bluuebunny/crossref_metadata_2025 huggingface dataset:
Field and laboratory measurements of cloud‐forming properties of combustion aerosols
Authors: Hudson J. G. , Hallett J. , Rogers C. F.
Published: February 2008

Measurements of condensation nuclei (CN) and cloud condensation nuclei (CCN) were obtained from aircraft penetrations of controlled burns of chaparral, pine forest, and a JP‐4 (jet fuel) pool fire. Vegetative burns gave rise to large numbers of CN, most of which were also CCN at a supersaturation of less than 1%. This is to be contrasted with the much lower activity of smoke from JP‐4 burns which gave only 1–2% CCN activity under identical conditions. The field observations are consistent with laboratory results under conditions which simulate natural clouds. This implies that although droplets readily grow on smoke from vegetative burns leading to activation of a significant number of the particles, mutual competition ensures that a large number of interstitial haze particles remain. By contrast, in clouds produced from smoke from jet fuel combustion, a larger fraction of the nonactive interstitial particles remain after cloud formation. Penetrations of a forest fire capping cloud show high concentrations (>104 cm−3) of small (2 μm diameter) but optically active particles together with high concentrations (5×105 cm−3) of nonactivated haze particles. Photogrammetric measurements of vertical velocities of clouds from controlled burns showed that weakly sheared plumes penetrated upward more effectively than strongly sheared plumes with cloud and smoke cap velocities as large as 20 m s−1. This implies vertical velocities twice this value and cloud supersaturations of ∼2% under the observation conditions. Implications for particle removal by in‐cloud scavenging and precipitation are discussed.
Should bulk cloudwater or fogwater samples obey Henry's law?
Authors: Pandis Spyros N. , Seinfeld John H.
Published: February 2008

In this work we prove that mixing of droplets with different pH that are individually in Henry's law equilibrium with the surrounding atmosphere always results in a bulk mixture that is supersaturated with weak acids like S(IV) and HCOOH and bases like NH3 with respect to the original atmosphere. The degree of supersaturation of the bulk liquid water sample for a particular species depends on its dissociation constant, on the initial pH of the bulk droplet mixture, and on the distribution of the pH and of the liquid water over the droplet spectrum. High supersaturations result only when the pH of the bulk droplet mixture exceeds the pKa of the species, in which pH range large pH differences among droplets of different sizes lead to large deviations from Henry's law for the bulk mixture. The deviation is shown to depend on the ratio of the arithmetic mean to the harmonic mean of the hydrogen ion concentrations of the droplets with the liquid water content used as weighting factor in the calculation of the means. The theory developed can explain observed discrepancies from Henry's law in atmospheric samples and also other observed phenomena like the reported increase of pH values of bulk aqueous samples during storage.
Measurements in an air settling tube of the terminal velocity distribution of soil material
Authors: Malcolm L. P. , Raupach M. R.
Published: February 2008

For wind erosion studies the distribution of terminal velocity (Wt) is a far more relevant soil property than the particle size distribution. An air settling tube was constructed to measure the distribution of Wt for the soil particles in a given sample. The apparatus consists of a vertical tube (height h = 6.09 m) down which a small soil sample is dropped onto a weighing device which records the accumulated mass as a function of time t since release of the sample; this yields the distribution of average fall velocity (Wa = h/t) for the sample. A maximum sample size to avoid clustering effects was determined empirically. To convert Wa to Wt, a correction for initial acceleration is needed: three correction methods, at different levels of simplification, were developed. The settling tube was then tested with four different kinds of material. (1) Glass spheres were used to verify the acceleration correction methods experimentally: the most sophisticated method worked well for all sphere diameters and the simplest for diameters less than 0.25 mm, (2) Sand samples, sieved into size classes with median sieve diameter dS had Wt values equal to those of spheres with equivalent sphere diameter d=0.9ds, with a scatter of ±20% dependent on dryness. (3) For organic material, Wt could be approximated (to ±30%) by its value for an equivalent sphere diameter d equal to the cylinder diameter for cylindrical or fibrous particle forms, the particle length for cubelike forms, and 0.5 of the square root of area for platelike forms. (4) For field soils, Wt distributions depended on wind credibility: the distributions were unimodal and sharply peaked near 1 m s−1, while for nonerodible soils they were broad and tended to a bimodal form with the lower peak near 0.3 m s−1. For the aggregated nonerodible soils, size distributions inferred from the settling tube differed substantially from sieved size distributions, yielding more large particles and fewer small particles.
Climatology and trends of the middle atmospheric temperature (33–87 km) as seen by Rayleigh lidar over the south of France
Authors: Hauchecorne Alain , Chanin Marie‐Lise , Keckhut P.
Published: February 2008

