bluuebunny/crossref_metadata_2025 huggingface dataset:
Cenozoic intracontinental dextral motion in the Okhotsk‐Japan Sea Region
Authors: Jolivet Laurent , Fournier Marc , Huchon Philippe , Rozhdestvenskiy Vitali S. , Sergeyev Konstantin F. , Oscorbin Leonid S.
Published: February 2008

A right‐lateral shear zone trending northerly along more than 2000 km is recognized from central Japan to northern Sakhalin. It was active mainly during the Neogene and has accommodated several hundreds of kilometers of displacement. The whole structure of Sakhalin is built on this shear zone. En échelon sigmoidal folds and thrusts, en échelon narrow Miocene basins, and a major discontinuity which is observed along more than 600 km, the Tym‐Poronaisk fault, characterize the deformation there. In Hokkaido, en échelon folds and thrusts and a ductile shear zone with high‐temperature metamorphism constitute the southern extension of this transpressional shear zone. It continues to the south as a zone of transtensional deformation along the eastern margin of Japan Sea, as en échelon basins and dextral transfer faults observed as far south as Noto peninsula and Yatsuo basin. The style of the shear zone thus evolves from transpressional in the north far from the subduction zone, to transtensional in the south in the back‐arc region. Strike‐slip motion along this shear zone was primarily responsible for the dextral pull‐apart opening of Japan Sea during the early and middle Miocene. Dextral motion is still active in the north along the Tym‐Poronaisk fault in Sakhalin as well as on the continental margin of Japan Sea (Korea and Asia mainland). Active E‐W compression replaced the dextral motion along the eastern margin of Japan Sea in late Miocene time, and incipient subduction began in the early Quaternary.
Accretion of Japanese island arcs and implications for the origin of Archean greenstone belts
Authors: Taira A. , Pickering K. T. , Windley B. F. , Soh W.
Published: February 2008

The present‐day region of arc‐arc collision between the Izu‐Bonin Arc and mainland Japan (Honshu Arc) in the western Pacific (called the Izu Collision Zone or ICZ) provides a useful kinematic model for the development of many Archean greenstone belts. The compositional assemblage, thermal structure and structural style of the crust in the ICZ are very similar to those inferred for many Archean greenstone belts. In both cases, thick, young and flaky arc crust with a high heat flux is in collision with another crustal block. The ICZ has resulted in the imbrication of very thick slices of crust and associated sediments juxtaposed against older accretionary prisms. Many Archean greenstone belts show similar geological features, and we suggest that the incremental imbrication of the crust was a common tectonic style in some Archean convergent margins.
A major Late Devonian‐Early Carboniferous (Hercynian) Thermotectonic event at the NW Margin of the Arabian‐Nubian Shield: Evidence from zircon fission track dating
Authors: Kohn B. P. , Eyal M. , Feinstein S.
Published: February 2008

Zircon fission track (ZFT) ages of 17 Precambrian samples from deep boreholes and outcrops in southern Israel and Sinai fall within the range 328–373 Ma (Late Devonian‐Early Carboniferous). Single zircon grain age distributions are unimodal with a high chi‐square probability. The age data indicate total resetting of the ZFT clocks but only partial resetting of coexisting sphenes, constraining the temperatures attained to about 225° ± 50°C, followed by relatively rapid regional cooling at the times indicated. In the study area, the lower Paleozoic section presently overlying Precambrian rocks is limited to Cambrian strata, up to 300 m thick. Further, stratigraphic evidence for sub‐Carboniferous erosion is preserved only in SW Sinai. To the east, in southern Jordan, a 2–2.5 km thick lower Paleozoic succession is reported. Despite the lack of stratigraphic evidence in the study area, the ZFT data (1) strongly suggest that an equivalent or thicker section also existed, (2) constrain the timing of the erosion to Late Devonian‐Early Carboniferous (Hercynian), and (3) indicate that thermal gradients may have reached ≥50°C/km prior to the uplift/erosion event. Regional stratigraphic evidence indicates that the Late Devonian‐Early Carboniferous event was confined to a relatively narrow belt extending from the Gulf of Suez area to the vicinity of NE Syria and SE Turkey.
Rates of tectonic uplift in the Corinth and Megara Basins, central Greece
Authors: Collier R. E. L. , Leeder M. R. , Rowe P. J. , Atkinson T. C.
Published: February 2008

We present evidence of the rates of late Quaternary tectonic uplift that have affected parts of central Greece during this period of active extension and basin formation. Dual lines of evidence indicate upper Pleistocene to Holocene uplift rates of the order of 0.3 mm yr−1 for the Corinth and Megara basins. First, U‐series disequilibrium ages of Acropora sp. corals from uplifted marine sediments are used to derive minimum average rates of vertical displacement since deposition. Second, the geometries of cyclical transgressive sequences and of erosional terraces are consistent with the radiometric evidence and the known history of late Quaternary sea level fluctuations. Two types of uplift are distinguished on the basis of structural relationships: (1) fault block rotation about a horizontal axis (tilting) in response to footwall uplift on the active normal fault bounding the Alkyonides Gulf and (2) a more regional uplift which affects the Corinth Basin and Peloponnesos to the south. The results of U‐series dating are discussed in the light of initial 234U/238U activity ratios, derived from the coral samples, which are higher than for average marine waters (1.17–1.31 compared to 1.14). These values may be related to a variable freshwater input to the structurally confined Gulf of Corinth or, alternatively, they may reflect a previously higher global 234U/238U activity ratio in marine waters, or post‐mortem enrichment in 234U, although the mechanism of the latter is not yet understood.
Geometric changes of plate boundaries along part of the northern Dead Sea Transform: Geochronologic and paleomagnetic evidence
Authors: Heimann Ariel , Ron Hagai
Published: February 2008

