bluuebunny/crossref_metadata_2025 huggingface dataset:
Macro‐Level and Genetic‐Level Responses of Bacillus subtilis to Shear Stress
Authors: Sahoo Susmita , Verma Rajesh K. , Suresh A. K. , Rao K. Krishnamurthy , Bellare Jayesh , Suraishkumar G. K.
Published: December 2003

Responses of bacterial (Bacillus subtilis) cells under different shear levels, from both the macro and genetic viewpoints, have been presented. The responses were studied using a novel, couette flow bioreactor (CFB), in which the entire cultivation can be performed under defined shear conditions. Oxygen supply, the normal limiting factor for entire cultivations under defined shear conditions, has been achieved by passing air through a poly(tetrafluoroethylene) (PTFE) membrane fixed on the inner cylinder of the CFB. More importantly, analyses of the oxygen transfer capabilities as well as the shear rates show that in this CFB, the effects of defined shear can be studied without interference from the effects of oxygen supply. Further, the shake flask can be used as a proper control for studying the shear effects, mainly because the shear rate in the shake flask under normal shaker operating conditions of 190 rpm has been estimated to be a negligible 0.028 s‐1 compared to a value of 445 s‐1 at the lowest rpm employed in the CFB. At the macro level the cell size decreased by almost 50% at 1482 s‐1 compared to that at 0.028 s‐1, the growth rate increased by 245%, and the maximum cell concentration increased by 190% when the shear rate was increased from 0.028 to 1482 s‐1. The specific intracellular catalase level increased by 335% and protease by 87% at 1482 s‐1 as compared to the control cultures at a shear rate 0.028 s‐1. In addition, the specific intracellular reactive oxygen species level (siROS) at the highest shear rate was 9.3‐fold compared to the control conditions. At the genetic level we have established the involvement of the transcription factor, σB, in the bacterial responses to shear stress, which was unknown in the literature thus far; the σB expression correlated inversely with the siROS. Further, through experiments with ROS quenchers, we showed that ROS regulated σB expression under shear.
An approach for simulating the phenology of savanna ecosystems in the Laboratoire de Météorologie Dynamique General Circulation Model
Authors: Ciret C. , Polcher J. , Le Roux X.
Published: December 2003

Plant phenology, defined here as the seasonal variations of green and dead biomasses in response to climatic conditions, is an important parameter for the modeling of biophysical exchanges between vegetation and atmosphere. However, the adequate simulation of plant phenology, particularly in tropical regions, is still lacking in current general circulation models (GCMs). This paper proposes a modeling approach to simulate the phenology of savanna grasses in the Laboratoire de Météorologie Dynamique (LMD) GCM. A plant production and phenology model (PPP) is developed to simulate the temporal variations of green and dead aboveground biomasses and leaf area index (LAI) using climate variables computed by the LMD GCM. In addition, the PPP model simulates the occurrence of savanna fire. Predictions are compared to harvest measurements of grasses from two different regions of savanna: the region of Lamto, West Africa, and the region of Victoria River district, northern Australia. Results show that the PPP model generates reasonably realistic plant seasonal variations in these two regions, despite the existing biases in the simulated climate variables. Both the frequency and timing of fire occurrence are, moreover, realistically simulated. This model, linked to the GCM, could be used as a tool to investigate the effects of fire disturbances and short‐term (i.e., seasonal and interannual) savanna vegetation feedbacks on climate.
Secular and tidal strain across the Main Ethiopian Rift
Authors: Bilham Roger , Bendick R. , Larson K. , Mohr P. , Braun J. , Tesfaye S. , Asfaw L.
Published: December 2003

Using a combination of laser ranging and GPS data acquired between 1969 and 1997 we derive a separation velocity for the Somali and Nubian plates in Ethiopia (4.5±1 mm/yr at N108±10E). This vector is orthogonal to the NNE‐trending neotectonic axis (Wonji fault belt) of the Ethiopian rift axis. Current rifting is concentrated within a 33‐km‐wide zone that includes a 7‐km‐wide belt of late Quaternary faulting where maximum surface strain rates are comparable to those at active plate boundaries (0.1 μstrain/yr). The strain‐field suggests that thin (<5 km) elastic crust separates thick continental lithosphere, a geometry quite different from oceanic rifting, and a mechanical configuration that favors the amplification of regional strain. Semidiurnal strain tides, however, as measured by kinematic GPS methods are not amplified along or across the rift, indicating that the rift zone's low rigidity applies only at periods of years.
Postglacial left slip rate and past occurrence ofM≥8 earthquakes on the Western Haiyuan Fault, Gansu, China
Authors: Lasserre C. , Morel P.‐H , Gaudemer Y. , Tapponnier P. , Ryerson F. J. , King G. C. P. , Métivier F. , Kasser M. , Kashgarian M. , Liu Baichi , Lu Taiya , Yuan Daoyang
Published: December 2003

