bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface sediment diatom distribution and Holocene paleotemperature variations in the Greenland, Iceland and Norwegian Sea
Authors: Koc Karpuz Nalân , Schrader Hans
Published: February 2008

One hundred and four surface sediment samples and two piston cores from the Greenland, Iceland and the Norwegian (GIN) Sea (Hopkins, 1988) were analyzed. Diatoms were common to abundant in most surface sediment samples and throughout the Holocene. Q mode factor analysis allowed the definition of six significantly different floral assemblages which explained 91.7% of the total variance. Mapping of the six factors showed their close affinity to hydrographic regimes. These are the Norwegian‐Atlantic Current assemblage (Thalassionema nitzschioides, Paralia sulcata, Proboscia alata), Arctic Water assemblage (Thalassiosira gravidaspores), Sea Ice assemblage (Nitzschia grunowii, Nitzschia cylindra, Thalassiosira hyalina), Arctic‐Norwegian Waters Mixing assemblage (Rhizosolenia hebetata f. semispina, Rhizosolenia borealis), Atlantic assemblage (Thalassiosira oestrupii), and Norwegian‐Arctic Waters Mixing assemblage (Thalassiosira gravidavegetative cells). Transfer functions (GINT2) relating factor distributions to winter (February) and summer (August) surface water temperatures were generated. The transfer functions have a standard error of estimate of ±1.5°C (August) and ±1.0°C (February). Downcore studies of core 52–43 from the Norwegian Basin and core 57–5 from the Iceland Plateau revealed diatom abundance and sea surface paleotemperature trends in the area during the Holocene. The first appearance of diatoms in cores 52–43 and 57–5 occurs within the Vedde ash layer (10,600 years B.P.) and the Saksunarvatn ash layer (9100 years B.P.), respectively. Diatom abundances increase steadily throughout the Pre‐Boreal‐Atlantic time to 25 and 35 million valves per gram dry sediment in the Norwegian Basin and Iceland Plateau cores, respectively. Application of the temperature transfer functions (GINT2) to the two Holocene records revealed higher than present sea surface temperatures during the Boreal‐Atlantic chronozones for the Iceland Plateau and during the middle Younger Dryas‐Sub Boreal chronozones for the Norwegian Basin core. Temperatures decreased steadily since then with a slight increase to the present values. Both the Iceland and the Norwegian seas experienced a strong influx of temperate Atlantic surface waters in the beginning of the Holocene. Sea surface temperatures dropped steadily in the latter part of the Holocene as the influx of the Atlantic surface waters diminished.
Differential dissolution: Modification of Late Pleistocene oxygen isotope records in the western equatorial Pacific
Authors: Wu Guoping , Herguera J. C. , Berger W. H.
Published: February 2008

Deep‐sea records of the Pacific Ocean show dramatic variations in the dissolution intensity of calcium carbonate through the late Pleistocene. Extremes are characterized by much depressed dissolution intensity during deglaciation (preservation spikes) and much enhanced dissolution intensity during ice growth (dissolution spikes). Increased dissolution intensity at dissolution spikes distorts δ18O records by preferential removal of 16O‐rich shells, resulting in heavier δ18O values at these sections. The δ18O values tend to remain unaltered at deglacial preservation spikes. Thus the fluctuations of carbonate dissolution intensity modify the late Pleistocene oxygen isotope records in such a fashion that apparent “climate optima” (as defined by the lightest δ18O values) tend to shift toward preservation spikes, while apparent “glacial maxima” (characterized by the heaviest δ18O values) shift toward dissolution spikes.
The age and origin of the “Younger Dryas climate event” in Greenland ice cores
Authors: Fairbanks Richard G.
Published: February 2008

230Th/234U and 14C dating of Barbados corals has extended the calibration of 14C years B.P. to calendar years B.P. beyond the 9200 year tree ring series (Bard et al., 1990). This now permits the conversion of 14C chronozones, which delimit major climate shifts in western Europe, to calendar years. The Younger Dryas chronozone, defined as 11,000 to 10,000 14C years B.P., corresponds to 13,000 to 11,700 calendar years B.P. This calibration affects the interpretation of an intensely studied example of the “Younger Dryas climate event,” the δ18O anomaly between 1785 and 1793 m in Dye 3 ice core. The end of the δ18O anomaly in Dye 3 ice core has been dated by measurements of 14C in air bubbles (Andree et al., 1984, 1986) and by annual layer counting (Hammer et al., 1986). The older 14C dates fall out of the range of the tree ring calibration series but can now be calibrated to calendar years using the Barbados 230Th/234U calibration. The 14Ccorrected age for the end of the δ18O event is 10,300 ± 400 calendar years B.P. compared to the annual layer counting age of 10,720 ± 150 years B.P. Thus, the “Younger Dryas” event in the Dye 3 ice core ends in the Preboreal chronozone (11,700 to 10,000 calendar years B.P.) and is not correlative with the end of the Younger Dryas event identified in pollen records marking European vegetation changes. The end of the Dye 3 δ18O event is, however, correlative with the end of meltwater pulse IB (Fairbanks, 1989), marking a period of intense deglaciation with meltwater discharge rates exceeding 13,000 km³/yr.
Geostrophic motion
Authors: Phillips Norman A.
Published: February 2008

