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91.
92.
J. Mclelland J. Morrison B. Selleck B. Cunningham C. Olson K. Schmidt 《Journal of Metamorphic Geology》2002,20(1):175-190
Quartz–sillimanite segregations, quartz–albite lithologies (Ab95–98), and Kiruna‐type low‐Ti iron‐oxide deposits are associated with late‐ to post‐tectonic (c. 1055 Ma) leucogranites of Lyon Mountain Gneiss (LMG) in the Adirondack Mountains, New York State. Most recent interpretations of these controversial features, which are global in occurrence, favour hydrothermal origins in agreement with results presented here. Field relations document that quartz–sillimanite veins and nodules cut, and therefore post‐date, emplacement of host LMG leucogranites. Veins occur in oriented fracture networks, and aligned trains of nodules are interpreted as disrupted early veins. Late dykes of leucogranite cut veins and nodules demonstrating formation prior to terminal magmatism. Veins and nodules consist of sillimanite surrounded by quartz that commonly embays wall‐rock feldspar indicating leaching of Na and K from LMG feldspar by acidic hydrothermal fluids. Subsequent, and repeated, ductile flow disrupted earlier veins into nodular fragments but produced little grain shape fabric. Geochemical and petrographic studies of quartz–albite rock indicate that it formed through metasomatic replacement (albitization) of LMG microperthite by sodic hydrothermal fluids that resulted in diagnostic checkerboard albite. Low‐Ti iron‐oxide ores are commonly associated with the quartz–albite sub‐unit, and it is proposed that hydrothermal fluids related to albitization transported Fe as well. The regional extent of sodic alteration suggests large quantities of surface‐derived hydrothermal fluids. Fluid inclusion and oxygen isotope data are consistent with high temperature, regionally extensive fluids consisting primarily of evolved surface‐derived brines enriched in Na and Cl. Quartz–sillimanite veins and nodules, which are significantly more localised phenomena and require acidic fluids, were most likely formed from local magmatic fluids in the crystallizing carapaces of LMG plutons. 相似文献
93.
Ling Ren Nancy N. Rabalais R. Eugene Turner Wendy Morrison Warren Mendenhall 《Estuaries and Coasts》2009,32(5):958-974
The Davis Pond Diversion (DPD) was constructed to divert Mississippi River (MR) water into the Barataria Basin to reduce the
salinity in support of wetland restoration on the Louisiana coast. To assess the phytoplankton nutrient limitation in adjacent
water systems and potential impacts of DPD, 12 seasonal nutrient-phytoplankton bioassay experiments were conducted from October
2003 to July 2004 using the natural phytoplankton assemblages from freshwater and brackish-water lakes, Cataouatche and Salvador,
LA (USA), which receive Mississippi River water from the DPD, and from a nearby freshwater lake, Lac des Allemands, that does
not. Dissolved inorganic nitrogen (N), phosphorus (P), and silicate (Si) were added with different combinations at Redfield
ratios in 10-l microcosms. Nitrogen was found to be the sole or primary limiting nutrient in all 12 experiments. N and P colimitations
were found in seven of 12 experiments, but N was always the stronger limiting factor. P limitation was never observed to be
the sole limiting nutrient. The results showed that a low concentration of P and a relatively high concentration of N do not
necessarily indicate only P limitation in these lakes. Lake Cataouatche and Lake Salvador were dominated by centric diatoms,
and Anabaena spp. were detected at high levels, particularly in summer. Lac des Allemands was generally dominated by N-fixing Anabaena spp. and other cyanobacteria, and their biomass responded significantly to N addition but not to P addition, indicating that
nitrogen fixation in Lac des Allemands may be inhibited by other factors such as iron. Our bioassay results demonstrate that
whether a water body is N- or P-limited is the consequence of the nutrient status and not the salinity regime. The results
suggest that the addition of nutrient-rich waters via diversions of Mississippi River water into these lakes might increase
the frequency of algal blooms, including noxious and toxic freshwater cyanobacteria. 相似文献
94.
M. E. Davies V. K. Abalakin M. Bursa J. H. Lieske B. Morando D. Morrison P. K. Seidelmann A. T. Sinclair B. Yallop Y. S. Tjuflin 《Celestial Mechanics and Dynamical Astronomy》1995,63(2):127-148
Every three years the IAU/IAG/COSPAR Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Stallites revises tables giving the directions of the north poles of rotation and the prime meridians of the planets, satellites, and asteroids. Also presented are revised tables giving their sizes and shapes. 相似文献
95.
Joel L. Morrison 《地理信息系统科学与遥感》2013,50(1):13-14
The results of measurements of sea surface temperature (SST) in a large hydrological test area are discussed. Data recorded by the AVHRR radiometer, an instrument for measuring surface temperature towed by a scientific research ship, an STD sounder, and two LOBAN-TM drifting buoys are used. Data measurement and processing methods are described. Maps of the spatial distributions of sea surface temperature are compared. Accuracy in retrieving the sea surface temperature field from satellite data is evaluated. 相似文献
96.
97.
