bluuebunny/crossref_metadata_2025 huggingface dataset:
Resurfacing history of Tempe Terra and surroundings
Authors: Frey Herbert V. , Grant Tammie D.
Published: February 2008

The resurfacing history of the Tempe Terra region is determined using the Neukum and Hiller [1981] technique of breaking cumulative frequency curves into separate branches where the curves depart from a standard production curve. We find four surfaces recorded in the heavily cratered portions of Tempe Terra, with crater retention ages N(1) = [242,100], [95,700], [20,800], and [5500]. This is interpreted to indicate three major resurfacing events occurred in this region, ending at N(1) = [95,700], [20,800], and [5500]. The ridged plains on the Tempe Terra plateau have an oldest recorded surface age of [20,400], identical to that of the second resurfacing event recorded in the heavily cratered areas. A single resurfacing of the ridged plains (which may have been a second episode of ridged plains volcanism) occurred at N(1) = [7800]. The knobby plains to the north west and east of Tempe Terra also show a resurfacing at [20,000] and additional events at [5400] and perhaps [1600]. Mottled plains to the northeast record surfaces with crater retention age [7500], [5000], and [3900], where the first age is determined by a single surviving crater. It appears that the Lunae Planum Age (LPA) (at N(1) = [20,000]) resurfacing event seen elsewhere on Mars was widespread and effective in this region. A second widespread event appears to have ended at N(1) = [5000]. We estimate the thickness of the resurfacing materials corresponding to the LPA event to be less than 90 m in the heavily cratered areas but 300–500 m in the ridged plains themselves. Later resurfacing materials were generally thicker farther north in the mottled plains (300 m) than in the knobby plains (200 m).
Dark materials in Valles Marineris: Indications of the style of volcanism and magmatism on Mars
Authors: Geissler Paul E. , Singer Robert B. , Lucchitta Baerbel K.
Published: February 2008

Rifting on the equatorial canyon system of Valles Marineris provides a unique view of the interior of the Martian crust to depths reaching 7 km, exposing several in situ bedrock units which testify to past volcanic and magmatic processes on Mars. A thick, regionally extensive deposit observed in Coprates and Juventae chasmata is interpreted on the basis of spectral reflectance, erosional morphology, and tendency for eolian mobilization to be composed of mafic glass, possibly an ancient Martian analogue of the lunar terra mantling deposits. Spectral mapping suggests that the dark floor‐covering materials in the lower canyons are derived from this unit. A series of cliffs in the Ophir Chasma wall rock is interpreted to be exposures of resistant bedrock; the spectral signature of this massive and uniform unit most closely resembles that of terrestrial mafic rocks altered to or coated by crystalline hematite. Application of computer mapping techniques to probable young volcanic materials in the central troughs yields an inferred distribution of volcanic activity consistent with the interpretation of extrusion along faults near the margins of the canyon floors. This result supports the hypothesis that the valles originated through tectonic extension.
Thermal emission spectra of Mars (5.4–10.5 μm): Evidence for sulfates, carbonates, and hydrates
Authors: Pollack James B. , Roush Ted , Witteborn Fred , Bregman Jesse , Wooden Diane , Stoker Carol , Toon Owen B. , Rank David , Dalton Brad , Freedman Richard
Published: February 2008

We have obtained spectra of the thermal emission from Mars in the 5.4–10.5 μm wavelength domain at a resolving power of about 60 from the Kuiper Airborne Observatory. Spectra were obtained for several large spots on Mars, whose ground temperatures and air masses through the Martian atmosphere differed significantly. These data were taken at two times during the flight. By taking the ratio of the spectral flux from one spot to that of a second spot, we obtained results that were independent of uncertainties in the instrument's spectral response and the transmission of the Earth's atmosphere. These data, as well as spectral fluxes of single spots based using the star α Tau as a calibration standard, show a number of emission and absorption features. They are present in sets of spectra taken at two different times. Some of the absorption features are due to gaseous CO2 in the Martian atmosphere. The remainder of the absorption and emission features are due to minerals present in the airborne dust and on the surface. Comparison of the strength of features seen at similar times, but with three different air masses and ground temperatures, suggests that the emission features arise primarily from surface emissivity spectral variations and that the absorption features arise from components of the atmosphere. Based on comparisons of the observed features with laboratory data for a broad ensemble of minerals, spectra of other solar system bodies, and relevant compositional information about Mars, we have made the following tentative identifications of the observed features. Emission features at 7.8 and 9.7 μm are attributed to surface silicates; an emission feature at 6.1 μm is attributed to a molecular water component of the surface material; an absorption band at 8.7 μm as well as possibly one at 9.8 μm is ascribed to sulfate or bisulfate anions, probably located in a distorted crystalline site; and an absorption band at 6.7 μm is attributed to carbonate or bicarbonate anions located in a distorted crystalline site, although we cannot totally rule out a nitrate origin for this feature. We have simulated these spectra with radiative transfer programs for the atmosphere and surface. These simulations indicate that the sulfate‐ and carbonate‐bearing minerals are contained in the same particles of the airborne dust as the dominant silicate minerals, that the dust optical depth was about 0.6 at a reference wavelength of 0.3 μm over the area of the observed spots, and that sulfates and carbonates constitute about 10–15% and 1–3% by volume of the airborne dust, respectively. These results imply that minerals formed by weathering processes represent major reservoirs of volatile species on current Mars.
Atmospheric measurements at Mars via gamma ray spectroscopy
Authors: Metzger Albert E. , Haines Eldon L.
Published: February 2008

