bluuebunny/crossref_metadata_2025 huggingface dataset:
Regional variation of magnetization of oceanic crust subducting beneath the Nankai Trough
Authors: Kido Yukari , Fujiwara Toshiya
Published: March 2004

We present the characteristics of marine magnetic anomalies in the Nankai Trough and the northern Shikoku Basin. The marine magnetic anomalies are clearly visible over the Shikoku Basin but gradually disappear across the Nankai Trough. The expected reason for the decrease in the marine magnetic anomaly amplitudes across the trough is the increase in depth of the magnetic source: the subducting oceanic crust. Forward and inverse magnetic modeling results, which take into account the slab depth distribution, show variations in magnetization that cannot be explained solely by increasing depth of the slab. We identify five zones along the trough axis on the basis of the pattern of the magnetic amplitude profile: two ridges, a seamount chain, and two basement zones. The magnetic inversion analysis indicates cyclic intensity variations along the ridge zones. The largest contrast in magnetization along the N‐S lineation before the deformation front occurs off Ashizuri (AS). Low‐temperature chemical oxidation effects are most likely the main cause of the reduction in magnetization. There are considerable differences in the original carrier of magnetic intensity in the AS and Kii Peninsula (KP) zones, and the original carrier in AS is characterized by much higher original magnetic intensities. This indicates several possibilities: the oceanic crust originated from asymmetric spreading; there was magma injection during the late stage volcanism; or the AS zone was affected by an anomalous heat source. It would be concluded from the current data that the basement in AS originally had a much stronger magnetic carrier and suffered stronger low‐temperature oxidation effects than the eastern part of the Shikoku Basin. The regional differences in intensity strongly suggest a variety of magnetic minerals and phase changes associated with temperature and mechanical dislocation.
The role of hot uprising plumes in the initiation of plate‐like regime of three‐dimensional mantle convection
Authors: Yoshida Masaki , Ogawa Masaki
Published: March 2004

Three‐dimensional numerical models are presented for thermal convection of non‐Newtonian fluid with viscosity that depends on temperature and stress to understand development of moving plates on the Earth. A hysteresis is assumed in the relationship between stress and viscosity to make the viscosity depend on stress‐history. The stress‐history dependence due to hysteresis induces a regime where plates or highly viscous pieces of lithosphere separated by narrow and mechanically weak plate margins rigidly move by their own weight. The plate margins newly develop when a stress high enough to cause lithospheric rupture is induced in the lithosphere by the help of hot cylindrical uprising plumes but do not spontaneously develop by the weight of lithosphere itself. The high rupture strength of lithosphere makes the plate‐like motion rather steady without the help of viscosity reduction by melting in the asthenosphere.
Structure and effects of a long lived vortex in the Greenland Sea
Authors: Budéus Gereon , Cisewski Boris , Ronski Stephanie , Dietrich Desirée , Weitere Markus
Published: March 2004

Direct observations of the velocity field of a submesoscale coherent vortex in the Greenland Sea by a vessel mounted ADCP, together with a detailed and complete investigation of its hydrographic structure, show that within the eddy the hydrographic structure differs from the background and indicate that the entire water column of 3.7 km depth is included in an anticyclonic rotation with maximum azimuthal speeds at roughly 2000 m depth. Within a radius of about 9 km the water layers rotate in a solid body fashion. The lifetime of the eddy is long enough and the exchange between its interior and the background is small enough to result in a persistent and pronounced anomaly with respect to physical as well as biological parameters. Due to the unique possibility in the high latitudes to 'recharge' the eddy by surface forcing during winter and a corresponding long lifetime such eddies represent key areas for future bottom water production.
Solitary waves in the Earth's magnetosphere: Nonlinear stage of the lower‐hybrid Buneman instability
Authors: Jovanović D. , Shukla P. K.
Published: March 2004

A drift‐kinetic theory for electron phase‐space vortices in magnetized space plasmas is formulated in the frequency range of lower‐hybrid waves excited by the Buneman instability in the presence of an electron beam. The nonlinear model accounts for the effects of the electron polarization, anisotropic electron temperature and ion mobility, and it provides a theoretical explanation for some of the electrostatic and weakly electromagnetic bipolar structures observed by the Cluster, Polar and FAST spacecrafts in the Earth's magnetosheath, magnetopause and in the auroral zone. Quasi‐3‐D electron holes have the form of either elongated cylinders oblique to the magnetic field, or spheroids.
Time domain presentation for ELF pulses with accelerated convergence
Authors: Nickolaenko Alexander P. , Rabinowicz Leonid M. , Hayakawa Masashi
Published: March 2004

A compact time domain solution is constructed for natural electromagnetic pulses propagating in the Earth‐ionosphere cavity. An algorithm is discussed for accelerating the convergence of the time series presenting the pulsed waveform. Compact formulae are derived and computational results are presented for a set of the source distances.
Development of shoulders and plumes in the frame of the interchange instability mechanism for plasmapause formation
Authors: Pierrard V. , Lemaire J. F.
Published: March 2004

The mechanism of plasmapause formation based on interchange instability and a Kp‐dependent magnetospheric electric field model, enables us to determine the position of the plasmapause as a function of Kp and local time. We illustrate here how this physical mechanism is able to account for the formation of shoulders like those observed by EUV on IMAGE. A wide variety of other structures observed by IMAGE like tails (also called plumes), and notches are also obtained with this mechanism for the formation of a “knee” in the high altitude cross‐L distribution of the cold plasma density distribution.
How efficient is cloud droplet formation of organic aerosols?
Authors: Lohmann Ulrike , Broekhuizen Keith , Leaitch Richard , Shantz Nicole , Abbatt Jonathan
Published: March 2004

