bluuebunny/crossref_metadata_2025 huggingface dataset:
A new experimental approach to detect long‐range conformational changes transmitted between the membrane and cytosolic domains of LmrA, a bacterial multidrug transporter
Authors: Vigano Catherine , Grimard Vinciane , Margolles Abelardo , Goormaghtigh Erik , van Veen Hendrik W , Konings Wil N , Ruysschaert Jean-Marie
Published: October 2002

LmrA confers multidrug resistance to Lactococcus lactis by mediating the extrusion of antibiotics, out of the bacterial membrane, using the energy derived from ATP hydrolysis. Cooperation between the cytosolic and membrane‐embedded domains plays a crucial role in regulating the transport ATPase cycle of this protein. In order to demonstrate the existence of a structural coupling required for the cross‐talk between drug transport and ATP hydrolysis, we studied specifically the dynamic changes occurring in the membrane‐embedded and cytosolic domains of LmrA by combining infrared linear dichroic spectrum measurements in the course of H/D exchange with Trp fluorescence quenching by a water‐soluble attenuator. This new experimental approach, which is of general interest in the study of membrane proteins, detects long‐range conformational changes, transmitted between the membrane‐embedded and cytosolic regions of LmrA. On the one hand, nucleotide binding and hydrolysis in the cytosolic nucleotide binding domain cause a repacking of the transmembrane helices. On the other hand, drug binding to the transmembrane helices affects both the structure of the cytosolic regions and the ATPase activity of the nucleotide binding domain.
PIAS3 induces SUMO‐1 modification and transcriptional repression of IRF‐1
Authors: Nakagawa Koji , Yokosawa Hideyoshi
Published: October 2002

Interferon regulatory factor‐1 (IRF‐1) is a transcriptional activator that is involved in interferon response, regulation of cell growth and oncogenesis. To try to identify the molecules that regulate the function of IRF‐1, we performed yeast two‐hybrid screening and isolated protein inhibitor of activated STAT3 (PIAS3) as an IRF‐1‐binding protein. This protein was also found to bind with small ubiquitin‐related modifier‐1 (SUMO‐1) and ubiquitin‐conjugating enzyme 9, an E2 in the SUMO‐1‐conjugating system. Co‐expression of PIAS3 induced SUMO‐1 modification of IRF‐1 in a RING finger domain‐dependent manner and also repressed transcriptional activity of IRF‐1. Thus, PIAS3 functions as a SUMO‐1 ligase for IRF‐1 and also as a repressor of IRF‐1 transcriptional activity.
β‐Helical catalytic domains in glycoside hydrolase families 49, 55 and 87: domain architecture, modelling and assignment of catalytic residues
Authors: Rigden Daniel J , Franco Octávio L
Published: October 2002

X‐ray crystallography and bioinformatics studies reveal a tendency for the right‐handed β‐helix domain architecture to be associated with carbohydrate binding proteins. Here we demonstrate the presence of catalytic β‐helix domains in glycoside hydrolase (GH) families 49, 55 and 87 and provide evidence for their sharing a common evolutionary ancestor with two structurally characterized GH families, numbers 28 and 82. This domain assignment helps assign catalytic residues to each family. Further analysis of domain architecture reveals the association of carbohydrate binding modules with catalytic GH β‐helices, as well as an unexpected pair of β‐helix domains in GH family 55.
Psychosocial Factors and Their Association with Clinical Outcomes in Patients with Heart Failure: Why Clinicians Do not Seem to Care
Authors: Moser Debra K
Published: October 2002

Poor quality of life, social isolation, depression and anxiety all have been linked to increased risk of rehospitalization and mortality in patients with heart failure. Yet, despite evidence of their importance to outcomes in heart failure patients, psychosocial factors are assessed and treated infrequently in clinical practice. Potential reasons for this include: (1) inadequate dissemination of research about the link between psychosocial factors and outcomes; (2) insufficient training in heart–mind interactions that precludes clinicians from taking advantage of what is known; (3) perceived problems with interventions or with the science of heart–mind interactions that interfere with acceptance of what is known; (4) concerns about how to measure psychosocial factors in clinical practice; and (5) lack of curiosity from clinicians about the role of psychosocial factors in their patients. In this article, each of these possible explanations is explored and recommendations suggested.
Recognising and Treating the Diabetic Patient in Cardiovascular Care
Authors: Bartnik Malgorzata , Malmberg Klas , Rydén Lars
Published: October 2002

