bluuebunny/crossref_metadata_2025 huggingface dataset:
Indications of sulfate minerals in the Martian soil from Earth‐based spectroscopy
Authors: Blaney Diana L. , McCord Thomas B.
Published: February 2004

Telescopic measurements of Mars between 4.40 and 5.13 μm at a spectral resolution (λ/Δλ) of 300 were made on August 19, 1988, UT at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. This wavelength region contains radiation from both solar reflection and thermal emission. Additionally, the Martian atmosphere has numerous atmospheric gas absorption features, dominated by the 4.2‐μm CO2 fundamental band. The Mars spectrum rise out of the 4.2 to 4.4‐μm CO2 band on the long‐wavelength side cannot be matched solely by atmospheric gas constituents. An absorption must be added at roughly 4.5 μm in order to decrease the reflectance rise and produce the 4.5‐μm inflection which is present in the data. The location of this feature at the position of the 2v3 overtone of the SO42− anion indicates that the surface absorption is probably caused by sulfates on the Martian surface and/or in atmospheric dust. This is consistent with the known presence of sulfates on the Martian surface from the Viking results. An exact spectral match to a terrestrial sulfur mineral has not been made, but we suggest that the mineral on Mars has very weak band structure, probably due to an ion environment in the mineral with a high degree of electric field symmetry. Significant variation exists at 4.5 μm among the observed spectra for different locations on Mars. In order of strength, from strongest absorption to weakest, are Eastern Solis Planum, Argyre Basin, Eastern Tharsis, and Valles Marineris for the four regions measured at similar Mars atmospheric conditions.
Formation and evolution of volcanic edifices on the Dione Regio rise, Venus
Authors: Keddie Susan T. , Head James W.
Published: February 2004

Mapping of Dione Regio, Venus, a regional highland 1200 by 2700 km in size with mean elevation of 6052 km located in the southern hemisphere to the NW of Lavinia Planitia, reveals a region characterized by early tectonically dominated structure and later widespread volcanism and centralized edifice construction. Small patches of complexly deformed terrain (tessera) and larger regions of plains characterized by a single direction of deformation (tectonized plains), preserved as inliers, are embayed by more recent widespread volcanic plains. Smaller‐scale plains resurfacing superposed these plains following a pervasive compressional event that lead to distributed wrinkle ridge formation. Four major volcanoes dominate the topographically irregular highland, each with similar early‐stage radar‐dark lava flow deposits but significantly different late‐stage eruptions. These late‐stage differences are manifested as dark, diffuse deposits (possibly pyroclastic in origin) and construction of a single steep‐sided dome at Ushas Mons, a small shield‐volcano field at Nepthys Mons, and bright diffuse deposits (possible pyroclastic deposits) with summit dome and pit formation at Innini and Hathor Montes. The presence at all of these volcanoes of radial lineaments and graben, interpreted to be related to near‐surface lateral dyke emplacement, and late‐stage summit constructional features indicate that shallow magma chambers occur at each edifice. Variations in the evolutionary history of and eruptions from these chambers may explain the differences observed in the deposits at these major edifices. It is also possible, however, that fundamental differences in the magma source region was a major factor in determining the appearance of the deposits. Of the several models considered for the formation of the region, secondary upwellings from a single large mantle plume or the near‐contemporaneous upwelling of multiple smaller plumes best explain the observed characteristics at the rise. A comparison to other volcanic highlands suggests that there are at least two classes of volcanic rises on Venus, an areally and topographically large type with significant volcanism and rift zone formation (like Beta Regio) and a smaller‐scale type with extensive volcanism but moderate rifting (like Western Eistla Regio). These two classes reflect a spectrum in size and vigor of mantle upwellings. The Dione rise is most like Western Eistla Regio in terms of areal extent, topographic elevation, and geologic complexity.
Age relations of Martian highland drainage basins
Authors: Maxwell Ted A. , Craddock Robert A.
Published: February 2004

Dendritic valley patterns in the equatorial highlands of Mars show evidence of internal drainage into restricted basins, which are interpreted to be floored with sedimentary fill. Based on crater frequency characteristics of six areas of enclosed basins, the origin of these intercrater plains fill units ranges from middle to late Noachian. In contrast, the age of modification of the same plains units derived from the frequency of fresh craters occupies a relatively narrow range centered on the Noachian/Hesperian boundary. In half the areas studied the timing of highlands and plains crater modification is consistent with a sedimentary origin for basin fill materials. The other plains units most likely consist of interlayered sedimentary and volcanic materials. Relations between the age of stability of these internally drained highland units and their elevation are not as distinct as prior studies suggested; a trend of decreasing age with decreasing elevation for the plains materials is not matched by similarly derived ages of the dissected highlands. Remapping and age dating of the dissected highlands and associated basins suggest that volcanic plains may be more extensive than those used in past models for magma and volatile evolution, and support local volcanism rather than a global‐scale magmatic head model for highlands plains formation.
Influx of cometary volatiles to planetary moons: The atmospheres of 1000 possible Titans
Authors: Griffith Caitlin A. , Zahnle Kevin
Published: February 2004

