bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of bed level change in a saturated surf zone
Authors: Saulter A. N. , Russell P. E. , Gallagher E. L. , Miles J. R.
Published: May 2003

Sonar altimeter measurements of bed level change were made in conjunction with instantaneous measurements of sea surface elevation and currents at a fixed position in a saturated surf zone (water depths less than 1 m). Two types of bed behavior were observed, classified as “progressive,” where mean bed level showed a steady increase or decrease with time, and “oscillatory,” where the bed level took a periodic motion (amplitudes 0.5–1.5 cm, periods 10–30 min). “Mixed” combinations of the two behaviors were also observed. Comparisons between bed behavior and a wave‐based mobility number parameter (Ψ) observed oscillatory beds for Ψ < 40 and mixed behavior for 40 < Ψ < 80, suggesting that bed level oscillations were due to the presence of small‐scale migratory bedforms (ripples). Bed oscillations were suppressed with increased wave energy, such that progressive bed behavior was observed when 80 < Ψ. The increase in mobility numbers associated with progressive beds was due to the presence of an energetic infragravity component (Euig/Eui > 1 and Euig > 0.05 m2s−2) and strong mean current (>0.1 ms−1). A fractal analysis of the bed level time series was used to test the hypothesis that the process of ripple migration is nonlinear (“self‐organised”) rather than a direct response to variations in the forcing component. For low wave energy conditions, when ripples were observable (oscillatory and mixed time series), values of the Local Hurst Exponent (0 < HL < 1) suggested fractal behavior at ripple migration timescales, indicating that the process by which ripples migrate is nonlinear and is allowed to flourish when the hydrodynamic forcing is weak.
On the wave age dependence of wind stress over pure wind seas
Authors: Drennan William M. , Graber Hans C. , Hauser Danièle , Quentin Céline
Published: May 2003

Data from five recent field campaigns are selected for pure wind sea, deep water, and fully rough flow conditions. The combined data set includes a wide range of wave ages, with high variability in both friction velocity and wave phase speed. These data, which are expected to follow Monin‐Obukhov similarity scaling, are used to investigate the influence of wave age on wind stress. The relationship between the dimensionless roughness and inverse wave age is found to be zo/σ = 13.4 (u*/cp)3.4, where zo is the surface roughness length, σ is the standard deviation of the surface elevation, u* is the friction velocity, and cp is the wave phase speed at the peak of the spectrum. This relationship, which represents a significant dependence of roughness on wave age, was obtained using a procedure that minimizes the effects of spurious correlation in u*. It is also shown to be consistent with the wave age relationship derived using an alternate form of the dimensionless roughness, namely, the Charnock parameter zog/u*2, where g is the gravitational constant.
An assessment of the effect of sea surface surfactant on global atmosphere‐ocean CO2 flux
Authors: Tsai Wu‐ting , Liu Kon‐Kee
Published: May 2003

We assess the possible impact of the distribution of naturally occurring surfactants on the direct integration of the global atmosphere‐ocean CO2 flux across the ocean surface. The global atmosphere‐ocean CO2 flux is calculated using the monthly mean ΔpCO2 climatology compiled by Takahashi et al. [1997] as well as satellite wind speed and sea‐surface temperature data. In the absence of any global map of surfactant coverage and as it is known that phytoplankton exudates and degradation products are the major sources of marine surfactants, ocean primary productivity, which can be derived from the satellite‐based estimate of chlorophyll concentration, is used as an indicator of the presence of surfactants as proposed by Asher [1997]. From the calculated results it is found that suppression of the upward and downward CO2 fluxes by marine surfactants exhibits an asymmetric effect: The average percent reduction of absorption flux by surfactants is about twice that of outgassing, which results in an overall decrease in the net global CO2 uptake by the oceans. For almost half of the year (between January and May) the presence of surfactants does not affect CO2 outgassing from global oceans. In contrast, throughout the entire year the presence of surfactants suppresses CO2 absorption by the oceans. The major reduction in absorption fluxes occurs in the northern Pacific and Atlantic (10°N to 70°N) in all seasons and in the Southern Ocean (south of 40°S) in austral spring and summer. However, the most significant decrease in outgassing fluxes occurs in the equatorial and southern Pacific Ocean (40°S to 10°N), particularly in the eastern equatorial and subtropical waters off the southern American coast, in the period of austral spring and summer. Annual net CO2 flux is reduced by approximately 20% under the surfactant coverage condition that the primary productivity is above a threshold value of 25 g‐C m−2 mom−1 and by about 50% with a threshold of 15 g‐C m−2 mom−1.
Synoptic imaging of nearshore bathymetric patterns
Authors: Clarke L. B. , Werner B. T.
Published: May 2003

