bluuebunny/crossref_metadata_2025 huggingface dataset:
Megaregolith insulation and the duration of cooling to isotopic closure within differentiated asteroids and the Moon
Authors: Warren Paul H. , Haack Henning , Rasmussen Kaare L.
Published: February 2008

Ages determined for extraterrestrial samples by the Sm‐Nd and Rb‐Sr techniques are commonly assumed to record igneous crystallization events, because in solid silicates, Nd and Sr diffuse at exceedingly slow rates. However, we find that for coarse‐grained igneous cumulate rocks from the Moon or from a large, thoroughly brecciated asteroid, this assumption may not be reliable. The Moon and at least one asteroid (the parent body of the eucrite, diogenite, and howardite meteorites) appear to have been largely molten at or about the time they formed. We have modeled global cooling of the Moon and large (R = 40–250 km) asteroids, starting at or near the solidus. A crucial factor in determining the prevailing interval (Ic) of cooling between igenous crystallization and isotopic closure, for any given depth in the crust, is the extent to which the body is insulated by a regolith/megaregolith layer of porous, fragmental impact debris. Given plausible assumptions regarding the thicknesses of such layers on the Moon and the eucrite parent asteroid (and regarding the radius of the eucrite asteroid), our results indicate that deep‐crustal regions tend to remain above the Nd and Sr isotopic closure temperature for intervals that are long in comparison to the precision of modern Nd‐ and Sr‐based age measurements, and in comparison to suggested chronologic scenarios of global differentiation. Ic intervals of as long as 100 m.y. may be common among available samples of primordial, deep‐crustal cumulates from both bodies. Chronologies for the gross solidification of the Moon and the eucrite asteroid should allow for the possibility that any single age for a coarse‐grained “plutonic” or cumulate‐textured rock might be many tens of millions of years younger than the igneous crystallization age.
Zonal structure of Cenozoic basalts related to mantle upwelling in southwest Japan
Authors: Iwamori Hikaru
Published: February 2008

Cenozoic olivine‐bearing basaltic rocks in the central Chugoku district form eight provinces, each 20 to 30 km in diameter. These provinces can be grouped into three zones almost parallel to the elongation of the SW Japan arc, based on geological and petrological characteristics. The San‐yo zone (the closest to the Nankai trough) is characterized by a small amount of alkaline basalt. In the Sekiryo zone (intermediate zone), transitional basalt is dominant. The San‐in zone along the Japan Sea coast is characterized by subalkaline basalt and a large amount of andesitic rocks. The eruption volume of these volcanics exponentially increases toward the back arc side (less than 1 km3 to more than 100 km3). Chemical compositions of relatively undifferentiated basalts show systematic across‐arc variations. SiO2 and Al2O3increase, and FeO*, MgO and CaO decrease toward the back arc side (44 to 54, 13 to 18, 11 to 6, 13 to 7 and 12 to 8 wt % at FeO*/MgO=0.85, respectively). Melting experiments on the basalt‐H2O‐CO2 systems show that the pressure and temperature of magma segregation decrease toward the back arc side (17–19 kbar and 1340°–1320°C to 8 kbar and 1250°C), and the coexisting phases change from a spinel lherzolite assemblage to a harzburgite assemblage. These PT conditions define a trend which can be interpreted as a PT path for adiabatic upwelling of the mantle material. Consequently, the observed volcanism and zonation may have been caused by upwelling of a plume from a deep part of the mantle.
Paleomagnetic evidence for the age and extent of Middle Tertiary counterclockwise rotation, Dixie Valley Region, west central Nevada
Authors: Hudson Mark R. , Geissman John W.
Published: February 2008

Paleomagnetic data obtained from Oligocene to lower Miocene igneous rocks and middle Miocene basaltic rocks at fifteen localities from a region surrounding Dixie Valley in west central Nevada indicate that parts of the area experienced counterclockwise vertical‐axis rotation, and these data provide constraints on the extent and timing of rotation. Counterclockwise vertical‐axis rotation probably exceeding 30° is indicated for Oligocene to lower Miocene rocks in the central part of the study area. Calculated rotations increase with increasing age of the Oligocene to lower Miocene rocks, indicating that vertical‐axis rotation was concurrent with ash‐flow deposition (about 23–33 Ma). Paleomagnetic data indicate that middle Miocene basaltic rocks (about 10–17 Ma) postdate significant counterclockwise vertical‐axis rotation, although this interpretation is complicated because the rocks were erupted episodically in pulses that apparently were short lived with respect to geomagnetic secular variation. Counterclockwise rotation was related to a deformation event that predated development of the present basin and range physiography of the area. The total amount of crustal rotation in Tertiary time in the area is poorly known. Rotation estimates calculated from time‐averaged mean directions that incorporate data from a broad range of the Oligocene to lower Miocene units probably underestimate total Tertiary rotation because the mean directions include data from units that postdate much of the rotation. For example, a rotation estimate for a composite sequence from the central part of the study area is −23° ± 15°, whereas estimates from older and younger halves of the sequence are −37° ± 21° and −11° ± 16°, respectively. Paleomagnetic data indicate that Oligocene to lower Miocene rocks at some localities in the northern and southern parts of the study area (e.g., the Golconda Canyon locality) probably did not experience significant Tertiary counterclockwise rotation. Although the paleomagnetic data alone are insufficient to fully define the geographic area subjected to Tertiary counterclockwise rotation, the data suggest that a discrete subregion was affected rather than the entire Basin and Range province.
Modeling sea level changes as the Atlantic replaces the Pacific: Submergent versus emergent observers
Authors: Dockal James A. , Worsley Thomas R.
Published: February 2008