Geostrophic motion occurs when the horizontal components of the pressure and Coriolis forces are in approximate balance and frictional effects are confined to thin ‘boundary’ layers. Two special cases have proved useful in studying atmospheric and oceanic motions: type 1, characterized by a horizontal length scale (L) smaller than the radius of the earth, and type 2, which hasLcomparable with the radius of the earth. A detailed scale analysis of type 1 motion is presented, including a derivation of the so‐called ‘β plane.’ The energetic properties of type 1 motion are summarized, and several successful applications to atmospheric and oceanic problems are described (wave instability, vertical propagation of energy, numerical weather prediction, Gulf Stream meanders). Motion of type 2 has quite different properties; its principal application has been in analysis of the very slow motion and thermocline structure of the interior ocean. In the atmosphere, observations suggest that there is appreciable interaction between the motions of very large scale (type 2) and those of smaller scale (type 1). Laboratory analogs of certain features of geostrophic flow in the atmosphere and ocean have also been constructed.
The atmospheric electric fog effect
Authors: Dolezalek Hans
Published: February 2008

Atmospheric electric parameters show significant variations in a period of hours before the formation of fog becomes visible. The same is true for the dissipation of fog. Apparently the recording of the electric parameters yields a sensitive measure for condensation and evaporation processes in nature. In addition, the electric variations indicate the existence of processes in the transition time between clear weather and fog that are not yet understood. Thus an investigation of this atmospheric electric fog effect promises to increase our knowledge of the formation and dissipation of natural fogs. Of course, it also indicates a method for short‐range forecasting of these events. This review describes the discovery of the effect and the present experimental knowledge. Some attempted explanations are discussed, and are found to be insufficient. The fundamental possibilities for the explanation are treated in some detail, and material for further investigations is provided.
The convection current hypothesis
Authors: Knopoff L.
Published: February 2008

The linear stability problem for a number of models of the mantle of the earth is considered. For appropriate values of the physical parameters of the mantle it seems likely that the Rayleigh number for mantle‐wide convection is far in excess of the value necessary for marginal instability. For very high Rayleigh numbers the velocities in the models can be derived from solutions for turbulent convection. But even for very high Rayleigh numbers the inhomogeneity in Bullen's region C is amply strong enough to prevent mantle‐wide convection from occurring, whether the inhomogeneity involves a phase transition or represents a chemical inhomogeneity. Convection on a smaller scale is also considered. Convection in the upper mantle may occur. These events are not widespread and are of small scale, having dimensions of about 1200–1500 km in lateral extent and depths of the order of 400 km. Large Rayleigh numbers and associated turbulent convection are not ruled out for the lower mantle. The conclusions depend crucially on the assumptions of the values of the viscosity and of the strength of the mantle. The model of turbulent convection in the lower mantle is consistent with localizing a material of high strength and high viscosity in the upper mantle and with the observation that earthquakes are not observed to occur in the lower mantle.
Dispersive digital filters
Authors: Robinson Enders A. , Treitel Sven
Published: February 2008

Suites of wavelets or filters having identical amplitude spectrums are of interest because of the insight they can yield into the fundamental nature of the seismic pulse. Wavelets of a given suite are obtainable from each other by passing them through an appropriate set of dispersive filters. Such filters are of the pure phase‐shift kind; that is, their amplitude characteristic is constant and independent of frequency, whereas their phase‐lag characteristic is a prescribed function of frequency. In general, the wavelets of a given suite can be distinguished from each other on the basis of the ‘partial energy’ curve. This curve describes how the energy of a wavelet is distributed over the time range of its duration. The ‘minimum‐delay’ wavelet of a suite is the one whose energy is concentrated at its front, whereas the ‘maximum‐delay’ wavelet of the same suite is the one whose energy is concentrated at its end. Wavelets whose energies are concentrated at intermediate positions between these extreme cases are of the ‘mixed‐delay’ type. Of the wavelet members of a given suite, the minimum‐delay wavelet has a phase‐lag characteristic that lies as near as possible to the frequency axis, whereas the maximum delay wavelet has a phase‐lag characteristic which lies as far away as possible from the frequency axis. The phase‐lag characteristics of the mixed‐delay wavelets of a given suite all fall between the phase‐lag characteristics of the minimum‐ and maximum‐delay wavelet members of this suite.