The technique of the Rayleigh lidar provides temperature profiles with a good temporal and vertical resolution in the middle atmosphere. Data obtained by 2 Rayleigh lidars set up at the Observatory of Haute‐Provence (44°N, 6°E) and at Biscarrosse (44°N, 1°W) from 1978 to 1989 led to a unique set of data of 1200 night‐mean temperature profiles from 37 to 87 km. A climatology of the temperature over the south of France has been established from this data base and new results concerning both the short‐term and long‐term variability of the middle atmosphere are presented in this paper. The observed temperature around 44°N, 0°W is in general colder than the mean temperature given in the COSPAR International Reference Atmosphere (1986) near 75 km and warmer above 80 km. A clear semiannual variation is observed near 65 km with maxima occurring just after the equinoxes. The study of the short‐term variability indicates clearly two frequency domains: long periods below 65 km with a maximum in December–January which relate to planetary waves and shorter periods above 65 km induced by the breaking of gravity waves. A correlation with the 11‐year solar cycle, negative in the stratosphere and positive in the mesosphere, is found to be well above the 95% confidence level with an amplitude larger in winter than in summer. However, with only 11 years of data it is obviously difficult to conclude that this atmospheric perturbation is induced by the solar forcing. A cooling of the mesosphere of about −4 K/decade at 60–70 km is found but is at the limit of the 95% confidence level, whereas we do not observe any significant trend in the stratosphere.
Tropospheric ozone in the nineteenth century: The Moncalieri series
Authors: Anfossi D. , Sandroni S. , Viarengo S.
Published: February 2008

A 26‐year (1868–1893) data series of daily ozone readings performed at Moncalieri, northern Italy, by the Schönbein test paper technique has been analyzed. The availability of a series of simultaneous readings by the Schönbein and a quantitative technique (Levy, 1877) and the conversion chart for humidity by Linvill et al. (1980) allowed us to develop a procedure to convert the Moncalieri data into parts per billion by volume values. The results seem to indicate that in comparison to one century ago, the ozone level in Europe has increased by more than twice not only at the surface but also in the free troposphere.
Soil emissions of nitric oxide in a seasonally dry tropical forest of México
Authors: Davidson Eric A. , Vitousek Peter M. , Matson Pamela A. , Riley Ralph , García‐Méndez Georgina , Maass J. Manuel
Published: February 2008

Soil emissions of NO were measured at the Chamela Biological Station, México, using soil covers and a field apparatus for NO detection based on CrO3 conversion of NO to NO2 and detection of NO2 by chemiluminescence with Luminol. Mean NO fluxes from forest soils ranged from 0.14 to 0.52 ng NO‐N cm−2 hr−1 during the dry season and from 0.73 to 1.27 ng NO‐N cm−2 hr−1 during the wet season. A fertilized floodplain pasture exhibited higher fluxes, but an unfertilized upland pasture, which represents the fastest growing land use in the region, had flux rates similar to the forest sites. Wetting experiments at the end of the dry season caused large pulses of NO flux, equaling 10% to 20% of the estimated annual NO emissions of 0.5–1.0 kg N ha−1 from the forest sites. Absence of a forest canopy during the dry season and the first wet season rain probably results in substantial NOx export from the forest system that may be important to regional atmospheric chemical processes. Wetting experiments during the wet season and a natural rain event had little or no stimulatory effect on NO flux rates.
An energy balance climate model with hydrological cycle: 2. Stability and sensitivity to external forcing
Authors: Jentsch Volker
Published: February 2008

The stability of a thermodynamic climate model with three prognostic variables (two for temperature and one for humidity) is investigated. Two stable equilibrium points are found which, in agreement with earlier work, refer to the current (warm) climate and a cold climate. However, perturbations in global temperature must be extremely large (< −20°C) to drive the warm climate into the cold climate. The domains of attraction in phase space are dependent on temperature, but also on humidity. Starting from an ice covered state, the climatic trajectory approaches the present state, if humidity is above some threshold value initially, but evolves into the cold state, if it lies below. Numerical experiments show that the model is not only remarkably stable to internal perturbation but also relatively insensitive to changes in external parameters. The solar constant must be reduced by approximately 20% to obtain total ice cover; the atmospheric CO2‐ content must be doubled to obtain 1.5°C global warming. However, the surface temperature response of the model increases to 3.5°C if cloud temperature rather than cloud height is held fixed. In addition to the cloud height feedback, other positive feedbacks are ice albedo, water vapor and the oceanic heat flux. The great stabilizers of the model are IR damping and the atmospheric heat transport which is assumed to depend quadratically on the meridional temperature gradient. In addition, precipitation and evaporation effectively damp the surface temperature response of the all ocean model to increased atmospheric trace gases.
Hydrogen sulfide and radon in and over the western North Atlantic Ocean
Authors: Andreae T. W. , Cutter G. A. , Hussain N. , Radford‐knoery J. , Andreae M. O.
Published: February 2008

Atmospheric measurements of radon and hydrogen sulfide, and seawater measurements of total sulfide, free sulfide, and carbonyl sulfide, were made on a cruise in the western North Atlantic Ocean (October 24 to November 9, 1989). Measured values for 222Rn ranged from 3 to 70 pCi m−3, those for atmospheric hydrogen sulfide from 1 to 85 parts per trillion, and those for dissolved total and free sulfide in seawater from 33 to 930 pmol L−1 and 0 to 73 pmol L−1, respectively. A positive correlation between 222Rn and atmospheric H2S was observed. Both 222Rn and H2S were high in air masses traced back to North America. Measurements in seawater showed that uncomplexed sulfides were approximately 13% of total sulfide at 2 m depth. Atmospheric H2S and dissolved H2S in seawater were usually not far from saturation equilibrium. Our results indicate that the ocean acted at some times as a source of atmospheric H2S but more frequently as a sink. Hydrolysis of COS and atmospheric deposition of H2S both may contribute to the budget of dissolved sulfide in seawater of the western North Atlantic Ocean. On a global scale the ocean/atmosphere exchange of H2S appears to play a minor role in the atmospheric sulfur cycle.
Seasonal variability of gravity wave activity and spectra in the mesopause region at Urbana
Authors: Senft Daniel C. , Gardner Chester S.
Published: February 2008

