Ancient graphite in the Eoarchean quartz-pyroxene rocks from Akilia in southern West Greenland II: Isotopic and chemical compositions and comparison with Paleoproterozoic banded iron formations     

Dominic Papineau  Bradley T. De Gregorio  Andrew Steele  Kurt Konhauser  Marilyn L. Fogel 《Geochimica et cosmochimica acta》2010,74(20):5884-5905

We present detailed petrographic surveys of apatite grains in association with carbonaceous material (CM) in two banded iron formations (BIFs) from the Paleoproterozoic of Uruguay and Michigan for comparison with similar mineral associations in the highly debated Akilia Quartz-pyroxene (Qp) rock. Petrographic and Raman spectroscopic surveys of these Paleoproterozoic BIFs show that apatite grains typically occur in bands parallel to bedding and are more often associated with CM when concentrations of organic matter are high. Carbonaceous material in the Vichadero BIF from Uruguay is generally well-crystallized graphite and occurs in concentrations around 0.01 wt% with an average δ¹³C_gra value of −28.6 ± 4.4‰ (1σ). In this BIF, only about 5% of apatite grains are associated with graphite. In comparison, CM in the Bijiki BIF from Michigan is also graphitic, but occurs in concentrations around 2.4 wt% with δ¹³C_gra values around −24.0 ± 0.3‰ (1σ). In the Bijiki BIF, more than 78% of apatite grains are associated with CM. Given the geologic context and high levels of CM in the Bijiki BIF, the significantly higher proportion of apatite grains associated with CM in this rock is interpreted to represent diagenetically altered biomass and shows that such diagenetic mineral associations can survive metamorphism up to the amphibolite facies.Isotope compositions of CM in muffled acidified whole-rock powders from the Akilia Qp rock have average δ¹³C_gra values of −17.5 ± 2.5‰ (1σ), while δ¹³C_carb values in whole-rock powders average −4.0 ± 1.0‰ (1σ). Carbon isotope compositions of graphite associated with apatite and other minerals in the Akilia Qp rock were also measured with the NanoSIMS to have similar ranges of δ¹³C_gra values averaging −13.8 ± 5.6‰ (1σ). The NanoSIMS was also used to semi-quantitatively map the distributions of H, N, O, P, and S in graphite from the Akilia Qp rock, and relative abundances were found to be similar for graphite associated with apatite or with hornblende, calcite, and sulfides. These analyses revealed generally lower abundances of trace elements in the Akilia graphite compared to graphite associated with apatite from Paleoproterozoic BIFs.Graphite associated with hornblende, calcite, and sulfides in the Akilia Qp rock was fluid-deposited at high-temperature from carbon-bearing fluids, and since this graphite has similar ranges of δ¹³C_gra values and of trace elements compared to graphite associated with apatite, we conclude that the Akilia graphite in different mineral associations formed from the same source(s) of CM. Collectively our results do not exclude a biogenic origin of the carbon in the Akilia graphite, but because some observations can not exclude graphitization of abiogenic carbon from CO₂- and CH₄-bearing mantle fluids, there remain ambiguities with respect to the exact origin of carbon in this ancient metasedimentary rock. Accordingly, there may have been several generations of graphite formation along with possibly varying mixtures of CO₂- and CH₄-bearing fluids that may have resulted in large ranges of δ¹³C_gra values. The possibility of fluid-deposited graphite associated with apatite should be a focus of future investigations as this may prove to be an alternative pathway of graphitization from phosphate-bearing fluids. Correlated micro-analytical approaches tested on terrestrial rocks in this work provide insights into the origin of carbon in ancient graphite and will pave the way for the search for life on other ancient planetary surfaces.  相似文献   

Use of chemical tracers in assessing the diet and foraging regions of eastern North Pacific killer whales     

Krahn MM  Herman DP  Matkin CO  Durban JW  Barrett-Lennard L  Burrows DG  Dahlheim ME  Black N  LeDuc RG  Wade PR 《Marine environmental research》2007,63(2):91-114

Top predators in the marine environment integrate chemical signals acquired from their prey that reflect both the species consumed and the regions from which the prey were taken. These chemical tracers-stable isotope ratios of carbon and nitrogen; persistent organic pollutant (POP) concentrations, patterns and ratios; and fatty acid profiles-were measured in blubber biopsy samples from North Pacific killer whales (Orcinus orca) (n=84) and were used to provide further insight into their diet, particularly for the offshore group, about which little dietary information is available. The offshore killer whales were shown to consume prey species that were distinctly different from those of sympatric resident and transient killer whales. In addition, it was confirmed that the offshores forage as far south as California. Thus, these results provide evidence that the offshores belong to a third killer whale ecotype. Resident killer whale populations showed a gradient in stable isotope profiles from west (central Aleutians) to east (Gulf of Alaska) that, in part, can be attributed to a shift from off-shelf to continental shelf-based prey. Finally, stable isotope ratio results, supported by field observations, showed that the diet in spring and summer of eastern Aleutian Island transient killer whales is apparently not composed exclusively of Steller sea lions.  相似文献   

