<Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating of the eruptive history of Mount Erebus,Antarctica: volcano evolution     

Richard?P.?EsserEmail author  Philip?R.?Kyle  William?C.?McIntosh 《Bulletin of Volcanology》2004,66(8):671-686

Mt. Erebus, a 3,794-meter-high active polygenetic stratovolcano, is composed of voluminous anorthoclase-phyric tephriphonolite and phonolite lavas overlying unknown volumes of poorly exposed, less differentiated lavas. The older basanite to phonotephrite lavas crop out on Fang Ridge, an eroded remnant of a proto-Erebus volcano and at other isolated locations on the flanks of the Mt. Erebus edifice. Anorthoclase feldspars in the phonolitic lavas are large (~10 cm), abundant (~30–40%) and contain numerous melt inclusions. Although excess argon is known to exist within the melt inclusions, rigorous sample preparation was used to remove the majority of the contaminant. Twenty-five sample sites were dated by the ⁴⁰Ar/³⁹Ar method (using 20 anorthoclase, 5 plagioclase and 9 groundmass concentrates) to examine the eruptive history of the volcano. Cape Barne, the oldest site, is 1,311±16 ka and represents the first of three stages of eruptive activity on the Mt. Erebus edifice. It shows a transition from sub-aqueous to sub-aerial volcanism that may mark the initiation of proto-Erebus eruptive activity. It is inferred that a further ~300 ky of basanitic/phonotephritic volcanism built a low, broad platform shield volcano. Cessation of the shield-building phase is marked by eruptions at Fang Ridge at ~1,000 ka. The termination of proto-Erebus eruptive activity is marked by the stratigraphically highest flow at Fang Ridge (758±20 ka). Younger lavas (~550–250 ka) on a modern-Erebus edifice are characterized by phonotephrites, tephriphonolites and trachytes. Plagioclase-phyric phonotephrite from coastal and flank flows yield ages between 531±38 and 368±18 ka. The initiation of anorthoclase tephriphonolite occurred in the southwest sector of the volcano at and around Turks Head (243±10 ka). A short pulse of effusive activity marked by crustal contamination occurred ~160 ka as indicated by at least two trachytic flows (157±6 and 166±10 ka). Most anorthoclase-phyric lavas, characteristic of Mt. Erebus, are less than 250 ka. All Mt. Erebus flows between about 250 and 90 ka are anorthoclase tephriphonolite in composition.Editorial responsibility: J. Donelly-Nolan  相似文献   

Sulfur geochemistry of hydrothermal waters in Yellowstone National Park,Wyoming, USA. III. An anion-exchange resin technique for sampling and preservation of sulfoxyanions in natural waters     

Greg?K?Druschel  Martin?AA?SchoonenEmail author  D?Kirk?Nordstrom  James?W?Ball  Yong?Xu  Corey?A?Cohn 《Geochemical transactions》2003,4(1):12

A sampling protocol for the retention, extraction, and analysis of sulfoxyanions in hydrothermal waters has been developed in the laboratory and tested at Yellowstone National Park and Green Lake, NY. Initial laboratory testing of the anion-exchange resin Bio-Rad™ AG1-X8 indicated that the resin was well suited for the sampling, preservation, and extraction of sulfate and thiosulfate. Synthetic solutions containing sulfate and thiosulfate were passed through AG1-X8 resin columns and eluted with 1 and 3 M KCl, respectively. Recovery ranged from 89 to 100%. Comparison of results for water samples collected from five pools in Yellowstone National Park between on-site IC analysis (U.S. Geological Survey mobile lab) and IC analysis of resin-stored sample at SUNY-Stony Brook indicates 96 to 100% agreement for three pools (Cinder, Cistern, and an unnamed pool near Cistern) and 76 and 63% agreement for two pools (Sulfur Dust and Frying Pan). Attempts to extract polythionates from the AG1-X8 resin were made using HCl solutions, but were unsuccessful. Bio-Rad™ AG2-X8, an anion-exchange resin with weaker binding sites than the AG1-X8 resin, is better suited for polythionate extraction. Sulfate and thiosulfate extraction with this resin has been accomplished with KCl solutions of 0.1 and 0.5 M, respectively. Trithionate and tetrathionate can be extracted with 4 M KCl. Higher polythionates can be extracted with 9 M hydrochloric acid. Polythionate concentrations can then be determined directly using ion chromatographic methods, and laboratory results indicate recovery of up to 90% for synthetic polythionate solutions using AG2-X8 resin columns.  相似文献   

A catalogue of Spanish archaeomagnetic data     

M. Gómez-Paccard  G. Catanzariti  V. C. Ruiz-Martínez  G. McIntosh  J. I. Núñez  M. L. Osete  A. Chauvin  Ph. Lanos  D. H. Tarling  D. Bernal-Casasola  J. Thiriot  'Archaeological Working Group'ast 《Geophysical Journal International》2006,166(3):1125-1143