Phase‐shift filters may be either one‐sided or two‐sided; that is, phase‐shift filters may have a pure memory component, a pure anticipation component, or both a memory and an anticipation component. Phase‐shift filters with a pure anticipation component are the inverses of corresponding phase‐shift filters with a pure memory component. This paper treats the general class of phase‐shift filters, but with primary emphasis on the important subclass of dispersive filters. The amplitude characteristic of such filters is unity for all frequencies, whereas their phase‐lag characteristic is such that differential delays or advances are introduced into each frequency component. A pulse passed through such a filter will change its shape, even though its amplitude characteristic remains unaltered.

We consider the impulsive response of a horizontally stratified, perfectly elastic and homogeneous medium, whose deepest interface is a perfect reflector. Both source and detector are located at the surface, and we treat only normally incident P‐wave motion. Then the reflected response of the layered medium is expressible as the transfer function of a dispersive filter. This means that the partial energy curve of the reflected response lies everywhere below the partial energy curves of an arbitrary source wavelet used to excite the medium.
The closure problem in a system of random gravity waves
Authors: Newell Alan C.
Published: February 2008

The time behavior of weakly interacting random gravity waves is examined, and equations are derived governing the long‐time behavior of the spectral cumulants. Without any specific statistical assumptions, it is shown that these equations form a closed set, thus rendering the problem theoretically solvable. In particular, the mechanism for energy transfer is found to be primarily due to resonance phenomena. The retraceability of solutions; is discussed in the appendix.
Rapid estimation of the topographic disturbance to superficial thermal gradients
Authors: Lachenbruch Arthur H.
Published: February 2008

The Jeffreys‐Bullard theory of the topographic correction to geothermal gradients cannot be applied with confidence if the height of the relief is large relative to the horizontal distance and depth of the measurement points. It cannot be generally applied to shallow probe measurements in the ocean bottom if bold relief occurs on a scale exceeding a few meters, or on continents to observation in shallow boreholes in extremely rugged terrain.

In an important special case, where the measurement depth is small relative to the distance to the relief, the ‘superficial’ gradient anomaly may be approximated by the value applicable at zero depth. A fairly general two‐dimensional steady‐state theory for this case can be based on the solution for heat flux through an inclined plane of arbitrary height and slope angle. These two parameters are easily visualized and represented graphically so that models which approximate or bracket real topography can be identified quickly. The results can be applied to stations on planes, valleys, ridges, or benches bounded by irregular slopes. They are valid for points arbitrarily close to slopes of any height or inclination. Finite slope and curvature of the surface at the station can be accommodated if they are not too great. Even if other theories of the topographic correction are applicable, the present method can be useful, as it leads to rapid estimates by graphical means and to useful limits even if the superficial condition is not satisfied.

Curvature in an ocean‐bottom temperature profile justifies suspicion of a topographic disturbance from undetected relief. The temperature probe's length should be 2 or 3 times the uncertainty in local elevation difference, and measured curvature should be negligible for reasonable assurance that undetected relief is not causing gradient errors greater than ±10%. Relief not detectable with conventional echo sounders, but of the type observed with deeply towed sounding equipment, can cause heat‐flow anomalies of 50–100%, and relatively little curvature will be indicated by probes a few meters long. The very high oceanic heat flows are difficult to explain by undetected relief, but the very low ones are not.
Understanding and constructively using the effects of underground nuclear explosions
Authors: Rodean Howard C.
Published: February 2008

This report describes the unclassified research that is directed toward the understanding of underground nuclear explosion phenomena and that is applied to developing constructive applications for nuclear explosions.

The equations of state for geological materials are of fundamental importance in describing the response of these materials to nuclear explosions. These equations are based on geophysical and laboratory measurements of chemical and physical properties and on theoretical calculations for the high‐pressure and high‐temperature conditions not accessible to measurement. Physical measurements of ground motion generated by explosions are used, together with the equations of state, chemical and thermodynamic theory, and the laws of continuum mechanics, to develop mathematical models for predicting explosion phenomena.

Postshot exploration is necessary to determine the residual explosion effects, such as heat deposition, rock fracturing, and chimney formation. These explorations give physical and chemical clues that aid in the interpretation of the experiment. Furthermore, the residual effects are of interest in many engineering applications.

Safety considerations include airblast and seismic motion that may damage property and radioactivity that may be a health hazard. Significant progress has been made in predicting airblast, ground motion, and radioactivity distribution, but more work needs to be done in order that these hazards be predictable with a known statistical accuracy.