We use a Monte Carlo model to simulate impact histories of possible Titans, Callistos, and Ganymedes. Comets create or erode satellite atmospheres, depending on their mass and velocity distributions: faster and bigger comets remove atmophiles; slower or smaller comets supply them. Mass distributions and the minimum total mass of comets passing through the Saturn system were derived from the crater records of Rhea and Iapetus. These were then scaled to give a minimum impact history for Titan. From this cometary population, of 1000 initially airless Titans, 16% acquired atmospheres larger than Titan's present atmosphere (9 × 1021 g), and more than half accumulated atmospheres larger than 1021 g. In contrast to the work of Zahnle et al. (1992), we find that, in most trials, Callisto acquires comet‐based atmospheres. Atmospheres acquired by Callisto and, especially, Ganymede are sensitive to assumptions regarding energy partitioning into the ejecta plume. If we assume that only the normal velocity component heats the plume, the majority of Ganymedes and half of the Callistos accreted atmospheres smaller than 1020 g. If all the impactor's velocity heats the plume, Callisto's most likely atmosphere is 1017 g and Ganymede's is negligible. The true cometary flux was most likely larger than that derived from crater records, which raises the probability that Titan, Ganymede, and Callisto acquired substantial atmospheres. However, other loss processes (e.g., sputtering by ions swept up by the planetary magnetic field, solar UV photolysis of hydrocarbons) are potentially capable of eliminating small atmospheres over the age of the solar system. The dark material on Callisto's surface may be a remnant of an earlier, now vanished atmosphere.
Competition between Na2SO4 and Na sulfide in the upper crust of Io
Authors: Burnett D. S.
Published: February 2004

The Na atmosphere of Io requires a Na‐S‐O phase in the outer surface layers. Considering the various mechanisms for extraction of Na to the surface, the possible primary phases are Na2O, Na2Sx and Na2SO4. However, regardless of the primary phases brought to the surface, the shallow crustal recycling of material implied by the ongoing volcanism will tend to produce thermochemical equilibrium and cause all Na to end up as Na2SO4 or Na2Sx. This hypothesis is investigated by relatively model‐independent thermodynamic calculations. The major assumption is that material is statistically circulated to sufficiently high temperatures by burial that thermochemical equilibrium can be attained. For a wide range of assumed crustal (PT) conditions, Na2O will be converted to Na2SO4. During residence in the shallowest crustal regions dominated by liquid SO2, e.g., SO2 geysers or fumaroles, or for any crustal regimes where SO2 and S are in comparable abundances, Na‐sulfides will be converted to Na2SO4. However, in high‐temperature, low‐pressure regimes with a low relative abundance of SO2 relative to S (e.g., due to outgasing of SO2), Na2SO4 is converted to Na sulfides. Such regimes could be relatively common on Io, e.g., associated with flows, lava lakes, or shallow intrusions. Consequently, because of thermochemical equilibration in different crustal environments, both Na2SO4 and Na sulfides will coexist on the Io surface.
Regular baroclinic transient waves in a simplified global circulation model of the Martian atmosphere
Authors: Collins M. , James I. N.
Published: February 2004

Meteorological observations from the Viking landers showed that baroclinic waves on Mars are much more periodic than those seen on Earth. A global circulation model of the Martian atmosphere, with simplified parametrizations of heating and friction, has been used to examine baroclinic waves in the parameter range appropriate to the Martian atmosphere. Two distinct flow regimes are found to be dependent on the magnitude of thermal and frictional dissipation. The flow is composed of small‐amplitude disturbances propagating around a zonally oriented midlatitude jet in an irregular fashion or a highly persistent large‐amplitude zonal wavenumber 3 wave. The large‐amplitude waves are much like those seen in differentially heated rotating annuli. It is shown that the large amplitude waves are not the linearly most unstable modes of the system, rather nonlinear effects are dominant. Attractor reconstructions, using empirical orthogonal functions, show the regime transition as a bifurcation from a messy aperiodic attractor to, what is essentially, a limit cycle. Analysis of the potential vorticity budgets of the large‐amplitude waves shows that a large free mode component is present. A mechanism is suggested whereby the sources and sinks of potential vorticity balance departures from the free mode form, thus maintaining the large‐amplitude waves.
Simulations of the lunar sodium atmosphere
Authors: Flynn B. , Mendillo M.
Published: February 2004

A new Monte Carlo type model of the lunar sodium atmosphere has been developed and applied to recent ground‐based imaging observations. The model assumes a steady state atmosphere with production of sodium due to a spatially uniform source (e.g., meteor impact vaporization) or a solar zenith angle dependent source (e.g., solar wind sputtering or photodesorption). The loss processes included in the model are surface adsorption and photoionization. Solar radiation pressure is also accounted for. The model output is analyzed for overall spatial structure and compared with recent observations and theory. The results indicate that a sodium release mechanism that decreases in source rate with increasing solar zenith angle is best able to reproduce imaging data taken on September 30, 1991.
The dimensions of the Chicxulub impact crater and impact melt sheet
Authors: Kring David A.
Published: February 2004

