GHOST – A Novel Airborne Gas Chromatograph for In Situ Measurements of Long-Lived Tracers in the Lower Stratosphere: Method and Applications

A novel fully-automated airborne gas chromatograph for in situmeasurements of long-lived stratospheric tracers hasbeen developed, combining the high selectivity of a megabore PLOTcapillary column with recently developed sampling and separationtechniques. The Gas cHromatograph for theObservation of Stratospheric Tracers (GHOST)has been successfully operated during three STREAM campaigns(Stratosphere TRoposphere Experiment byAirborne Measurement) onboard a Cessna Citation IIaircraft in two different modes: Either N₂O andCF₂Cl₂(CFC-12) or CFC-12 and CFCl₃ (CFC-11) have been measuredsimultaneously, with a time resolution of 2 min for both modes.Under flight conditions the instrument precision (1) forthese species is better than 0.9%, and the accuracy(1) is better than 2.0% of the tropospheric values ofall measured compounds. The detection limits (3) arebelow 28 ppb for N₂O, 14 ppt for CFC-12, and 8 ppt forCFC-11, respectively, i.e., well below 10 % of the troposphericvalues of all measured compounds. Post-mission optimization of thechromatographic separation showed a possible enhancement of thetime resolution by up to a factor of 2, associated with acomparable increase in precision and detection limit. As test ofactual performance of GHOST results from an in-flight N₂Ointercomparison with a tunable diode laser absorptionspectrometer (TDLAS) are presented. They yield an excellentagreement between both instruments. Furthermore, on the basis ofthe hitherto most extensive set of upper tropospheric and lowerstratospheric data, the relative stratospheric N₂2O lifetime isre-assessed. When referenced to the WMO reference CFC-11 lifetimeof 45 ± 7 years an N₂O lifetime of 91 ± 15 yearsis derived, a value substantially smaller than the WMO referencelifetime of 120 years. Moreover, this value implies astratospheric N₂O sink strength of 16.3 ± 2.7 Tg (N)yr^–1 which is 30% larger than previous estimates.     

Petrology of lavas from the Puu Oo eruption of Kilauea Volcano: III. The Kupaianaha episode (1986–1992)

 The Puu Oo eruption has been remarkable in the historical record of Kilauea Volcano for its duration (over 13 years), volume (>1 km³) and compositional variation (5.7–10 wt.% MgO). During the summer of 1986, the main vent for lava production moved 3 km down the east rift zone and the eruption style changed from episodic geyser-like fountaining at Puu Oo to virtually continuous, relatively quiescent effusion at the Kupaianaha vent. This paper examines this next chapter in the Puu Oo eruption, episodes 48 and 49, and presents new ICP-MS trace element and Pb-, Sr-, and Nd-isotope data for the entire eruption (1983–1994). Nearly aphyric to weakly olivine-phyric lavas were erupted during episodes 48 and 49. The variation in MgO content of Kupaianaha lavas erupted before 1990 correlates with changes in tilt at the summit of Kilauea, both of which probably were controlled by variations in Kilauea's magma supply rate. These lavas contain euhedral olivines which generally are in equilibrium with whole-rock compositions, although some of the more mafic lavas which erupted during 1990, a period of frequent pauses in the eruption, accumulated 2–4 vol.% olivine. The highest forsterite content of olivines (∼85%) in Kupaianaha lavas indicates that the parental magmas for these lavas had MgO contents of ∼10 wt.%, which equals the highest observed value for lavas during this eruption. The composition of the Puu Oo lavas has progressively changed during the eruption. Since early 1985 (episode 30), when mixing between an evolved rift zone magma and a more mafic summit reservoir-derived magma ended, the normalized (to 10 wt.% MgO) abundances of highly incompatible elements and CaO have systematically decreased with time, whereas ratios of these trace elements and Pb, Sr, and Nd isotopes, and the abundances of Y and Yb, have remained relatively unchanged. These results indicate that the Hawaiian plume source for Puu Oo magmas must be relatively homogeneous on a scale of 10–20 km³ (assuming 5–10% partial melting), and that localized melting within the plume has apparently progressively depleted its incompatible elements and clinopyroxene component as the eruption continued. The rate of variation of highly incompatible elements in Puu Oo lavas is much greater than that observed for Kilauea historical summit lavas (e.g., Ba/Y 0.09 a^–1 vs ∼0.03 a^–1). This rapid change indicates that Puu Oo magmas did not mix thoroughly with magma in the summit reservoir. Thus, except for variable amounts of olivine fractionation, the geochemical variation in these lavas is predominantly controlled by mantle processes. Received: 8 March 1996 / Accepted: 30 April 1996     

