bluuebunny/crossref_metadata_2025 huggingface dataset:
Nutrients, plankton, and productivity in a warm‐core ring in the western Gulf of Mexico
Authors: Biggs D. C.
Published: February 2008

Argos drift buoy trajectory data showed that a region of anticyclonic circulation about 100 km in diameter was present over the upper continental slope of the NW corner of the Gulf of Mexico in September–October, 1988. Guided by these data, Texas A&M University scientists joined by colleagues from Mexico's Direccion General de Oceanografia Naval surveyed the area from October 17–22 on R/V Gyre cruise 88G‐05 with a dense grid of conductivity‐temperature‐depth and expendable bathythermograph stations. The presense of a subsurface salinity maximum greater than 36.5 psu within the upper 150 m of this anticyclone indicated that it had originated as a warm‐core eddy of the Loop Current; however, a maximum of only 36.54 psu at σt = 25.5 in contrast to as much as 36.88 psu at this density surface in a “fresh” ring indicated that this feature had spent many months in the western gulf since its separation from the Loop Current. Biologically, the warm‐core ring was oligotrophic: its surface waters were generally depleted in nitrate to depths of more than 100 m, and chlorophyll standing stocks ( < 20 mg m−2), primary productivity ( < 0.4 mg C m−3 h−1), and Zooplankton biomass (only 4 mL 100 m−3 day and 6 mL 100 m−3 night in the upper 200 m) were all extremely low. Deployments of floating sediment traps within the feature on two consecutive days intercepted fluxes of only 10–20 mg dry weight m−2 d−1 at 50 m and at 100 m. By comparison, at ring periphery where there was measurable nitrate at 100 m (0.2–1 μg‐at. L−1), chlorophyll standing stocks and primary production in the surface mixed layer were 1.5–2 times higher.
Transient eddy formation around headlands
Authors: Signell Richard P. , Geyer W. Rockwell
Published: February 2008

Eddies with length scales of 1–10 km are commonly observed in coastal waters and play an important role in the dispersion of water‐borne materials. The generation and evolution of these eddies by oscillatory tidal flow around coastal headlands is investigated with analytical and numerical models. Using shallow water depth‐averaged vorticity dynamics, eddies are shown to form when flow separation occurs near the tip of the headland, causing intense vorticity generated along the headland to be injected into the interior. An analytic boundary layer model demonstrates that flow separation occurs when the pressure gradient along the boundary switches from favoring (accelerating) to adverse (decelerating), and its occurrence depends principally on three parameters: the aspect ratio [b/a], where b and a are characteristic width and length scales of the headland; [H/CDa], where H is the water depth, CD is the depth‐averaged drag coefficient; and [Uo/σa], where Uo and σ are the magnitude and frequency of the far‐field tidal flow. Simulations with a depth‐averaged numerical model show a wide range of responses to changes in these parameters, including cases where no separation occurs, cases where only one eddy exists at a given time, and cases where bottom friction is weak enough that eddies produced during successive tidal cycles coexist, interacting strongly with each other. These simulations also demonstrate that in unsteady flow, a strong start‐up vortex forms after the flow separates, leading to a much more intense patch of vorticity and stronger recirculation than found in steady flow.
Coastal‐trapped waves on the Labrador Shelf
Authors: Middleton John F. , Wright Daniel G.
Published: February 2008

Approximately nine months of bottom pressure data obtained from 10 sites on the Labrador Shelf are used to determine the amplitudes and origins of the three gravest coastal‐trapped wave modes. Using geostrophic wind data, the three waves driven by local wind forcing on the shelf are found to account for about 30% of bottom pressure variability in the spectral bands between 600 and 60 hours; Cape Chidley at the northern tip of the shelf is identified as a geographical origin. The amplitudes of the coastal‐trapped waves that are forced remotely from the shelf are also determined using all observations and the mode fitting technique of Haines et al. (this issue). The technique is here extended to determine the statistical relations between modal amplitude and forcing by remote wind stress and Hudson Bay atmospheric pressure; the latter can drive an oscillatory mass flux through Hudson Strait leading to coastal‐trapped wave generation. At low frequencies (600‐hour period) modes 1 and 2 are found to be of comparable magnitude, highly coherent and out of phase: results suggest that these modes originate from the scattering of a mode 1 wave, incident on an abrupt decrease in shelf depth at the northern tip of the shelf. The Kelvin wave is also found to be of comparable magnitude although incoherent with these modes, and the model so determined is shown to provide an excellent fit to the observations. At higher frequencies (86‐hour period) modes 1 and 2 and the Kelvin wave are found to have amplitudes in the ratio (1:⅕:½) that are consistent with theoretical expectations for wave generation by atmospheric pressure forcing over the Hudson Bay/Strait system. The model fit to the data is poorer than at low frequencies, notably at the southernmost sites across Hamilton Bank. Wave scattering by the abrupt saddles and banks on the shelf is thought to be severe at high frequencies and responsible for the poorer fit.
Infragravity waves in the deep ocean
Authors: Webb Spahr C. , Zhang Xin , Crawford Wayne
Published: February 2008