Nuclear explosions are intense sources of neutrons; therefore, experiments are conducted to measure neutron cross sections and to produce heavy elements. The heaviest nuclide produced to date by this technique has a mass number of 257. The seismic waves generated by nuclear explosions have been used by geophysicists for more than two decades to determine the internal structure of the earth with a precision not possible with earthquakes. Finally, research is under way to relate the effects of an explosion to its intended use (in the petroleum industry, for example).
Consequences of a magnetospheric plasma
Authors: Kennel Charles F.
Published: February 2008

We explore the hypothesis that, in some cases, instabilities in the magnetospheric plasma create the maximum dissipation available to them. In the case of pitch‐angle diffusion instabilities, the tendency toward isotropy on auroral lines of force is evidence for strong pitch‐angle diffusion. The location of the auroral precipitation boundary may be computed by balancing convection with strong‐diffusion precipitation. The radial diffusion required to balance precipitation losses of energetic protons and electrons in the Van Allen zone could approach the Bohm diffusion rate, probably another maximum dissipation limit, at least for instabilities in the drift scaling.
Geostrophic adjustment
Authors: Blumen William
Published: February 2008

The conservation of potential vorticity of a rotating homogeneous or stratified fluid may, in principle, be used to determine steady‐state field distributions from a given initial state. If the governing equations are linear, if the basic‐state is one of rest, and if the initial field of motion is geostrophically balanced, then no change in this equilibrium state occurs. However, nongeostrophic initial conditions excite transient gravity‐inertia waves that redistribute mass and momentum to ultimately establish a geostrophic steady state, whose potential vorticity is equal to the potential vorticity of the initial state. A steady state may not become established if, for example, hydrodynamic instabilities occur or if wave energy becomes trapped because of inherent refractive properties of the medium. Some examples, which illustrate the properties of geostrophic adjustment and nonadjustment, are presented and discussed. A simple model, which incorporates gross features of atmospheric and ocean flows, is also presented in order to summarize the relationships between the spatial scales associated with the initial conditions and the partition of energy between the allowable modes of oscillation, both transient and steady. The oceanic response to imposed stresses from atmospheric circulation systems and the atmospheric response to sources of wave energy, which includes the introduction of incorrect initial data into numerical simulations, provide practical applications of the theory.
equatorial undercurrent: Measurements and theories
Authors: Philander S. G. H.
Published: February 2008

An eastward jet in the equatorial thermocline and, below it, a weaker westward current extending to a depth of about 1200 meters have been observed at practically all longitudes. In the western Pacific the flow in the deep (150 meter) mixed layer above the thermocline is westward at and near the surface and eastward at greater depths when the winds are westward. These shallow currents appear to reverse direction when the monsoons do. At longitudes where a deep mixed layer is absent, the Atlantic and eastern part of the Pacific, the undercurrent in the thermocline is symmetric about the equator, has its downstream flow in geostrophic balance, and is marked by deep penetration of warm water of high oxygen concentration when the winds are light. When the southeast trades gain in strength, the core of the undercurrent moves upwind, its zonal flow becomes ageostrophic, the westward surface flow becomes stronger, the subsurface eastward flow becomes weaker, the ridging of isotherms at the equator becomes more pronounced, and the troughing becomes less pronounced. The evidence in favor of these variations occurring systematically is very tenuous. For a constant‐density model to be relevant to the motion observed in the mixed layer of the western Pacific, it must be nonlinear and the vertical diffusion of momentum must be important at all depths. The results of such models are in reasonable agreement with observations if the winds are westward. To explain the eastward flow in the thermocline below the mixed layer, a stratified model is necessary. According to one such model, density gradients, in the absence of local winds, give rise to an eastward surface current in the equatorial thermocline and below it to a westward current. The meridional circulation is marked by equatorial downwelling. The modification of these ‘thermally’ driven currents by local winds is consistent with the earlier description of the flow at longitudes where a mixed surface layer is absent.
Stable auroral red arcs
Authors: Hoch R. J.
Published: February 2008

Stable auroral red (SAR) arcs are diffuse, persistent, practically monochromatic (λλ 6300–6364 Å) auroral forms peculiar to mid‐latitude regions of earth. Measurements of such parameters as spectral composition, geomagnetic location, range of intensity, and frequency of occurrence lead to the conclusion that the phenomenon is due to the excitation of atomic oxygen by hot electrons in the plasmapause region. However, on the basis of the data available, it is not clear whether fresh electrons are precipitating into the region of the arc or whether ambient electrons are being heated in place. There is strong evidence that the source of energy in either case is the ring current. Suggested mechanisms by which energy is transferred from the ring current to the electrons in the SAR arc region are (1) heat flow, that is, transfer of kinetic energy to the SAR arc region by Coulomb collisions, (2) transfer of ring current proton kinetic energy to hydromagnetic waves, which are in turn damped by the electrons in the SAR arc region, and (3) direct influx of energetic electrons into the SAR arc region. Which of these mechanisms predominates is still not resolved at this time. There are other open questions as well, including questions dealing with the motion of the arcs and the spectral composition.
Auroral particle precipitation and Birkeland Currents
Authors: Arnoldy R. L.
Published: February 2008

