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101.
102.
Geoff Kilgour Jon Blundy Kathy Cashman Heidy M. Mader 《Contributions to Mineralogy and Petrology》2013,166(2):371-392
Historical eruptions from Mt. Ruapehu (New Zealand) have been small (<0.001 km3 of juvenile magma) and have often occurred without significant warning. Developing better modelling tools requires an improved understanding of the magma storage and transport system beneath the volcano. Towards that end, we have analysed the volatile content and major element chemistry of groundmass glass and phenocryst-hosted melt inclusions in erupted samples from 1945 to 1996. We find that during this time period, magma has been stored at depths of ~2–9 km, consistent with inferences from geophysical data. Our data also show that Ruapehu magmas are relatively H2O-poor (<2 wt%) and CO2-rich (≤1,000 ppm) compared to typical arc andesites. Surprisingly, we find that melt inclusions are often more evolved than their transporting melt (as inferred from groundmass glass compositions). Furthermore, even eruptions that are separated by less than 2 years exhibit distinct major element chemistry, which suggests that each eruption involved magma with a unique ascent history. From these data, we infer that individual melt batches rise through, and interact with, crystal mush zones formed by antecedent magmas. From this perspective, we envision the magmatic system at Ruapehu as frequently recharged by small magma inputs that, in turn, cool and crystallise to varying degrees. Melts that are able to erupt through this network of crystal mush entrain (to a greater or lesser extent) exotic crystals. In the extreme case (such as the 1996 eruption), the resulting scoria contain melt inclusion-bearing crystals that are exotic to the transporting magma. Finally, we suggest that complex interactions between recharge and antecedent magmas are probably common, but that the small volumes and short time scales of recharge at Ruapehu provide a unique window into these processes. 相似文献
103.
Barbara J. Inyan Mark W. Williams Kathy Tonnessen John T. Turk Donald H. Campbell 《自然地理学》2013,34(5):406-420
In the Rocky Mountains, the association of increases in acidic deposition with increased atmospheric loading of sulfate and direct changes in surface water chemistry has been well established. The importance, though, of increased nitrogen (N) deposition in the episodic acidification of alpine lakes and N saturation in alpine ecosystems is only beginning to be documented. In alpine areas of the Colorado Front Range, modest loadings of N in deposition have been associated with leakage of N to surface waters. On the Colorado western slope, however, no leakage of N to surface waters has been reported. A 1995 study that included early season under-ice water samples that were not available in earlier studies showed that there is, in fact, N leakage to surface waters in some western slope basins. Under-ice nitrate (NO- 3) concentrations were as high as 10.5 μeq L-1 and only decreased to detection limits in September. Landscape type appears to be important in leakage of N to surface waters, which is associated with basins having steep slopes, thin soils, and large amounts of exposed bedrock. NO- 3 leakage compounds the existing sensitivity to episodic acidification from low acid neutralizing capacity (ANC), which is less than 40 μeq L-1 in those basins. [Key words: episodic acidification, nitrogen deposition, nitrate, alpine ecosystems, landscape type, Rocky Mountains.] 相似文献
104.
Peter Jenniskens Ed Tedesco Jayant Murthy Christophe O. Laux Stephen Price 《Meteoritics & planetary science》2002,37(8):1071-1078
Abstract— We used the ultraviolet to visible spectrometers onboard the midcourse space experiment to obtain the first ultraviolet spectral measurements of a bright meteor during the 1997 Leonid shower. The meteor was most likely a Leonid with a brightness of about‐2 magnitude at 100 km altitude. In the region between 251 and 310 nm, the two strongest emission lines are from neutral and ionized magnesium. Ionized Ca lines, indicative of a hot T ? 10 000 K plasma, are not detected. The Mg and Mg+ line intensity ratio alone does not yield the ionization temperature, which can be determined only by assuming the electron density. A typical air plasma temperature of T = 4400 K would imply a very high electron density: ne = 2.2 times 1018 m‐3, but at chondritic abundances of Fe/Mg and Si/Mg ? 1. For a more reasonable local‐thermodynamic‐equilibrium (LTE) air plasma electron density, the Mg and Mg+ line ratio implies a less than chondritic Fe/Mg = 0.06 abundance ratio and a cool non‐LTE T = 2830 K ionization temperature for the ablation vapor plasma. The present observations do not permit a choice between these alternatives. The new data provide also the first spectral confirmation of the presence of molecular OH and NO emission in meteor spectra. 相似文献
105.