The Chicxulub impact crater, which is the principal source of impact debris in Cretaceous‐Tertiary boundary sediments, is currently buried by a ∼1 km thick sequence of carbonate sediments. Because the crater is not exposed for direct scrutiny, its size has remained uncertain, and in particular, estimates ranging from ∼100 to ∼300 km have been made on the basis of gravity and magnetic field data. In this study, the physical properties of the K/T boundary impact ejecta and Chicxulub impact melt sheet have been used to test the geophysical estimates of the impact crater's size. On the basis of the measured thickness of impact ejecta in Haiti and North America, the calculated volume of the impact melt sheet, and the chemical and isotopic composition of the melt sheet, the Chicxulub impact crater is inferred to be ∼180 km in diameter and to contain a ∼3 to 7 km thick melt sheet and breccia sequence within a centrally located ∼100 km diameter region that corresponds to the limits of the transient cavity.
The geology of Callisto
Authors: Schenk Paul M.
Published: February 2004

The geology of Callisto is not boring. Although cratered terrain dominates Callisto (a key end‐member of the Jovian satellite system), a number of more interesting features are apparent. Cratered terrain is broken into irregular mappable bright and dark subunits that vary in albedo by a factor of 2, and several relatively smooth units are depleted of small craters. Some of these areas may have been volcanically resurfaced. Lineaments, including parallel and radial sets, may be evidence for early global tectonism. Frost deposition occurs in cold traps, and impact scars have formed from tidally disrupted comets. Geologic evidence suggests that Callisto does have a chemically differentiated crust. Central pit and central dome craters and palimpsests are common. The preferred interpretation is that a relatively ice‐rich material, at depths of 5 km or more, has been mobilized during impact and exposed as domes or palimpsests. The close similarity in crater morphologies and dimensions indicates that the outermost 10 km or so of Callisto may be as differentiated as on Ganymede. The geology of cratered terrain on Callisto is simpler than that of cratered terrain on Ganymede, however. Orbital evolution and tidal heating may provide the answer to the riddle of why Callisto and Ganymede are so different (Malhotra, 1991). We should expect a few surprises and begin to answer some fundamental questions when Callisto is observed by Galileo in late 1996.
Lunar surface aluminum and iron concentration from Galileo solid state imaging data, and the mixing of mare and highland materials
Authors: Fischer Erich M. , Pieters Carle M.
Published: February 2004

Apollo X ray spectrometer data provide chemical information for 9% of the lunar surface. Galileo solid state imaging system (SSI) multispectral data for the Moon are employed to reexamine the long‐accepted positive correlation between lunar surface reflectance (or albedo) and aluminum concentration, derived from Apollo X ray spectrometer data. The overall goal of the analysis is to quantify the relationship between reflectance and aluminum, and to take advantage of the extensive spatial coverage of the SSI data (∼75% of the lunar surface) to calculate aluminum concentration from SSI reflectance for the majority of the lunar surface. After removing nonmature highlands from the analysis, it is found that the relationship between lunar surface reflectance and X ray spectrometer‐derived aluminum concentration is described by two diffuse endmembers, representing highland and mare materials, and an apparent mixing line suggestive of mixtures of mare and highland materials. Regression analysis is utilized to show that whereas the correlation between reflectance and aluminum for the entire lunar soil system is fairly good, the correlations for mare soils alone and for highland soils alone are extremely low. The low precision of the X‐ray data may at least in part be responsible for the observed poor correlations. Although the low correlation for the individual soil types precludes the precise calculation of aluminum concentration from reflectance, approximate aluminum contents can be determined. The excellent inverse correlation between aluminum and iron concentration for returned lunar soils allows an estimation of iron content to be made as well. An extensive zone of mixtures of mare and highland soils exists in the vicinity of mare‐filled impact basins, and around smaller craters. This zone occurs in morphologically defined mare and highland units. Physical mixing of more mafic and less mafic material due to vertical and lateral transport by impact and downslope movement can account for the widespread mixing zones.
Hydrogen and deuterium in the thermosphere of Venus: Solar cycle variations and escape
Authors: Hartle R. E. , Donahue T. M. , Grebowsky J. M. , Mayr H. G.
Published: February 2004