A new technique for near real‐time optical imaging of surf zone morphology, synoptic imaging, implemented at Scripps Beach, La Jolla, California, permits simultaneous measurements of the time‐varying position of individual linear and lunate megaripples, fields of bed forms, rocks, cobble patches, beach steps and sandbars, and troughs. A varying threshold filter for brightness is applied to video frames sampled at 1 Hz to remove pixels corresponding to surface foam and suspended bubbles or sediment. Remaining fragments of the video frames are averaged over time intervals generally ranging from 5 to 10 min to produce images of the surf zone sand bed. To facilitate accurate measurement of the position of sand bed features, these images are enhanced to increase feature visibility, transformed to plan view, and corrected for refraction using surveyed bathymetry and tide level. Contrast in the images results from differences in water depth, shading variations from tilted bed surfaces, and changes in bed material. The surveyed positions of megaripples and sandbars correspond to the positions of persistent features in the images. A ray path model quantifying sand bed contrast as a function of water depth, angle of line‐of‐sight, and light attenuation coefficient in water predicts that for the Scripps Beach field site, bed forms with height as small as 0.03–0.2 m can be detected in water depths up to 2.5 m, in accord with observations, and that visibility can be improved by changing the line of sight toward overhead viewing. Bed visibility is reduced by persistent surface foam and water turbidity generated by waves with period <8 s and height exceeding 1.5 m. Example images showing transitions between linear and lunate megaripples, location of megaripple crestlines, and the interaction between sandbars, bed form fields, and cobble patches illustrate the potential of synoptic imaging.
A study of tropical cyclone influence on the generation of internal tides
Authors: Davidson Fraser J. M. , Holloway Peter E.
Published: May 2003

An investigation is made into modifications of the semidiurnal internal tide on the Western Australian Shelf by a passing tropical cyclone. Current mooring observations are presented, taken during the passage of Tropical Cyclone Bobby (1995) over these mooring locations. The observations reveal large vertical excursions at near‐inertial frequency of the isotherm during and following the cyclone's passage. This coincides with diminishing semidiurnal baroclinic tides. To gain dynamical insight into the observations, a fully three‐dimensional, free surface, nonlinear, hydrostatic model is applied to the Western Australian Shelf. The model is initialized with realistic stratification and forced by representative tides and cyclone winds. The wind‐forcing is derived from an idealized analytical cyclone model prescribed from observed cyclone track and central pressure data, and the tidal forcing allows for the generation of internal tides. The cyclone modifies stratification by turbulent mixing, upwelling/downwelling and density advection up or down the shelf slope. This results in significant changes to internal tide characteristic paths and hence the internal tide generation process on the continental slope. Mixing is enhanced over the shelf due to shallow topography with respect to the shelf slope region creating a strong density front at the shelf edge. Observations and modeling show that the water column response to the cyclone passage is most abrupt in shallow water at 125 m, then at 300 m depth. The model reproduces the main features of the observed inertial oscillations concomitant with the dampening of M2 internal tides after the passage of the cyclone.
A radiometric calibration for the Clementine HIRES camera
Authors: Robinson Mark S. , Malaret Erick , White Travis
Published: May 2003

We have successfully characterized the Clementine HIRES multispectral sensor entirely from inflight measurements. Relative calibration is obtained through dark subtraction (additive) and sensor spatial nonuniformity (multiplicative) on a pixel‐by‐pixel basis. Relative residuals from frame‐to‐frame are typically less than 1%. Absolute coefficients are obtained through comparisons with calibrated Clementine UVVIS images acquired nearly simultaneously with HIRES sequences. Residuals between the coregistered UVVIS and HIRES calibrated images are typically 5% but may be as high as 20%. The residual is found most likely to be the result of increased scattered light in the UVVIS relative to the HIRES. Application of the calibration allows for seamless mosaicking of monochromatic and color sequences aiding in interpretation of surface features of the Moon at the scale of about 25 m/pixel. The calibrated HIRES color sequences represent the highest resolution spectral image data of the Moon.
Crustal attributes of lunar basins from terrain‐correlated free‐air gravity anomalies
Authors: Potts Laramie V. , von Frese Ralph R. B.
Published: May 2003

For the major lunar basins between ±64° latitude, uncompensated mass components as well as crustal ring and transient cavity attributes were evaluated from the free‐air anomaly components of the Lunar Prospector gravity model (LP75G) that are spectrally correlated at 100‐km altitude with the gravity effects of the Clementine terrain model (GLTM‐2). Inversion of the terrain‐correlated anomalies inferred incipient radial adjustments of the Moho that equilibrate the basin topography, assuming the lunar crust is mainly compensated by thickness variations. Nearly all nearside multiring basins are marked by mascon gravity anomalies that reflect mass concentrations from superisostatic mantle plugs plus mare fill. Farside basins, by contrast, are mostly characterized by maslite gravity anomalies from mass deficiencies due to subisostatic mantle plugs with marginal or no mare fill. The preponderance of maslites on the farside is consistent with crust that responded more rigidly to impacts than the nearside crust, which had a higher thermal gradient due to enhanced abundances of radioactive elements in the nearside mantle and crust. However, the extended thermal evolution of the lunar lithosphere also may have promoted the development of interfering mascon and maslite effects for tectonically complicated regions like the farside Freundlich‐Sharonov basin. The Moho adjustments also revealed well‐defined concentric zones of maxima and minima about the central basins that are strongly correlated with photogeologically inferred basin rings. In addition, the innermost zero‐contour of the radial adjustments provides an effective estimate for the diameter of the transient cavity. The inferred transient cavity diameters correlated negatively with crustal thickness for basins with superisostatic mantle plugs and positively with the relative ages of the nearside basins. On the farside, superisostatic mantle plugs apparently developed in thinner crust up to thicknesses of about 30 km, whereas in thicker crust mantle plugs developed only to subisostatic levels. For the nearside, mass balance calculations between the equilibrium mantle plug and excavated basin materials support the proportional scaling relation of roughly 0.1 for the excavation depth‐to‐diameter ratio of the transient cavity that photogeologic studies have obtained. However, for the Serenitatis and Imbrium basins with possibly atypical nearside crustal properties, this proportionality may overestimate excavation depths by 28% and 37%, respectively. For nearside and farside basins apparently lacking mare flooding, shallow excavation depths were also inferred.
Numerical simulations of shock attenuation in solids and reevaluation of scaling law
Authors: Mitani Noriko K.
Published: May 2003