We evaluate the sea level changes caused by changing the age/area relationship of the seafloor by altering the thermal structure and hence the elevation of the world seafloor. We do this by having a passive‐margined (and therefore continuously aging) “Atlantic‐type” ocean open at a uniform rate at the expense of an active‐margined (and therefore constant age) “Pacific‐type” ocean. This run of the model was specifically constructed to answer the question of how much sea level would change if the Atlantic opened at a uniform rate. Therefore it specifically excludes the other major processes that change sea level. These would include changes in ice volume, other changes in plate generation/consumption rates, continental orogeny and epeirogeny, lithospheric stretching, lithospheric flexure, and thermally induced subsidence at passive margins and amplification thereof caused by water and sediment loading. The isostatic effects of continental flooding and oceanic unloading are accommodated by application of balanced global isostasy to an Earth model consisting of 121 independent columns. The lithospheric portions of the columns are linked to the hypsographic curve. Sea level changes are viewed from two different observational positions: (1) geologically stable and continually emerged continental plateau and (2) geologically stable and continually submerged shelf break. The modeled sea level that results from changing the age/area relationship of the seafloor since 160 Ma peaks at ∼85 Ma and is ∼30% less for the emerged observer (34 m) than for the submerged observer (48 m). Furthermore, the peak is in phase with, but only ∼1/4; (48 m versus 200+ m) of that portrayed by either the “eustatic” curves inferred from seismic stratigraphy or the isostatically readjusted positions of marine strandlines of the stable platform of North America. We therefore conclude that the other 3/4 of sea level rise that accompanies the opening of the Atlantic must be partitioned among the other causes suggested above.
Tessera Terrain, Venus: Characterization and models for origin and evolution
Authors: Bindschadler Duane L. , Head James W.
Published: February 2008

Tessera terrain is the dominant tectonic landform in the northern high latitudes of Venus mapped by the Venera 15 and 16 orbiters and is concentrated in the region between the mountain ranges of western Ishtar Terra and Aphrodite Terra. Tesserae are characterized by regionally high topography, a high degree of small scale surface roughness, and sets of intersecting tectonic features. Available Pioneer Venus line of sight gravity data suggest that tessera terrain is compensated at shallow depths relative to many topographic highs on Venus and may be supported by crustal thickness variations. Three types of tessera terrain can be defined on the basis of structural patterns: subparallel ridged terrain (Tsr), trough and ridge terrain (Ttr) and disrupted terrain (Tds). Observed characteristics of tessera terrain are compared to predictions of models in order to begin to address the question of its origin and evolution. Formational models, in which high topography is created along with surface deformation, include (1) horizontal convergence, (2) mantle upwelling, (3) crustal underplating, and (4) a seafloor spreading analogy. Modificational models, in which deformation occurs as a response to the presence of elevated regions, consist of (1) gravity sliding and (2) gravitational relaxation. We find that horizontal convergence and late stage gravitational relaxation are the most consistent with basic observations for subparallel ridged terrain and disrupted terrain. Understanding of the basic structural characteristics of trough and ridge terrain is more tentative, and models involving a spreading process or convergence and relaxation merit further study.
Kuroshio path variation south of Japan: 1. Barotropic inflow‐outflow model
Authors: Akitomo Kazunori , Awaji Toshiyuki , Imasato Norihisa
Published: February 2008

We examined the dynamics of the variation in the path of the Kuroshio current along the south coast of Japan by use of a barotropic inflow‐outflow ocean model. The model basin has an inclined coastline and includes a part of the East China Sea so that we could investigate the effect of Kyushu on the Kuroshio. We obtained three regimes of the Kuroshio's path variation according to the magnitude of its inlet velocity Vmax, similar to the previous study. The Kuroshio takes a straight path along the south coast of Japan in regime I with a low Vmax, a meandering path in regime II with a high Vmax, and both of these paths (multiple‐equilibrium state) in regime III with an intermediate Vmax. The transition from the straight state to the meandering state occurs with an increase in Vmax from regime I (III) to II, preceded by an eastward progression of a small meander which is produced as a separated vortex by the nonlinear effect of the flow and the effect of Kyushu. It takes 120 days, consistent with observations. The nonlinearity of the flow has two effects in the transition. One causes a downstream shift of the small meander, and the other enlarges it by pulling out positive vorticity from the no‐slip coast. With an increase in the meander scale due to the latter effect, the former effect becomes small to be balanced with the beta effect, causing an upstream shift of the meander. Thus a large‐meander path is formed. A small meander does not progress eastward to develop into a large meander until Vmax exceeds a critical value. This behavior causes a multiple‐equilibrium state in Regime III and only the meandering path in Regime II.
A numerical investigation of jets and eddies near an eastern ocean boundary
Authors: McCreary Julian P. , Fukamachi Yasushi , Kundu Pijush K.
Published: February 2008

