bluuebunny/crossref_metadata_2025 huggingface dataset:
Model‐guided Lagrangian observation and simulation of mountain polar stratospheric clouds
Authors: Wirth M. , Tsias A. , Dörnbrack A. , Weiß V. , Carslaw K. S. , Leutbecher M. , Renger W. , Volkert H. , Peter T.
Published: December 2003

Gravity‐wave‐induced polar stratospheric clouds (PSCs) were observed over the Scandinavian mountains by airborne lidar on January 9, 1997. Guided by the forecasts of a mesoscale dynamical model, a flight path was chosen to lead through the coldest predicted region parallel to the wind at the expected PSC level (23–26 km). Because of the nearly stationary nature of the wave‐induced PSC the individual filaments visible in the backscatter data of the clouds can be interpreted as air parcel trajectories. Assuming dry adiabatic behavior and fixing the absolute temperature to the ice frost point in the ice part of the cloud enables detailed microphysical simulations of the whole life cycle of the cloud particles. Optical calculations are used to adjust open parameters in the microphysical model by optimizing the agreement with the multichannel lidar data. This case is compared with former work from the Arctic winter 1994/1995. The influence of the stratospheric H2SO4 content and the cooling rate on the type of cloud particles (liquid ternary solution droplets or solid nitric acid hydrates) released from the ice part of the cloud is evaluated.
Characteristics of marine boundary layers during two Lagrangian measurement periods: 1. General conditions and mean characteristics
Authors: Wang Qing , Suhre Karsten , Krummel Paul , Siems Steve , Pan Linlin , Bates Timothy S. , Johnson James E. , Lenschow Donald H. , Heubert Barry J. , Kok Gregory L. , Schillawski Richard D. , Prévot Andre S. H. , Businger Steven
Published: December 2003

Two sets of Lagrangian measurements were made during the southern Aerosol Characterization Experiment (ACE1) south of Tasmania, Australia, in December 1995. This paper intends to provide an overview of the general conditions encountered during the two intensive observational periods. The measurements by the NCAR C‐130 provide the main data set for this study. We also use the sea surface temperature obtained from the R/V Discoverer and the European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses field for the large‐scale divergence field. Emphases of the paper are on the atmospheric and oceanic environment and the boundary layer mean structure during the six flights in the two Lagrangian measurement periods. The large scale features, such as variations of sea surface temperature, synoptic conditions, and large‐scale velocity fields, are discussed. These large‐scale environments had significant influences on boundary layer turbulence and the inversion structure. The boundary layer mean structure and its evolution along the Lagrangian trajectory are also studied using two‐dimensional cross‐section plots of vertical and horizontal (along the flight track) variation of potential temperature, water vapor, wind components, and ozone concentration. The most prominent feature of the boundary layer is the two‐layered structure observed throughout Lagrangian B and during the last flight of Lagrangian A. The two layers have detectable differences in potential temperature, water vapor, and, to a lesser extent, ozone concentration. These differences make it necessary to study the exchange between the two layers. Low‐level cloud structure and cloud microphysics are also discussed. We emphasize, though, that the results on cloud fractions should be used with caution due to the variable nature of the cloud bands observed during ACE1.
Intercomparison of airborne and surface‐based measurements of condensation nuclei in the remote marine troposphere during ACE 1
Authors: Weber R. J. , McMurry P. H. , Bates T. S. , Clarke A. D. , Covert D. S. , Brechtel F. J. , Kok G. L.
Published: December 2003

Intercomparisons of aerosol particle number concentrations measured with various condensation particle counters (CPCs) during the first Aerosol Characterization Experiment (ACE 1) are made to assess the accuracy of the airborne measurements. When no ambient 3–10 nm diameter particles (nanoparticles) were present, median concentrations from four CPCs on the National Center for Atmospheric Research (NCAR) C‐130 aircraft agreed to within ∼6% and were highly correlated (r>0.9). These instruments sampled from several different inlets and used various arrangements (e.g., tubing size and length, flow rates) to transport sampled air to the detectors. When the ambient aerosol contained significant numbers of nanoparticles, agreement between the CPCs deteriorated, likely from differences in nanoparticle transmission and detection efficiencies. During these periods, average total number concentrations measured by two ultrafine CPCs varied on average by 60% with a correlation coefficient of 0.85. Intercomparisons of airborne and surface‐based measurements were made during low‐altitude flybys of surface measurement sites. During flybys, few nanoparticles were detected, and measured total condensation nuclei (CN) concentrations differed by roughly +5 to −20% (CNsurface/CNairborne−1) suggesting that the airborne measurements of fine aerosols agreed with ambient surface values to within 20%. Overall, we found that ambient fine particles (∼20–100 nm diameter) are fairly insensitive to airborne sampling techniques and thus are likely to be measured accurately. Sampling losses of smaller particles, however, may lead to a significant undermeasurement of ambient CN concentrations in rare instances when the number spectra are dominated by the smallest particles. This intercomparison involves measurements made in regions absent of liquid water to avoid artifact particles produced by fragmenting water droplets.
Statistical estimation of locations of lightning events
Authors: Pensky Marianna , Cannon John R.
Published: December 2003