In order to reevaluate the scaling law on impact fragmentation, attenuation of shock waves induced by impact events is numerically simulated in two‐dimensional axial symmetry using the cubic interpolation propagation method in wide stress regime: not only the regime where targets respond plastically, but also the regimes where shock stresses are comparable to the Hugoniot elastic limit (HEL) of target materials. As a constitutive equation of state for brittle materials that lose the strength, we newly propose a “brittle model” based on experimental data. Comparing our results with previous studies on shock attenuation, an “elastic‐plastic regime” in the vicinity of HEL where the attenuation becomes rapid is newly found. We calculate the antipodal stresses normalized by the dynamic compressive strength through simulations for some previous impact experiment data using rocks and ices and reevaluate a scaling law of the impact fragmentation. The results suggest that the description of the fragmentation process that the largest fragment is mainly produced by the tensile waves emanated from the free surface at the antipodal point is plausible.
An n = 90 internal potential function of the Martian crustal magnetic field
Authors: Cain Joseph C. , Ferguson Bruce B. , Mozzoni David
Published: May 2003

A potential function using spherical harmonics up to degree and order 90 was derived from a selection of Mars Global Surveyor vector data. These included all three components of those taken below 200 km altitude during the two aerobraking phases (AB1 and AB2), the Science Phase Orbits (SPO), and the higher‐altitude (367–435 km) data taken on the nightside during the Mapping Phase Orbits (MPO). The merger of these sets of data provided total global coverage. The technique used was a least squares minimization developed for Earth field analysis whereby the relative weighting of each data source was determined by the width of a Gaussian fit to the residual distribution about the potential function. Also, data selection by area and area weight functions were used to improve normalization. The residual misfit distributions for the vertical component for different data sources are (nT) AB1, 6.5; AB2 (in shadow), 6.7; AB2 (sunlit), 10.3; SPO, 6.4; and MPO, 5.9. The horizontal component misfits are about the same for MPO and AB2 in shadow, but for data taken in sunlight the scatter of horizontal component residuals increases by 50% for AB1, a factor of two for SPO, and 30% for AB2. The energy density spectrum evaluated at 3535 km radius (the mean altitude of the AB and SPO data) decreased from a high of 0.2 J/km3 near n = 20 to an order of magnitude less at n = 90. Most of the power in the spectrum lies between n = 15 and n = 40. The dipole moment was only 8 × 1016 A · m2, which is likely close to the noise of the coefficients. This spectrum is 40 times greater than that of Earth at the scale sizes represented by values of n from 20 to 40. Comparisons with other published maps and models for Mars show general agreement with the field representations at MPO altitudes, but disagreements up to several hundred nT in components calculated for areodetic altitudes below 200 km.
A 0.55‐Ma paleotemperature record from the Subantarctic zone: Implications for Antarctic Circumpolar Current development
Authors: Becquey Sabine , Gersonde Rainer
Published: May 2003

Estimates of summer sea surface temperatures (SSSTs) derived from planktic foraminiferal associations using the Modern Analog Technique and combined with isotopic analyses and determination of ice‐rafted debris, mirror the Pleistocene evolution of the planktic Subantarctic surface waters in the Atlantic Ocean. The SSSTs indicate that the isotherms that define the modern polar front zone and Subantarctic front, were located at more northerly latitudes (up to 7°) during most of the investigated period, which covers the past 550 kyr. Exceptions are during climatic optima in the early Holocene, at marine isotope stages (MIS) 5.5, 7.1, 7.5, 9.3, and presumably during MIS 11.3 when SSSTs exceeded modern values by 1°–5°C. The close similarity between the SSST and the Vostok temperature indicates strong regional temperature correlation. Both records show that MIS 9.3 was the warmest period during the last 420 kyr whereas SSSTs obtained for MIS 11.3 are overestimated due to strong carbonate dissolution. Spectral analysis corroborates that the initiation of warming in southern high latitudes heralds the start of deglaciation on the Northern Hemisphere.
Sedimentary phosphorus record from the Oman margin: New evidence of high productivity during glacial periods
Authors: Tamburini Federica , Föllmi Karl B. , Adatte Thierry , Bernasconi Stefano M. , Steinmann Philipp
Published: May 2003

