bluuebunny/crossref_metadata_2025 huggingface dataset:
Concordant estimates of oceanic carbon monoxide source and sink processes in the Pacific yield a balanced global “blue‐water” CO budget
Authors: Zafiriou Oliver C. , Andrews Steven S. , Wang Wei
Published: May 2003

Studies to characterize sources and sinks of carbon monoxide (CO) in the mixed layer were carried out at sites covering large regions of the north and south Pacific. Apparent quantum yield spectra for the photochemical production of CO from colored dissolved organic matter were measured, as were first‐order net microbial CO consumption rate constants. Contrary to initial expectations, neither photoproduction nor biooxidation parameters exhibited strong regional variations, except that in the Southern Ocean CO biooxidation rate coefficients were very low. Global “blue‐water” CO flux terms derived from the data (in Tg carbon from CO per year, CO‐C a−1) are: photochemical source, 50 (estimated range, 30–70), microbial sink, 32 (estimated range, 10–60) and total CO sink (microbial plus gas exchange), 38 (estimated range, 13–60). Considering uncertainties and extrapolation biases, these independently estimated source and sink terms are thus in, or close to, balance at ∼40 (range of overlap, 30–60) Tg CO‐C a−1. The simplest interpretation of this balance is that no major net sources or sinks (i.e., light‐independent production, photoproduction at >450 nm) remain undiscovered, though considerable uncertainty in actual process rates remains. These CO fluxes are, however, very much smaller than some recently estimated values. The origins and implications of these discrepancies are discussed, and the coastal budget term is approximated.
Global distribution of C3and C4vegetation: Carbon cycle implications
Authors: Still Christopher J. , Berry Joseph A. , Collatz G. James , DeFries Ruth S.
Published: May 2003

The global distribution of C3and C4plants is required for accurately simulating exchanges of CO2, water, and energy between the land surface and atmosphere. It is also important to know the C3/C4distribution for simulations of the carbon isotope composition of atmospheric CO2owing to the distinct fractionations displayed by each photosynthetic type. Large areas of the land surface are spatial and temporal mosaics of both photosynthetic types. We developed an approach for capturing this heterogeneity by combining remote sensing products, physiological modeling, a spatial distribution of global crop fractions, and national harvest area data for major crop types. Our C3/C4distribution predicts the global coverage of C4vegetation to be 18.8 million km2, while C3vegetation covers 87.4 million km2. We incorporated our distribution into the SiB2 model and simulated carbon fluxes for each photosynthetic type. The gross primary production (GPP) of C4plants is 35.3 Pg C yr−1, or ∼23% of total GPP, while that of C3plants is 114.7 Pg C yr−1. The assimilation‐weighted terrestrial discrimination against13CO2is −16.5‰. If the terrestrial component of the carbon sink is proportional to GPP, this implies a net uptake of 2.4 Pg C yr−1on land and 1.4 Pg C yr−1in the ocean using a13C budgeting approach and average carbon cycle parameter values for the 1990s. We also simulated the biomass of each photosynthetic type using the CASA model. The simulated biomass values of C3and C4vegetation are 389.3 and 18.6 Pg C, respectively.
Changes in the 13C/12C of dissolved inorganic carbon in the ocean as a tracer of anthropogenic CO2 uptake
Authors: Quay P. , Sonnerup R. , Westby T. , Stutsman J. , McNichol A.
Published: May 2003

Measurements of the δ13C of dissolved inorganic carbon primarily during World Ocean Circulation Experiment and the Ocean Atmosphere Carbon Exchange Study cruises in the 1990s are used to determine ocean‐wide changes in the δ13C that have occurred due to uptake of anthropogenic CO2. This new ocean‐wide δ13C data set (∼25,000 measurements) substantially improves the usefulness of δ13C as a tracer of the anthropogenic CO2 perturbation. The global mean δ13C change in the surface ocean is estimated at −0.16 ± 0.02‰ per decade between the 1970s and 1990s with the greatest changes observed in the subtropics and the smallest changes in the polar and southern oceans. The global mean air‐sea δ13C disequilibrium in 1995 is estimated at 0.60 ± 0.10‰ with basin‐wide disequilibrium values of 0.73, 0.63, and 0.23‰ for the Pacific, Atlantic, and Indian oceans, respectively. The global mean depth‐integrated anthropogenic change in δ13C between the 1970s and 1990s was estimated at −65 ± 33‰ m per decade. These new estimates of air‐sea δ13C disequilibrium and depth‐integrated δ13C changes yield an oceanic CO2 uptake rate of 1.5 ± 0.6 Gt C yr−1 between 1970 and 1990 based on the atmospheric CO2 and 13CO2 budget approaches of Quay et al. [1992] and Tans et al. [1993] and the dynamic method of Heimann and Maier‐Reimer [1996]. Box‐diffusion model simulations of the oceanic uptake of anthropogenic CO2 and its δ13C perturbation indicate that a CO2 uptake rate of 1.9 ± 0.4 Gt C yr−1 (1970–1990) explains both the observed surface ocean and depth‐integrated δ13C changes. Constraining a box diffusion ocean model to match both the observed δ13C and bomb 14C changes yields an oceanic CO2 uptake rate of 1.7 ± 0.2 Gt C yr−1 (1970–1990). The oceanic CO2 uptake rates derived from anthropogenic changes in ocean δ13C are similar to rates determined by atmospheric CO2 and O2 budgets [Battle et al., 2000], atmospheric δ13C and CO2 measurements [Ciais et al., 1995], and GCM simulations [Orr et al., 2001].
Elevated atmospheric CO2 effects and soil water feedbacks on soil respiration components in a Colorado grassland
Authors: Pendall E. , Del Grosso S. , King J. Y. , LeCain D. R. , Milchunas D. G. , Morgan J. A. , Mosier A. R. , Ojima D. S. , Parton W. A. , Tans P. P. , White J. W. C.
Published: May 2003