High‐resolution (HR) air photographs and a 1‐m horizontal and 2‐m vertical resolution digital elevation model derived from them by stereophotogrammetry provide new constraints on the behavior of the western stretch of the active Haiyuan fault, in Gansu province, China. The photographs cover three swaths along the fault, each about 2‐km‐long and at least 500‐m‐wide, near the village of Songshan, at 103.5°E. This high‐resolution data set is used to map and measure cumulative horizontal offsets of alluvial terraces and risers that range between 115 and 135 m, and 70 and 90 m, at two sites. Dating these terraces with14C yields minimum and maximum ages of 8400 and 7600, and 14,200 years B.P., respectively. This leads to a postglacial slip rate of 12±4 mm/yr, with a most likely minimum value of 11.6±1.1 mm/yr. The smallest stream offsets observed on the HR photographs range between 8 and 16 m and are interpreted as coseismic displacements of the last few earthquakes withM≥ 8 that ruptured the 220‐km‐long Tianzhu gap of the fault, west of the Yellow River. Earthquakes of that size within this gap, which has been quiescent for at least 800 years, would recur at intervals of 1050±450 years.
The disparate evolution of three Agulhas rings in the South Atlantic Ocean
Authors: Arhan Michel , Mercier Herlé , Lutjeharms Johann R. E.
Published: December 2003

Hydrographic sections carried out in January‐March 1995 across the pathway of Agulhas rings in the Cape Basin are used for a brief description of the mesoscale thermohaline variability in this region and a detailed study of three rings that were identified in the data. The three eddies exhibited remarkably diverse dimensions, vertical structures, and water mass characteristics. One of them, R1, was located near the Agulhas retroflection, had a diameter of 200 km, a maximum azimuthal speed of 0.40 m s−1, core oxygen values in excess of 260 μmol kg−1 and was characterized by a well‐developed thermostad of 11.6°C. A second ring, R2, at 31°30′S, 9°W, by contrast, had a diameter of about 500 km, a core temperature of 17.1°C, and azimuthal speeds of 0.50 m s−1, suggesting a very different history. A third ring, R3, at 26°S, 9°W, although farthest north of the three, had characteristics similar to ring R1, but with a deeper thermostad. Satellite altimetric data allow one to infer the natural histories of these vortices. Ring Rl detached from the retroflection at the beginning of March 1994 and spent the whole of the subsequent winter south of 42°S. This could explain the estimated heat loss of 620 W m−2. The two rings observed at 9°W were spawned as one feature in April 1993, but interaction with the Erica seamount split it into two eddies; R3 being stalled in the retroflection region for the winter, while R2 moved off rapidly into the South Atlantic, by contrast, retaining most of its heat. These histories account for the observed differences between the rings. They also demonstrate that the interaction of Agulhas rings with their environment, including ambient water masses, the overlying atmosphere, and the bottom topography, is critical to their eventual hydrographic characteristics and the manner in which they contribute to the transport of heat and salt from the Indian to the South Atlantic Ocean.
The role of the Indonesian Throughflow in equatorial Pacific thermocline ventilation
Authors: Rodgers Keith B. , Cane Mark A. , Naik Naomi H. , Schrag Daniel P.
Published: December 2003

The role of the Indonesian Throughflow (ITF) in the thermocline circulation of the low‐latitude Pacific Ocean is explored using a high‐resolution primitive equation ocean circulation model. Seasonally forced runs for a domain with an open Indonesian passage are compared with seasonally forced runs for a closed Pacific domain. Three cases are considered: one with no throughflow, one with 10 Sv of imposed ITF transport, and one with 20 Sv of ITF transport. Two idealized tracers, one that tags northern component subtropical water and another that tags southern component subtropical water, are used to diagnose the mixing ratio of northern and southern component waters in the equatorial thermocline. It is found that the mixing ratio of north/south component waters in the equatorial thermocline is highly sensitive to whether the model accounts for an ITF. Without an ITF, the source of equatorial undercurrent water is primarily of North Pacific origin, with the ratio of northern to southern component water being approximately 2.75 to 1. The ratio of northern to southern component water in the Equatorial Undercurrent with 10 Sv of ITF is approximately 1.4 to 1, and the ratio with 20 Sv of imposed ITF is 1 to 1.25. Estimates from data suggest a mean mixing ratio of northern to southern component water of less than 1 to 1. Assuming that the mixing ratio changes approximately linearly as the ITF transport varies between 10 and 20 Sv, an approximate balance between northern and southern component water is reached when the ITF transport is approximately 16 Sv. It is also shown that for the isopycnal surfaces within the core of the equatorial undercurrent, a 2°C temperature front exists across the equator in the western equatorial Pacific, beneath the warm pool. The implications of the model results and the temperature data for the heat budget of the equatorial Pacific are considered.
Spaceborne observations of the global distribution of carbon monoxide in the middle troposphere during April and October 1994
Authors: Connors Vickie S. , Gormsen Barbara B. , Nolf Scott , Reichle Henry G.
Published: December 2003