Energetic pressure fluctuations at periods longer than 30 s are a ubiquitous feature of pressure spectra from instruments sited on the deep seafloor in both the Atlantic and the Pacific oceans. We show these pressure fluctuations are caused by freely propagating ocean surface waves. The waves are generated in the near shore region along the entire coastline of an ocean basin through nonlinear transfer of energy from short‐period waves. This view contrasts with some earlier work, which described these long‐period pressure fluctuations as trapped waves tied to groups of short waves. We have constructed a model based on the average energy in the short (wind driven and swell) wave band along the North Atlantic coast to predict the energy in the long wave band at a site in the Atlantic. Maximum likelihood wave number‐frequency spectra calculated on data from an 11 element array in the North Pacific confirm that the long wave energy is confined to wave numbers corresponding to the surface gravity wave dispersion relation. We have used the wave number spectra to isolate particular regions of the Pacific Ocean which are sources of long wave energy. Energetic short‐period waves are incident on the coastline in these regions. Long waves are detected at the array which originate in the Gulf of Alaska, the northwestern Pacific, and at the southern tip of South America.
Seasonal and interannual variability of wind stress curl over the Nordic Seas
Authors: Jónsson Steingrímur
Published: February 2008

Over 32 years of wind data, which are based on surface pressure maps, from the Hindcast data base that has been developed by the Norwegian Meteorological Institute have been used to study the wind stress curl field, over the Nordic Seas. The mean wind stress curl pattern is characterized by very large values over most of the area, especially over the Greenland Sea. Within the framework of Sverdrup dynamics this gives rise to a cyclonic circulation in the area, with a maximum transport in the western boundary current of about 35 Sv. Only one gyre is present, and its center is situated between Jan Mayen and Greenland. The seasonal variation of the wind stress curl is very large, with almost negligible values during summer, from May through August. During September the wind stress curl starts to build up and has reached its full winter strength by November. This maximum is maintained until April, when it begins to decline to typical summer values. In order to study the spatial and temporal scales of the wind stress curl, an empirical orthogonal function analysis was performed on the wind stress curl after filtering it with a half‐power period of 50 days and then resampling the wind stress curl every 30 days. A Monte Carlo method is used to estimate the statistical significance of the various modes. The first 11 modes are found to be significant, and they represent 83.6% of the total variance of the data set. The first mode clearly shows the seasonal fluctuations of the mean wind stress curl pattern, representing the seasonal variation in the intensity of the Icelandic low. The next two modes show mostly interannual variability, with a decadal time scale. Most of these variations are happening in the northern part of the Greenland Sea. The other significant modes are mainly describing variability that is limited either in space or in time. A large part of this anomalous variability occurs in the 1980s.
South Atlantic interbasin exchange
Authors: Rintoul Stephen Rich
Published: February 2008

Hydrographic data and inverse methods are used to estimate the exchange of mass and heat between the South Atlantic poleward of 32°S and the neighboring ocean basins. The Antarctic Circumpolar Current (ACC) carries a surplus of intermediate water into the South Atlantic through Drake Passage, which is compensated by a surplus of deep and bottom water leaving the basin south of Africa. As a result, the ACC loses 0.25±0.18× 1015 W of heat in crossing the Atlantic. At 32°S the meridional flux of heat is 0.25±0.12×1015 W equatorward, consistent in sign but smaller in magnitude than other recent estimates. Attempts to force the system to carry a larger heat flux across 32°S led to unreasonable circulations. The meridional heat flux is carried primarily by an overturning cell in which the export of 17×106 m3 s−1 of North Atlantic Deep Water (NADW) is balanced by an equatorward return flow equally split between the surface layers, and the intermediate and bottom water. No input of warm Indian Ocean thermocline water is necessary to account for the equatorward heat flux across 32°S; in fact, a large transfer of warm water from the Indian Ocean to the Atlantic is shown to be inconsistent with the present data set. Together these results demonstrate that the global thermohaline cell associated with the formation and export of NADW is closed primarily by a “cold water path,” in which deep water leaving the Atlantic ultimately returns as intermediate water entering the basin through Drake Passage.
Ocean frontal variability in the Frontal Air‐Sea Interaction Experiment
Authors: Eriksen Charles C. , Weller Robert A. , Rudnick Daniel L. , Pollard R. T. , Regier Lloyd A.
Published: February 2008

Oceanographic observations during the Frontal Air‐Sea Interaction Experiment (FASINEX) in the Sargasso Sea indicate that upper ocean fronts in the subtropical convergence are strongly surface‐intensified coherent flow structures which have a preferred orientation and translation speed. Fronts grow as they propagate in this region such that currents roughly double in strength in a time that they translate by twice their width. While currents are dominated by geostrophic momentum balance, the Rossby number of these flows can reach a few tenths. Mixed layer water from the cold side of fronts appears to subduct under warm‐side near‐surface waters, since isolated lenses of water with cold‐side temperature and salinity characteristics are found embedded in the seasonal thermocline on the warm side of fronts. Although plausible vertical speeds were observed, no actual rates of subduction could be estimated. Typical frontal widths, temperature contrasts, horizontal currents, vertical shears, vertical currents, and translation speeds of fronts in the region studied are 20 km, 1°C, 0.5 m s−1, 0.005 s−1, 0.0005 m s−1, and 0.2 m s−1, respectively.
On the wave age dependent drag coefficient and roughness length at sea
Authors: Nordeng Thor Erik
Published: February 2008