The Korazim block, an elevated pressure‐ridge, along with the faults bounding the Sea of Galilee and Hula pull‐apart basins are internal structures of the Dead Sea Transform plate boundary. K‐Ar dates and paleomagnetic data from basalt flows and sedimentary strata are utilized to determine the stratigraphy and the deformation of the region. The integration of the two methods, together with structural data, yield high‐resolution age determination of the stratigraphic sequence and provides insight into the timing and style of deformation. The Korazim block is covered in its southern and central areas by Pliocene basalt flows (the Cover Basalt, 5.1–3.6 Ma, and Ruman Basalt, 2.9–2.2 Ma, formations) and in its northern area by basalts (Yarda Basalt, 0.9–0.8 Ma) and sediments (3.0–2.3 and 1.6–0.9 Ma) of Plio‐Pleistocene age. The magnetic polarity of a total of 29 lava flows and intercalated sedimentary strata is mixed; the mean magnetic declination of the 29 sites shows an anomalous direction which yields 11.4° ± 4.0° counterclockwise rotation with respect to the expected field. The mean inclination of 46.0° ± 4.1° does not significantly deviate from the expected field. The anomalous declination is interpreted as the consequence of faulting and block rotation accommodating internal deformation. This deformation did not begin before late Pliocene to early Pleistocene, probably not before 0.9 Ma, and may still be active. Simultaneous right‐lateral slip (of 50–175 m) with a small reverse component (of 30–90 m) along NW trending faults and 11° counterclockwise rotation created internal deformation of the Korazim pressure ridge. This deformation is the consequence of left‐lateral slip along the Almagor strand of the Dead Sea transform, subparallel to the plate slip vector. Thus a compression component was formed which presumably led to the internal deformation of the Korazim block. The recent deformation of the Korazim block in relation to the age of adjacent structures and to the age of the Dead Sea Transform permits temporal resolution of geometric changes which must typify transform boundaries such as the Dead Sea Transform. Internal structures within transforms may change, along with the transform internal geometry, and become inactive, while new structural features may develop.
Timing and kinematics of deformation in the Malaguide Complex, internal zone of the Betic Cordillera, southeast Spain
Authors: Lonergan Lidia
Published: February 2008

The Betic Cordillera of southern Spain forms the westernmost of the Mediterranean Alpine orogenic belts and is divided, traditionally, into Internal and External Zones. In the External Zone fold and thrust belt, unmetamorphosed cover rocks of the Iberian margin were deformed from the early Miocene onward. In contrast, Internal Zone rocks are dominantly metamorphic and are generally assumed to have been deformed and metamorphosed in an Alpine event resulting from Late Cretaceous/Palaeogene convergence between Africa and Europe. In the Sierra Espuña, at the northern edge of the Internal Zone in the Eastern Betics, the uniquely preserved Permo‐Triassic to Miocene stratigraphy of the unmetamorphosed Malaguide Complex, offers a rare opportunity to date the Internal Zone deformation. Kinematic data, thrust geometries and structural facing of folds suggest that the imbricate thrust stack of Malaguide rocks formed as a result of NNW‐directed motion, within present geographical coordinates. A fossilized front to this thrust stack, preserved beneath a thick sequence of Oligocene conglomerates, indicates that the timing of the thrust deformation is late Eocene in age. Deformation propagated into the foreland basin in the late Oligocene with renewed thrusting. Subsequently, the whole stack has been folded into a N‐NW vergent regional recumbent fold, the Espuña fold, during the early Miocene.
Evolution of retreating subduction boundaries formed during continental collision
Authors: Royden Leigh H.
Published: February 2008

Retreating subduction boundaries, formed where the rate of subduction exceeds the rate of overall plate convergence, appear to be commonly developed features within regions of early or incomplete continent‐continent collision. They are characterized by regional extension within the overriding plate and, at their leading edge, by thin‐skinned arcuate thrust belts that are concave towards the overriding plate. As is illustrated by examples from the Mediterranean region, the formation of retreating subduction boundaries is intimately related to the process of continental collision. During the early stages of collision, retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary. Retreating plate boundaries can also form before the main collision, and the associated thrust belts emplaced as precollisional accretionary assemblages. Because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab (slab pull), subduction usually ceases when, and only when, thick buoyant continental crust enters the subduction zone. Thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted. In some cases, retreating subduction boundaries may “escape” into the open ocean, where they form nearly isolated, local tectonic systems. In these systems the rate of subduction is approximately compensated by the rate of upper plate extension, and migration of the system across the oceanic region may be very rapid. For example, the Horseshoe Seamounts, located about 800 km offshore in the eastern North Atlantic, may be the active expression of an east dipping, westwardly migrating retreating subduction boundary that has evolved from the Betic Cordillera‐Rif system active in Miocene time and may now be progressing across the Atlantic at approximately 50 mm/yr. An analogous situation may be represented by the Scotia Arc system, a westward dipping retreating subduction system located between the South American and Antarctic plates, which may have “escaped” into the South Atlantic ocean from a zone of crustal shortening in the Andes and is now progressing across the Atlantic at a rate of about 80 mm/yr.
A seasonal three‐dimensional ecosystem model of nitrogen cycling in the North Atlantic Euphotic Zone
Authors: Sarmiento J. L. , Slater R. D. , Fasham M. J. R. , Ducklow H. W. , Toggweiler J. R. , Evans G. T.
Published: February 2008