Link between sewage-derived nitrogen pollution and coral disease severity in Guam     

Jamey E. Redding  Roxanna L. Myers-Miller  David M. Baker  Marilyn Fogel  Laurie J. Raymundo  Kiho Kim 《Marine pollution bulletin》2013

The goals of this study were to evaluate the contribution of sewage-derived N to reef flat communities in Guam and to assess the impact of N inputs on coral disease. We used stable isotope analysis of macroalgae and a soft coral, sampled bimonthly, as a proxy for N dynamics, and surveyed Porites spp., a dominant coral taxon on Guam’s reefs, for white syndrome disease severity. Results showed a strong influence of sewage-derived N in nearshore waters, with δ¹⁵N values varying as a function of species sampled, site, and sampling date. Increases in sewage-derived N correlated significantly with increases in the severity of disease among Porites spp., with δ¹⁵N values accounting for more than 48% of the variation in changes in disease severity. The anticipated military realignment and related population increase in Guam are expected to lead to increased white syndrome infections and other coral diseases.  相似文献   

Scaling forces to asteroid surfaces: The role of cohesion   总被引：1，自引：0，他引：1  

D.J. Scheeres  C.M. Hartzell  P. Sánchez  M. Swift 《Icarus》2010,210(2):968-984

The scaling of physical forces to the extremely low ambient gravitational acceleration regimes found on the surfaces of small asteroids is performed. Resulting from this, it is found that van der Waals cohesive forces between regolith grains on asteroid surfaces should be a dominant force and compete with particle weights and be greater, in general, than electrostatic and solar radiation pressure forces. Based on this scaling, we interpret previous experiments performed on cohesive powders in the terrestrial environment as being relevant for the understanding of processes on asteroid surfaces. The implications of these terrestrial experiments for interpreting observations of asteroid surfaces and macro-porosity are considered, and yield interpretations that differ from previously assumed processes for these environments. Based on this understanding, we propose a new model for the end state of small, rapidly rotating asteroids which allows them to be comprised of relatively fine regolith grains held together by van der Waals cohesive forces.  相似文献   

Anesthesia and critical-care delivery in weightlessness: A challenge for research in parabolic flight analogue space surgery studies     

Chad G. Ball  Marilyn A. Keaney  Rosaleen Chun  Michelle Tyssen  Timothy J. Broderick 《Planetary and Space Science》2010,58(4):732-740

Background

Multiple nations are actively pursuing manned exploration of space beyond low-earth orbit. The responsibility to improve surgical care for spaceflight is substantial. Although the use of parabolic flight as a terrestrial analogue to study surgery in weightlessness (0 g) is well described, minimal data is available to guide the appropriate delivery of anesthesia. After studying anesthetized pigs in a 0 g parabolic flight environment, our group developed a comprehensive protocol describing prolonged anesthesia in a parabolic flight analogue space surgery study (PFASSS). Novel challenges included a physically remote vivarium, prolonged (>10 h) anesthetic requirements, and the provision of veterinary operating room/intensive care unit (ICU) equivalency on-board an aircraft with physical dimensions of <1.5 m² (Falcon 20). Identification of an effective anesthetic regime is particularly important because inhalant anesthesia cannot be used in-flight.

Methods

After ethical approval, multiple ground laboratory sessions were conducted with combinations of anesthetic, pre-medication, and induction protocols on Yorkshire-cross specific pathogen-free (SPF) pigs. Several constant rate infusion (CRI) intravenous anesthetic combinations were tested. In each regimen, opioids were administered to ensure analgesia. Ventilation was supported mechanically with blended gradients of oxygen. The best performing terrestrial 1 g regime was flight tested in parabolic flight for its effectiveness in sustaining optimal and prolonged anesthesia, analgesia, and maintaining hemodynamic stability. Each flight day, a fully anesthetized, ventilated, and surgically instrumented pig was transported to the Flight Research Laboratory (FRL) in a temperature-controlled animal ambulance. A modular on-board surgical/ICU suite with appropriate anesthesia/ICU and surgical support capabilities was employed.

Results

The mean duration of anesthesia (per flight day) was 10.28 h over four consecutive days. A barbiturate and ketamine-based CRI anesthetic regimen supplemented with narcotic analgesia by bolus administration offered the greatest prolonged hemodynamic stability through an IV route (within multiple transport vehicles and differing gravitational environments). Standardization and pre-packaging of anesthesia, emergency pharmaceuticals, and consumables were found to facilitate the interchange of the veterinary anesthesia team members between flights. This operational process was extremely challenging.