Three methods are presented for measuring the mass of the Martian atmosphere using an orbiting gamma ray spectrometer. Withsingle‐line attenuation; atmospheric thickness is measured by the extent to which it modulates a line flux emitted from a surface whose composition is both known and uniform to a depth of a meter or more. Direct determination derives atmospheric thickness based on the atmospheric concentration of a particular component. Alternatively, if atmospheric thickness is known, concentration may be determined. Differential attenuation utilizes the ratio of paired emission line fluxes and requires adequate energy contrast and line intensities as well as knowledge of the production mechanism. The sensitivity of these methods as a fraction of the atmospheric thickness is nominally 2–5% over the range of 2.5–30 g/cm2 for accumulation times of 100 hours. This precludes the observation of short‐period phenomena such as diurnal oscillations but permits the tracking of more gradual variations, particularly the basic seasonal cycle on a regional, zonal, hemispheric, or whole planet basis. The three methods may be combined not only to improve the sensitivity with which atmospheric thickness may be measured but also to provide additional information including the presence of carbon in the regolith, the extent of atmospheric fractionation in south polar regions during winter, and the effect of stratification on surface gamma ray emission.
The Greenland Gravitational Constant Experiment
Authors: Zumberge Mark A. , Ander Mark E. , Lautzenhiser Ted V. , Parker Robert L. , Aiken Carlos L. V. , Gorman Michael R. , Nieto Michael Martin , Cooper A. Paul R. , Ferguson John F. , Fisher Elizabeth , Greer James , Hammer Phil , Hansen B. Lyle , McMechan George A. , Sasagawa Glenn S. , Sidles Cyndi , Stevenson J. Mark , Wirtz Jim
Published: February 2008

An Airy‐type geophysical experiment was conducted in a 2‐km‐deep hole in the Greenland ice cap at depths between 213 m and 1673 m to test for possible violations of Newton's inverse square law. The experiment was done at Dye 3, the location of a Distant Early Warning Line radar dome and the site of the deepest of the Greenland Ice‐Sheet Program (GISP) drill holes. Gravity measurements were made at eight depths in 183‐m intervals with a LaCoste&Romberg borehole gravity meter. Prior to the experiment the borehole gravity meter was calibrated with an absolute gravity meter, and the wireline depth‐rinding system used in the borehole logging was calibrated in a vertical mine‐shaft against a laser geodimeter. The density of the ice in the region was calculated from measurements taken from ice cores obtained from earlier drilling observations. Ice penetrating radar was employed in order to correct the gravity data for the topography of the ice‐rock interface. Surface gravity observations were made to assess the extent to which density variations in the sub‐ice rock could affect the vertical gravity gradient. The locations of the gravity observation points were determined with a combination of GPS recording, first‐order leveling, and EDM surveying. An anomalous variation in gravity totaling 3.87 mGal (3.87×10−5 m/s2) in a depth interval of 1460 m was observed. This may be attributed either to a breakdown of Newtonian gravity or to unexpected density variations in the rock below the ice.
Fast instantaneous oceanic plate velocities recorded by the Cretaceous Laytonville limestone: Paleomagnetic analysis and kinematic implications
Authors: Tarduno John A. , McWillams Michael , Sleep Norman
Published: February 2008

New paleomagnetic results from 101–89 Ma Laytonville Limestone of the Franciscan Central Belt mélange of northern California confirm a southern hemisphere origin as first proposed by Alvarez et al. (1980). Discovery and study of new Laytonville Limestone outcrops extend the paleomagnetic record and provide a definitive determination of age, stratigraphic polarity, and hemisphere of deposition. Paleontological determinations show that five sections are presently overturned and four are presently right side up, as expected from a random distribution of nine blocks in a mélange. The exact accretion time is unknown, but geologically reasonable estimates range between 70 and 50 Ma, leading to “averaged” estimates of poleward velocity between 30 and 14 cm/yr. The “averaged” values are obtained by dividing the total paleolatitude shift by the difference between magnetization and estimated accretion ages; they reflect net poleward transport over a long time interval and are minimum estimates because they record only the poleward component of motion. An “instantaneous” poleward velocity is recorded by the systematic inclination decrease of 160 paleomagnetic samples with respect to decreasing age over the 12 m.y. section. Conservative estimates place this minimum velocity at 15 cm/yr. The consistency between the values predicted by the average velocity calculations and those measured within the outcrops serves as an important check on the primary nature of the magnetization. This minimum velocity is much higher than any present‐day plate velocity. The subduction of old oceanic crust at the boundary of a relatively small plate is hypothesised as a driving mechanism to explain the measured velocities. Coupled with the minimum instantaneous poleward velocities, this hypothesis suggests that the velocities of subducting plates may vary up to a factor of 5. Similar plate geometries and resultant velocities have probably existed at other times in the past, but their discovery may have been hindered by low preservation potential.
Decrepitation and crack healing of fluid inclusions in San Carlos olivine
Authors: Wanamaker B. J. , Wong Teng‐Fong , Evans Brian
Published: February 2008