A strong solar cycle variation in hydrogen and deuterium densities is observed in the nightside thermosphere of Venus when Pioneer Venus Orbiter (PVO) measurements made during the first three Venus years of the mission are compared with those made during the preentry phase of the mission. Solar maximum conditions prevailed during the former period, while near solar minimum conditions occurred during the latter. Pronounced density enhancements in H of 6.5 times and D of 4 times are observed in the nightside bulge region as solar activity decreased from maximum to near‐minimum values. We attribute the buildup of H and D to a reduction in the escape fluxes as solar activity decreased, a behavior that is consistent with the known properties of the dominant escape processes due to the charge separation electric field (E) and charge exchange (CE). Application of this simple concept leads to expressions for the H and D escape fluxes which relate solar cycle variations of the respective bulge densities and escape fluxes to the dayside source fluxes. Planet averaged escape fluxes in the ranges
and
are obtained by this method without specifying any particular escape mechanism. Considering the uncertainties in the measured parameters, these flux ranges are in reasonable agreement with the escape fluxes derived from the specific processes, E and CE. When fractionation without or with an external source of water (e.g., comets) is applied to the range of possible escape fluxes, a fractionation factor f = 0.44 is obtained and an ancient reservoir of water equivalent to the range 125 m to 570 m of liquid uniformly distributed on the surface or 3.7% to 17% of a full terrestrial ocean is derived. When the specific escape processes E and E + CE are considered, the f values are 0.15 and 0.1 and the magnitudes of the reservoirs are lower, having a range of equivalent depths of 4.1 m to 36.8 m, respectively.
Sputtering of water ice surfaces and the production of extended neutral atmospheres
Authors: Shi M. , Baragiola R. A. , Grosjean D. E. , Johnson R. E. , Jurac S. , Schou J.
Published: February 2004

Plasma and UV photon bombardment of an icy object in the outer solar system can lead to ejection of atoms and molecules from the surface which can, in turn, produce an extended neutral atmosphere. We present new laboratory studies of the sputtering of water ice by keV ions (H+ through Ne+) made using a sensitive microbalance technique that allows measurements at very low ion fluences. These results for the sputtering yield of ice by keV O+ ions, the dominant sputtering agents in the Saturnian magnetosphere, are much larger than those used previously to model the neutral cloud associated with the icy satellites. The data presented are used to recalculate previously published sputtering rates for the icy satellites of Jupiter and Saturn, and for the E‐ring grains at Saturn. The new results can account, in part, for the discrepancy between the predicted and observed OH cloud near Tethys in Saturn's inner magnetosphere. We compare the yields induced by the incident ions to the recently measured UV photosputtering yield, and discuss possible synergism between UV photon and plasma ion induced erosion.
Midinfrared (5.0 – 25 μm, 2000 – 400 cm−1) optical constants of hydrous carbonate, sulfate, and nitrate
Authors: Roush Ted L.
Published: February 2004

Fresnel reflectance and dispersion analysis are used to derive the real and imaginary indices of refraction of hydrous carbonate (dypingite) and hydrous sulfate (fibroferrite), in the 5.0 – 25 μm wavelength region, and hydrous nitrate/sulfate (darapskite) in the 5 – 17 μm wavelength region. These indices are useful for theoretical modeling of the radiative transfer that occurs within atmospheres of planets and particulate surfaces of solid bodies in the solar system.
The magnetic fields of Uranus and Neptune: Methods and models
Authors: Holme Richard , Bloxham Jeremy
Published: February 2004

We present new models of the magnetic fields of Uranus and Neptune, based on data provided by the Voyager II magnetic field experiment. We find the simplest models that satisfy the data, and use the observed surface heat flow as a constraint on the magnetic field structure. Our models are similar to the previously described Q3 and O8 models far from the planets, but resolve smaller‐scale structure close to the planets' surfaces. The field of Neptune is much better constrained than that of Uranus, and the field in the northern hemisphere of Neptune is much better constrained than that in the southern hemisphere, of importance for studies of Neptunian northern hemisphere radio sources. Using extremal models, we show that the large dipole tilts and nondipole dominance of the fields are robust features required by the data. Scaling analysis suggests that the toroidal field that would be required for a magnetostrophic balance in the dynamo region would result in ohmic dissipation greater than the observed surface heat flow. Thus we suggest that the dynamos of Uranus and Neptune are energy limited, and that the subsequent lack of magnetostrophic balance may account for the radically different field morphologies of Uranus and Neptune compared with the Earth, Jupiter, and Saturn.
O(1S) production following electron impact dissociative excitation of NO
Authors: LeClair Lance R. , Derbyshire Joseph M. , McConkey J. William
Published: February 2004

Solid Xe was used to detect oxygen atoms in the 1S metastable state following their production by electron impact on nitric oxide. Time‐of‐flight spectra of O(1S) for several electron impact energies were obtained. The repulsive portion of the potential curve for one of the parent states of NO which led to O(1S) was deduced from the data.
A δ13C record of Upper North Atlantic Deep Water during the past 2.6 million years
Authors: Oppo D. W. , Raymo M. E. , Lohmann G. P. , Mix A. C. , Wright J. D. , Prell W. L.
Published: February 2004