The dynamics of the circulation near an eastern‐ocean boundary are investigated using a 2½‐layer numerical model that includes entrainment of cool water into the upper layer. Solutions are found in a regional ocean basin and are forced by an upwelling‐favorable, alongshore wind field without curl. Dynamically simpler versions of the model are also utilized in order to isolate the effects of various physical processes; in particular, a linearized instability model is used to study the unstable waves associated with various background coastal circulations. The model is quite successful in simulating many features of the observed flow and SST fields. Initially, the “main run” solution spins up as in a linear model, generating a surface jet, an undercurrent, and an upwelling front. Subsequently, small‐scale, “fingerlike” disturbances appear along the coast and grow rapidly in amplitude and scale. The growth in scale has two causes: the slower development of larger‐scale disturbances, and eddy coalescence via nonlinear interactions. Eventually, the solution adjusts to a realistic equilibrium state that contains upwelling filaments, squirts, eddies, dipole eddy pairs, and a realistic mean circulation. Entrainment is a crucial process in the dynamics of the mean flow. In particular, entrainment damps the westward propagation of Rossby waves, thereby ensuring that the currents remain coastally trapped. (In this aspect entrainment plays a dynamical role similar to vertical mixing in continuously stratified models.) Eddies influence the mean flow primarily by providing a strong heat source near the coast, but they have very little effect on the mean momentum field. The small‐scale, fingerlike disturbances are caused by a frontal instability that requires the existence of an upper‐layer temperature gradient. Some dynamically simpler solutions indicate that the larger‐scale disturbances are caused by baroclinic instability. On the other hand, unstable‐wave solutions to the linearized instability model suggest that their cause is frontal instability, becoming pure baroclinic instability only when there is no temperature gradient.
The detection of coastal‐trapped waves
Authors: Haines John W. , Thompson Keith R. , Wiens Doug P.
Published: February 2008

We outline a simple method for estimating the cross‐spectral matrix of coastal‐trapped wave amplitudes, A, from a set of oceanographic observations. Specifically, we propose that A may be estimated by (M′M)−1M′ÛM(M′M)−1 where a prime denotes conjugate transpose, Û is the sample cross‐spectral matrix of observations and M is a matrix which has the spatial form of the waves for columns. In general, M will be complex and frequency‐dependent. We discuss the bias of this estimator and show how to estimate the variance of the power and cross spectra of wave amplitudes. We also outline an ad hoc scheme for assessing the predictive skill of the coastal trapped wave representation and finally give some advice on how to interpret Â. Although the method is presented in the context of shelf circulation and coastal trapped waves, it may be applied to any linear system where the spatial forms of the waves are known and the cross‐spectral matrix of their amplitudes is required.
Angular momenta of modeled ocean gyres
Authors: Holloway Greg , Rhines Peter
Published: February 2008

Total angular momentum of fluid within an ocean basin consists of a part due to center of mass of the fluid rotating about Earth's axis and a part due to relative motion within the basin. In rotating planar geometry (ƒ plane) the relative angular momentum due to motion within a basin can be expressed as an integral of mass transport stream function. This simple relationship is used to examine the consistency of free‐slip “sidewall” boundary conditions applied to a homogeneous ocean model with viscous interior. One finds that the fluid exchanges angular momentum with the basin by means of the normal component of viscous stress, so that a closed angular momentum budget is recovered despite the use of free‐slip boundary conditions. Cases of flow in an enclosed rectangular basin and in an open (infinite) channel are considered. Resolution of budget questions for these idealized cases opens a question concerning real ocean gyres: How is wind‐supplied angular momentum disposed?
A two‐layer wind‐driven coastal circulation model
Authors: Poon Ying‐Keung , Madsen Ole Secher
Published: February 2008

A simple two‐layer water circulation model is developed for the application in homogeneous coastal regions. The objective is to develop a two‐layer model with a relatively thin upper layer that can respond better than a depth‐averaged model to a changing wind field, hence give better predictions of the near‐surface velocity. The governing equations for each water layer are derived from depth averaging of the Navier‐Stokes equations. Coupling between the upper and lower water layers is through the mass and momentum transfer at the interface. To obtain the stress‐transfer function at the interface, the problem of wind‐driven circulations in finite water depth is solved with a bilinear eddy viscosity model that assumes the vertical eddy viscosity to increase linearly with the distance from both the water surface and the bottom boundary. It is found that the stresses at the interface, τi, can be related to the mean flows, above and below the interface, V1 and V2, by a simple constitutive law, τi = 0.18 ρ u*s (V1 ‐ V2) where ρ is the water density and u*s is the shear velocity at the water surface. Comparisons of the two‐layer circulation model with commonly used depth‐averaged models for the prediction of coastal circulation reveal that the use of the two‐layer model gives more realistic predictions of the water motion. As an example, the upper water layer of the two‐layer model is coupled with that of an ice circulation model and it is found that the coupled ice‐water circulation model gives accurate predictions of ice floe movements obtained from field measurements.
A coupled model representing the deep‐sea organic carbon mineralization and oxygen consumption in surficial sediments
Authors: Rabouille C. , Gaillard J.‐F.
Published: February 2008