The wave age dependent drag coefficient and roughness length at sea have been studied theoretically by using the simple Phillips spectrum with a wave age dependent Phillips coefficient. It is shown that the turbulent surface stress, which is computed in a reference frame moving with the surface waves according to Kitaigorodskii's ideas, leads to a wave age dependent Charnock constant in the range 0.010 to 0.022. The wave‐induced stress is computed by using well‐established empirical functions of wave growth and assuming that there is a cutoff frequency above which the atmospheric momentum goes to the turbulent stress only. This leads to a total surface stress depending on wave age such that the drag coefficient has a maximum for intermediate wave age numbers (∼10). The total surface stress (turbulent and wave induced) is used to compute an effective Charnock constant, which is found to vary from 0.012 to 0.085. The results are compared with published observations.
Backscattering by nonspherical particles: A review of methods and suggested new approaches
Authors: Bohren Craig F. , Singham Shermila Brito
Published: February 2008

Scattering of electromagnetic radiation near the backward direction is more sensitive to particle shape than scattering near the forward direction. Mie theory is therefore of dubious applicability to predicting backscattering by atmospheric particles known to be irregular or to inverting measurements on such particles. An irregular particle is one with an uncertain shape. In the face of uncertainty one must adopt a statistical approach in which scattering properties of ensembles are determined. To obtain ensemble averages, a basis is needed for averaging over a set of electromagnetic microstates. Ensemble averages based on the Rayleigh theory for small ellipsoids and on the T matrix method for spheroids agree better with measurements than Mie theory does. The coupled‐dipole method also provides a basis for ensemble averaging. This method also leads to a simple physical interpretation of why backscattering is so sensitive to particle shape and can be used to calculate scattering by one‐ and two‐dimensional analogs to three‐dimensional irregular particles.
A description of the correlated k distribution method for modeling nongray gaseous absorption, thermal emission, and multiple scattering in vertically inhomogeneous atmospheres
Authors: Lacis Andrew A. , Oinas Valdar
Published: February 2008

We describe a radiative transfer method for treating nongray gaseous absorption and thermal emission in vertically inhomogeneous multiple scattering atmospheres. We derive probability density distributions of absorption coefficient strength from line‐by‐line calculations to construct line‐by‐line and band model based k distributions. The monotonic ordering of absorption coefficient strengths in these k distributions implicitly preserves the monochromatic structure of the atmosphere at different pressure levels, thus simulating monochromatic spectral integration at a fraction of the line‐by‐line computing cost. The k distribution approach also permits accurate modeling of overlapping absorption by different atmospheric gases and accurate treatment of nongray absorption in multiple scattering media. To help verify the accuracy of the correlated k distribution method, we compare radiative cooling rates by atmospheric water vapor, CO2, and ozone against line‐by‐line calculations. The results show the correlated k distribution method is capable of achieving numerical accuracy to within 1% of cooling rates obtained with line‐by‐line calculations throughout the troposphere and most of the stratosphere.
Long‐term changes in the total ozone mapping spectrometer relative to world primary standard Dobson spectrometer 83
Authors: McPeters Richard D. , Komhyr W. D.
Published: February 2008

We have examined the stability of the calibration of the Nimbus 7 solar backscatter ultraviolet (SBUV) and total ozone mapping spectrometer (TOMS) instruments by comparing their ozone measurements with those made by a single, very stable Dobson instrument: the world primary standard Dobson spectrometer number 83. Measurements of ozone made with instrument 83 at Mauna Loa observatory in eight summers between 1979 and 1989 were compared with coincident TOMS ozone measurements. The comparison shows that relative to instrument 83, ozone measured by TOMS (and SBUV) was stable between 1979 and approximately 1983, had decreased by 3% by 1986, and had decreased by almost 7% by 1989. A similar time dependence is seen when data from an ensemble of 39 Dobson stations throughout the world is compared with TOMS over the period 1979–1987. The most likely reason for the relative drift is that the diffuser plate used by both SBUV and TOMS to measure solar flux has suffered an uncorrected wavelength dependent degradation, with most of the degradation occurring after 1983. The recently released version 6 TOMS data, corrected using the internal “pair justification” technique, show almost no drift relative to Dobson instrument 83. We conclude from these comparisons that accurate measurements of long‐term global ozone change will require a coherent system incorporating both ground based and satellite based ozone measurements.
Sources and sinks of methane in the African savanna. CH4 emissions from biomass burning
Authors: Delmas R. A. , Marenco A. , Tathy J. P. , Cros B. , Baudet J. G. R.
Published: February 2008