Benthic foraminiferal δ13C data from site 502 in the Caribbean Sea (sill depth ∼1800 m) indicate that throughout the past 2.6 m.y., glacial δ13C values in the middepth Atlantic were higher during glaciations than interglaciations. This is interpreted as indicating a greater proportion of Upper North Atlantic Deep Water (UNADW) relative to southern source waters during glaciations. The contribution of UNADW during interglaciations to the middepth Atlantic remained approximately constant, and the contribution during glaciations may have been as much as 10 % higher in the late Pleistocene than in the late Pliocene. This small increase is in striking contrast to the much larger decrease in glacial Lower North Atlantic Deep Water (LNADW) contribution relative to southern sources, from about 80% to about 20%, that occurred over the past 2.6 m.y. Glacial intensification over the past 2.6 m.y. was probably coupled with a decrease in northward heat transport by the upper limb of the North Atlantic circulation cell, as was previously suggested on the basis of a LNADW record alone. Late Pleistocene (1 Ma‐present) δ13C values in the Caribbean Sea were approximately 0.2‰ higher than they were from 2.6 to 2.0 Ma. The δ13C rise is not due to an increase in the mean ocean δ13C value, nor can it be entirely attributed to an increase in the proportion of high‐δ13C source waters. An increase in the δ13C value of the surface source waters must have contributed to the δ13C rise.
Holocene paleoceanography and paleoenvironments of the Skagerrak‐Kattegat, Scandinavia
Authors: Conradsen Keld , Heier‐Nielsen Susanne
Published: February 2004

Paleoceanographic and paleoenvironmental interpretations based on foraminifera, sedimentary data, radiocarbon dates, and stable isotope measurements were derived from two sections in the Skagerrak: a 115‐m‐thick Holocene marine section drilled onshore at Skagen near the northernmost tip of Jutland, Denmark, and a 9‐m piston core from the Skagerrak, north of Skagen. The foraminiferal data show that arctic‐subarctic environments in the deep Skagerrak‐Kattegat area were succeeded by boreal conditions at 9.6 ka. This was a result of northward migration of the Atlantic polar front and inflow of warm Atlantic water into the area through the Norwegian Channel. A gradual warming of the water masses after 9.6 ka is indicated by the data. Rare foraminifera and high sedimentation rates are found between approximately 8.6 ka and 7.6 ka at both core locations. The modern foraminiferal assemblages of the area were fully established at 7.6 ka indicating that the modern circulation pattern in the Skagerrak‐Kattegat after the opening of the English Channel and the Danish Straits was not established before this date. At 5.5 ka a sudden change to coarser sediments (higher‐energy environments) and the appearance of the foraminifer Eoeponidella laesoeensis is recorded in the Skagen core. This indicates a rapid change in the hydrography reflecting altered meteorological and hydrographic conditions in the Skagerrak‐Kattegat, including a strengthening of the Jutland Current and increased inflow of North Sea water into the Kattegat. The event is interpreted as a response to cooling at the end of the Holocene climatic optimum in late Atlantic time and possibly reflects a rapid cooling event of North Atlantic surface water masses.
Glacial to interglacial surface nutrient variations of Bering Deep Basins recorded by δ13C and δ15N of sedimentary organic matter
Authors: Nakatsuka Takeshi , Watanabe Kazuki , Handa Nobuhiko , Matsumoto Eiji , Wada Eitaro
Published: February 2004

Stable carbon and nitrogen isotopic ratios (δ13C and δ15N) of organic matter were measured in three sediment cores from deep basins of the Bering Sea to investigate past changes in surface nutrient conditions. For surface water reconstructions, hemipelagic layers in the cores were distinguished from turbidite layers (on the basis of their sedimentary structures and 14C ages) and analyzed for isotopic studies. Although δ13C profiles may have been affected by diagenesis, both δ15N and δ13C values showed common positive anomalies during the last deglaciation. We explain these anomalies as reflecting suppressed vertical mixing and low nutrient concentrations in surface waters caused by injection of meltwater from alpine glaciers around the Bering Sea.

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Three hundred eighty thousand year long stable isotope and faunal records from the Red Sea: Influence of global sea level change on hydrography
Authors: Hemleben Christoph , Meischner Dieter , Zahn Rainer , Almogi‐Labin Ahuva , Erlenkeuser Helmut , Hiller Birgit
Published: February 2004

Stable isotope and faunal records from the central Red Sea show high‐amplitude oscillations for the past 380,000 years. Positive δ18O anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the Arabian Sea was reduced due to a reduced geometry of the Bab el Mandeb Strait. Salinities as high as 53‰ and 55‰ are inferred from pteropod and benthic foraminifera δ18O, respectively, for the last glacial maximum. During this period all planktonic foraminifera vanished from this part of the Red Sea. Environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level. The foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka. Spectral analysis of the planktonic δ18O record documents highest variance in the orbital eccentricity, obliquity, and precession bands, indicating a dominant influence of climatically ‐ driven sea level change on environmental conditions in the Red Sea. Variance in the precession band is enhanced compared to the global mean marine climate record (SPECMAP), suggesting an additional influence of the Indian monsoon system on Red Sea climates.
Recent advances in understanding the interaction of groundwater and surface water
Authors: Winter Thomas C.
Published: February 2004