The shortgrass steppe is a semi‐arid grassland, where elevated CO2 reduces stomatal conductance and promotes soil moisture storage. Enhanced biomass growth from elevated CO2 has been attributed in part to soil moisture effects. However, the influence of this soil moisture feedback on C cycling has received little attention. We used open‐top chambers to increase atmospheric CO2 concentrations to twice‐ambient for four growing seasons. Soil respiration rates and stable C isotopes of soil CO2 were measured during the third and fourth seasons. Elevated CO2 increased soil respiration rates by ∼25% in a moist growing season and by ∼85% in a dry season. Stable C isotope partitioning of soil respiration into its components of decomposition and rhizosphere respiration was facilitated on all treatments by a 13C disequilibrium between currently growing plants and soil organic matter. Decomposition rates were more than doubled by elevated CO2, whereas rhizosphere respiration rates were not changed. In general, decomposition rates were most significantly correlated with soil temperature, and rhizosphere respiration rates were best predicted by soil moisture content. Model simulations suggested that soil moisture feedbacks, rather than differences in substrate availability, were primarily responsible for higher total respiration rates under elevated CO2. By contrast, modeling demonstrated that substrate availability was at least as important as soil moisture in driving CO2 treatment differences in soil organic matter decomposition rates.
Spatial and temporal variability in phytoplankton iron limitation along the California coast and consequences for Si, N, and C biogeochemistry
Authors: Firme Giselle F. , Rue Eden L. , Weeks Debra A. , Bruland Kenneth W. , Hutchins David A.
Published: May 2003

Iron limitation was investigated along the Northern California coast in the summer of 1999. Small‐volume (1 l) shipboard iron addition bottle experiments were performed at 44 stations to gain the greatest possible temporal and spatial coverage of the area. Parameters measured in these 4‐day incubations included size‐fractionated chlorophyll a and particulate nutrients (C, N, and Si). Degrees of community iron limitation were quantified and compared using various iron limitation indexes, calculated as the ratio of chlorophyll a, particulate organic nitrogen, or particulate organic carbon produced in Fe‐amended bottles to the amounts produced in controls. Iron limitation occurred most frequently and was most severe on stations off the continental shelf, away from sedimentary sources of iron, as well as during relaxation events in aged upwelled water. Size‐fractionated chlorophyll a data did not suggest large Fe‐mediated changes in phytoplankton community composition. Fe limitation reduced phytoplankton production of particulate organic nitrogen and carbon, but had much less effect on biogenic silica production. The result is an increase in particulate Si:N and Si:C ratios of control samples, which were frequently double those of Fe‐amended samples. Particulate C:N ratios also decreased under Fe limitation, indicating that iron availability exerts a strong control on C, N, and Si elemental composition of phytoplankton, and thus on the biogeochemical cycling of these nutrients in the California upwelling region.
Isotopic composition of carbon dioxide from a boreal forest fire: Inferring carbon loss from measurements and modeling
Authors: Schuur Edward A. G. , Trumbore Susan E. , Mack Michelle C. , Harden Jennifer W.
Published: May 2003

Fire is an important pathway for carbon (C) loss from boreal forest ecosystems and has a strong effect on ecosystem C balance. Fires can range widely in severity, defined as the amount of vegetation and forest floor consumed by fire, depending on local fuel and climatic conditions. Here we explore a novel method for estimating fire severity and loss of C from fire using the atmosphere to integrate ecosystem heterogeneity at the watershed scale. We measured the δ13C and Δ14C isotopic values of CO2 emitted from an experimental forest fire at the Caribou‐Poker Creek Research Watershed (CPCRW), near Fairbanks, Alaska. We used inverse modeling combined with dual isotope measurements of C contained in aboveground black spruce biomass and soil organic horizons to estimate the amount of C released by this fire. The experimental burn was a medium to severe intensity fire that released, on average, about 2.5 kg Cm−2, more than half of the C contained in vegetation and soil organic horizon pools. For vegetation, the model predicted that approximately 70–75% of pools such as needles, fine branches, and bark were consumed by fire, whereas only 20–30% of pools such as coarse branches and cones were consumed. The fire was predicted to have almost completely consumed surface soil organic horizons and burned about half of the deepest humic horizon. The ability to estimate the amount of biomass combusted and C emission from fires at the watershed scale provides an extensive approach that can complement more limited intensive ground‐based measurements.
Projecting future climate change: Implications of carbon cycle model intercomparisons
Authors: Kheshgi Haroon S. , Jain Atul K.
Published: May 2003