Correlated measurements that provide information on Birkeland (field aligned) currents are reviewed. Because of the obvious importance of field‐aligned electric fields with regard to Birkeland currents, the last section of the paper is devoted to a presentation of recent data on the observations of field‐aligned auroral electron fluxes and monoenergetic peaks in the spectrum. Experimental data cannot yet define the overall magnetospheric pattern of the Birkeland current system. The largest body of data regarding these currents comes from polar‐orbiting satellites. These data indicate that current sheets are associated with auroral displays and that field‐aligned electron fluxes on the order of 1‐keV energy are significant charge carriers for the conventional current out of the atmosphere. Rocket observations verify that electrons responsible for the production of auroral forms carry a significant fraction of the current necessary to produce local magnetic effects that require Birkeland currents for their explanations. There are a few measurements that suggest that the return current might be carried by low‐energy electrons (less than a few hundred electron volts) streaming out of the atmosphere.
The atmosphere of Titan
Authors: Gross S. H.
Published: February 2008

Titan, a satellite of Saturn, is unique in that it is the only satellite in the solar system with an extensive atmosphere, possibly more massive than that of the earth. Methane and hydrogen have been discovered, and a greenhouse effect is apparent from infrared measurements. It may be enshrouded by clouds, and this intriguing body may, in time, provide clues to the evolution of the major planets and their satellites. At present, interpretation of the observational evidence concerning the properties of Titan is somewhat speculative and controversial. The status of the observations and theoretical studies is assessed.
The dynamics and energetics of mature tropical cyclones
Authors: Anthes Richard A.
Published: February 2008

Rapid progress toward the understanding of tropical cyclones has been made during the past 10 years, largely as a result of the development of numerical models. The dynamics and energetics of the mature tropical cyclone are reviewed in this article. First, the pressure, wind, temperature, and moisture structures of the hurricane are summarized. Then a scale analysis is applied over four separate regions of the hurricane domain to emphasize the most important dynamic processes in each region. The energetics of the tropical cyclone is examined in detail. The storm is shown to be a self‐sustaining quasi‐steady thermodynamic heat engine that is driven primarily by latent heat release. The relationship between latent heating and production of kinetic energy is discussed from the available potential energy viewpoint. The possibility of a steady state axisymmetric hurricane in a closed domain is considered. Although such a model appears possible from an energetic viewpoint, angular momentum considerations reveal that a steady axisymmetric closed system is impossible on any scale. For small domains (radius ∼500 km), in which axisymmetric circulations are possible, the system must be open in order that angular momentum be imported from the environment. For larger domains, axisymmetric circulations are unrealistic. The water vapor budget of the hurricane is examined to indicate the relative importance of evaporation and horizontal transport of water vapor in maintaining the moisture supply. Evaporation is shown to be an important percentage of the precipitation in the mature storm. Finally, the numerical modeling of tropical cyclones is summarized. An important problem in the development of hurricane models is the treatment or parameterization of the cumulus cloud scale and the hurricane scale interactions. The implications of the concept of conditional instability of the second kind on hurricane modeling are discussed. Results from several axisymmetric (two‐dimensional) hurricane models, including attempts to simulate hurricane modification experiments, are summarized. Some recent results from a time‐dependent three‐dimensional hurricane model are presented.
Ionospheric propagation of HF and VHF radio waves across the geomagnetic equator
Authors: Nielson Donald L. , Crochet Michel
Published: February 2008

Transequatorial propagation is influenced by many of the same equatorial F region events that have been identified by using other radio and optical sensors. The daytime equatorial ionosphere provides unusual long‐range propagation conditions because of the peculiar latitudinal profile created by vertical drift over the magnetic equator. Radio signals reflected from this configuration are narrowly spread (coherent) yet have maximum frequencies that at times may reach 60 MHz. The inhomogeneities in the postsunset F region lead to a different, scatterlike propagation. Because of the wide range of scale sizes and plasma densities in the nighttime equatorial ionosphere, frequencies throughout the HF and VHF band are significantly distorted, and reflections can occur as high as 100 MHz. The irregularities responsible for these conditions follow the diurnal and seasonal trends of spread F only with certain qualifications. Horizontal and vertical drift of the scattering centers is evident from the use of both directional antennas and Doppler analysis. The reflection mechanisms are only partially accounted for, and the causes of the F region irregularities at all scale sizes are as yet unknown.
Maximum entropy spectral analysis and autoregressive decomposition
Authors: Ulrych Tad J. , Bishop Thomas N.
Published: February 2008

The duality between the maximum entropy method (MEM) of spectral analysis and the autoregressive (AR) representation of the data allows the application of recent advances in AR analysis to MEM in an attempt to obviate some shortcomings in this method of spectral decomposition. Specifically, this paper investigates the work of Akaike (1969a,b) on a criterion for choosing the length of the required prediction error filter and compares two methods of determining the filter coefficients. Recent work by Kromer (1970) on asymptotic properties of the AR spectral estimator is also of importance. Some preliminary results of the splitting of the normal modes of the earth are presented as an illustration of the application of MEM to geophysics.
Aeronomy of the major planets: Photochemistry of ammonia and hydrocarbons
Authors: Strobel Darrell F.
Published: February 2008