Fluid inclusions break, or decrepitate, when the fluid pressure exceeds the least principal lithostatic stress by a critical amount. After decrepitation, excess fluid pressure is relaxed, resulting in crack arrest; subsequently, crack healing may occur. Existing models of decrepitation do not adequately explain several experimentally observed phenomena. We developed a linear elastic fracture mechanics model to analyze new data on decrepitation and crack arrest in San Carlos olivine, compared the model with previous fluid inclusion investigations, and used it to interpret some natural decrepitation microstructures. The common experimental observation that smaller inclusions may sustain higher internal fluid pressures without decrepitating may be rationalized by assuming that flaws associated with the inclusion scale with the inclusion size. According to the model, the length of the crack formed by decrepitation depends on the lithostatic pressure at the initiation of cracking, the initial sizes of the flaw and the inclusion, and the critical stress intensity factor. Further experiments show that microcracks in San Carlos olivine heal within several days at 1280 to 1400°C; healing rates depend on the crack geometry, temperature, and chemistry of the buffering gas. The regression distance of the crack tip during healing can be related to time through a power law with exponent n = 0.6. Chemical changes which become apparent after extremely long heat‐treatments significantly affect the healing rates. Many of the inclusions in the San Carlos xenoliths stretched, decrepitated, and finally healed during uplift. The crack arrest model indicates that completely healed cracks had an initial fluid pressure of the order of 1 GPa. Using the crack arrest model and the healing kinetics, we estimate the ascent rate of these xenoliths to be between 0.001 and 0.1 m/s.
Phase relations in peridotite+CO2 Systems to 12 GPa: Implications for the origin of kimberlite and carbonate stability in the Earth's upper mantle
Authors: Canil Dante , Scarfe Christopher M.
Published: February 2008

The phase relations of synthetic peridotites in the systems CaO‐MgO‐SiO2‐CO2 (CMS‐CO2), CaO‐MgO‐Al2O3‐SiO2‐CO2 (CMAS‐CO2) and CaO‐MgO‐SiO2‐CO2‐H2O (CMS‐CO2‐H2O) were studied from 4 to 12 GPa using a multi‐anvil apparatus. Peridotite solidi in both the CMS‐CO2 and CMAS‐CO2 systems have similar topologies. Carbonates are the first phases consumed at, or above, the solidus in peridotite+CO2 at pressures above 4 GPa. Magnesite solid‐solutions are stable subsolidus phases in peridotite+CO2 to pressures of at least 12 GPa. It is demonstrated that if uncontaminated, diamond‐bearing kimberlites emplaced in the Earth's crust are primary magmas, then they could be derived by partial melting of carbonated peridotite at 5 to 7 GPa in the upper mantle beneath the cratonic areas of continents. “Proto‐kimberlites” may be generated at pressures above 7 GPa in the upper mantle, but no such magmas are represented on the Earth's surface. Mineral chemical data from experimental run products indicate that: 1) the discrete sub‐calcic clinopyroxene nodules found in some kimberlites represent phenocrysts which crystallized at high pressure in the kimberlite magma and, 2) the spatial association of kimberlite and melilitite observed in the field is not related to a common source region for both these magmas in the mantle. If the oxygen fugacity recorded in samples from the upper 150 km of the mantle is maintained at greater depths, then carbonates are potential hosts for carbon in the mantle to depths of at least 350 km.
Reversals of the orthoenstatite‐clinoenstatite transition at high pressures and high temperatures
Authors: Pacalo R. E. G. , Gasparik T.
Published: February 2008

The MgSiO3 orthoenstatite‐clinoenstatite (OEn‐CEn) phase boundary has been reversed between pressures of 70 and 110 kbar and temperatures of 900°C and 1700°C with a split‐sphere anvil apparatus (USSA‐2000). Starting materials contained PbO‐PbF2 (1∶1) flux to promote equilibration of the charges and eliminate a potential effect of deviatoric stresses on the phase boundary. The phase boundary separating orthoenstatite from clinoenstatite at high pressures and temperatures can be described by the equation P (kbar) = 0.031 T (°C)+50. Our results are consistent with previous unreversed determinations of the boundary at these high‐pressure, high‐temperature conditions. However, the dP/dT slope determined in the present study is much smaller than that implied by earlier experimental studies of the orthoenstatite/low clinoenstatite boundary at low pressures and temperatures. We propose that the clinoenstatite observed at high pressures and temperatures is a new high‐pressure clinoenstatite phase which is possibly an analogue of MgGeO3 clinopyroxene.
Zircon inheritance in mafic inclusions from Bega batholith granites, southeastern Australia: An ion microprobe study
Authors: Chen Y. D. , Williams I. S.
Published: February 2008

