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81.
Bulk compositions of igneous and microbreccia lithic fragments, glasses, and chondrules from Luna 16 fines as well as compositions of minerals in basaltic lithic fragments were determined with the electron microprobe. Igneous lithic fragments and glasses are divided into two groups, the anorthositic-noritic-troctolitic (hereafter referred to as ANT) and basaltic groups. Chondrules are always of ANT composition and microbreccia lithic fragments are divided into groups 1 and 2. The conclusions reached may be summarized as follows: (1) Luna 16 fines are more similar in composition to Apollo 11 than to Apollo 12 and 14 materials (e.g. Apollo 11 igneous lithic fragments and glasses fall into similar ANT and basaltic groups; abundant norites in Luna 16 and Apollo 11 are not KREEP as in Apollo 12 and 14; Luna 16 basaltic lithic fragments may represent high-K and low-K suites as is the case for Apollo 11; rare colorless to greenish, FeO-rich and TiO2-poor glasses were found in both Apollo 11 and Luna 16; Luna 16 spinels are similar to Apollo 11 spinels but unlike those from Apollo 12). (2) No difference was noted in the composition of lithic fragments, glasses and chondrules from Luna 16 core tube layers A and D. (3) Microbreccia lithic fragments of group 1 originated locally by mixing of high proportions of basaltic with small proportions of ANT materials. (4) Glasses are the compositional analogs to the lithic fragments and not to the microbreccias; most glasses were produced directly from igneous rocks. (5) Glasses show partial loss of Na and K due to vaporization in the vitrification process. (6) Luna 16 chondrules have ANT but not basaltic composition. It is suggested that either liquid droplets of ANT composition are more apt to nucleate from the supercooled state; or basaltic droplets have largely been formed in small and ANT droplets in large impact events (in the latter case, probability for homogeneous and inhomogeneous nucleation is larger. (7) No evidence for ferric iron and water-bearing minerals was found. (8) Occurrence of a great variety of igneous rocks in Luna 16 samples (anorthosite, noritic anorthosite, anorthositic norite, olivine norite, troctolite, and basalt) confirm our earlier conclusion that large-scale melting or partial melting to considerable depth and extensive igneous differentiation must have occurred on the moon. 相似文献
82.
Michael F. Rosenmeier David A. Hodell Mark Brenner Jason H. Curtis Jonathan B. Martin Flavio S. Anselmetti Daniel Ariztegui Thomas P. Guilderson 《Journal of Paleolimnology》2002,27(1):117-131
Stratigraphic shifts in the oxygen isotopic (18O) and trace element (Mg and Sr) composition of biogenic carbonate from tropical lake sediment cores are often interpreted as a proxy record of the changing relation between evaporation and precipitation (E/P). Holocene 18O and Mg and Sr records from Lakes Salpetén and Petén Itzá, Guatemala were apparently affected by drainage basin vegetation changes that influenced watershed hydrology, thereby confounding paleoclimatic interpretations. Oxygen isotope values and trace element concentrations in the two lowland lakes were greatest between ~ 9000 and 6800 14C-yr BP, suggesting relatively high E/P, but pollen data indicate moist conditions and extensive forest cover in the early Holocene. The discrepancy between pollen- and geochemically-inferred climate conditions may be reconciled if the high early Holocene 18O and trace element values were controlled principally by low surface runoff and groundwater flow to the lake, rather than high E/P. Dense forest cover in the early Holocene would have increased evapotranspiration and soil moisture storage, thereby reducing delivery of meteoric water to the lakes. Carbonate 18O and Mg and Sr decreased between 7200 and 3500 14C-yr BP in Lake Salpetén and between 6800 and 5000 14C-yr BP in Lake Petén Itzá. This decline coincided with palynologically documented forest loss that may have led to increased surface and groundwater flow to the lakes. In Lake Salpetén, minimum 18O values (i.e., high lake levels) occurred between 3500 and 1800 14C-yr BP. Relatively high lake levels were confirmed by 14C-dated aquatic gastropods from subaerial soil profiles ~ 1.0–7.5 m above present lake stage. High lake levels were a consequence of lower E/P and/or greater surface runoff and groundwater inflow caused by human-induced deforestation. 相似文献
83.
