bluuebunny/crossref_metadata_2025 huggingface dataset:
Euclidean and fractal models for the description of rock surface roughness
Authors: Power William L. , Tullis Terry E.
Published: February 2008

Accurate description of the topography of rock surfaces is essential because surface roughness affects frictional strength, the flow of fluids in joints and fractures, the seismic behavior of faults, and the formation of gouge and breccia in fault zones. Real rock surfaces can be described using self‐similar and self‐affine fractal models of surface roughness. If a surface is self‐similar, a small portion of the surface, when magnified isotropically, will appear statistically identical to the entire surface. If a surface is self‐affine, a magnified portion of the surface will only appear statistically identical to the entire surface if different magnifications are used for the directions parallel and perpendicular to the surface. At least two parameters are required to describe a fractal model; one parameter typically describes how roughness changes with scale, while the other specifies the variance or surface slope at a reference scale. The divider method and the spectral method are in common use to determine the best fit fractal model from surface profile data. Power spectra from self‐similar surfaces have slopes of −3 on log‐log plots of power spectral density versus spatial frequency, while spectra from self‐affine surfaces have slopes other than −3. Power spectra can be interpreted with greater facility if dimensionless amplitude to wavelength ratios are contoured on plots of power spectral density versus frequency. The topography of many natural rock surfaces, including both fractures and faults, is approximately self‐similar within the 6.5 order of magnitude wide wavelength band of 10 μm to 40 m. Within smaller wavelength bands, natural rock surfaces may exhibit self‐affine behavior.
Collision and fan‐shaped compressional stress pattern in the Izu Block at the northern edge of the Philippine Sea Plate
Authors: Ukawa Motoo
Published: February 2008

The Izu block in central Japan, which is surrounded by the Nankai‐Suruga trough and the Sagami trough, is considered to be colliding with the Eurasian (EUR) plate at the northern edge of the Philippine Sea (PHS) plate. The stress state in the Izu block is investigated from focal mechanism data mainly obtained by the seismic network of the National Research Institute for Earth Science and Disaster Prevention. The predominant focal mechanisms in the central to eastern part of the Izu block indicate strike‐slip faulting with P axes oriented N–S to NW–SE and T axes oriented E–W to NE–SW, whereas focal mechanisms in the western part are strike‐slip and reverse faulting with P axes oriented N–S to NE–SW, indicating that the compressional axes remain horizontal throughout the region. The compressional stress trajectories estimated from the P axes show a fan‐shaped pattern, radiating from the northern edge of the Izu block where the collision is considered to be occurring. The fan‐shaped pattern of compressional stress trajectories is interpreted to be the result of the collision of the Izu block with EUR plate. Plane stress analysis by the finite element method supports this conclusion. The stable distribution of the T axis directions in the central to eastern part is basically interpreted as resulting from the slab pull force by the subducting PHS plate along the Sagami trough. Furthermore this model can explain the seismic quiescence in the northern part of the Suruga Bay region.
Instability of flow with temperature‐dependent viscosity: A model of magma dynamics
Authors: Whitehead J. A. , Helfrich Karl R.
Published: February 2008

In material whose viscosity is very temperature dependent, flow from a chamber through a cooled slot can develop a fingering instability or time‐dependent behavior, depending on the elastic properties of the chamber, the viscosity‐temperature relationship, and the geometry of the slot. A laboratory experiment is described where syrup flows from a reservoir through a tube immersed in a chilled bath to an exit hole at constant pressure. Flow is either steady or periodic depending on the temperature of the bath and the flow rate into the reservoir. A theory indicates that the transition from steady to periodic flow depends on nonlinearities in the steady state relation between pressure and flow rate. A general stability criterion is advanced that states that the Peclet number must be within a certain range for instability to develop. Parameters governing the oscillation period are determined. Theory also indicates that flow through a slot would develop finger‐like instabilities under certain conditions. Qualitative laboratory experiments with paraffin spreading over a cold plate reveal the fingering.
Geology and petrology of Jasper Seamount
Authors: Gee Jeff , Staudigel Hubert , Natland James H.
Published: February 2008