Ion microprobe U‐Th‐Pb dating zircons from four mafic inclusions from the Palaeozoic granites of the Glenbog and Blue Gum suites, Bega Batholith, shows that while most of the zircons are probably magmatic, the cores of some are premagmatic. The mean 206Pb/238U ages of the magmatic zircons are 412±3 Ma and 414±2 Ma for two inclusions from the Glenbog Granodiorite, 406±6 Ma for an inclusion from the Anembo Granodiorite, and 377±3 Ma for an inclusion from the Blue Gum Tonalite. The mafic inclusions and inherited zircons come from the granites' source rocks. The abundance of inherited zircons in the inclusions is less than in the granites. Most of the inherited zircons, as in the granites, are 430–630 Ma old, which probably represents the time interval of underplating of the crust prior to granite genesis, or a period of prolonged metamorphism of earlier underplated material. Rare Proterozoic inherited zircons are probably from a sedimentary component in the source. The inclusions do not appear to contain inherited zircons ∼1000 Ma old, which are common in the granites.
Evolution of a magmatic system during continental extension: The Mount Taylor Volcanic Field, New Mexico
Authors: Perry Frank V. , Baldridge W. Scott , DePaolo Donald J. , Shafiqullah Muhammad
Published: February 2008

In this paper we present geologic mapping, K‐Ar chronology, major and trace element data, mineral chemistry, and Nd, Sr, and O isotopic data for volcanic rocks of the Mount Taylor volcanic field (MTVF). The MTVF lies on the tectonic boundary between the Basin and Range province and the southeastern Colorado Plateau and is dominated by Mount Taylor, a composite volcano active from ≈ 3 to 1.5 m.y. ago. Growth of the volcano began with eruption of rhyolite, followed by quartz latite and finally latite. Basalts erupted throughout the lifetime of the volcano. The compositional variations of MTVF rocks resulted primarily from fractional crystallization of mildly alkaline hy‐hawaiite magmas. Differentiation of magmas occurred in multiple, short‐lived magma chambers, a result of a low magma flux from the mantle that could not support a single, long‐lived chamber. Rare mixing of evolved hy‐hawaiite and rhyolite produced a few intermediate magmas, primarily in the early history of the field. Mixing may have occurred when rhyolite magmas in the lower crust ascended to upper crustal levels and were injected into the bases of mafic magma chambers. Small amounts of crustal assimilation accompanied fractional crystallization and affected all the evolved MTVF rocks. Assimilation/fractional crystallization occurred primarily in the lower crust as hy‐hawaiite differentiated to mugearite or latite. Early in the history of the field, evolved lower crustal magmas ascended into the upper crust, where density filtering and a reduced tensional stress field inhibited further ascent until magmas evolved to rhyolite or quartz latite. Later in the history of the field, latite magmas ascended directly from the lower crust and erupted without further significant differentiation because of increased crustal extension.
Stratigraphic development and hydrothermal activity in the Central Western Cascade Range, Oregon
Authors: Cummings Michael L. , Pollock J. Michael , Thompson Gordon D. , Bull Marilyn K.
Published: February 2008

Two volcanic sequences bounded by erosional unconformities compose the stratigraphy of the North Santiam mining district, Western Cascade Range, Oregon. Diorite, granodiorite, and leucocratic quartz porphyry dikes, stocks, and sills intrude the breccias, flows, and tuffs of a volcanic center in the older Sardine Formation. Tourmaline‐bearing breccia pipes are associated with the porphyritic granodiorite intrusions. An erosional unconformity separates the Sardine Formation from the overlying Elk Lake formation. The alteration patterns in the two formations are consistent with the development of hydrothermal systems during the eruption of each formation. However, the development of the two hydrothermal systems is separated by a period of erosion of the older volcanic pile. Early formation of mineralization that resembles porphyry copper deposits occurred within the Sardine Formation, and later, after eruption of the Elk Lake formation, epithermal veins and alteration developed along faults, fractures, and the margins of dikes in the Sardine Formation.
Shear velocity structure of the northern California lithosphere
Authors: Levander Alan R. , Kovach Robert L.
Published: February 2008

We have determined the regional shear velocity structure of the lithosphere beneath the Coast Ranges and the Great Valley in northern California from inversion of three fundamental mode Rayleigh wave phase velocity curves. The dispersion measurements were made along three different paths crossing the Coast Ranges and Great Valley roughly perpendicular to die North American‐Pacific plate boundary. The three dispersion curves diverge at periods greater than about 20 s; phase velocities are systematically higher from the northwest to the southeast along the transform margin. Inverting the phase velocities for crustal and upper mantle structure shows that this divergence is indicative of a 3–5% increase in the upper mantle shear velocity from the Napa‐Great Valley region to the Diablo Range‐Great Valley region. Crustal shear velocities are consistent with the lithologies expected in the middle and lower crust. The increase in mantle shear velocity from northwest to southeast is anticipated by a tectonic model for the development of the California transform margin in which asthenospheric material is emplaced at the base of the North American crust in the slab gap south of the Mendocino triple junction. Adjacent to the plate boundary, this process creates a subcrustal corridor of cooling asthenosphere which is gradually incorporated in the lithosphere lid. We suggest that this causes the observed increase in upper mantle shear velocity away from the triple junction. Finite difference simulations of Rayleigh wave propagation across asthenosphere corridor models produce synthetic phase velocity curves which are similar to the field observations.
Thermal history of crystalline nappes of the Maria Fold and Thrust Belt, west central Arizona
Authors: Knapp James H. , Heizler Matthew T.
Published: February 2008