Spaceborne measurements of tropospheric carbon monoxide (CO) were made by the Measurement of Air Pollution from Satellites (MAPS) experiment during April 9–19, 1994, and September 30 to October 11, 1994, from the space shuttle Endeavour. During the April mission, MAPS operated for 211 hours, with 736,471 s of nadir‐viewing data, of which 161,619 s were cloud‐free. In the October mission, MAPS operated for 256 hours, with 821,502 s of nadir‐viewing data, of which 192,004 s were cloud‐free. During the two 10‐day Space Radar Laboratory flights, extensive and internally consistent correlative measurements and observations were made on the ground at nearly 30 sites between 70°N and 67°S, from five aircraft in three countries, and by the astronaut crews from the space shuttle. These ancillary measurements provided critical information on the nature of the atmospheric environment during the flights, the distribution of the CO mixing ratios in the boundary layer and in the middle troposphere, and the vertical distribution of CO at some locations. Although the airborne CO measurements are the key validation data sets for the MAPS measurements, the ground‐based CO measurements provide a near‐surface CO boundary condition for modeling applications and for CO emissions investigations. This paper will present the measurements of the April and October 1994 and the October 1984 MAPS CO data. These MAPS results compare well (±10%) with the intercalibrated airborne measurements from the NASA DC‐8 flights over North America, and CO profiles from the Commonwealth Scientific and Industrial Research Organisation aircraft near Cape Grim, Tasmania. Longitudinal and latitudinal transects of the MAPS CO measurements show significant seasonal variability consistent with the seasonal shifts in the locations and strengths of the CO sources. In April the highest average CO values (∼120 ppbv, averaged throughout the depth of the atmosphere) are found over the high northern latitudes, with decreasing amounts (∼45 to 60 ppbv) toward the southern middle and high latitudes. The CO distribution changed dramatically by October with the CO gradient being reversed from that measured during April. During October the highest CO values (greater than 135 ppbv) are concentrated in a tropical envelope extending over central South America, southern Africa, southern India, Indonesia, and northern Australia. Numerous and extensive fires in these areas were observed and photographed by the STS 68 astronaut flight crew.
Characteristics of the marine boundary layers during two Lagrangian measurement periods: 2. Turbulence structure
Authors: Wang Qing , Lenschow Donald H. , Pan Linlin , Schillawski Richard D. , Kok Gregory L. , Prévot Andre S. H. , Laursen Krista , Russell Lynn M. , Bandy Alan R. , Thornton Donald C. , Suhre Karsten
Published: December 2003

Characteristics of turbulence mixing in remote marine boundary layers are analyzed using aircraft measurements from six flights during the two intensive Lagrangian measurement periods of ACE1 (the southern hemisphere Aerosol Characterization Experiment). The six cases studied here represent a variety of boundary layer conditions in the region south of Tasmania, Australia. Our study indicated that (1) Lagrangian A (LA) had stronger turbulence mixing and entrainment compared to Lagrangian B (LB) due to greater shear generation of turbulence kinetic energy (TKE), (2) strong mesoscale variation in boundary layer turbulence and thus turbulence mixing existed in the ACE1 region during LB due to variations in sea surface temperature (SST), (3) stable thermal stratification in the boundary layer was found during the last flight of each Lagrangian, consequently, TKE decreased rapidly with height resulting in small or near‐zero entrainment rate in spite of strong shear forcing at the surface and in the boundary layer; and (4) the buffer layer, which lies above the boundary layer and below the main inversion, had weak and intermittent turbulence mostly associated with cloud bands and cumulus. Evidence of entrainment was found in the buffer layer. However, it is difficult to quantify by flux measurements due to the weak and intermittent nature of the turbulence field.
Ozone and peroxy radical budgets in the marine boundary layer: Modeling the effect of NOx
Authors: Cox R. A.
Published: December 2003

A one‐dimensional box model has been formulated to describe the ozone budget and HOx photochemistry in the marine boundary layer. The model includes a simple description of vertical exchange with the free troposphere and the ocean surface, and a photochemical scheme including oxidation of CO and CH4. Model calculations are compared with data collected during the summer season at two midlatitude coastal sites in the northern and southern hemispheres (Mace Head, Ireland, and Cape Grim, Tasmania). Results using small, prescribed NOx concentrations gave compensation points, where ozone loss by photolysis and physical removal is balanced by its production via NOx chemistry, of ∼30 ppt and ∼15 ppt at the two sites, respectively, in line with conclusions from the observational data. Changes in the dependence of peroxy radical concentrations on solar intensity were also in line with observations. The simple model involving CO and CH4 chemistry should be adequate for defining oxidizing capacity in the unpolluted marine boundary layer.
Surface formation rates and impact crater densities on Venus
Authors: Campbell Bruce A.
Published: December 2003

Impact crater density has been used to estimate relative ages of major Venus geologic units, typically based on the assumption of short, globally synchronous formation periods. The total number density of craters is the only parameter which may be quantified for most Venus subregions, in contrast to the size‐frequency analysis often used for other planetary studies. This paper examines the statistical limits on such crater counts and the predicted crater density for various possible time‐varying surface formation rate functions. These results show that (1) the true mean crater density is poorly constrained due to the limited sample size provided by aggregate geologic units, and (2) any given crater density can be accommodated by a very short pulse of unit formation at some age T, Gaussian‐distributed formation functions of mean age <T, exponential functions with initiation ages between T and 2T, or a host of other more complicated rate functions. These results, when coupled with the unknown rate of crater removal by tectonic or volcanic activity, indicate that the crater counts for specific landforms on Venus offer little constraint on the relative timing or duration of their development. The hypothesis of globally synchronous formation of landforms such as volcanoes or coronae cannot be validated with the available crater data.
Transport of SO2 by explosive volcanism on Venus
Authors: Glaze Lori S.
Published: December 2003