Fifteen dredges on the summit and upper flanks of Jasper Seamount (122°44'W; 30°27'N) recovered a wide variety of lithologies, including pillow lavas, vesicular lapillistones from shallow submarine explosive volcanism, and a range of xenoliths. On the basis of dredge locations, geochemical characteristics, and 40Ar/39Ar age data, three distinct phases of volcanism can be distinguished, a shield‐building tholeiitic/transitional phase (Flank Transitional Series, FTS), followed by a flank alkalic series (FAS), and a late‐stage Summit Alkalic Series (SAS). All three series consist exclusively of differentiated (Mg# = 54 to 21; Mg# = Mg2+/(Mg2++Fe2+)) compositions. The FTS represents a low‐pressure differentiation trend from tholeiitic/transitional basalts to quartz‐normative residual liquids and probably accounts for more than 90% of the volume of Jasper. 40Ar/39Ar age data, the dominant reversed polarity of Jasper, and a plausible duration (< 1 m.y.) for shield construction suggest FTS volcanism began about 11 Ma and ended about 10 Ma. FTS lavas probably erupted from a NW trending, hotspot track‐parallel rift system. The intermediate alkalinity FAS lavas, which probably comprise 3–8% of the volume of Jasper, erupted from 8.7 to 7.5 Ma, possibly after a brief volcanic hiatus or period of reduced eruptive activity. Normative projections suggest the FAS lavas are the product of fractionation or equilibration at elevated pressures. The hawaiites and mugearites of the SAS erupted between 4.8 and 4.1 Ma, after a probable 2.7 m.y. period of volcanic quiescence, and probably constitute <1% of the seamount volume. A suite of Xenoliths incorporated in SAS lavas includes (1) tholeiitic basalt fragments from either the ocean crust or seamount interior, (2) a range of differentiated gabbros largely derived from the ocean crust, (3) residual mantle spinel lherzolites, and (4) pyroxenite and peridotite cumulates. The abundance of crustal gabbro and spinel lherzolite xenoliths in evolved lavas of the SAS suggests that these lavas probably fractionated in a magma chamber at the crust‐mantle boundary. The occurrence of orthopyroxene‐bearing alkalic cumulate xenoliths in these lavas, however, is enigmatic and may reflect complexities such as magma mixing or the inappropriateness of pressure estimates. The SAS vents of Jasper define a NE‐SW volcanic trend which is orthogonal to the FTS rift. The pattern of volcanic activity, including periods of volcanic quiescence, and the general increase in alkalinity, as well as the structural reorganization of magmatic feeder systems of Jasper Seamount, is strikingly similar to the patterns observed on Hawaiian volcanoes. Thus our data from Jasper (690 km3) extend the concepts of structural and petrological evolution of hotspot volcanoes based on Hawaii to moderate‐sized seamounts.
The chemical composition of the dust‐free Martian atmosphere: Preliminary results of a two‐dimensional model
Authors: Moreau D. , Esposito L. W. , Brasseur G.
Published: February 2008

This paper describes a two‐dimensional model of the Martian atmosphere, in which chemical, radiative and dynamical processes are treated interactively. The model is developed for a carbon dioxide‐hydrogen‐oxygen‐nitrogen atmosphere and provides estimates of concentrations for 19 chemical species. The dynamical equations are expressed in the transformed Eulerian coordinates. The wave driving and eddy mixing coefficients resulting from gravity and Rossby wave absorption are computed consistently with the evolving distribution of the mean zonal wind. The net diabatic heating/cooling rate is derived from a detailed radiative scheme including the contributions of CO2 O3, H2O and O2 and is computed consistently with the calculated distribution of temperature and trace species quantities. The computed temperature field as well as the meridional and seasonal variations of ozone column abundance are in good agreement with the distributions observed by Mariner 9 and Viking spacecrafts and the results obtained by previous studies. The present version of the model does not include the effects of dust, clouds and polar hood and only the chemistry in a dust‐free atmosphere is considered.
Terrestrial water storage and polar motion
Authors: Kuehne John , Wilson Clark R.
Published: February 2008

This study compares observed polar motion for the period 1900–1985 with meteorologic and hydrologic data for the world over the same period, in an effort to determine whether water storage, in combination with air mass redistribution, can account for the observed variance of polar motion. Monthly time series of estimated continental water storage and air mass excitation functions have been compared at the annual frequency and at the Chandler frequency using power, coherence, multiple coherence, and phase spectra. There is a discrepancy in accounting for more than half the variance of polar motion across a broad range of frequencies. Similar results have been obtained in recent studies of polar motion at frequencies above 1 cycle per year using modern space geodetic determinations of polar motion. The persistence of the discrepancy at the annual frequency and its broadband nature suggest a source of polar motion excitation due to air and water motion which has either not been correctly estimated or not yet identified.
Geologic setting and tertiary structural evolution of southwestern Arizona and southeastern California
Authors: Sherrod David R. , Tosdal Richard M.
Published: February 2008

Volcanic and sedimentary rocks and structures record the Tertiary structural evolution of the lower Colorado River region in southwestern Arizona and southeastern California. A late Eocene or early Oligocene (prior to ∼33 Ma) episode of faulting is indicated by medium‐ to coarse‐grained arkosic rocks in the Chocolate and southern Trigo Mountains. Much of the area was relatively quiescent tectonically during extrusion of volcanic rocks from ∼33 to 22 Ma, but the southernmost part was periodically uplifted and eroded into its underlying crystalline rocks. A major episode of extensional deformation and tilting occurred after deposition of welded tuff about 22 Ma and affected the entire area from the Palo Verde Mountains on the west to the Kofa Mountains on the east. Extension‐related faulting quickly waned and had largely ceased by about 20 Ma in the Kofa Mountains; elsewhere the timing is poorly constrained. By ∼13 Ma, thick alluvial fans filled many grabens and half grabens among tilted fault blocks throughout the area. Volcanism in the lower Colorado River region may have been coincident with a broad structural depression now oriented east‐west. The northern limit of the volcanic terrane defines a tilt‐domain boundary. The northern boundary, reaching from the New Water Mountains in Arizona to the little Chuckwalla Mountains in California, ultimately evolved to separate a terrane of relatively untilted crystalline horsts on the north from a series of east or northeast dipping fault blocks on the south. The southern margin is less well defined but is subparallel to the northern boundary and to the Chocolate Mountains anticlinorium.
Stability and the initiation of channelized surface drainage: A reassessment of the short wavelength limit
Authors: Loewenherz Deborah S.
Published: February 2008