The most common image of the interaction of groundwater and surface water is that of the interaction of streams with a contiguous alluvial aquifer. This type of system has been the focus of study for more than 100 years, from the work of Boussinesq (1877) to the present, and stream‐aquifer interaction continues to be the most common topic of papers discussing the interaction of groundwater and surface water. However, groundwater and surface water interact in a wide variety of landscapes from alpine to coastal. Within these landscapes, ground‐water systems range in scale from local to regional, and the types of surface water include streams, lakes, wetlands, and oceans. Given the broad spectrum of the topic of groundwater and surface water interaction, an overview of studies of this topic could be organized according to surface water type, landscape type, scale of hydrologic systems, or field and analytical methods. All these factors are discussed, but this paper is organized according to landscape type because of the great increase in studies of the interaction of groundwater and surface water in landscapes other than riverine systems in the last 15 years. Furthermore, discussing studies by landscape type facilitates comparison of methods and results from different geologic and climatic settings. The general landscapes discussed are mountain terrane, riverine systems, coastal terrane, hummocky terrane, and karst terrane.
Major greenhouse cooling (yes, cooling): The upper atmosphere response to increased CO2
Authors: Roble R. G.
Published: February 2004

Is the Earth's atmosphere becoming more Venus‐like because of increased trace gas emissions from human activity? Venus apparently has a runaway “Greenhouse” where massive amounts of carbon dioxide have caused the atmospheric temperature near the surface to reach 700K with an atmospheric vertical temperature profile that decreases monotonically from the surface to the thermosphere (100 km altitude) where temperatures are on the order 100–250K. In fact, the nighttime thermospheric temperature of Venus is so low, 100K, that it has received the name “Venus Cryosphere.” The Venus atmosphere temperature structure is established by trapped infrared (IR) radiation from CO2 near the surface that raises it's temperature to unbearably high levels, but, the IR radiation that escapes to space from the upper atmosphere is so large that the resulting temperature is very cold.
Seismic studies of the upper mantle and transition zone
Authors: Shearer Peter M.
Published: February 2004

In the last few years, seismic studies of the upper mantle and transition zone have achieved significant new results in several areas. Progess has been driven largely by the increasing size, quality and accessibility of digital seismic datasets from global and regional networks and from experiments using portable instruments. This paper focuses on a few of the most interesting and important developments. These include: (1) measurements of upper mantle anisotropy, obtained using a variety of techniques, which can reveal details of the flow regimes and tectonic history of the upper mantle, (2) improvements in models of upper mantle velocity and attenuation structure, with some controversy arising regarding how deep slow velocity anomalies extend beneath oceanic ridges, (3) direct seismic observations of topography on the 410‐ and 660‐km discontinuities in the upper mantle, providing constraints on mantle temperatures and dynamics, and (4) observations suggesting secondary seismic discontinuities in some regions.
Geophysical Laboratory and Center for High‐Pressure Research, Carnegie Institution of Washington
Authors: Duffy Thomas S , Hemley Russell J.
Published: February 2004

The Earth's temperature distribution is intimately connected to problems of the structure, composition, dynamic state, and evolution of the planet. The high temperatures in the interior provide the driving force for the Earth's convective engine and are ultimately responsible for the vigorous geological activity on the surface of the planet. The past quadrennium has witnessed major advances in our understanding of the thermal structure of the Earth. In this short review of primarily U.S. work, only a few highlights of recent advances can be summarized. While considerable progress has been made, a number of aspects of the Earth's temperature structure remain highly controversial.
The viscosity structure of the mantle
Authors: King Scott D
Published: February 2004

During 1991–1994,the four year period covered by this report,there has been a shift in emphasis away from one‐dimensional (radial) mantle viscosity models and toward an understanding of the three‐dimensional (radial and lateral) structure of mantle viscosity. Our understanding of mantle viscosity comes primarily from two sources: studying the creep properties of mantle minerals under appropriate pressures and temperatures and using theoretical flow models to predict surface observables, such as: plate velocities, gravity, geoid, and heat flow. Laboratory measurements of deformation indicate that the rheology of upper mantle minerals such as olivine ((Mg,Fe)2SiO4) is a strong function of temperatue, grain size, and stress [cf., Karato and Wu, 1993]. The deformation of minerals under mantle conditions generally follows a flow law of the form

urn:x-wiley:87551209:media:rog1798:rog1798-math-0001
where ϵ is the deformation rate,σ is the deviatoric stress, μ is the shear modulus,d is the grain size of the rock, Q is the activation energy for the deformation mechanism,T is the temperature in Kelvin,R is the gas constant and A is a constant. Viscosity is defined as

urn:x-wiley:87551209:media:rog1798:rog1798-math-0002
therefore, deformation is directly related to viscosity. Substituting equation (1) into equation (2), an effective viscosity,

urn:x-wiley:87551209:media:rog1798:rog1798-math-0003
can be defined.For temperature changes of 100 degrees K, the viscosity changes by an order of magnitude at constant stress [cf., Karato and Wu,1993].Changes of deviatoric stress by a factor of 2 change the viscosity by an order of magnitude [cf., Karato and Wu,1993]. Other factors, such as partial pressure of oxygen and water content may also have important effects.
The ionosphere as a screen for magnetospheric processes
Authors: Lyons L. R.
Published: February 2004