Davis JA May MD Greenfield BK Fairey R Roberts C Ichikawa G Stoelting MS Becker JS Tjeerdema RS 《Marine pollution bulletin》2002,44(10):1117-1129
In 1997, seven sport fish species were sampled from seven popular fishing areas in San Francisco Bay. Mercury exceeded a human health screening value in 44 of 84 (52%) samples. All collected samples of leopard shark and striped bass exceeded the mercury screening value of 0.23 microg/g wet weight. PCBs exceeded the screening value in 51 of 72 (71%) samples. DDT, chlordane, and dieldrin, had lower numbers of samples above screening values: 16 of 72 (22%) for DDT, 11 of 72 (15%) for chlordanes, and 27 of 72 (37%) for dieldrin. Concentrations of PCBs and other trace organics were highest in white croaker and shiner surfperch, the two species with the highest fat content in their muscle tissue. Fish from one location, Oakland Harbor, had significantly elevated wet weight concentrations of mercury, PCBs, DDTs, and chlordanes compared to other locations. Removal of skin from white croaker fillets reduced lipid concentrations by 27-49% and concentrations of trace organics by 33-40%. 相似文献
84.
85.
Ho KT Burgess RM Pelletier MC Serbst JR Ryba SA Cantwell MG Kuhn A Raczelowski P 《Marine pollution bulletin》2002,44(4):286-293
The identification of toxicants affecting aquatic benthic systems is critical to sound assessment and management of our nation's waterways. Identification of toxicants can be useful in designing effective sediment remediation plans and reasonable options for sediment disposal. Knowledge of which contaminants affect benthic systems allows managers to link pollution to specific dischargers and prevent further release of toxicant(s). In addition, identification of major causes of toxicity in sediments may guide programs such as those developing environmental sediment guidelines and registering pesticides, while knowledge of the causes of toxicity which drive ecological changes such as shifts in benthic community structure would be useful in performing ecological risk assessments. To this end, the US Environmental Protection Agency has developed tools (toxicity identification and evaluation (TIE) methods) that allow investigators to characterize and identify chemicals causing acute toxicity in sediments and dredged materials. To date, most sediment TIEs have been performed on interstitial waters. Preliminary evidence from the use of interstitial water TIEs reveals certain patterns in causes of sediment toxicity. First, among all sediments tested, there is no one predominant cause of toxicity; metals, organics, and ammonia play approximately equal roles in causing toxicity. Second, within a single sediment there are multiple causes of toxicity detected; not just one chemical class is active. Third, the role of ammonia is very prominent in these interstitial waters. Finally, if sediments are divided into marine or freshwater, TIEs perforMed on interstitial waters from freshwater sediments indicate a variety of toxicants in fairly equal proportions, while TIEs performed on interstitial waters from marine sediments have identified only ammonia and organics as toxicants, with metals playing a minor role. Preliminary evidence from whole sediment TIEs indicates that organic compounds play a major role in the toxicity of marine sediments, with almost no evidence for either metal or ammonia toxicity. However, interpretation of these results may be skewed because only a small number of interstitial water (n = 13) and whole sediment (n = 5) TIEs have been completed. These trends may change as more data are collected. 相似文献
86.
Jonathan Baron 《Climatic change》2006,77(1-2):137-150
Attitudes toward global warming are influenced by various heuristics, which may distort policy away from what is optimal for the well-being of people. These possible distortions, or biases, include: a focus on harms that we cause, as opposed to those that we can remedy more easily; a feeling that those who cause a problem should fix it; a desire to undo a problem rather than compensate for its presence; parochial concern with one’s own group (nation); and neglect of risks that are not available. Although most of these biases tend to make us attend relatively too much to global warming, other biases, such as wishful thinking, cause us to attend too little. I discuss these possible effects and illustrate some of them with an experiment conducted on the World Wide Web. 相似文献
87.