A seven‐component upper ocean ecosystem model of nitrogen cycling calibrated with observations at Bermuda Station “S” has been coupled to a three‐dimensional seasonal general circulation model (GCM) of the North Atlantic ocean. The aim of this project is to improve our understanding of the role of upper ocean biological processes in controlling surface chemical distributions, and to develop approaches for assimilating large data sets relevant to this problem. A comparison of model predicted chlorophyll with satellite coastal zone color scanner observations shows that the ecosystem model is capable of responding realistically to a variety of physical forcing environments. Most of the discrepancies identified are due to problems with the GCM model. The new production predicted by the model is equivalent to 2 to 2.8 mol m−2 yr−1 of carbon uptake, or 8 to 12 GtC/yr on a global scale. The southern half of the subtropical gyre is the only major region of the model with almost complete surface nitrate removal (nitrate<0.1 mmol m−3). Despite this, almost the entire model is nitrate limited in the sense that any addition of nitrate supply would go predominantly into photosynthesis. The only exceptions are some coastal upwelling regions and the high latitudes during winter, where nitrate goes as high as ∼10 mmol m−3.
Can climate variability contribute to the “missing” CO2sink?
Authors: Dai Aiguo , Fung Inez Y.
Published: February 2008

The contemporary carbon budget for the atmosphere requires a large “missing” carbon sink to balance anthropogenic carbon inputs. We investigated climatic effects on carbon exchanges between the atmosphere and the undisturbed biosphere and assessed the possible contribution of climate variability to the carbon sink. Empirical models and global temperature and precipitation data sets were used in the study. It was found that climate perturbations during 1940‐1988 caused considerable variations in plant productivity and soil respiration. The different sensitivities of the fluxes to climate perturbations led to a significant carbon accumulation in the biosphere. The cumulative carbon sink for the period 1950‐1984 (∼20±5 GtC or 1012kg C) was predominantly located in mid‐latitudes in the northern hemisphere (30°–60°N) and could amount to half of the missing CO2sink as derived from deconvolution analyses. Our results indicate that climate variations have unequal impacts on biospheric carbon fluxes from different ecosystems and imply that caution must be exercised in generalizing in situ observations to the globe.
Isotopic fractionation of oxygen by respiring marine organisms
Authors: Kiddon John , Bender Michael L. , Orchardo Joe , Caron David A. , Goldman Joel C. , Dennett Mark
Published: February 2008

We measured the respiratory isotope effect ϵresp for seven representative unicellular marine organisms. The bacterium Pseudomonas halodurans, the diatom Phaeodactylum tricornutum, the phytoflagellates Cryptomonas baltica and Dunaliella tertiolecta, the heterotrophic flagellates Paraphysomonas imperforata and Bodo sp., and the ciliate Uronema sp. exhibit ϵresp values in the range 14‐26‰. We also measured ϵresp for three metazoans. The ϵresp for the copepod Acartia tonsa ranged from 17 to 25‰, while two larger organisms, the mollusk Mercenaria mercenaria and the salmon Salmo salmar, respire with a smaller ϵresp of 5‐10‰. The average respiratory isotope effect of the dominant marine respirers (the bacteria, microalgae and zooplankton) is about 20 ± 3‰. An ϵresp of this magnitude supports the hypothesis that the photosynthesis‐respiration cycle is responsible for the 23.5‰ enrichment in the δ18O ratio of atmospheric O2 relative to seawater (the Dole effect). The large value and high variability in the average ϵresp limits the usefulness of a proposed method using the δ18O of naturally fractionated dissolved O2 in seawater as a tracer of primary production in the oligotrophic ocean.
Cyclotron absorption of ion‐cyclotron waves at the bi‐ion frequency
Authors: Thorne R. M. , Horne R. B.
Published: February 2008

We demonstrate that geomagnetically trapped ion‐cyclotron waves that are generated near the equator with frequencies below ΩHe+, can experience significant O+ cyclotron resonant absorption near the reflection point at frequencies just above the bi‐ion frequency. The absorption is strongest when the wave normal angle is highly oblique and when the heavy ions are relatively hot (T > 1 keV) with a concentration of no more than 1 or 2%. This suggests that wave absorption near the bi‐ion frequency could contribute to the heating process for energetic ring current O+; in the outer radiation zone during geomagnetic storms.
Field measurements of the roughness of fault surfaces
Authors: Schmittbuhl Jean , Gentier Sylvie , Roux Stéphane
Published: February 2008