Sources and sinks of atmospheric methane are studied in savanna regions of west and central Africa. Flux measured over dry savanna soils, using static chambers, is always negative the average uptake rate being 2×1010 molecules/cm2/s. In these regions, sources are linked to biomass burning. Methane and CO2 emission from combustion of savanna plants and wood is studied by both field experiments and laboratory experiments using a combustion chamber. For savanna plants most of the carbon (85%) contained in the biomaterial is volatilized as CO2 and 0.1 to 0.25% as methane. For graminaceous plants like loudetia simplex the ratio C‐CH4/C‐CO2 is 0.11%; it is 0.28% for hyparrhenia the other main type of savanna plants and it attains 1.4% for the combustion of wood. In natural fire plumes this ratio is around 0.26% for savanna fires and 0.56 to 2.22% for forest fires. These results show that methane release is highly dependent on the type of combustion. Methane to CO2 ratios are also studied in vertical profiles in the troposphere taken during the TROPOZ I campaign, an aerial research expedition carried out over west Africa during the bushfire period. Within polluted layers, the average ratio of CH4 to CO2 excess over ambient air concentration is 0.34%. These results show that biomass burning in tropical Africa constitutes an important source of atmospheric methane estimated to about 9.2×106 T(CH4)/yr.
Impact of interannual variability (1979–1986) of transport and temperature on ozone as computed using a two‐dimensional photochemical model
Authors: Jackman Charles H. , Douglass Anne R. , Chandra Sushil , Stolarski Richard S. , Rosenfield Joan E. , Kaye Jack A. , Nash Eric R.
Published: February 2008

Eight years of NMC (National Meteorological Center) temperature and SBUV (solar backscattered ultraviolet) ozone data were used to calculate the monthly mean heating rates and residual circulation for use in a two‐dimensional photochemical model in order to examine the interannual variability of modeled ozone. Fairly good correlations were found in the interannual behavior of modeled and measured SBUV ozone in the upper stratosphere at middle to low latitudes, where temperature dependent photochemistry is thought to dominate ozone behavior. The calculated total ozone is found to be more sensitive to the interannual residual circulation changes than to the interannual temperature changes. The magnitude of the modeled ozone variability is similar to the observed variability, but the observed and modeled year to year deviations are mostly uncorrelated. The large component of the observed total ozone variability at low latitudes due to the quasi‐biennial oscillation (QBO) is not seen in the modeled total ozone, as only a small QBO signal is present in the heating rates, temperatures, and monthly mean residual circulation. Large interannual changes in tropospheric dynamics are believed to influence the interannual variability in the total ozone, especially at middle and high latitudes. Since these tropospheric changes and most of the QBO forcing are not included in our model formulation, it is not surprising that the interannual variability in total ozone is not well represented in our model computations.
Measurement of stratospheric distributions of H216O, H218O, H217O, and HD16O from far infrared spectra
Authors: Dinelli Bianca Maria , Carli Bruno , Carlotti Massimo
Published: February 2008

The stratospheric concentration profiles of H216O and of the isotopic species H218O, H217O, and HD16O, are retrieved from far‐infrared emission spectra recorded by a balloon‐borne Fourier transform spectrometer with 0.0035 cm−1 resolution. The retrievals were carried out using the global‐fit procedure on a statistically significant number of transitions for each isotope in the 40–85 cm−1 spectral region. The concentration and the relative mixing ratio distributions of each isotope are given along with the resulting isotopic ratios. A comparison of these results with the natural isotopic abundances shows that there is a depletion of up to 56±8% of the D‐containing isotope of water, while no significant deviation is obtained for the other isotopes within the error bars. A comparison of our results with previously reported measurements is also given.
Diabatic heating rate estimates from European Centre for Medium‐Range Weather Forecasts analyses
Authors: Christy John R.
Published: February 2008

Vertically integrated diabatic heating rate estimates (H) calculated from 32 months of European Centre for Medium‐Range Weather Forecasts daily analyses (May 1985–December 1987) are determined as residuals of the thermodynamic equation in pressure coordinates. Values for global, hemispheric, zonal, and grid point H are given as they vary over the time period examined. The distribution of H is compared with previous results and with outgoing longwave radiation (OLR) measurements. The most significant negative correlations between H and OLR occur for (1) tropical and northern hemisphere mid‐latitude oceanic areas and for (2) zonal and hemispheric mean values for periods less than 90 days. Largest positive correlations are seen in periods greater than 90 days for the northern hemispheric mean and continental areas of North Africa, North America, northern Asia, and Antarctica. The physical basis for these relationships is discussed. An interyear comparison between 1986 and 1987 reveals the El Niño‐Southern Oscillation signal.
Paleoenvironmental events during the last 13,000 years in the central Red Sea as recorded by pteropoda
Authors: Almogi‐Labin Ahuva , Hemleben Christoph , Meischner Dieter , Erlenkeuser Helmut
Published: February 2008

A high‐resolution record was obtained by investigating a sedimentary sequence from two cores taken in the central Red Sea (R/V Meteor cruise 5, leg 2). The numerical variations between nonmigratory and migratory pteropods and their stable isotopic record were studied together with variations in the carbonate and total organic carbon content in order to estimate changes in the structure of the water column during the last 13 kyr. The results indicate the existence of a highly stratified water column during deglaciation and early Holocene (13–8.5 ka). During this period the depth of the mixed layer varied between less than 50–100 m at most, and productivity was markedly reduced in comparison to the recent situation. The intermediate and deep water were constantly highly depleted in oxygen. A pronounced Younger Dryas event was recognized at 10.4 ka which coincides with an arid phase on the border land. The oxygenation of the intermediate water improved remarkably after 7.5 ka and peaked during the period between 4.6 and 2.0 ka. During this period the mixed layer reached its present depth and the productivity which was maximal during middle Holocene attained present level during the last 4.6 kyr.
Late Pleistocene/Holocene radiolarian and pollen records from sediments in the Sea of Okhotsk
Authors: Morley Joseph J. , Heusser Linda E. , Shackleton Nicholas J.
Published: February 2008