In this paper, a statistical approach to the retrieval of lightning locations is proposed for the first time. This novel approach views the errors of the time measurements as random variables rather than unknown numbers. The unknown location (x, y, z) as well as the standard deviation σ of the errors are treated as unknown parameters of a statistical model and are estimated using the maximum likelihood estimation (MLE) technique. On the basis of Monte Carlo simulations these statistical estimators are compared with the least squares estimators (LSE), as well as the solutions of the system of linear equations proposed by Koshak and Solakiewicz [1996]. Although the method is general, the Lightning Detection and Ranging (LDAR) system currently used at the Kennedy Space Center is chosen as a model for simulations. Simulations show that the MLE always gives better precision than the LSE technique. Also, it is demonstrated that if the time measurements are fairly accurate and a thunderstorm takes place in the neighborhood of the measuring sites (the distance is less than 80 km), the MLE significantly improves the accuracy of the solutions of the system of linear equations.
Hypervelocity impact experiments on aerogel dust collector
Authors: Kitazawa Yukihito , Fujiwara Akira , Kadono Toshihiko , Imagawa Kichiro , Okada Yutaka , Uematsu Kazuo
Published: December 2003

Laboratory hypervelocity impact experiments were conducted to verify the performance of aerogel dust collectors used for gathering meteoroids and space debris in the near‐Earth environment and to derive the relationships of various parameters characterizing the projectile with morphology of tracks left by the penetrating projectile in the aerogel collector pad. Silica aerogel collectors of 0.03 g/cm3 density were impacted at velocities ranging from 1 to 14 km/s with projectiles of aluminum oxide, olivine, or soda‐lime glass, with diameters ranging from 10 to 400 μm. At impact velocities below 6 km/s the projectiles were captured without fragmentation by the aerogel collector and, in many instances, without complete ablation even at 12 km/s. The shapes and dimensions of the penetration tracks left in the aerogel collector were correlated with the impact parameters, and the results permitted derivation of a series of equations relating the track dimensions to incoming projectile size, impact energy, and other projectile parameters. A simplified model, similar to meteor‐entry phenomena, was used to predict the trends in experimental penetration track lengths and the diameters of captured projectiles.
Geology of the Upheaval Dome impact structure, southeast Utah
Authors: Kriens Bryan J. , Shoemaker Eugene M. , Herkenhoff Ken E.
Published: December 2003

Two vastly different phenomena, impact and salt diapirism, have been proposed for the origin of Upheaval Dome, a spectacular scenic feature in southeast Utah. Detailed geologic mapping and seismic refraction data indicate that the dome originated by collapse of a transient cavity formed by impact. Evidence is as follows: (1) sedimentary strata in the center of the structure are pervasively imbricated by top‐toward‐the‐center thrust faulting and are complexly folded as well; (2) top‐toward‐the‐center normal faults are found at the perimeter of the structure; (3) clastic dikes are widespread; (4) the top of the underlying salt horizon is at least 500 m below the surface at the center of the dome, and there are no exposures of salt or associated rocks of the Paradox Formation in the dome to support the possibility that a salt diapir has ascended through it; and (5) planar microstructures in quartz grains, fantailed fracture surfaces (shatter surfaces), and rare shatter cones are present near the center of the structure. We show that the dome formed mainly by centerward motion of rock units along listric faults. Outcrop‐scale folding and upturning of beds, especially common in the center, are largely a consequence of this motion. We have also detected some centerward motion of fault‐bounded wedges resulting from displacements on subhorizontal faults that conjoin and die out within horizontal bedding near the perimeter of the structure. The observed deformation corresponds to the central uplift and the encircling ring structural depression seen in complex impact craters.
Effects of the redistribution of water in the solar nebula on nebular chemistry
Authors: Cyr Kimberly E. , Sharp Christopher M. , Lunine Jonathan I.
Published: December 2003

We quantify the effects on solar nebula chemistry of variations in the C to O ratio brought on by diffusive and advective redistribution of water vapor. The SOLGASMIX chemical equilibrium code was used to compute abundances of nebular elements and major molecular species, C, N, S and others, for a variety of water‐depleted nebular settings produced by the water distribution models, and for low‐ and high‐pressure (10−5 and 10−3 atm) nebulae. Both relatively oxidizing and reducing nebular conditions can occur across 0.1–5 AU, varying over time. This variety of conditions may help explain the variation in oxidation state of meteorites. Additionally, abundances of organics increase over what would be expected to form from a solar composition gas. Modest increases occur in a relatively oxidizing nebula assuming a solar C/O ratio of 0.42, while large increases of several orders of magnitude occur in a more reducing nebula with solar C/O of 0.6. The increase in organics in the inner nebula could have allowed local accretion of organics to the terrestrial planets, and perhaps supplied organics to the Jovian planetesimal formation region and beyond via outward mixing processes. Lastly, nebular water could have been directly supplied to Earth and the other terrestrial planets via icy body drift and scattering.
Spectrophotometry of Saturn's small satellites and rings from Hubble Space Telescope images
Authors: Poulet François , Karoschka Erich , Sicardy Bruno
Published: December 2003