The range of responses of alternate detailed models for the ocean and biosphere components of the global carbon cycle, cataloged in model intercomparison studies, are simulated by a reduced form Earth system model employing a range of model parameters. The reduced form model, parameterized in this way, allows the integration of these components of the carbon cycle with an energy balance climate model with a prescribed range of climate sensitivity. We use this model to construct ranges of: (1) past carbon budgets given past CO2 concentrations, fossil carbon emissions, and temperature records, (2) future CO2 concentrations and temperature for given emission scenarios, and (3) CO2 emissions and temperature for given trajectories of future CO2 concentrations leading to constant levels within the next several centuries. Carbon cycle is an additional contributor to uncertainty in climate projections that is calculated to expand the range of projected global temperature beyond that reported in the 2001 Intergovernmental Panel on Climate Change assessment.
The application and interpretation of Keeling plots in terrestrial carbon cycle research
Authors: Pataki D. E. , Ehleringer J. R. , Flanagan L. B. , Yakir D. , Bowling D. R. , Still C. J. , Buchmann N. , Kaplan J. O. , Berry J. A.
Published: May 2003

Photosynthesis and respiration impart distinct isotopic signatures to the atmosphere that are used to constrain global carbon source/sink estimates and partition ecosystem fluxes. Increasingly, the “Keeling plot” method is being used to determine the carbon isotope composition of ecosystem respiration (δ13CR) in order to better understand the processes controlling ecosystem isotope discrimination. In this paper we synthesize emergent patterns in δ13CR by analyzing 146 Keeling plots constructed at 33 sites across North and South America. In order to interpret results from disparate studies, we discuss the assumptions underlying the Keeling plot method and recommend standardized methods for determining δ13CR. These include the use of regression calculations that account for error in the x variable, and constraining estimates of δ13CR to nighttime periods. We then recalculate δ13CR uniformly for all sites. We found a high degree of temporal and spatial variability in C3 ecosystems, with individual observations ranging from −19.0 to −32.6‰. Mean C3 ecosystem discrimination was 18.3‰. Precipitation was a major driver of both temporal and spatial variability of δ13CR, suggesting (1) a large influence of recently fixed carbon on ecosystem respiration and (2) a significant effect of previous climatic effects on δ13CR. These results illustrate the importance of water availability as a key control on atmospheric 13CO2 and highlight the potential of δ13CR as a useful tool for integrating environmental effects on dynamic canopy and ecosystem processes.
Theistareykir revisited
Authors: Stracke Andreas , Zindler Alan , Salters Vincent J. M. , McKenzie Dan , Blichert‐Toft Janne , Albarède Francis , Grönvold Karl
Published: May 2003

Postglacial basalts from Theistareykir (younger than 10,000 years), northern Iceland, define the depleted end of the spectrum of chemical and isotopic compositions observed in Icelandic volcanics but extend to some of the most enriched chemical and isotopic compositions found in Icelandic tholeiites. A spectacular feature of these basalts is the impressive correlations observed between radiogenic isotope ratios (Sr, Nd, Hf, and Pb) and almost the entire spectrum of major and trace element concentrations and ratios. The radiogenic isotope and major and trace element compositions are little affected by crystal fractionation and are essentially unaffected by interaction with the preexisting crust. The Theistareykir basalts must therefore be relatively close in composition to primary melts from the mantle. Consequently, their chemical and isotopic compositions provide a unique opportunity to investigate the nature of melting beneath Iceland and the geochemical character and origin of the mantle source. Large variations in incompatible element abundances require source heterogeneity, as well as variable extents of melting, to be important factors in determining the final chemical composition of the melts. Melting integrates over a large pressure range and is dominated by melting a depleted peridotite similar to the ambient depleted North Atlantic mantle. The isotopically enriched component is of relatively minor abundance and probably has a lower solidus temperature compared to the depleted component. More than one isotopically enriched component must be involved, but it is difficult to identify the end‐member compositions using those of the lavas because of preeruptive averaging and damping of the enriched isotopic signals by mixing with the ambient depleted mantle or melts thereof, suggesting that the isotopic signals in Icelandic melts represent a somewhat muted isotopic signal of the enriched component(s) in the Icelandic source mantle. Comparison of the isotopic arrays of Icelandic basalts with those of global OIB suggests that the dominant enriched component may have a HIMU (high μ) affinity rather than representing a component similar to the enriched end of the Iceland isotopic arrays, and small amounts of an enriched component similar to enriched mantle (EMI)‐ type OIB sources are probably also involved.
Constraint of fault parameters inferred from nonplanar fault modeling
Authors: Aochi Hideo , Madariaga Raul , Fukuyama Eiichi
Published: May 2003

We study the distribution of initial stress and frictional parameters for the 28 June 1992 Landers, California, earthquake through dynamic rupture simulation along a nonplanar fault system. We find that observational evidence of large slip distribution near the ground surface requires large nonzero cohesive forces in the depth‐dependent friction law. This is the only way that stress can accumulate and be released at shallow depths. We then study the variation of frictional parameters along the strike of the fault. For this purpose we mapped into our segmented fault model the initial stress heterogeneity inverted by Peyrat et al. [2001] using a planar fault model. Simulations with this initial stress field improved the overall fit of the rupture process to that inferred from kinematic inversions, and also improved the fit to the ground motion observed in Southern California. In order to obtain this fit, we had to introduce an additional variations of frictional parameters along the fault. The most important is a weak Kickapoo fault and a strong Johnson Valley fault.
An updated digital model of plate boundaries
Authors: Bird Peter
Published: May 2003