We recorded the height of a granitic fault surface as a function of position along one‐dimensional profiles. We show that the profiles exhibit an “anisotropic” scaling invariance: self‐affinity. The difference between the maximum and the minimum height, and the standard deviation of the height, over a length L are proportional to Lζ, where ζ ≈ 0.84. Other properties such as the Return Probability distribution or the Power Spectrum of the profile comfort this result. This self‐affine property is in good agreement with recent works on artificial fractured surfaces. Previous studies at field scale are consistent with this concept.
Methane flux: Water table relations in northern wetlands
Authors: Moore T. R. , Roulet N. T.
Published: February 2008

Water table position, through the creation of aerobic and anaerobic conditions in the soil profile, plays an important role in controlling CH4 flux from wetlands. A laboratory study of peat columns revealed that CH4 emission rates initially increased and then decreased as the water table was lowered from the peat surface to a depth of 50 cm, with the release of CH4 trapped in pores. There was a strong hysteresis between CH4 flux on the falling and rising water table limbs (falling > rising). When expressed as seasonal average values, there was a strong relationship (r² 0.08 – 0.74) between log CH4 flux and water table position for sites within 5 wetland regions in boreal‐subarctic Canada. The regression coefficients were similar among regions (0.022 – 0.037), but there were differences in the regression constants (0.47 – 1.89). CH4 flux from drained, forested peatland soils decreased as the water table depth increased, and several sites were transformed from sources to sinks of CH4. Global CH4 emissions to the atmosphere may have been reduced by ≈ 1 Tg yr−1 by peatland drainage during the last 100 yr.
Plume structures in the hard‐turbulent regime of three‐dimensional infinite Prandtl number convection
Authors: Malevsky A. V. , Yuen D. A.
Published: February 2008

Numerical simulations of three‐dimensional infinite Prandtl number thermal convection with Rayleigh number (Ra) up to 108 are reported. Convection with Ra higher than 107 is characterized by the appearance of disconnected thermal plumes. The smaller plumes are detached by the currents produced by the larger plumes. The low wavenumber portion of a thermal power spectrum near the boundary layer becomes flat at high Ra, while the spectrum measured in the interior shows a positive slope for low wavenumbers. Differences are found in the thermal spectra between 2D and 3D models.
Origin of ureilite meteorites and implications for planetary accretion
Authors: Scott Edward R. D. , Taylor G. Jeffrey , Keil Klaus
Published: February 2008

Although ureilites have been considered bizarre meteorites, our analysis of their properties suggests that they formed by simple, well‐known processes. We conclude that: (1) ureilites are the sole rock type in a major fraction of their parent body; (2) they are partial melt residues and not cumulates; (3) removal of 90% of the Al in the basalts would largely stop radioactive heating if26Al was the heat source, ensuring that large volumes of ureilite‐like material were generated; (4) they formed in a large chondritic body that had a heterogeneous O isotopic composition; (5) slow diffusion of O in solid and molten silicates ensured that partial melting did not homogenize the O isotopes of the residues; (6) the puzzling absence of the basaltic melts that accompanied ureilite formation probably results from ejection into space by explosive volcanism. Together, these conclusions provide a simple, plausible origin for ureilites that accounts for most of their properties: ureilites are residues from the partial melting of isotopically heterogeneous chondritic material. We suggest that other meteorite parent bodies and planetesimals may have experienced similar histories, and that ureilites provide important constraints on the accretionary and igneous histories of planets and asteroids.
Self‐consistent formation of parallel electric fields in the auroral zone
Authors: Schriver David , Ashour‐Abdalla Maha
Published: February 2008

This paper presents results from a fully self‐consistent kinetic particle simulation of the time dependent formation of large scale parallel electric fields in the auroral zone. The results show that magnetic mirroring of hot plasma that streams earthward from the magnetotail leads to a charge separation potential drop of many kilovolts over an altitude range of a few thousand kilometers. Once the potential drop is formed it remains relatively static and is maintained in time by the constant input of hot plasma from the tail; the parallel electric field accelerates ions away from Earth and ionospheric electrons towards the Earth. At altitudes above where the ions are mirror reflected and accelerated by the parallel electric field, low frequency waves are generated, possibly due to an ion/ion two‐stream interaction.
Particle tracing in the magnetosphere: New algorithms and results
Authors: Sheldon R. B. , Gaffey J. D.
Published: February 2008

We use a fast, efficient method to trace charged particles through realistic magnetospheric electric and magnetic fields, greatly reducing computer simulation times. The method works for particles having arbitrary charge, energy, or pitch angle but which conserve the first two adiabatic invariants. We also apply an efficient method of classifying drift orbits, which greatly simplifies the task of identifying the last closed drift path or other drift boundaries. Finally, we calculate the time‐independent evolution of the bounce‐averaged phase space density along convective drift orbits. With these three tools, convective evolution of the particle distribution from the tail can now be described quantitatively, an essential step in understanding the production of unstable distributions in the magnetosphere. One can also categorize topologically different drift orbits, which is necessary to understand the unique particle signatures of the convecting plasma such as Alfvén layers and the plasmapause. These signatures can then be used to extract the electric and magnetic fields or to test the validity of the model fields. The method is particularly appropriate for particles in the energy range 0.01<E<100 keV, which are influenced by both electric and magnetic fields, and for time periods without invariant destroying waves.
Rate constant for quenching of CO2(010( by atomic oxygen
Authors: Pollock D. S. , Scott G. B. I. , Phillips L. F.
Published: February 2008

