bluuebunny/crossref_metadata_2025 huggingface dataset:
Minor trace gas radiative forcing calculations using the k distribution method with one‐parameter scaling
Authors: Kratz David P. , Chou Ming‐Dah , Yan Michael M.‐H. , Ho Chang‐Hoi
Published: February 2004

The k distribution method with one‐parameter pressure and temperature scaling, first developed for water vapor, has now been applied to the minor trace gas (N2O, CH4, CFCs, and two minor bands of CO2) absorption in the infrared window region (800–1380 cm−1). The derivation of the k distributions is based upon an exponential sum fitting to the monochromatically calculated transmission functions at a predetermined reference pressure and temperature. For nonhomogeneous path lengths, one‐parameter scaling is utilized in conjunction with the k distribution method. To determine the accuracies of the k distribution method as compared to the monochromatic calculations, fluxes and cooling rates are calculated for a wide variety of atmospheric conditions. For the entire 800–1380 cm−1 spectral range the effect of the minor trace gases on the fluxes calculated using the k distribution method is within 2.3% of the monochromatic method. In addition to being accurate, this method is computationally very fast. When implemented into the Goddard EOS general circulation model, the computing time for the longwave flux calculations is increased by only 20% despite the inclusion of the minor trace gas absorption bands.
Discriminating clear sky from clouds with MODIS
Authors: Ackerman Steven A. , Strabala Kathleen I. , Menzel W. Paul , Frey Richard A. , Moeller Christopher C. , Gumley Liam E.
Published: February 2004

The MODIS cloud mask uses several cloud detection tests to indicate a level of confidence that the MODIS is observing clear skies. It will be produced globally at single‐pixel resolution; the algorithm uses as many as 14 of the MODIS 36 spectral bands to maximize reliable cloud detection and to mitigate past difficulties experienced by sensors with coarser spatial resolution or fewer spectral bands. The MODIS cloud mask is ancillary input to MODIS land, ocean, and atmosphere science algorithms to suggest processing options. The MODIS cloud mask algorithm will operate in near real time in a limited computer processing and storage facility with simple easy‐to‐follow algorithm paths. The MODIS cloud mask algorithm identifies several conceptual domains according to surface type and solar illumination, including land, water, snow/ice, desert, and coast for both day and night. Once a pixel has been assigned to a particular domain (defining an algorithm path), a series of threshold tests attempts to detect the presence of clouds in the instrument field of view. Each cloud detection test returns a confidence level that the pixel is clear ranging in value from 1 (high) to zero (low). There are several types of tests, where detection of different cloud conditions relies on different tests. Tests capable of detecting similar cloud conditions are grouped together. While these groups are arranged so that independence between them is maximized, few, if any, spectral tests are completely independent. The minimum confidence from all tests within a group is taken to be representative of that group. These confidences indicate absence of particular cloud types. The product of all the group confidences is used to determine the confidence of finding clear‐sky conditions. This paper outlines the MODIS cloud masking algorithm. While no present sensor has all of the spectral bands necessary for testing the complete MODIS cloud mask, initial validation of some of the individual cloud tests is presented using existing remote sensing data sets.
Radiative forcing by mineral dust aerosols: Sensitivity to key variables
Authors: Liao H. , Seinfeld J. H.
Published: February 2004

We examine diurnally averaged radiative forcing by mineral dust aerosols in shortwave and longwave spectral regions using a one‐dimensional column radiation model. At the top of the atmosphere (TOA), net (shortwave plus longwave) dust radiative forcing can be positive (heating) or negative (cooling) depending on values of key variables. We derive an analytical expression for the critical single‐scattering albedo at which forcing changes sign for an atmosphere containing both cloud and aerosol layers. At the surface, net dust forcing can be positive or negative under clear‐sky conditions, whereas it is always cooling in the presence of a low‐level stratus cloud. Longwave radiative forcing is essentially zero when clouds are present. We also study the sensitivity of dust diurnally averaged forcing to the imaginary part of refractive index (k), height of the dust layer, dust particle size, and dust optical depth. These variables play different roles as follows: (1) under both clear‐ and cloudy sky conditions, net TOA forcing is more sensitive to k than net surface forcing; (2) clear‐sky longwave forcing and cloudy‐sky TOA shortwave forcing are very sensitive to the altitude of the dust layer; although clear‐sky shortwave forcing is not sensitive to it; (3) clear‐sky shortwave forcing is much more sensitive to particle size than cloudy‐sky shortwave forcing; longwave forcing is not sensitive to particle size; and (4) all forcings are sensitive to optical depth except cloudy‐sky longwave forcing.
Parameterizations of the microphysical and shortwave radiative properties of boundary layer stratus from ground‐based measurements
Authors: Dong Xiquan , Ackerman Thomas P. , Clothiaux Eugene E.
Published: February 2004