Instability leading to channel initiation occurs when advective processes dominate diffusive processes in the transport of surface material. Smith and Bretherton's (1972) linear treatment of this stability/instability phenomenon is here reexamined. Slopes of finite length are considered and a turning point analysis is used to construct a full asymptotic solution for the short wavelength limit. The analysis shows that the initial longitudinal profiles of marginally unstable surface incisions are deepest at a point corresponding to the convex/concave boundary in the base state profile and may actually extend upslope some distance from that point. The extent of the upslope incision is dependent upon the diffusion coefficient for the surface material and the wave number of the disturbance. In the original stability model, the growth rate of the short wavelength instability increases with decreasing wavelength, so that the shortest wavelengths are the most unstable. By introducing a surface material transport function which accounts for microscale nonlocal transfer, the shortest wavelengths are damped and the unstable growth rates are largest at moderate values of the wave number. The lengthscale set by nonlocal material transport represents the spatial scale at which the continuum description underlying the stability model breaks down. The neutral stability diagram for slope length‐wave number space illustrates that when the very shortest wavelengths are damped, concave slope segments may exhibit stability, at least while the system is within a linear regime. The most promising field application of the linear model lies in the characterization of shallow surface incisions, such as rills, which are in initial stages of development.
Toward a mathematical model of oxygen transfer to and within bottom sediments
Authors: Svensson Urban , Rahm Lars
Published: February 2008

A mathematical model of the benthic boundary layer and the porous bottom is presented and explored. Emphasis is placed on the transition between the Ekman layer flow and the Darcian flow deep in the sediments. The predicted flow field in the porous region is verified against analytical solutions. The effective exchange coefficient for a substance with a large Schmidt number, for example, oxygen, is calculated taking different physical processes like turbulence, diffusion and dispersion into account. It is found that vertical transport may be considerably enhanced in a thin layer near the sediment/water interface, i.e., within the Brinkman layer, due to a dispersion mechanism. The oxygen distribution in the sediment/water system has been investigated for different porosities and consumption rates.
A numerical study of interannual ocean forcing on Arctic ice
Authors: Fleming Gordon H. , Semtner Albert J.
Published: February 2008

A fully prognostic coupled ice‐ocean model is used to examine the importance of interannually variable ocean forcing, on large‐scale monthly simulations of the Arctic ice cover. The model is forced by a prescribed interannually variable atmosphere. Simulations are conducted for a 120‐month period and validated with observed ice concentration data. The model produces very reasonable simulations of the ice edge position, particularly in the Barents and Greenland seas. The use of interannual ocean forcing produces major improvements to the simulation of the ice concentration for both the annual cycle and interannual variations, as compared with simulations in which the ocean forcing is a prescribed mean annual cycle. Vertical ocean heat flux appears to be the dominant mechanism controlling localized ice area anomalies and the overall ice concentration. Consistent errors in simulated ice concentration and thickness remain, including a slightly exaggerated melt‐freeze cycle and insufficient ice thickness. The lack of a nonprognostic mixed layer and the coarse vertical resolution are apparently inadequate to represent the vertical mixing, stratification, and diffusion processes properly.
Strain in shore fast ice due to incoming ocean waves and swell
Authors: Fox Colin , Squire Vernon A.
Published: February 2008

Using a development from the theoretical model presented by Fox and Squire (1990), this paper investigates the strain field generated in shore fast ice by normally incident ocean waves and swell. After a brief description of the model and its convergence, normalized absolute strain (relative to a 1‐m incident wave) is found as a function of distance from the ice edge for various wave periods, ice thicknesses, and water depths. The squared transfer function, giving the relative ability of incident waves of different periods to generate strain in the ice, is calculated, and its consequences are discussed. The ice is then forced with a Pierson‐Moskowitz spectrum, and the consequent strain spectra are plotted as a function of penetration into the ice sheet. Finally, rms strain, computed as the incoherent sum of the strains resulting from energy in the open water spectrum, is found. The results have implications to the breakup of shore fast ice and hence to the floe size distribution of the marginal ice zone.
The seasonal variation of the intrusion of the Philippine sea water into the South China Sea
Authors: Shaw Ping‐Tung
Published: February 2008

The seasonal variation of the intrusion of the Philippine Sea Water into the South China Sea was studied by analyzing the historical hydrographic station data in the northern South China Sea and the Philippine Sea. Water masses at 150, 200, and 250 m were classified by discriminant analysis according to their temperature‐salinity characteristics. At each depth, most water in the study region was classified into two groups representing the Philippine Sea Water and the South China Sea Water, respectively. The geographic distribution of water masses in the South China Sea shows that the Philippine Sea Water was present along the continental margin south of China between October and January. A westward current in the northern South China Sea in winter was inferred from the distribution of the intrusion water.
Circulation in the Gulf of Mexico from Geosat altimetry during 1985–1986
Authors: Johnson Donald R. , Thompson J. Dana , Hawkins Jeffrey D.
Published: February 2008