The photochemistry of hydrocarbons and ammonia is reviewed for the cold, H2‐dominated atmospheres of the major planets and their satellites. Detailed discussions are given of primary dissociation paths, chemical kinetics, aeronomical models, the formation of complex hydrocarbons, and the role that these constituents and their photolysis products play in the energy balance of planetary atmospheres. It is concluded that the formation rate of complex hydrocarbons by gas phase kinetics is at most a few percent of the CH4 dissociation rate. On Jupiter, large concentrations of C2H6 and C2H2 are predicted, which are in reasonable agreement with observational estimates. A consideration of the Lyman α albedo, the UV albedo between 2000 and 2300 Å, and the NH3 photochemistry suggests that Jupiter's eddy diffusion coefficient is >108 cm² s−1 near the turbopause but only ∼104 cm² s−1 in the lower stratosphere. Large amounts of C2H6 and C2H2 may be present on Titan.
Gabbro‐eclogite reaction rate and its geophysical significance
Authors: Ahrens Thomas J. , Schubert Gerald
Published: February 2008

The gabbro‐garnet granulite‐eclogite transformation may play a significant role in driving the motions of terrestrial lithospheric plates. Whether or not this transformation is in fact important as a driving mechanism for plate tectonics depends on the relationship of the reaction time to geologic time. Solid state diffusion under completely dry conditions is investigated as a possible model for the gabbro‐eclogite reaction, with the result that it could not produce the transition in geologically meaningful times at temperatures less than circa 600°–800°C in the earth's upper mantle. Other reaction mechanisms must exist for the geologically rapid occurrence of the phase change at lower temperatures. It is found that one of these mechanisms can be grain interstitial diffusion in a mantle with minute amounts of water. In this model, dissolved ions migrate through water films surrounding mineral grains to sites of reaction. A water‐undersaturated mantle contains a small quantity of hydrous phases, such as chlorite, amphibole, or talc, the presence of which implies that interstices within the rock can contain water in equilibrium with these minerals and at a pressure PH 2O which is less than the pressure in the rock. Implicit then is the presence of other gases and/or structural rock integrity. This PH 2O is calculated for serpentine, tremolite, and talc as a function of temperature and rock pressure. Various pertinent cations are sufficiently mobile in aqueous solution that at high temperature and high pressure, diffusion through water will not significantly slow the reaction. Rather, pressure‐induced solubility of ions in this water vapor is the important rate‐limiting process in the model. Rock pressure and temperature must be such as to generate at least ∼0.5‐1 kbar of PH 2O in the presence of the hydrous phases for geologically short reaction times. Under ambient conditions PH 2O is quite small, the cations are relatively insoluble, and the reaction time is geologically long. Upon subduction of a basaltic upper crust or lithosphere, for example, an increase in PH 2O occurs, and with increasing pressure the mineral solubility in this supercritical water increases dramatically, yielding geologically short reaction times; for example, ∼20 m.y. for chlorite‐containing rocks with ∼10−5‐cm film thickness for ion diffusion at depths of ∼15‐30 km and at temperatures of ∼150°–300°C for different heating models of the descending slab. For gabbros in which amphibole (tremolite)‐pyroxene equilibria buffer the partial pressure of water, depths of ∼55–70 km and temperatures of 400°–550°C are required for rapid eclogitization, again for different slab heating models. Thus contrary to previous suggestions, the gabbro‐eclogite transformation, as it probably occurs in the descending or spreading lithosphere, is not simply rate‐controlled by temperature but depends heavily on pressure and on the nature of the minor hydrous minerals present.
Experimental igneous petrology
Authors: Boettcher A. L.
Published: February 2008

Experimental igneous petrology in the period 1971–1975 produced many exciting results that aided significantly our understanding of conceptual mechanisms involved in global‐scale tectonics. The investigation of melting and other phase relationships of rocks and synthetic systems ranging from intermediate to ultrabasic in composition, particularly in the presence of H2O and H2O‐CO2vapors, has established limits to conditions under which anatexis and phase transformations can occur, particularly at plate boundaries. Much of the H2O in the upper mantle and lower crust is bound in hydrous minerals such as amphiboles and micas; establishment of the conditions under which these phases are stable in the laboratory has provided the basis of several models for the genesis of orogenic zone calc‐alkaline rocks and for melting and other transformations of subducted lithosphere. Because of the significance of H2O, CO2, and other volatile components in upper mantle processes, considerable effort was devoted to the study of solubilities of these species in silicate melts at high pressures, and some thermodynamic data derived from measurements at high pressures and temperatures enabled the calculation of phase relations previously unobtainable. Many new experimental techniques were developed to extend the capabilities of reproducing natural conditions in the laboratory. Nevertheless, many more refinements and new developments must be made; for example, new alloys for encapsulation of Fe‐bearing samples must be sought.
Experimental metamorphic petrology
Authors: Hewitt D. A. , Gilbert M. C.
Published: February 2008

The past quadrennium, 1971–1974 inclusive, has seen a great variety of published work in experimental metamorphic petrology. Numerous phase equilibrium studies as well as many determinations of physical properties of minerals have been produced. Whereas the last report contained 270 references, this report contains over 475, illustrative not only of the activity of the science but also of the wider scope of articles necessary to describe the interactions within modern petrology.