In earlier work a δ2‐stream radiative transfer model was used in conjunction with ground‐based measurements to retrieve the rnicrophysical and shortwave radiative properties of boundary layer stratus. The effective radii output by the retrieval scheme for optically thick clouds have now been parameterized as a function of the cloud liquid water path, the transmission ratio, and the cosine of the solar zenith angle. The parameterization enables estimation of stratus cloud microphysical properties using ground‐based measurements that are readily available at a number of locations. To validate the retrieved and parameterized cloud microphysics, ∼5 hours of data were analyzed and compared to collocated in situ measurements made by a Forward Scattering Spectrometer Probe. On average, the retrieved values of the cloud droplet effective radius and the cloud droplet number concentration differed from the corresponding aircraft measurements by 7% and 27%, respectively, while the parameterized values differed from the aircraft measurements by 15% and 32%, respectively. Averaging all of the data to 30‐min resolution significantly reduced the differences between the aircraft data and the retrieved and parameterized results, suggesting that both the aircraft and the ground‐based data are capable of characterizing the cloud microphysics over this temporal scale. The parameterizations of the stratus shortwave radiative properties were generally within 5% of Slingo's four‐band, model‐derived parameterization when absorption above cloud top was incorporated into the Slingo parameterization.
Atmospheric transmission in the ultraviolet and visible: Aerosols in cloudy atmospheres
Authors: Erlick Carynelisa , Frederick John E. , Saxena V. K. , Wenny Brian N.
Published: February 2004

This study considers the effects of aerosols in cloudy atmospheres on the wavelength dependence of atmospheric transmission in the ultraviolet and visible parts of the solar spectrum. Normalizing the transmission to that of a cloud‐ and aerosol‐free atmosphere, we examine the competing influences of clouds and aerosols on the shape of the transmission function when clouds and aerosols are mixed; while pure water clouds cause the normalized transmission to decrease with wavelength from around 320 nm through the visible, aerosol particles cause the normalized transmission to increase with wavelength from 320 nm through the visible. The results show that when clouds are superimposed on an aerosol profile with the cloud drops and aerosol particles externally mixed, the shape of the normalized transmission spectrum is dominated by the effect of the cloud drops, unless the optical depth of the aerosols begins to approach the optical depth of the cloud. This is the case for an optically thin stratus cloud and an urban aerosol profile. When cloud drops and aerosol particles are internally mixed through coagulation, the shape of the normalized transmission spectrum is again dominated by the effect of the cloud drops, unless there is an unrealistically high volume fraction of strongly absorbing aerosols embedded in the droplets. While measurements of the mass fraction of absorbing aerosols such as soot in cloud and rainwater range from 3.0×10−9 to 6.9×10−6, a soot volume fraction of 1×10−4 is necessary to cause the normalized transmission to increase with wavelength from 320 nm through the visible. The model results are also shown to be consistent with Brewer spectrophotometer irradiance measurements under cloudy and hazy conditions.
Substorm effects of ionosphere and HF propagation
Authors: Blagoveshchensky D. V. , Borisova T. D.
Published: February 2004

Four subauroral HF radio paths are investigated during substorms of various intensities. The principal substorm effects are both an increase of the signal strength 1–2 hours before the substorm expansion phase and a change in the azimuth of the received signal. The latter is explained by increasing the intensities of irregularities caused by particle precipitation on the poleward edge of the main ionospheric trough. Model calculation of the signal amplitude variations during the substorm growth phase has been carried out. Excellent agreement between the model and observations is achieved when the critical frequency of the F2 layer is increased by several megacycles and the height of the F2 layer maximum is reduced by 20–40 km at the reflection point the nearest to the receiving center. Similar investigations may be useful for quantitative description of any ionospheric model within disturbed periods.
Remagnetization of Cretaceous forearc strata on Santa Margarita and Magdalena Islands, Baja California Sur: Implications for northward transport along the California margin
Authors: Hagstrum Jonathan T. , Sedlock Richard L.
Published: February 2004

Paleomagnetic data for two sections of Cretaceous forearc strata with different structural attitudes on Santa Margarita and Magdalena Islands in Baja California Sur, Mexico, indicate that these rocks have been remagnetized, probably during the late Cenozoic. The in situ paleomagnetic directions, however, are similar to data from other Cretaceous rocks on peninsular California with unexpectedly shallow inclinations and easterly declinations. These data have been interpreted as indicating either northward tectonic transport (10°–15° of latitude) and clockwise rotation (>20°) or compaction shallowing of magnetic inclinations in sedimentary rocks combined with southwestward tilting of plutonic rocks. The available paleomagnetic data for Cretaceous forearc strata in southern and Baja California can be divided into three groups: (1) sections with normal‐polarity magnetizations that fail fold tests and are remagnetized, (2) sections with normal‐polarity magnetizations with no or inconclusive fold tests that may or may not be remagnetized, and (3) sections with both normal‐and reversed‐polarity intervals where pervasive remagnetization has not occurred. Other rocks of the Mesozoic Great Valley Group, Coast Range ophiolite, and Franciscan Complex in California also have secondary magnetizations with directions similar to younger geomagnetic field directions. Although these widespread remagnetizations could have variable local causes, we propose regional burial and uplift, related to changes in subduction parameters, as a possible explanation. Two episodes of remagnetization are apparent: one in the Late Cretaceous and a second in the late Cenozoic. On the other hand, the unremagnetized and apparently reliable data from sedimentary and plutonic rocks on the Baja Peninsula consistently indicate northward translation (14° ± 3°) and clockwise rotation (29° ± 8°) with respect to North America since the Late Cretaceous.
Radiocarbon as a diagnostic tracer in ocean and carbon cycle modeling
Authors: Guilderson Thomas P. , Caldeira Kenneth , Duffy Philip B.
Published: February 2004