We investigate the photometric properties of four of Saturn's inner satellites (Prometheus, Pandora, Janus, and Epimetheus) and five ring regions (the A, B, and C rings; the Cassini division; and the F ring). We have used Hubble Space Telescope images taken in July 1991 and during the Saturn's ring plane crossings by the Earth (August 1995) and the Sun (November 1995). The spectral range of this study is ∼0.30–0.95 μm. We confirm qualitatively but not quantitatively several interesting color properties of the main rings already derived by Estrada and Cuzzi [1996]. The derived albedos of Prometheus and Pandora are consistent with the lower limits based on Voyager images [Thomas et al., 1983]. The albedos of the coorbital satellites Janus and Epimetheus are smaller than previously determined. The colors of Janus and Pandora are similar to those of the main rings, indicating the presence of ices altered by red contaminants. Epimetheus is more neutral, with spectral shape similar to that of the G ring. Our data for Prometheus are fragmentary in terms of wavelength coverage; otherwise, the satellite looks like the F ring, which is neutral or slightly blue. This unusual color could be explained if there is an inward migration of the F ring particles through Poynting‐Robertson drag, which subsequently sandblast the surface of the satellite. We find a correlation of color with the distance from Saturn. This indicates that the inner satellites are spectrally closer to the main rings than to the major Saturnian satellites. The implications for the origin of the inner satellites are discussed.
Spectral properties of the Marius Hills volcanic complex and implications for the formation of lunar domes and cones
Authors: Weitz Catherine M. , Head James W.
Published: December 2003

We have used multispectral data from the Clementine UV‐visible camera to study the volcanic features of the Marius Hills complex and their comparison to other lunar domes and cones. There are several mare units identified in the complex, each with a unique Ti content, as indicated by their 415/750 nm value. The domes in Marius Hills are spectrally identical to the mare plains of the complex, supporting similar compositions. In contrast, most of the volcanic cones of the complex are lower in reflectance, bluer in color, and have weaker mafic absorptions than the mare and domes. The spectral characteristics of the cones can best be explained by fine‐grained crystallization in the spatter that compose the cones. Other lunar cones, such as Mons Esam in northern Tranquillitatis, have spectral properties similar to those at Marius Hills. The Rima Parry cones and their associated dark mantle deposit appear redder with a stronger mafic absorption than the Marius Hills cones. The cones Isis and Osiris in southern Mare Serenitatis, the domes of Rumker Hills, and several domes in northern Mare Tranquillitatis are spectrally similar to adjacent mare units. The Mairan and Gruithuisen domes in northern Oceanus Procellarum have a feldspathic signature characteristic of highland material although they are redder and brighter than adjacent highland soils. They appear to represent highland material that resembles domes rather than actual mare domes, like those at Marius and Rumker Hills. The diversity of lunar volcanic features can best be explained by differences in accumulation rates and cooling of ejected clasts from various eruption styles. Mare domes may have formed at lower effusion rates, thereby allowing lava to construct small shields with slopes <3°. The steeper domes at Marius Hills require higher viscosities resulting from even lower effusion rates and enhanced crystallization in the magmas during the terminal stages of earlier eruptions that emplaced the mare. Cones like Mons Esam, Rima Parry, Isis, and Osiris are aligned along linear rules and are interpreted to result from degassing of near‐surface dikes. In contrast, the cones of Marius Hills show no linear alignment and may result from strombolian eruptions at the terminal stages of earlier effusive eruptions that emplaced the domes and mare in the complex.
Chemistry of the galactic cosmic ray induced ionosphere of Titan
Authors: Molina‐Cuberos G. J. , López‐Moreno J. J. , Rodrigo R. , Lara L. M.
Published: December 2003

Titan's lower ionosphere (from 1 to 400 km) has been studied with a one‐dimensional ion‐neutral model. In this region of the atmosphere, galactic cosmic rays (GCRs) are the main ionization source. They penetrate to the deeper atmosphere and ionize the neutral constituents of Titan's atmosphere (mainly N2, CH4, Ar, H2, and CO) to produce N2+, N+, Ar+, CH4+, CH3+, CH2+, H2+, H+, and CO+. Fast reactions with the neutrals convert these ions into ions such as CH5+, C2H5+, and N2H+. Different pathways are proposed to obtain the ion and electron densities. The most abundant ions are cluster ions, like CH5+·CH4, HCO+·H2, and HCNH+·C2H4, and long chain hydrocarbon ions. In atmospheres very rich in N2, such as Titan's, ions like H4C7N+ and CH3CNH+ also represent an important contribution to the total positive ion density. Three‐body reactions may play an important role in the dense atmosphere of Titan, and special attention is devoted to them. The calculated electron density in the lower atmosphere reaches a peak of ≈ 2150 cm−3 at an altitude of 90 km.
Lobate scarps and the Martian crustal dichotomy
Authors: Watters Thomas R. , Robinson Mark S.
Published: December 2003