A total of 58 new archaeomagnetic directions has been determined from archaeological structures in Spain. Together with five previous results they allow the compilation of the first archaeomagnetic catalogue for Spain, which includes 63 directions with ages ranging between the 2nd century BC and the 20th century AD. Characteristic remanence directions have been obtained from stepwise thermal and alternating field demagnetization. The hierarchical structure has been respected in the calculation of the mean site directions. Rock magnetic experiments reveal that the main magnetic carrier is magnetite or titanomagnetite with different titanium contents. The age estimate of the studied structures is generally well justified by archaeological constraints. For six structures the proposed date is also supported by physical methods. The data are in close agreement with the French secular variation (SV) curve. This catalogue represents the first step in the construction of a SV curve for the Iberian Peninsula, which will be of much use in archaeomagnetic dating and in modelling of the Earth's magnetic field in Western Europe.  相似文献   

Small-scale spatial variations of natural radionuclide and trace metal distributions in sediments from the Hudson River estuary     

Huan Feng  J. Kirk Cochran  David J. Hirschberg  Robert E. Wilson 《Estuaries and Coasts》1998,21(2):263-280

Multiple sediment cores were collected in June 1994 in the turbidity maximum zone of the Hudson River estuary off Manhattan, New York. Results from X-radiography of the sediments and measurements of natural radionuclides (²³⁴Th,⁷Be, and²¹⁰Pb) and trace metals (Ag, Cd, Cu, Pb, and Zn) show significant spatial variability of sediment composition and structure and patchy distributions of radionuclides activities and trace metal concentrations in this small area (0.6 km × 0.5 km). Radionuclide and trace metal analyses confirm prior work (Olsen et al. 1978; Olsen et al. 1981; Hirschberg et al. 1996) that show the western margin area of the river acts as a repository of these chemical constituents at least for the short-term period (0.5–1 yr), and the mid-channel area is not a depositional area for sediments and associated chemical constituents.⁷Be profiles reveal short-term sediment deposition rates ranging from 6 cm yr^?1 to 26 cm yr^?1 in the western margin area. Significant spatial variations in excess²³⁴Th and⁷Be inventories (up to a factor of 10 and 5 for²³⁴Th and⁷Be, respectively) are found in the western margin depositional area, although the inventories are balanced, on average, with in situ production in water column and atmospheric supply. The spatial variation of surficial excess²¹⁰Pb and trace metal concentrations in depositional areas of the western margin are ≤10% for Ag, Cu, Pb, and Zn and 29% for Cd. However, the variations in the transition zone range from 28% to 93%. This variability is likely related to variations in tidal current velocity, bottom shear stress, and river channel morphology.  相似文献   

Inversion of Thick-Target Bremsstrahlung Spectra from Nonuniformly Ionised Plasmas     

Brown  John C.  McArthur  Guillian K.  Barrett  Richard K.  McIntosh  Scott W.  Emslie  A. Gordon 《Solar physics》1998,179(2):379-404

The effects of non-uniform plasma target ionisation on the spectrum of thick-target HXR bremsstrahlung from a non-thermal electron beam are analysed. In particular the effect of the target ionisation structure on beam collisional energy losses, and hence on inversion of an observed photon spectrum to yield the electron injection spectrum, is considered and results compared with those obtained under the usual assumption of a fully ionised target.The problem is formulated and solved in principle for a general target ionisation structure, then discussed in detail for the case of a step function distribution of ionisation with column depth as an approximation to the sharp coronal–chromospheric step structure in solar flare plasmas. It is found that such ionisation structure has very dramatic effects on derivation of the thick-target electron injection spectrum F₀(E₀) as compared with the result F*₀(E ₀) obtained under the usual assumption of a fully ionised target: (a) Inferred F*₀ contain more electrons than F ₀ and in some cases include electrons at energies where none are actually present. Although the total (energy-integrated) beam fluxes in the two cases do not differ by a factor of more than A_ee/A_eH, the spectral shapes can differ greatly over finite energy intervals resulting in the danger of misleading results for total fluxes obtained by extrapolation. (b) The unconstrained mathematical solution for F₀ for any photon spectrum is never unique, while that for F*₀ is unique. When the physical constraint F₀ 0 is added, for some photon spectra solutions for F₀ may not exist or may not be unique. (This is not an effect of noise but of real analytic ambiguity.) (c) For data corresponding to F*₀ with a low-energy cut-off, or a cut-off or rapid enough exponential decline at high energies, a unique solution F₀ does exist and we obtain a recursive summation for its evaluation.Consequently, in future work on the inversion of HXR bremsstrahlung spectra it will be vital for algorithms to include the effects of target ionisation if spurious results on thick-target electron spectra are not to be inferred. Finally it is pointed out that the depth of the transition zone, and its evaporative evolution during flares may be derivable from its effect on the HXR spectrum.  相似文献   