Models which are used to study the evolution of oceanic anthropogenic CO2uptake in a warmer climate need to be adequately tested before their results are used to influence science and national policy, let alone predict future regional climate. In order to study circulation and the redistribution of carbon in the ocean, we have simulated the uptake and redistribution of bomb radiocarbon in a state of the art ocean general circulation model. The model does reasonably well in simulating the gross surface prebomb distribution of radiocarbon as well as some of the finer details resolved during Geochemical Ocean Section Study and World Ocean Circulation Experiment observations. In areas of downwelling the simulated surface‐ocean bomb14C maxima occur too early with too much amplitude. This indicates inadequate vertical mixing and coupling between the wind driven and deeper regions of the ocean with a piling up of radiocarbon and CO2in the upper ocean. This inadequacy will hamper efforts to predict ocean CO2uptake on decadal to centennial timescales, the equivalent ventilation time of the respective water masses. These results are not specific to our model and indicate a systemic problem in many ocean models.
A process‐based, climate‐sensitive model to derive methane emissions from natural wetlands: Application to five wetland sites, sensitivity to model parameters, and climate
Authors: Walter Bernadette P. , Heimann Martin
Published: February 2004

Methane emissions from natural wetlands constitute the largest methane source at present and depend highly on the climate. In order to investigate the response of methane emissions from natural wetlands to climate variations, a one‐dimensional process‐based climate‐sensitive model to derive methane emissions from natural wetlands is developed. In the model the processes leading to methane emission are simulated within a one‐dimensional soil column and the three different transport mechanisms, diffusion, plant‐mediated transport, and ebullition, are modeled explicitly. The model forcing consists of daily values of soil temperature, water table, and net primary productivity, and at permafrost sites the thaw depth is included. The methane model is tested using observational data obtained at five wetland sites located in North America, Europe, and Central America, representing a large variety of environmental conditions. It can be shown that in most cases seasonal variations in methane emissions can be explained by the combined effect of changes in soil temperature and the position of the water table. Our results also show that a process‐based approach is needed because there is no simple relationship between these controlling factors and methane emissions that applies to a variety of wetland sites. The sensitivity of the model to the choice of key model parameters is tested and further sensitivity tests are performed to demonstrate how methane emissions from wetlands respond to longer‐term climate variations.
Approaches for reducing uncertainties in regional forest carbon balance
Authors: Chen Wenjun , Chen Jing , Liu Jane , Cihlar Josef
Published: February 2004

Accurate estimation of regional terrestrial ecosystem carbon (C) balance is critical in formulating national and global adaptation and mitigation strategies in response to global changes. Since the regional C balance cannot be measured directly, it has been estimated using various models. In such studies, errors often exceeded the magnitude of the estimated C balance due to two types of uncertainties: noninclusion of some important factors in the C cycle and the fact that the C balance is a small difference between several large fluxes that can each be determined with only a limited accuracy. In this study, we propose new approaches to reduce these uncertainties and implement them in an Integrated Terrestrial Ecosystem C‐budget model (InTEC). To minimize the first type of uncertainties, InTEC considers all the major factors presently known to affect C balance (including climate, atmospheric CO2 concentration, N deposition, and disturbances). To reduce the second type of uncertainties, InTEC estimates the C balance from historical changes in these factors, relative to the preindustrial period. InTEC is built on the basis of widely tested Century C cycling model, Farquhar's leaf photosynthesis model, and age‐NPP relationships, and is constrained by N cycling. As a general regional‐scale terrestrial ecosystem C budget model, InTEC has so far been applied to Canada's forests [Chen et al., this issue]. The sensitivity analysis showed that these two new approaches reduce the uncertainty in the C balance of Canada's forests substantially.
Annual carbon balance of Canada's forests during 1895–1996
Authors: Chen Jing , Chen Wenjun , Liu Jane , Cihlar Josef , Gray Stephen
Published: February 2004

This paper reports annual carbon (C) balance of Canada's forests during 1895–1996 estimated using the Integrated Terrestrial Ecosystem C‐budget model (InTEC) [Chen et al. this issue]. During 1895–1910, Canada's forests were small sources of 30±15 Tg C yr−1 due to large disturbances (forest fire, insect‐induced mortality, and harvest) in late nineteenth century. The forests became large sinks of 170±85 Tg C yr−1 during 1930–1970, owing to forest regrowth in previously disturbed areas and growth stimulation by nondisturbance factors such as climate, atmospheric CO2 concentration, and N deposition. In recent decades (1980–1996), Canada's forests have been moderate sinks of 50±25 Tg C yr−1, as a result of a tradeoff between the negative effects of increased disturbances and positive effects of nondisturbance factors. The nondisturbance factors, in order of importance, are (1) atmospheric N deposition (measured by a national monitoring network), (2) net N mineralization and fixation (estimated from temperature and precipitation records), (3) growing season length increase (estimated from spring air temperature records), and (4) CO2 fertilization (estimated from CO2 records using a leaf‐level photosynthesis model). The magnitudes of modeled nondisturbance effects are consistent with simulation results by the Carnegie‐Ames‐Stanford Approach (CASA) and are also in broad agreement with flux measurements above mature forest stands at several locations in Canada. Results for the disturbance effects agree with a previous study [Kurz and Apps, 1996]. The overall C balance from InTEC generally agrees with that derived from tree ring data [Auclair and Bedford, 1997] and from forest inventories. The combination of our result and that of Houghton et al. [1999] for the United States suggests that North America (> 15°N) was probably a C sink of 0.2‐0.5 Pg C yr±−1 during 1980s, much less than that of 1.7 Pg C yr±−1 estimated by Fan et al. [1998] using an atmospheric inversion method.
Atmospheric pCO2 sensitivity to the biological pump in the ocean
Authors: Archer David E. , Eshel Gidon , Winguth Arne , Broecker Wallace , Pierrehumbert Ray , Tobis Michael , Jacob Robert
Published: February 2004