Conclusions

With careful organization of caregivers, equipment and protocols, providing anesthesia and life support in weightlessness is theoretically possible. Unfortunately, human resource costs are extensive and likely overwhelming. Comprehensive algorithms for extended spaceflight must recognize these costs prior to making assumptions or attempting to provide critical care in space.  相似文献   

Coastal marinas in South Australia: environmental issues and strategic planning     

Nick Harvey  Peter Swift 《The Australian geographer》1990,21(2):141-150

Coastal marina proposals have recently been the subject of significant environmental controversy in South Australia. In response, the South Australian government formed a Marina Assessment Advisory Committee to produce guidelines for the planning and development of coastal marinas, examine the level of demand for marina berths and recommend suitable sites. This article outlines the characteristics of coastal marina developments in South Australia and examines some of the results of the marina committee's work in light of the planning problems associated with marina development.  相似文献   

Passive microwave remote sensing of the ocean—A review     

C. T. Swift 《Boundary-Layer Meteorology》1980,18(1):25-54

This paper reviews the current status of passive microwave remote sensing of the ocean. The physics of emission and instrumentation are highlighted in order to establish a relationship between the thermal emission and retrieved geophysical parameters. A discussion then follows on measurements of temperature, salinity, windspeed, etc. using passive microwave systems. These measurements are related to the accuracy and spatial resolution required by the users. The status of passive microwave remote sensing is summarized and recommendations for future research are presented.Part of this work was done while on leave at the NOAA Wave Propagation Laboratory, Boulder, CO 80302  相似文献   

A numerical model of fine sediment transport on the continental shelf     

Thomas L. Clarke  Donald J. P. Swift  Robert A. Young 《Environmental Geology》1982,4(2):117-129

A numerical model of fine-grained sediment dispersion in the New York Bight of the North American continental shelf is presented. Large amounts of waste material have been dumped in this region and the dispersal patterns of this material are of great interest to environmental managers. The model assumes that fine sediment resuspension is determined by surface wave activity and that transport is determined by tidal currents. Considering surface wave activity to be a random process reduces sediment motion to a random walk which is governed by a diffusion equation. The diffusion equation is solved numerically by an implicit time difference, finite element algorithm for a number of initial conditions. Initial conditions corresponding to ocean dumping sites show patterns of dispersal controlled by the geometry of the study region and the anisotropy of the tides. Material dumped at currently used dump sites reaches sensitive coastal areas before it leaves the continental shelf. Examination of the diffusion coefficients suggests an alternative dump site for fine-grained material. This dump site is relatively near sources of dumped material but produces minimal impact on coastal areas. This site should be considered as a possible alternative to expensive direct disposal at deep ocean sites.  相似文献   

Biogeochemistry of the stable hydrogen isotopes     

Marilyn F. Estep  Thomas C. Hoering 《Geochimica et cosmochimica acta》1980,44(8):1197-1206

The fractionation of H isotopes between the water in the growth medium and the organically bonded H from microalgae cultured under conditions, where light intensity and wavelength, temperature, nutrient availability, and the H isotope ratio of the water were controlled, is reproducible and light dependant. All studies were based either on the H isotope ratios of the total organic H or on the lipids, where most of the H is firmly bonded to C. H bonded into other macromolecules, proteins, carbohydrates and nucleic acids, does not exchange with water, when algae are incubated in water enriched with deuterium. Only after the destruction of quaternary H bonds are labile hydrogens in macromolecules free to exchange with water. By growing algae (18 strains), including blue-green algae, green algae and diatoms, in continuous light, the isotope fractionations in photosynthesis were reproducibly ?93 to ?178 %. depending on the organism tested. This fractionation was not temperature dependent. Microalgae grown in total darkness with an organic substrate did not show the isotope fractionation seen in cells grown in light. In both light- and dark-grown algae, however, additional depletion of deuterium (?30 to ?60%.) in cellular organic matter occurs during the metabolism of carbohydrates to form lipids. Plants from several natural populations also fractionated isotopes during photosynthesis by an average of ?90 to ?110%. In addition, the organically bonded H in nonsaponifiable lipids was further fractionated by ?80%. from that in saponifiable lipids, isolated from two geographically distinct populations of marsh plants. This difference between H isotope ratios of these two groups of lipids provides an endogenous isotopic marker.  相似文献   

Lithium Needs and Resources: edited by S.S. Penner. Pergamon Press. 1978, 183 pp. $32.00     

Marilyn G. Truscott 《Geochimica et cosmochimica acta》1980,44(11):1911

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