Electromagnetic mapping of electrical conductivity beneath the Columbia basalts1

Sedimentary rocks beneath the Columbia River Basalt Group are recognized as having potential for oil and gas production, but the overlying layered basalts effectively mask seismic reflections from the underlying sediments. Four electromagnetic (EM) methods have been applied on profiles crossing Boylston Ridge, a typical east–west trending anticline of the Yakima Fold Belt, in an attempt to map the resistivity interface between the basalts and the sediments and to map variations in structure and resistivity within the sediments. The EM surveys detected strong variations in resistivity within the basalts, and in particular the continuous magnetotelluric array profiling (EMAP) revealed resistivity lows beneath the surface anticlines. These low resistivity zones probably coincide with fracturing in the core of the anticlines and they appear to correlate well with similar zones of low seismic velocity observed on a nearby seismic profile. The controlled-source EM surveys (in-loop transient, long-offset transient, and variable-offset frequency-domain) were designed in anticipation of relatively uniform high resistivity basalts, and were found to have been seriously distorted by the intrabasalt conductors discovered in the field. In particular, the resistivity sections derived from 1D inversions were found to be inconsistent and misleading. The EMAP survey provided the most information about the subsurface resistivity distribution, and was certainly the most cost-effective. However, both controlled-source and EMAP surveys call for accurate 2D or 3D inversion to accommodate the geological objectives of this project.     

Late Quaternary sediment dating and quantification of lateral sediment redistribution applying230Thex: a study from the eastern Atlantic sector of the Southern Ocean

High-resolution records of the natural radionuclide²³⁰Th were measured in sediments from the eastern Atlantic sector of the Antarctic circumpolar current to obtain a detailed reconstruction of the sedimentation history of this key area for global climate change during the late Quaternary. High-resolution dating rests on the assumption that the²³⁰Th_ex flux to the sediments is constant. Short periods of drastically increased sediment accumulation rates (up to a factor of 8) were determined in the sediments of the Antarctic zone during the climate optima at the beginning of the Holocene and the isotope stage 5e. By comparing expected and measured accumulation rate of²³⁰Th_ex, lateral sediment redistribution was quantified and vertical particle rain rates originating from the surface water above were calculated. We show that lateral contributions locally were up to 6.5 times higher than the vertical particle rain rates. At other locations only 15% of the expected vertical particle rain rate were deposited.     

A structural phase-transition in K(Mg1−xCux)F3 perovskite

A complete solid-solution series between cubic (Pm 3 m) KMgF₃ and tetragonal (I4/mcm) KCuF₃ was synthesized at 730–735 °C in an inert atmosphere. X-ray powder-diffraction at room temperature shows that the transition between the cubic and tetragonal perovskite structures in the series K (Mg_1?xCu_x) F₃ occurs at x ～ 0.6. Rietveld structure-refinements were done for selected compositions. In the cubic phase, all parameters are linear with composition up to the transition point. At the transition point, there is a strong discontinuity in the cell volume; this is strongly anisotropic with expansion along the a axes and contraction along the c axis due to a pronounced axial elongation of the (Mg, Cu) F₆ octahedron that increases with increasing Cu content. The phase transition is first-order, with a discontinuity of ≈2% in the symmetry-breaking strain at x_C. It is proposed that the phase transition in K (Mg, Cu) F₃ is due to the onset of the cooperative Jahn-Teller effect. Compositional relationships for lattice vibrations in this solid solution were established using thin-film infrared spectroscopy. A phase transition occurring above 60 mole % KCuF₃ is indicated by the appearance of one of the two modes expected for the tetragonal phase; the weaker mode is not resolved below 80 mole % KCuF₃. Modes common to both structures vary smoothly and continuously across the binary; however, frequencies do not depend linearly on composition, nor is mode-softening discernable. Two-mode behaviour is observed only for the bending motion of the cubic phase, because this peak alone has non-overlapping end-member components.     