The nightly and seasonal variations in gravity wave activity in the mesopause region are examined by analyzing 60 nights of Na lidar observations obtained during a 5‐year period at Urbana, Illinois. The lidar data were used to calculate the atmospheric density perturbations and their spectra. The atmospheric density variances, density vertical shear variances, vertical wind variances, ω spectra magnitudes, and m spectra magnitudes all exhibit considerable nightly variability as well as strong annual and semiannual variations with the largest values in summer. The annual mean values of the rms density perturbations, density shear variance, and rms vertical wind velocity are respectively 5.6%, 37 (%/km)2, and 1.3 m/s. The midsummer values for these parameters are typically 2 to 3 times larger than the annual means. the equivalent Richardson number for the wave field varies between 1/2 and 2 for most of the year. However, during summer, Ri decreases appreciably and sometimes falls well below 1/4. The ω spectra exhibit power law shapes with slopes varying between −1.28 and −2.45. The m spectra also exhibit power law shapes with slopes varying between −2.20 and −3.55. The annual mean slopes are −1.82 for the ω spectra and −2.90 for the m spectra. The magnitudes of both the ω spectra and m spectra vary by more than a factor of 10 throughout the year at all periods between 5 min and 4 hours and vertical scales between 1 and 10 km, with the largest values in summer. The observed variability of the m spectra slopes and magnitudes is not consistent with the predictions of linear instability theory and the concept of a universal vertical wave number spectrum. The characteristic periods (T* = 2π/ω*) vary between 3 and 50 hours with an annual mean of 9.7 hours. The characteristic vertical wavelengths (λz* = 2π/m*) vary between 8.9 and 27 km with an annual mean of 14.1 km. The characteristic wavelengths λz* exhibit a weak seasonal variation with smaller values in summer ( ) compared to winter ( ). The rms bandwidths of the wave field have mean values of and . The two‐dimensional density spectra are not separable.
Space shuttle exhausted aluminum oxide: A measured particle size distribution
Authors: Cofer W. R. , Purgold G. C. , Winstead E. L. , Edahl R. A.
Published: February 2008

Aluminum oxide (A2O3) particles were collected from the space shuttle exhaust plume immediately following the launch of STS‐34 on October 18, 1989. A2O3 samples were obtained at 2.4, 3.0, 3.2, and 7.4 km in altitude. The samples were analyzed using scanning electron microscopy to develop particle size distributions. There were no indications that the particle size distribution changed as a function of altitude. The particle number concentrations per cubic meter of air sampled (Nc) for the four collections was found to fit the exponential expression Nc = (3.2×108) 10−0.89d, where d is particle diameter in micrometers, over the interval of 0.3–7 μm. The mass median diameter for this distribution occurred at about 4 μm.
Further analysis of the global outgoing longwave radiative flux observed by Nimbus
Authors: Auer Lawrence H. , Kao Chih‐Yue Jim
Published: February 2008

A multiyear decrease in the total global outgoing longwave radiation (OLR) is revealed by the Nimbus 7 data set. The size of the change is of the order of 1 W m−2. The data have been analyzed using spectral harmonic decomposition on the monthly averages. The two lowest order fitting coefficients (i.e., C00 and C10) directly yield the temporal behavior of the global OLR and the hemispheric difference in OLR between the northern and southern hemispheres, respectively. Using a hypothetical detrending technique, it is found that the decreasing signal in the global OLR cannot be ascribed to a drift in the instrumental sensitivity. The secular change in terms of decreasing with time is also found in C10. This represents that the OLR from the northern hemisphere is decreasing faster than that from the Southern hemisphere. Thus a single detrending fit to the instrumental sensitivity cannot remove the drift in the OLR. As a previous study showed that the annually averaged C00 variability is strongly correlated with observed variability of global mean surface air temperature (Ts), we show that C10 variability is also consistent with the relative variabilities of the hemispheric mean Ts. Finally, the analysis on the solar insolation during the same period shows that the decreasing insolation may be a contributing factor to the decrease of OLR.
Relative contributions of discrete and continuum absorption to the photodissociation of vibrationally excited O2 (v = 12–20)
Authors: Saxon R. P. , Slanger T. G.
Published: February 2008

It has been proposed that photodissociation of highly vibrationally excited O2 in the B3Σu− −X3g−Σg Schumann‐Runge bands is a source of ozone in the upper stratosphere. Simultaneously, this O2(vib) population could be excited into the continua of the O2(B) and 13Πu states, providing additional ozone. Laboratory measurements indicate that both discrete and continuous processes are operative. Calculations of the Schumann‐Runge continuum cross sections have now been carried out for v″ = 12–20, spanning the 200‐ to 320‐nm wavelength range. The maximum cross sections are in the 1–2×10−18 cm2 range, with the O2(B) state contributing 2–3 orders of magnitude greater absorption than the 13Π state. For v″ = 12, it is shown that the Schumann‐Runge band and continuum cross sections merge smoothly at 250 nm. In laboratory experiments on ozone photodissociation at 248 nm, the principal absorption in product O2(vib) involves the Schumann‐Runge 2–7 band and Schumann‐Runge continuum absorption from vibrational levels at v″ = 12 or higher. Although the cross section for line absorption is much higher than that for the continuum, it is shown that as a result of a variety of processes and mechanisms, photodissociation yields in the bands and the continuum are comparable in magnitude, thereby providing consistency with the laboratory observations. For linear absorption systems, such as the terrestrial atmosphere, high v″ absorption in the Schumann‐Runge bands should be substantially more important than continuum absorption.
Cloud condensation nuclei near marine stratus
Authors: Hudson James G. , Frisbie Paul R.
Published: February 2008