The ionosphere acts like a television screen by lighting up with animated displays of aurora, which result from the bombardment of particles from the magnetosphere. The particles travel along magnetic‐field lines, and important information about remote magnetospheric processes is revealed by the ionospheric emissions they stimulate. More than this, the remote processes involve structured electric fields and currents, which are also conveyed along magnetic‐field lines to the ionosphere. Consequently, ionospheric observations offer the exciting opportunity to monitor magnetospheric processes in two dimensions and to thus provide an increasingly important complement to in‐situ magnetospheric observations. This type of remote sensing helps to overcome the current sparsity of satellite missions to the magnetosphere. It is also relatively low‐cost and has the potential for global coverage and high temporal and spatial resolution. Such observations are indeed becoming increasingly valuable for the study of processes occurring in the Earth's magnetosphere. The NSF Geospace Environment Modeling (GEM) program, for example, is incorporating ionospheric observations as an integral part of its program to study magnetospheric processes.
Chaos, fractals, nonlinear phenomena in Earth sciences
Authors: Turcotte Donald L.
Published: February 2004

Many problems in geophysics can be solved using linear equations. Examples include seismic waves, the earth's gravity and magnetic field, and problems involving heat flow and elasticity. However, other problems are essentially non linear; the classic example is fluid turbulence. In the past twenty years major advances have been made in the understanding of nonlinear problems. In the past four years many of these advances have been applied to geophysical problems.
Coronal mass ejections: The key to major interplanetary and geomagnetic disturbances
Authors: Webb David F.
Published: February 2004

For years it was thought that solar flares were responsible for major interplanetary (IP) particle events and geomagnetic storms. However, recently we have seen an important paradigm shift such that now coronal mass ejections (CMEs), not flares, are considered the key causal link with solar activity. CMEs are vast structures of plasma and magnetic fields that are expelled from the sun into the heliosphere. We now know that CMEs drive all large geomagnetic storms and their attendant effects, such as auroral displays. Fast CMEs produce transient IP shocks which cause sudden commencements at Earth. The CME‐related shocks also accelerate the solar energetic particle (SEP) events associated with major IP disturbances and with radiation hazards at Earth. This new paradigm has important implications for prioritizing the development of instruments and techniques to predict IP disturbances and geomagnetic activity.
Recent advances associated with large scale field experiments in hydrology
Authors: Kustas William P.
Published: February 2004

Recent efforts have concentrated on developing models that couple the hydrologic cycle with climate because evaporated water (latent heat flux) from the land surface and oceans has a significant impact in regulating the energy balance of the atmosphere, which in turn feedbacks to drive atmospheric circulation and weather. The coupling of the hydrologic cycle and climate occurs at different tune and spatial scales and is not well understood. For example, evaporation from the land‐surface and atmospheric boundary layer development interact at time scales or hours whereas changes in root zone soil moisture and synoptic weather patterns occur over time scales of days to weeks. Moreover, it is difficult to validate model simulations at regional and certainly at the global circulation model (GCM) scale. On the other hand, it is imperative that we validate GCM output because unless these models can reliably simulate the observed water and energy cycles in the present climate, future predictions of climate change are rather tenuous (Kinter and Shukla, 1990).
Recent advances in remote sensing in hydrology
Authors: Engman Edwin T.
Published: February 2004

Remote sensing has held a great deal of promise for hydrology, mainly because of the potential to observe areas and entire river basins rather than merely points. In addition, as the remote sensing science has developed we have learned of the potential to make entirely new measurements of hydrologic variables not generally possible with traditional techniques. In spite of this promise, applied or engineering hydrology has been slow to embrace remote sensing as a useful source of data, presumably because existing techniques and data have been satisfactory for limited applications. Most of the advances in using remote sensing for hydrology have come from new areas of hydrologic analysis; areas where existing methods were unsatisfactory or limiting and areas where sufficient data were sparse or nonexistent. These areas include General Circulation Model (GCM) land parameterizations, advances in snow hydrology and the measurement of soil moisture.
U.S. science in a changing context: A perspective
Authors: Radford Byerly, Jr.
Published: February 2004