The rate of quenching of CO2(010) by O(³P) has been measured at room temperature by a temperature‐jump method. The rate constant value obtained is in good agreement with a previous room‐temperature measurement based on steady‐state analysis of a hollow‐cathode discharge in CO2. The results of fitting the room‐temperature result to trajectory calculations with a curve‐crossing (Nikitin) energy‐transfer mechanism lead to the conclusion that the quenching rate constant should increase only slowly with increasing temperature.
Milankovitch cycles and carboniferous climate
Authors: Crowley Thomas J. , Yip Kuor‐Jier Joseph , Baum Steven K.
Published: February 2008

Cyclical Permo‐Carboniferous sea level fluctuations have long been linked to glacial‐interglacial fluctuations on Gondwanaland. Similar to the Pleistocene, such fluctuations may in turn have been driven by variations in orbital insolation forcing. Herein we report results from climate model simulations that examine the effect of Milankovitch insolation variations on the climate of the Gondwanan supercontinent. Utilizing maximum summer insolation values typical of interglacials, we simulate completely snow‐free conditions, with summer temperatures at the South Pole >20°C. Modifying orbital configuration to minimum summer insolation receipt results in a large area of below freezing temperatures. Comparison of model‐generated summer snow cover for the latter run with reconstructions of glacial ice extent indicates a good first‐order agreement. These calculations support the cyclothem model and suggest that the entire glacial‐interglacial couplet for the Carboniferous can be simulated with a minimum number of adjustable parameters.
Multifractals and extreme rainfall events
Authors: Hubert P. , Tessier Y. , Lovejoy S. , Schertzer D. , Schmitt F. , Ladoy P. , Carbonnel J. P. , Violette S. , Desurosne I.
Published: February 2008

Based on a multifractal structure hypothesis for temporal rainfall processes, a general formula relating maximum possible point rainfall accumulations is derived as a function of the duration and sample size. This formula appears to be in agreement with empirical observations. Such a result may reconcile some opposite points of view regarding extreme rainfall events, and suggests new ways of exploiting the scaling properties of rain processes.
Internal structure of the Sierra Nevada batholith based on specific gravity and gravity measurements
Authors: Oliver H. W. , Moore J. G. , Sikora R. F.
Published: February 2008

About 6,000 specific‐gravity (SG) measurements of samples collected from nearly 200 granitic plutons comprising the central Sierra Nevada batholith yield a SG contour map across the batholith from 36.25° to 38° north latitude. With notable exceptions, SG decreases from values generally greater than 2.7 in the west to less than 2.6 over a few small areas of high‐silica, high‐potassium granites near the east edge. A good correlation between measured SG and analyzed weight percent SiO2 enables estimation of average silica variations across the batholith. The average SG is 2.69 corresponding to an average of 68 wt. % SiO2 for the 18,000 km² central part of the batholith.

A 1‐km gridded version of the SG measurements has been used to generate a series of synthetic gravity maps, assuming that the SG of rocks at the surface extends unchanged to various depths. The synthetic map computed for a depth of 10 km shows the best correspondence with the isostatic residual gravity map indicating that variations in the observed gravity residuals are largely caused by SG variations of the plutonic rocks exposed at the surface that apparently extend downward to an average depth of about 10 km.

Although the 10‐km synthetic gravity map gives the best overall fit to the observed gravity data, comparison of individual anomalies indicates that the bottoms of the plutons as defined by SG variations at the surface are generally shallower along the west edge of the Sierra Nevada (7±2 km) and deeper in the younger and more felsic eastern part (12±3 km). These depths do not necessarily represent a distinct base of the Sierra Nevada batholith. They may indicate the depth below which density homogenization occurs, either by igneous, or possibly, structural processes.
Laboratory assessment of the equivalent apertures of a rock fracture
Authors: Piggott Andrew R. , Elsworth Derek
Published: February 2008

Hydraulic, electrical, and tracer test results are presented for a natural fracture in granite. The hydraulic and electrical apertures of the fracture are similar and suggest minimal fracture surface‐to‐surface contact. Tracer aperture exceeds hydraulic aperture indicating transport at a rate less than that predicted on the basis of hydraulic aperture. Numerical simulation of tracer transport reveals that transport within the fracture is not explicable in terms of parallel plate flow and that transport occurs locally at rates in excess of the overall rate defined by tracer aperture.
Large massive sulfide deposits in a newly discovered active hydrothermal system, The High‐Rise Field, Endeavour Segment, Juan De Fuca Ridge
Authors: Robigou Véronique , Delaney John R. , Stakes Debra S.
Published: February 2008

Submersible observations and side‐scan sonar imagery delineate ten large venting sulfide‐sulfate‐silica structures located on an uplifted block of the axial valley floor on the central portion of the Endeavour Segment, Juan de Fuca Ridge. This newly discovered vent field lies 1.8 km north of the main Endeavour vent field. The axial valley, a horst, and faults controlling sulfide deposition trend parallel to the ridge axis. The horst rises 10 to 15 m above the valley floor and offsets a lava lake which extended 500 m in width across the valley. The largest sulfide structures are perched along the major horst‐bounding faults. One structure is the tallest single edifice (45 m) reported in the Pacific Ocean. Smaller, less‐active and inactive sulfide edifices are associated with faulted remnants of the lava lake surface, fissured pressure ridges, and at the edge of collapse pits.