The thermal history of the crust in west central Arizona, as documented by 40Ar/39Ar step‐heating analysis of mineral suites from crystalline nappes of the Maria fold and thrust belt, is characterized by three distinct stages for Late Cretaceous and Tertiary time. Regional heating of the crust occurred during basement‐involved folding and thrust faulting in middle Late Cretaceous time (∼80–90 Ma) and represents the earliest phase recorded by the 40Ar/39Ar data. The second stage was dominated by uplift and slow cooling (5–10°C/m.y.) of the crust throughout latest Cretaceous and early Tertiary lime. Tectonic denudation in late Oligocene to early Miocene time resulted in rapid uplift and cooling of midcrastal rocks in the footwall of the Whipple‐Buckskin‐Rawhide detachment system, marking the final thermal signature in the region. Evidence for variable argon loss in the hornblende spectra implies exposure of differing structural levels within the thrust belt and/or significant thermal heterogeneity in the crust during Late Cretaceous orogenesis. Partially outgassed hornblende in the northern Granite Wash Mountains reflects temperatures of ∼450°C, whereas complete resetting of hornblende at Mesquite Mountain suggests that this area attained temperatures in excess of 500°C. In contrast, data from the northern Plomosa Mountains indicate that this area did not attain temperatures sufficient to completely degas biotite or K‐feldspar (>350°C) during Late Cretaceous time. The range of early Tertiary muscovite and biotite ages in the region reflects slow cooling, presumably associated with uplift and erosion following crustal thickening. K‐feldspars yield saddle‐shaped age spectra with minimum apparent ages ranging from 22–28 Ma, and reflect quenching due to rapid exhumation of midcruslal to upper crustal rocks in the detachment terrain. Collectively, the data are consistent with either of two models for the thermal evolution of the crust in middle to late Tertiary time. Either (1) lower plate rocks were still sufficiently hot following Late Cretaceous heating that argon clocks were set simply due to rapid cooling or (2) the area experienced a renewed thermal input associated with extension, causing argon loss from previously cool rocks. Based on consideration of diffusion domain behavior in K‐feldspars, we infer that a renewed thermal pulse was associated with the early stages of extension and was related to the cause for crustal weakening.
Heat flow and sediment thickness in the Queensland Trough, western Coral Sea
Authors: Choi D. R. , Liu Y. S. B. , Cull J. P.
Published: February 2008

Twenty new heat flow values have been obtained from a relatively narrow zone of the Queensland Trough in the western Coral Sea. The average heat flow in the trough (60 mW/m2) is close to the world average. The heat flow is relatively high (generally over 60 mW/m2) in areas of basement (pre‐Jurassic) high and basin margins but low (less than 55 mW/m2) in basin centers, decreasing with increasing sediment thickness. Steady state geothermal models suggest that the systematic decrease in the observed heat flow toward the basin center can be explained by the presence of low‐conductivity sediments thickening toward the basin center. This study demonstrates the importance of heat refraction along the basin margins which causes broad variation of heat flow in a relatively narrow area. Although future detailed studies based on transient state solutions are necessary, the results of this study can be used for improved interpretation of paleo‐heat flow and geothermal analysis of sedimentary basins.
Melting, thermal expansion, and phase transitions of iron at high pressures
Authors: Boehler R. , von Bargen N. , Chopelas A.
Published: February 2008

The melting curve of iron to 1.2 Mbar was remeasured in a laser‐heated diamond anvil cell. A defocused 35 W Nd∶YAG laser beam provided low‐temperature gradients which were measured within an area of 2 μm in diameter with a chromatically corrected optical geometry. Argon to 350 kbar and A12O3 to 1.2 Mbar were used as pressure media. Melting was detected by in situ measurements of optical reflectivity and electrical resistivity and by visual observation of the surface texture. At 1.2 Mbar, iron melts at 3000 ± 100 K. The same laser‐heating technique was used to measure volumes of fcc‐(γ)‐iron to 168 kbar and 2000 K using synchrotron radiation, leading to a decrease in the thermal expansion coefficient of γ‐iron represented by (∂ In α/∂ In V)T = 6.5±0.5. The α‐ε transition of iron has been studied by X ray and by the change in resistivity of a fine wire using a variety of pressure media. The hysteresis of the transition changes systematically with the shear strength of the pressure medium with an equilibrium transition pressure at 130±10 kbar.
Static compression of iron to 300 GPa and Fe0.8Ni0.2 alloy to 260 GPa: Implications for composition of the core
Authors: Mao H. K. , Wu Y. , Chen L. C. , Shu J. F. , Jephcoat Andrew P.
Published: February 2008

We report the results of X ray diffraction experiments with the diamond anvil cell to pressures above 300 GPa at room temperature on pure iron and an iron‐nickel alloy. These data extend throughout the pressure range of the bulk of the outer core of the Earth and provide for the first time direct pressure‐volume measurements on geophysically important materials at such conditions. Both iron and iron‐nickel are observed to remain in the hexagonal close‐packed structure to the maximum pressures. A combined fit to all recent compression data up to 300 GPa gives the following Birch‐Murnaghan equation‐of‐state (EOS) parameters for iron: V02 = 6.73(1) cm3 mol−1, K02 = 165(4) GPa, and K′02 = 5.33(9). (Value in parentheses refers to the uncertainty of the last digit; e.g., 6.73(1) refers to 6.73+0.01.). Similar parameters are obtained with a recent “universal” form of the EOS of solids. For an Fe0.8 Ni0.2 alloy, the equation‐of‐state parameters are nearly identical, within error: V02 = 6.737(5) cm3 mol−1, K02 = 172(2) GPa, and K′02 = 4.95(9). In terms of volume, the alloy equation‐of‐state is indistinguishable from that of pure iron and the densities differ (dominantly in proportion to their atomic weights) by ∼0.3 Mg m−3 at 330 GPa. Within the range of uncertainty in Earth model densities and trade‐offs with the percentage light component in the core, nickel could be present in the core in an amount at least equal to its estimated abundance in the Earth. A direct comparison with (solid) inner core densities is now possible and places direct constraints on the thermal models of the Earth's interior.
Thermal regime of the San Andreas Fault near Parkfield, California
Authors: Sass J. H. , Williams C. F. , Lachenbruch Arthur H. , Galanis S. P. , Grubb F. V.
Published: February 2008