In models of the global carbon cycle, the pCO2of the atmosphere is more sensitive to the chemistry of the high‐latitude surface ocean than the tropical ocean. Because sea‐surface nutrient concentrations are generally high in the high latitudes,pCO2sensitivity to high‐latitude forcing also determinespCO2sensitivity to the biological pump globally. We diagnose high‐latitude sensitivity of a range of ocean models using atmosphericpCO2above an abiotic ocean; cold high‐latitude waters pull abioticpCO2to low values. Box models are very high‐latitude sensitive, while most global circulation models are considerably less so, including a two‐dimensional overturning model, two primitive equation models, the Hamburg class of large scale geostrophic (LSG) general circulation models (GCMs), and the MICOM isopycnic GCM. High‐latitude forcing becomes more important in a depth‐coordinate GCM when lateral diffusion is oriented along isopycnal surfaces, rather than horizontally, followingRedi [1982]. In two different GCMs (a primitive equation model and LSG), addition of the Gent and McWillams[1990] isopycnal thickness diffusion scheme had only minor impact on high‐latitude sensitivity. Using a simplified box model, we show that high‐latitude sensitivity depends on a high‐latitude monopoly on deep water formation. In an attempt to bridge the gap between box models and GCMs, we constructed a simple slab overturning model with an imposed stream function which can be discretized at arbitrary resolution from box model to GCM scale. High‐latitude sensitivity is independent of model resolution but very sensitive to vertical diffusion. Diffusion acts to break the high‐latitude monopoly, decreasing high‐latitude sensitivity. In the isopycnal GCM MICOM, however, high‐latitude sensitivity is relatively insensitive to diapycnal diffusion of tracers such as CO2. This would imply that flow pathways in MICOM take the place of vertical diffusion in the slab model. The two nominally most sophisticated ocean models in the comparison are the isopycnal model MICOM and the depth‐coordinate GCM withRedi [1982] and Gent and McWilliams [1990] mixing. Unfortunately, these two models disagree in their abiotic CO2behavior; the depth‐coordinate isopycnal mixing GCM is high‐latitude sensitive, in accord with box models, while MICOM is less so. The rest of the GCMs, which have historically seen the most use in geochemical studies, are even less high‐latitude sensitive than MICOM. This discrepancy needs to be resolved. In the meantime, the implication of the MICOM/traditional GCM result would be that box models overestimate high‐latitude sensitivity of the real ocean. This would eliminate iron dust fertilization of the ocean as an explanation for the glacialpCO2 range of 180–200 μatm [Archer et al., 2000].
Testing the Hole‐in‐the‐Pipe Model of nitric and nitrous oxide emissions from soils using the TRAGNET Database
Authors: Davidson Eric A. , Verchot Louis V.
Published: February 2004

Because several soil properties and processes affect emissions of nitric oxide (NO) and nitrous oxide (N2O) from soils, it has been difficult to develop effective and robust algorithms to predict emissions of these gases in biogeochemical models. The conceptual “hole‐in‐the‐pipe” (HIP) model has been used effectively to interpret results of numerous studies, but the ranges of climatic conditions and soil properties are often relatively narrow for each individual study. The Trace Gas Network (TRAGNET) database offers a unique opportunity to test the validity of one manifestation of the HIP model across a broad range of sites, including temperate and tropical climates, grasslands and forests, and native vegetation and agricultural crops. The logarithm of the sum of NO + N2O emissions was positively and significantly correlated with the logarithm of the sum of extractable soil NH4+ + NO3−. The logarithm of the ratio of NO:N2O emissions was negatively and significantly correlated with water‐filled pore space (WFPS). These analyses confirm the applicability of the HIP model concept, that indices of soil N availability correlate with the sum of NO+N2O emissions, while soil water content is a strong and robust controller of the ratio of NO:N2O emissions. However, these parameterizations have only broad‐brush accuracy because of unaccounted variation among studies in the soil depths where gas production occurs, where soil N and water are measured, and other factors. Although accurate predictions at individual sites may still require site‐specific parameterization of these empirical functions, the parameterizations presented here, particularly the one for WFPS, may be appropriate for global biogeochemical modeling. Moreover, this integration of data sets demonstrates the broad ranging applicability of the HIP conceptual approach for understanding soil emissions of NO and N2O.
General model for N2O and N2 gas emissions from soils due to dentrification
Authors: Del Grosso S. J. , Parton W. J. , Mosier A. R. , Ojima D. S. , Kulmala A. E. , Phongpan S.
Published: February 2004