Landforms reflecting crustal shortening are found in the ancient highlands of the eastern hemisphere of Mars. These structures, referred to as lobate scarps, are interpreted to be thrust faults. Lobate scarps occur near and are oriented roughly parallel to the Martian crustal dichotomy, a major geologic and topographic boundary that divides the heavily cratered highlands from the relatively smooth, featureless northern lowlands. The long‐ and short‐wavelength topography of lobate scarps in the northern Terra Cimmeria‐Amenthes region have been analyzed using photoclinometry, Earth‐based radar altimetry, and Mars Orbiter Laser Altimeter data. The measured relief of lobate scarps in this region ranges from ∼110 to 1230 m, and they occur on gentle regional slopes that dip both toward and away from the dichotomy. Estimates of the horizontal shortening across the lobate scarps studied range from roughly 0.24 to 2.6 km (n = 9), assuming fault plane dips of 25°. The displacement‐length (D‐L) relationships of thrust faults associated with the lobate scarps are consistent with those observed for terrestrial fault populations. The compressional strain in the heavily cratered highlands near the dichotomy, determined using the D‐L data for the lobate scarps, is estimated to be ∼0.17%. Topographic data indicate that the dichotomy in the northern Terra Cimmeria‐Amenthes region has a distinct topographic signature. The spatial and temporal relationship of the lobate scarps to the boundary suggests that they are related to its formation, supporting models for a tectonic origin of the crustal dichotomy.
Tsiolkovsky crater: A window into crustal processes on the lunar farside
Authors: Pieters Carlé M. , Tompkins Stefanie
Published: December 2003

Mineralogy and distribution of rock types in the Tsiolkovsky region of the lunar farside are evaluated in terms of crustal stratigraphy and evolution. Calibrated multispectral images from five orbits of Clementine data provide compositional information at a scale that allows diverse geologic features to be analyzed and compared. The entire region is seen to be highly anorthositic, with outcrops of relatively pure anorthosite quite common. The crater itself has excavated blocks of anorthosite and noritic anorthosite from the near‐surface highland crust, often in a mixed jumble. The central peaks of Tsiolkovsky, which have exhumed much deeper material, however, are composed of relatively pure anorthosite with olivine‐rich zones concentrated near the ridge crests. Boundaries between the anorthosite and olivine‐rich zones are sharp, but spatial relations suggest the coherent olivine‐rich zone is relatively thin (<1 km). The composition of the mare material filling Tsiolkovsky is shown to be low‐titanium basalt. Smaller exposures of mare basalt occur about one crater radius from the rim. The crustal structure to ∼25 km in this region prior to the Tsiolkovsky impact appears to be (top to bottom) a few kilometers of anorthositic breccias comprising the megaregolith, a zone of crystalline anorthosite with pockets of noritic anorthosite, a zone of anorthosite devoid of iron‐bearing minerals, and a zone of relatively pure anorthosite containing olivine‐rich material, possibly emplaced as intrusions.
Europa: Morphological characteristics of ridges and triple bands from Galileo data (E4 and E6) and assessment of a linear diapirism model
Authors: Head James W. , Pappalardo Robert T. , Sullivan Robert
Published: December 2003

Galileo solid‐state imaging (SSI) images of Europa provide high‐resolution data on the morphological characteristics of ridges and permit the development of nomenclatural schemes for their description and classification. Key observations are that ridges (1) are remarkably consistent in their along‐strike linearity, width, and height, (2) form long linear features in which preexisting structures can sometimes be traced up the outer slopes of the ridges and in other cases appear to be buried, (3) contain narrow apical zones of small‐scale, ridge‐parallel faulting, (4) are sometimes flanked by narrow troughs and ridge‐parallel fractures, and (5) often display associated color variations. On the basis of the characteristics and associated features of ridges, we find that a process in which initial fracturing (most plausibly related to tidal deformation) of a brittle layer overlying a buoyant ductile substrate leading to linear diapiric upwelling provides a consistent explanation for the observed features. In this process the upwelling linear diapir causes flexure (bending and faulting) of the region marginal to the fracture, the deformation and uplift of adjacent plains material and its preexisting structures to form the apical part of the ridge, the exposure of the inner walls of the crack, and the mass wasting of the inner and outer walls of the ridge to modify, but often not completely destroy, the preexisting structure of the adjacent plains. Specifically, this mechanism can account for many characteristics of the ridges, including their linearity, their consistent and regular morphology over their great lateral extent, their positive topography, the presence of preexisting structure on the outer ridges (caused by upbowing of background ridged plains), the formation of marginal troughs (as diapiric rim synclines), the detailed nature of their outer and inner slopes (caused largely by faulting and mass‐wasting processes), and their sequential formation with multiple orientations (related to tidal deformation processes). Linear diapirism also provides a possible explanation for color and albedo characteristics, related to thermal effects of the upwelling warm ice (e.g., inducing volatile migration and grain‐size variations). As the vast majority of deformation is vertical in this scenario, this mechanism minimizes the necessity for complementary compressional deformation required by some other models.
Topographic wavelengths of Ganymede groove lanes from Fourier analysis of Galileo images
Authors: Patel Jiganesh G. , Pappalardo Robert T. , Head James W. , Collins Geoffrey C. , Hiesinger Harald , Sun Jie
Published: December 2003