A model based on transport reaction equations has been developed, introducing a new bacterial kinetic term for the oxidation of organic matter by oxygen. This formulation is known as the Monod rate law. As it depends on both the oxygen and the organic carbon concentrations, it allows in a single model the representation of sediments undergoing totally oxic or oxic plus suboxic diagenesis. It results, however, in a system of coupled nonlinear second‐order ordinary differential equations. As the common numerical solutions to such systems are not straightforward, it has infrequently been used in diagenetic modeling. By applying a numerical iterative method which utilizes the previous computation step to solve nonlinearity, the numerical instabilities of the usual methods were avoided. In order to illustrate the wide application field of this model to various diagenetic situations, verifications and sensitivity studies were performed. Rather large variations in bioturbation coefficients and kinetic constants led to small changes in the distribution of oxygen and organic carbon. On the other hand, small variations in the organic carbon rain rate or bottom water oxygen concentrations resulted in large changes in the calculated depth of the oxic‐suboxic boundary. In contrast, the effect of varying sedimentation rate was negligible. Organic carbon preservation was very sensitive to sedimentation rate, the flux of organic carbon, and the bottom water concentration of oxygen. This emphasizes the importance of these three parameters and the key role of their precise determination for the quantification of the organic carbon recycling in the sediments. The effect of near‐surface compaction was also estimated in order to assess the influence of physical processes on the early diagenesis of organic carbon and oxygen. The inclusion of this compaction produced a maximum departure of 30% in the oxygen penetration depth and may multiply the carbon preservation by almost a factor of 2 in certain cases. Finally, the effect of varying the kinetics as a function of burial was predicted. It showed that organic carbon might be preserved under oxic diagenetic conditions when an appropriate rate of organic carbon is reached. This addresses the question of the formation and the preservation of refractory carbon in sediments, but more experimental work needs to be done in order to confirm or disprove this hypothesis.
Radium isotopes in the lower Mississippi River
Authors: Kraemer T. F. , Curwick P. B.
Published: February 2008

Radium isotopes have been measured in Mississippi River water at several locations between St. Francisville and Venice, Louisiana. Measured activities averaged 11.1 dpm/100 L (disintegrations per minute per 100 L) for dissolved 226Ra with a 228Ra/226Ra activity ratio of 1.04 and a 224Ra/228Ra activity ratio of 1.06 for the section of river above a phosphogypsum waste‐discharge input. Down river from this site, the dissolved 226Ra activity averaged 22.4 dpm/100 L with a 228Ra/226Ra activity ratio of 0.55 and a 224Ra/228Ra activity ratio of 0.87. Chemical and isotopic reequilibration of the radium in the waste with that in the river water and suspended sediments occurs very rapidly. Fluxes of 226Ra are calculated to be 2.44×1014 dpm/yr (disintegrations per minute per year) for the main stem of the Mississippi during phosphogypsum disposal compared to 0.98×1014 dpm/yr when no phosphogypsum disposal is occurring. 28Ra flux is calculated to be 1.06×1014 dpm/yr during disposal and 1.01×1014 dpm/yr in the absence of disposal. The radium flux is estimated to be 45% in the dissolved state and 55% in the adsorbed state.
Reconstruction of oceanic microstructure by tomography: A numerical feasibility study
Authors: Rouseff Daniel , Winters Kraig B. , Ewart Terry E.
Published: February 2008

We consider the feasibility of using small‐scale acoustic tomography to reconstruct oceanic microstructure. In contrast to alternate measurement techniques, acoustic tomography can produce quantitative, fully three‐dimensional images. Tomography uses acoustic data measured by probing the medium from several different directions. To test the proposed approach, numerical realizations typical of anisotropic microstructure are first simulated and then reconstructed by tomography. Two specific forms are evaluated: conventional computed tomography that uses only travel time delay data, and diffraction tomography that requires coherent field measurements. Conventional tomography is shown to produce high‐quality cross‐sectional images. The effects of reducing the number of views are studied, and error maps are generated. Issues in experimental implementation are considered. This study can serve as a guide to the design of an experimental device.
Nutrient transport and mixing in the Gulf Stream
Authors: Pelegrí J. L. , Csanady G. T.
Published: February 2008

The distribution of nutrient flux (geostrophic velocity times concentration) in five sections across the Gulf Stream‐North Atlantic Current (from the Florida Straits to 35°W) is characterized by an intense core, centered at the depth of the 26.8 σt isopycnal surface (typically 500 m). This “nutrient stream” carries nutrient transports of the order of 103 kmol s−1 of nitrate and proportional amounts of other nutrients. Between the Florida Straits and the Mid‐Atlantic Bight, water transport doubles, but nutrient transport trebles, because along‐isopycnal inflow from the subtropical gyre is concentrated in the layers of the upper thermocline, which are rich in nutrients. Beyond the Mid‐Atlantic Bight, both water and nutrient transports decline slowly. Water mass and nutrient balances of nine isopycnal layers reveal significant upward entrainment and mixing of thermocline waters in the sector of the stream between the Florida Straits and the Mid‐Atlantic Bight. A two‐box model of the nutrient‐depleted surface layers (σt < 26.8) and the nutrient‐rich thermocline layers (26.8 < σt < 27.5) shows an upward entrainment rate of about 1.6 m2 s−1 per unit length of the stream, or a diapycnal velocity of 2×10−5 m s−1 over the 80‐km width of the stream. In addition, there is two‐way diapycnal mass exchange at approximately the same rate. The rate of inflow from the surface layers of the Sargasso Sea is about 12×106 m3 s−1, from the thermocline layers 15×106 m3 s−1.
Observation of wave refraction at an ice edge by synthetic aperture radar
Authors: Liu Antony K. , Vachon Paris W. , Peng Chih Y.
Published: February 2008