Observations of N gas loss from incubations of intact and disturbed soil cores were used to model N2O and N2 emissions from soil as a result of denitrification. The model assumes that denitrification rates are controlled by the availability in soil of NO3 (e− acceptor), labile C compounds (e− donor), and O2 (competing e− acceptor). Heterotrophic soil respiration is used as a proxy for labile C availability while O2 availability is a function of soil physical properties that influence gas diffusivity, soil WFPS, and O2 demand. The potential for O2 demand, as indicated by respiration rates, to contribute to soil anoxia varies inversely with a soil gas diffusivity coefficient which is regulated by soil porosity and pore size distribution. Model inputs include soil heterotrophic respiration rate, texture, NO3 concentration, and WFPS. The model selects the minimum of the NO3 and CO2 functions to establish a maximum potential denitrification rate for particular levels of e− acceptor and C substrate and accounts for limitation of O2 availability to estimate daily N2+N2O flux rates. The ratio of soil NO3 concentration to CO2 emission was found to reliably (r2=0.5) model the ratio of N2 to N2O gases emitted from the intact cores after accounting for differences in gas diffusivity among the soils. The output of the ratio function is combined with the estimate of total N gas flux rate to infer N2O emission. The model performed well when comparing observed and simulated values of N2O flux rates with the data used for model building (r2=0.50) and when comparing observed and simulated N2O+N2 gas emission rates from irrigated field soils used for model testing (r2=0.47).
Evaluating annual nitrous oxide fluxes at the ecosystem scale
Authors: Groffman Peter M. , Brumme Rainer , Butterbach‐Bahl Klaus , Dobbie Karen E. , Mosier Arvin R. , Ojima Dennis , Papen Hans , Parton William J. , Smith Keith A. , Wagner‐Riddle Claudia
Published: February 2004

Evaluation of N2O flux has been one of the most problematic topics in environmental biogeochemistry over the last 10–15 years. Early ideas that we should be able to use the large body of existing research on terrestrial N cycling to predict patterns of N2O flux at the ecosystem scale have been hard to prove due to extreme temporal and spatial variability in flux. The vast majority of the N2O flux measurement and modeling activity that has taken place has been process level and field scale, i.e., measurement, analysis and modeling of hourly and daily fluxes with chambers deployed in field plots. It has been very difficult to establish strong predictive relationships between these hourly and daily fluxes and field‐scale parameters such as temperature, soil moisture, and soil inorganic N concentrations. In this study, we addressed the question of whether we can increase our predictive understanding of N2O fluxes by examining relationships between flux and environmental parameters at larger spatial and temporal scales, i.e., to explore relationships between annual rather than hourly or daily fluxes and ecosystem‐scale variables such as plant community and soil type and annual climate rather than field‐scale variables such as soil moisture and temperature. We addressed this question by examining existing data on annual fluxes from temperate forest, cropland, and rangeland ecosystems, analyzing both multiyear data sets from individual sites as well as cross‐site comparison of single annual flux values from multiple sites. Results suggest that there are indeed coherent patterns in annual N2O flux at the ecosystem scale in forest, cropland, and rangeland ecosystems but that these patterns vary by region and only emerge with continuous (at least daily) flux measurements over multiple years. An ecosystem approach to evaluating N2O fluxes will be useful for regional and global modeling and for computation of national N2O flux inventories for regulatory purposes but only if measurement programs are comprehensive and continuous.
A revised nitrogen budget for the Arabian Sea
Authors: Bange H. W. , Rixen T. , Johansen A. M. , Siefert R. L. , Ramesh R. , Ittekkot V. , Hoffmann M. R. , Andreae M. O.
Published: February 2004

Despite its importance for the global oceanic nitrogen (N) cycle, considerable uncertainties exist about the N fluxes of the Arabian Sea. On the basis of our recent measurements during the German Arabian Sea Process Study as part of the Joint Global Ocean Flux Study (JGOFS) in 1995 and 1997, we present estimates of various N sources and sinks such as atmospheric dry and wet depositions of N aerosols, pelagic denitrification, nitrous oxide (N2O) emissions, and advective N input from the south. Additionally, we estimated the N burial in the deep sea and the sedimentary shelf denitrification. On the basis of our measurements and literature data, the N budget for the Arabian Sea was reassessed. It is dominated by the N loss due to denitrification, which is balanced by the advective input of N from the south. The role of N fixation in the Arabian Sea is still difficult to assess owing to the small database available; however, there are hints that it might be more important than previously thought. Atmospheric N depositions are important on a regional scale during the intermonsoon in the central Arabian Sea; however, they play only a minor role for the overall N cycling. Emissions of N2O and ammonia, deep‐sea N burial, and N inputs by rivers and marginal seas (i.e., Persian Gulf and Red Sea) are of minor importance. We found that the magnitude of the sedimentary denitrification at the shelf might be ∼17% of the total denitrification in the Arabian Sea, indicating that the shelf sediments might be of considerably greater importance for the N cycling in the Arabian Sea than previously thought. Sedimentary and pelagic denitrification together demand ∼6% of the estimated particulate organic nitrogen export flux from the photic zone. The main northward transport of N into the Arabian Sea occurs in the intermediate layers, indicating that the N cycle of the Arabian Sea might be sensitive to variations of the intermediate water circulation of the Indian Ocean.
Paleoclimate and vegetation of the Last Glacial Cycles in Jerusalem from a Speleothem Record
Authors: Frumkin Amos , Ford Derek C. , Schwarcz Henry P.
Published: February 2004