In two cores with oxygen isotope stratigraphy from the southern Okhotsk Sea, marine pollen and siliceous microfauna record concurrent late glacial through Holocene variations in regional terrestrial and marine environments. Glacial vegetation around the southern Okhotsk basin, which resembles the present tundra/steppe of the northwest coast of this marginal sea, yields to spruce‐dominated boreal forests during the glacial/interglacial transition. Temperate forest components, such as oak, peak during the mid‐Holocene. Decreasing oak accompanied by increasing spruce reflects the effect of global cooling on local vegetation during the last 4 kyr. Although the radiolarian fauna in the Okhotsk Sea samples is similar to that present in the northwest Pacific, the dominant species in both regions differ. Concentrations of radiolarians are low in latest glacial samples, with higher concentrations occurring above and below this interval. Cycladophora davisiana, the dominant radiolarian species in the majority of Holocene Okhotsk Sea sediments, is present at lower percentages in late glacial samples from our two sites. Thus, this species' Holocene/latest Pleistocene abundance pattern in Sea of Okhotsk sediments is the reverse of that recorded in high‐latitude open ocean sites. The combined marine pollen and radiolarian records indicate changes in the Sea of Okhotsk's physical oceanographic conditions and surrounding vegetation during the late glacial which were associated with this region's response to global climate change.
Block rotation and continental extension in Afar: A comparison to oceanic microplate systems
Authors: Acton Gary D. , Stein Seth , Engeln Joseph F.
Published: February 2008

The reorganization of oceanic spreading centers separating major plates often appears to occur by a process in which discrete microplates form and evolve by rift propagation. To see whether such microplate behavior has implications for continental rifting, we investigate the application of a microplate model to the Afar region at the Nubia‐Somalia‐Arabia triple junction. Studies of marine magnetic anomalies, volcanic ages, bathymetry, and seismicity suggest that the westward propagating Gulf of Aden spreading center has propagated into eastern Afar within the past 2 m.y., causing rifting and extension within the continent. We derive constraints on the extension history from the geometry and timing of rift formation and from paleomagnetic data indicating that Pliocene to Pleistocene age rocks have undergone a clockwise rotation of ∼11°. We suggest that the history of rifting, the rotation, and several other features of the regional geology can be described by combining features of an oceanic microplate model and the concept of rift localization previously proposed for Afar. In this scenario, motion occurring on several rifts within an extensional zone preceding the propagating spreading center is gradually transferred to a single rift. While motion is transferred, the overlap region between the growing and dying rifts acts as one or more microplates or blocks that rotate relative to the surrounding major plates. The rifting history and rotations in eastern Afar are thus related to the rift propagation and localization that occurs as the plate boundary evolves. Provided the constraints we use are appropriate, our model better describes the regional kinematics than alternative block models including one based on “bookshelf” faulting. If the tectonics of Afar are typical for continental breakup, they have interesting implications for the geometry of passive margins. In particular, asymmetric rifted margins can be produced if the final location of the rift axis is not at the center of the zone of initially disrupted lithosphere. Additionally, if the rate of rift propagation and the rate and location of rift localization are not uniform, then along‐axis structural variations will result.
Paleomagnetism of coastal California and Baja California: Alternatives to large‐scale northward transport
Authors: Butler Robert F. , Dickinson William R. , Gehrels George E.
Published: February 2008

Paleomagnetic data from the Santa Lucia‐Orocopia (SLOA) and Baja‐Borderland (BBA) allochthons of coastal California and Baja California have been interpreted to indicate up to 2500 km of post‐mid‐Cretaceous northward transport of these regions with respect to interior North America. However, with Neogene strike‐slip offsets taken into account, geological interpretations correlate basement rocks of the coastal allochthons with continental basement rocks directly across the San Andreas and related fault systems. We have examined paleomagnetic data from SLOA and BBA and conclude that apparent discordances can be explained without large‐scale pre‐Neogene tectonic transport. Three major observations are fundamental to this analysis: (1) Paleolatitudes derived from volcanic rocks of the Jurassic Eugenia Formation of BBA and Coast Range ophiolite of SLOA are concordant when compared to revised Jurassic reference paleomagnetic poles from interior North America. (2) Isotopic and paleobarometric data from the Peninsula Ranges batholith in southern California indicate that the batholith has been tilted northeast‐side‐up by an amount that can account for discordant paleomagnetic directions observed in plutonic rocks of the batholith without large‐scale northward transport. (3) Literal interpretation of the paleolatitudes determined from paleomagnetic directions in Upper Cretaceous and Paleogene marine sedimentary rocks of SLOA and BBA requires north‐then‐south‐then‐north transport and a complex motion history between the two allochthons. However, concordant paleolatitudes are indicated by some sedimentary rocks while coeval or younger sedimentary rocks of the same allochthon have discordant paleolatitudes. Coupled with recent documentations of compaction shallowing of paleomagnetic inclination in other marine sedimentary rocks, these inconsistencies suggest that paleolatitudes derived from most of the marine sedimentary rocks of SLOA and BBA are biased towards low paleolatitudes by compaction shallowing.
Reexamination of the O(3P→1D) excitation rate by thermal electron impact
Authors: Mantas George P. , Carlson Herbert C.
Published: February 2008