Extensive airborne measurements of cloud condensation nucleus (CCN) spectra and concentrations of total particles, or condensation nuclei (CN), below, in, and above the stratus cloud decks off the southern California coast point to important aerosol‐cloud interactions. Consistently low CCN concentrations below cloud appear to be due to cloud scavenging processes which include Brownian coagulation, nucleation, coalescence, and drizzle. The higher CCN and CN concentrations above cloud are associated with ambient ozone concentrations which suggest a link with continental, probably anthropogenic, sources, even at distances of 500 km from the California coast.
Methane spectral line widths and shifts, and dependences on physical parameters
Authors: Fox K. , Quillen D. T. , Jennings D. E. , Wagner J. , Plymate C.
Published: February 2008

High‐resolution measurements of widths and shifts of vibrational‐rotational lines in infrared spectra of gaseous methane have been made in the laboratory. This research introduced at ambient temperatures the rare gases helium, neon, argon, krypton, and xenon and the diatomics hydrogen, nitrogen, oxygen, and carbon monoxide at pressures from 100 to 700 torr Detailed quantitative studies of correlations with masses, polarizabilities and quadrupole moments suggest that there may be some functional dependences on these physical parameters.
Alteration of the UV‐visible reflectance spectra of H2O ice by ion bombardment
Authors: Sack N. J. , Boring J. W. , Johnson R. E. , Baragiola R. A. , Shi M.
Published: February 2008

Satellites in the Jovian and Saturnian system exhibit differences in reflectivity between their “leading” and “trailing” surfaces which can affect the local vapor pressure. Since these differences are thought to be due to differences in the flux of bombarding magnetospheric ions, we studied the influence of ion impact on the UV‐visible reflectance of water ice surfaces (20–90 K) by keV ion bombardment. An observed decrease in reflectance in the UV is attributed to rearrangement processes that affect the physical microstructure and surface “roughness.” The ratio in reflectance of bombarded to freshly deposited films is compared to the ratio of the reflectance of the leading and trailing hemispheres for Europa and Ganymede.
Thermal budget of multicomponent porous ices
Authors: Steiner Gerhard , Kömle Norbert I.
Published: February 2008

A relation for the temperature evolution of multicomponent porous ices is derived from the energy equation of multicomponent systems. It is demonstrated that the predominant energy transfer mechanisms can be incorporated into an effective thermal conductivity (λeƒƒ), which is strongly temperature dependent, and that the heat conduction equation can be written in a Fourier type form. The vapor of volatile ices significantly contributes to λeƒƒ by the transfer of latent heat of sublimation but otherwise hardly affects the energy balance. The general results are applied to porous water ice, porous H2O–CO2 ice and porous H2O–CO ice. In all cases it is found that the major part of the deposited energy per unit volume is consumed for heating of the ice. Depending on the material parameters and temperature, energy is transferred mainly by solid state conduction or by the transport of latent heat due to sublimation‐condensation processes.
Corona structures on Venus: Models of origin
Authors: Stofan Ellen R. , Bindschadler Duane L. , Head James W. , Parmentier E. Marc
Published: February 2008

Coronae on Venus are circular to elongate structures with maximum widths of 150–1000 km characterized by annuli of concentric ridges surrounding complex interiors. The features have raised topography relative to the surroundings, they are associated with volcanic activity, and most are partially surrounded by a peripheral trough. Variations in morphology between individual coronae are due to differences in their stage of evolution and/or differences in the relative significance of the geologic processes that occur in each stage. We examine models for three processes that may be involved in corona origin and evolution: (1) a hotspot or rising mantle diapir model, (2) a sinking mantle diapir model, and (3) gravitational relaxation of topography. Rising mantle diapirs are caused by heating at depth (e.g., hotspot), while sinking mantle diapirs may result from cooling or a phase change causing increased density and negative buoyancy at the base of the lithosphere. The hotspot model is most consistent with the major characteristics of coronae, with gravitational relaxation occurring as a modificational process. The sinking mantle diapir would produce dominant central compression that has not been observed at coronae; however, higher‐resolution image and altimetry data from Magellan can be used to distinguish more fully between the two models. Coronae in various states of formation and degradation can be identified in the Venera 15/16 data, suggesting that the process may be continuing today.
Terrace width variations in complex Mercurian craters and the transient strength of cratered Mercurian and Lunar crust
Authors: Leith Andrew C. , McKinnon William B.
Published: February 2008