Using altimetry data obtained from the Geosat Geodetic Mission (April 1985 to October 1986), low‐frequency sea surface height (SSH) variations are investigated in the Gulf of Mexico. SSH time series are formed using the method of Fu and Chelton and are used to calculate surface geostrophic current vectors. Spatial patterns of SSH and current vector variations enable the tracking of two major rings shed from the Loop Current. The rings drifted southwestward across the gulf and into the western boundary region at an average speed of about 3.4 cm/s. The buildup of the Loop Current was monitored, as well as the appearance of an eddy of uncertain origin in the southwestern gulf. Verification of the Geosat results are provided with surface drifters, AVHRR imagery, and hydrography.
A two‐dimensional thermodynamic model for sea ice advance and retreat in the Newfoundland marginal ice zone
Authors: Tang C. L.
Published: February 2008

A time dependent two‐dimensional ice‐ocean coupled thermodynamic model is developed to study the ice edge advance and retreat, development of the oceanic mixed layer, and oceanic response to ice movement, ice melt, and heat balance in the Newfoundland marginal ice zone. The model domain is a vertical section of the ocean along the direction of the ice velocity. Initially, the ocean is free of ice and has a deep mixed layer formed by winter surface cooling. An ice sheet then moves into the domain from the upstream boundary at constant velocity. It melts from the bottom and a shallow mixed layer beneath the ice is developed. Heat and buoyancy fluxes at the air‐sea and ice‐water interfaces and at the bottom of the mixed layer determine the melt rate and change of the mixed layer properties. The ice edge reaches a maximum distance and starts to retreat when the ice is being melted by the warm water faster than it is being advected into the area. The oceanic properties change with the ice movement. During the advancing phase of the ice movement, the heat loss to the ice bottom from ice melting exceeds the heat gain by surface heating and entrainment, causing the mixed layer temperature to drop. But since the buoyancy created by the melting is not sufficient to overcome the effect of wind mixing, the mixed layer deepens rapidly. During the retreating phase, the mixed layer becomes shallower and warmer because of the increasing surface heating and buoyance production by ice melting. The most important factors controlling the melt rate and the excursion distance are the air temperature and the ambient water temperature. Higher wind speeds increase the mixed layer depth but do not have a strong effect on the melt rate.
The intercomparison of radiation codes in climate models: An overview
Authors: Ellingson Robert G. , Fouquart Yves
Published: February 2008

The recognition of the central role of radiative processes in many proposed climate change mechanisms and the perception of possibly significant uncertainties in the estimates of these fundamental processes led the Joint Scientific Committee of the World Climate Research Programme and the International Radiation Commission of the International Association of Meteorology and Atmospheric Physics to initiate the International Intercomparison of Radiation Codes in Climate Models (ICRCCM). The results from model calculations with specified clear‐and‐cloudy conditions show that many radiation algorithms may have unidentifiable but large errors that may significantly affect the conclusions of the studies in which they are used. This is true for climate modeling but may also be the case for other applications such as the estimation of radiation fluxes at the surface from satellite observations. As the study has progressed over a 4‐year period, there has been a narrowing of results as errors were found in some codes and as the understanding of many modeling problems increased. Many of the results, particularly for clear‐sky conditions, indicate that we are close to the range of (relative) accuracy for calculating flux quantities necessary for many climate programs. However, not all models will give such accuracy. It is recommended that the ICRCCM test cases be used to test radiation algorithms prior to their application to climate‐related problems. The participants feel that the rather large discrepancies revealed during ICRCCM cannot be decisively resolved by further calculation. Therefore the group recommends the organization of a program to simultaneously measure spectral radiance at high spectral resolution along with the atmospheric data necessary to calculate radiances.
Aerosol backscatter measurements at 10.6 micrometers with airborne and ground‐based CO2 Doppler lidars over the Colorado High Plains: 2. Backscatter structure
Authors: Bowdle David A. , Rothermel Jeffry , Vaughan J. Michael , Post Madison J.
Published: February 2008

Measurements of tropospheric aerosol volume backscatter coefficients at 10.6‐μm wavelength were obtained with airborne continuous wave and ground‐based pulsed CO2 Doppler lidars over the Colorado High Plains during a 20‐day period in summer 1982. A persistent “background” layer was found between 6‐ and 10‐km altitude, with a generally uniform backscatter mixing ratio of ∼10−10 m2 kg−1 sr−1. The upper boundary of this background layer varied with the tropopause height; the lower boundary varied with the strength and diurnal cycle of convective mixing in the planetary boundary layer (PBL). For quiescent meteorological conditions the transition from the PBL to the background layer was usually very sharp, with backscatter decreases sometimes as large as 3 decades in ∼70 m. Sharp gradients were also found at the boundaries of shallow (tens of meters) subvisible cirrus clouds. For less stable conditions, associated with vertical aerosol transport by deep cumuliform clouds, backscatter tended to decrease exponentially with altitude.
Extracting information on surface properties from bidirectional reflectance measurements
Authors: Pinty Bernard , Verstraete Michel M.
Published: February 2008