A speleothem isotopic record taken from Jerusalem is used to reconstruct regional climate over the last 170,000 years. Glacial periods in Jerusalem were generally cooler and wetter than the present climate. Stage 5e in the desert margin of Jerusalem was extremely unstable, dry, and warm, and instability persisted throughout the transition to glacial conditions. The climate after stage 5e became gradually cooler and wetter over a 20,000‐year interval and did not recover to interglacial conditions in stages 5c and 5a. The δ13C varied by up to 12‰, from glacial (stages 6, 4, 3, 2) values of −10 to −12‰ that reflect dense C3 vegetation above the studied cave, and up to 0‰ in early stage 5 when there was probably complete loss of vegetation. The climatic instability during interglacial periods is much larger than during glacial periods, and glacial/interglacial transitions do not behave the same in each climatic cycle in this region.
Distinguishing melt and fluid subduction components in Umnak Volcanics, Aleutian Arc
Authors: Class Cornelia , Miller Daniel M. , Goldstein Steven L. , Langmuir Charles H.
Published: February 2004

Plate processing at convergent margins plays a central role in the distribution of elements among major earth reservoirs. The mechanisms by which this distribution occurs, however, have remained poorly constrained. This paper provides new constraints through a detailed isotope and trace element study of volcanic rocks from Umnak Island, Central Aleutian Arc. The data require the addition of three distinct subduction components to the subarc mantle, which are characterized and quantified: (1) a hydrous fluid from subducted oceanic crust, with mid‐ocean ridge basalt (MORB)‐like isotopic compositions but high Pb/Nd; (2) a hydrous fluid from subducted sediment, with sediment‐like isotopic compositions and an enrichment in fluid‐mobile elements; (3) a sediment partial melt, with sediment‐like isotopic compositions and high Th/Nd and Th/Nb compared to both regional and global sediments. The sediment melt is depleted in fluid‐mobile elements, indicating loss of fluid prior to melting. The high Th/Nb of the sediment melt indicates presence of a Ti‐rich residual phase such as rutile during partial melting. The observation that sediment fluid and sediment melt can be distinguished in different volcanic rocks suggests that they arrive separately at the sites of arc magma formation. This indicates release of multiple discrete fluid and melt phases from sediment to the overlying mantle wedge, which can be viewed as a natural consequence of progressive metamorphism of the subducting slab.
Age and geochemistry of basaltic complexes in western Costa Rica: Contributions to the geotectonic evolution of Central America
Authors: Hauff Folkmar , Hoernle Kaj , van den Bogaard Paul , Alvarado Guillermo , Garbe‐Schönberg Dieter
Published: February 2004

The age and origin of magmatic complexes along the Pacific Coast of Central America have important implications for the origin and tectonic evolution of this convergent plate margin. Here we present new 40Ar/39Ar laser age dates, major and trace element data, and initial Sr‐Nd‐Pb isotope ratios. The 124–109 Ma tholeiitic portions of the Santa Elena complex formed in a primitive island arc setting, believed to be part of the Chortis subduction zone. The geochemical similarities between the Santa Elena and Tortugal alkaline volcanic rocks suggest that Chortis block may extend south of the Hess Escarpment. The Nicoya, Herradura, Golfito, and Burica complexes and the tholeiitic Tortugal unit formed between 95 and 75 Ma and appear to be part of the Caribbean Large Igneous Province, thought to mark the initiation of the Galápagos hotspot. The Quepos and Osa complexes (65–59 Ma) represent accreted sections of an ocean island and an aseismic ridge, respectively, interpreted to reflect part of the Galápagos paleo‐hotspot track. An Oligocene unconformity throughout Central America may be related to the mid‐Eocene accretion of the Quepos and Osa complexes.
A shallow, chemical origin for the Marquesas Swell
Authors: McNutt Marcia , Bonneville Alain
Published: February 2004

Young hotspot volcanoes within plate interiors are frequently surrounded by smooth, broad regions of shallow seafloor termed midplate swells. These swells are typically hundreds of kilometers wide and can be more than a kilometer in elevation. The most frequently invoked explanation for these swells is that they represent the thermal and dynamic surface uplift from rising mantle plumes. Here we argue that buoyancy of a volcanic unit underplating the Marquesan volcanoes just below the Moho, as imaged by a seismic refraction experiment, is capable of producing much, if not all, of what has been previously interpreted as a thermal swell in both the bathymetry and the geoid. The shallow compensation depth previously calculated for the swell based on geoid observations is thus expected given that the compensation resides at 20‐km depth. The volcanic unit underplating the islands would also be expected to have a thermal effect, but its contribution to swell uplift is never more than 10% of the chemical contribution. The predicted increase in heat flow, on the other hand, is very large, but the thermal transient rapidly decays in the first 2 million years after emplacement. If similar large volumes of underplated material underlie other hotspot volcanoes, problems in explaining the lack of heat flow anomalies at later times and negligible rates of swell subsidence can be alleviated. Although volcanic underplating is unlikely to explain the entire swell signature for particularly large and wide swells, the results from the Marquesas suggest that at least some portion of hotspot swells may not be thermal in origin. After removing the geoid signature from the Marquesas volcanoes and swell, what remains in the geoid are stripes of amplitude 1 m and wavelength 650 km trending normal to the fracture zone. The anomalies are presumably relict from when this crust was created, but their amplitude is too large to be caused by variations in isostatically compensated crustal thickness.
Magnetic Properties Experiments on the Mars Polar Lander
Authors: Mogensen C. T. , Knudsen J. M. , Madsen M. B. , Bertelsen P. , Hviid S. F. , Hargraves R. B. , Smith P. , Paige D. A.
Published: February 2004