The theoretical and experimental electron impact excitation cross sections for the O(3P→1D) transition that have been reported in the literature the last two decades are used to derive O(3P→1D) excitation rates by thermal electron impact. The derived rates are represented by a simple parametric formula which should prove useful in atmospheric 6300‐Å airglow and electron gas thermal balance studies.
Variations of thermal electron energy distribution associated with field‐aligned currents
Authors: Abe Takumi , Okuzawa Takashi , Oyama Koh‐Ichiro , Fukunishi Hiroshi , Fujii Ryoichi
Published: February 2008

Relationships between thermal electrons and field aligned currents (FACs) in the auroral region have been investigated using data simultaneously obtained from the Thermal Electron Detector (TED) and the fluxgate magnetometer both onboard the EXOS‐D satellite. Several features resulted from the observations are summarized as; (1) At altitudes from 300 to 1800km, electron temperature in the upward FAC region is higher than that of the neighboring no FAC region by the increment ΔT=1100∼9500K, while the temperature is lower in the downward FAC region by the decrement −ΔT=500∼1500K. (2) The electron temperature increase in the upward‐current region grows with an increase of the FAC density. (3) The thermal electrons do not have Maxwell distribution in the upward‐current region at altitudes higher than about 2000km.
Propagation characteristics of Omega signals and their triggered emissions observed by EXOS‐D satellite
Authors: Sawada Akira , Kishi Youji , Yamamoto Masayuki , Sakurai Akihiro , Kasahara Yoshiya , Kimura Iwane
Published: February 2008

Omega signals have been frequently observed by the Japanese satellite EXOS‐D (Akebono) in the magnetosphere. We have statistically analyzed VLF‐WBA (wide‐band analyzer) data in a period of 6 months, which were acquired by Kagoshima (KSC) and Prince Albert (PA) satellite tracking stations. About a quarter of the data obtained at KSC contain Omega signals from Australia and about a sixth of the data at PA contain those from North Dakota. Ray tracing calculons for the Australian Omega signals are consistent with the results of observations. 10 cases of triggered emissions are also found in the analyzed data. Amplitude and phase characteristics along an Omega pulse are investigated for the triggering event and an apparent phase lead, corresponding to a frequency increase by about 10 Hz was found at the center frequency of signals after the triggering starts.
Ion burst event in the Earth's dayside magnetosheath
Authors: Paschalidis N. P. , Krimigis S. M. , Sarris E. T. , Sibeck D. G. , McEntire R. W. , Christon S. P. , Zanetti L. J.
Published: February 2008

The MEPA instrument on the AMPTE/CCE Spacecraft provided ion angular distributions as rapidly as every 6 sec for H, He, and O at energies of 10 keV to 2 MeV in the dayside magnetosheath whenever the solar wind pressure compressed the magnetopause within 8.75 RE, the CCE apogee. In this report we discuss a burst of energetic particles in the subsolar magnetosheath and its association with rapid changes in the local magnetic field direction in such a way that the magnetic field connected the spacecraft to the magnetopause during the enhancement. We find that magnetosheath angular distributions outside the burst peaked at 90° pitch angles, whereas during the burst they exhibited field aligned streaming either parallel or antiparallel to the magnetic field combined with a clear earthward gradient. The clear earthward gradients at E ≥ 10 KeV, the streaming, and the slope change in the burst‐time magnetosheath spectrum at ∼10 KeV suggest magnetospheric source for the burst‐time ≥10 KeV ions and heated solar wind for E < 10 KeV.
Free air gravity anomalies associated with glacial isostatic disequilibriu: Load history effects on the inference of deep mantle viscosity
Authors: Mitrovica J. X. , Peltier W. R.
Published: February 2008

The free air gravity anomaly over Canada, which has been associated with glacial isostatic disequilibrium, has traditionally been an important datum in the inference of deep mantle viscosity. In this study we investigate the sensitivity of the inference on the assumed space and time dependent geometry of the Laurentide ice sheet. We find, in particular, that the computed peak anomaly is extremely sensitive to the timing of the final ice sheet collapse at the centre of Laurentia; a fact which has not previously been fully appreciated or quantified. As an example, the deep mantle viscosity preferred on the basis of a deglaciation model which maintains an equilibrium plastic profile can differ by a factor of four from that obtained using a model with the same maximum thickness but a fixed ice sheet perimeter. Furthermore, discrepancies in the inference of deep mantle viscosity can reach orders of magnitude when certain commonly used models of the deglaciation process are adopted.
A simplified spring‐block model of earthquakes
Authors: Brown Stephen R. , Scholz Christopher H. , Rundle John B.
Published: February 2008

The time interval between earthquakes is much larger than the actual time involved during slip in an individual event. We have used this fact to construct a cellular automaton model of earthquakes. This model describes the time evolution of a 2‐D system of coupled masses and springs sliding on a frictional surface. The model exhibits power law frequency‐size relations and can exhibit large earthquakes with the same scatter in the recurrence time observed for actual earthquakes.
Cosmic‐ray produced neon in Antarctic rocks
Authors: Graf Th. , Kohl C. P. , Marti K. , Nishiizumi K.
Published: February 2008