Based on laboratory findings that small amounts of a soluble aerosol, such as ammonium sulfate (AS), drastically decrease the activation diameter of moderately soluble organic aerosols, we performed studies with an adiabatic parcel model for cloud droplet nucleation. Moderately soluble organics, such as adipic acid (AA), which represents a class of partially soluble aerosols as found in atmospheric aerosols, require a larger supersaturation and result in fewer cloud droplets as compared to pure AS and vice versa when compared to a completely insoluble species such as dust. Adding only 10% AS to AA dramatically increases its ability to become activated resulting in 36–92% of the cloud droplets that would be obtained from pure AS, whereas the droplet concentration in the almost pure AA aerosol is only 11–47% of that of AS. Addition of a surface active species, such as nonanoic acid, instead of AS to AA reduces its activated fraction by 3–34% as compared to the AA/AS system.
Downward emission of runaway electrons and bremsstrahlung photons in thunderstorm electric fields
Authors: Torii Tatsuo , Nishijima Takeshi , Kawasaki Zen‐Ichiro , Sugita Takeshi
Published: March 2004

Intensive radiations presumably associated with lightning activities have sometimes been detected around nuclear facilities in Japan. In order to investigate the generation of bremsstrahlung photons caused by thunderstorm electric fields, we calculated the behavior of secondary cosmic ray electrons and photons in electric fields by Monte Carlo technique. The photon flux increased greatly in the region where the field strength exceeded 280(ρ(z)/ρ(0)) kV/m, and the photon energy spectrum showed a large increase in the energy region of several MeV. These are consistent with the observed results during the winter thunderstorms.
What determines the nocturnal cooling timescale at 2 m?
Authors: Pattantyús‐Ábrahám M. , Jánosi I. M.
Published: March 2004

An evaluation of high‐frequency temperature observations revealed, that annually there exist 80–100 calm weather days, when a significant part of the nocturnal cooling period can be well fitted with a simple exponential function. Statistics of characteristic time constants indicates a wide, skewed distribution and the lack of an annual cycle. A search for basic meteorological variables determining the magnitude of the cooling rate remained inconclusive. No correlation was found with daily average temperature anomaly, soil moisture, absolute air humidity, wind speed, pressure, nighttime outgoing and daytime incoming radiation. The air temperature is more strongly coupled to the soil temperature, but surprisingly, the cooling rate in the soil seems to be very weakly correlated with the cooling rate of air at 2 m.
Geoid heights due to a crustal low viscosity zone in glacial isostatic adjustment modeling: A sensitivity analysis for GOCE
Authors: van der Wal W. , Schotman H. H. A. , Vermeersen L. L. A.
Published: March 2004

Seismic observations and the occurrence of post‐seismic deformation in several continental regions indicate the presence of one or more layers with relative low (1018–1019 Pas) viscosity in the Earth's crust. This study simulates the effect of thickness, viscosity and depth of such a low viscosity zone (LVZ) on geoid heights that are the result of glacial isostatic adjustment to Pleistocene ice loads. It is found that an LVZ introduces variations in geoid heights up to 1 meter with spactial scales larger than a few hundred kilometers underneath and just outside former glaciated areas. The response to changes in the properties of the LVZ is shown to be wavelength‐dependent. The LVZ induced geoid signal is within the accuracy of the upcoming GOCE satellite mission, which means that in principle it should be possible to detect the presence of a supposed LVZ with GOCE data.
MIPAS measurement of sulphur hexafluoride (SF6)
Authors: Burgess A. B. , Grainger R. G. , Dudhia A. , Payne V. H. , Jay V. L.
Published: March 2004

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a polar orbiting high resolution mid‐infrared emission stratospheric limb sounder with a nominal vertical resolution of 3 km. Work to extend the list of interesting, routinely retrieved species led to the examination of SF6, a potent greenhouse gas and a useful tracer species. We demonstrate the feasibility of profile retrievals in the range 6–30 km based on single scans. Additionally, we investigate latitudinal variation using coaddition to improve signal‐to‐noise. A mean mid‐latitude profile shows tropospheric (4.32 ± 0.03 pptv, 6–12 km) and stratospheric (3.50 ± 0.03 pptv, 21–30 km) regimes, in September 2002, similar to accepted values. The global mean contains an inter‐hemispheric variability of the order of 0.3 pptv in the lower stratosphere, in line with age of air. Finally, the continuation of acknowledged global trends in atmospheric concentration, is estimated at +0.28 pptv yr−1 (6.5 ± 1.3% yr−1).
Association of kilometric continuum radiation with plasmaspheric structures
Authors: Green James L. , Boardsen Scott , Fung Shing F. , Matsumoto H. , Hashimoto K. , Anderson R. R. , Sandel B. R. , Reinisch B. W.
Published: March 2004