The Mars Polar Lander carries an instrument package called the Magnetic Properties Experiments. This package consists of one magnet array, one tip‐plate magnet, and three Thermal and Evolved Gas Analyzer (TEGA) magnets. The magnet array and the tip‐plate magnet are identical to those flown on Mars Pathfinder and will be passively exposed to airborne dust. The TEGA magnets are a new addition to the package designed to study actively sampled material collected from three different depths in the trench that will be dug by the robotic arm soil sampler.
The “Procellarum KREEP Terrane”: Implications for mare volcanism and lunar evolution
Authors: Wieczorek Mark A. , Phillips Roger J.
Published: February 2004

Geophysical, remote‐sensing, and sample data demonstrate that the Procellarum and Imbrium regions of the Moon make up a unique geochemical crustal province (here dubbed the Procellarum KREEP Terrane). Geochemical studies of Imbrium's ejecta and the crustal structure of the Imbrium and Serenitatis basins both suggest that a large portion of the lunar crust in this locale is composed of a material similar in composition to Apollo 15 KREEP basalt. KREEP basalt has about 300 times more uranium and thorium than chondrites, so this implies that a large portion of Moon's heat‐producing elements is located within this single crustal province. The spatial distribution of mare volcanism closely parallels the confines of the Procellarum KREEP Terrane and this suggests a causal relationship between the two phenomena. We have modeled the Moon's thermal evolution using a simple thermal conduction model and show that as a result of the high abundance of heat‐producing elements that are found in the Procellarum KREEP Terrane, partial melting of the underlying mantle is an inevitable outcome. Specifically, by placing a 10‐km KREEP basalt layer at the base of the crust there, our model predicts that mare volcanism should span most of the Moon's history and that the depth of melting should increase with time to a maximum depth of about 600 km. We suggest that the 500‐km seismic discontinuity that is observed in the Apollo seismic data may represent this maximum depth of melting. Our model also predicts that the KREEP basalt layer should remain partially molten for a few billion years. Thus the Imbrium impact event most likely excavated into a partially molten KREEP basalt magma chamber. We postulate that the KREEP basalt composition is a by‐product of mixing urKREEP with shallow partial melts of the underlying mantle. Since Mg‐suite rocks are likely derived from crystallizing KREEP basalt, the provenance of these plutonic rocks is likely to be unique to this region of the Moon.
The MVACS Robotic Arm Camera
Authors: Keller H. U. , Hartwig H. , Kramm R. , Koschny D. , Markiewicz W. J. , Thomas N. , Fernades M. , Smith P. H. , Reynolds R. , Lemmon M. T. , Weinberg J. , Marcialis R. , Tanner R. , Boss B. J. , Oquest C. , Paige D. A.
Published: February 2004

The Robotic Arm Camera (RAC) is one of the key instruments newly developed for the Mars Volatiles and Climate Surveyor payload of the Mars Polar Lander. This lightweight instrument employs a front lens with variable focus range and takes images at distances from 11 mm (image scale 1:1) to infinity. Color images with a resolution of better than 50 μm can be obtained to characterize the Martian soil. Spectral information of nearby objects is retrieved through illumination with blue, green, and red lamp sets. The design and performance of the camera are described in relation to the science objectives and operation. The RAC uses the same CCD detector array as the Surface Stereo Imager and shares the readout electronics with this camera. The RAC is mounted at the wrist of the Robotic Arm and can characterize the contents of the scoop, the samples of soil fed to the Thermal Evolved Gas Analyzer, the Martian surface in the vicinity of the lander, and the interior of trenches dug out by the Robotic Arm. It can also be used to take panoramic images and to retrieve stereo information with an effective baseline surpassing that of the Surface Stereo Imager by about a factor of 3.
Mars Volatiles and Climate Surveyor Robotic Arm
Authors: Bonitz Robert , Slostad Jeffrey , Bon Bruce , Braun Dave , Brill Russ , Buck Carl , Fleischner Richard , Haldeman Albert , Herman Jennifer , Hetzel Mark , Noon Don , Pixler Greg , Schenker Paul , Ton Thieu , Tucker Curtis , Zimmerman Wayne , Paige David
Published: February 2004