The global prevalence of diabetes mellitus has continuously and rapidly increased, and the number of diabetic people in the adult population is predicted to double within 30 years. The prevalence of and mortality from all forms of cardiovascular diseases is two- to eight-fold higher in diabetic individuals as compared with their non-diabetic counterparts. The excess of risk attributable to diabetes related heart disease accounts for 2.9% of the all cause annual mortality. Moreover, the cardiovascular risk increases continuously throughout a wide spectrum of glycaemia starting already at what, according to present definitions, is considered as normal blood glucose levels. Therefore, screening for diabetes and hyperglycaemia is recommended in various clinical settings. Criteria for classification of hyperglycaemic states are provided together with their relation to risk for cardiovascular events. The evidence-based treatment of cardiovascular disease in patients with concomitant diabetes is summarised. Degree of under-treatment of patients with diabetes and cardiovascular diseases is discussed. Finally, the potential impact that nurses may have on the quality and efficacy of care in the vulnerable patient with combined chronic diseases such as diabetes and cardiovascular disease and the improvement of the outcomes are discussed.
Anxiety and Well-Being in First-Time Coronary Angioplasty Patients and Repeaters
Authors: Lenzen Mattie J , Gamel Claudia J , Immink Atie W
Published: October 2002

Introduction: Preparatory information before an invasive procedure has positive effects (e.g. on recovery, well-being and anxiety). However, preparation of patients for a repeat procedure is hardly investigated. The question is whether these patients benefit from the same preparatory information. Aims: To determine whether there are differences in terms of anxiety and well-being between patients undergoing their first percutaneous transluminal coronary angioplasty (PTCA) and those undergoing a repeat PTCA. Design: Descriptive correlational study with a quantitative and qualitative research component. Method: First-time PTCA patients ( n=46) and re-PTCA patients ( n=40) were asked to complete three psychological self-report questionnaires (HADS, HPPQ and VAS) before the procedure. Five re-PTCA patients were interviewed the day after the procedure. Results: We were not able to show statistically significant differences between the two groups. On the anxiety scales re-PTCA patients scored 6.5 (HADS) and 4.0 (VAS) vs. 5.0 ( P=0.25) and 2.6 ( P=0.30) for first-time PTCA patients. On well-being (HPPQ) these differences were 18.0 vs. 19.0 ( P=0.40). Once the interview data were coded, four themes were apparent, namely: recurrent symptoms, information, experience and future prospects. Conclusion: A trend is seen towards a worse condition in the re-PTCA group with respect to anxiety and well-being. However, the differences are not statistically significant, they seem to be clinically relevant. The interviews point out that the return of symptoms and future prospects, rather than the procedure itself, are an important part in preparing for a repeat intervention. This aspect is currently no part of the provided preparatory information. Future research will have to determine the most beneficial method of preparing these patients (e.g. tailored preparation, emotional support, coaching).
The Effect of Nursing Interventions Utilizing Music Therapy or Sensory Information on Chinese Patients’ Anxiety Prior to Cardiac Catheterization: A Pilot Study
Authors: Taylor-Piliae Ruth E , Chair Sek-Ying
Published: October 2002

Background: Unrelieved anxiety can produce an increase in sympathetic nervous system activity leading to an increase in cardiac workload. Nursing interventions using music therapy or sensory information among patients with coronary artery disease has resulted in anxiety reduction, though results in Chinese subjects has not previously been published. Aims: To determine the effects of using nursing interventions of music therapy or sensory information, on reducing anxiety and uncertainty, and improving negative mood among Chinese subjects immediately prior to cardiac catheterization. Methods: An experimental three-group repeated measures design for this pilot study was used. Forty-five hospitalized adults (15/group) undergoing cardiac catheterization were randomly assigned to either (1) a music therapy intervention, (2) a sensory information intervention or (3) treatment as usual (control). Anxiety, uncertainty and mood state were measured using self-reported questionnaires and physiological measures were made at baseline, post-intervention to determine their effect and post-cardiac catheterization to determine whether these interventions had any long-lasting effect. Results: The control group was found to be significantly older ( P=0.001) than the two experimental groups. Older age was associated with lower anxiety scores ( r=−0.31, P=0.04 at baseline; r=−0.30, P=0.04 post-intervention; r=−0.22, P=0.15 post-cardiac catheterization). After controlling for age, the use of music therapy or sensory information did not significantly reduce anxiety, improve mood state, reduce uncertainty, decrease heart or respiratory rate among subjects undergoing cardiac catheterization. Conclusion: The non-significant result may have been affected by the small sample, and the social and cultural expectations regarding the public display of emotions among Chinese populations.
Changes in Health Status, Psychological Distress, and Quality of Life in Implantable Cardioverter Defibrillator Recipients Between 6 Months and 1 Year After Implantation
Authors: Carroll Diane L , Hamilton Glenys A , Kenney Barbara J
Published: October 2002