A year's worth of observations of kilometric continuum (KC) from the plasma wave instrument (PWI) on GEOTAIL and extreme ultraviolet (EUV) images of the plasmasphere from IMAGE are compared. In the vast majority (∼94%) of the 87 cases when simultaneous data from both spacecraft were available, KC was observed to be associated with density depletions or notch structures in the plasmasphere. From a careful analysis of 1 month of EUV data comprising 13 notch structures, only one notch structure was found in which no accompanying KC was observed when GEOTAIL was in a low‐latitude position and therefore should have observed the emission if it were generated. IMAGE observations from the radio plasma imager (RPI) during passage through a plasmaspheric notch structure found that KC was generated in or very near the magnetic equator at steep gradients in density and associated with emissions in the upper hybrid resonance band as previously reported by others at lower frequencies. Statistical analysis of the KC events associated with plasmaspheric notch structures shows that the typical source region is at an equatorial radial distance of ∼2.4 RE (Earth radii) in the magnetic equator and produces an emission cone that is ∼40° in longitude and ∼20° in latitude. These results show that a density depletion or notch structure in the plasmasphere is typically a critical condition for the generation of KC but that the notch structures do not always provide the conditions necessary for the generation of the emission.
Role of projection effects on solar coronal mass ejection properties: 1. A study of CMEs associated with limb activity
Authors: Burkepile J. T. , Hundhausen A. J. , Stanger A. L. , St.Cyr O. C. , Seiden J. A.
Published: March 2004

Many properties of Coronal Mass Ejections (CMEs), such as size, location and brightness, have been determined from measurements of white light coronal observations. We expect the average properties derived from these measurements contain systematic inaccuracies due to projection effects and suggest that CME properties are most accurately determined for those events occurring near the plane‐of‐the‐sky (i.e., over the solar limb as observed from Earth), where projection effects are minimized. A set of 111 such “limb” events have been identified in Solar Maximum Mission (SMM) white light observations through associations with Erupting Prominences at the Limb (EPLs), and X‐ray and limb optical flares. These “limb” CMEs have greater average speeds (519 ± 46 km/sec) and masses (4.5 ± .5 × 1015 grams) than the average values obtained from all SMM CMEs, consistent with the expected behavior of projection effects. Only a very small percentage of “limb” CMEs are centered at high latitudes, suggesting there are many fewer “true” high latitude CMEs than has previously been reported. No “limb” CMEs have widths greater than 110°, consistent with the interpretation that very wide CMEs (i.e., halos) are actually events of more typical widths originating away from the solar limb and viewed in projection. Only a small percentage of “limb” CMEs have measured speeds below 200 km/sec, indicating there may be fewer “true” subsonic SMM CMEs than previously reported. The correlation detected between the kinetic energy of the “limb” CMEs and the peak intensity of the associated GOES X‐ray flares, is stronger than was previously found using a set of CMEs of undetermined limb distances. All these results provide strong evidence that projection effects systematically influence the deduced properties of CME events.
Fluid inclusion evidence for subsurface phase separation and variable fluid mixing regimes beneath the deep‐sea PACMANUS hydrothermal field, Manus Basin back arc rift, Papua New Guinea
Authors: Vanko David A. , Bach Wolfgang , Roberts Stephen , Yeats Christopher J. , Scott Steven D.
Published: March 2004

Altered volcanic rocks were cored from over 350 m below the seafloor at the Papua New Guinea‐Australia‐Canada Manus Basin Hydrothermal Field (PACMANUS) deep‐sea hydrothermal field, in the eastern Manus back arc basin. Fluid inclusions in anhydrite veins reveal phase separation and fluid mixing beneath the seafloor. The anhydrite precipitated from high‐temperature fluids (150–385°C). At Roman Ruins, a site of active high‐temperature venting (220–276°C, measured by submersible), the fluid inclusion thermal depth profile is uniform and high temperature (242–368°C). At Snowcap, a site of warm water effusion (6–65°C), the fluid inclusions indicate high temperatures at depth (270–385°C) but both low and high temperatures in the shallower section. This indicates a flow regime dominated by vertical advection and shallow entrainment and mixing with cool seawater. Inclusions at Snowcap exhibit extreme salinity variations due to phase separation at temperatures above 350°C. Fluids contain Na, Cl, Fe, Zn, Mg, and Ba and a minor gas component such as CO2 or CH4. Most inclusions at Roman Ruins exhibit salinities that fall within the range of those observed at modern active vent sites along the mid‐ocean ridge system. Fluid inclusion temperatures support a hypothesis, developed previously from Sr‐isotopic analysis, that the subseafloor at Snowcap is characterized by mixing between deep‐sourced hot hydrothermal fluids and cold seawater‐like fluid. Both heating of seawater and cooling of upwelling hydrothermal fluids can be recognized by combining isotopic and fluid inclusion data. In contrast to Snowcap, the regime at Roman Ruins is less varied, with uniformly high‐temperature upwelling fluids that have hydrothermally dominated Sr‐isotopic ratios.
Mechanical and electrical response due to fluid‐pressure equilibration following an earthquake
Authors: Pride Steven R. , Moreau Frédérique , Gavrilenko Pierre
Published: March 2004

The mechanical and electrical response in a uniform porous crust are determined following a shear dislocation (earthquake) on an internal slip surface. A uniform crust is studied because many exact analytical relations hold between the various response fields in this case. The initial stress field that is created immediately following the earthquake subsequently relaxes through time as the fluid pressure equilibrates by fluid flow. Maps of the electric field generated due to the fluid flow (electrokinetic coupling) are presented. Using conservative estimates of the various parameters involved, electric fields significantly larger than the diurnal (magnetotelluric) fields are generated. Quantitative results for how various components of the stress tensor change due to the fluid equilibration are also presented. The Coulomb stress can easily change by 100% (and more) in the months following an earthquake due to the fluid‐pressure equilibration.
Combination of ScaRaB‐2 and CERES with Meteosat‐5 to remove time sampling bias and improve radiation budget estimations in the INDOEX region
Authors: Viollier M. , Kandel R. , Raberanto P.
Published: March 2004

