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911.
Measurements are reported of the 10Be concentrations in 15 sediments from the sea off southern California. The sedimentation patterns are modelled with a two component system, one component having the high 10Be concentration of pelagic sediment and the other the low concentration of continental runoff. The pelagic component, brought to the region by the California Current with the Pacific Ocean as reservoir, is very likely the source not only of anomalously high 10Be deposition but also of similar effects with 2101Pb, 239,240pu and 241Pu. 相似文献
912.
The arguments justifying the revised timing of breakup between Australia and Antarctica (Cande and Mutter, 1982) and the reconstruction of Broken Ridge and Kerguelen Plateau (Mutter and Cande, 1983) are reviewed and considered with respect to new subsidence data. The age of breakup was revised from anomaly 22 time (55 My B.P.) to anomaly 34 time (85 My B.P.). The rough topography of the Diamantina Zone can be attributed to very slow spreading (−5 mm/yr.) beginning between the times of anomaly 34 and anomaly 19. The reconstruction of Broken Ridge and Kerguelen Plateau at anomaly 34 time shows overlap of these two features, but the overlap problem is nearly resolved by anomaly 18 time ( ~ 42 My B.P.). Normal seafloor spreading rates (22 mm/yr.) commenced at anomaly 19 time ( ~ 43 My B.P.). Subsidence patterns calculated from biostratigraphic data from wells drilled along Australia's southern margin are interpreted as more consistent with the revised age of Australia-Antarctic breakup. Subsidence curves systematically show rapid subsidence associated with the rift phase of margin development followed by much slower thermally-controlled subsidence during the drift phase. The timing of the rift-to-drift transition is believed to coincide with the age of breakup ( ~ 60 to 110 My B.P.). In addition, the subsidence curves indicate a west-to-east propagation of breakup along the southern margin. Magnetic anomaly patterns and stratigraphie observations are consistent with this hypothesis. 相似文献
913.
Basalts from DSDP Site 417 (109 Ma) exhibit the effects of several stages of alteration reflecting the evolution of seawater-derived solution compositions and control by the structure and permeability of the crust. Characteristic secondary mineral assemblages occur in often superimposed alteration zones within individual basalt fragments. By combining bulk rock and single phase chemical analyses with detailed mineralogic and petrographic studies, chemical changes have been determined for most of the alteration stages identified in the basalts.
- Minor amounts of saponite, chlorite, and pyrite formed locally in coarse grained portions of massive units, possibly at high temperatures during initial cooling of the basalts. No chemical changes could be determined for this stage.
- Possible mixing of cooled hydrothermal fluids with seawater resulted in the formation of celadonite-nontronite and Fe-hydroxide-rich black halos around cracks and pillow rims. Gains of K, Rb, H2O, increase of Fe3+/FeT, and possibly some losses of Ca and Mg occurred during this stage.
- Extensive circulation of oxygenated seawater resulted in the formation of various smectites, K-feldspar, and Fe-hydroxides in brown and light grey alteration zones around formerly exposed surfaces. K, Rb, H2O, and occasionally P were added to the rocks, Fe3+/FeT increased, and Ca, Mg, Si and occasionally Al and Na were lost.
- Anoxic alteration occurred during reaction of basalt with seawater at low water-rock ratios, or with seawater that had previously reacted with basalt. Saponite-rich dark grey alteration zones formed which exhibit very little chemical change: generally only slight increases in Fe3+/FeT and H2O occurred.
- Zeolites and calcite formed from seawater-derived fluids modified by previous reactions with basalt. Chemical changes involved increases of Ca, Na, H2O, and CO2 in the rocks.
- A late stage of anoxic conditions resulted in the formation of minor amounts of Mn-calcites and secondary sulfides in previously oxidized rocks. No chemical changes were determined for this stage.
914.
915.
The occurrence and distribution of low molecular weight α-hydroxy carboxylic and dicarboxylic acids was studied in reducing marine sediments collected in the Santa Barbara Basin and the Cariaco Trench. Four compounds were found to occur in both basin sediments: glycolic, lactic, oxalic and succinic acids. In general concentrations were low (? 1 μmol/g for the hydroxy acids and ? 100μmol/g for the dicarboxylic acids), and generally decreased with depth. Subsurface maxima were observed for lactate and succinate in the Santa Barbara Basin. Both the vertical profiles and lactate enantiomer ratios suggested microbial origin and control for the distribution of these compounds. A preliminary model for the microbial mediation of the early diagenesis of organic compounds in reducing marine sediments is presented. 相似文献
916.