Widths of slump terraces of complex craters can be used to determine the effective cohesion of the cratered region during crater collapse. We have measured terrace widths for complex craters on Mercury: these generally increase outward toward the rim for a given crater, and the width of the outermost major terrace is generally an increasing function of crater diameter. Similar observations apply to lunar complex craters, but the widths of the outermost slump terraces of Mercurian complex craters are less than those of similarly sized lunar complex craters. Using the terrace widths on Mercury and a gravity‐driven slump model, we estimate the strength of the cratered region immediately after impact (specifically, during the modification stage of crater formation) to be ∼1–2 MPa. Comparison with the previous study of lunar complex craters by Pearce and Melosh indicates that the transient strength of cratered Mercurian crust is no greater than that of the Moon. The strength estimates only vary slightly with the geometric model used to restore the outermost major terrace to its precollapse configuration and are consistent with independent strength estimates from the simple‐to‐complex crater depth/diameter transition, in particular, the most recent depth/diameter study of Mercurian craters by Pike. Thus, contrary to previous work, the difference in “target properties” between Mercury and the Moon may be small, and systematic morphological differences between craters on the two worlds may be largely caused by the factor of 2 difference in surface gravity.
Seasonal Variability in the δ18O and δ13C of Planktonic Foraminifera from an Upwelling Environment: Sediment Trap Results from the San Pedro Basin, Southern California Bight
Authors: Sautter Leslie Reynolds , Thunell Robert C.
Published: February 2008

Stable isotopic analyses (δ18O and δ13Crpar; on four species of planktonic foraminifera collected from high‐resolution time series sediment trap sampling indicate that rapid and significant seasonal variability occurred in response to rapid changes in both the hydrographic environment and the isotopic composition of ambient seawater. Specimens were collected at a depth of 500 m for 28 consecutive 1‐week periods in the San Pedro Basin, within the Southern California Bight, a region seasonally influenced by upwelling. Hydrographic monitoring of the study area revealed a 6‐week period (late April to mid‐June) during which pulses of upwelling occurred, causing significant increases in the oxygen isotopic composition of surrounding waters, while decreasing the carbon isotopic composition. Analyses of Globigerina bulloides, Orbulina universa, Neogloboquadrina dutertrei, and Neogloboquadrina pachyderma (right‐coiling) indicate that during the upwelling period these species live, respectively, at the surface, in the surface mixed layer, within the thermocline, and below the thermocline. Globigerina bulloides ascends from well below the thermocline to the surface at the onset of upwelling and increases production to its maximum simultaneously as its morphology changes to less‐calcified, open forms. Both N. dutertrei and N. pachyderma follow isothermal ranges, migrating to shallower waters during upwelling and subsequently descending after upwelling ceases. Neogloboquadrina dutertrei appears to inhabit the region associated with both the thermocline base and chlorophyll maximum when it is most abundant, following upwelling. Orbulina universa increases its depth habitat as solar irradiance increases, but this species decreases in abundance during upwelling. The δ18O signal of O. universa appears to be a useful indicator of seasonal temperature variations above the thermocline, whereas the δ18O of G. bulloides documents near‐surface temperatures during upwelling. The δ13C signal of both N. dutertrei and N. pachyderma appears to record the δ13C of equilibrium calcite for the regions of the thermocline and just below the thermocline, respectively. Due to the relative preservation potentials of the four species analyzed, only N. dutertrei and N. pachyderma are likely to be preserved in the sedimentary record in regions of oxygenated bottom waters. Thus an actual record of hydrographic conditions during upwelling, as would be found in tests of G. bulloides, is not preserved; instead, conditions before (N. pachyderma) and just after (N. dutertrei) are more likely recorded.
Paleoenvironmental Changes in the Japan Sea During the Last 85,000 Years
Authors: Oba T. , Kato M. , Kitazato H. , Koizumi I. , Omura A. , Sakai T. , Takayama T.
Published: February 2008

Five distinct changes in the paleoenvironment of the Japan Sea within the last 85,000 years are revealed from the sedimentary record of a piston core recovered from the Oki Ridge. Changes in both surface and deepwater conditions are registered by changes in lithology, calcium carbonate content, organic carbon content, oxygen and carbon isotope ratios, and microfossil assemblages including calcareous nannoplankton, diatoms, radiolaria, and foraminifera. Between 85 and 27 ka the warm Tsushima Current did not flow into the Japan Sea, and cold surface water conditions prevailed. Environments at the seafloor fluctuated between dysaerobic to weakly oxic conditions. Between 27 and 20 ka, freshwater input to the Japan Sea, probably from the Huang Ho River in China, stratified the water column, and the severe anoxic conditions eliminated most benthic fauna. Between 20 and 10 ka the cold Oyashio Current flowed into the Japan Sea through the Tsugaru Strait, reestablishing deepwater ventilation. Shallow water benthic assemblages of the North Pacific Ocean subsequently colonized the Japan Sea and occupied the vacant niches of the deep basins. Between 10 and 8 ka the foraminifer compensation level (FCL) gradually rose to a depth shallower than 1000 m, and bottom conditions changed from dysaerobic to oxic. At 10 ka the warm Tsushima Current started to flow into the Japan Sea through the Tsushima Strait to establish the modern oceanographic regime which has existed since 8 ka. The eustatic sea level during the last glacial maximum was above the sill depths (130 m) of the Tsushima and Tsugaru straits, assuming that tectonic movements at these straits were negligible for the last 20 ka.
Meltwater and Deglaciation, SE Baffin Shelf (NE Margin Laurentide Ice Sheet) Between 13.5 and 7 KA: From O and C Stable Isotopic Data
Authors: Andrews J. T. , Erlenkeuser H. , Evans L. W. , Briggs W. M. , Jull A. J. T.
Published: February 2008