Observations by the Pioneer Venus orbiter and many different types of analyses have suggested the possibility of contemporary explosive volcanism on Venus. The rise of volcanic eruption plumes on Venus is reexamined using recent improvements in buoyant plume modeling. The first‐order model applied to Venus by previous authors features nonphysical discontinuous solutions for all of the model parameters and lacks internal consistency in the formulation of the governing equations. This makes it difficult to assess the validity of the Venus applications and conclusions derived from these models. The model used here contains several improvements including two corrections to the formulation and a change in the criterion for the transition of the plume from the jet region to the buoyancy‐driven region. The model used in earlier works assumed a discontinuous transition between these two regions, resulting in an overestimate of the transition height as well as the maximum plume height. The effect of the transition criterion is magnified on Venus, where the continuous solution appears to have very little dependence on initial vent size. In contrast, the discontinuous solution shows a very strong dependence on initial vent size. The continuous solution used here indicates that plumes on Venus become dominated by buoyancy effects almost immediately above the vent. Use of the discontinuous solution, however, suggests that jets up to 10 km above the vent are possible for the boundary conditions considered. The combined effect of using the older model for conditions on Venus is a 5–8% overestimate of the maximum plume height for vent radii ranging from 20 to 250 m. The influence of latitude and elevation are also explored. For large eruptions on Venus, plumes rising in the Northern Highlands would rise much higher than plumes with identical boundary conditions erupted in the equatorial Lowlands. This is due to the greater stability of the upper atmosphere at higher latitudes and the sharp decrease in atmospheric pressure as a function of altitude. To examine the net effect of all the model assumptions and ambient influences, eruptions are simulated for a range of conditions at Maat Mons and compared with results in the literature. These simulations indicate that for small mass fluxes, the new model predicts smaller plumes than the older model. For larger mass fluxes, however, the new model predicts larger plumes than the older model. Because the Maat Mons summit elevation is already more than 9 km above the mean planetary radius, the reduced atmospheric pressure results in a plume with enough buoyancy to more than compensate for all of the model effects. These results continue to support the possibility that explosive eruptions on Venus may be capable of producing plumes that rise buoyantly to heights detected by the Pioneer Venus orbiter.
Does Europa have a subsurface ocean? Evaluation of the geological evidence
Authors: Pappalardo R. T. , Belton M. J. S. , Breneman H. H. , Carr M. H. , Chapman C. R. , Collins G. C. , Denk T. , Fagents S. , Geissler P. E. , Giese B. , Greeley R. , Greenberg R. , Head J. W. , Helfenstein P. , Hoppa G. , Kadel S. D. , Klaasen K. P. , Klemaszewski J. E. , Magee K. , McEwen A. S. , Moore J. M. , Moore W. B. , Neukum G. , Phillips C. B. , Prockter L. M. , Schubert G. , Senske D. A. , Sullivan R. J. , Tufts B. R. , Turtle E. P. , Wagner R. , Williams K. K.
Published: December 2003

It has been proposed that Jupiter's satellite Europa currently possesses a global subsurface ocean of liquid water. Galileo gravity data verify that the satellite is differentiated into an outer H2O layer about 100 km thick but cannot determine the current physical state of this layer (liquid or solid). Here we summarize the geological evidence regarding an extant subsurface ocean, concentrating on Galileo imaging data. We describe and assess nine pertinent lines of geological evidence: impact morphologies, lenticulae, cryovolcanic features, pull‐apart bands, chaos, ridges, surface frosts, topography, and global tectonics. An internal ocean would be a simple and comprehensive explanation for a broad range of observations; however, we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm, soft ice with only localized or partial melting. Two different models of impact flux imply very different surface ages for Europa; the model favored here indicates an average age of ∼50 Myr. Searches for evidence of current geological activity on Europa, such as plumes or surface changes, have yielded negative results to date. The current existence of a global subsurface ocean, while attractive in explaining the observations, remains inconclusive. Future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within Europa today.
Radiolarian‐based transfer function for the estimation of sea surface temperatures in the Southern Ocean (Atlantic Sector)
Authors: Abelmann Andrea , Brathauer Uta , Gersonde Rainer , Sieger Rainer , Zielinski Uli
Published: December 2003

A new radiolarian‐based transfer function for sea surface temperature (SST) estimations has been developed from 23 taxa and taxa groups in 53 surface sediment samples recovered between 35° and 72°S in the Atlantic sector of the Southern Ocean. For the selection of taxa and taxa groups ecological information from water column studies was considered. The transfer function allows the estimation of austral summer SST (December–March) ranging between −1 and 18°C with a standard error of estimate of 1.2°C. SST estimates from selected late Pleistocene squences were sucessfully compared with independent paleotemperature estimates derived from a diatom transfer function. This shows that radiolarians provide an excellent tool for paleotemperature reconstructions in Pleistocene sediments of the Southern Ocean.
Assessing the seasonality of the oceanic sink for CO2 in the northern hemisphere
Authors: Lefèvre Nathalie , Watson Andrew J. , Cooper David J. , Weiss Ray F. , Takahashi Taro , Sutherland Stewart C.
Published: December 2003