Using data available over the INDOEX area, Meteosat‐5 visible and infrared data have been combined with ScaRaB/Resurs and CERES/TRMM broadband data for March 1999, and with CERES/TRMM and CERES/Terra data for March 2000. The study proceeds by collocation of the data sets, comparison of narrowband Meteosat radiances to broadband ScaRaB radiances, and conversion of radiances to fluxes. In the longwave (LW) domain, a multiple regression is found between ScaRaB and CERES fluxes, the two Meteosat infrared channels (infrared window and water vapor) and the viewing zenith angle. In the shortwave (SW) domain, narrowband‐to‐broadband (NB‐BB) and ERBE‐like radiance‐to‐flux conversions are applied. The RMS differences between the ScaRaB/CERES and Meteosat instantaneous flux retrievals are about 10 Wm−2 and 40 Wm−2 respectively in the LW and SW domains. A large part of these differences comes from the residual coregistration and narrow‐band‐to‐broadband conversion errors. On the contrary, the mean difference or bias between all data sets is very small, consistent at the 1% (LW) and 4% (SW) level. The LW and SW conversion equations have been used to convert Meteosat observations at each half hour into instantaneous broadband flux estimates consistent with the instantaneous CERES flux estimates for the same day. New monthly means are computed in this way: the changes are small in the LW but significant in the SW domain (regional means: ∼20 Wm−2, 20°S–20°N means: ∼4 Wm−2), especially for studies of long‐term changes.
Semianalytical cloud retrieval algorithm as applied to the cloud top altitude and the cloud geometrical thickness determination from top‐of‐atmosphere reflectance measurements in the oxygen A band
Authors: Rozanov Vladimir V. , Kokhanovsky Alexander A.
Published: March 2004

The paper is devoted to the development of the asymptotic algorithm for the cloud top heighthand the geometrical thicknessldetermination using measurements of the cloud reflection function. It is based on the asymptotic theory of the radiative transfer in the oxygen absorption bands and simple parameterization of the radiative transport in the atmosphere above and under a cloud. In particular, we have studied the influence of the error of the developed approximate theory on the accuracy of the retrieval of the pair (h,l). It was assumed that there is only a single cloud layer having the same value of the liquid water content in all points inside the cloud. The values (h,l) have been found, solving the inverse problem having as input the synthetic spectra of backscattered light. The synthetic spectra were found using the exact solution of the forward problem for given values of (h,l). The retrieval technique was based on the asymptotic theory. We have found that the error of the cloud top height determination is smaller than 20 m, and the error of the cloud geometrical thickness determination is smaller than 500 m for solar angles 20–70 degrees, values ofhin the range 1–12 km, values of geometrical thicknesslin the range 0.5–2 km, and values of the cloud optical thickness changing in the range 10–50. The surface albedo has been assumed to be equal zero. We have also studied the influence of the cloud liquid water profile on the results of the retrieval of the pair (h,l). It was found that the error of the cloud top height determination increases up to 600 m, if the assumed cloud has a changing with height liquid water content, and retrievals are made applying the inversion with assumed constant liquid water content profile. The error in the geometrical thickness increases up to 1 km in this case. Errors of the retrieval increase even further if the retrieval, on the basis of the homogeneous layer theory, is applied to the two‐layered cloud system (e.g., the upper cloud consists of ice crystals and the lower cloud is in a liquid phase). This signifies the importance of the cloud vertical inhomogeneity on the retrieval results.
Changes in daily precipitation frequency and distribution in Italy over the last 120 years
Authors: Brunetti Michele , Maugeri Maurizio , Monti Fabio , Nanni Teresa
Published: March 2004

A new data set of 45 daily precipitation series, covering quite uniformly Italian territory for the period 1880–2002, was recovered. The series have been homogenized on daily basis, completed by means of statistical methods and grouped into five regions by a Principal Component Analysis. Seasonal and yearly total precipitation, number of wet days, and precipitation intensity were analyzed for each station record and averaged into five regional series for a synthetic description of the results. Proportion and frequency of daily rainfall amounts, belonging to six precipitation class‐intervals, defined on the basis of some percentiles of the precipitation distribution, were also analyzed. The results show a negative significant trend in the number of wet days all over Italy, and a positive trend in precipitation intensity, which is significant only in the northern regions. The negative trend in wet days has persisted since the end of 19th century and is due to the marked decrease in the number of low intensity precipitation events. An increase in the number of events belonging to the highest intensity class interval was observed too, but only in northern regions.
Electric and magnetic signatures of dust devils from the 2000–2001 MATADOR desert tests
Authors: Farrell W. M. , Smith P. H. , Delory G. T. , Hillard G. B. , Marshall J. R. , Catling D. , Hecht M. , Tratt D. M. , Renno N. , Desch M. D. , Cummer S. A. , Houser J. G. , Johnson B.
Published: March 2004