Based on the relationship between faults and sulfide structures, the morphology of sulfide edifices, and their venting characteristics, we infer that sulfide structures grow vertically by chimney accumulation and laterally by flange development. Late stage deposition of amorphous silica toughens the large deposits and may be responsible for the unusual size and aspect ratio of Endeavour edifices.
Large‐scale volcanism associated with coronae on Venus: Implications for formation and evolution
Authors: Magee Roberts Kari , Head James W.
Published: February 2008

Large‐scale volcanism, in the form of areally extensive flow fields, is a previously unrecognized important aspect of the evolution of at least 41% of all coronae on Venus. The timing and scale of many coronae flow fields is consistent with an origin due to the arrival and pressure‐release melting of material in the head of a mantle plume or diapir. The production of voluminous amounts of volcanism at some coronae is proposed to be the result of larger plume size and/or the intersection of mantle upwellings with regions of lithospheric extension and rifting.
Comparison of marine gravity from shipboard and high‐density satellite altimetry along the Mid‐Atlantic Ridge, 30.5°–35.5°S
Authors: Neumann Gregory A. , Forsyth Donald W. , Sandwell David
Published: February 2008

We compare new marine gravity fields derived from satellite altimetry with shipboard measurements over a region of more than 120,000 square kilometers in the central South Atlantic. Newly declassified satellite data were employed to construct free‐air anomaly maps on 0.05 degree grids [Sandwell and Smith, 1992; Marks et al., 1993]. An extensive gravity and bathymetry dataset from four cruises along the Mid‐Atlantic Ridge from 30.5–35.5°S provides a benchmark for testing the two‐dimensional resolution and accuracy of the satellite measurements where their crosstrack spacing is near their widest. The satellite gravity signal is coherent with bathymetry in this region down to wavelengths of 26 km (γ²=0.5), compared to 12.5 km for shipboard gravity. Residuals between the shipboard and satellite datasets have a roughly normal distribution. The standard deviation of satellite gravity with respect to shipboard measurements is nearly 7 mGal in a region of 140 mGal total variation, whereas the internal standard deviation at crossovers for GPS‐navigated shipboard data is 1.8 mGal. The differences between shipboard and satellite data are too large to use satellite gravity to determine crustal thickness variations within a typical ridge segment.
Correlation dimension and affinity of AE data and bicolored noise
Authors: Takalo J. , Timonen J. , Koskinen H.
Published: February 2008

We have made a detailed analysis of several periods of the AE time series and find that the average correlation dimension is 3.4. We have generated bicolored noise and shown that it shares many properties with the AE data. We also find that the AE time series is self‐affine such that the affinity exponent changes on a time scale of about two hours, which is a typical length of magnetospheric substorms. We suggest that this same time scale appears as a spectral break at about 5.6 × 10−5Hz (5‐hour period) in the power spectrum of the AE data.
Intermediate‐scale observations of the Earth's deep interior from the APT89 Transportable Teleseismic Experiment
Authors: Silver Paul G. , Meyer Robert P. , James David E.
Published: February 2008

The Archean‐Proterozoic Transition Seismic Experiment of 1989 (APT89) represents one of the first of a new class of teleseismic experiments aimed at examining deep‐earth structure using portable instruments. We show in the following three articles that such arrays can be utilized to examine properties of the Earth in great detail, from the surface of the Earth to the core.
First epoch geodetic GPS measurements across the Afar Plate Boundary Zone
Authors: Ruegg J. C. , Briole P. , Feigl K. L. , Orsoni A. , Vigny C. , Abdallah M. Anis , Bellier O. , de Chabalier J. ‐B. , Huchon P. , Jacques E. , Al Kirbash S. , Laike A. , d'Oreye N. , Prévot M.
Published: February 2008

In November 1991, a geodetic network was installed across the actively rifting plate boundary zone between Africa and Arabia. Using the microwave signals transmitted by the satellites of the Global Positioning System (GPS), the relative positions of 37 stations are estimated with an average WRMS scatter of 12 or 14 mm for lines shorter or longer than 100 km, respectively. Assuming that the measurements can be repeated with the same precision in 1999, we expect to obtain horizontal uncertainties of 2.1 or 2.4 mm/yr in the rate of change in the short and long lines, respectively. This level of precision will tightly constrain geological models for the spatial distribution of deformation around the rift in Djibouti, and for the far‐field plate motions surrounding the Afar depression.
W phase
Authors: Kanamori Hiroo
Published: February 2008

The recent Nicaragua tsunami earthquake (September 2, 1992) produced a distinct ramp‐like long‐period (up to 1000 sec) phase which begins between P and S waves on displacement seismograms. In terms of ray theory, this phase consists of long‐period P, PP, S, SS, SP, PS, etc and its propagation mechanism is similar to that of a whispering gallery. In terms of normal‐mode theory, it represents a group of higher‐mode Rayleigh waves with a group velocity close to, but slower than, that of P wave. This phase has not been recognized as a distinct phase in the seismological practice because of clipping of seismograms for very large earthquakes. With the advent of modern wide‐dynamic range seismographs, this phase can be easily identified for all large earthquakes. In view of its use for identifying slow earthquakes, determining whether slow deformation is precursory or coseismic to the regular short‐period energy release, and determining velocity structures between the source and the station, we propose that this phase be called the “W phase”.
First records of a field experiment on fertilizer effects on methane emission from rice fields in Hunan‐Province (PR China)
Authors: Wassmann R. , Wang M. X. , Shangguan X. J. , Xie X. L. , Shen R. X. , Wang Y. S. , Papen H. , Rennenberg H. , Seiler W.
Published: February 2008