Seasonal CO2 fluxes are estimated from quarterly maps of ΔpCO2 (difference between the oceanic and atmospheric partial pressure of CO2) and associated error maps. ΔpCO2 maps were interpolated from pCO2 measurements in the North Atlantic and the North Pacific Oceans using an objective mapping technique. Negative values correspond to an uptake of CO2 by the ocean. The CO2 flux for the North Atlantic Ocean, between 10°N and 80°N, ranges from −0.69 GtC/yr, for the first quarter (January‐March), to −0.19 GtC/yr for the third quarter (July‐September) using the gas exchange coefficient of Tans et al. [1990], satellite wind speeds, and a correction for the skin effect. On annual average, the North Atlantic ocean (north of 10°N) is a sink of CO2 ranging from −0.23 ± 0.08 GtC/yr (gas exchange coefficient of Liss and Merlivat [1986] with Esbensen and Kushnir [1981] wind field) to −0.48 ±0.17 GtC/yr (gas exchange coefficient of Tans et al. with satellite wind field). The CO2 flux for the North Pacific, between 15°N and 65°N, ranges from −0.66 GtC/yr from April to June to zero from July to September. For the Atlantic, the errors are generally small, that is, less than 0.19 GtC/yr, but for the Pacific considerably larger uncertainties are generated due to the less extensive data coverage. The northern hemisphere ocean (north of 10°N) is a net sink of CO2 to the atmosphere which is stronger in spring (April‐June), due to the biological activity, with an estimate of −1.23 ± 0.40 GtC/yr averaged over this period. The annual mean northern hemisphere ocean flux is −0.86 ± 0.61 GtC/yr.
Spatiotemporal patterns of carbon‐13 in the global surface oceans and the oceanic suess effect
Authors: Gruber Nicolas , Keeling Charles D. , Bacastow Robert B. , Guenther Peter R. , Lueker Timothy J. , Wahlen Martin , Meijer Harro A. J. , Mook Willem G. , Stocker Thomas F.
Published: December 2003

A global synthesis of the 13C/12C ratio of dissolved inorganic carbon (DIC) in the surface ocean is attempted by summarizing high‐precision data obtained from 1978 to 1997 in all major ocean basins. The data, mainly along transects but including three subtropical time series, are accompanied by simultaneous, precise measurements of DIC concentration and titration alkalinity. The reduced isotopic ratio, δ13C, in the surface ocean water is governed by a balance between biological and thermodynamic processes. These processes have strongly opposing tendencies, which result in a complex spatial pattern in δ13C with relatively little variability. The most distinctive feature in the spatial distribution of δ13C seen in our data is a maximum of δ13C near the subantarctic front with sharply falling values to the south. We attribute this feature to a combination of biological uptake of CO2 depleted in 13C (low δ13C) and air‐sea exchange near the front and upwelling further south of waters with low δ13C resulting from the remineralization of organic matter. Additional features are maxima in δ13C downstream of upwelling regions, reflecting biological uptake, and minima in the subtropical gyres caused by strongly temperature dependent thermodynamic isotopic fractionation. At the time series stations, two in the North Atlantic Ocean and one in the North Pacific, distinct seasonal cycles in δ13C are observed, the Pacific data exhibiting only about half the amplitude of the Atlantic. Secular decreases in δ13C caused by the invasion of isotopically light anthropogenic CO2 into the ocean (the 13C Suess effect) have been identified at these time series stations and also in data from repeated transects in the Indian Ocean and the tropical Pacific. A tentative global extrapolation of these secular decreases yields a surface oceanic 13C Suess effect of approximately −0.018‰ yr−1 from 1980 to 1995. This effect is nearly the same as the 13C Suess effect observed globally in the atmosphere over the same period. We attribute this response to a deceleration in the growth rate of anthropogenic CO2 emissions after 1979, which subsequently has reduced the atmospheric 13C Suess effect more than the surface ocean effect.
Geochemistry and intrusive directions in sheeted dikes in the Troodos ophiolite: Implications for mid‐ocean ridge spreading centers
Authors: Staudigel Hubert , Tauxe L. , Gee J. S. , Bogaard P. , Haspels J. , Kale G. , Leenders A. , Meijer P. , Swaak B. , Tuin M. , Van Soest M. C. , Verdurmen E. A. Th. , Zevenhuizen A.
Published: December 2003

Sheeted dikes at mid‐ocean ridge volcanoes represent the link between deep magma production and storage processes and shallow processes such as volcanism and hydrothermal activity. As such, they are crucial for the interpretation of many observations at mid‐ocean ridges or other volcanoes with pronounced rift zones, including topography, hydrothermal systems, petrology, and geochemistry. We carried out a structural, magnetic, and chemical investigation of a 4 × 10 km sheeted dike section in the Troodos ophiolite, Cyprus. On the basis of major and trace element geochemistry, we distinguish dikes that may be correlated with the basal high‐Ti series (HTS) lavas from those of the overlying low‐Ti series (LTS) lavas. All dikes studied are nearly parallel to each other, with vertical or steeply dipping planes whose strike likely indicates the orientation of the spreading center. Anisotropy of magnetic susceptibility measurements suggests that the HTS and LTS dikes intrude in fundamentally different ways. HTS dikes reflect the intrusive behavior of dikes in the vicinity of a magma supply system and define ridge parallel intrusive sheets that radiate out from the magma chamber. LTS dikes show a bimodal, orthogonal set of intrusive directions, one shallow and one near vertical. Near‐lateral propagating dikes provide a means for delivery of magma into distant portions of a rift system, and near‐vertical dike propagation directions are probably associated with feeder dikes to down‐rift surface flows. Our study suggests that the types of dike intrusive behavior in the Troodos ophiolite may also be typical for “normal” mid‐ocean ridges or other major shield volcanoes with well‐developed rift zones.
Isotope topology of individual hotspot basalt arrays: Mixing curves or melt extraction trajectories?
Authors: Phipps Morgan Jason
Published: December 2003