Stable isotopic values on planktonic foraminifera in a suite of cores from basins across the SE Baffin Shelf are used to extract a record of meltwater events during Termination I deglaciation. Resolution and Hatton basins lie on the SE Baffin Shelf at water depths > 500 m, seaward of major conduits for ice drainage from the eastern sector of the Laurentide Ice Sheet (LIS). Accelerator mass spectrometry 14C dates are used to constrain our chronology of events in ten cores. In Resolution Basin, three cores have 14C AMS dates on foraminifera of > 20 ka at their bases; whereas Hatton Basin cores terminate in sediments < 13 kyr. Sedimentation rates varied between 0.1 to 4.5 m/ka. Stable oxygen and carbon isotopic ratios were obtained on 146 samples of the planktonic foraminifera Neogloboquadrina pachyderma (Ehrenberg) sinistral, from seven of the ten cores. No evidence was found to indicate that test morphology or size affected ∂18O. Between 7 and 13.5 ka the surface water on the shelf was on average 1 ‰ lower than the open ocean signal. Significant temporal variations were found in both ∂18O and ∂13C. Evidence for significant low ∂18O events occurred between 13 and 8 ka. The ∂13C record from the planktonic foraminifera suggests a threefold division of events between 13 and 7 ka, with positive values between 10.8 and 13.0 ka, negative values between 9 and 10.8 ka, and positive values from 7 to 9 ka. The ∂18O data suggest the presence of meltwater on the shelf some 3,000 years prior to the first late glacial dates on terrestrial deglaciation (at circa 10.4 ka).

“Hudson Strait must be the real key to the importance of the calving process during deglaciation, because it is potentially the largest marine outlet for the Laurentide Ice Sheet and because it leads into the very center of the ice sheet.....the rates of calving through Hudson Strait during the period of initial ∂18O rise unfortunately are unknown.”

W. F. Ruddiman (1987, p. 151)
Evolution of Gaussian beams in the nonuniform Earth‐ionosphere waveguide
Authors: Baranov V. A. , Karpenko A. L. , Popov A. V.
Published: February 2008

In a uniform refraction waveguide the transversal width of a Gaussian beam oscillates with an approximately linearly growing amplitude. There exists a special set of initial data which eliminates its global diffraction divergency. We obtain an analogous result for a horizontally nonuniform Earth‐ionosphere duct. By choosing initial elevation angle and operating frequency it is possible to concentrate a narrow radio wave beam at any given point of the Earth's surface. Our analysis is based on asymptotic integration of the ray equations which is outlined in appendix.
The generalization of Rytov's method to the case of inhomogeneous media and HF propagation and scattering in the ionosphere
Authors: Zernov N. N. , Gherm V. E. , Zaalov N. Yu. , Nikitin A. V.
Published: February 2008

Rytov's method is generalized for the case when the regularly inhomogeneous ionosphere contains local irregularities of deterministical and statistical nature. An integral representation of the point source field is constructed which takes into account the multibeam effects including strong interference of the beams field, i.e., caustics and foci formation and so on. By means of the representation developed, some problems of HF wave propagation are solved. Among these is the diffraction of a point source field on an ambipolar diffusing local inhomogeneity of the ionosphere. The calculations of the power spectra of the fluctuations of the phase and amplitude of a single‐hop path field due to ionospherical electron density irregularities are also presented. The calculations are compared with the results of experimental investigations.
Petrogenetic and tectonic significance of young leucogranites from the northwestern Himalaya, Pakistan
Authors: Zeitler Peter K. , Chamberlain C. Page
Published: February 2008

In the Himalaya of northwestern Pakistan, small discordant bodies of leucogranite intrude metamorphosed basement of the Indian crust. As the first step in assessing the tectonic significance of these granites, we have used the SHRIMP ion microprobe to obtain U‐Pb dates on zircon. Zircons of igneous appearance are scarce in the leucogranites, and with one exception are associated with xenocrystic components, which occur as discrete grains and as cores rimmed by young zircon. Zircons of igneous appearance are high in U [5000 to 40,000 ppm], low in Th/U [0.01 to 0.05], and frequently colored a distinct blue. Xenocrystic components give a range of Proterozoic ages consistent with ages previously reported for Indian crust. In sharp contrast, zircons of igneous appearance yield clusters of concordant Tertiary ages. Two leucogranite dikes from southern localities yield rather old emplacement ages of about 35 Ma (Swat) and about 50 Ma (Naran). Together with previously determined 40Ar/39Ar and fission track cooling ages, these ages document immediate and rapid metamorphism and denudation following Eocene collision. Three leucogranite dikes from northern localities within the Nanga Parbat‐Haramosh Massif are very young, having emplacement ages of about 2.3 Ma, 5 Ma, and 7 Ma. The formation and emplacement of these leucogranites during the rapid late Tertiary denudation of the Nanga Parbat region suggests to us that decompression melting may be a viable mechanism for leucogranite genesis.
The gravity field of eastern Hudson Bay: Evidence for a flextural origin for the Hudson Bay (Nastapoka) Arc?
Authors: Hynes Andrew
Published: February 2008

