 m³ ha^?1, 50.4 m³ ha^?1, and 116.3 m³ ha^?1 in the semiarid boreal, subtropical, and semiarid temperate sites, respectively. Observed patterns support the hypothesis that the largest downed LW volumes occur in the semiarid temperate mountain sites, which is likely linked to a combination of moderate‐to‐high net primary productivity, temperature‐limited decomposition rates, and resulting slow wood turnover time. Floodplain LW volumes differ among vegetation types within the semiarid boreal and semiarid temperate mountain regions, reflecting differences in species composition. Lateral channel migration and flooding influence vegetation communities in the semiarid boreal sites, which in turn influences floodplain LW loads. Other forms of disturbance such as fires, insect infestations, and blowdowns can increase LW volumes in the semiarid boreal and semiarid temperate mountain sites, where rates of wood decay are relatively slow compared with the subtropical lowland sites. Although sediment is the largest floodplain carbon reservoir, floodplain LW stores substantial amounts of organic carbon and can influence floodplain sediment storage. In our study sites, floodplain LW volumes are lower than those in adjacent channels, but are higher than those in upland (i.e. non‐floodplain) forests. Given the important ecological and physical effects of floodplain LW, efforts to add LW to river corridors as part of restoration activities, and the need to quantify carbon stocks within river corridors, we urge others to quantify floodplain and instream LW volumes in diverse environments. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Characterizing spatiotemporal trends in extreme precipitation in Southeast Texas     

Fagnant  Carlynn  Gori  Avantika  Sebastian  Antonia  Bedient  Philip B.  Ensor  Katherine B. 《Natural Hazards》2020,104(2):1597-1621

Natural Hazards - Rainfall extreme value analysis provides information that has been crucial in characterizing risk, designing successful infrastructure systems, and ultimately protecting people...  相似文献   

Multiple lithic clasts in lunar breccia Northwest Africa 7948 and implication for the lithologic components of lunar crust     

Xiaojia Zeng  Katherine H. Joy  Shijie Li  John F. Pernet-Fisher  Xiongyao Li  Dayl J. P. Martin  Yang Li  Shijie Wang 《Meteoritics & planetary science》2018,53(5):1030-1050

This study presents the petrography, mineralogy, and bulk composition of lunar regolith breccia meteorite Northwest Africa (NWA) 7948. We identify a range of lunar lithologies including basaltic clasts (very low-titanium and low-titanium basalts), feldspathic lithologies (ferroan anorthosite, magnesian-suite rock, and alkali suite), granulites, impact melt breccias (including crystalline impact melt breccias, clast-bearing impact melt breccias, and glassy melt breccias), as well as regolith components (volcanic glass and impact glass). A compositionally unusual metal-rich clast was also identified, which may represent an impact melt lithology sourced from a unique Mg-suite parent rock. NWA 7948 has a mingled bulk rock composition (Al₂O₃ = 21.6 wt% and FeO = 9.4 wt%) and relatively low concentrations of incompatible trace elements (e.g., Th = 1.07 ppm and Sm = 2.99 ppm) compared with Apollo regolith breccias. Comparing the bulk composition of the meteorite with remotely sensed geochemical data sets suggests that the sample was derived from a region of the lunar surface distal from the nearside Th-rich Procellarum KREEP Terrane. Our investigations suggest that it may have been ejected from a nearside highlands-mare boundary (e.g., around Mare Crisium or Orientale) or a cryptomare region (e.g., Schickard-Schiller or Mare smythii) or a farside highlands-mare boundary (e.g., Mare Australe, Apollo basin in the South Pole–Aitken basin). The distinctive mineralogical and geochemical features of NWA 7948 suggest that the meteorite may represent lunar material that has not been reported before, and indicate that the lunar highlands exhibit wide geological diversity.  相似文献