In this note the refraction of waves at the ice edge is studied by using aircraft synthetic aperture radar (SAR). Penetration of a dominant swell from open ocean into the ice cover was observed by SAR during the Labrador Ice Margin Experiment (LIMEX), conducted on the marginal ice zone (MIZ) off the east coast of Newfoundland, Canada, in March 1987. At an ice edge with a large curvature, the dominant swell component disappeared locally in the SAR imagery. Six subscenes of waves in the MIZ from the SAR image have been processed, revealing total reflection, refraction, and energy reduction of the ocean waves by the ice cover. The observed variations of wave spectra from SAR near the ice edge are consistent with the model prediction of wave refraction at the ice edge due to the change of wave dispersion relation in ice developed by Liu and Mollo‐Christensen (1988).
The intercomparison of radiation codes used in climate models: Long wave results
Authors: Ellingson Robert G. , Ellis James , Fels Stephen
Published: February 2008

An international program of intercomparison of radiation codes used in climate models has been initiated because of the central role of radiative processes in many proposed climate change mechanisms. During the past 6 years, results of calculations from such radiation codes have been compared with each other, with results from the most detailed radiation models (line‐by‐line models) and with observations from within the atmosphere. Line‐by‐line model results tend to agree with each other to within 1%; however, the intercomparison shows a spread of 10–20% in the calculations of radiation budget components by the less detailed climate model codes. The spread among the results is even larger (30–40%) for the sensitivities of the codes to changes in radiatively important variables, such as carbon dioxide and water vapor. The analysis of the model calculations shows that the outliers to many of the clear‐sky calculations appear to be related to those models that have not tested the techniques used to perform the integration over altitude. When those outliers are removed, the agreement between narrow band models and the line‐by‐line models is about ±2% for fluxes at the atmospheric boundaries, about ±5% for the flux divergence for the troposphere, and to about ±5% for the change of the net flux at the tropopause as CO2 doubles. However, this good agreement does not extend to the majority of the models currently used in climate models. The lack of highly accurate flux observations from within the atmosphere has made it necessary to rely on line‐by‐line model results for evaluating model accuracy. As the intercomparison project has proceeded, the number of models agreeing more closely with the line‐by‐line results has increased as the understanding of the various parameterizations has improved and as coding errors have been discovered. The most recent results indicate that several climate model techniques are in the marginal range of (relative) accuracy for longwave flux calculations for many climate programs. However, not all such models will give such accuracy. It is recommended that a code not be accepted to provide such accuracy until it has made comparisons to the line‐by‐line results of this study. The data necessary to make such comparisons are included herein. However, uncertainties in the physics of line wings and in the proper treatment of the water vapor continuum make it impossible for the line‐by‐line models to provide an absolute reference for evaluating less‐detailed model calculations. A dedicated field measurement program is recommended for the purpose of obtaining accurate spectral radiance rather than integrated fluxes as a basis for evaluating model performance.
Approaches to the simulation of regional climate change: A review
Authors: Giorgi Filippo , Mearns Linda O.
Published: February 2008

The increasing demand by the scientific community, policy makers, and the public for realistic projections of possible regional impacts of future climate changes has rendered the issue of regional climate simulation critically important. The problem of projecting regional climate changes can be identified as that of representing effects of atmospheric forcings on two different spatial scales: large‐scale forcings, i.e., forcings which modify the general circulation and determine the sequence of weather events which characterize the climate regime of a given region (for example, greenhouse gas abundance), and mesoscale forcings, i.e., forcings which modify the local circulations, thereby regulating the regional distribution of climatic variables (for example, complex mountainous systems). General circulation models (GCMs) are the main tools available today for climate simulation. However, they are run and will likely be run for the next several years at resolutions which are too coarse to adequately describe mesoscale forcings and yield accurate regional climate detail. This paper presents a review of these approaches. They can be divided in three broad categories: (1) Purely empirical approaches, in which the forcings are not explicitly accounted for, but regional climate scenarios are constructed by using instrumental data records or paleoclimatic analogues; (2) semiempirical approaches, in which GCMs are used to describe the atmospheric response to large‐scale forcings of relevance to climate changes, and empirical techniques account for the effect of mesoscale forcings; and (3) modeling approaches, in which mesoscale forcings are described by increasing the model resolution only over areas of interest. Since they are computationally inexpensive, empirical and semiempirical techniques have been so far more widely used. Their application to regional climate change projection is, however, limited by their own empiricism and by the availability of data sets of adequate quality. More recently, a nested GCM‐limited area model methodology for regional climate simulation has been developed, with encouraging preliminary results. As it is physically, rather than empirically, based, the nested modeling framework has a wide range of applications.
Structural interpretation of the Eastern Sulaiman Foldbelt and Foredeep, Pakistan
Authors: Humayon Mansoor , Lillie Robert J. , Lawrence Robert D.
Published: February 2008