Albedos for 57 asteroids were determined using diameters obtained from stellar occultations. For 18 objects, the occultation albedos were determined to accuracies better than 5%. The effect on the occultation albedo due to errors in the asteroid absolute magnitude is discussed and correlations between the occultation albedos and IRAS and polarimetric albedos are presented. The higher-quality occultation albedos presented here are suitable for calibrating albedos obtained by indirect methods. 相似文献
106.
Abstract— Important improvements have been made in recent years in understanding the likely origins of near‐Earth objects (NEOs), and extensive observational campaigns are ongoing in order to assess their current inventory. From these studies we can hope to obtain a much better understanding of the different populations of minor bodies, their relationship with meteorites, and the overall history of the solar system. At the same time, NEOs are important also in terms of impact hazard. Both the purely scientific issues, and the more pragmatic point of view focused on the need of developing credible strategies of impact mitigation, require a major effort in order to improve the current knowledge of the physical properties of these objects. 相似文献
107.
Hydrogeochemistry of Roccamonfina volcano (Southern Italy) 总被引:1,自引:1,他引:0
Emilio Cuoco Giuseppe Verrengia Stefano De Francesco Dario Tedesco 《Environmental Earth Sciences》2010,61(3):525-538
This is the first hydro-geochemical investigation carried out on the Roccamonfina Volcanic Complex groundwaters. The chemistry
of Roccamonfina waters is defined by water–rock and water–rock–gas interactions. In fact, interactions between rocks of the
first eruptive high-K formations and circulating groundwaters are recognized by high K concentrations. On the other hand,
inverse concentration of calcium versus alkali metals is related to two different rock interactions occurring in different
areas of the volcano: (a) within the caldera where groundwaters flow within latite and pyroclastic formations releasing calcium,
and (b) similarly at the base of the volcano where groundwaters flowing from surrounding carbonates got strongly enriched
in Ca. These geochemical processes are also associated with K (SE of caldera) and Mg/Ca (in sites located at the NE base of
the volcano) decrease. Completely different dynamics occurs at Riardo groundwaters (SE). Here waters are the result of a mix
between the Roccamonfina deep aquifer and the carbonate aquifer of the Riardo plain. Rich-CO2 emissions make these waters strongly mineralized. Minor elements show a similar geochemical behavior of major ions and are
crucial defining interactions processes. The evolution of Roccamonfina groundwaters is also evident along the simultaneous
enrichment of Ba, Sr, and Ca. Ba increase is the result of deep local carbonate alteration enhanced by CO2 emissions and, the lower Sr/Ca ratio, from 10 to 2 (ppb/ppm), is also due to the same process. In the light of our results
the Roccamonfina aquifer can be schematically divided into two main reservoirs: (a) a superficial aquifer which basically
follows the volcanic structure morphology and tectonics and (b) a deeper reservoir, originating within the oldest Roccamonfina
volcano ultra potassic lavas and then flowing into the carbonate aquifers of the neighboring plain. Eventually, the chemistry
of the Roccamonfina aquifer does not show any specific and visible pollution, contrary to what happens in the volcano surrounding
plains. In fact, only 14% of the samples we collected (206) show a NO3 content >30 mg/l. These sites are all located at the base of the volcano, near the plain. 相似文献
108.
The California spiny or red rock lobster, Panulirus interruptus, is an ecologically and economically important species that has been exploited since the 1800s. No previous study in California has assessed the impacts of the recreational or commercial lobster harvest. Before the 2003–04 commercial and recreational lobster seasons, we conducted a fishery‐independent trap survey at Santa Catalina Island to document the impact of the lobster fisheries on the size structure, abundance, and sex ratios of mature P. interruptus (>65 mm carapace length (CL)). We concurrently sampled a predominantly commercially fished area, a recreationally fished area, and a 23‐year‐old invertebrate no‐take (INT) reserve. Relative to the INT reserve, legal‐size lobsters in the recreational area were similar in CL, but 31% less abundant. Legal‐size lobsters in the commercial area were 8% smaller and 70% less abundant than those in the INT reserve. The sex ratio of legal‐size lobsters, although near 50:50 in the recreational and INT reserve areas, was male‐dominated (67:33) in the commercial area. Differences in CPUE and mean CL of sub‐legal lobsters in the recreational and commercial areas suggest that factors in addition to harvesting pressure may affect these populations. Total biomass of mature lobsters in the recreational and commercial areas was 92% and 45%, respectively, of biomass in the INT reserve. Fecundity in the recreational and commercial areas was 83% and 42%, respectively, of fecundity in the INT reserve. This study provides preliminary data for future ecological studies and fisheries management evaluations. 相似文献
109.