Fertilizer effects on methane emission from Chinese rice fields were investigated by a praxis‐oriented approach applying balanced amendments of N, P and K. The data set obtained covered the emission rates of app. one month in early rice and one month in late rice 1991. An intercomparison between the 4 treatments showed pronounced differences in the magnitudes of methane emission rates. The combined organic/mineral fertilizer application, commonly used as local farming practice, resulted in relatively high seasonal averages of methane emission rates (26.5 mg CH4 m−2 h−1 in early rice and 50.1 mg CH4 m−2 h−1 in late rice). The lowest emission rates were observed in the plot with pure mineral fertilization (6.5 mg CH4 m−2 h−1 in early rice and 14.3 mg CH4 m−2 h−1 in late rice). Pure organic fertilizers by unfermented substances yielded the highest methane emission rates of all field trials (38.6 mg CH4 m−2 h−1 in early rice and 56.2 CH4 m−2 h−1 in late rice). The fertilization with fermented material derived from biogas generators resulted in substantially lower emission rates than the other trials with organic amendments, the seasonal averages corresponded to 15.9 mg CH4 m−2 h−1 (early rice) and 22.5 mg CH4 m−2 h−1 (late rice). Interpretation of the results can be obtained from the different potentials of these fertilizers for methane production. Based on this concept the different methane emission rates observed with organic/mineral, pure mineral and pure unfermented‐organic fertilizers could directly be attributed to the different quantities of organic matter incorporated into the soil. The low methane emission from the plot treated with fermented material could be explained by a depletion of potential methane precursors resulting from the preceding fermentation. The results of this investigation provide evidence that the extensive use of specific chemical fertilizers and the application of sludge from the operation of biogas generators could lead to a net reduction of the methane emission from rice fields.
New evidence for geomagnetically trapped anomalous cosmic rays
Authors: Cummings J. R. , Cummings A. C. , Mewaldt R. A. , Selesnick R. S. , Stone E. C. , von Rosenvinge T. T.
Published: February 2008

We report new observations of ≥ 15 MeV/nuc trapped heavy ions with Z ≥ 2, made on the polar‐orbiting SAMPEX spacecraft in late 1992 and early 1993. A trapped population that includes He, N, O, and Ne is found to be located at L ≈ 2. We conclude that the observed N, O, and Ne ions are “anomalous” cosmic rays, trapped by the mechanism proposed by Blake and Friesen. While it is not expected that this mechanism would also trap anomalous He, the characteristics of the trapped He population are generally consistent with those of N, O, and Ne.
GPS measurement of relative motion of the Cocos and Caribbean Plates and strain accumulation across the Middle America Trench
Authors: Dixon Timothy H.
Published: February 2008

Global Positioning System (GPS) measurements in 1988 and 1991 on Cocos Island (Cocos plate), San Andres Island (Caribbean plate), and Liberia (Caribbean plate, mainland Costa Rica) provide an estimate of relative motion between the Cocos and Caribbean plates. The data for Cocos and San Andres Islands, both located more than 400 km from the Middle America Trench, define a velocity that is equivalent within two standard errors (7 mm/yr rate, 5 degrees azimuth) to the NUVEL‐1 plate motion model. The data for Liberia, 120 km from the trench, define a velocity that is similar in azimuth but substantially different in rate from NUVEL‐1. The discrepancy can be explained with a simple model of elastic strain accumulation with a subduction zone that is locked to a relatively shallow (20±5 km) depth.
Double‐polytropic closure in the magnetosheath
Authors: Hau L. ‐N. , Phan T. ‐D. , Sonnerup B. U. Ö , Paschmann G.
Published: February 2008

The magnetosheath plasma is usually neither isotropic nor adiabatic. This paper contains an attempt to decribe its thermodynamic properties in terms of two polytropic laws, p⟂/ρBγ⟂−1 = C⟂ and p∥Bγ∥−1 / ργ∥ = C∥, such that for γ⟂ = 2, γ∥ = 3 the usual Chew‐Goldberger‐Low double‐adiabatic expressions are recovered and for γ⟂ = 1, γ∥ = 1 double‐isothermal conditions are obtained. Using data from the AMPTE/IRM spacecraft, we show that the subsolar magnetosheath plasma may be better described by the double‐polytropic laws than by the mirror instability threshold, in particular in the low beta region near the magnetopause. The inferred polytropic exponents vary from event to event but are typically in the ranges of γ⟂ = 0.94 ± 0.10 and γ∥ =1.14 ± 0.13 for the 29 cases we have examined.
Intraplate earthquakes in the southwest Pacific Ocean Basin and the seismotectonics of the southern Tasman Sea
Authors: Valenzuela Raúl W. , Wysession Michael E.
Published: February 2008

An examination of 311 intraplate earthquakes in the Australian plate portion of the Pacific Ocean basin reported from 1918 to 1990 reveals that only 113 events are reliably intraplate, with most of the rest relocating to active trenches and transforms. The non‐random distribution of the reliably intraplate events gives insight into the tectonic stresses present. The central Tasman Sea is mostly aseismic except for a swarm of activity at the predicted site of the Tasmantid hot spot. To the north, the broad regions of the Coral Sea, South Fiji Basin and Lord Howe Rise show very little intraplate seismicity, yet the narrow Norfolk Ridge and Three Kings Rise, caught between the double convergence of the New Hebrides and Tonga subduction zones, support many more earthquakes.