The northern region of the Arabian Sea is one of the biologically most fertile regions of the world oceans, with present productivity rates varying between 150 and 2500 mgC/m2 × day [Madhupratap et al., 1996]. This is related to the influence of the southwesterly summer monsoon which causes vigorous upwelling along the Oman margin. Upwelling ceases during northeasterly winter monsoon activity; productivity rates, however, remain relatively high (about 800 mgC/m2 × day), related to deep water mixing [Madhupratap et al., 1996]. The goal of this study is to verify if during the last glacial period, a period in which winter monsoon conditions prevailed, productivity rates were similarly high. With an analysis of phosphorus phases, stable nitrogen isotopes, organic matter content, and bulk mineralogy of the upper 10 m of the cores of ODP Hole 724C (corresponding to the last 140,000 years, sample resolution is ∼5 kyr), we provide new evidence of high productivity during this last glacial period (marine isotopic stages 2, 3, and 4). This was probably related to the combined effect of (1) increased eolian input of iron‐containing dust due to dryness on the adjacent continent and stronger winter monsoon, and (2) regeneration and diffusion of dissolved phosphorus from the sediments to the water column due to variations in the position and intensity of the Oxygen Minimum Zone. These findings suggest that there is no one‐to‐one relationship between summer monsoon activity and productivity, which emerges to be a quasi‐persistent phenomenon across glacial and interglacial stages.
Plasma theory of solar radar echoes
Authors: Mel'nik V. N.
Published: May 2003

Radar scattering by the ion‐sound turbulence accompanied by Type III Langmuir turbulence is considered. It is shown that such scattering explains reflections from heights >1.6R0 observed by James [1966, 1970].
Simultaneous MST radar and radiosonde measurements at Gadanki (13.5°N, 79.2°E) 2. Determination of various atmospheric turbulence parameters
Authors: Ghosh A. K. , Jain A. R. , Sivakumar V.
Published: May 2003

A campaign of one month simultaneous MST radar and radiosonde observations has been carried out from a tropical station Gadanki (13.5°N, 79.2°E) in India during summer monsoon season (July–August). The observed signal spectral width by radar, temperature and pressure by radiosonde are made use to estimate the various atmospheric turbulence parameters such as eddy dissipation rate (ε), vertical eddy diffusivity (Kh), inner scale size (l0) and buoyancy scale length (LB) in troposphere and lower stratosphere between 4–20 km. Applicability of the correction to the observed spectral width due to beam, shear and transience broadening is examined for the present series of measurements using Indian MST radar. The correction due to shear broadening of spectral width is noticed to be significant. The height structure of turbulence parameters from these measurements shows some distinct features. These features are discussed in terms of the observed background atmospheric parameters and magnitude of various turbulence parameters compared with those reported in literature and discussed in detail.
Scintillations of centimeter waves and the atmospheric irregularities from radio occultation data
Authors: Yakovlev Oleg I. , Matyugov Stanislav S. , Anufriev Vladimir A.
Published: May 2003

The analysis of field strength fluctuations of radio waves in the wavelength band λ = 2 cm of radio occultation measurements between orbital station MIR and a geostationary satellite is presented. Examples of field strength E dependences on altitude H0 of the ray path are given. We find two types of fluctuations connected to turbulence and stratified formations in the atmosphere. The RMS deviations of field strength are investigated as function H0 for both types. The frequency spectra of the field strength scintillation G(F) are analyzed to determine a spectral index n and characteristic frequency of fluctuations F0 for different minimum altitudes of the ray path H0. It is shown that the troposphere at H0 < 7 km in the high‐frequency part of the spectrum is described by a function G(F) ∼ F−n, where the spectral index n on average is equal to 2.5, which corresponds to the theoretical value for the Kolmogorov spatial spectrum. In the stratosphere at H0 = 15–35 km the mean value n equals 3.6, and only in 13% of the cases there are spectra that are in agreement with the Kolmogorov law. At the basis of the analysis of the connection between the spatial spectrum of the refractive index fluctuations and the frequency spectrum of field strength fluctuations, we discuss the application of the radio occultation technique for investigation of the atmospheric inhomogeneities.
D.O.R.T. method as applied to electromagnetic subsurface sensing
Authors: Micolau G. , Saillard M.
Published: May 2003

The decomposition of the time reversal operator (D.O.R.T.) method allows detection and localization of point‐like scatterers through a very simple and robust process. Here, with the aim of applying this method to the detection and the localization of buried objects, we focus on the influence of the restriction of the measurements to a line of receivers. The finite size of the objects is also taken into account, as well as losses in the embedding medium. A simple behavior of the time reversal operator is exhibited, almost independent of the polarization, which permits one to detect scatterers in the resonance domain, with very low ambiguity. Experimental data obtained in an anechoïc chamber confirm our theoretical predictions.
Pressure drawdown well tests in fractured porous media
Authors: Bogdanov I. I. , Mourzenko V. V. , Thovert J.‐F. , Adler P. M.
Published: May 2003

A general three‐dimensional numerical model for single‐phase, slightly compressible flow through fractured porous media is introduced. It is based on a discrete fracture representation. Applications to the simulation of pressure drawdown well tests are presented, for complex situations where the well intercepts a random fracture network with various fracture densities and conductivities. The well pressure response can be modeled as a function of its interconnectivity with the fracture network.
Extension of a temperature effects model for capillary pressure saturation relations
Authors: Grant Steven A.
Published: May 2003