Arrays of basalts from the same hotspot usually plot within an elongate tube‐like field in 87Sr/86Sr–143Nd/144Nd–206Pb/204Pb space (Hart et al., 1992). Each hotspot array tube (HART) is commonly interpreted as the result of melting multiple basalt sources that are variably proportioned mixtures of the hotspot source components. I propose instead that a HART is the isotopic trace of the melt extraction trajectory produced by progressive melting of a heterogeneous source mixture characteristic to that hotspot. melt extraction trajectories form when the sources of the individual hotspot basalts differ in the amount of previous melt extraction from the upwelling and melting plume mantle mixture. Sequential melts along a melt extraction trajectory trace a one‐dimensional path in through isotope space, independent of the number of distinct isotopic components in the initial source mixture. Subsequent partial mixing of the melts produced along a melt extraction trajectory would still tends to preserve this tube‐like isotope topology. The melting physics that leads to a melt extraction trajectory also provides straightforward explanations for the 187Os/188Os contrasts between mid‐ocean ridge basalts and their presumed abyssal peridotite source and for the enigmatic trace element and isotopic patterns of pyroxenite veins and peridotite exposed within orogenic lherzolites.
Dehydration and melting experiments constrain the fate of subducted sediments
Authors: Johnson Marie C. , Plank Terry
Published: December 2003

Geochemical tracers demonstrate that elements are cycled from subducted sediments into the arc melting regime at subduction zones, although the transfer mechanism is poorly understood. Are key elements (Th, Be, Rb) lost during sediment dehydration or is sediment melting required? To investigate this question, we conducted phase equilibria and trace element partitioning experiments on a pelagic red clay for conditions appropriate to the slab beneath arc volcanoes (2–4 GPa, 600°–1000°C). Using both piston cylinders and multianvils, we determined the solidus, phase stabilities, and major element compositions of coexisting phases. The solidus (H2O + Cl fluid‐saturated) was located at 775 ± 25°C at 2 GPa, 810 ± 15°C at 3 GPa, and 1025 ± 25°C at 4 GPa with noevidence for complete miscibility between melt and fluid. This sediment composition produces a profusion of phases both above and below the solidus: garnet, jadeitic pyroxene, alkali‐rich amphibole, phengite, biotite, magnetite, coesite, kyanite, apatite, zircon, Cl‐rich fluids, and peraluminous to peralkaline granitic melts. At 2 GPa the phengite dehydration solidus is at 800°–825°C, while biotite breaks down between 850° and 900°C. To explore trace element partitioning across the solidus at 2 GPa, we used diamonds to trap fluids and melts. Both the bulk sediment residues and diamond traps were analyzed postexperiment by inductively coupled plasma–mass spectrometry (ICP‐MS) and inductively coupled plasma–atomic emission spectrometry (ICP‐AES) for 40 elements for which we calculated bulk partition coefficients (D = Csolid/Cfluid). Below the solidus, Rb, Sr, Ba, and Pb showed the greatest mobility (D ∼ 0.5–1.0), while at the solidus, Th and Be became notably partitioned into the melt (D values changing from >2.0 to <1.0). K and Rb D values fall below 1.0 when the micas breakdown. Only at the solidus do Th and Rb attain similar partition coefficients, a condition required by arc data. Taken together, the experimental results indicate that critical elements (Th and Be) require sediment melting to be efficiently transferred to the arc. This conclusion is at odds with most thermal models for subduction zones, which predict slab temperatures more than 100°C lower than sediment solidi. Thus the condition of sediment melting (with oceanic crust dehydration) may provide new constraints on the next generation of thermal/geodynamical models of subduction zones.
Dynamics of the South Java Current in the Indo‐Australian Basin
Authors: Sprintall Janet , Chong Jackson , Syamsudin Fadli , Morawitz Werner , Hautala Susan , Bray Nan , Wijffels Susan
Published: December 2003

A year‐long deployment of a mooring in the South Java Current (SJC) of Indonesia provides a fascinating insight into this poorly understood, semi‐annually reversing boundary current. A striking three‐week period of southeastward flow begins in mid‐May 1997. An analytical model directly account for changes in velocity at this time due to the passage of a westerly wind‐forced, downwelling Kelvin wave from the equatorial western Indian Ocean. The entire water column is warmed, with a fresh cap overlying salty water, consistent with the Indian Ocean source. Following the wave passage, the SJC is north‐westward, and the prevailing south‐easterly monsoon winds lead to upwelling of cold, salty water. In early August, the SJC abruptly returns to south‐eastward flow, and remains so until November 1997 in the face of steady south‐easterly local winds. The anomalous flow direction and cooler water are related to an upwelling Kelvin wave, forced by unseasonal prolonged easterly wind anomalies in the equatorial Indian Ocean. After a small reversal of flow in November 1997, the SJC is south‐eastward, as expected during the north‐east monsoon. A trend toward increasing salinities in the record is attributed to the increased input of salty Indian Ocean water, enhanced evaporation, and a lack of freshwater advection due to the regionally reduced precipitation during the 1997‐98 El Niño.
Diapycnal mixing in the Banda Sea: Results of the first microstructure measurements in the Indonesian Throughflow
Authors: Alford Matthew H. , Gregg Michael C. , Ilyas Muhammed
Published: December 2003

Models involving basin‐averaged T/S properties [Ffield and Gordon, 1992; Hautala et al., 1996] and barotropic/baroclinic tidal energy conversion [Sjöberg and Stigebrandt, 1992] suggest that the Indonesian archipelago is a site of active mixing. This paper describes the first microstructure measurements made in the region. Aboard the R/V Baruna Jaya IV, we repeated 18 km legs centered on (6.5°S, 128°E), in the central Banda Sea, for two weeks during Oct/Nov 1998.