The retrieval of surface parameters from remotely sensed data is of prime interest for the estimation of surface properties of various planets in the solar system, including the Earth. Bidirectional reflectance measurements taken over natural surfaces in visible and near‐infrared spectral bands represent one data set from which these surface properties could be estimated. To achieve this goal, it is necessary to have both physical models predicting the bidirectional reflectance field as a function of the relevant surface parameters, and numerical procedures allowing the inversion of these models using a limited sampling of the bidirectional reflectance field. Given that theoretical models of the bidirectional reflectance have been published (Hapke, 1981, 1984, 1986; Verstraete et al., 1990) and that numerical procedures are available (Pinty et al., 1990), this paper focuses on the errors and uncertainties in the retrieved parameters which may arise because of (1) the weaknesses in our theoretical understanding and representation of the surface radiation transfer and (2) the errors in the bidirectional reflectance data. For instance, it is shown that the addition a posteriori of an amplitude parameter in the function accounting for the opposition effect can drastically modify the retrieved values of the optical and morphological parameters of the surface. The consequences of uncertainties in the reflectance data are also investigated, and the redistribution, by the inversion procedure, of such uncertainties on the retrieved parameters is discussed. Finally, synthetic reflectance data contaminated by a known random noise are used to examine the numerical stability of the retrieval and the compatibility between the models.
Observations and modeling of the reactive nitrogen photochemistry at a rural site
Authors: Trainer M. , Buhr M. P. , Curran C. M. , Fehsenfeld F. C. , Hsie E. Y. , Liu S. C. , Norton R. B. , Parrish D. D. , Williams E. J. , Gandrud B. W. , Ridley B. A. , Shetter J. D. , Allwine E. J. , Westberg H. H.
Published: February 2008

Ambient concentrations of key trace gases were measured concurrently at a rural site in the eastern United States during the summer of 1986. The extensive data set allows the evaluation of certain aspects of photochemical oxidant models. A 4‐day high‐pressure period is chosen for a comparison of the model predictions with observations. The emphasis of this analysis is on the discussion of the photochemistry of the reactive nitrogen species and their role in shaping the ozone budget. Observations of the NO2/NO ratio provide an estimate of the peroxy radical concentration at the site. The peroxy radical concentration so derived indicates a significant in‐situ O3 formation which is in accordance with the observed diurnal variation of O3. Isoprene, a natural hydrocarbon, is shown to be much more important than the anthropogenic hydrocarbons in this O3 formation. At this rural site NO, NO2, HNO3, and peroxyacetyl nitrate (PAN) account for 85% or more of NOy, (the sum of the reactive nitrogen species). The diurnal cycle of the reactive nitrogen species and their partitioning is determined by transport and photochemical conversion. At night in the boundary layer defined by a low‐level inversion, NOx is the major NOy, species at this site. Nitric acid and PAN are suppressed by dry deposition and, in the case of PAN, thermal decomposition. During the daytime the NOx contribution to NOy decreases first as higher concentrations of HNO3 and PAN are mixed downward upon the breakup of the nocturnal inversion followed by NOx conversion to other NOy species in photochemical reactions.
Tests of stratospheric models: The reactions of atomic chlorine with O3 and CH4 at low temperature
Authors: DeMore W. B.
Published: February 2008

The reactions of atomic chlorine with O3 and CH4 are very important in stratospheric ozone photochemistry. The relative rates of these reactions strongly influence the ClO/HCl ratio. However, there remains considerable uncertainty in the absolute rate constants for the two reactions at stratospheric temperatures. Since only the relative rate is of primary importance in the stratosphere, experiments on the competitive chlorination of O3/CH4 mixtures have been carried out at 197–217 K, with the objective of directly measuring the rate constant ratio in this temperature range. The results show that the absolute rate constants recommended by the NASA Panel for Data Evaluation (DeMore et al., 1990) are accurate on a relative basis to within 15% at stratospheric temperatures. The following rate constant upper limits are also established for temperatures near 200 K: ClO + CH3O2 → ClOO + CH3O, k < 4 × 10−12; ClO + CH3O2 → OClO + CH3O, k < 1 × 10−15 cm3 molec−1 s−1.
Evolution of Modern Deepwater Circulation: Evidence from the Late Miocene Southern Ocean
Authors: Wright James D. , Miller Kenneth G. , Fairbanks Richard G.
Published: February 2008