A series expression describing the effect of temperature on capillary pressure saturation relations was derived from the chemical thermodynamics of interfaces. Most systems studied could be described well by truncations of the series expression that retained one or two parameters. The one‐parameter expression was appropriate for describing capillary pressures of soils experiencing modest changes in temperature. Thevan Genuchten [1980] equation modified with the one‐parameter expression could be fitted precisely to 36 of 41 water‐air capillary pressure saturation relations determined at more than one temperature. The residuals of the fitted equation were unaffected by degree of saturation. The one‐parameter expression could describe equally well the effect of temperature on capillary pressures of homogeneous synthetic and natural heterogeneous porous media, for which a theoretical explanation was proposed. Asymptotic standard errors of the estimates for nonlinear regression analysis for the one‐parameter expression fitted to water‐oil and water‐NAPL systems were of the order of the parameters themselves. This lack of fit may be more due to the wide temperature ranges studied for many of the water‐oil and water‐NAPL systems than the nature of the nonwetting phase. The two‐parameter expression was appropriate for systems, such as petroleum reservoirs, subjected to pronounced changes in temperature. When compared to nonlinear regression fits to the one‐parameter model, fits of van Genuchten's equation modified with the two‐parameter expression generally reduced the errors of the parameter estimates but yielded only slight improvement in the mean square errors of the predicted values. A theoretical derivation indicates that the one‐parameter expression should be appropriate also to describe the effect of temperature on the capillary pressures in very dry soils.
Representation of the carbon cycle in box models and GCMs: 1. Solubility pump
Authors: Toggweiler J. R. , Gnanadesikan A. , Carson S. , Murnane R. , Sarmiento J. L.
Published: May 2003

Bacastow [1996], Broecker et al. [1999], and Archer et al. [2000] have called attention recently to the fact that box models and general circulation models (GCMs) represent the thermal partitioning of CO2 between the warm surface ocean and cold deep ocean in different ways. They attribute these differences to mixing and circulation effects in GCMs that are not resolved in box models. The message that emerges from these studies is that box models have overstated the importance of the ocean's polar regions in the carbon cycle. A reduced role for the polar regions has major implications for the mechanisms put forth to explain glacial ‐ interglacial changes in atmospheric CO2. In parts 1 and 2 of this paper, a new analysis of the ocean's carbon pumps is carried out to examine these findings. This paper, part 1, shows that unresolved mixing and circulation effects in box models are not the main reason for box model‐GCM differences. The main factor is very different kinds of restrictions on gas exchange in polar areas. Polar outcrops in GCMs are much smaller than in box models, and they are assumed to be ice covered in an unrealistic way. This finding does not support a reduced role for the ocean's polar regions in the cycling of organic carbon, the subject taken up in part 2.
Can CFCs be used to determine anthropogenic CO2?
Authors: Matear R. J. , Wong C. S. , Xie L.
Published: May 2003

From model simulations of the uptake of CFC‐11, CFC‐12 and anthropogenic CO2, we investigate the method of using CFC‐derived water ages to determine the anthropogenic CO2 accumulation in the ocean. The CFC age method is best suited to water younger than 30 years where CFC water ages are most reliable. For water younger than 30 years, the CFC‐12 and CFC‐11 age method can estimate the global 1980–1990 accumulation of anthropogenic CO2 to within 10% and 22%, respectively. With the exception of the Southern Ocean south of 50°S and the equatorial upwelling areas, these CFC‐derived estimates of the water column inventory of anthropogenic CO2 are within 10% of the simulated values. Our results suggest that the CFC age method provides another way of determining the accumulation of anthropogenic CO2 in the ocean. We applied the CFC age method to observed CFC data to estimate the accumulation of anthropogenic CO2 in the North Pacific (20°N–65°N) between 1980 and 1990. For water younger than 30 years the CFC‐derived estimate of accumulation is 1.1 Gt C. In comparison, the estimate from the simulated CFC distribution is 1.3 Gt C. Our model simulation overestimated the accumulation north of 40°N and underestimated the penetration of anthropogenic CO2 into the subtropical gyre. From the observed CFC data we estimate the anthropogenic CO2 uptake by the North Pacific to be 1.1 Gt C/yr for the 1980s.
Four years' observations of terrestrial lipid class compounds in marine aerosols from the western North Pacific
Authors: Kawamura K. , Ishimura Y. , Yamazaki K.
Published: May 2003