Knowledge of the temperature variation with depth near the San Andreas fault is vital to understanding the physical processes that occur within the fault zone during earthquakes and creep events. Parkfield is near the southern end of the Coast Ranges segment of the San Andreas fault. This segment has higher mean heat flow than the Cape Mendocino segment to the northwest or the Mojave segment to the southeast. Boreholes were drilled specifically for the U.S. Geological Survey's Parkfield earthquake prediction experiment or converted from other uses at 25 sites within a few kilometers of the fault near Parkfield. These holes, which range in depth from 150 to over 1500m, were intended mainly for the deployment of volumetric strain meters, water‐level recorders, and other downhole instruments. Temperature profiles were obtained from all the holes, and heat flow values were estimated from 17 of them. For a number of reasons, including a paucity of thermal conductivity data and rugged local topography, the accuracy of individual determinations was not sufficiently high to document local variations in heat flow. Values range from 54 to 92 mW m−2, with mean and 95% confidence limits of 74±4 mW m−2. This mean is slightly lower than the mean (83±3) of 39 previously published values from the central Coast Ranges, but it is consistent with the overall pattern of elevated heat flow in the Coast Ranges, and it is transitional to the mean of 68±2 mW m−2 that characterizes the Mojave segment of the San Andreas fault immediately to the south. The lack of a heat flow peak near the fault underscores the absence of a frictional thermal anomaly and provides additional support for a very small resolved shear stress parallel to the San Andreas fault and the nearly fault‐normal maximum compressive stress observed in this region. Estimates of subsurface thermal conditions indicate that the seismicaseismic transition for the Parkfield segment corresponds to temperatures in the range of 350°–400°C. Increasing heat flow to the northwest of Parkfield corresponds to a transition from locked to creeping sections and to a shallowing of the base of seismicity and confirms the importance of temperature in controlling the thickness of the seismogenic crust. Lateral variations in heat flow do not appear to have any major role in determining the regularity of M5.5–6 earthquakes at Parkfield.
Temporal and latitudinal variations of stratospheric trace gases: A critical comparison between theory and experiment
Authors: Wofsy Steven C.
Published: February 2008

Global calculations of stratospheric HOx, Clx, and NOx are presented which include the effects of planetary albedo and diurnal and seasonal variations of the insolation. Comparisons are made with a wide range of atmospheric measurements at different latitudes and altitudes. Agreement between theory and observations is generally within a factor of 2. The theory appears to explain adequately the major features of latitude and seasonal distributions of NO2 and HNO3. The results indicate that mesospheric OH makes an appreciable contribution to the total OH column abundance and strongly suggest that nitrogen oxides exist principally in the form of HNO3 at high latitudes in winter. There are difficulties in reconciling OH, ClO, and O3 observations in the upper stratosphere.
Salinity: Its definition and calculation
Authors: Lewis E. L. , Perkin R. G.
Published: February 2008

Salinity data used to trace water movement or compute density are normally derived from measurements of chlorinity or electrical conductivity, temperature, and pressure. The latter technique has a precision about 1 order of magnitude greater than that of a typical chlorinity titration, but both are sensitive, in different ways, to variations in the ionic ratios of seawater. Present definitions of salinity are also ion dependent, causing significant variations in the salinity‐density relationship which cannot be simply expressed. In order to obtain density to an accuracy commensurate with the available precision it is best to define salinity in relation to a water mass of known ionic content so that a density correction to be applied to other water masses may be expressed as variations from a fixed standard. These corrections then appear in the form of simple additive constants for most waters, and where density difference is the important parameter, no correction is necessary within a specific water mass. The new salinity definition is based on dilution by weight of a conductivity ratio labeled standard seawater. It would be invariant under compositional variations and in accord with the proposed new equation of state (Grasshoff, 1976). It is conservative within acceptable limits, would provide a ‘practical salinity scale’ for use by oceanographers of all levels of sophistication, and would greatly facilitate data comparisons between institutions. The present variety of computational procedures for in situ data reduction would be replaced by one set of definitive equations that would not be subject to change as the precision of physical or chemical measurement improved. A great part of the data base necessary to write these equations exists, and the remainder should be available by 1978.
The annual variation in the global heat balance of the Earth
Authors: Ellis J. S. , Haar T. H. Vonder , Levitus S. , Oort A. H.
Published: February 2008

An annual variation with a range of 31 W m−2 is found in the global net radiation balance of the earth. The net radiation flux values measured from satellites and the changes in total heat content computed from independent sets of atmospheric and oceanic data show annual variations which are consistent with each other in both phase and magnitude. The net energy gain and loss by the planet within a year is stored and released within the system primarily by the oceans.
The vertical structure of North Pacific temperature anomalies
Authors: Bryan Kirk , Ripa P.
Published: February 2008