The Sulaiman foldbelt is an active tectonic feature on the northwestern margin of the Indian plate. Seismic reflection data have been combined with surface geological mapping and drill hole data to interpret the structural style and tectonic shortening of the eastern Sulaiman foldbelt and its adjacent foredeep. The data show that the basement is more than 8 km deep near the deformation front and that it deepens towards the west. The foredeep adjacent to the eastern Sulaiman foldbelt is a broad synclinal structure with a steep western limb; the more gentle eastern limb has monoclinal dips from near zero to 2.5°. Several salt‐cored anticlines are observed on the eastern part of the monocline, but the salt structures are lacking in the western foredeep and in the frontal part of the Sulaiman foldbelt. The basal decollement under the Sulaiman lobe lies either in ductile Eocambrian salt or within a deep zone of other material that undergoes ductile behavior. Near the deformation front, ramps from the basal detachment become flats in Lower Triassic and Lower Cretaceous shales. A steep and highly elevated zone immediately to the west of the frontal folds is interpreted to be underlain by a passive‐roof duplex. The culmination wall of this oblique duplex is separated from the overlying roof sequence by a passive‐roof thrust in Lower Cretaceous shales. The roof‐thrust has a backthrust sense of movement, relative to the forelandward propagating duplex, and may extend obliquely 100 km into the interior of the foldbelt. Fault‐propagation and fault‐bend folds are present in the frontal portion of the eastern Sulaiman foldbelt. Palinspastic restoration of a balanced cross section shows 108 km of shortening in the eastern Sulaiman foldbelt, east of the Kingri strike‐slip fault. The presence of more than 11 km of pre‐Neogene strata on top of basement suggests that the Mesozoic rifted margin of the Indian subcontinent may lie beneath the Sulaiman foldbelt. This interpretation is also favored by the presence of ophiolites and flysch deposits overthrusted on Late Cretaceous shelf strata.
Methane transport and oxidation in the unsaturated zone of aSphagnumpeatland
Authors: Fechner Elizabeth J. , Hemond Harold F.
Published: February 2008

Efflux rates and oxidation rates of methane (CH4) were measured in a northernSphagnumbog, Thoreau's Bog in Concord, Massachusetts, by using a gradient methodology which does not change in situ conditions. A remote‐sampling technique was devised to obtain undisturbed CH4profiles as a function of depth in the peat; effective diffusion coefficients in peat were estimated both physically and by using propane as a tracer. By combining these techniques we estimated the average late summer CH44 flux from deep, anaerobic methanogenic sediments to the unsaturated zone to be 3.5 × 10−11mol cm−2s−1(± 1.0 × 10−10mol cm−2s−1), while the CH4flux from this unsaturated zone to the atmosphere was 3.7 × 10−12mol cm−2s−1(± 5.0 × 10−12mol cm−2s−1). Therefore a large fraction of the CH4flux was consumed before it reached the atmosphere. Most CH4consumption, presumably by oxidation, occurred between the water table, located 12 to 15 cm below the bog surface, and about 6 cm below the bog surface. In this region, CH4concentrations and oxidation rates were unevenly distributed, probably following patterns of upward transport of CH4by bubbles via fissures and tubes in the saturated zone. Between the surface of the bog and 6‐cm depth, CH4concentrations were more uniformly distributed, most likely because of greater horizontal mixing in this depth range. Analysis of CH4distributions in unsaturated peat is a straightforward and practical technique to measure both net CH4efflux and CH4oxidation with minimal disturbance to the peat structure and gas exchange conditions.
Minor ion composition in the polar ionosphere
Authors: Yau Andrew W. , Whalen Brian A. , Sagawa Eiichi
Published: February 2008

Ion composition measurements from the EXOSD Suprathermal Ion Mass Spectrometer (SMS) are presented. Ions other than H+, notably O+, He+, O++ N+ and N++, are found to constitute a significant (>0.1) and at times dominant (>0.5) component of the thermal ion population in the high‐altitude polar ionosphere. Their relative abundance and occurrence are highly variable. Ion flux ratios in the range of 0.1–0.5 are typical for 0+/H+, 0.1–0.3 for He+/H+, 0.1–0.3 for 0++/O+, and 0.05–0.1 for N++/N+. Our observations show that (1) ions other than H+, notably He+, O+, O++ and N+, often constitute a significant component (>0.1) of the thermal ion population in the high‐altitude polar ionosphere; (2) doubly charged oxygen and nitrogen (O++ and N++) are sometimes present with fluxes up to 0.1 of the singly‐charged (O+ and N+) ion fluxes; and (3) the He+ and O++ fluxes are sometimes comparable to the H+ and O+ fluxes.
Parameterized rotating convection for core and planetary atmosphere dynamics
Authors: Zhang Keke
Published: February 2008

New types of convective instability and associated nonlinear phenomena in rapidly rotating spherical systems have been discovered through numerical simulations. The Prandtl number, defined as the ratio of the viscous and thermal diffusivities of a fluid, Pr = ν/k, plays a crucial role in determining the fundamental features of both the instabilities and the corresponding nonlinear convection. The results shed new light on regimes of convection in the earth's core and the atmospheres of the major planets.
Thermal diffusivity of MgSiO3 perovskite
Authors: Osako Masahiro , Ito Eiji
Published: February 2008