High levels of intraplate seismicity in the southern Tasman Sea adjacent to the Macquarie Ridge Complex (MRC) indicate that this region may be undergoing internal deformation due to the unusual nature of the Australia‐Pacific plate boundary. Additional support exists in the form of intraplate focal mechanisms similar to those at the plate boundary and a set of parallel gravity rolls which are observed in recent geoid maps. Some aftershocks of the Mw = 8.2 Macquarie Ridge earthquake of 1989 occurred in a fracture zone west of the Macquarie Ridge Complex [Das, 1992], but we have found several earthquakes from as early as 1924 which relocate to this feature, suggesting that its reactivation may be more significant than previously thought. This reactivation of a fossil fracture zone may be the result of the increasing amount of oblique convergence between the Australia and Pacific plates at the Macquarie Ridge Complex, formerly a spreading center, and the stresses associated with subducting recently formed Australian ocean crust beneath the older Pacific plate.
The interaction with the lower ionosphere of electromagnetic pulses from lightning: Excitation of optical emissions
Authors: Taranenko Y. N. , Inan U. S. , Bell T. F.
Published: February 2008

A self consistent and fully kinetic simulation of the interaction of lightning radiated electromagnetic (EM) pulses with the nighttime lower ionosphere indicates that optical emissions observable with conventional instruments would be excited. For example, emissions of the 1st and 2nd positive bands of N2 occur at rates reaching 7 × 107 and 107 cm−3 s−1 respectively at ∼92 km altitude for a lightning discharge with an electric field E100 = 20 V/m (normalized to a 100 km distance). The maximum height integrated intensities of these emissions are 4 × 107 and 6 × 106 R respectively, lasting for ∼50 µs.
Latitudinal variation of solar wind corotating stream interaction regions: Ulysses
Authors: Gosling J. T. , Bame S. J. , McComas D. J. , Phillips J. L. , Pizzo V. J. , Goldstein B. E. , Neugebauer M.
Published: February 2008

Ulysses‧ initial transit to high heliographic latitudes at a heliocentric distance of ∼5 AU has revealed systematic effects in the latitudinal evolution of corotating interaction regions (CIRs). At a latitude corresponding roughly to, but slightly less than, the inferred tilt of the coronal streamer belt and embedded heliospheric current sheet, the strong forward shocks commonly associated with CIRs at lower latitudes disappeared almost entirely; however, the reverse shocks associated with these CIRs persisted to latitudes ∼ 10° above the streamer belt. Systematic meridional flow deflections observed in association with the forward and reverse waves bounding the CIRs demonstrate that the above effect is the result of the fact that the forward waves propagate to lower latitudes and the reverse waves to higher latitudes with increasing heliocentric distance. These observational results are in excellent agreement with the predictions of a three‐dimensional model of corotating solar wind flows that originate in a tilted dipole geometry back at the Sun.
Non‐steady‐state transport of superthermal electrons in the plasmasphere
Authors: Khazanov George V. , Liemohn Michael W. , Gombosi Tamas I. , Nagy Andrew F.
Published: February 2008

Numerical solutions to the time‐dependent kinetic equation, which describes the transport of superthermal electrons in the plasmasphere between the two conjugate ionospheres, are presented. The model calculates the distribution function as a function of time, field‐aligned distance, energy, and pitch‐angle. The processes of refilling, depleting, and establishing steady‐state conditions of super‐thermal electrons in the plasmasphere are discussed.
Latitudinal distribution of solar wind as deduced from Lyman alpha measurements: An improved method
Authors: Summanen T. , Lallement R. , Bertaux J. L. , Kyrölä E.
Published: February 2008

In this work we examine the possibility of deducing the latitudinal distribution of the solar ionization rate using Prognoz 6 Lyman alpha data in a more general and flexible way than previously examined. Using so‐called hot model for the hydrogen distribution and the optically thin model for the resonance scattering, theoretical Lyman alpha intensity for the interstellar hydrogen is calculated and compared with the intensity data measured by Prognoz 6. Varying the latitudinal dependence of the ionization rate, the distributions, which produce the best fit with the data, are analyzed for four different measuring sessions. As a result, we get four ionization rate distributions that have two common features. The ionization rate is enhanced near the solar equator, and large broad plateaus exist around heliographic latitudes ±30° to ±70°. The latitudinal distribution of the average ionization rate about the solar minimum deviates clearly from the spherically symmetric and sinusoidally (harmonically) with the latitude‐varying models used so far. The growth of the solar wind mass flux from the solar polar areas toward the equator corresponds to the earlier results concluded from Lyman alpha measurements. The method used in this work allows a higher latitudinal resolution of the ionization rates. However, there are several uncertainties both in the simulations and in the measurements. The exclusion of time‐dependent effects as well as multiple scattering requires that the results be considered only suggestive.