Historical 1942 Ecuador and 1942 Peru subduction earthquakes and earthquake cycles along Colombia-Ecuador and Peru subduction segments

Two large shallow earthquakes occurred in 1942 along the South American subduction zone inclose proximity to subducting oceanic ridges: The 14 May event occurred near the subducting Carnegie ridge off the coast of Ecuador, and the 24 August event occurred off the coast of southwestern Peru near the southern flank of the subducting Nazca ridge. Source parameters for these for these two historic events have been determined using long-periodP waveforms,P-wave first motions, intensities and local tsunami data.We have analyzed theP waves for these two earthquakes to constrain the focal mechanism, depth, source complexity and seismic moment. Modeling of theP waveform for both events yields a range of acceptable focal mechanisms and depths, all of which are consistent with underthrusting of the Nazca plate beneath the South American plate. The source time function for the 1942 Ecuador event has one simple pulse of moment release with a duration of 22 suconds, suggesting that most of the moment release occurred near the epicenter. The seismic moment determined from theP waves is 6–8×10²⁰N·m, corresponding ot a moment magnitude of 7.8–7.9. The reported location of the maximum intensities (IX) for this event is south of the main shock epicenter. The relocated aftershcks are in an area that is approximately 200 km by 90 km (elongated parallel to the trench) with the majority of aftershocks north of the epicenter. In contrast, the 1942 Peru event has a much longer duration and higher degree of complexity than the Ecuador earthquake, suggesting a heterogeneous rupture. Seismic moment is released in three distinct pulses over approximately 74 seconds; the largest moment release occurs 32 seconds after rupture initiation. the seismic moment as determined from theP waves for the 1942 Peru event is 10–25×10²⁰N·m, corresponding to a moment magnitude of 7.9–8.2. Aftershock locations reported by the ISS occur over a broad area surrounding the main shock. The reported locations of the maximum intensities (IX) are concentrated south of the epicenter, suggesting that at least part of the rupture was to the south.We have also examined great historic earthquakes along the Colombia-Ecuador and Peru segments of the South American subduction zone. We find that the size and rupture length of the underthrusting earthquakes vary between successive earthquake cycles. This suggests that the segmentation of the plate boundary as defined by earthquakes this century is not constant.     

Modeling and estimation of C1–P1 bias in GPS receivers

 Modern dual-frequency global positioning system (GPS) receivers are capable of providing direct measurements of both L1 C/A (C1) and P code (P1) without the use of the Y-codes under Anti-Spoofing. A discrepancy or bias between the C1 and P1 measurements from these receivers has however been of concern to operators and users of GPS reference networks. For the purpose of modeling and estimation, the nature and characteristics of the discrepancy must be investigated. The research results presented indicate that the discrepancy between the C1 and P1 measurements contains two different types of components: one is of constant type while another is time variant. A method has been developed for their modeling and estimation. The residual C1–P1 time series after a satellite-dependent bias removal agree at a few-centimeter level, indicating the effectiveness of the proposed model. This allows the C1–P1 discrepancy, both constant and non-constant components, to be removed from GPS reference network solutions. Numerical results are provided to support the analysis. Received: 12 October 1999 / Accepted: 11 May 2000     

Evolving planning systems in Madrid,Rome, and Athens

Although possessing ancient and distinguished histories, the recent urbanization and planning approaches of Madrid, Rome and Athens are relatively unknown to English-speaking planners and urban geographers. This paper reviews the development of each city from the mid-19th century to the present. Special attention is given to the planning instruments developed in each city to guide growth. Each city experienced rapid growth over the past century because of its capital city functions. As a result of strong growth pressures, city planning policies were frequently subverted by private sector interests. Only in the latter part of the 20th century have planning measures become effective in controlling and directing urban growth.