Redistribution of sea level rise associated with enhanced greenhouse warming: a simple model study   总被引：1，自引：0，他引：1  

Hsieh  William W.  Bryan  Kirk 《Climate Dynamics》1996,12(8):535-544

Future sea level rise from thermal expansion of the World Ocean due to global warming has been explored in several recent studies using coupled ocean-atmosphere models. These coupled models show that the heat input by the model atmosphere to the ocean in such an event could be quite non-uniform in different areas of the ocean. One of the most significant effects predicted by some of the models is a weakening of the thermohaline circulation, which normally transports heat poleward. Since the greatest heat input from enhanced greenhouse warming is in the higher latitudes, a weakening of the poleward heat transport effectively redistributes the heat anomaly and the associated sea level rise to lower latitudes. In this study, the mechanism of ocean circulation spindown and heat redistribution was studied in the context of a much simpler, linearized shallow water model. Although the model is much simpler than the three-dimensional ocean circulation models used in the coupled model experiments, and neglects several important physical effects, it has a nearly 10-fold increase in horizontal resolution and clearer dynamical interpretations. The results indicated that advanced signals of sea level rise propagated rapidly through the action of Kelvin and Rossby waves, but the full adjustment toward a more uniform sea level rise took place much more slowly. Long time scales were required to redistribute mass through narrow currents trapped along coasts and the equatorial wave guide. For realistic greenhouse warming, the model showed why the sea level rise due to ocean heating could be far from uniform over the globe and hence difficult to estimate from coastal tide gauge stations.  相似文献   

The steric component of sea level rise associated with enhanced greenhouse warming: a model study     

Kirk Bryan 《Climate Dynamics》1996,12(8):545-555

Climate change due to enhanced greenhouse warming has been calculated using the coupled GFDL general circulation model of the atmosphere and ocean. The results of the model for a sustained increase of atmospheric carbon dioxide of 1% per year over a century indicate a marked warming of the upper ocean. Results of the model are used to study the rise in sea level caused by increase in ocean temperatures and associated changes in ocean circulation. Neglecting possible contributions due to changes in the volume of polar ice sheets and mountain glaciers, the model predicts an average rise in sea level of approximately 15 ± 5 cm by the time atmospheric carbon dioxide doubles. Heating anomalies are greatest in subpolar latitudes. This effect leads to a weakening of the ocean thermohaline circulation. Changes in thermohaline circulation redistribute heat within the ocean from high latitudes toward the equator, and cause a more uniform sea level rise than would occur otherwise.  相似文献   

Effect of Trapped Gas on Dissolved Oxygen Transport — Implications for In Situ Bioremediation     

Virginia A. Fry  Jonathan D. Istok  Kirk T. O'Reilly 《Ground water》1996,34(2):200-210

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Calculating climate attractor dimension from δ18O records by the Grassberger-Procaccia algorithm     

Kirk A Maasch 《Climate Dynamics》1989,4(1):45-55

The Grassberger-Procaccia method of calculating dimension from a time series is applied to 14 late Pleistocene ¹⁸O records. The difficulties encountered when using this algorithm on limited data sets are reviewed and the step-by-step procedure actually used to calculate the dimension of each record is explicitly listed. Although the results must be viewed with caution, they do indicate that the dimension cannot be measured accurately enough to determine whether or not it is fractal. However, in spite of inaccuracies in the time scale, the underlying dynamics do not appear to be random and there is a suggestion that a lower bound to the Grassberger-Procaccia dimension is somewhere between 4 and 6.  相似文献   

Association of X-ray arches with chromospheric neutral lines     

Patrick S. McIntosh  A. S. Krieger  J. T. Nolte  G. Vaiana 《Solar physics》1976,49(1):57-77

Daily maps of magnetic neutral lines derived from H observations have been superimposed on solar X-ray images for the period 15–30 June 1973. Nearly all X-ray-emitting structures consist of systems of arches covering chromospheric neutral lines. Areas of low emissivity, coronal holes, appear as the areas between arcades of arches. The presence of a coronal hole, therefore, is determined by the spacing between neutral lines and the scale of the arches over those neutral lines. X-ray emissivity on the solar disk extends from neutral lines in proportion to the vertical and horizontal scale of the arches over those neutral lines. Increasing scale of arches corresponds with increasing age of magnetic fields associated with the neutral line. All X-ray filament cavities coincided with neutral lines, but filaments appeared under cavities for only part of their length and for only a fraction of the disk passage.A substantial portion of this work was done while a visitor at American Science and Engineering, Cambridge, Mass. 02139, U.S.A.  相似文献