Henry P. Huntington Michelle Boyle Gwenn E. Flowers John W. Weatherly Lawrence C. Hamilton Larry Hinzman Craig Gerlach Rommel Zulueta Craig Nicolson Jonathan Overpeck 《Climatic change》2007,82(1-2):77-92
Human activities in the Arctic are often mentioned as recipients of climate-change impacts. In this paper we consider the
more complicated but more likely possibility that human activities themselves can interact with climate or environmental change
in ways that either mitigate or exacerbate the human impacts. Although human activities in the Arctic are generally assumed
to be modest, our analysis suggests that those activities may have larger influences on the arctic system than previously
thought. Moreover, human influences could increase substantially in the near future. First, we illustrate how past human activities
in the Arctic have combined with climatic variations to alter biophysical systems upon which fisheries and livestock depend.
Second, we describe how current and future human activities could precipitate or affect the timing of major transitions in
the arctic system. Past and future analyses both point to ways in which human activities in the Arctic can substantially influence
the trajectory of arctic system change. 相似文献
88.
Jonathan Reynolds 《GeoJournal》1998,45(4):245-254
The internationalising activities of retailers have tended to precede the theoretical contributions of academics. This is
particularly the case for the cultural context within which retail internationalisation takes place. Following an examination
of the growth of international retailing activity, the article reviews generic difficulties in studying inter-cultural differences
before considering the specific steps which retail practitioners have taken to understand the comparative characteristics
of retail and consumer markets through the growth of geodemographic and lifestyle analysis. Finally, we relate one of the
most significant integrative intercultural theoretical instruments to the case of retail internationalisation within Western
Europe. We find that significant insights into retailer behaviour and strategy can be gained from an understanding of the
culturally-specific characteristics of the activity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
89.
Sharmishtha Dattagupta Jonathan Martin Shu-min Liao Robert S. Carney & Charles R. Fisher 《Marine Ecology》2007,28(1):193-198
Bathynerita naticoidea (Gastropoda: Neritidae) is a numerically dominant heterotrophic gastropod found at hydrocarbon seep sites on the upper Louisiana slope of the Gulf of Mexico. Snails of this species are commonly associated with beds of the methanotrophic mussel Bathymodiolus childressi (Bivalvia: Mytilidae), and their population structure mirrors that of the mussels they are found among. Previous studies have shown that these snails feed on bacteria and decomposing periostracum on the B. childressi shell. We predicted that B. naticoidea might be attracted to cues specific to its preferred habitat, such as dissolved methane, mucus from conspecific snails, or metabolites produced by B. childressi mussels. To examine this, we used a flow‐through Y‐maze system to investigate the behavior of B. naticoidea exposed to these potential cues. We found that the nerite is not attracted to methane, but is strongly attracted to seawater conditioned with B. childressi. The attractant appears to be specific to this type of mussel, and is not a soluble cue produced by conspecific snails. 相似文献
90.
Graeme T. Swindles Ivan P. Savov Charles B. Connor Jonathan Carrivick Elizabeth Watson Ian T. Lawson 《Geology Today》2013,29(6):214-217
The volcanic ash or ‘tephra’ cloud resulting from the relatively small (volume and VEI) eruption of the Icelandic volcano Eyjafjallajökull in 2010 caused major air travel disruption, at substantial global economic cost. On several occasions in the past few centuries, Icelandic eruptions have created ash and/or sulphur dioxide clouds which were detected over Europe (e.g. Hekla in 1947, Askja in 1875, and Laki in 1783). However, these historical observations do not represent a complete record of events serious enough to disrupt aviation in Europe. The only feasible evidence for this is within the geological tephra record. Ash layers are preserved in bogs and lakes where tephra deposited from the atmosphere is incorporated in the peat/mud. In this article we: 1, introduce the analysis of the Northern European sedimentary tephra record; 2, discuss our findings and modelling results; 3, highlight how these were misinterpreted by the popular media; and 4, use this experience to outline several existing problems with current tephra studies and suggest agendas for future research. 相似文献