Background: Living with an implantable cardioverter defibrillator (ICD) has positive health benefits but the impact on well-being and quality of life over a period of time has not been studied in depth. Aim: To follow patients prospectively over the first year and to compare the changes from time of ICD implantation, to 6 months and 1 year. Methods: Generalized linear models were used to assess changes through examination of health status (SF-36), psychological distress (POMS), and quality of life (QLI) scores. Results: There were 19 females (27%) and 51 males (73%) in the sample with a mean age of 64 years. There were significant improvements over time in 3 of the 8 sub-concepts of health status: role physical ( P<0.001), vitality ( P<0.013) and social functioning ( P<0.001). The Profile of Mood States revealed significantly less total psychological distress at 6 months with a non-significant leveling off or increase at 1 year. The quality of life index revealed no significant changes over time. Conclusions: The effects of living with an ICD are not well understood. Research should continue to identify the impact over time in this population and sub-groups so that health care providers can address the social and psychological needs of this population.
High‐resolution fields of global runoff combining observed river discharge and simulated water balances
Authors: Fekete Balázs M. , Vörösmarty Charles J. , Grabs Wolfgang
Published: October 2002

This paper demonstrates the potential of combining observed river discharge information with climate‐driven water balance model (WBM) outputs to develop composite runoff fields. Such combined runoff fields simultaneously reflect the numerical accuracy of the discharge measurements and preserve the spatial and temporal distribution of simulated runoff. Selected gauging stations from the World Meteorological Organization Global Runoff Data Centre (GRDC) data archive were geographically coregistered to a gridded simulated topological network at 30′ (longitude × latitude) spatial resolution (STN–30p). Interstation regions between gauging stations along the STN–30p network were identified, and annual interstation runoff was calculated. The annual interstation runoff was compared with outputs from WBM calculations, which were performed using long‐term mean monthly climate forcings (air temperature and precipitation). The simulated runoff for each cell was multiplied by the ratio of observed to simulated runoff of the corresponding interstation region from the GRDC data set to create spatially distributed runoff fields at 30′ resolution. The resulting composite runoff fields (UNH/GRDC Composite Runoff Fields V1.0) are released to the scientific community along with intermediate data sets, such as station attributes and long‐term monthly regimes of the selected gauging stations, the simulated topological network (STN–30p), STN–30p derived attributes for the selected stations, and gridded fields of the interstation regions along STN–30p. These data sets represent high‐resolution fields that are of value to a broad range of water‐related research, including terrestrial modeling, climate‐atmosphere interactions, and global water resource assessments.
A model of suboxic sedimentary diagenesis suitable for automatic tuning and gridded global domains
Authors: Archer D. E. , Morford J. L. , Emerson S. R.
Published: October 2002