Dust devils are significant meteorological phenomena on Mars: They are ubiquitous, continually gardening the Martian surface, and may be the primary atmospheric dust‐loading mechanism in nonstorm seasons. Further, dust grains in the swirling dust devils may become electrically charged via triboelectric effects. Electrical effects associated with terrestrial dust devils have been reported previously, but these were isolated measurements (electric fields only) with no corroborating measurements. To study the fluid and electrical forces associated with dust devils, NASA's Human Exploration and Development of Space (HEDS) enterprise sponsored a set of desert field tests with a suite of mutually compatible and complementary instruments in order to determine the relationship between electric, magnetic, and fluid forces. The project (originally a selected flight project) was entitled “Martian ATmosphere And Dust in the Optical and Radio” (MATADOR). In this work, we present a number of interesting examples of the electromagnetic nature of the dust devil. We also describe potential hazards of the dust devil and how similar devil‐ and storm‐related forces on Mars might affect any human occupation.
Controls on the strength of coupling among climate, erosion, and deformation in two‐sided, frictional orogenic wedges at steady state
Authors: Whipple K. X. , Meade B. J.
Published: March 2004

Many important insights regarding the coupling among climate, erosion, and tectonics have come from numerical simulations using coupled tectonic and surface process models. However, analyses to date have left the strength of the coupling between climate and tectonics uncertain and many questions unanswered. We present an approximate analytical solution for two‐sided orogenic wedges obeying a frictional rheology, and in a condition of flux steady state, that makes explicit the nature and sensitivity of the coupling between climate and deformation. We make the simplifying assumption that the wedge grows in a self‐similar fashion consistent with Airy isostasy such that topographic taper is invariant with orogen width, tectonic influx rate, and climate. We illustrate first how and why the form of the erosion rule matters to orogen evolution and then derive a physically based orogen‐scale erosion rule. We show that steady state orogen width, crest elevation, and crustal thickness are controlled by the ratio of accretionary flux to erosional efficiency to a power dictated by the erosion process. Remarkably, we show that for most combinations of parameters in the erosion law, rock uplift rate is more strongly controlled by erosional efficiency than it is by the accretionary flux. Further, assuming frontal accretion with no underplating, the spatial distribution of erosional efficiency dictates the relative rock uplift rates on the pro‐wedge and retro‐wedge and the time‐averaged trajectories of rocks through the orogen. The restriction to invariant frictional properties is conservative in these respects; systems subject to positive feedback between erosion and rheology will exhibit even stronger coupling among climate, erosion, and deformation than shown here.
230Th normalization: An essential tool for interpreting sedimentary fluxes during the late Quaternary
Authors: Francois Roger , Frank Martin , Rutgers van der Loeff Michiel M. , Bacon Michael P.
Published: March 2004

There is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates. Notwithstanding its common incidence, this process (generally referred to as sediment focusing) is often difficult to recognize. If redistribution is near synchronous to deposition, the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked. Ignoring it, however, can lead to serious misinterpretations of sedimentary fluxes, particularly when past changes in export flux from the overlying water are inferred. In many instances, this problem can be resolved, at least for sediments deposited during the late Quaternary, by normalizing to the flux of 230Th scavenged from seawater, which is nearly constant and equivalent to the known rate of production of 230Th from the decay of dissolved 234U. We review the principle, advantages and limitations of this method. Notwithstanding its limitations, it is clear that 230Th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates.
A fossil coral perspective on western tropical Pacific climate ∼350 ka
Authors: Kilbourne K. Halimeda , Quinn Terrence M. , Taylor Frederick W.
Published: March 2004

The nature of tropical climate variability ∼350 ka is addressed using δ18O and Sr/Ca records from a modern and a fossil coral from Vanuatu (southwestern tropical Pacific Ocean). Modern El Niño events at Vanuatu produce positive coral δ18O and Sr/Ca anomalies; similar anomalies observed in the fossil coral records suggest that El Niño was operative 350 kyr ago. Seasonal variations in coral Sr/Ca, a sea surface temperature (SST) proxy, have the same amplitude in both corals, whereas seasonal δ18O variations are smaller in the fossil coral than in the modern coral. This is consistent with displacement of the South Pacific Convergence Zone toward the southwest during the boreal summer ∼350 ka. Mathematical modeling results preclude warmer SST and higher SSS at Vanuatu during this time, but permit the surface ocean to be ∼2°C cooler and 0–2 psu fresher than today. Assessing the potential of variations in late Quaternary seawater Sr/Ca remains the largest obstacle to accurately reconstructing tropical SST using pristine fossil corals.
Rapid switch‐like sea ice growth and land ice–sea ice hysteresis
Authors: Sayag Roiy , Tziperman Eli , Ghil Michael
Published: March 2004

Rapid and extensive growth of sea ice cover was suggested to play a major role in the sea ice switch mechanism for the glacial cycles as well as on shorter millennial scales [Gildor and Tziperman, 2000]. This mechanism also predicts a hysteresis between sea ice and land ice, such that land ice grows when sea ice cover is small and withdraws when sea ice cover is more extensive. The switch‐like sea ice growth and the hysteresis were previously demonstrated using a simple, highly idealized box model. In this work we demonstrate a switch‐like sea ice behavior as well as the sea ice–land ice hysteresis using a coupled climate model that is continuous in the latitudinal dimension. It is shown that the switch‐like sea ice growth occurs when the initial meridional atmospheric temperature gradient is not too strong. It is also shown that the meridional extent to which sea ice grows in a switch‐like manner is not affected by the intensity of the thermohaline circulation, which does, however, influence the climate cooling that is needed to trigger such rapid sea ice growth.
Dunk tectonics: A multiple subduction/eduction model for the evolution of the Scandinavian Caledonides
Authors: Brueckner Hannes K. , van Roermund Herman L. M.
Published: March 2004