Galileo images have shown that grooved terrain on Ganymede consists of pervasive ridges and grooves at a variety of spatial scales, which complicates visual interpretation. We use Fourier analysis to separate complex surface deformation into its component dominant wavelengths (closely correlated to topographic wavelengths) to determine spatial relationships within and among grooved terrain units. We analyze groove lanes in four Galileo target sites (Uruk Sulcus, Byblus Sulcus, Tiamat Sulcus, and Nicholson Regio), spanning a range of resolutions and lighting geometries, and we find multiple dominant wavelengths in each. Fourier analysis of the complexly deformed Uruk Sulcus shows both similarities and differences in wavelength distribution among its tectono‐stratigraphic subunits (a range of 0.5 to 6 km, with a concentration at 1.2 km); favorable comparison is made to a stereo‐derived topographic model. Of the dominant wavelengths displayed by Byblus Sulcus (∼1, 3.3, and 10 km), the longest wavelength is revealed by profiles across both high‐ and low‐resolution images with very different lighting geometries. Tiamat Sulcus displays different dominant wavelengths north (5 to 10 km) and south (3 to 5 km) of the orthogonally trending Kishar Sulcus. Groove lanes in Nicholson Regio are significantly different from the other sites because they are isolated within dark terrain. Fourier analysis of these dark terrain groove lanes shows dominant wavelengths (∼2.1, 3.2, and 8.0 km) that are similar to those in lanes of more typical grooved terrain. This suggests that the tectonic style and lithospheric characteristics in this portion of Ganymede's dark terrain were similar to those in bright grooved terrain at the time of deformation. Our results support the hypothesis that longer topographic wavelengths in Ganymede's groove lanes formed by means of extensional necking of the lithosphere, while multiple shorter wavelengths formed by normal faulting of the brittle lithosphere, in both bright and dark terrains. The similar wavelengths of deformation seen in several groove lanes in both bright and dark terrain suggest similarity in lithospheric thickness, composition, and mechanical structure at these disparate sites. A global process (such as differentiation) could be responsible for creating a similar planet‐wide strain and thermal regime during the time of grooved terrain formation.
The topography of Tycho Crater
Authors: Margot Jean‐Luc , Campbell Donald B. , Jurgens Raymond F. , Slade Martin A.
Published: December 2003

Three‐dimensional mapping of the Moon can be accomplished with an Earth‐based radar interferometer. Elevation data and radar imagery obtained with this technique are presented for the Tycho Crater area, with a spatial resolution of 200 m and a height resolution of 30 m. The radar maps are displayed in standard cartographic projections with appropriate corrections for elevation‐induced geometric distortions. The digital elevation model allows detailed morphometry of the 85 km diameter crater: the floor of Tycho lies 3970 m below a 1738 km radius sphere, and the crater's central peak rises 2400 m above the floor. The average rim crest elevation is 730 m above the 1738 km datum, giving a mean rim to floor depth of 4700 m. The floor has two distinct units with the western section being higher in elevation by ∼200 m. This dichotomy is consistent with an asymmetry in the crater shape which reveals that maximum wall slumping occurred in the western and southwestern regions of the crater. Comparison of the radar‐derived topography with 87 altimetry points from the Clementine lidar experiment shows rms deviations of ∼90 m after a 0.11° latitude correction to the location of all the Clementine altimetry points.
North Atlantic Intermediate Waters in the Late Pliocene to Early Pleistocene
Authors: Mc Intyre K. , Ravelo A. C. , Delaney M. L.
Published: December 2003

We generated benthic isotope records from Ocean Drilling Program (ODP) site 981 on the Feni drift (2173 m water depth) and from ODP site 983 on the Gardar drift (1983 m water depth) to examine the interaction between North Atlantic Deep Water (NADW) and Glacial North Atlantic Intermediate Water (GNAIW) formation from 2.0 to 1.4 Ma. We find NADW at both sites during interglacial periods, and a mix of NADW and Southern Ocean water at the Feini drift during most glacial periods. Prior to 1.7 Ma we find no evidence ofr GNAIW at the Gardar drift site. Instead, glacial Gardar drift δ13C values are as low or lower than values for all other sites in the North Atlantic and reflect continued glacial overflow from the Nordic seas. After 1.7 Ma Gardar drift δ13C values increase and suggest that there was GNAIW at the Gardar drift site during some glacial intervals. Overall, we find that NADW and GNAIW production changed around 1.7 Ma in concert with changes in sea surface temperature and salinity and in the Earth's obliquity cycle.
Hydrological relationship between the North Atlantic Ocean and the Mediterranean Sea during the past 15‐75 kyr
Authors: Paterne Martine , Kallel Nejib , Labeyrie Laurent , Vautravers Maryline , Duplessy Jean‐Claude , Rossignol‐Strick Martine , Cortijo Elsa , Arnold Maurice , Fontugne Michel
Published: December 2003

The Mediterranean Sea hydrology at the time of the Heinrich formation in the North Atlantic Ocean was analyzed by comparing sea surface temperatures (SSTs) and oxygen isotope composition of seawater (δw) changes during the past 75 kyr in two marine cores. These were compared to the palynological variations derived in the Mediterranean Sea core. During the last glacial the two oceanic SST records show similar and synchronous patterns, with several long‐term cooling periods, ending by abrupt SST increases. At the time of the Heinrich events, cold SSTs and low salinity prevailed in the Mediterranean Sea. The freshwater budget was similar to the modern one, permitting the presence of a mixed forest on the Mediterranean borderlands. The post‐Heinrich periods are marked by a freshwater budget decrease, limiting oak and fir tree growth in the Mediterranean region. Increase of precipitation or reduction of evaporation is observed before the Heinrich episode, and is associated with a well‐developed mixed Mediterranean forest.
Paleoceanographic reconstructions from planktonic foraminifera off the Iberian Margin: Temperature, salinity, and Heinrich events
Authors: Cayre Olivia , Lancelot Yves , Vincent Edith , Hall Michael A.
Published: December 2003