The Nastapoka Arc, on the east coast of Hudson Bay, is almost perfectly circular and closely follows the unconformable contact between Archean Superior province gneisses and shallowly seaward dipping early Proterozoic Nastapoka Group supracrustals. Its form may be explained by flexing of the lithosphere due to loading by thrust sheets from the Trans‐Hudson orogen to the west. Such flexing produces a peripheral bulge east of the coast which should be reflected in a positive gravity anomaly there. Gravity data averaged around the arc show such a positive anomaly, although its precise amplitude is uncertain because of local variation in the gravity field. Lithospheric flexure of the arc due to loading can be modeled by superposition of discshaped loads centered on the arc. For a lithospheric Young's modulus of 1.0 × 1011 N m−2 and Poisson's ratio 0.25, the present geometry of the arc can be reproduced only by reducing the elastic thickness to 20±2 km. The peripheral bulge predicted for the model yields a gravity anomaly very similar to that observed if it is fully imaged at the Moho. The absence of a regional negative gravity anomaly over the arc, despite a great thickness of transported rocks present at its center, requires that the crust in the region was unusually thin before thrust emplacement. The unusually low elastic thickness required for the model may reflect highly fractured crust. Both features are consistent with the former presence of a rifted continental margin in the region, as predicted for many models of the Trans‐Hudson orogen.
Cooling and inferred uplift/erosion history of the Grenville Orogen, Ontario: Constraints from 40Ar/39Ar thermochronology
Authors: Cosca Michael A. , Sutter John F. , Essene Eric J.
Published: February 2008

Stepwise 40Ar/39Ar degassing experiments of 57 mineral separates of hornblende, muscovite, biotite, and perthitic microcline have been used in conjunction with petrologic observations to place regional constraints on the postmetamorphic cooling and the inferred uplift and erosion history of the Grenville Orogen in Ontario. The 40Ar/39Ar data support an interpretation of slow, nearly uniform cooling (1°–4°C/m.y.) from temperatures of ˜500°C to below ˜150°C. In the Central Gneiss Belt (CGB) hornblendes cooled through Ar closure between 930 and 1025 Ma, whereas in the Central Metasedimentary Belt (CMB) hornblendes record the following range in 40Ar/39Ar cooling ages: 1104 Ma in the Frontenac terrane, 1007–1067 Ma in the Sharbot Lake terrane, 919–1026 Ma in the Elzevir terrane, and 972 Ma in the Central Metasedimentary Belt Boundary Zone. Regional uplift/erosion rates of 0.03–0.14 km/m.y. have been estimated for the Grenville Orogen in Ontario based on the 40Ar/39Ar data, a model retrograde P‐T path for rocks of the CGB, and an upper time constraint provided by flat, overlying Cambrian and Ordovician sediments. These erosion rates are consistent with rates estimated for other Proterozoic or Archean granulite terranes but are an order of magnitude slower than active orogens such as the Alps and Himalayas. A regular variation in hornblende 40Ar/39Ar cooling ages is observed in rocks that traverse highly strained often mylonitic shear zones that separate the four major terranes of the CMB. The pattern of 40Ar/39Ar ages is interpreted to reflect late‐tectonic extension, consistent with field observations in the Central Metasedimentary Belt Boundary Zone and elsewhere in the CMB. Up to 13 km of vertical displacement is inferred for some rocks in the CMB between the time they cooled below closure to argon diffusion in hornblende (˜500°C) and their exposure at the surface (˜25°C).
Strain variations in an ancient accretionary complex: Implications for forearc evolution
Authors: Fisher Donald M. , Byrne Tim
Published: February 2008

Strain magnitudes and orientations and incremental strain histories are characterized throughout the Kodiak Formation, a portion of a Late Cretaceous‐early Tertiary accretionary prism. The results of these analyses are used to evaluate the history of underplating, penetrative strain, and unroofing in the forearc of the southwest Alaskan convergent margin. Five major deformation events are recognized in the Kodiak Formation: (1) layer‐parallel extension and layer‐parallel shear (D1) related to underthrusting, (2) seaward verging fold and thrust deformation (D2) with development of both a slaty cleavage (S2) and a downdip stretching lineation (L2) related to underplating and early penetrative strain within the wedge, (3) development of a regional scale antiform (D3), (4) development of a shear zone along the northwest limb of the D3 antiform (D4), and (5) right‐lateral strike‐slip faulting and penetrative right‐lateral simple shear in the seaward half of the Kodiak Formation (D5). Based on sharp differences in structural style and the magnitude and orientation of strain associated with D2, the Kodiak Formation has been subdivided into three structural units informally called the landward, central, and seaward belts. The structural variations observed in these three belts correspond to differences in structural relief of 1–5 km associated with the D3 antiform; the lowest D2 structural level is in the core of the antiform (central belt) and progressively higher structural levels are exposed on both limbs (landward and seaward belts). The regional distribution of incremental strain histories associated with D2, D3, D4, and D5 has been quantified by using syntectonic fibers in pressure shadows around spherical pyrite framboids. From the highest to the lowest structural level, D2 strain is characterized by (1) an increase in the magnitude of finite strain, (2) a change in the orientation of finite extension from nearly vertical to gently northwest plunging, (3) a change in the incremental extension direction from nearly vertical to moderately northwest plunging, and, finally, (4) a change in the strain history from coaxial to noncoaxial with a sense of rotation consistent with southeast directed thrusting. We interpret these D2 strain patterns to reflect a strain field that was fixed relative to the basal decollement, with coaxial subhorizontal shortening in the interior of the prism and noncoaxial strain (probably simple shear) near the base. Subsequent variations in the orientation of incremental extension associated with D3 are consistent with relatively rapid, vertical translation of the accreted sequences relative to the D2 strain field. We specifically propose two periods of wedge thickening in response to a combination of underplating and penetrative strain. These two wedge thickening events correspond with episodes of subaerial exposure and erosional unroofing in the Late Cretaceous and middle Tertiary.
Paleomagnetic evidence for en echelon crustal extension and crustal rotations in western Montana and Idaho
Authors: Doughty P. Ted , Sheriff Steven D.
Published: February 2008