A global set of present plate boundaries on the Earth is presented in digital form. Most come from sources in the literature. A few boundaries are newly interpreted from topography, volcanism, and/or seismicity, taking into account relative plate velocities from magnetic anomalies, moment tensor solutions, and/or geodesy. In addition to the 14 large plates whose motion was described by the NUVEL‐1A poles (Africa, Antarctica, Arabia, Australia, Caribbean, Cocos, Eurasia, India, Juan de Fuca, Nazca, North America, Pacific, Philippine Sea, South America), model PB2002 includes 38 small plates (Okhotsk, Amur, Yangtze, Okinawa, Sunda, Burma, Molucca Sea, Banda Sea, Timor, Birds Head, Maoke, Caroline, Mariana, North Bismarck, Manus, South Bismarck, Solomon Sea, Woodlark, New Hebrides, Conway Reef, Balmoral Reef, Futuna, Niuafo'ou, Tonga, Kermadec, Rivera, Galapagos, Easter, Juan Fernandez, Panama, North Andes, Altiplano, Shetland, Scotia, Sandwich, Aegean Sea, Anatolia, Somalia), for a total of 52 plates. No attempt is made to divide the Alps‐Persia‐Tibet mountain belt, the Philippine Islands, the Peruvian Andes, the Sierras Pampeanas, or the California‐Nevada zone of dextral transtension into plates; instead, they are designated as “orogens” in which this plate model is not expected to be accurate. The cumulative‐number/area distribution for this model follows a power law for plates with areas between 0.002 and 1 steradian. Departure from this scaling at the small‐plate end suggests that future work is very likely to define more very small plates within the orogens. The model is presented in four digital files: a set of plate boundary segments; a set of plate outlines; a set of outlines of the orogens; and a table of characteristics of each digitization step along plate boundaries, including estimated relative velocity vector and classification into one of 7 types (continental convergence zone, continental transform fault, continental rift, oceanic spreading ridge, oceanic transform fault, oceanic convergent boundary, subduction zone). Total length, mean velocity, and total rate of area production/destruction are computed for each class; the global rate of area production and destruction is 0.108 m2/s, which is higher than in previous models because of the incorporation of back‐arc spreading.
Deformation near the Coyote Creek fault, Imperial County, California: Tectonic or groundwater‐related?
Authors: Mellors Robert J. , Boisvert Alex
Published: May 2003

Interferometric synthetic aperture radar (InSAR) measurements show a consistent, 40‐km2 wedge‐shaped area of deformation partially bounded by a branch of the Coyote Creek fault (a southern extension of the San Jacinto fault) in Imperial County, California, west of the Salton Sea. The deformation is centered at 33.1 N latitude, 116.0 W longitude. 18 ERS‐1 and ERS‐2 (descending) interferograms falling within 1992 to 2000 are analyzed. An average line‐of‐sight range change over the area of 6 ± 3 mm per year away from the satellite is observed with peak values up to 12 ± 3 mm per year. The southwestern edge of the deformation is partially bounded by a fault segment that ruptured in the 1968 Mw 6.5 Borrego Mountain earthquake and which also showed triggered slip after the 1987 Superstition Hills earthquakes. The southeastern edge of the deformation also coincides with a mapped fault. The deformation is centered on a farming area that has pumped approximately 5.8 × 10−6 m3 per year of groundwater from 5 wells on the property and which shows declining water levels of 1.4 m per year. The area of highest change appears to be centered on location of the wells and away from the faults. The aquifer is at a depth of roughly 100 to 200 m and consists of sands with interbedded clays. It appears that the most likely explanation is subsidence due to groundwater withdrawal in a fault‐bounded aquifer rather than tectonic slip.
Stress‐driven melt segregation in partially molten rocks
Authors: Holtzman B. K. , Groebner N. J. , Zimmerman M. E. , Ginsberg S. B. , Kohlstedt D. L.
Published: May 2003

We demonstrate that deformation of partially molten ductile rocks can produce melt segregation by two‐phase flow. In simple shear experiments on several melt‐rock systems at high temperature and pressure, melt segregates into distinct melt‐rich layers oriented 20° to the shear plane. Melt segregates in samples in which pressure gradients can develop at length scales less than the sample thickness. A simple scaling argument combined with a comparison of length scale data suggests that such pressure gradients can develop in the samples with compaction lengths less than or on the order of the sample thickness. In nature, stress‐driven melt segregation may produce both high‐permeability pathways that contribute to rapid extraction of melt and localization of deformation that increases the anisotropy in viscosity of partially molten regions of the upper mantle and lower crust.
REE inverse modeling of HSDP2 basalts: Evidence for multiple sources in the Hawaiian plume
Authors: Feigenson Mark D. , Bolge Louise L. , Carr Michael J. , Herzberg Claude T.
Published: May 2003