We studied three Antarctic rocks and quartz separates thereof for their records of cosmic‐ray produced 21Ne. All three samples reveal an excess of 21Ne and in two of them a cosmic‐ray origin is documented by the spallation ratios 22Ne/21Ne. 3He is shown to be incompletely retained in quartz (<10%). Previous studies have shown the suitability of quartz as a monitor for cosmic‐ray produced radionuclides 10Be and 26Al, and therefore as a tracer for geological processes. 26Al/10Be ratios allow the calculation of minimum exposure ages and maximum erosion rates, and measured ratios 21Ne/10Be and 21Ne/26Al add significant information to exposure histories, especially in the case of a complex exposure. This information is necessary for an evaluation of erosion rates and to define geological processes, such as uplift and variations in the Antarctic ice cover.
Large‐amplitude pressure oscillations in the western Mediterranean
Authors: Monserrat Sebastian , Ramis Clemente , Thorpe Alan J.
Published: February 2008

Pressure oscillations with unusually large amplitude of some 3 mb and periods of about 50 min have been registered in the Balearic Islands (western Mediterranean sea) during summer 1989. These large pressure oscillations are maintained over several hours and have been recorded on several occasions. The synoptic pattern and vertical structure of the atmosphere simultaneous with these oscillations is described. The large amplitude waves described here do not appear to be directly related to convective activity. Some of the characteristics of these waves are described, however, their source mechanism remains unclear.
A two dimensional shock capturing, hydrodynamic model of the Venus ionosphere
Authors: Nagy A. F. , Körösmezey A , Kim J. , Gombosi T. I.
Published: February 2008

A two‐dimensional, time‐dependent, shock capturing single‐species (O+) hydrodynamic model of the Venus ionosphere, which solves the coupled continuity, momentum and energy equations for the altitude range of 150–500 km and the solar zenith angle range of 0°–180° has been developed and is presented in this paper. It was again demonstrated that the introduction of topside heat inflows leads to calculated dayside electron and ion temperatures, which are consistent with the measured values. In order to reproduce the measured electron temperatures, which are roughly constant over all SZA's, the heat inflows had to be reduced significantly over the nightside compared to the dayside values. The calculated transterminator ion flows are supersonic and relatively close to the observed average values. The model predicts a deceleration shock at a SZA of about 135°, consistent with the ion temperature and velocity observations.
Wellbore heat flow from the Toa Baja Scientific Drillhole, Puerto Rico
Authors: Anderson Roger N. , Larue David K.
Published: February 2008

Heat Flow values, determined from temperature logs and estimates of thermal conductivity from geophysical logs range from 23 to 37 mW/m2 from 800 to 2500 m depth in the Toa Baja scientific drillhole on the north, central coast of Puerto Rico. Near the target seismic reflector at the base of the well, an active hydrothermal system was encountered in which heat flow of up to 90 mW/m2 was found in a mineralized zone beneath a volcanic sill or flow. The heat flow then dropped to 50 mW/m2 beneath this subhorizontal flow zone. The mining of heat from downdip is proposed to account for this thermal anomaly, as well as the scatter in the heat flow determined from the few other wells drilled into Puerto Rico. The time‐temperature history of the well indicates that Eocene volcaniclastics of the lower 2 km were deposited into a geothermal gradient of 60°C/km north of an active arc (heat flow estimated to have been 120–180 mW/m2). Uplift, erosion and cooling occurred between 40 and 30 Ma. Reburial and deposition of Oligocene‐Miocene Limestones produced the present‐day geothermal gradient of 15 °C/km (heat flow of 30–50 mW/m2). Based upon comparisons with slab cooling models, the crustal thickness beneath Puerto Rico is estimated to be closer to continental than oceanic.
Carbon and oxygen stable isotopes in the Toa Baja Well, Puerto Rico: Implications for burial diagenesis and hydrocarbon generation
Authors: González Luis A.
Published: February 2008

The Toa Baja Well was drilled on the coastal plains of northern Puerto Rico with a total depth of 2705 m [Larue, 1990]. Interstratified limestone, quartz‐bearing calcareous sandstones, and shales dominate the uppermost 580 m and are separated from underlying rocks by an unconformity. Below this unconformity continuing to total depth, lithologies encountered consist of volcaniclastic sandstones/siltstones, pelagic carbonates, volcanic flows and either plutonic rocks or coarse‐grained immature sandstones derived from plutonic bodies.

Stable isotopic data of carbonates suggest diagenetic modification under a meteoric and meteoric‐marine mixing environments for sediments above 915 m. A fracture zone near 915 m coincides with an abrupt shift in δ18O compositions indicating the presence of hotter fluids during alteration of these sediments. The depleted δ13C signatures occurring above a fault at 1220 m are suggestive of isotopically light gaseous hydrocarbons migrating through the fault and being oxidized as they dispersed through the sediment column. The abrupt shift in δ18O compositions and its coincidence with the fracture zone at 915 m suggest geopressuring and thermal buildup due to accumulation of hotter, upward migrating formational fluids. Estimated burial temperatures for the interval above 915 m do not exceed 40°C and are possibly lower due to circulating colder meteoric fluids. Maximum estimated burial temperatures for sediments below 915 m range from 80° to a a maximum of 150°C at 2400 m. The data suggests that the bulk of the sediment pile has not been exposed to temperatures above the oil window and possibly hydrocarbons have been generated deeper in the basin.
The Toa Baja Drilling Project, Puerto Rico: Scientific drilling into a non‐volcanic island arc massif
Authors: Larue D. K.
Published: February 2008