In this review, metamorphism has generally been taken to cover the temperature range from 10O°C to the solidus in the appropriate bulk compositions and mineral groups. A few articles containing liquidus data have been referenced when significant subsolidus data were also included. Most of the references are in the English language and from North American—or European‐based publications. Unavoidably, many pertinent foreign experimental data are excluded. Nevertheless, trends in research are thought to be reasonably well displayed. An attempt was made to keep the review as current and useful as possible by including abstracts from the principal meetings, in 1974, of the Geological Society of America and the American Geophysical Union.
The state of stress in the Earth's crust
Authors: Haimson Bezalel C.
Published: February 2008

This article is limited to a short state of the art report on available methods of stress determination in situ and a summary of findings to date.

Stress determination at depth requires the drilling of a hole to the level of interest. Most of the methods employ sophisticated instrumentation down the hole and require overcoring for relieving the stresses. Because of the necessity to overcore, hole length is limited to 30–40 m. Hence these methods are useful only in stress measurements near the surface of the earth or at depth if previous access has been obtained through underground chambers, tunnels, or mine openings. A variety of measuring methods have been developed which determine either changes in hole diameter or strain on the bottom of the hole resulting from the complete relief of the stress due to overcoring.
Fracture in rock
Authors: Friedman Melvin
Published: February 2008

Fracture is perhaps the most important topic in rock mechanics today, primarily because it is the dominant mechanism of rock failure at the relatively low pressures and temperatures at shallow depths in the earth's crust and because existing fractures strongly influence the physical and mechanical behavior of the rock mass. Fracture considerations therefore pervade all of man's interests dealing with exploration and production of natural resources, engineering projects under or on the earth's surface, and the prediction, modification, and control of earthquakes. For example, (1) estimates indicate that about 5% of the energy generated in the United States is consumed in fracturing rocks [Lewis, 1966]; (2) in the petroleum industry an understanding of fracture is essential in relation to ‘fracture porosity’ reservoirs, hydraulic fracturing, secondary recovery programs, structural inferences from existing fractures, underground storage of gas, and drilling technology; (3) in certain geothermal projects, fractures serve both as subsurface permeability channels and as surfaces to heat circulating waters; (4) the in situ ‘mining’ of oil shale or of the gasification of coal is primarily a matter of man's ability to fracture the rock mass under controlled conditions; (5) in mining and tunneling operations, fractures influence the stability of the openings as well as the extraction of rock or ore; and (6) recent developments in earthquake research have focused attention on fracture (dilatancy) as the source of a host of premonitory events from which it may someday be possible to predict earthquakes [Nur, 1972; Whitcomb et al., 1973; Scholz et al., 1973]. Accordingly, there is ample mission orientation for even the most basic research designed to gain a better understanding of fracture processes in rock and of the mechanical behavior of rock masses containing fractures.
Internal waves in the ocean
Authors: Briscoe Melbourne G.
Published: February 2008

Progress in measuring, describing, and understanding oceanic internal gravity waves during the quadrennium 1971–1974 is reviewed. Emphasis is given to trends in techniques and ideas that hold promise for the future. An extensive bibliography is provided.
General circulation of the atmosphere
Authors: Arakawa Akio
Published: February 2008

Lorenz[1970] presented the commonly accepted view of the general circulation of the atmosphere, which can be summarized as follows: Without surface irregularities and variable heating there can be a mathematically possible steady axially symmetric circulation. Even with surface irregularities there can still be a mathematically possible steady circulation (i.e., one without migratory cyclones or similar transient eddies), but such a circulation would be baroclinically unstable. It is due to this instability that the actual circulation contains fully developed large‐scale migratory eddies. The transient atmospheric eddies receive available potential energy from the axially symmetric component of the circulation and give up some kinetic energy by dissipation. They transport poleward both large amounts of angular momentum across subtropical latitudes near the tropopause level and large amounts of heat across middle latitudes in the lower and the middle troposphere. The result is to induce direct meridional cells in low latitudes (the Hadley circulation) and indirect meridional cells in middle latitudes, which help to maintain the trade winds and the middle‐latitude surface westerlies. The direct meridional cells also carry large amounts of water vapor toward the equator, thus producing the heavy equatorial rainfall. The accompanying release of latent heat supplies additional drive to the low latitude direct cells.
Climatic change
Authors: Gates W. Lawrence , Imbrie John
Published: February 2008

