A strategy for the use of bomb-produced radiocarbon as a tracer for the transport of fossil fuel CO2 into the deep-sea source regions

Because the equilibration time for CO₂ gas between the surface ocean and atmosphere is an order of magnitude shorter than the equilibration time for the isotopes of carbon, bomb-produced radiocarbon cannot be simply used as a tracer for fossil fuel CO₂. This difference is especially important for the areas of deep water formation. In this paper we derive the relationship between the isotopic equilibration time and chemical equilibration times for carbon between sea and air. We also show that if the distribution of a second transient tracer is measured, it is possible to circumvent the ambiguity associated with this exchange time difference. Tritium, while adequate in purely diffusive models, is not ideal as the second transient in models involving advection (i.e., downwelling). For such models⁸⁵Kr or freon is a much better choice.     

The distribution of3He anomalies in the deep Atlantic

The³He/⁴He results of the Atlantic GEOSECS program are interpreted in terms of a simple mixing model which allows the contribution of the³He-rich southern component of deep water to be separated from that of the³He-poor northern component. The anomalies from the mixing line connecting these components reveal a³He-rich zone over the Mid-Atlantic Ridge 16° south of the equator and one against the North American continental margin off New Jersey at about the same elevation. The origin of the latter feature remains a mystery.     

Induction of auroral zone electric currents within the Alaska pipeline

The Alaskar pipeline is a highly conducting anomaly extending 800 miles (1300 km) from about 62° to 69° geomagnetic latitude beneath the most active regions of the ionospheric electrojet current. The spectral behavior of the magnetic field from this current was analyzed using data from standard geomagnetic observatories to establish the predictable patterns of temporal and spatial changes for field pulsation periods between 5 min and 4 hr. Such behavior is presented in a series of tables, graphs and formulae. Using 2- and 3-layer models of the conducting earth, the induced electric fields associated with the geomagnetic changes were established. From the direct relationship of the current to the geomagnetic field variation patterns one can infer counterpart temporal and spatial characteristics of the pipeline current. The relationship of the field amplitudes to geomagnetic activity indices,A _p, and the established occurrence of various levels ofA _p over several solar cycles were employed to show that about half of the time the induced currents in the pipe would be under 1 A for the maximum response oscillatory periods near 1 hr. Such currents should be of minimal consequence in corrosion effects for even a section of the pipeline unprotected by sacrificial electrodes. Of greater interest was the result that the extreme surges of current should reach over one-hundred amperes in the pipeline during high activity.     

A direct comparison of 14C and 230Th ages at Searles Lake,California

Thorium-230 dating on saline of the Lower Salt unit in pluvial Searles Lake, California, shows that this unit was formed between 24,500 and 32,000 years ago. The initial apparent ¹⁴C age of the lake is estimated to be about 900 years. After correcting for nonradiogenic ²³⁰Th and for the initial ¹⁴C age, excellent agreement between ²³⁰Th and ¹⁴C ages is obtained. The reliability of ²³⁰Th dating on salt deposit opens a new way for continuation of absolute chronology below the Lower Salt in Searles Lake.     

Mineralogy and petrology of xenoliths in a diatreme from south Westland,New Zealand

Xenoliths up to a metre in length occur in a carbonatitic diatreme member of a lamprophyric dike swarm at Moeraki River, south Westland, New Zealand. The xenoliths reported here consist of Iherzolite (chromite, orthopyroxene, clinopyroxene and olivine) and harzburgite (chromite, olivine and orthopyroxene). A clinopyroxene xenocryst is also reported. Analyses of these phases are presented. The chemistry, low CaO and high Al₂O₃ and Na₂O content of the clinopyroxenes; low CaO and high forsterite content of the olivine, suggests that these phases were in equilibrium under high pressures within the spinel Iherzolite field. An orthopyroxene-chromite intergrowth is described and is interpreted as the product of the re-equilibration of garnet in passing from the garnet Iherzolite field to the spinel Iherzolite field.     

Origin of the in situ stress field in south-eastern Australia

The in situ stress field of south‐eastern Australia inferred from earthquake focal mechanisms and bore‐hole breakouts is unusual in that it is characterised by large obliquity between the maximum horizontal compressive stress orientation (S_Hmax) and the absolute plate motion azimuth. The evolution of the neotectonic strain field deduced from historical seismicity and both onshore and offshore faulting records is used to address the origin of this unusual stress field. Strain rates derived from estimates of the seismic moment release rate (up to ～10^?16 s^?1) are compatible with Quaternary fault–slip rates. The record of more or less continuous tectonic activity extends back to the terminal Miocene or early Pliocene (10–5 Ma). Terminal Miocene tectonic activity was characterised by regional‐scale tilting and local uplift and erosion, now best preserved by unconformities in offshore basins. Plate‐scale stress modelling suggests the in situ stress field reflects increased coupling of the Australian and Pacific Plate boundary in the late Miocene, associated with the formation of the Southern Alps in New Zealand.     