The Toa Baja Drilling Project was a broad, interdisciplinary experiment to document the in situ geology and geophysics of a non‐volcanic island arc massif. This overview provides a brief summary of oil exploration on Puerto Rico that lead up to the present investigation, and summarizes some of the problems addressed by drilling.
Upstream waves in Saturn's foreshock
Authors: Cattaneo M. B. Bavassano , Cattaneo P. , Moreno G. , Lepping R. P.
Published: February 2008

Waves in the foreshock of Saturn have been studied using data from the plasma and magnetic field experiments onboard Voyager 1. The appearance of the waves, in the plasma as well as in the magnetic field data, is related to magnetic connection of the spacecraft to the bow shock. Their relative amplitude ΔB/B lies between 0.3 and 0.8 and their period in the spacecraft frame is ∼500 s. The waves are elliptically polarized and propagate at ∼30° to the average magnetic field direction.
The relative permeabilities of quartzites and schists during active metamorphism at mid‐crustal levels
Authors: Chamberlain C. Page , Conrad Mark E.
Published: February 2008

The ‘hot spot’ near Bristol, New Hampshire was an area of high fluid flow during metamorphism. In order to determine the mechanisms of fluid flow through the area, we made a detailed study of the δ18O values of quartz from an outcrop of interlayered quartzites and schists. Results indicate that the permeability of the quartzite was very low in comparison to that of the schist.

The δ18qtz values from schist layers are remarkably homogenous (15.5–15.8), in contrast to the δ18qtz values of schist units outside of the hot spot, which vary widely. Quartz veins that cut the quartzites and pinch out in the schists have the same δ18O values (15.7) as quartz from the schists. In the quartzites, δ18qtz values immediately adjacent to the veins and schists are similar to those in the veins and schists, but decrease by ∼1 permil in the centers of the layer.

We interpret these results to indicate that fluid flow in the hot spot was mainly through the schists and fractures in the quartzites. The oxygen isotope exchange fronts in the quartzites prove that there was some flow from the the schists and the fractures into the quartzites. Comparisons of the shapes of these exchange fronts with exchange fronts predicted by two different models of fluid flow in rocks indicate that fluid transport in the quartzite was predominantly by advection and that the kinetic rates of isotope exchange were fast relative to the advective velocity of the fluid infiltrating the system. Considering the slow rate of oxygen isotope exchange between quartz and a fluid, this implies that fluid flow from the schist and vein fracture into the quartzite was extremely limited.
Geochronological evidence for tectonically driven brine migration during the Early Proterozoic Kheis Orogeny of southern Africa
Authors: Duane Michael J. , Kruger F. Johan
Published: February 2008

The 2.1–1.9 Ga Kheis orogeny on tne western margin of the Kaapvaal Craton of Southern Africa induced regional heating, tilting and extensive fluid flow which isotopically reset and altered rocks and minerals of older Proterozoic formations and parts of the Archean cratonic basement. This tectonic event is recognised in the Ar, Rb‐Sr, Pb‐Pb and U‐Pb (zircon) geochronological and palaeomagnetic studies on the Transvaal and underlying basement rocks.
Crustal‐scale fluid transport: Magnitude and mechanisms
Authors: Torgersen Thomas
Published: February 2008

Fluids in the crust of the Earth play an important role in the geochemical and geophysical structure of the crust. They are responsible for a multitude of chemical/rock reactions and couple directly with geophysical processes and the geophysical imaging of the crust. The known depth of significant fluid reaction/transport has been increasing in recent years with the detailed study of drilled and exhumed solid phase samples. From both isotopic and chemical evidence, it is clear that meteoric fluids can penetrate at least 10 kilometers into the crust of the Earth (fluids have also been sampled directly from a depth of 12 km in the Kola Peninsula Drillhole) and the horizontal scale of fluid transport is now known to extend 100's of kilometers. Furthermore, as the kinetics and reaction dynamics (rather than simple equilibrium)are included to explain these observations, estimates of the fluid volumes (expressed as a water/rock ratio)required to emplace these fluid derived rock suites and deposits have increased steadily.
Percolation networks and fluid transport in the crust
Authors: Gueguen Yves , David Christian , Gavrilenko Pierre
Published: February 2008

Percolation networks are useful tools to investigate transport properties at various scales in heterogeneous media. They consist of conductances distributed over a geometrical network. Transport properties depend on the topology, on the type of distribution functions and on the connectivity of these networks. Two examples of applications are presented at two different scales: the first one is the pressure dependence of permeability in rocks and the second one is the fracture density variation through the crust The model suggests that the existence of fractal networks of fractures could result from the fact that natural media are close to a threshold.
use of apparent complex frequencies of free oscillations to estimate aspherical structure of the Earth
Authors: Shibata Naoki , Suda Naoki , Fukao Yoshio
Published: February 2008

A formula is developed to relate observed apparent complex frequencies of a multiplet to the interaction coefficients of the splitting matrix. This formula is then incorporated into an inversion scheme: estimating the interaction coefficients from the observed apparent complex frequencies. The numerical experiments demonstrated an excellent predictability of our method both in data (apparent complex frequencies) space and in model (aspherical structure of elasticity and anelasticity) space.