The evolution of the Caledonides of Scandinavia included at least four events that resulted in high‐pressure (HP) and ultrahigh‐pressure (UHP) eclogite facies metamorphism and the introduction of peridotite from the mantle into the crust. Two are the classic Finnmarkian orogeny at ∼500 Ma and the Scandian orogeny between 400 and 425 Ma. We have dated a third HP metamorphism in the Seve Nappe Complex in Jämtland, central Sweden, at ∼454 Ma. Identical Upper Ordovician ages from eclogite of the Troms region, northern Norway, date a simultaneous fourth HP event that occurred in a different tectonic setting, probably western Iapetus. Recently reported Late Silurian ages from eclogite of the Bergen Arcs District, southern Norway, suggest a possible fifth event. We propose that all HP/UHP events in the Scandinavian Caledonides occurred through the subduction of crustal slabs into the mantle and their subsequent buoyancy‐enhanced exhumation toward the surface (eduction). The slabs are recognized as intensely deformed, high‐grade (eclogite and HP granulite facies) metamorphic rocks although HP metamorphism is not necessarily penetrative and retrogression to medium grade assemblages is common. The HP/UHP metamorphic terranes are bounded by thrust faults at the base and low‐angle normal detachments at the top and are separated by these shear zones from less deformed terranes of lower pressure metamorphic grade. The peridotite bodies were introduced from the overlying mantle wedge during subduction or eduction. The evolution of metamorphic terranes in other orogens might be better understood through successive subduction/eduction events, a process we provisionally call “dunk” tectonics.
Landscape controls on nitrate removal in stream riparian zones
Authors: Vidon Philippe G. F. , Hill Alan R.
Published: March 2004

We examined how landscape hydrogeologic characteristics influence groundwater nitrate removal by eight stream riparian sites on glacial till and outwash landscapes in southern Ontario, Canada. During high water table periods in 2000–2002, mean NO3−‐N input concentrations from adjacent cropland to the riparian sites ranged from 0.15 to 44.7 mg L−1. Seven of the eight sites had a mean nitrate removal efficiency of >90%. This removal occurred within the first 15 m of the riparian zone at three sites with loamy sand and sandy loam soils overlying a shallow confining layer at 1–2 m. However, at four of five sites with more conductive sand and cobble sediments the width required for 90% nitrate removal varied from >25 m to a maximum of 176 m at a site with a confining layer at 6 m. Sites linked to an extensive thick (>6 m) upland aquifer with a slope gradient of >15% at the riparian perimeter had high nitrate inputs throughout the year and were large nitrate sinks. Sites with gentle topography (<4–5%) and <2 m of permeable sediments were minor nitrate sinks because of small nitrate inputs that were limited to the late autumn‐spring period. A conceptual model linking landscape hydrogeologic characteristics to riparian zone nitrate removal capacity is developed to understand and predict the effectiveness of riparian buffers at the landscape scale.
Prediction of regional water balance components based on climate, soil, and vegetation parameters, with application to the Illinois River Basin
Authors: Niemann Jeffrey D. , Eltahir Elfatih A. B.
Published: March 2004

This paper presents a framework for studying regional water balance in which the physical processes are first described at the local instantaneous scale and then integrated to the annual, basin‐wide scale. The integration treats the relative soil saturation (i.e., the soil moisture divided by the porosity) and precipitation intensities as stochastic variables in space and time. A statistical equilibrium characterizes the annual water balance, resulting in a specific relation that predicts the space‐time average of soil saturation in terms of soil, climate, and vegetation parameters. Specific relationships are proposed to relate the space‐time average soil saturation to runoff, groundwater recharge, and evapotranspiration. This framework is applied to the Illinois River Basin. The shape of the spatial and temporal distributions of soil saturation are determined from observations. The other parameters are determined from the physical characteristics of the basin and calibration procedures. The resulting model is able to reproduce an observed relation between the space‐time average soil saturation and precipitation. It is also able to reproduce observed relations between space‐time average soil saturation and space‐time average evapotranspiration, surface runoff, and groundwater runoff.
Pharmacokinetic study on the utilisation of 5‐methyltetrahydrofolate and folic acid in patients with coronary artery disease
Authors: Willems Frank F , Boers Godfried H J , Blom Henk J , Aengevaeren Wim R M , Verheugt Freek W A
Published: March 2004

Methylenetetrahydrofolate reductase (MTHFR) is a regulating enzyme in folate‐dependant homocysteine remethylation, because it catalyses the reduction of 5,10 methylenetetrahydrofolate to 5‐methyltetrahydrofolate (5‐MTHF).

Subjects homozygous for the 677C → T mutation in the MTHFR enzyme suffer from an increased cardiovascular risk. It can be speculated that the direct administration of 5‐MTHF instead of folic acid can facilitate the remethylation of homocysteine in methionine.

The aim of this study was to determine the pharmacokinetic properties of orally administered 6[R,S] 5‐MTHF versus folic acid in cardiovascular patients with homozygosity for 677C → T MTHFR.

This is an open‐controlled, two‐way, two‐period randomised crossover study. Patients received a single oral dose of either 5 mg folic acid or 5 mg 5‐MTHF in each period. The concentrations of the 6[S] 5‐MTHF and 6[R] 5‐MTHF diastereoisomers were determined in venous blood samples.