Thermal diffusivity of MgSiO3 perovskite has been measured in the temperature range of 160 K to 340 K using a sample synthesized in a uniaxial split‐sphere high‐pressure apparatus. At 300 K the thermal diffusivity of perovskite is 1.72 × 10−6 m2s−1, from which the thermal conductivity is evaluated to be 5.1 Wm−1K−1. Our model calculation shows that lattice thermal conductivity of the perovskite increases by a factor of 4 with depth throughout the lower mantle and reaches to 12 Wm−1K−1 in the vicinity of the mantle‐core boundary. The D″ layer might not be a thermal boundary layer insulating the high core‐temperature, if this layer mainly consists of the perovskite.
Zeolite to prehnite‐pumpellyite facies metamorphism in the Toa Baja Drill Hole, Puerto Rico
Authors: Cho Moonsup
Published: February 2008

Secondary mineral assemblages in Eocene volcanic and volcaniclastic rocks of the Toa Baja drill hole progressively change as a function of depth. Four metamorphic zones are delineated with increasing depth: Caclinoptilolite→heulandite→laumontite→prehnite–purnpellyite zone. The deepest belongs to the prehnite‐pumpellyite facies, whereas the three zones at shallower depths (<2350 m) belong to the zeolite facies. Ca‐clinoptilolite and heulandite exhibit continuous solid solution with varying Si/Al (2.9–5.2) and Ca/(Ca+Na+K) ratios (0.45–0.89). Pumpellyites are characterized by extensive variation in the Fe/(Fe+Al+Mg) ratio (0.29–0.74) and extreme Fe‐enrichment in the laumontite zone. Temperatures estimated from mineral assemblages and fades transitions suggest that the North Coast Basin, Puerto Rico, has been subject to a metamorphic field gradient of ∼50 to 70°C/km.
Slip rate, earthquake recurrence, and seismogenic potential of the Rodgers Creek Fault Zone, northern California: Initial results
Authors: Budding Karin E. , Schwartz David P. , Oppenheimer David H.
Published: February 2008

Instrumental seismicity defines a seismic gap along the Rodgers Creek fault zone (RCFZ) between Santa Rosa and San Pablo Bay. Results of a paleoseismicity study within the gap, using offset channels in late Holocene alluvial deposits as piercing points, indicate a minimum slip rate of 2.1 to 5.8 mm/yr for the past 1300 years, a preferred range for the maximum recurrence interval of 248 to 679 years, and a surface offset of 2 +0.3, −0.2 m during the most recent event. The RCFZ has produced past M7 earthquakes, and historical seismicity data indicate a minimum elapsed time of 182 years since the most recent earthquake of this size.
Unusual high‐stress drop subevent during the M5.5 Earthquake, The largest event of the 1989 Ito‐Oki swarm activity
Authors: Fukuyama Eiichi , Kinoshita Shigeo , Yamamizu Fumio
Published: February 2008

On July 13, 1989, the Ito‐oki submarine volcano was created and erupted after an earthquake swarm and volcanic tremor. At the final stage of the swarm activity, on July 9, 1989, a mainshock (M5.5) occurred. This earthquake consisted of two events separated 45 seconds from each other. The second event included high stress drop faulting (asperity). In this paper, the M5.5 earthquake was analyzed focusing on this asperity. The results are that 1) the radius and dynamic stress drop of the asperity were approximately 300m and 50MPa, respectively; 2) the epicenter of the asperity was estimated at 5km west of the erupted volcano and its depth was 6km; and 3) without this strong asperity, the waveforms of the two events were very similar, suggesting a similar source process except for the asperity.
Mechanisms driving groundwater flow near salt domes
Authors: Evans David G. , Nunn Jeffrey A. , Hanor Jeffrey S.
Published: February 2008

Groundwater flow near salt domes is complex because groundwater is subject to a variety of driving forces including the release of geopressured fluids, large lateral density gradients, and regional hydraulic head gradients. The complexity of this environment is born out by recent geochemical and geophysical observations that indicate the occurrence of upward groundwater flow near some salt domes. In order to evaluate the relative importance of different mechanisms driving groundwater flow near salt domes, we have developed a numerical model that couples groundwater flow, heat transport, and transport of dissolved salt, and accounts for salt diapirism. Our calculations indicate that upward groundwater flow can occur as the result of thermal convection when the regional background salinity is greater than 15 weight percent, a value typical of many areas of the south Louisiana salt dome province. For lower background salinities, dissolution causes salt‐laden groundwater near the dome to sink, leading to depressed isotherms. While the release of geopressured fluids is difficult to quantify, it remains a likely mechanism for driving upward groundwater flow near some salt domes.
The timing of caldera collapse at Mount Katmai in response to magma withdrawal toward Novarupta
Authors: Hildreth Wes
Published: February 2008