Deepwater circulation plays an important role in climate modulation through its redistribution of heat and salt and its control of atmospheric CO2. Oppo and Fairbanks (1987) showed that the Southern Ocean is an excellent monitor of deepwater circulation changes for two reasons: (1) the Southern Ocean is a mixing reservoir for incoming North Atlantic Deep Water and recirculated water from the Pacific and Indian oceans; and (2) the nutrient/δ13C tracers of deepwater are not significantly changed by surficial processes within the Southern Ocean. We can extend these principles to the late Miocene because tectonic changes in the Oligocene and early and middle Miocene developed near‐modern basinal configurations. However, on these time scales, changes in the oceanic carbon reservoir and mean ocean nutrient levels also affect the δ13C differences between ocean basins. From 9.8 to 9.3 Ma, Southern Ocean δ13C values oscillated between high North Atlantic values and low Pacific values. The Southern Ocean recorded δ13C values similar to Pacific values from 9.2 to 8.9 Ma, reflecting a low contribution of Northern Component Water (NCW). The δ13C differences between the NCW and Pacific Outflow Water (POW) end‐members were low from 8.9 to 8.0 Ma, making it difficult to discern circulation patterns. NCW production may have completely shutdown at 8.6 Ma, allowing Southern Component Water (SCW) to fill the North Atlantic and causing the δ13C values in the North Atlantic, Pacific, and Southern oceans to converge. Deepwater δ13C patterns resembling the modern distributions evolved by 7.0 Ma: δ13C values were near 1.0‰ in the North Atlantic; 0.0‰ in the Pacific; and 0.5‰ in the Southern Ocean. Development of near‐modern δ13C distributions by 7.0 Ma resulted not only from an increase in NCW flux but also from an increase in deepwater nutrient levels. Both of these processes increased the δ13C difference between the North Atlantic and Pacific oceans. Deepwater circulation patterns similar to today's operated as early as 9.8 Ma, but were masked by the lower nutrient/δ13C differences. During the late Miocene, “interglacial” intervals prevailed during intervals of NCW production, while “glacial” intervals occurred during low NCW production.
A summary of subsurface hydrological and hydrochemical models
Authors: Mangold Donald C. , Tsang Chin‐Fu
Published: February 2008

Numerical simulation in space and time is an established method in fluid flow and solute transport studies. Similarly, the modeling of equilibrium chemistry of aqueous systems has been well developed. Coupling hydrologic transport models and aqueous chemical models is being actively pursued by a number of research groups. To provide a review for researchers as well as field practitioners who may need to select and use models of varying degrees of complexity, summaries of 56 major numerical codes are made in comparative tables with selected references for three broad classes of codes: hydrologic transport models, geochemical models, and hydrochemical models that combine the chemical and transport models. Criteria for code selection and explanations as to how their characteristics were compiled are described. The governing equations for hydrologic flow, solute transport, and chemical relations are briefly described and discussed in light of the assumptions made by the different codes that employ them. Limitations of current modeling conceptualization and practice and areas of present active research effort are noted. Some comments are also given on model validation, a topic of current concern for modeling. Experience in model applications for each code and available information regarding its verification and validation are given in the appendix.
Hotspots, mantle plumes, flood basalts, and true polar wander
Authors: Duncan R. A. , Richards M. A.
Published: February 2008

Persistent, long‐lived, stationary sites of excessive mantle melting are called hotspots. Hotspots leave volcanic trails on lithospheric plates passing across them. The global constellation of fixed hotspots thus forms a convenient frame of reference for plate motions, through the orientations and age distributions of volcanic trails left by these melting anomalies. Hotspots appear to be maintained by whole‐mantle convection, in the form of upward flow through narrow plumes. Evidence suggests that plumes are deflected little by horizontal flow of the upper mantle. Mantle plumes are largely thermal features and arise from a thermal boundary layer, most likely the mantle layer just above the core‐mantle boundary. Experiments and theory show that gravitational instability drives flow, beginning with the formation of diapirs. Such a diapir will grow as it rises, fed by flow through the trailing conduit and entrainment of surrounding mantle. The structure thus develops a large, spherical plume head and a long, narrow tail. On arrival at the base of the lithosphere the plume head flattens and melts by decompression, producing enormous quantities of magma which erupt in a short period. These are flood basalt events that have occurred on continents and in ocean basins and that signal the beginning of major hotspot tracks. The plume‐supported hotspot reference frame is fixed in the steady state convective flow of the mantle and is independent of the core‐generated (axial dipole) paleomagnetic reference frame. Comparison of plate motions measured in the two frames reveals small but systematic differences that indicate whole‐mantle motion relative to the Earth's spin axis. This is termed true polar wander and has amounted to some 12° since early Tertiary time. The direction and magnitude of true polar wander have varied sporadically through the Mesozoic, probably in response to major changes in plate motions (particularly subduction zone location) that change the planet's moments of inertia.
Thermal evolution of the Sierra Nevada: Tectonic implications of new heat flow data
Authors: Saltus Richard W. , Lachenbruch Arthur H.
Published: February 2008