A quantitative analysis of planktonic foraminifera in a core from the Iberian Margin allows a reconstruction of the evolution of oceanographic parameters during the last glacial cycle with a resolution of ∼1000 years. A principal component analysis performed on 19 species allows the identification of 11 intervals characterized by increased abundances of the subpolar species. The youngest six of these intervals are correlated with the last 6 Heinrich events (HEs). The five cold events older than stage 4 are dated at 81, 90, 110, 129, and 140 ka, respectively. Paleotemperatures reconstructed using the modern analog technique indicate 4°C decreases during all even‐numbered isotopic stages and stage 3. During the HEs, temperature decreases reach ∼10°C and seawater δ18O anomalies reach ∼1‰. Temperature and salinity reconstructions indicate that the environment of the Iberian Margin has been under the combined influence of global factors such as the migration of the polar front and iceberg discharge and of regional factors such as the precipitation/evaporation regime on both oceanic and continental area.
Indenter growth in analogue models of Alpine‐type deformation
Authors: Bonini Marco , Sokoutis Dimitrios , Talbot Christopher J. , Boccaletti Mario , Milnes Alan G.
Published: December 2003

A series of analogue experiments were carried out to simulate continental convergence, as seen in a profile through the Central Alps. A rigid indenter, representing the Adriatic plate, was driven laterally into a sand pack representing the brittle upper crust of Europe, detached and thickening above its subducting ductile lower crust. The rigid indenter advanced at the same steady rate in each experiment, but the dip of its front face was steepened in 15° increments from 15° to 90°. Where the rigid indenter face dipped at 45° or less, a sand wedge rose and was bound by a series of forekinks that nucleated at the toe of the indenter. Where the face of the rigid indenter dipped 60° or more, the wedge was defined by a single forekink and one or more backkinks that nucleated from a point advancing in front of the indenter toe. We interpret these results as indicating that slices of the sand pack and rising wedge are transferred across kink bands to build an “effective” indenter with a frontal dip closer to that dictated by the changing shear strength of the sand pile, which thickens vertically as it shortens laterally. One of our models (with a rigid indenter dipping 75°) simulates most of the major structures shown in recent syntheses of surface geology and deep seismic data in the Central Alps, without the isostatic lithospheric depression. This model accounts for the late collisional stage (Oligocene to Present) complex strain and metamorphic histories in the core of the orogenic wedge, the rapid rise and extrusion of small pips of Alpine eclogites, and the current passivity of the Insubric Line. It also emphasizes that lateral extension along gently dipping “thrusts” (orogen‐normal horizontal escape) is confined to the extruded portion of the rising wedge.
Flexural expression of European continental lithosphere under the western outer Carpathians
Authors: Zoetemeijer Reini , Tomek Čestmir , Cloetingh Sierd
Published: December 2003

We present the results of an analysis of the flexural down bending of the European lithosphere under the western outer Carpathians for a grid of five profiles with a lateral spacing of about 100 km crossing the Carpathians and its foreland. Seismic sections, including two deep seismic reflection lines, and numerous wells allowed us to quantify the flexural curvature of the lithosphere. In addition, gravity data are used to obtain independent constraints. Two evolutionary scenarios involving subduction/underthrusting of passive margin and a phase change in the lower crust are investigated in a context of relatively flat Moho under the area. Furthermore, recent uplift, expressing itself in erosional features observed along the distal margin of the foredeep, is quantified. The generally modest Bouguer gravity anomaly points to nonisostatic processes causing this uplift. Steeply dipping basement under the Carpathians to about 10 km depth at the location of the Pieniny Klippen Belt is explained by relatively weak lithosphere, which is expressed in the predicted low values of effective elastic thickness of 16 km decreasing locally to 3 km. The low strength of the European lithosphere in this region is probably caused by mechanical weakening controlled by partial yielding due to high flexural curvature. The weakest parts of the lithosphere along the profiles, corresponding to low effective elastic thicknesses, are concentrated in the areas of maximum bending. Predicted flexural bending stresses as a function of bending moment and effective elastic thickness increase dramatically under the outer zone of the Carpathian belt, explaining reactivations of older basement structures in these regions.
Comparison of a genetic algorithm and mathematical programming to the design of groundwater cleanup systems
Authors: Aly Alaa H. , Peralta Richard C.
Published: December 2003

We present and apply a new simulation/optimization approach for single‐ and multiple‐planning period problems in groundwater remediation. Instead of the traditional control locations for contaminant concentrations, we use an L∞ norm as a global measure of aquifer contamination (CMAX). We use response‐surface constraints to represent CMAX within the optimization model. We compare the performance of formal mixed integer nonlinear programming and a genetic algorithm for several optimization scenarios.
Model simulation of changes in N2O and NO emissions with conversion of tropical rain forests to pastures in the Costa Rican Atlantic Zone
Authors: Liu Shuguang , Reiners William A. , Keller Michael , Schimel David S.
Published: December 2003