Chemical and isotopic signatures were determined in groundwater samples to aid in distinguishing the source of contamination in three desert arroyos and a buried channel (the swale) near Shiprock, New Mexico. The contamination in the swale and one of the arroyos, Many Devils Wash, was previously attributed to a former uranium mill site because of the similar suite of contaminants (nitrate, selenium, sulfate, and uranium) and the close (0.8 km) proximity. The other two arroyos are far removed from the mill site and could not have received contamination from it. Principal component and cluster analysis indicated similarities in groundwater chemistry among the swale and the three arroyos that contrasted with groundwater chemistry at the disposal cell. Disposal cell groundwater is characterized by high uranium and bicarbonate concentrations, whereas that in remaining study areas is characterized by high sodium and sulfate, but lower uranium concentrations. Mancos Shale forms the bedrock in the region and contains elevated concentrations of the same chemical constituents that appear in the swale and arroyo groundwater. Dissolved sulfate in arroyo groundwater was depleted in sulfur‐34, in contrast to mill‐derived sulfate with more enriched sulfur‐34. Uranium‐234 to uranium‐238 activity ratios (ARs) were near the secular equilibrium value of 1 in mill site groundwater, whereas ARs in all arroyo groundwater samples exceeded 2. Elevated tritium activities present in mill site groundwater (49 to 142 pCi/L) are attributed to the mill being operated during atomic bomb testing in the 1950s and 1960s. The combined chemical and isotopic results indicate that groundwater in Many Devils Wash and the swale was likely derived from the Mancos Shale and not from the milling operation. 相似文献
98.
A computational program, called the groundwater flow calculator, was created to quickly and easily determine the hydraulic gradient and direction of groundwater flow. The groundwater flow calculator automates the hand‐drawn process by Ralph Heath in the U.S. Geological Survey (USGS) Water Supply Paper 2220. In addition, a mobile app was developed to allow this procedure to run on a smart phone for use in the field. 相似文献
99.
Edward L. Chapin Alexandra Pope † Douglas Scott Itziar Aretxaga Jason E. Austermann Ranga-Ram Chary Kristen Coppin Mark Halpern David H. Hughes James D. Lowenthal Glenn E. Morrison Thushara A. Perera Kimberly S. Scott Grant W. Wilson Min S. Yun 《Monthly notices of the Royal Astronomical Society》2009,398(4):1793-1808
We present results from a multiwavelength study of 29 sources (false detection probabilities <5 per cent) from a survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field at 1.1 mm using the Astronomical Thermal Emission Camera (AzTEC). Comparing with existing 850 μm Submillimetre Common-User Bolometer Array (SCUBA) studies in the field, we examine differences in the source populations selected at the two wavelengths. The AzTEC observations uniformly cover the entire survey field to a 1σ depth of ∼1 mJy. Searching deep 1.4 GHz Very Large Array (VLA) and Spitzer 3–24 μm catalogues, we identify robust counterparts for 21 1.1 mm sources, and tentative associations for the remaining objects. The redshift distribution of AzTEC sources is inferred from available spectroscopic and photometric redshifts. We find a median redshift of z = 2.7 , somewhat higher than z = 2.0 for 850 μm selected sources in the same field, and our lowest redshift identification lies at a spectroscopic redshift z = 1.1460 . We measure the 850 μm to 1.1 mm colour of our sources and do not find evidence for '850 μm dropouts', which can be explained by the low signal-to-noise ratio of the observations. We also combine these observed colours with spectroscopic redshifts to derive the range of dust temperatures T , and dust emissivity indices β for the sample, concluding that existing estimates T ∼ 30 K and β∼ 1.75 are consistent with these new data. 相似文献
100.
Darren M. Parsons Mark A. Morrison Simon F. Thrush Crispin Middleton Matt Smith Keren T. Spong Dane Buckthought 《Marine Ecology》2013,34(4):492-500
Estuarine and sheltered coastal habitats that contain physical structure are potentially important nurseries for juvenile fish. Many of these structured habitats, however, are potentially vulnerable to stressors such as elevated turbidity. Quantifying the benefits that structured habitats provide to juvenile fish may therefore be an important step in the management process. We investigated the value of structured habitat for juvenile fishes in northeastern New Zealand, using artificial seagrass units (ASUs) with varying blade density. ASUs were predominantly settled by juvenile snapper (Pagrus auratus) and spotty (Notolabrus celidotus). The density of both snapper and spotty was greatest on ASUs with the highest blade density. For snapper, a gradient in abundance was present (with higher abundance closer to the harbour mouth), suggesting either a gradient in the supply of recruits or a potential recruitment shadow effect. The size distribution of juvenile snapper (12–70 mm fork length) was very similar on both sampling trips, despite the 2‐month interim period, suggesting an ontogenetic habitat shift dependent on size. The condition of juvenile snapper from ASUs with the highest blade density was also greater than the other ASU treatments. Overall, these results provide new empirical evidence that habitats with physical structure within shallow estuarine systems are important to early stage juvenile fishes such as snapper, and indicate that the location‐specific context of that habitat is also likely important. 相似文献