Eight new heat flow measurements in the southern Sierra Nevada constrain models of thermal evolution and lithospheric structure. Low reduced heat flows (18 to 21 mW/m²) in the southwest Sierra Nevada are consistent with previous results from the northwestern and central Sierra Nevada and extend the known region of linear heat flow‐heat production correlation an additional 150 km to the south. Isostatic residual gravity and measured rock densities are also linearly correlated in the central Sierra Nevada, suggesting a general association between the upper crustal distribution of density and heat production. The linear residual gravity‐density relation implies that isostatic residual gravity anomalies have upper crustal sources and therefore is evidence against a flexural model of Cenozoic Sierra Nevada uplift. New reduced heat flows measured in the southeast Sierra Nevada are relatively high (32 to 57 mW/m²) and correlate spatially with a region of high seismicity that includes extensional earthquake swarms; this correlation supports the view that Basin and Range extensional tectonics and associated magmatic processes are encroaching on the eastern Sierra Nevada. In the stable southwest Sierra Nevada, as in the central and northwestern Sierra Nevada, the persistence of low reduced heat flow at the surface is consistent with a thermal origin for the Cenozoic uplift of the Sierra Nevada, provided the conductive lithosphere is at least 60 to 90 km thick. Simple order‐of‐magnitude calculations show that thermal uplift models combining mechanisms such as advective warming and thinning of the mantle lithosphere, advection of basaltic magma and heat into the crust, simple thermal expansion, and eclogite‐to‐basalt phase conversion can account for the timing and amount of Cenozoic Sierra Nevada uplift. Thermal models do not need the assumptions of unusual lithospheric strength and crustal buoyancy required by mechanical models for Cenozoic uplift driven by a Mesozoic crustal root.
Location of the Martian bow shock measurements by the plasma wave system on Phobos 2
Authors: Trotignon Jean Gabriel , Grard Réjean , Klimov Stanislas
Published: February 2008

During the early months of 1989, the Plasma Wave System, PWS, onboard the Soviet spacecraft Phobos‐2 made plasma and electric‐field spectrum measurements near the Martian bow shock. A total of 26 shock boundaries were unambiguously identified in the PWS data coming from the high‐resolution mode. The location of these boundaries was modeled and the results compared with other studies. Despite the limited coverage of the Phobos‐2 observations, the previous shock‐surface models and ours show a relatively good agreement.
Solute transport in fracture channel and parallel plate models
Authors: Berkowitz Brian , Braester Carol
Published: February 2008

Many studies of flow and solute transport in fractured rocks are based on a conceptual model whereby flow occurs between parallel plates which approximate the fracture walls. Recently, it has been observed that this representation is not consistent with actual fractures. Real fractures are actually composed of a complex system of void spaces of varying aperture, and contact areas which are closed to flow. In such fractures, flow takes place through a network of channels and dead‐end regions. The present investigation analyzes and compares the behavior of solute breakthrough curves in these channels and parallel plate representations. Numerical experinents show that breakthrough curves obtained with channel models are characterized by a long tail and jumps in the solute concentration, consistent with those observed experimentally. It is concluded that the considered channel models provide a sound explanation for the behavior of real breakthrough curves, which cannot be reproduced by parallel plate models.
Giotto's Mission to planet Earth
Authors: Glassmeier K.‐H. , Neubauer F. M. , Brach G. , Marschall H. , Acuña M. H. , Burlaga L. F. , Mariani F. , Musmann G. , Ness N. F. , Wallis M. K. , Ungstrup E. , Schmidt H. U.
Published: February 2008

After its successful encounter with comet P/Halley and a four‐years hibernation period ESA's Giotto spacecraft has been reactivated in February 1990 and performed the first‐ever Earth gravity‐assisted maneuver on July 2, 1990 to be retargeted for comet P/Grigg‐Skjellerup. This swing‐by is of unique scientific interest due to Giotto's hyperbolic, high‐inclination orbit. Here, we shall report on scientific results of the Giotto magnetic field experiment. Due to the high fly‐by velocity and the relative quietness of the magnetosphere during the swingby period these measurements present a snapshot view of the Earth magnetosphere with clearly identified inbound and outbound bow shock and magnetopause crossings. The outbound crossings are of particular interest as surface waves at the polar magnetopause at a distance of 28 RE as well as a strong quasi‐perpendicular bow shock at a distance of about 64 RE are observed
Dynamics of the equatorial mesosphere: First results with a new generation partial reflection radar
Authors: Vincent R. A. , Lesicar D.
Published: February 2008

The first observations of mesospheric winds made between January–August 1990 with an MF partial reflection radar located on Christmas Island (2°N, 157°W) in the central Pacific are described. The mean zonal winds are in general westward, but show clear evidence for a wave‐driven circulation. Power spectral studies indicate that waves are present over a wide range of periods. Ultra‐fast Kelvin waves are especially evident in January–March, with peak amplitudes ∼20 ms−1, and intrinsic phase speeds of ∼150 ms−1 indicated. The Kelvin waves are estimated to contribute an eastward acceleration of up to 10 ms−1 day−1. Gravity wave amplitudes are also found to be almost as large as those observed at mid‐latitude sites, which suggests that convection is a major source of gravity wave activity.
The Earth as an Antineutrino star
Authors: Kobayashi Masao , Fukao Yoshio
Published: February 2008