Nitrous oxide (N2O) and nitric oxide (NO) are among the trace gases of concern because of their importance in global climate and atmospheric chemistry. Modeling techniques are needed for simulating the spatial and temporal dynamics of N2O and NO emissions from soils into the atmosphere. In this study, we modified the ecosystem model CENTURY to simulate changes in N2O and NO soil emissions through the process of converting tropical moist forests to pastures in the Atlantic Lowlands of Costa Rica. Measurements of water‐filled pore space (WFPS) and fluxes of N2O and NO from a chronosequence of pastures were used for calibration and testing of the model. It was found that the N2O+NO — WFPS and N2O:NO — WFPS relationships as developed from primary forests could be generalized to the chronosequence of pastures and other land use systems in the region. Modeled net increases (compared to primary forests) in total N2O and NO production after conversion from forest to pasture were 514 kg N ha−1 during the first 15 years under normal field conditions. The nitrogen loss in the form of N2O and NO during the first 15 years could range from 401 to 548 kg N ha−1, depending on the amounts of forest residue remaining on pasture sites. N2O‐N accounted for 90% of the gas fluxes, while NO‐N accounted for 10%. Sensitivity analysis indicated that the impacts of forest‐pasture conversion on N2O and NO emissions from soil into the atmosphere were complex, depending on the initial conditions of the forest‐derived pastures, management practices, soil physical and chemical conditions and their changes over time, N availability, and climate. It is therefore important to incorporate the spatial and temporal heterogeneities of those controlling factors in estimating regional and global N2O and NO emissions from soils into the atmosphere.
Evaluating timescales of carbon turnover in temperate forest soils with radiocarbon data
Authors: Perruchoud Daniel , Joos Fortunat , Fischlin Andreas , Hajdas Irka , Bonani Georges
Published: December 2003

Timescales of soil organic carbon (SOC) turnover in forests were investigated with soil radiocarbon data. The12C/14C ratios were measured by accelerated mass spectroscopy on soil sampled from a deciduous temperate forest in Switzerland during 1969–1995. The resulting Δ14C values (125–174‰) were in line with previously published14C soil data. We applied FORCLIM–D, a model of nonliving organic matter decomposition including nine litter and two soil compartments to estimate SOC turnover times for this forest type. Carbon 14 aging in woody vegetation was explicitly accounted for. Parameters were calibrated to match radiocarbon ratios observed for forest soils at Meathop Wood, United Kingdom [Harkness et al., 1986]. We estimated that roughly 50–94% (best estimate, 49%) of foliar litter carbon and 11–74% (73%) of fine root litter carbon are eventually respired as CO2at Meathop Wood; the rest is transferred to soil humus, where it undergoes further decomposition. Turnover times for the 0–20 cm mineral soil layer ranged from 9–50 years (25 years) for a fast overturning soil compartment comprising 38–74% (68%) of bulk SOC and 155–10,018 years (3,570 years) for a slowly overturning compartment. For the Swiss site, SOC turnover times were in the same range. Parameter uncertainties were correlated and induced by uncertainties in14C observations from small‐scale spatial inhomogeneities, sample preparation and by lack of reliable14C observations for the “prebomb” test period. Model‐based estimates of soil organic C turnover derived from14C data must be used cautiously since they depend on the underlying model structure: bypassing litter in FORCLIM‐D overestimated SOC turnover by a factor of 2.5. Such an error might remain undetected in studies lacking samples from the late 1960s and early 1970s. Thus litter C turnover should be included when estimating SOC turnover in temperate forests from14C data.
A global database of sea surface dimethylsulfide (DMS) measurements and a procedure to predict sea surface DMS as a function of latitude, longitude, and month
Authors: Kettle A. J. , Andreae M. O. , Amouroux D. , Andreae T. W. , Bates T. S. , Berresheim H. , Bingemer H. , Boniforti R. , Curran M. A. J. , DiTullio G. R. , Helas G. , Jones G. B. , Keller M. D. , Kiene R. P. , Leck C. , Levasseur M. , Malin G. , Maspero M. , Matrai P. , McTaggart A. R. , Mihalopoulos N. , Nguyen B. C. , Novo A. , Putaud J. P. , Rapsomanikis S. , Roberts G. , Schebeske G. , Sharma S. , Simó R. , Staubes R. , Turner S. , Uher G.
Published: December 2003

A database of 15,617 point measurements of dimethylsulfide (DMS) in surface waters along with lesser amounts of data for aqueous and particulate dimethylsulfoniopropionate concentration, chlorophyll concentration, sea surface salinity and temperature, and wind speed has been assembled. The database was processed to create a series of climatological annual and monthly 1°×1° latitude‐longitude squares of data. The results were compared to published fields of geophysical and biological parameters. No significant correlation was found between DMS and these parameters, and no simple algorithm could be found to create monthly fields of sea surface DMS concentration based on these parameters. Instead, an annual map of sea surface DMS was produced using an algorithm similar to that employed byConkright et al.[1994]. In this approach, a first‐guess field of DMS sea surface concentration measurements is created and then a correction to this field is generated based on actual measurements. Monthly sea surface grids of DMS were obtained using a similar scheme, but the sparsity of DMS measurements made the method difficult to implement. A scheme was used which projected actual data into months of the year where no data were otherwise present.
Effect of seasonal changes in the pathways of methanogenesis on the δ13C values of pore water methane in a Michigan peatland
Authors: Avery G. Brooks , Shannon Robert D. , White Jeffrey R. , Martens Christopher S. , Alperin Marc J.
Published: December 2003