With the Modular Microstructure Profiler, we gathered 519 profiles of potential temperature, salinity, potential density, pressure and kinetic energy dissipation rate. The cruise‐mean diapycnal diffusivity from 20–300 m is
, similar to “open ocean” [Garrett and Munk, 1975] values (Kρ = 5.1 × 10−6 m²s−1), and an order of magnitude below basin‐ and time‐averaged values obtained from the Ffield and Gordon [1992] and Hautala et al. [1996] models (Kρ ≥ 1 × 10−4 m²s−1). Sea‐surface temperature displays some evidence of a fortnightly modulation, interpreted by Ffield and Gordon [1996] as evidence for tidal mixing, but is uncorrelated with the dissipation rate just below the mixed layer.
The deep structure of Corsica as inferred by a broad band seismological profile
Authors: Bethoux Nicole , Deschamps Anne , Nolet Guust , Bertrand Etienne , Contrucci Isabelle , Sosson Marc , Ferrandini Jean
Published: December 2003

To investigate the influence of inherited inhomogeneity in a lithosphere under extension, we studied the deep structure of Corsica, an island in the Mediterranean sea, at the boundary of the extensional Tyrrhenian basin, using a temporary array of eight broad‐band seismographs. Between the stations in the western Hercynian part of the island and the stations in eastern Alpine Corsica, an average static station delay of 0.4 s was observed for P waves, and 0.7 s for S waves. The crustal structure is obtained through seismic data, gravity modeling and the receiver function method. The difference in crustal structure between the west and east of Corsica can explain only about half of the anomaly. Consequently we postulate a sharp increment in the thickness of the lithosphere to account for the remaining 0.2 s of P anomaly.
Global plate motion models incorporating the velocity field of ITRF96
Authors: Zhang Qiang , Zhu Wenyao , Xiong Yongqin
Published: December 2003

In this paper, incorporating the ITRF96 velocity field that is free of any tectonic plate model assumption, a new present‐day plate motion model relative to the ITRF96 reference frame, called the ITRF96VEL, is determined. The total angular momentum of all tectonic plates with regards to the ITRF96VEL shows that the ITRF96 rotates in a right‐handed sense relative to the no‐net‐rotation (NNR) reference frame at 0.164°/m.yr. about 50.7°S, 65.8°E. This means that ITRF96 is not sufficiently concordant with the definition of the Conventional Terrestrial Reference System (CTRS). In order to more properly compare plate motions from the ITRF96 velocity field with the NNR‐NUVEL1A, another plate motion model relative to the NNR reference frame, called the NNR‐ITRF96VEL, is also established. The results indicate that the NNR‐ITRF96VEL is quite consistent with the NNR‐NUVEL1A. The consistency testifies to the reliability of the NNR‐NUVEL1A, and shows the tectonic plate motions were steady over past millions of years.
Groundwater‐level changes in response to bursts of seismic activity off the Izu Peninsula, Japan
Authors: Ohno Masao , Sato Tsutomu , Notsu Kenji , Wakita Hiroshi , Ozawa Kunio
Published: December 2003

At two strain‐sensitive wells located close (∼5km) to seismic swarm activities off the Izu Peninsula, Japan, we observed water‐level changes that were synchronized with bursts of seismic activity during an active period in October 1996. The water levels started to drop at the onset of each burst, and stopped dropping as it ceased. This is the first hydrological observation in response to bursts in this area. The data suggests the occurrence of some local crustal deformation at the time of the bursts of seismicity.
Large asymmetrical temperature trends at Mount Wilson, California
Authors: Balling Robert C. , Periconi Darlene A. , Cerveny Randall S. , Baliunas Sallie L.
Published: December 2003

We compiled and analyzed a daily time series of temperatures and precipitation totals from Mount Wilson, California from 1918 to 1998. Our results show a large decline in maximum temperature, no change or an upward trend in minimum temperature, and a substantial decline in the diurnal temperature range (DTR). The interannual variations in monthly maximum temperature and DTR are significantly correlated with monthly precipitation levels, sea‐surface temperatures (SSTs) off the coast of Southern California, and the Southern Oscillation Index (SOI). El Niño periods and/or months with high SST anomalies tend to be wet with lower maximum temperatures and DTR while La Niña periods and/or months of lower SSTs are hotter and drier with higher DTR values. It is noteworthy that the SOI and SSTs have significant trends toward more El Niño‐like conditions with higher SSTs off Southern California.
Thermal evolution of the mantle following continental aggregation in 3D convection models
Authors: Lowman Julian P. , Gable Carl W.
Published: December 2003