The rare earth element (REE) concentrations of lavas from the Hawaiian Scientific Drilling Project (HSDP2) can be used to provide additional constraints on phase equilibria and the nature of the Hawaiian source. Major element analyses separate Mauna Kea lavas into two distinct populations, a high‐silica and a low‐silica suite. The low‐silica samples can be separated stratigraphically into an upper low‐silica alkalic series and a low‐silica tholeiitic group that occurs deeper in the section. These contrasting groups could result from different extents of source partial fusion, or lithologically distinct source regions, or some combination of both factors. Petrologic modeling is performed to calculate that primary magma compositions contain about 20% MgO, and can be formed by 8–15% melting of a depleted mantle source for low‐silica alkalic and high‐silica lavas, respectively. The low‐silica tholeiites could be generated by higher degrees of melting of a more fertile source. REE ratios and various isotopic systems reinforce the division of the low‐SiO2 samples into the upper alkalic series, characterized by high Gd/Yb, and the deeper low‐silica tholeiitic group, with low Gd/Yb. REE inverse modeling of fractionation‐corrected basalts is consistent with lower degrees of melting to generate the late‐stage alkalic lavas, with garnet present as a residual phase. The relatively constant Gd/Yb for low‐silica tholeiites suggests that garnet is not an important residual phase during partial melting, implying higher extents of melting. The low‐silica tholeiites are characterized by relatively enriched isotopic signatures that are consistent with contributions from a primitive source or from recycled subduction components. High 3He/4He associated with the low‐silica lavas could derive from primitive mantle, mass transfer from the core, or from a refractory lithospheric contribution to a recycled subduction package. However, the combination of major element, REE and isotopic data suggests that the deeper low‐silica suite is sampling the relatively fertile, interior part of the Hawaiian plume, whereas the high‐silica lavas are extracted from the more depleted periphery; later alkalic lavas are generated from a depleted source as the volcano moves off the hot spot.
Synthesis of large high‐quality forsterite single crystals to 200 mm length and its significance
Authors: Ito Kazuhiko , Sato Hiroki , Takei Humihiko , Tamada Osamu , Kitazawa Tsuneo
Published: May 2003

Comprehensive and conclusive understanding of the anisotropic upper mantle relies on the physical property measurements on high‐quality homogeneous specimens of various crystallographic directions. Such specimens are ultimately prepared from one large single crystal. Large forsterite single crystals were synthesized for use in property measurements and laboratory experiments including anisotropic studies. We are capable of producing large homogeneous single crystals over 50 mm diameter and 200 mm length.
Implications for crustal accretion at fast spreading ridges from observations in Jurassic oceanic crust in the western Pacific
Authors: Pockalny Robert A. , Larson Roger L.
Published: May 2003

Downhole logging data and basement stratigraphy interpretations are used to determine the spreading environment and crustal accretion history of the ocean basement cored at ODP Hole 801C located in the Jurassic Magnetic Quiet Zone of the western Pacific. High‐resolution microresistivity data obtained with the Formation MicroScanner are used to measure the dip of the extrusive layers and indicate a 10°–30° increase in dip down the drill hole with lava flow contacts dipping back toward the original ridge axis. This structural pattern and the high proportion of massive flows relative to pillow units are consistent with prevailing crustal accretion models proposed for faster spreading ridges (e.g., >60 km/m.y., full‐rate). A detailed analysis of the age data, basement lithology, related geochemistry, and structural attitudes suggest the shallowest 100 m of the drilled section (e.g., Sequences I–III) were emplaced just off the ridge (Sequence III) or significantly farther off‐axis up to 5–15 m.y. later (Sequences I and II). The remainder of the drilled section (e.g., Sequences IV–VIII) has geochemical, lithological and physical trends that are assumed to be representative of crust created at faster spreading ridges. The pattern of dipping lava flow contacts from this deeper section of the drill hole suggests lava flows emanating from the ridge axis are limited to 1–2 km off‐axis. Our results suggest ocean crust drilled at Hole 801C was created at faster spreading rates; however, caution should be used when incorporating Sequences I–III into geochemical reference sections for faster spreading ridges.
Noble gases in olivine phenocrysts from drill core samples of the Hawaii Scientific Drilling Project (HSDP) pilot and main holes (Mauna Loa and Mauna Kea, Hawaii)
Authors: Althaus Tilmann , Niedermann Samuel , Erzinger Jörg
Published: May 2003

We have determined concentrations and isotopic compositions of all noble gases in olivine phenocrysts from the Hawaii Scientific Drilling Project (HSDP) drill core, comprising Mauna Loa lavas in the top 247 m and Mauna Kea lavas down to the preliminary depth of 3109 m. Our aim was to describe the long‐term isotopic evolution of noble gases over a significant time fraction of the active life of a major Hawaiian volcano. The He isotopic signature displays a clear temporal trend: 3He/4He ratios increase from MORB‐like 9 RA in the youngest lavas to 15 RA in the Mauna Loa section and from ∼7 RA to ∼12 RA in the subaerial Mauna Kea deposits. They remain close to 12 RA in most of the submarine Mauna Kea samples, except for a few excursions with 3He/4He ratios of up to 21 RA in borehole depths between 2000 and 2600 m. The average 3He/4He ratio of 12 RA is lower than that observed in recent eruptions of Kilauea and Loihi seamount and supports the idea of a concentrically zoned Hawaiian plume [Kurz et al., 1996]. The Ne isotopic signature does not show a temporal evolution. It remains plume‐like (plotting close to the Loihi–Kilauea correlation line in a Ne three‐isotope diagram) over the whole Mauna Kea section in those samples which are not dominated by air‐like Ne. Maximum 20Ne/22Ne and 21Ne/22Ne ratios reach 12.10 ± 0.36 and 0.0360 ± 0.0042, respectively. 40Ar/36Ar ratios vary widely between 360 and ∼3300 in the ≥1000°C release steps due to variable atmospheric contributions. In at least one sample, a 40Ar/36Ar ratio of 14,300 ± 910 demonstrates the presence of a MORB‐like Ar component. Kr and Xe isotopic compositions are atmospheric throughout. We discuss several possibilities on how to explain the isotopic trends of the noble gases and their correlation to other geochemical parameters. Simple admixture of MORB‐like noble gases to the plume component cannot account for the observations. We favor a model involving early melt extraction from the outer plume sections, followed by radiogenic ingrowth and, possibly, some interaction with ambient mantle material.
Paleointensity in Hawaiian Scientific Drilling Project Hole (HSDP2): Results from submarine basaltic glass
Authors: Tauxe Lisa , Love Jeffrey J.
Published: May 2003