The δ13C value of pore water methane produced in a Michigan peatland varied by 11‰ during the year. This isotopic shift resulted from large seasonal changes in the pathways of methane production. On the basis of mass balance calculations, the δ13C value of methane from CO2reduction (average = −71.4 ± 1.8‰) was depleted in13C compared to that produced from acetate (−44.4 ± 8.2‰). The dissolved methane at the site remained heavy (approximately −51‰) during most of the year. Tracer experiments using14C‐labeled CO2indicated that during January 110 ± 25% of the methane was produced by CO2reduction. Because of low‐methane production rates during the winter, this13C‐depleted methane had only a slight effect on the isotopic composition of the methane pool. In early spring when peat temperatures and methane production rates increased, the δ13C value of the dissolved methane in shallow peat was influenced by the isotopically light methane and approached −61‰. Peat incubation experiments conducted at 15°C in May and June (when the peat reaches its maximum temperature) indicated that an average of 84 ± 9% of the methane production was from acetate and had an average δ13C value of −48.7 ± 5.6‰. Rising acetate concentrations during April‐May (approaching 1 mmol L−1(mM)) followed by a rapid decrease in acetate concentrations during May‐June reflected the shift toward methane production dominated by acetate fermentation. During this period, dissolved methane in shallow peat at the site returned to heavier values (approximately −51‰) similar to that produced in the incubation experiments.
Carbon and peat accumulation over the past 1200 years in a landscape with discontinuous permafrost, northwestern Canada
Authors: Robinson Stephen D. , Moore Tim R.
Published: December 2003

Apparent recent carbon and peat accumulation rates over the past 1200 years were measured in five peat landforms in the discontinuous permafrost zone near Fort Simpson, Northwest Territories, Canada. The White River volcanic ash layer was used as a chronostratigraphic horizon to ensure a consistent time span of peat deposition among peat cores and to allow a large core sample size (n = 20 cores in each landform) without the expense of radiocarbon dating. Apparent recent carbon accumulation rates were not significantly different (p>0.05) among rich fen (13.58 ± 1.07 g C m−2yr−1), peat plateau (13.31 ± 2.20 g C m−2yr−1) and collapse fen (13.54 ± 1.50 g C m−2yr−1). Poor fen and ombrotrophic bog accumulation rates were 20.34 ± 2.86 and 21.81 ± 3.25 g C m−2yr−1, respectively, and were not significantly different from each other. Variation within the poor fen and ombrotrophic bog cores is attributed to microtopography, with hollows accumulating carbon at significantly greater rates than hummocks. Vertical peat accumulation rates vary significantly in the poor fen, with hummocks showing a greater annual vertical accumulation rate than hollows. Vertical peat accumulation rates ranged from 0.282 ± 0.052 mm yr−1in the peat plateau to 0.563 ± 0.070 mm yr−1in the ombrotrophic bog. Variations in mean core bulk density were also significant and ranged from 0.071 ± 0.011 g cm−3(collapse fen) to 0.102 ± 0.011 g cm−3(poor fen). A regional survey incorporating measurements from other parts of the southwestern Northwest Territories and the southeastern Yukon show rates similar to those near Fort Simpson. These rates are significantly lower than published rates from other parts of northern Canada, Finland, and the former Soviet Union. Low and variable summer precipitation in the region may contribute to the low carbon accumulation rates through decreased plant production and/or increased aerobic decomposition.
Global distribution of aerosols over the open ocean as derived from the Coastal Zone Color Scanner
Authors: Stegmann P. M. , Tindale N. W.
Published: December 2003

Climatological maps of monthly mean aerosol radiance levels derived from the coastal zone color scanner (CZCS) were constructed for the world's ocean basins. This is the first study to use the 7.5‐year CZCS data set to examine the distribution and seasonality of aerosols over the open ocean on a global scale. Examination of our satellite images found the most prominent large‐scale patch of elevated aerosol radiances in each month off the coast of northwest Africa. The well‐known, large‐scale plumes of elevated aerosol levels in the Arabian Sea, the northwest Pacific, and off the east coast of North America were also successfully captured. Radiance data were extracted from 13 major open‐ocean zones, ranging from the subpolar to equatorial regions. Results from these extractions revealed the aerosol load in both subpolar and subtropical zones to be higher in the Northern Hemisphere than in the Southern Hemisphere. Aerosol radiances in the subtropics of both hemispheres were about 2 times higher in summer than in winter. In subpolar regions, aerosol radiances in late spring/early summer were almost 3 times that observed in winter. In general, the aerosol signal was higher during the warmer months and lower during the cooler months, irrespective of location. A comparison between our mean monthly aerosol radiance maps with mean monthly chlorophyll maps (also from CZCS) showed similar seasonality between aerosol and chlorophyll levels in the subpolar zones of both hemispheres, i.e., high levels in summer, low levels in winter. In the subtropics of both hemispheres, however, chlorophyll levels were higher in winter months which coincided with a depressed aerosol signal. Our results indicate that the near‐IR channel on ocean color sensors can be used to successfully capture well‐known, large‐scale aerosol plumes on a global scale and that future ocean color sensors may provide a platform for long‐term synoptic studies of combined aerosol‐phytoplankton productivity interactions.