During the past 4 years, interest in the problem of climatic change has increased greatly, owing in part to growing recognition of its impact on human affairs. This has been matched by a surge of scientific research on nearly all aspects of the problem, especially the areas of climatic data analysis and climatic modeling for both present and past climates. During this period the large‐scale distribution of the global climate was successfully simulated by a variety of numerical models, and extensive efforts are underway to further improve their accuracy. Climate models have also been used in new diagnoses of the mechanisms of both past and possible future climatic changes, an activity which has underscored the need for more complete documentation of both recent instrumentally observed climatic changes and those inferred from historical and paleoclimatic sources.
Meteorology of the upper atmosphere
Authors: Dickinson Robert E.
Published: February 2008

Upper atmosphere meteorologists are concerned with the structure and dynamics of the neutral atmosphere from roughly the tropopause through the thermosphere, especially on a global scale. Some of the exciting developments in upper atmospheric meteorology over the last 4 years include advances in understanding the role of various trace gases in the stratosphere that influence the photochemistry of ozone; a description of seasonal, latitudinal, and diurnal variations of winds and composition in the thermosphere; and significant advances in interpreting various upper atmosphere circulation systems in terms of coupling to the troposphere by various types of tropical and extratropical wave processes. Notable on the methodology side has been the application of increasingly advanced in situ and remote sensing techniques utilizing satellite platforms, especially the use of mass spectrometers for measuring composition in the thermosphere and infrared radiometers for inferring global stratospheric temperature. Numerical models of dynamic processes have increased in sophistication with, on the one hand, extension of tropospheric general circulation models to stratospheric levels and, on the other hand, development of a large number of different simplified dynamic models for treating various aspects of thermospheric dynamics. This paper reviews progress over the last 4 years in upper atmospheric meteorology.
Thermal structure of the ionosphere
Authors: Brace L. H.
Published: February 2008

This report presents a brief review of the progress that has been made in the past 4 years or so toward gaining a more complete understanding of the thermal structure of the ionosphere, with particular emphasis on research in the United States.

Knowledge of the electron temperature Te and the ion temperature Ti is of fundamental importance in our attempts to understand the processes that occur in the upper reaches of our atmosphere because most thermospheric processes tend to heat or cool the electrons that make up the ionosphere, and the ion temperature is coupled to both the electron temperature and the neutral gas temperature Tn. The current state of theoretical knowledge about the ionosphere temperature has been reviewed by Schunk and Walker [1973], who provided references for the work up to that time.
A review of F region dynamics
Authors: Evans J. V.
Published: February 2008

The photochemical processes responsible for the formation of the F region of the ionosphere were identified from radio wave reflection and rocket experiments prior to 1960 (for review, see Rishbeth [1967a], D. R. Bates [1973, 1974], and Ratcliffe [1974]). It was long recognized that dynamical processes are also extremely important in governing the F layer, but it was not until the decade between 1960 and 1970 that two of the most important processes for setting the plasma in motion horizontally, namely, thermospheric winds and magnetospheric convection, were recognized and confirmed by observation. During the past 4 years, progress in understanding the dynamics of the F layer has largely been made through experimental measurements that have provided detailed information on these two phenomena.

On the theoretical side, there have been considerable advances in developing time‐dependent computer models of the F region which incorporate the photochemical processes, the thermal structure, and the transport arising as a result of neutral winds in an internally self‐consistent manner. These permit one to test the relative importance of various phenomena in contributing to the observed behavior and estimating the magnitude of some parameters which remain poorly known. There have also been important developments in understanding the phenomenon of the escape of plasma at high latitudes into field tubes that have been emptied of ionization; however, many of these ideas still await experimental confirmation.
The sensitivity and dynamic range of inertial seismographs
Authors: Melton Ben S.
Published: February 2008

The literature on earth noise over the spectrum of periods from 0.1 s to 12 h is reviewed and presented as accelerations which, when expressed as spectral‐noise density, allow all seismographs to be considered on a common basis of sensitivity. Their ultimate sensitivity is limited by thermal agitation of their suspended masses and is calculable by considering the energy flow to and from their lossy elements in accordance with principles elucidated by Nyquist. Practical instruments, including those with feedback loops, are considered as examples. Seismometers and accelerometers are treated here as resonant systems having one degree of freedom. The electrical outputs of their transducers are classified as ‘velocity’ or ‘displacement.’ The dynamic range required to record these outputs depends on the range of accelerations imposed on the instrument and upon the combined filtering effects of the resonant system and transducer. Gravitational variation, tilt, and tidal accelerations are considered as they affect the instrumental problem.