Several thin layers of nonjuvenile lithic‐rich tephra from Mount Katmai are intercalated with 1912 plinian pumice‐fall deposits that originated at Novarupta 10 km away, demonstrating that caldera collapse at Katmai and eruption at Novarupta were synchronous. Emplaced by phreatic explosions and avalanche‐generated dustclouds, each Katmai‐derived layer is thickest and coarsest at the caldera rim and pinches out within 5–8 km. In contrast, thicknesses and clast sizes of plinian Layers A‐G decrease radially away from Novarupta. The first Katmai‐derived layer lies between Novarupta‐derived Layers B2 and B3, indicating that collapse began after release of ∼6.9 km³ of magma at Novarupta. The first major earthquake (Ms=6.5) at 2356 h on 6 June, ∼11 hours after the eruption began, may have marked the onset of collapse. The Katmai River landslide and several debris‐flow deposits are also sandwiched within the plinian deposits, indicating that they too were emplaced during the eruption.
Dispersion of B‐values in Gutemberg‐Richter Law as a consequence of a proposed fractal nature of continental faulting
Authors: Sornette Didier , Vanneste Christian , Sornette Anne
Published: February 2008

Depending on the area in which the earthquakes are sampled, the exponent b/c of the distribution of seismic moment or energy of earthquakes fluctuates from one region to another in a range typically between 0.5 and 1. To explain this observation, we propose a general mechanism which accounts for fluctuations in the b/c‐value as being related to the variations of the fractal dimension of the set of faults on which the Gutemberg‐Richter law is measured.
A geodetic network in the Novarupta area, Katmai National Park, Alaska
Authors: Kleinman Jack W. , Iwatsubo Eugene Y.
Published: February 2008

A small geodetic network was established in 1989 and 1990 to monitor ground deformation in the Novarupta area, Katmai National Park, Alaska. Slope distances and zenith angles for three lines were repeated in 1990. A comparison of the two surveys indicates changes that are within the error of the measurements. Mean mark‐to‐mark slope distance changes are 1.17±1.46 ppm. Two benchmarks were added to the network in 1990 to configure a five‐endpoint braced quadrilateral centered about the Novarupta dome.
Using the F‐test for eigenvalue decomposition problems to find the statistically ‘optimal’ solution
Authors: Jacobson R. S. , Shaw P. R.
Published: February 2008

A fundamental problem using linear inverse theory to solve geophysical problems using eigenvalue decomposition algorithms is to determine how many eigenvalues to include in the solution. If very small eigenvalues are included, the solution variance increases rapidly, particularly if zero‐values eigenvalues are computed as positive small numbers and are misidentified. F‐tests can be applied to a succession of solutions, each containing an incremental number of eigenvalues, to determine statistical significance of the data variance reduction. This methodology is widely used for multiple variable regression analysis, but has not been applied to eigenvalue problems. The F‐test is a statistical criterion for choosing an ‘optimal’ solution along the trade‐off curve of model resolution and model variance for a particular model parameterization.
Argillic alteration in the Novarupta Vent Region, Katmai National Park, Alaska
Authors: Keith Terry E. C.
Published: February 2008

Secondary mineralogy in the 1912 vent region at Novarupta illustrates an alteration history that evolved from high‐temperature degassing of ejecta through surficial argillic alteration to near‐neutral, wet‐steam alteration as the posteruptive volcanic system cooled. The locallized distribution of surficial argillization appears to have been controlled mainly by fractures related to slumping and compaction in the near‐surface fallback ejecta. The fractures guiding the surviving warm, near‐neutral fumarolic fluids, however, must be connected with deeper vent structures that reach a subsurface heat source, perhaps the boiling zone of a hydrothermal system. Trace metals, including Mo, Pb, Cu, Cd, and Zn, concentrated by high‐temperature, vapor‐phase mobilization, have subsequently been partly removed by argillization processes; in contrast, Hg, Sb, Tl, Bi, and As remain high even though the fumaroles now emit only low‐temperature, near‐neutral wet steam.
Consequences of wave‐particle interactions on chaotic acceleration
Authors: Schriver David , Ashour‐Abdalla Maha
Published: February 2008

The recent model of Ashour‐Abdalla et al., [1991b] has proposed that the Earth's plasma sheet can be formed by chaotic acceleration in a magnetotail‐like field configuration. The ion velocity distributions created by chaotic acceleration have unstable features and represent robust free energy sources for kinetic plasma waves that can modify the original distributions. In the plasma sheet boundary layer, field‐aligned ion beamlets are formed which drive a host of instabilities creating a broadbanded noise spectrum and cause thermal spreading of the beamlets. In addition there is strong heating of any cold background plasma that may be present. In the central plasma sheet, ion anti‐loss cone distributions are created which are unstable to very low frequency waves that saturate by filling the anti‐loss cone.
Gyro‐phase effects near the storm‐time boundary of energetic plasma
Authors: Delcourt D. C. , Moore T. E. , Sauvaud J. A.
Published: February 2008

The non‐adiabatic acceleration of plasma sheet ions during the expansion phase of substorms is examined by means of single‐particle codes. It is shown that, in the near‐Earth plasma sheet, the gyration phase at substorm onset controls the net ion energization, as the gyro‐period is locally comparable to the field variation time scale. This can yield a particularly significant decrease of the particle magnetic moment. It is accordingly argued that, via adiabatic invariant violation, the dipolarization of magnetospheric field lines can induce a “de‐trapping” of inner plasma sheet populations and, hence, give rise to short‐lived precipitation enhancements over the auroral zone. As this effect depends upon cyclotron frequency, it is expected to occur at distinct latitudes for different ion species. This contrasts with non‐adiabatic ion behavior further out into the geotail, which is characterized by intense perpendicular heating and a likely collective trapping.