The Bitterroot metamorphic core complex is one of many Eocene core complexes in the northern Cordillera. A middle Eocene dike swarm cuts the Bitterroot metamorphic core complex and its hanging wall, the Skalkaho slab. A 26° change in strike of the dikes across the core complex suggests either a refracted stress field or rotation during Eocene or younger extension. The nearby Bitterroot Valley and Big Hole Basin also indicate tectonic rotation. To distinguish between the hypotheses of refracted stress and tectonic rotation, we collected paleomagnetic data from 28 dikes. Nineteen sites provide reliable results. Eight sites from the hanging wall east of the mylonite zone give Dec = 46°, Inc = 69°, α95 = 13°; 11 dikes to the west yield Dec = 334°, Inc = 64°, α95 = 6°. The declinations diverge from the expected direction; the inclinations do not. The hanging wall rocks are rotated 58° ± 32° clockwise at the 95 % confidence level. The footwall shows 14° ± 11° of counterclockwise rotation. Both normal and reversed polarity dikes are present in each area, indicating that the dike swarms may adequately average paleosecular variation. Vertical contacts reveal that the dikes have not tilted since emplacement. These paleomagnetic results and available geochronologic data show that the Bitterroot dome was pulled from beneath the Skalkaho slab in the Eocene. As the dome slid toward the northwest, it experienced a slight counterclockwise rotation, while the upper plate moved clockwise around a vertical axis near its northern edge. Rotation of the Skalkaho slab occurs because the slab lies between en echelon extensional detachments of the core complex and the next basin to the east, the Big Hole Basin. The Boehls Butte area, north central Idaho, occupies a step in the Lewis and Clark fault zone and is probably a core complex related to right‐lateral motion on the fault system. Similarities in both the style and timing of extension suggest that Eocene ductile/brittle extension occupies a swath from British Columbia, past the Bitterroot metamorphic core complex, to the Pioneer core complex in south central Idaho.
Diachronous cleavage development in the Robertson Bay Terrane, Northern Victoria Land, Antarctica: Tectonic implications
Authors: Dallmeyer R. D. , Wright Thomas O.
Published: February 2008

The Robertson Bay terrane is the easternmost of three regional lithotectonic units comprising Northern Victoria Land. It is largely represented by a thick succession of Cambrian‐Ordovician distal turbidites (Robertson Bay Group), which has been folded into upright structures with development of an associated, regionally penetrative cleavage during maintenance of regionally uniform, low‐grade regional metamorphic conditions. Whole rock 40Ar/39Ar incremental‐release analysis of slate/phyllite documents diachronous cleavage development between ∼500 Ma (west) and 460 Ma (east) during the Ross orogeny. This systematic regional variation in age is consistent with tectonic models for the Ross orogeny that involve southwest directed subduction of the outboard Robertson Bay terrane beneath the Bowers terrane. Convergence rates of ∼0.4–1.0 cm/yr are suggested.
Large‐scale duplexes within the New Britain Accretionary Wedge: A possible example of accreted ophiolitic slivers
Authors: Bernstein‐Taylor Barrie L. , Kirchoff‐Stein Kimberly S. , Silver Eli A. , Reed Donald L. , Mackay Mary
Published: February 2008

A multichannel seismic line acquired in the western Solomon Sea images reflectors within the New Britain accretionary wedge which we interpret as accreted duplexes of the downgoing oceanic plate. The seaward edge of the largest duplex is located just 6 km from the toe of the accretionary wedge suggesting recent incorporation into the wedge. These data therefore provide an excellent opportunity to determine the dynamics of oceanic basement accretion. The oceanic basement is represented by a high‐amplitude, low‐frequency reflector that can be traced up to 40 km arcward of the toe of the accretionary wedge on several seismic lines in this survey. Another prominent reflector, similar in character to the basement reflector, lies approximately one second higher in at least one seismic section. This reflector is likely to be the top of a basement duplex. Structures imaged above the basement duplex define a preduplex accretionary wedge, whereas those at the toe indicate a new episode of postduplex accretion. We have tested this interpretation using both magnetic modeling and interval velocity analysis. Magnetic models of the wedge that include basement duplexes provide a good match to the observed magnetic data and provide limits on the size and interval velocities of the slivers. Interval velocities between the two strong reflectors, calculated using stacking velocities and constrained through magnetic modeling, exceed 5000 m/s and are consistent with our interpretation of ophiolitic slivers within the accretionary wedge.