In order to understand the long‐range atmospheric transport of terrestrial organic matter over the open ocean, marine aerosol samples were collected on a biweekly basis from 1990 to 1993 in a remote island, Chichi‐Jima, in the western North Pacific. The samples were analyzed for lipid class compounds using a capillary gas chromatography (GC) and GC/mass spectrometry (GC/MS). A homologous series of n‐alkanes (C20‐C40), alcohols (C13‐C34), fatty acids (C9‐C34) and α,ω‐dicarboxylic acids (C7‐C28) were detected in the aerosol samples. Distributions of n‐alkanes (0.17–14 ngm−3, average 1.7 ngm−3) are characterized by a strong odd‐carbon number predominance (CPI ratios, average 4.5) with a maximum at C29 or C31, indicating that n‐alkanes are mainly derived from terrestrial higher plant waxes. Fatty alcohols (0.19–23 ngm−3, average 2.0 ngm−3) show an even‐carbon number predominance with a maximum generally at C26 or C28, again indicating a contribution from terrestrial higher plants. On the other hand, fatty acids (2.5–38 ngm−3, average 14 ngm−3) show a bimodal distribution with two maxima at C16 and C24 or C28. Lower molecular weight fatty acids (generally <C20) that are mainly derived from marine organisms showed higher concentrations in summer. In contrast, higher molecular weight fatty acids (C21‐C34) derived from terrestrial higher plants, together with C25‐C35 alkanes, C20‐C34 alcohols and C20‐C28 dicarboxylic acids, generally showed higher concentrations in winter to spring seasons. This seasonal trend is most likely interpreted as atmospheric transport of terrestrial organic matter from Asian continent in winter/spring, when westerly winds dominate over the western North Pacific. Backward trajectory analyses supported the long‐range atmospheric transport of higher plant‐ and soil‐derived organic matter from the Asian continent over the Pacific Ocean. This study also suggested that the atmospheric transport is the main pathway for the terrestrial lipid compounds that are abundantly present in the deep‐sea sediments in the Central Pacific.
Representation of the carbon cycle in box models and GCMs, 2, Organic pump
Authors: Toggweiler J. R. , Murnane R. , Carson S. , Gnanadesikan A. , Sarmiento J. L.
Published: May 2003

Box models of the ocean/atmosphere CO2 system rely on mechanisms at polar outcrops to alter the strength of the ocean's organic carbon pump. GCM‐based carbon system models are reportedly less sensitive to the same processes. Here we separate the carbon pumps in a three‐box model and the GCM‐based Princeton Ocean Biogeochemistry Model to show how the organic pumps operate in the two kinds of models. The organic pumps are found to be quite different in two respects. Deep water in the three‐box model is relatively well equilibrated with respect to the pCO2 of the atmosphere while deep water in the GCM tends to be poorly equilibrated. This makes the organic pump inherently stronger in the GCM than in the three‐box model. The second difference has to do with the role of polar nutrient utilization. The organic pump in the GCM is shown to have natural upper and lower limits that are set by the initial PO4 concentrations in the deep water formed in the North Atlantic and Southern Ocean. The strength of the organic pump can swing between these limits in response to changes in deep‐water formation that alter the mix of northern and southern deep water. Thus, unlike the situation in the three‐box model, the organic pump in the GCM can become weaker or stronger without changes in polar nutrient utilization.
Distribution and storage of soil organic carbon in China
Authors: Wu Haibin , Guo Zhengtang , Peng Changhui
Published: May 2003

Surface soils hold the largest terrestrial organic carbon pool, although estimates of the world's soil organic carbon storage remain controversial, largely due to spatial data gaps or insufficient data density. In this study, spatial distribution and storage of soil organic carbon in China are estimated using the published data from 34,411 soil profiles investigated during China's second national soil survey. Results show that organic carbon density in soils varies from 0.73 to 70.79 kg C/m2 with the majority ranging between 4.00 and 11.00 kg C/m2. Carbon density decreases from east to west. A general southward increase is obvious for western China, while carbon density decreases from north to south in eastern China. Highest values are observed in forest soils in northeast China and in subalpine soils in the southeastern part of the Tibetan Plateau. The average density of ∼8.01 kg C/m2 in China is lower than the world's mean organic carbon density in soil (∼10.60 kg C/m2), mainly due to the extended arid and semi‐arid regions. Total organic carbon storage in soils in China is estimated to be ∼70.31 Pg C, representing ∼4.7% of the world storage. Carbon storage in the surface organic horizons which is most sensitive to interactions with the atmosphere and environmental change is ∼32.54 Pg C.
CO2 emissions from liming of agricultural soils in Brazil
Authors: Bernoux Martial , Volkoff Boris , Carvalho Maria da Conceição S. , Cerri Carlos C.
Published: May 2003

This paper presents a first estimation of net CO2 fluxes from liming of agricultural soils in Brazil for the period 1990–2000. The calculation was based on the methodology proposed by the IPCC, but separately conducted for the five administrative Brazilian regions. The summarized annual CO2 emission for Brazil varied from 4.9 to 9.4 Tg CO2 yr−1 with a mean CO2 emission of about 7.2 Tg CO2 yr−1. The South, Southeast and Center region accounted for a least 92% of total emission. Neglecting the emissions from organic soils, the CO2 fluxes from soils (reported under the category 5‐D in the National Inventories of Greenhouse Gas Emission) amounted an updated value of around 51.9 Tg CO2 yr−1 for the period 1975–1995. Uncertainties, projection and other correlated fluxes related with liming are briefly discussed.
Hawaiian lava flows in the third dimension: Identification and interpretation of pahoehoe and ′a′a distribution in the KP‐1 and SOH‐4 cores
Authors: Katz Melissa G. , Cashman Katharine V.
Published: May 2003