Stability analysis of real‐time dynamic substructuring using delay differential equation models

Real‐time dynamic substructuring is an experimental technique for testing the dynamic behaviour of complex structures. It involves creating a hybrid model of the entire structure by combining an experimental test piece—the substructure—with a numerical model describing the remainder of the system. The technique is useful when it is impractical to experimentally test the entire structure or complete numerical modelling is insufficient. In this paper, we focus on the influence of delay in the system, which is generally due to the inherent dynamics of the transfer systems (actuators) used for structural testing. This naturally gives rise to a delay differential equation (DDE) model of the substructured system. With the case of a substructured system consisting of a single mass–spring oscillator we demonstrate how a DDE model can be used to understand the influence of the response delay of the actuator. Specifically, we describe a number of methods for identifying the critical time delay above which the system becomes unstable. Because of the low damping in many large structures a typical situation is that a substructuring test would operate in an unstable region if additional techniques were not implemented in practice. We demonstrate with an adaptive delay compensation technique that the substructured mass–spring oscillator system can be stabilized successfully in an experiment. The approach of DDE modelling also allows us to determine the dependence of the critical delay on the parameters of the delay compensation scheme. Using this approach we develop an over‐compensation scheme that will help ensure stable experimental testing from initiation to steady state operation. This technique is particularly suited to stiff structures or those with very low natural damping as regularly encountered in structural engineering. Copyright © 2005 John Wiley & Sons, Ltd.     

Storage and interaction of compositionally heterogeneous magmas from the 1986 eruption of Augustine Volcano, Alaska

Compositional heterogeneity (56–64 wt% SiO₂ whole-rock) in samples of tephra and lava from the 1986 eruption of Augustine Volcano, Alaska, raises questions about the physical nature of magma storage and interaction beneath this young and frequently active volcano. To determine conditions of magma storage and evolutionary histories of compositionally distinct magmas, we investigate physical and chemical characteristics of andesitic and dacitic magmas feeding the 1986 eruption. We calculate equilibrium temperatures and oxygen fugacities from Fe-Ti oxide compositions and find a continuous range in temperature from 877 to 947°C and high oxygen fugacities (ΔNNO=1–2) for all magmas. Melt inclusions in pyroxene phenocrysts analyzed by Fourier-transform infrared spectroscopy and electron probe microanalysis are dacitic to rhyolitic and have water contents ranging from <1 to ∼7 wt%. Matrix glass compositions are rhyolitic and remarkably similar (∼75.9–76.6 wt% SiO₂) in all samples. All samples have ∼25% phenocrysts, but lower-silica samples have much higher microlite contents than higher-silica samples. Continuous ranges in temperature and whole-rock composition, as well as linear trends in Harker diagrams and disequilibrium mineral textures, indicate that the 1986 magmas are the product of mixing between dacitic magma and a hotter, more mafic magma. The dacitic endmember is probably residual magma from the previous (1976) eruption of Augustine, and we interpret the mafic endmember to have been intruded from depth. Mixing appears to have continued as magmas ascended towards the vent. We suggest that the physical structure of the magma storage system beneath Augustine contributed to the sustained compositional heterogeneity of this eruption, which is best explained by magma storage and interaction in a vertically extensive system of interconnected dikes rather than a single coherent magma chamber and/or conduit. The typically short repose period (∼10 years) between Augustine's recent eruptive pulses may also inhibit homogenization, as short repose periods and chemically heterogeneous magmas are observed at several volcanoes in the Cook Inlet region of Alaska.     

Enzyme leach anomalies associated with deep Mississippi Valley-type zinc ore bodies at the Elmwood Mine, Tennessee

Deeply buried Mississippi Valley-type deposits that have been or are currently being mined in North America were initially discovered by drilling. Conventional geochemical methods are ineffective for detecting these ‘blind' deposits when they occur deep within sequences of stable-platform carbonates and shales. The ‘enzyme' leach is a selective analytical technique for determining trace elements associated with amorphous Mn oxide coatings in soils. In many areas of the world, the enzyme leach method is useful for detecting low-level geochemical anomalies in soils, which are associated with blind mineral deposits. Enzyme leach analysis of soils, collected at the Elmwood Mine, Tennessee, revealed high-contrast anomalies over ore bodies 370 m below the surface. In areas where the soils are in chemical equilibrium, ‘combination' anomalies occur over Zn ore bodies. These are characterized by asymmetrical halogen halos which occur around a halogen ‘central low'. Commodity metals (Zn and Pb) and trace elements associated with the ore (Cd, Ba, and Mn) form apical anomalies, which occur over the ore bodies and within the halogen halo. Under most circumstances, agricultural practices do not affect enzyme leach results. However, agricultural activity in central Tennessee appears to have altered the proportion of amorphous Mn oxides in the soils in some locations. Where the MnO₂-form equilibrium of the soil has been disturbed, enzyme leach data are erratic. In the one instance where this was encountered, ratioing the data to Mn reveals anomalies which bracket the blind ore bodies.     

冬季大气环流对北太平洋海冰和黑潮暖流海温的强迫作用

本文应用奇异值分解等统计方法，探讨冬季北太平洋海冰浓度、海温与大尺度大气环流型间的联系。分析结果表明:冬季北太平洋海域海冰存在一个主要的分布型，即鄂霍次克海和白令海的海冰呈反位相。海冰的该种分布特征是与大气中的WP型紧密联系的，并以大气超前海冰一个月最为明显。同时，WP型强迫作用于黑潮暖流区的海温，海温滞后大气一个月。具体表现为在东亚冬季风较弱的年份，鄂霍次克海海冰增多，白令海海冰减少，黑潮暖流区海温增高，反之则相反。