The existence of large‐scale thermal anomalies in the North Pacific motivates a study of the reflection of a wind‐driven anomaly at the eastern boundary. A continuously stratified, linear model is used to calculate the vertical and horizontal structure of large‐scale waves forced by fluctuating wind stress patterns. Thermal anomalies caused by eastward, westward, and standing wind wave patterns are investigated. Although exact comparison with data is not possible, the model can predict downward phase propagation as observed at OWS station N without invoking friction or vertical mixing of heat. In the same solution, upward propagation is predicted at other locations. An eastward moving, forced anomaly in the thermocline transports energy toward the eastern boundary. In the model the anomaly is reflected at the wall in the form of westward moving, internal Rossby waves which have a much lower group velocity. A small amount of friction will attenuate the outgoing waves much more than the incoming waves, providing a mechanism for eastward intensification.
A diagnostic model of continental shelf circulation
Authors: Hsueh Y. , Peng Chich Yuan
Published: February 2008

Numerical integration of a steady state vorticity equation for barotropic currents (defined as the deepwater currents) provides estimates of the residual circulation over a continental shelf region that are consistent with a given dynamic height field. The threshold in time scale for motions for which these estimates apply is given by the inverse of the product of the Coriolis parameter ƒ and the ratio of the thickness δT of a topographic boundary layer to the longshore scale and is typically 20 days. In this steady limit, within a δT distance (∼50 km) from the coast, a flow of frictional equilibrium prevails in which turbulent vertical transfer of momentum enters as surface and bottom stresses. The stress at the shelf bottom proves to be easily expressible as proportional to the barotropic current velocity with a proportionality ƒδ cos α, where δ stands for the displacement thickness and α for the total angle of veering through the bottom Ekman layer. An application to the Coastal Upwelling Experiment 1 data off Oregon demonstrates the skill of the computation in that for a proper choice of δ it accounts for over 75% of the observed longshore difference in both the longshore and onshore‐offshore velocity components at the 60‐m depth between two pairs of current meter moorings along the 100‐m isobath.
Energy exchange over young sea ice in the central Arctic
Authors: Maykut Gary A.
Published: February 2008

A simple model of heat transport through young sea ice is combined with climatological data on air temperatures and incoming radiation in the central Arctic to predict how each component of the surface heat balance is affected by changes in ice thickness. Results indicate that during the cold months the net heat input to the atmosphere from ice in the 0‐ to 0.4‐m range is between 1 and 2 orders of magnitude larger than that from perennial ice. Once the ice exceeds a meter in thickness, there is little change in any of the heat fluxes as the ice thickens. Although both the amount of absorbed shortwave radiation and the emitted longwave radiation depend on ice thickness, it is the turbulent fluxes which undergo the largest changes. The rate of heat exchange over thin ice is shown to be extremely sensitive to snow depth and assumed boundary layer temperatures. It is concluded that with the present ice thickness distribution in the central Arctic, total heat input to the atmospheric boundary layer from regions of young ice is equal to or greater than that from regions of open water or thick ice.
A note on the effect of zonal boundaries on equatorial waves
Authors: Dickey T. D.
Published: February 2008

The purpose of this brief report is to determine the modification of equatorial waves of an ocean or atmosphere by the imposition of two infinite zonal walls. The region of interest lies within 30°S to 30°N. The geometry of two infinite zonal walls is relevant to numerical models in which walls are introduced along circles of latitude and possibly to the Caroline Basin (in the western Pacific). The numerical calculations agree with analytic solutions in the asymptotic limit.
Airborne particle and gas measurements in the emissions from six volcanoes
Authors: Stith Jeffrey L. , Hobbs Peter V. , Radke Lawrence F.
Published: February 2008

Airborne measurements of particle and gas emissions have been obtained in paroxysmal, intraeruptive, posteruptive, and extraeruptive emissions from six volcanoes. The paroxysmal and intraeruptive emissions contained relatively few small particles (<0.1 μm in size) and little gaseous sulfur in comparison to the posteruptive and extraeruptive emissions. The majority of the SO2 injected in the atmosphere (≃0.1 Tg) by the 1976 eruption of Saint Augustine probably occurred during the intraeruptive and posteruptive stages. The paroxysmal eruptions of Saint Augustine produced about 6 Tg of particles of 0.01–66 μm in size and about 0.2 Tg of particles 0.01–5 μm in size. An additional 0.05 Tg of 0.01‐ to 5‐μm sized particles were emitted during the posteruptive and intraeruptive periods. Estimated emission rates from the six volcanoes ranged from 3 × 102 to 5 × 10−4 kg s−1 (SO2), 4 × 10−1 to 2 × 10−4 kg s−1 (H2S), 1 × 105 to 1 × 101 kg s−1 (water vapor), 6 × 105 to 2 × 10−5 kg s−1 (particulate mass), 6 × 1019 to 3 × 1014 s−1 (condensation or Aitken nuclei), and 2 × 1018 to 1 × 1016 s−1 (cloud condensation nuclei). The impacts of these new measurements on previous estimates of worldwide particle and gas emissions from volcanoes are discussed.
Energy balance and wind effects in a shallow sound
Authors: Hart William E. , Murray Stephen P.
Published: February 2008