Paleointensity estimates based on the high quality Thellier‐Thellier data from the early Brunhes (420–780 ka) are rare (only 30 in the published literature). The Second Hawaiian Scientific Drilling Project (HSDP2) drill hole recovered submarine volcanics spanning the approximate time period of 420–550 ka. These are of particular interest for absolute paleointensity studies owing to the abundance of fresh submarine basaltic glass, which can preserve an excellent record of ancient geomagnetic field intensity. We present here new results of Thellier‐Thellier paleointensity experiments that nearly double the number of reliable paleointensity data available for the early Brunhes. We also show that the magnetizations of the associated submarine basalts are dominated by viscous magnetizations and therefore do not reflect the true ancient geomagnetic field intensity at the time of extrusion. The viscous contamination is particularly severe because of a combination of low blocking temperatures in the basalts and relatively high temperatures in the deeper parts of the drill core. Our new data, when placed on the approximate timescale available for HSDP and HSDP2, are at odds with other contemporaneous paleointensity data. The discrepancy can be reconciled by adjusting the HSDP timescales to be younger by about 35 kyr.
Significance of large, refractory dunite bodies in the upper mantle of the Bay of Islands Ophiolite
Authors: Suhr Günter , Hellebrand Eric , Snow Jonathan E. , Seck Hans A. , Hofmann Albrecht W.
Published: May 2003

The origin of large mantle dunites is considered critical for models of melt migration in the mantle. Their presence is not compatible with formation synchronous to a fracture‐related melt transport event. In models of porous channel systems for melt transport, they represent a strongly coalesced, high‐flux conduit. Dunites from the lower parts of the mantle sections in the Bay of Islands Ophiolite are investigated by detailed geochemical traverses and with single samples. Dunites tend to cluster in the sense that several smaller dunites are associated with larger dunites or several dunites occur together. The chemistry of the large bodies is very depleted (Mg# in olivine 92–94, CaO in olivine 0.05–0.08%, Cr# [100 Cr/(Cr + Al)] in spinel 65–85, TiO2 in clinopyroxene 0.01–0.04%, Sm/Yb 0.2 to 0.7 relative to N‐MORB). Detailed traverses across the dunites commonly show a decrease of NiO in olivine associated with an increase in the Mg# along the harzburgite‐dunite boundary. Internally, dunite bodies are nearly homogeneous. Thickness of dunite bodies correlates with chemistry, in particular Mg# in olivine and probably Cr# and ferric iron in spinel, but not NiO in olivine. Incompatible element data for the largest dunites argue for their formation by an extremely depleted, high Mg# (boninitic?) melt. We suggest that integrated refractory melt: rock ratios in the largest dunites (up to 40 m) were below 8, because of a low abundance of refractory melts in the crust, and a lack of a systematic change of NiO in olivine with dunite width or across single dunites in detailed chemical traverses. Tectonically, the formation of depleted melts in a late stage of the spreading center is indicated. Their melt feeders failed when approaching the base of the mantle lithosphere and generated large dunites as replacive bodies. The latest expression of this magmatism are orthopyroxenite dykes, in part draining the large dunites. Since the large majority of all deeper mantle dunites are of refractory chemical nature and not akin to MORB, we caution as universally taking large dunite bodies to represent deep‐reaching channels with high melt flux and to take the abundance and size distribution of all dunites in an ophiolitic mantle section to infer melt migration mechanisms. In the Bay of Islands Ophiolite, the largest dunites in the mantle section appear to have little to do with the main constructional stage of the spreading center.
Comparison of dynamic flow models for the Central Aleutian and Tonga‐Kermadec subduction zones
Authors: Billen Magali I. , Gurnis Michael
Published: May 2003

Using three‐dimensional (3‐D) instantaneous dynamic models of the Central Aleutian subduction zone, we show that a low viscosity, low density (δρ = 10 kg/m3) region in the wedge is needed to match observations of topography, the geoid and the stress‐state in the slab and overriding plate. Previous models of the Tonga‐Kermadec subduction zone also require a low viscosity, low density (δρ = 20 kg/m3) region in the wedge. A low viscosity region in the wedge decouples the overriding plate from the downward flow in the wedge caused by the sinking slab, reducing the magnitude of negative dynamic topography on the overriding plate and changing the state of stress in the slab from down‐dip tension to down‐dip compression. If the low viscosity region is large, as in the Tonga‐Kermadec models, then the decoupling may also cause the overriding plate to go into extension. These are the first dynamic models to simultaneously match the state of stress in the slab and overriding plate and suggest that the combination of stress state within the slab and overriding plate may provide an additional constraint on the viscosity structure within subduction zones.
Mathematica as a powerful and practical tool for displaying animated three‐dimensional structures of the Earth's interior
Authors: Sato Hiroki , Muro Kenichi , Hasegawa Akira , Zhao Dapeng
Published: May 2003