This paper examines the mean annual cycle, interannual variability, and leading patterns of the tropical Atlantic Ocean simulated in a long-term integration of the climate forecast system (CFS), a state-of-the-art coupled general circulation model presently used for operational climate prediction at the National Centers for Environmental Prediction. By comparing the CFS simulation with corresponding observation-based analyses or reanalyses, it is shown that the CFS captures the seasonal mean climate, including the zonal gradients of sea surface temperature (SST) in the equatorial Atlantic Ocean, even though the CFS produces warm mean biases and underestimates the variability over the southeastern ocean. The seasonal transition from warm to cold phase along the equator is delayed 1 month in the CFS compared with the observations. This delay might be related to the failure of the model to simulate the cross-equatorial meridional wind associated with the African monsoon. The CFS also realistically simulates both the spatial structure and spectral distributions of the three major leading patterns of the SST anomalies in the tropical Atlantic Ocean: the south tropical Atlantic pattern (STA), the North tropical Atlantic pattern (NTA), and the southern subtropical Atlantic pattern (SSA). The CFS simulates the seasonal dependence of these patterns and partially reproduces their association with the El Niño-Southern Oscillation. The dynamical and thermodynamical processes associated with these patterns in the simulation and the observations are similar. The air-sea interaction processes associated with the STA pattern are well simulated in the CFS. The primary feature of the anomalous circulation in the Northern Hemisphere (NH) associated with the NTA pattern resembles that in the Southern Hemisphere (SH) linked with the SSA pattern, implying a similarity of the mechanisms in the evolution of these patterns and their connection with the tropical and extratropical anomalies in their respective hemispheres. The anomalies associated with both the SSA and NTA patterns are dominated by atmospheric fluctuations of equivalent-barotropic structure in the extratropics including zonally symmetric and asymmetric components. The zonally symmetric variability is associated with the annular modes, the Arctic Oscillation in the NH and the Antarctic Oscillation in the SH. The zonally asymmetric part of the anomalies in the Atlantic is teleconnected with the anomalies over the tropical Pacific. The misplaced teleconnection center over the southern subtropical ocean may be one of the reasons for the deformation of the SSA pattern in the CFS. 相似文献
110.
Martin Sahlén Pedro T. P. Viana rew R. Liddle A. Kathy Romer Michael Davidson Mark Hosmer Ed Lloyd-Davies Kivanc Sabirli Chris A. Collins Peter E. Freeman Matt Hilton Ben Hoyle Scott T. Kay Robert G. Mann Nicola Mehrtens Christopher J. Miller Robert C. Nichol S. Adam Stanford Michael J. West † 《Monthly notices of the Royal Astronomical Society》2009,397(2):577-607
We forecast the constraints on the values of σ8 , Ωm and cluster scaling-relation parameters which we expect to obtain from the XMM Cluster Survey (XCS). We assume a flat Λ cold dark matter Universe and perform a Monte Carlo Markov Chain analysis of the evolution of the number density of galaxy clusters that takes into account a detailed simulated selection function. Comparing our current observed number of clusters shows good agreement with predictions. We determine the expected degradation of the constraints as a result of self-calibrating the luminosity–temperature relation (with scatter), including temperature measurement errors, and relying on photometric methods for the estimation of galaxy cluster redshifts. We examine the effects of systematic errors in scaling relation and measurement error assumptions. Using only ( T , z ) self-calibration, we expect to measure Ωm to ±0.03 (and ΩΛ to the same accuracy assuming flatness), and σ8 to ±0.05, also constraining the normalization and slope of the luminosity–temperature relation to ±6 and ±13 per cent (at 1σ), respectively, in the process. Self-calibration fails to jointly constrain the scatter and redshift evolution of the luminosity–temperature relation significantly. Additional archival and/or follow-up data will improve on this. We do not expect measurement errors or imperfect knowledge of their distribution to degrade constraints significantly. Scaling-relation systematics can easily lead to cosmological constraints 2σ or more away from the fiducial model. Our treatment is the first exact treatment to this level of detail, and introduces a new 'smoothed ML' (Maximum Likelihood) estimate of expected constraints. 相似文献