Hawaiian lava flows are classified as pahoehoe or 'a'a by their surface morphology. As surface morphology reflects flow emplacement conditions, the surface distribution of morphologic flow types has been used to study the evolution and eruptive history of basaltic volcanoes. We extend this analysis to the third dimension by determining the distribution of flow types in two deep drill cores, the Scientific Observation Hole‐4 (SOH‐4) core, drilled near Kilauea's East Rift Zone (ERZ), and the pilot hole (Kahi Puka‐1 (KP‐1)) for the Hawaiian Scientific Drilling Project (HSDP), drilled through distal flows from Mauna Loa and Mauna Kea. Flows are classified using both internal structures and groundmass textures, with the latter useful when identification based on mesoscopic flow features (e.g., surface morphology and vesicle content and distribution) is ambiguous. We then examine the temporal distribution of pahoehoe and ′a′a flows in proximal (SOH‐4) and distal (KP‐1) settings. Sequence analysis shows that the two flow types are not randomly distributed in either core but instead are strongly clustered. The proximal SOH‐4 core is dominated by thin pahoehoe flows (∼60% by volume), consistent with the common occurrence of surface‐fed pahoehoe flows in near‐vent settings. The distal KP‐1 core has a high proportion of ′a′a (∼58% by volume), although the proportion of pahoehoe and ′a′a varies dramatically throughout the Mauna Kea sequence. Thick inflated pahoehoe flows dominate when the drill site was near sea level, consistent with the numerous inflated pahoehoe fields on the current coastal plains of Kilauea and Mauna Loa. ′A′a flows are abundant when the site was far above sea level. As slope increases from the coastal plains to Mauna Kea's flank, this correlation may reflect the combined effect of long transport distances and increased slopes on flow emplacement. These results demonstrate that flow type and thickness variations in cores provide valuable information about both vent location and local site environment. Observed variations in flow type within the KP‐1 core raise interesting questions about feedback between volcano evolution and flow morphology and suggest that flow type is an important variable in models of volcano growth and related models for lava flow hazard assessment.
Adaptive whole Earth tomography
Authors: Sambridge Malcolm , Faletič Rado
Published: May 2003

An approach for seismic tomography is presented which allows the parameterization to be refined during the inversion. The objective is to use the data to refine the mesh and the velocity model together, and hence both are considered part of the solution. Some simple rules are used to identify the volumes of a three‐dimensional model in need of refinement. The self‐adaptive parameterization is applied to an initial mesh built from uniformly distributed spherical triangles and Delaunay tetrahedra. Application of the technique to a typical summary ray P‐wave arrival time data set shows it to be both feasible and practical for large scale whole Earth tomography. A noticeable trend in the resulting models, as the parameterization is refined, is the thinning of the Farallon and Tethys subduction features imaged in the mid mantle, together with an increase in amplitude of the velocity perturbation.
Testing the tracer ratio method for modeling active compositional fields in mantle convection simulations
Authors: Tackley Paul J. , King Scott D.
Published: May 2003

Tracer methods are attractive for modeling compositional fields because they offer the potential of zero numerical diffusion. Composition is typically taken to be proportional to the absolute local concentration of tracers, but an increasingly popular method is to have “dense” and “regular” tracers with composition being equal to the local fraction of “dense” tracers. This paper tests this “ratio” method using established benchmarks and by comparing the performance of the two tracer methods and grid‐based methods for simulating the long‐term evolution of a convecting mantle with a thick, dense, stable layer. For this scenario the ratio method is found to have several advantages, giving sharp, stable long‐term layering with no tracer settling, minimal statistical “noise” and low entrainment, even with only ∼5 tracers per cell. The method is equally applicable to finite volume and finite element treatments of the underlying flow. Entrainment in grid‐based advection methods is heavily dependent on resolution and numerical details, and is reduced ∼1 order of magnitude by the filter proposed by A. Lenardic. Numerical determination of physically correct entrainment rates remains a challenging problem. Comparing tracer and grid based methods, the spatial pattern of the thermal and chemical fields appear to be converging on the finest grids; however the estimated entrainment differs significantly.
Recycling oceanic crust: Quantitative constraints
Authors: Stracke Andreas , Bizimis Michael , Salters Vincent J. M.
Published: May 2003

Recycled ancient oceanic crust with variable amounts of aging, or inclusion of sediments of differing types and origins has often been invoked as a source for present‐day ocean island basalts (OIB), but the current evidence remains largely qualitative. Previous quantitative modeling has shown that much has to be learned in order to better understand the implications of crustal recycling on mantle heterogeneity. Here, we present new model calculations incorporating recent constraints on subduction‐zone processes and the composition of subducted sediments. Modeled compositions of the recycled oceanic crust vary widely as a function of the recycling age and composition of the oceanic crust. HIMU‐type sources can only be created by recycling igneous oceanic crust if it has undergone substantial modification during subduction. Although the required modifications are qualitatively consistent with dehydration processes in subduction zones, the many uncertainties prevent a precise estimate of the isotopic composition of ancient recycled igneous crust. Inclusion of sediments increases the isotopic variability and although the resulting Sr and Nd isotopic signatures can be similar to enriched mantle (EM) signatures, the Pb isotopic composition of EM‐type OIB is difficult to reconcile with the presence of sediment in their sources. The large variability of modeled compositions of the subducted crust suggests that if mantle heterogeneity is largely formed by crustal recycling, each OIB is likely to have a unique isotopic composition resulting from specific combinations of composition, age and subduction modification of the subducted crust. Given the variability of the recycled components, a small number of relatively well‐defined enriched compositions can only be explained if either the subduction processing of oceanic crust is a far better defined process than observation would seem to indicate, or, the intramantle disaggregation and mixing of compositionally diverse recycled materials is surprisingly efficient.
PaleoMac: A Macintosh™ application for treating paleomagnetic data and making plate reconstructions
Authors: Cogné J. P.
Published: May 2003