Seismic tomographic studies have determined three‐dimensional (3‐D) velocity structures, in detail, of the crust and the upper mantle of the Earth. Yet, simple two‐dimensional (2‐D) sections have generally been used to present 3‐D tomographic results. Here we show 3‐D views and animations of the Earth's structure that are made as easy as 2‐D sections, by using Mathematica. As an example, low‐velocity zones in the upper mantle are shown in three dimensions, together with major volcanoes, mid‐crustal reflectors, earthquake hypocenters, the Moho discontinuity and the upper plane of the subducted slab, that are observed in northeastern Japan. Low velocities in volcanic areas generally correspond to high temperatures, and indicate possible presence of magma. The 3‐D animations enable us to investigate the spatial relation between low‐velocity zones, volcanoes, reflectors, earthquakes and the slab, and thus enable us to study magma ascent pathways in detail.
Structural complexity in carbonatite liquid at high pressures
Authors: Williams Quentin , Knittle Elise
Published: May 2003

The structure of a carbonatite liquid is examined using Raman spectroscopy at simultaneous high pressures and temperatures. At a pressure of 1.6 GPa and ∼700°C, the carbonatite shows marked structural differences from crystalline carbonates. The symmetric stretching vibration of the carbonate group shows clearly that two different carbonate group environments are present in the liquid: a weak vibration is observed near 1070 cm−1 and a stronger peak near 970 cm−1. Of these two peaks, the one with lower amplitude is indicative of normal, symmetric carbonate units (with partial double C‐O bonds), while the higher amplitude feature is associated with single‐bonded C‐O units, and thus highly distorted, yet structurally discrete, carbonate units. This diversity of structural environments is likely associated with the high affinity of incompatible elements, such as the rare earths, for carbonatite liquids. These structural observations provide a microscopic rationale for the dramatic difference in element partitioning between carbonatite and silicate liquids.
Multi‐scale analysis of a straight jet streak using numerical analyses and an airborne Doppler lidar
Authors: Dabas A. , Drobinski P. , Reitebuch O. , Richard E. , Delville P. , Flamant P. H. , Werner C.
Published: May 2003

Meteorological analyses from synoptic to mesoscales are combined with wind and cloud observations from the new French‐German airborne Doppler lidar WIND to analyse the dynamics of an upper‐tropospheric jet‐streak. The results show the impact of ageostrophic circulations on mesoscale structure as observed by the lidar. Lidar data also reveal fine scale heterogeneities (horizontal wind shear over <40 km) at the edge of the jet streak associated to a structural modification of cirrus clouds.
Interpreting the seasonal cycles of atmospheric oxygen and carbon dioxide concentrations at American Samoa Observatory
Authors: Manning Andrew C. , Keeling Ralph F. , Katz Laura E. , Paplawsky William J. , McEvoy Elizabeth M.
Published: May 2003

We present seven years of atmospheric O2/N2 ratio and CO2 concentration data measured from flask samples collected at American Samoa. These data are unusual, exhibiting higher short‐term variability, and seasonal cycles not in phase with other sampling stations. The unique nature of atmospheric data from Samoa has been noted previously from measurements of CO2, methyl chloroform, and ozone. With our O2 data, we observe greater magnitude in the short‐term variability, but, in contrast, no clear seasonal pattern to this variability. This we attribute to significant regional sources and sinks existing for O2 in both hemispheres, and a dependence on both the latitudinal and altitudinal origins of air masses. We also hypothesize that some samples exhibit a component of “older” air, demonstrating recirculation of air within the tropics. Our findings could be used to help constrain atmospheric transport models which are not well characterized in tropical regions.
Role of low‐frequency modes in organizing the inner heliosphere
Authors: Heinen Oliver , Lanzerotti Louis J. , Heber B. , Kunow H. , Thomson David J.
Published: May 2003

Cosmic ray proton data (125 to >2000 MeV) measured in the inner three‐dimensional (3‐D) heliosphere over the years from 1993 into 2000 by the KET instrument on the Ulysses spacecraft are examined. The data are parameterized and characterized by fitting products of spherical harmonic and sinusoidal frequency functions to three individual proton energy data sets. It is found that the time dependence of the cosmic ray data sets can be rather well characterized by relatively few variables consisting of low‐order spherical harmonic modes and a few frequencies of the order of a solar cycle. The results can be useful for analytical and computational studies of cosmic rays in the inner 3‐D heliosphere.
How can Saturn impose its rotation period in a noncorotating magnetosphere?
Authors: Espinosa Stéphane A. , Southwood David J. , Dougherty Michèle K.
Published: May 2003