The claim that supercontinents insulate the mantle is largely based on recognition that seismically slow mantle below the Atlantic‐African geoid high coincides with the former location of Pangea. We investigate the viability of continental insulation by varying both plate geometries and mantle properties in six three‐dimensional (3D) mantle convection models. The efficiency of continental insulation is quantified by calculating the rate of change of the average temperature in the subcontinental mantle. Our findings generally agree with two‐dimensional (2D) modeling results. However, we conclude that 2D convection models may exaggerate subcontinental heating, particularly in largely bottom heated cases, and that subcontinental heating results from an absence of subduction in the subcontinental mantle rather than the insulation of active upwellings. Correspondingly, we find that when large degrees of internal heating are present in the mantle, hotter‐than‐average regions evolve below large oceanic plates.
Millennial‐scale climatic change during the Last Interglacial Period: Superparamagnetic sediment proxy from Paleosol S1, western Chinese Loess Plateau
Authors: Fang Xiao‐Min , Ji‐Jun Li , Banerjee Subir K. , Jackson Mike , Oches Eric A. , Van Der Voo Rob
Published: December 2003

Detailed magnetic analyses of samples from the Jiuzhoutai well section on the western Chinese Loess Plateau reveal high‐resolution signals of summer monsoon change. The last interglacial period is represented here by the 8‐meter thick S1 paleosol complex. We have used low‐temperature remanence studies to analyze variations in the concentration of Superparamagnetic (SP) grains, which previous studies have shown to be largely of pedogenic origin. The SP concentration, interpreted as a proxy for the extent of pedogenesis, shows millennial scale variations within S1. We conclude that the last interglacial period in Asia was characterized by rapid climate fluctuations, with at least one brief return to near‐glacial conditions in the middle of oxygen‐isotope substage 5e.
The Snake River Plain Experiment revisited. Relationships between a Farallon plate fragment and the transition zone
Authors: Beucler Eric , Chevrot Sébastien , Montagner Jean‐Paul
Published: December 2003

We reconsider the analysis of the 93 PASSCAL‐OREGON SRP experiment data. The techniques applied to the processing of Pds waves, which are P to S conversions at seismic discontinuities at depth d in the receiver region, differ from those employed by Dueker & Sheehan [1997]. We perform global move‐out corrections and migration, taking advantage of the alignment of seismicity along the great circle described by the array (South America, and the Kuril and Aleutians islands). We do not detect a deep signature of a mantle plume. The 410 km discontinuity exhibits a fragmented aspect, which prevents us from reliably estimating the transition zone thickness. The 660 km discontinuity is clearly more visible, and largely deflected in a large part of the profile. We associate this anomalous behaviour and the noisy aspect of the discontinuities with the presence of a Farallon plate fragment.
Implication of azelaic acid in a Greenland Ice Core for oceanic and atmospheric changes in high latitudes
Authors: Kawamura K. , Yokoyama K. , Fujii Y. , Watanabe O.
Published: December 2003

A Greenland ice core (450 years) has been studied for low molecular weight dicarboxylic acids (C2‐C10) using a capillary gas chromatography and mass spectrometer. Their molecular distribution generally showed a predominance of succinic acid (C4) followed by oxalic (C2), malonic (C3), glutaric (C5), adipic (C6), and azelaic (C9) acids. Azelaic acid, that is a specific photochemical reaction product of biogenic unsaturated fatty acids, gave a characteristic historical trend in the ice core; i.e., the concentrations are relatively low during late 16th to 19th century (Little Ice Age) but become very high in late 19th to 20th century (warmer periods) with a large peak in 1940s AD. Lower concentrations of azelaic acid may have been caused by a depressed emission of unsaturated fatty acids from seawater microlayers due to enhanced sea ice coverage during Little Ice Age. Inversely, increased concentrations of azelaic acid in late 19th to 20th century are likely interpreted by an enhanced sea‐to‐air emission of the precursor unsaturated fatty acids due to a retreat of sea ice and/or by the enhanced production due to a potentially increased oxidizing capability of the atmosphere.
Comparison of surface and tropospheric temperature trends estimated from a 63‐Station Radiosonde Network, 1958–1998
Authors: Angell James K.
Published: December 2003

Comparisons of surface and tropospheric (850–300 mb) temperature trends for climate zones, hemispheres and globe are presented for the period 1958–1998, based on seasonal and annual‐mean temperatures from a 63‐station radiosonde network. Globally, the surface warmed by 0.14±0.13K/decade during the 41‐year period, the 850–300 mb layer by 0.10±0.09K/decade. This small difference in global trend results from the surface warming by 0.12K/decade relative to the 850–300 mb layer in the northern hemisphere, but the 850–300 mb layer warming by 0.04K/decade relative to the surface in the southern hemisphere. In north polar and temperate zones the warming of the surface relative to the 850–300 mb layer is greatest in winter‐spring and there is little difference in trend in summer. There is a tendency for a similar seasonal variation in trend difference in south extratropics, warming of the surface relative to the 850–300 mb layer occurring only in winter in the south polar zone, and cooling of the surface relative to the 850–300 mb layer greatest in summer in the south temperate zone. Globally, the warming of the surface relative to the 850–300 mb layer is 0.11K/decade during 1979–1998, compared to 0.04K/decade during 1958–1998, but with the 95% confidence intervals approximately twice as great for the 20‐year period as for the 41‐year period.