This brief note provides an overview of a new Macintosh™ application, PaleoMac, (MacOS 8.0 or later, 15Mb RAM required) which permits rapid processing of paleomagnetic data, from the demagnetization data acquired in the laboratory, to the treatment of paleomagnetic poles, plate reconstructions, finite rotation computations on a sphere, and characterization of relative plate motions. Capabilities of PaleoMac include (1) high interactivity between the user and data displayed on screen which provides a fast and easy way to handle, add and remove data or contours, perform computations on subsets of points, change projections, sizes, etc.; (2) performance of all standard principal component analysis and statistical processing on a sphere [Fisher, 1953] etc.); (3) output of high quality plots, compatible with graphic programs such as Adobe Illustrator, and output of numerical results as ASCII files. Beyond its usefulness in treating paleomagnetic data, its ability to handle plate motion computations should be of large interest to the Earth science community.
Geochemistry and origin of the basal lherzolites from the northern Oman ophiolite (northern Fizh block)
Authors: Takazawa Eiichi , Okayasu Toshie , Satoh Keiichi
Published: May 2003

Abundances of major and trace elements in whole rocks and minerals in lherzolites and harzburgites from the northern Oman ophiolite are used to understand the mantle processes creating compositional variation in oceanic lithospheric mantle. Detailed mapping shows that lherzolites occur near the base of a mantle section in the northern Fizh block. Geochemical analyses identify two types of basal lherzolite. The first type (Type I lherzolite) displays porphyroclastic microstructure and occurs sporadically in the basal mylonite zone. Whole rock and clinopyroxene are highly depleted in incompatible elements such as Na, Ti, Zr, and rare earth elements (REE). The chondrite‐normalized patterns of Type I lherzolites show steep slopes from heavy REE (HREE) to light REE (LREE) that are ascribed to melt extraction, up to 12–18%, from a source containing a small amount of garnet. The chondrite‐normalized patterns have slight enrichment in LREE relative to the patterns expected for residues of partial melting thereby indicating reaction with a LREE‐enriched melt or fluid at a low melt/rock ratio. The second type (Type II lherzolite) shows mylonitic microstructure and only occurs at the contact between the mantle section and the metamorphic sole. Abundances of incompatible elements in whole rocks and clinopyroxenes are greater than those of Type I lherzolites, and clinopyroxenes in Type II lherzolites have high Na2O contents (>1 wt.%). To a first approximation, the high Na content of clinopyroxenes and whole rocks and the LREE‐depleted, chondrite‐normalized whole rock REE patterns are consistent with Type II lherzolite being in equilibrium with a mid‐ocean ridge basalt (MORB)‐type melt at relatively high pressure (>2 GPa). However, the flatness of chondrite‐normalized patterns for middle and heavy REE are inconsistent with residual garnet peridotite. The characteristics of Type II lherzolites are better explained by a mixing process in which residual peridotite was refertilized by addition of a LREE‐depleted melt. The large compositional gradient near the basal thrust in the northern Fizh block may have recorded a transient state in which the degree of partial melting was progressively decreased as a result of reducing mantle temperature and upwelling rate. This scenario is consistent with the inferred failing ridge associated with a transform zone in the western side of the northern Fizh block proposed by Nicolas et al. [2000]. In the detachment stage of the Oman ophiolite, a small amount of ascending melt may have crystallized near the basal part of mantle section thereby forming Type II lherzolites. Basal lherzolites and their spatial chemical variations in the northern Fizh block may provide a key for understanding the processes of ridge segmentation and detachment at fast spreading ridges.
Orbital and suborbital climate variability in the Sulu Sea, western tropical Pacific
Authors: Oppo D. W. , Linsley B. K. , Rosenthal Y. , Dannenmann S. , Beaufort L.
Published: May 2003

A detailed record of planktic δ18O from a sediment core in the Sulu Sea, located between the South China Sea and the western Pacific warm pool, reveals that for the past 400 kyr (1 kyr = 1000 years), δ18O variability on orbital timescales is similar to that caused by changes in ice volume alone. This result indicates that in the Sulu Sea, temperature‐driven changes in planktic δ18O on orbital times scales were generally compensated for by the effects of sea level and changes in seasonal monsoon intensity on the local freshwater budget, as well as by other changes in the tropical hydrologic cycle and their attendant effects on surface water δ18O. Increased freshening of the western tropical Pacific warm pool is reminiscent of La Niña conditions. However, we argue that the mean tropical climate state was not more La Niña‐like than today on broader spatial scales. Suborbital variability occurred in the Sulu Sea throughout the past 400 kyr, suggesting little sensitivity to ice volume or to glacial‐interglacial changes in tropical hydrology. Variations on 4–10 kyr timescales appear to be linked to those in the North Atlantic region, suggesting a common forcing of that variability. We suggest that Sulu Sea salinity variations were a response to suborbital climate variability in the North Atlantic region, transmitted via changes in the intensity of the East Asian summer monsoon. We suggest that a North Atlantic origin of that tropical suborbital variability can be reconciled with weak glacial amplification in the tropics if the tropical response is nonlinear.