All pharmacokinetic parameters demonstrate that the bioavailability of 5‐MTHF is higher compared to folic acid. The peak concentration of both isomers following the administration of 6[R,S] 5‐MTHF is almost seven times higher compared to folic acid, irrespective of the patient's genotype. However, at 1 week after the administration of a single dosage 6[R,S] 5‐MTHF, we detected 6[R] 5‐MTHF following the administration of folic acid, indicating storage of this isomer in the body.

Our results demonstrate that oral 5‐MTHF has a different pharmacokinetic profile with a higher bioavailability compared to folic acid, irrespective of the patient's genotype. Detrimental effects of the storage of high levels of the non‐natural isomer 6[R] 5‐MTHF cannot be excluded.

British Journal of Pharmacology (2004) 141, 825–830. doi:10.1038/sj.bjp.0705446
Contribution of vanilloid receptors to the overt nociception induced by B2 kinin receptor activation in mice
Authors: Ferreira Juliano , Da Silva Gisele L , Calixto João B
Published: March 2004

The vanilloid receptor (TRPV1) is viewed as a molecular integrator of several nociceptive stimuli. In the present study, we have investigated the role played by TRPV1 in the nociceptive response induced by the peripheral activation of kinin B2 receptor in mice.

The intraplantar (i.pl.) administration of bradykinin (BK) and the selective B2 agonist Tyr8‐BK, or the vanilloid agonists resiniferatoxin and capsaicin, into the mouse paw induced a dose‐related overt nociception of short duration. The B2 receptor antagonist Hoe 140 inhibited BK‐induced, but not capsaicin‐induced, nociceptive response. On the other hand, the TRPV1 antagonist capsazepine inhibited both capsaicin‐ and BK‐mediated nociception.

Repeated injections of BK or capsaicin produced desensitization to their nociceptive response. Capsaicin desensitization greatly reduced BK‐induced nociception, but in contrast, the desensitization to BK increased the capsaicin response.

Administration of low doses of capsaicin or acidified saline did not produce nociception when administered alone, but caused a pronounced effect when administered in association with a subthreshold dose of BK. Moreover, the degeneration of the subset of primary afferent fibers, sensitive to capsaicin, abolished both capsaicin‐ and BK‐induced nociception.

The inhibition of phospholipase C (PLC), protein kinase C or phospholipase A2 markedly decreased the nociception caused by BK, but not that of capsaicin. BK administration increased leukotriene B4 levels in the injected paw. Likewise, BK‐induced overt nociception was decreased by lipoxygenase (LOX) inhibition.

These results demonstrate that BK produces overt nociception mediated by TRPV1 receptor stimulation, via PLC pathway activation and LOX product formation.

British Journal of Pharmacology (2004) 141, 787–794. doi:10.1038/sj.bjp.0705546
ATP‐induced vasodilation in human skeletal muscle
Authors: Van Ginneken E E M , Meijer P , Verkaik N , Smits P , Rongen G A
Published: March 2004

The purine nucleotide adenosine‐5′‐triphosphate (ATP) exerts pronounced effects on the cardiovascular system. The mechanism of action of the vasodilator response to ATP in humans has not been elucidated yet. The proposed endothelium‐derived relaxing factors (EDRFs) were studied in a series of experiments, using the perfused forearm technique.

Adenosine 5′‐triphosphate (0.2, 0.6, 6 and 20 nmol dl−1 forearm volume min−1) evoked a dose‐dependent forearm vasodilator response, which could not be inhibited by separate infusion of the nonselective COX inhibitor indomethacin (5 μg dl−1 min−1, n=10), the blocker of Na+/K+‐ATPase ouabain (0.2 μg dl−1 min−1, n=8), the blocker of KCa channels tetraethylammonium chloride (TEA, 0.1 μg dl−1 min−1, n=10), nor by the KATP‐channel blocker glibenclamide (2 μg dl−1 min−1, n=10). All blockers, except glibenclamide, caused a significant increase in baseline vascular tone. The obtained results might be due to compensatory actions of unblocked EDRFs. Combined infusion of TEA, indomethacin and L‐NMMA (n=6) significantly increased the baseline forearm vascular resistance. The ATP‐induced relative decreases in forearm vascular resistance were 48±5, 67±3, 88±2, and 92±2% in the absence and 23±7, 62±4, 89±2, and 93±1% in the presence of the combination of TEA, indomethacin and L‐NMMA (P<0.05, repeated‐measures ANOVA, n=6). A similar inhibition was obtained for sodium nitroprusside (SNP, P<0.05 repeated‐measures ANOVA, n=6), indicating a nonspecific interaction due to the blocker‐induced vasoconstriction.

ATP‐induced vasodilation in the human forearm cannot be inhibited by separate infusion of indomethacin, ouabain, glibenclamide or TEA, or by a combined infusion of TEA, indomethacin, and L‐NMMA. Endothelium‐independent mechanisms and involvement of unblocked EDRFs, such as CO, might play a role, and call for further studies.

British Journal of Pharmacology (2004) 141, 842–850. doi:10.1038/sj.bjp.0705589
Protection by antioxidants against toxicity and apoptosis induced by the sulphur mustard analog 2‐chloroethylethyl sulphide (CEES) in Jurkat T cells and normal human lymphocytes
Authors: Han Suhua , Espinoza Luis A , Liao Hongling , Boulares A Hamid , Smulson Mark E
Published: March 2004

The mechanism of toxicity of sulphur mustard was investigated by examining the biochemical effects of the analog 2‐chloroethylethyl sulphide (CEES) in both human Jurkat cells as well as normal human lymphocytes.