Tidal energetics and wind effects in an extensive (3000 km2) shallow (∼3.5 m) sound with two widely separated entrances were studied numerically with a two‐dimensional vertically averaged model. A comparison of current predictions with observations from 15 current meter stations under differing tidal regimes proved the reliability of the model. Evaluation of the instantaneous energy balance equation showed the change in energy content to be nearly balanced by input energy flux, frictional energy dissipation being of secondary importance. In contrast to the equipartition of energy in classical long waves, there is on the average eight times more potential energy than kinetic energy. Input energy flow shows preferential pathways; the wide northern entrance mainly shows energy gain to the Sound, the southern entrance shows equal amounts of gain and loss, while small cuts through the barrier island chain serve mainly as conduits for energy loss. When real tidal input is used, the energy balance time‐averaged over a diurnal tidal cycle is not in a steady state (〈∂E/∂t〉 is 25% of the other terms), and frictional dissipation is the dominant term. Experiments showed that with winds in the 8‐ to 9‐m/s range, extensive setup can occur (20 cm), strongly dependent on wind direction. Increased speeds through the passages can significantly reduce the residence time in the Sound. Relaxation time of the wind perturbations is only about 3 hours.
A note on the spectral response of a model continental ice sheet
Authors: Birchfield G. E. , Weertman Johannes
Published: February 2008

Using a modified form of Weertman's (1976) model, predictions of ice age continental ice sheet growth and decay are made for the past 550,000 years by using Vernekar's (1972) insolation anomaly data. While forcing is at periods near 19,000, 23,000, and 41,000 years, model response consistently predicts dominant long‐period responses, most commonly at 100,000 and/or 400,000 years, in addition to significant responses at the forcing periods. The model response lends support to the hypothesis of Hays et al. (1976) that nonlinear response of the earth system to fluctuations of the orbital parameters is responsible for the long‐period climate fluctuations recorded in deep‐sea cores.
Surface type and its effect upon cloud cover: A climatological investigation
Authors: Henderson‐Sellers A.
Published: February 2008

A new objective method of comparing cloud amount frequency and distribution is described. The analysis, which uses the beta distribution to model cloud frequency curves, depends upon the numerical values of two defining parameters (η and γ). Comparison of cloud amount frequency derived from ground‐based data for six different climatological regions is made, and conclusions about the effect of the underlying surface type are drawn. The analysis seems to indicate that cloud amount frequency over land areas at different latitudes have pronounced similarities. This objective method will also be of use for climatological analysis of satellite observations of cloud cover.
On the middepth circulation and salinity field in the North Atlantic Ocean
Authors: Reid Joseph L.
Published: February 2008

Examination of the density field suggests that the large‐scale anticyclonic gyre generally supposed to obtain within the upper waters of the North Atlantic Ocean is considerably altered at middepths. Not only is there a strong return flow westward just south and east of the Gulf Stream‐North Atlantic Current, but this return flow also turns southward near 30°N and continues eastward all across the Atlantic. The warm and saline waters of the outflow from the Mediterranean Sea join the westward return flow south of the Gulf Stream‐North Atlantic Current and are carried westward as they spread and mix, providing the great wedge of warm, saline waters found from 600 to 2500 m in the North Atlantic.
The surface layer of the eastern North Pacific in winter
Authors: Kenyon Kern E.
Published: February 2008

Analyses of hydrographic data from a single winter cruise and of 29 years of climatological surface temperature data are used to describe some horizontal and vertical properties (and their interrelations) of a large‐scale longitudinal temperature maximum in the eastern North Pacific. The climatological surface temperature data for individual monthly means at 35° and 40°N from 1947 to 1975 show that (1) the position of the permanent large‐scale temperature maximum at 35°N in the eastern Pacific almost always lies to the west of that of the corresponding maximum at 40°N, and the average angle counterclockwise from the east of the line connecting the two maxima is about 40° and (2) a positive correlation exists between the temperature and east‐west scales of the longitudinal temperature variation at 40°N. Both results agree with preliminary analyses based on long‐term averages of monthly mean temperatures (Kenyon, 1977a). The hydrographic data from March and April 1976 along 35°N show that both the depth scale and the east‐west scale associated with the temperature maximum in the eastern Pacific can be related to the surface layer thickness and are about 100 m and 4000 km, respectively. The surface layer thickness, defined by a temperature‐salinity relation, is relatively large (small) when the surface temperature is relatively high (low), a relation which holds for the large‐scale horizontal variability in the eastern Pacific as well as for the smaller‐scale (500 km) variability in the western Pacific. The hydrographic data at 35°N show also that the maximum surface temperature in the eastern Pacific is significantly west of the maximum surface layer thickness. Beneath the maximum surface layer temperature, where the vertical temperature gradient is large, the isotherms slope downward from west to east. The geostrophic surface velocity relative to 250 dbar, where the isotherms are nearly level, has a northward component in a broad region surrounding the surface temperature maximum. The hydrographic data strengthen the interpretation that the longitudinal surface temperature maximum is predominantly associated with horizontal advection in the surface layer, which has a significant northward component, and is the surface expression of a mechanism of net poleward heat transport in the eastern Pacific.