A conceptual model is proposed, where Saturn can impose its rotation period in a noncorotating magnetosphere, as observed by Pioneer 11, Voyager 1 and 2. The fundamental hypothesis for this so‐called “Camshaft model” is that Saturn has an equatorial anomaly, likely to be magnetic. It is restricted in longitude, and the source is yet to be detected. This longitudinal asymmetry is equivalent to a variation of pressure for the magnetospheric subcorotating plasma, and therefore as the planet rotates, a compressional wave is generated. That is, we use the MHD fast mode, which can propagate across the magnetic field, rather than the transverse mode for momentum transfer from the planet to the magnetospheric plasma. The wave propagates radially outward across the background magnetic field, inducing a motion in the plasma that is decoupled from and superposed on its azimuthal motion. Consequently, as the planet rotates, magnetic field observations fixed in an inertial frame would present a periodic signature with the planetary rotation period. This is true at each local time, independently of the level of plasma subcorotation. We then show that the Camshaft model accounts very well for the previously reported observations of spin‐periodic perturbations in Saturn's magnetic field. Finally, we consider the perturbation magnetic field (obtained by subtracting only the model planetary field from the observations) measured by Pioneer 11 while outbound, and find its orientation consistent with the Camshaft model once the propagation delay of the compressional wave is included.
Ionospheric equivalent current distributions determined with the method of spherical elementary current systems
Authors: Pulkkinen Antti , Amm Olaf , Viljanen Ari
Published: May 2003

The ground magnetic field disturbance caused by ionospheric currents can be represented by equivalent currents placed to the ionospheric plane. Equivalent currents provide valuable information about the ionospheric electrodynamics, and thus they can be used, for example, in studies of space weather, ionosphere‐magnetosphere coupling, and the magnetotelluric source effect. We derive equivalent currents by using the spherical elementary current system method. The applicability of the method for the Baltic Electromagnetic Array Research (BEAR) magnetometer array is validated by means of synthetic ionospheric current models and by investigating the goodness of the fit between the modeled and measured ground magnetic field. The applicability of the method for the sparser International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network is also proved. In addition, the combination of the elementary current system method and the complex image method, used for the calculation of the induced electromagnetic fields on ground, is introduced, and the combination of the methods is tested by using geoelectric field data from the BEAR project. Our special interest is in the effects that rapidly varying ionospheric currents have on technological conductor systems at the surface of the Earth due to geomagnetically induced currents. Comparison between equivalent currents and the time derivative vector of the horizontal magnetic field emphasizes the importance of small‐scale structures.
A statistical study of large‐amplitude parallel electric fields in the upward current region of the auroral acceleration region
Authors: Hull A. J. , Bonnell J. W. , Mozer F. S. , Scudder J. D.
Published: May 2003

We present a survey of 64 direct observations of large‐amplitude parallel electric fields E∥ in the upward current region of the southern auroral acceleration zone, obtained by the three‐axis electric field experiment on Polar. These E∥ events range in amplitude from about 25 to 300 mV/m and represent a significant fraction of the total electric field strength (E∥/E⟂ ranges from ∼0.25 to O(10)). The E∥ structures, which tend to occur at the edges of oppositely directed (converging) pairs of perpendicular electric field structures (electrostatic shocks), have transverse (to the magnetic field) widths of ∼1.0–20 km at altitudes ranging from 0.8RE to 1.5RE, assuming the structures are stationary. The parallel potential drops associated with these large‐amplitude parallel electric fields are highly localized in altitude (e.g., tens of kilometers as opposed to thousands of kilometers). The amplitude of the parallel electric field shows a strong anticorrelation with the plasma density inferred from spacecraft potential measurements. We find no apparent correlation between the amplitude of the parallel electric field and altitudes sampled (between 0.8RE and 1.5RE), current density, and Kp, though there is a suggestion that the largest E∥/E⟂ ratios are confined to lower altitudes. Taking sampling biases into consideration, we find that the large parallel electric fields occur preferentially at higher values of Kp and within a thin layer centered about 1.28RE. A detailed analysis favors ambipolar effects over electron inertial effects as an explanation for the parallel electric field signatures.
Rebuilding process of the outer radiation belt during the 3 November 1993 magnetic storm: NOAA and Exos‐D observations
Authors: Miyoshi Yoshizumi , Morioka Akira , Misawa Hiroaki , Obara Takahiro , Nagai Tsugunobu , Kasahara Yoshiya
Published: May 2003

Using the data from the NOAA and Exos‐D satellites during the 3 November 1993 magnetic storm, the dynamic behavior of electrons with energies from a few tens of kiloelectronvolts to a few and its relation to plasma waves were examined. After the late main phase, relativistic electron flux started to recover from the heart of the outer radiation belt, where the cold plasma density was extremely low, and intense whistler mode chorus emissions were detected. The phase space density showed a peak in the outer belt, and the peak increased gradually. The simulation of the inward radial diffusion process could not reproduce the observed energy spectrum and phase space density variation. On the other hand, the simulated energy diffusion due to the gyroresonant electron‐whistler mode wave interactions, under the assumption of the Kolmogorov turbulence spectrum, could generate the relativistic electrons without the flux transport from the outer region. The present study suggested that the seed population of relativistic electrons, which appeared in the heart of the outer radiation belt during the late main phase, was the ring current electrons injected from the plasma sheet, and that the acceleration by whistler mode chorus via gyroresonant wave–particle interactions outside the plasmapause could play an important role to generate the relativistic electrons.