Exposure of both types of cells to CEES resulted in a marked decrease in the intracellular concentration of the reduced form of glutathione (GSH), and CEES‐induced cell death was potentiated by L‐buthionine sulphoximine, an inhibitor of GSH synthesis.

CEES increased the endogenous production of reactive oxygen species (ROS) in Jurkat cells, and CEES‐induced cell death was potentiated by hydrogen peroxide.

CEES induced various hallmarks of apoptosis, including collapse of the mitochondrial membrane potential, proteolytic processing and activation of procaspase‐3, and cleavage of poly (ADP‐ribose) polymerase.

The effects of CEES on the accumulation of ROS, the intracellular concentration of GSH, the mitochondrial membrane potential, and caspase‐3 activity were all inhibited by pretreatment of cells with the GSH precursor N‐acetyl cysteine or with GSH‐ethyl ester. Furthermore, CEES‐induced cell death was also prevented by these antioxidants.

CEES toxicity appears to be mediated, at least in part, by the generation of ROS and consequent depletion of GSH. Given that sulphur mustard is still a potential biohazard, the protective effects of antioxidants against CEES toxicity demonstrated in Jurkat cells and normal human lymphocytes may provide the basis for the development of a therapeutic strategy to counteract exposure to this chemical weapon.

British Journal of Pharmacology (2004) 141, 795–802. doi:10.1038/sj.bjp.0705591
Modulation of the baroreceptor reflex by α2A‐adrenoceptors: a study in α2A knockout mice
Authors: Niederhoffer Nathalie , Hein Lutz , Starke Klaus
Published: March 2004

Our objective was to determine whether α2A‐adrenoceptors modulate the baroreceptor reflex. The efficacy of the reflex was evaluated by measuring the spontaneous blood pressure and heart rate variability at rest and the heart rate responses to evoked changes in blood pressure. Experiments were carried out in conscious, unrestrained, and anaesthetized α2A‐adrenoceptor‐deficient (α2A‐KO) mice and WT mice.

In conscious α2A‐KO mice, the spontaneous blood pressure variability was greater, and the spontaneous heart rate variability was lower than in conscious WT mice. This was also observed in anaesthetized animals.

The reflex bradycardia after intravenous injection of phenylephrine was greatly attenuated in conscious α2A‐KO compared to conscious WT mice; the baroreceptor reflex gain (ratio maximal change in heart rate/maximal change in mean arterial pressure) was decreased by 40%.

Similar results were obtained when reflex bradycardia was elicited by intra‐arterial volume loading of conscious WT and α2A‐KO mice. The baroreceptor reflex gain upon volume loading was also low in anaesthetized α2A‐KO mice.

The reflex tachycardia evoked by intravenous sodium nitroprusside injection was also significantly less in α2A‐KO mice as compared to WT, conscious as well as anaesthetized; the baroreceptor reflex gains were decreased by 50 and 65%, respectively.

Direct stimulation of cardiac β‐adrenoceptors by the agonist isoprenaline produced similar cardioacceleration in α2A‐KO and WT animals.

Our results show that the baroreceptor reflex function is impaired in mice lacking α2A‐adrenoceptors. We conclude that central α2A‐adrenoceptors facilitate the reflex response to both loading and unloading of the arterial baroreceptors.

British Journal of Pharmacology (2004) 141, 851–859. doi:10.1038/sj.bjp.0705636
Characterisation of the vasorelaxant properties of the novel endocannabinoid N‐arachidonoyl‐dopamine (NADA)
Authors: O'Sullivan Saoirse E , Kendall David A , Randall Michael D
Published: March 2004

We have investigated the vascular effects of N‐arachidonoyl‐dopamine (NADA), a novel endocannabinoid/vanilloid. NADA caused vasorelaxant effects comparable to those of anandamide in small mesenteric vessels (G3), the superior mesenteric artery (G0) and in the aorta.

In G3, addition of NG‐nitro‐L‐arginine methyl ester (300 μM) or the dopamine (D1) receptor antagonist (SCH23390, 1 μM) did not affect responses to NADA. In the presence of 60 mM KCl, after de‐endothelialisation, or after K+ channel inhibition with charybdotoxin (100 nM) and apamin (500 nM), relaxant responses to NADA were inhibited.

In G3, pretreatment with the vanilloid receptor (VR) agonist capsaicin (10 μM) or the VR antagonist capsazepine (10 μM) reduced vasorelaxation to NADA.

In G3, application of the CB1 antagonist SR141716A at 1 μM but not 100 nM reduced the potency of NADA. Another CB1 antagonist, AM251 (100 nM and 1 μM), did not affect vasorelaxation to NADA. After endothelial denudation, SR141716A (1 μM) did not reduce the responses further. A combination of capsaicin and SR141716A (1 μM) reduced vasorelaxation to NADA further than with capsaicin pretreatment alone. The novel endothelial cannabinoid (CB) receptor antagonist O‐1918 opposed vasorelaxation to NADA in G3.

In the superior mesenteric artery (G0), vasorelaxation to NADA was not dependent on an intact endothelium and was not sensitive to O‐1918, but was sensitive to capsaicin and SR141716A or AM251 (both 100 nM).

The results of the present study demonstrate for the first time that NADA is a potent vasorelaxant. In G3, the effects of NADA are mediated by stimulation of the VR and the novel endothelial CB receptor, while in G0, vasorelaxation is mediated through VR1 and CB1 receptors.

British Journal of Pharmacology (2004) 141, 803–812. doi:10.1038/sj.bjp.0705643