In 1989 Francis Fukuyama, a senior policy analyst at the U.S. Department of State, wrote a paper about the end of the Cold War entitled “The End of History?” It offered an intriguing thesis: “What we may be witnessing is not just the end of the Cold War, or the passing of a particular period of postwar history, but the end of history as such; that is, the end point of mankind's ideological evolution and the universalization of Western liberal democracy as the final form of human government” [Fukuyama, 1989 p 4]. What Fukuyama calls “the end of history” is an important change in the context of science for two overlapping reasons. First, because the challenge of the communist Soviet Union drove United States science policy for much of the twentieth century. Second, because the atomic bomb and a subsequent series of events and circumstances—including SDI, the Green Revolution, AIDS, and now global change—have connected science to global geopolitics, irreversibly enlarging its relevant context.
Catching the wave: ULF research in the U.S. since 1991
Authors: Engebretson Mark J.
Published: February 2004

Variations in the ultra‐low frequency (ULF) range, with periods from 0.1 to 600 seconds, were noted in the Earth's magnetic field long before they were understood to be indicators of plasma processes in the Earth's space environment. They are now also recognized as a significant means of dissipating solar wind and/or magnetospheric energy and as a primary means of coupling magnetospheric and ionospheric processes. ULF waves also constitute the source field for electromagnetic induction studies of the structure and motions of conductive bodies in the Earth. Knowledge of the spatial and temporal variation of these waves thus can aid in our understanding of properties of both Earth's external plasma environment and its underlying oceans, crust, and mantle.
Biomineralization of magnetic minerals
Authors: Moskowitz Bruce M.
Published: February 2004

New developments and discoveries in biomineralization have occurred almost continuously in the intervening decade since the previous IUGG quadrennial report on biomineralization and biomagnetism was published [Kirschvink, 1983]. Biomineralization is widespread in the biosphere and over 60 different inorganic minerals are produced by a variety of organisms from bacteria to humans [Lowenstam and Weiner, 1989]. The literature on biomineralization is interdisplinary, combining research in microbiology, biotechnology, physics, geology, and paleomagnetism. For paleomagnetism and rock magnetism, iron biomineralization of magnetic minerals is of prime importance. From a paleomagnetism perspective, biogenic magnetic minerals can be deposited in sediments and acquire a natural remanent magnetization that preserves a record of the ancient geomagnetic field. From a rock magnetism perspective, biogenic magnetic minerals provide novel sources of magnetic material for experimental studies in fine particle magnetism. Both perspectives are interrelated through a common goal of developing magnetic techniques to detect biogenic magnetic minerals in sediments and soils. For example, the extent to which iron biominerals contribute to the fine‐grained magnetic mineral assemblages in freshwater and marine sediments is important for identifying and interpreting the magnetic record of environmental change [Oldfield, 1992; Reynolds and King, this issue].
Tracers, time scales, and the thermohaline circulation: The lower limb in the North Atlantic Ocean
Authors: Fine Rana A.
Published: February 2004

This paper reviews the contributions of transient tracer research to our understanding of the lower limb of the thermohaline circulation in the North Atlantic Ocean. The review is limited geographically to the North Atlantic because of its importance for decadal scale climate variability. The tracers reviewed are the transient tracers of anthropogenic origin that give decadal time scale information, the chlorofluorocarbons (CFCs) and tritium/3He. The emphasis is on work by United States (US) investigators from 1991–94. Also included are some non‐US and earlier contributions as they are linked to the recent work and have not been reviewed in this publication before.
Molecular markers of zooplankton dispersal in the ocean
Authors: Bucklin Ann
Published: February 2004

Ocean circulation patterns determine in large part the patterns of biological productivity in coastal and oceanic waters. Prediction of the spatial patterns of secondary production in the ocean is particularly difficult since dispersal of zooplankton is a function of both passive transport and active swimming by zooplankton, which may exhibit highly variable behavioral responses to flow. Quantitative estimates of dispersal are particularly difficult to obtain for marine zooplankton; the difficulty of direct observation of dispersal processes is magnified by their small size and numerical abundance and by the vast distances they traverse. The inaccessibility of the open ocean further compounds the problem, since many parts of the ocean are difficult to sample with the spatial intensity and temporal frequency necessary to determine dispersal processes. Unlike biomass and abundance estimates for marine planktonic species, dispersal processes may not be amenable to remote monitoring.
The GISP2 ice core record—Paleoclimate highlights
Authors: Mayewski Paul A. , Bender Michael
Published: February 2004

Understanding the Earth system and, in particular, its climate, remains one of the major intellectual challenges faced by science. The processes influencing climate, the mechanisms through which they act, and the responses they generate are, in general, as complex and poorly understood as they are important. Because observational records of climate processes span only the most recent years of Earth's history and, in many instances, are known to be markedly affected by anthropogenic influences, paleorecords of past climates are exceedingly important to the development of scientific understanding of local, regional, and global climate systems. Of the various paleorecords available to science, ice cores from polar ice sheets provide the most direct and highest resolution view of the paleoatmosphere.