The primary purpose of the Mars Volatiles And Climate Surveyor (MVACS) Robotic Arm is to support the other MVACS science instruments by digging trenches in the Martian soil; acquiring and dumping soil samples into the Thermal Evolved Gas Analyzer; positioning the Soil Temperature Probe in the soil; positioning the Robotic Arm Air Temperature Sensor at various heights above the surface, and positioning the Robotic Arm Camera for taking images of the surface, trench, soil samples, magnetic targets, and other objects of scientific interest within its workspace. In addition to data collected from the Robotic Arm sensors during science support operations, the Robotic Arm will perform experiments along with the other science instruments to yield additional information on Martian soil mechanics in the vicinity of the lander. The experiments include periodic imaging of dumped soil piles, surface scraping and soil chopping experiments, compaction tests, insertion of the various end‐effector tools into the soil, and trench cave‐in tests. Data from the soil mechanics experiments will yield information on Martian soil properties such as angle of repose, cohesion, bearing strength, and grain size distribution.
Habitability of Europa's crust: The role of tidal‐tectonic processes
Authors: Greenberg Richard , Geissler Paul , Tufts B. Randall , Hoppa Gregory V.
Published: February 2004

Jupiter's satellite Europa has been identified as one of the most likely sites for life in the solar system. The tidal‐tectonic processes that appear to have governed Europa's geology seem to require interaction with an ocean under only a very thin crust, providing a variety of evolving environmental niches. The mutually dependent relationship between orbital evolution and tidal processes in turn controls Europa's rotation, heating, and stress. Surface lineaments are correlated with global stress patterns, demonstrating that they form by crustal cracking, but only if a substantial ocean is present to give adequate tidal amplitude. Tidal driving of strike‐slip faulting indicates that cracks penetrate to a fluid layer, which is possible only with a very thin ice crust. The characteristic ridge sets that cover tectonic terrain are likely built by tidal pumping of fluid and slush to the surface on a daily basis. Widespread tectonic dilation creates new surface as material rises from below. Chaotic terrain has morphology and other characteristics indicative of melt‐through from below. Surface colorants correlate with locations, such as along large‐scale ridge systems and around chaotic terrain, where ocean water reached the surface. This model implies that as a result of tides, liquid water regularly bathed crustal cracks and surfaces with heat and whatever nutrients are included in the oceanic chemistry, creating a variety of habitable environments. The processes were recent and thus most likely continue today. Longer‐term evolution of environmental conditions provided the need for adaptation and opportunity for evolution.
Geological characterization of remote field sites using visible and infrared spectroscopy: Results from the 1999 Marsokhod field test
Authors: Johnson Jeffrey R. , Ruff Steven W. , Moersch Jeffrey , Roush Ted , Horton Keith , Bishop Janice , Cabrol Nathalie A. , Cockell Charles , Gazis Paul , Newsom Horton E. , Stoker Carol
Published: February 2004

Upcoming Mars Surveyor lander missions will include extensive spectroscopic capabilities designed to improve interpretations of the mineralogy and geology of landing sites on Mars. The 1999 Marsokhod Field Experiment (MFE) was a Mars rover simulation designed in part to investigate the utility of visible/near‐infrared and thermal infrared field spectrometers to contribute to the remote geological exploration of a Mars analog field site in the California Mojave Desert. The experiment simultaneously investigated the abilities of an off‐site science team to effectively analyze and acquire useful imaging and spectroscopic data and to communicate efficiently with rover engineers and an on‐site field team to provide meaningful input to rover operations and traverse planning. Experiences gained during the MFE regarding effective communication between different mission operation teams will be useful to upcoming Mars mission teams. Field spectra acquired during the MFE mission exhibited features interpreted at the time as indicative of carbonates (both dolomitic and calcitic), mafic rocks and associated weathering products, and silicic rocks with desert varnish‐like coatings. The visible/near‐infrared spectra also suggested the presence of organic compounds, including chlorophyll in one rock. Postmission laboratory petrologic and spectral analyses of returned samples confirmed that all rocks identified as carbonates using field measurements alone were calc‐silicates and that chlorophyll associated with endolithic organisms was present in the one rock for which it was predicted. Rocks classified from field spectra as silicics and weathered mafics were recognized in the laboratory as metamorphosed monzonites and diorite schists. This discrepancy was likely due to rock coatings sampled by the field spectrometers compared to fresh rock interiors analyzed petrographically, in addition to somewhat different surfaces analyzed by laboratory thermal spectroscopy compared to field spectra.
Distribution of chaotic terrain on Europa
Authors: Riley Jeannemarie , Hoppa Gregory V. , Greenberg Richard , Tufts B. Randall , Geissler Paul
Published: February 2004

The locations of chaotic terrain are mapped over all regions of Europa for which we have adequate resolution (∼200 m or better) and appropriate lighting geometry (Sun angle <35° from the local horizontal), comprising 9% of the total surface of the satellite. Nearly 30% of the mapped area is occupied by chaotic terrain recognizable at 200 m resolution, and sampling at higher resolution suggests that at least 10% more may be covered by small chaos features. The largest contiguous area of chaotic terrain is ∼1300 km across. Chaotic terrain displays variations in freshness of appearance, probably because of aging by fine‐scale tectonics. Resurfacing of previous chaotic terrain by larger‐scale tectonics or disruption by newer chaos are common. Chaos formation is not necessarily recent relative to tectonics; both types of process appear to have gone on diachronously. The size distribution shows no dominant or characteristic size and appears to have been controlled by competition from tectonics, which has created terrain that occupies more than half of the surface of Europa.