Antineutrinos are emitted in the Earth upon β decays of radioactive elements and reach the surface with little interaction with terrestrial materials. These antineutrinos are anticipated to carry unique information about the chemistry and energetics of the Earth. We make a systematic search for the candidate target materials that undergo nuclear reactions with incoming antineutrinos and therefore that could be used as an antineutrino detector. The target nuclides most preferable for the measurement are 3He and 1H. For 3He we suggest a liquid 3He scintillation counter, of which practicability depends on the feasibility of amassing at least 10 ton of 3He. For 1H we may design a H2O or liquid H2 scintillation counter with an appropriate activator, which should be capable of detecting scintillation light in a huge tank containing at least 104 ton of H2O or 103 ton of H2.
Magnetic properties of deuteric hematite in young lava flows from Iceland
Authors: Li Huiling , Beske‐Diehl S. J.
Published: February 2008

Seventy samples from six unaltered lava flows from Iceland allow study of magnetic properties of deuteric hematite. Our data indicate that the directions of the titanohematite and titanomagnetite components are identical for all samples for which both components could be determined. This result verifies the assumption that the direction of hematite due to deuteric oxidation should parallel that of titanomagnetite because magnetization occurs at the same time. The unblocking temperatures of titanohematite are between 610°–650°C and are consistent with its composition (0.027<×< 0.032). The titanohematite intensity and the ratio of the titanohematite intensity to that of titanomagnetite increase with deuteric oxidation.
Structure of young upper crust at the East Pacific Rise near 9°30'N
Authors: Christeson G. L. , Purdy G. M. , Fryer G. J.
Published: February 2008

Eight on‐bottom seismic refraction experiments are analyzed in an effort to resolve the structure of the emplacement zone of lavas and dikes at the fast‐spreading East Pacific Rise. The results suggest that the volcanic section doubles in thickness within ∼1 km of the axial summit caldera (ASC) due to the emplacement of lava that either overflows the ASC or is transported through lateral tube conduits, and the depth to the top of the sheeted dike complex increases from ∼160 m within the ASC to ∼340 m a kilometer away on the flank.
Infrared reflectance spectra (2.2–15 μm) of plagioclase feldspars
Authors: Nash Douglas B. , Salisbury John W.
Published: February 2008

Laboratory results show that (1) the Christiansen frequency (CF) feature in mid‐infrared reflectance spectra of powders can be used to accurately distinguish plagioclase composition, and (2) the wavelength position of the CF is not affected by vitrification of the plagioclase. Although the CF position does not distinguish glass from crystalline forms of plagioclase, other features (combination‐tone, overtone, restrahlen bands) in the mid‐IR spectra of plagioclase can be used for that purpose. These results have important implications for application of thermal emission spectroscopy to mapping the surface composition of regolith‐covered planetary bodies like the Moon, Mars, and asteroids.
Pitch angle scattering of cometary ions into monospherical and bispherical distributions
Authors: Miller Ronald H. , Gary S. Peter , Winske Dan , Gombosi Tamas I.
Published: February 2008

Low frequency magnetic fluctuations generated by solar wind/cometary ion distributions cause pitch‐angle scattering of cometary ions. The nature of this pitch angle scattering is examined by means of one‐dimensional hybrid simulations, in which newborn ions are created at a constant rate, and for various injection angles, α, relative to the magnetic field. Pitch angle scattering in the quasi‐perpendicular regime (α > 60°) results in a bispherical velocity distribution while in the quasi‐parallel regime (0 ≤ α ≤ 60°), pitch angle scattering can result in either a mono or bispherical distribution depending on the injection angle and initial beam velocity.
Wrinkle ridges in Lunae Planum Mars: Implications for shortening and strain
Authors: Plescia J. B.
Published: February 2008

Photoclinometric data for Lunae Planum wrinkle ridges indicate average relief of ∼130 m and distinct elevation discontinuities across the ridge of 55 m. Modelling ridges as the result of thrust faulting and associated upper‐plate folding indicates shortening across individual ridges of ∼131 m (90% faulting). Total shortening at 20°N across Lunae Planum is ∼1840 m corresponding to a regional compressive strain of 0.29%. Strain appears uniform across Lunae Planum, although it is accommodated by larger and fewer structures in the west than in the east.
Spatial patterns of oxygen isotope exchange during one‐dimensional fluid infiltration
Authors: Bowman John R. , Willett Sean D.
Published: February 2008

Solutions of one‐dimensional transport equations indicate that the time‐space evolution of oxygen isotope exchange between rock and infiltrating fluid is dependent on 1)the rate of fluid infiltration, 2)the dispersive properties of the rock matrix, 3)the rate of isotopic exchange, and 4)the mass oxygen ratio. The geometry of isotopic exchange fronts developed in a rock sequence depends on the interplay between these first three parameters. The change in isotopic ratio in a rock depends on its position in the flowpath and the rate of isotopic exchange with the fluid in addition to the cumulative fluid flux. Thus conventional water/rock (W/R) ratios will also depend on position in flow paths. Absence of significant 18O depletions in rock sequences does not require low W/R ratios, but may only mean that the rock is in a rock‐dominated segment of a flowpath or alternatively that fluid infiltration was characterized by nonequilibrium exchange.