The results are presented of a survey of mercury concentrations in various parts of the Icelandic environment. Values for air and gas samples include: <0.03 μg/m3 for Reykjavík, 15–20 km away from a hydrothermal area; 1–3 μg/m3 for air in a hydrothermal area near Lake Mývatn; 12–30 μg/m3 for air in Heimaey during the 1973 eruption; and 16 μg/m3 for a sample of fumarole gas. Values for fresh igneous rocks, of various compositions, extrusive (subaerial), subaqueous (up to 3000 m depth), and intrusive, range between 2 and 9 ppb. Highest values obtained for uncontaminated samples are 37 ppb for a pyrite-bearing zone in a hydrothermal drill hole, and 125 ppb for a volcanic sublimate. The sources of the mercury levels observed are briefly discussed. 相似文献
917.
δ13CPDB compositions for 39 samples of dissolved organic carbon (DOC) from the Gulf of Mexico-Caribbean Sea-Atlantic Ocean system, the South Pacific and Ross Sea are reported. Deep water values are similar with a mean of ?21.8%. attesting to the homogeneity of the oceanic DOC pool. In Antarctic waters, a 5%. difference between DOC and particulate organic carbon (POC), with POC having values similar to modern plankton (δ13CPDB approx ?27%.) supports the idea of the transient nature of POC as compared to DOC.Total, lipid, acid hydrolyzed, amino acid and residue fractions of POC are about 5, 3, 7, 5 and 3%. respectively, more negative in 2000 m water as compared to surface water samples from the Gulf of Mexico. 相似文献
918.
Kirsten Warrach Marc Stieglitz Jeffrey Shaman Victor C. Engel Kevin L. Griffin 《Climatic change》2006,75(4):455-493
During the 20th century the northeastern U.S.A. has undergone an annual temperature increase of 1 °C, the combined effect
of winter warming and an increase in daily summer minimum temperatures. A significant cooling of spring through autumn in
maximum air temperatures is also evident since 1950. Therefore, the primary objective of this study is to document these climate
trends and variability over the last century. A secondary objective is to provide a preliminary analysis of how these changes
may have impacted hydrologic and ecosystem processes. Specifically, with respect to ecosystem processes, we examine how the
cooling of daytime maximum temperatures may have impacted plant respiration and biomass accumulation. The study site is the
Black Rock Forest, an experimental forest located in Hudson Highlands of New York that has been maintained as a conservation
area over the last 100 years. For the region centered about the forest, there exists a climate/weather record and an extensively
maintained biomass record that extends continuously from the early part of the 20th century through present. With such an
extensive physical and biological record to draw from, this forest provides a microcosm for studying how changes in 20th century
local and regional climate may have impacted ecosystem processes such as species adaptation, biomass growth, and 20th century
carbon sequestration. In a subsequent paper we will more extensively explore the relationship between this record of changing
climate and eco-hydrological processes. 相似文献
919.
Attenuation of seismic waves in methane gas hydrate-bearing sand 总被引:4,自引:0,他引:4
920.
Christopher D. Elvidge Jeffrey Safran Benjamin Tuttle Paul Sutton Pierantonio Cinzano Donald Pettit John Arvesen Christopher Small 《GeoJournal》2007,69(1-2):45-53
Nightsat is a concept for a satellite system capable of global observation of the location, form and density of lighted infrastructure
and development within human settlements. Nightsat’s repeat cycle should be sufficient to produce an annual cloud-free composite
of surface lighting to enable detection of growth rates. Airborne and satellite imagery have been used to define the range
of spatial, spectral, and detection limit options for a future Nightsat mission. Our conclusion is that Nightsat should collect
data from a near-synchronous orbit in the early evening with 50–100 m spatial resolution and have detection limits of 2.5E−8 W cm−2 sr−1 μm−1 or better. Multispectral low-light imaging data would be better than panchromatic data by providing valuable information
on the type or character of lighting, a potentially stronger predictor of variables such as ambient population density and
economic activity. 相似文献