We present a new model for oxic and anoxic diagenesis of shallow and deep‐sea sediments based on an efficient solver for steady state pore water and solid phase diffusion/reaction/advection equations. The model, called “Muds”, is orders of magnitude faster than solvers of the corresponding time‐dependent equations. The model resolves Mn and Fe/S geochemistry as well as pore water pH and CaCO3 dissolution. The model speed opens application possibilities that are impossible for time‐dependent models, including automatic tuning of uncertain parameters, and deployment of the model in gridded global domains. The kinetic rate constants for respiration and bioturbation are parameterized as functions of the organic carbon rain to the seafloor, based on existing parameterizations in the literature. Seven uncertain model parameters, including many of the rate constant parameterizations, were tuned to minimize the misfit to observations from 53 sedimentary locations throughout the ocean. The model tuning knobs were the fractions of labile and refractory organic matter in the sedimenting material, the NO3−, Mn, Fe, and S respiration rate constant parameterizations, and the depth scales of respiration and of pore water irrigation. We searched for adequate fit values of these parameterizations using a simulated annealing method. The cost function (degree of misfit) was based on a comparison of pore water (NO3−, NH4+, Mn2+, and Fe2+) and solid phase (organic carbon and MnO2) model results with data. Many of the tuning parameters are constrained to ±50% or better. The model is most skillful at predicting organic carbon concentration, depth of NO3− penetration, and pore water Fe2+, and less so for Mn2+, NH4+, and solid phase MnO2. The model misses some of the very high sediment surface MnO2 concentrations observed in, for example, the California Borderlands. We believe that these sites must receive a higher input of reactive Mn than the crustal abundance of the clay rain. The model was deployed on every 2° × 2° grid point below 1000 m of the global seafloor, using gridded maps of organic carbon rain to the seafloor and overlying water chemistry. The deep‐sea carbon burial efficiency is 7%, with 95% of respiration by oxic metabolism. The model was also run against a new depth‐oxygen hypsometry of the global ocean, with sediment area as a function of overlying oxygen concentration and average depth related to carbon fluxes, to include the effects of shallow water sediments. This analysis predicts that shallow waters (<1000 m) account for 88% of respiration, and oxygen accounts for 66% of respiration overall. Denitrification is closely coupled to organic nitrogen fluxes to the sediment, and the global rate is estimated to be 1.4 × 1014 mol yr−1, a factor of 6–8 higher than the corresponding estimate from Middelburg et al. [1996], throwing the nitrogen cycle in the ocean into imbalance.
Response of central Siberian Scots pine to soil water deficit and long‐term trends in atmospheric CO2concentration
Authors: Arneth A. , Lloyd J. , Šantrůčková H. , Bird M. , Grigoryev S. , Kalaschnikov Y. N. , Gleixner G. , Schulze E.‐D.
Published: October 2002

Twenty tree ring13C /12C ratio chronologies fromPinus sylvestris(Scots pine) trees were determined from five locations sampled along the Yenisei River, spaced over a total distance of ∼1000 km between the cities of Turuhansk (66°N) and Krasnoyarsk (56°N). The transect covered the major part of the natural distribution of Scots pine in the region with median growing season temperatures and precipitation varying from 12.2°C and 218 mm to 14.0°C and 278 mm for Turuhansk and Krasnoyarsk, respectively. A key focus of the study was to investigate the effects of variations in temperature, precipitation, and atmospheric CO2concentration on long‐ and short‐term variation in photosynthetic13C discrimination during photosynthesis and the marginal cost of tree water use, as reflected in the differences in the historical records of the13C /12C ratio in wood cellulose compared to that of the atmosphere (Δ13Cc). In 17 of the 20 samples, trees Δ13Cchas declined during the last 150 years, particularly so during the second half of the twentieth century. Using a model of stomatal behaviour combined with a process‐based photosynthesis model, we deduce that this trend indicates a long‐term decrease in canopy stomatal conductance, probably in response to increasing atmospheric CO2concentrations. This response being observed for most trees along the transect is suggestive of widespread decreases in Δ13Ccand increased water use efficiency for Scots pine in central Siberia over the last century. Overlying short‐term variations in Δ13Ccwere also accounted for by the model and were related to variations in growing season soil water deficit and atmospheric humidity.
Production of methane from alasses in eastern Siberia: Implications from its 14C and stable isotopic compositions
Authors: Nakagawa Fumiko , Yoshida Naohiro , Nojiri Yukihiro , Makarov VladimirN.
Published: October 2002

The radiocarbon (14C) and stable isotopic (13C and D) compositions of methane and carbon dioxide from alasses (typical landforms in permafrost terrain, consisting of lakes and wetlands) were measured around Yakutsk, eastern Siberia, where few isotope studies have been done. The carbon isotopic compositions of methane and carbon dioxide were used to study the pathways of methane formation in alasses. The mean value of methane and of carbon dioxide in each alass ranged from −63.9 to −58.2‰ and from −16.7 to −0.6‰, respectively. In small alasses, where the supply of fresh organic matter from surrounding wetland ecosystems is large, methane was produced almost equally from acetate fermentation and CO2 reduction pathways. In larger alasses the CO2 reduction pathway slightly dominates over acetate fermentation, owing to a smaller supply of labile organic matter. The 13C enrichment in CO2 in large lakes indicates depletion of methane precursors. Gas‐bubble methane is depleted in deuterium (the mean δD value from lakes is −360 ± 14‰ and from shores is −380 ± 20‰), which reflects the deuterium‐depleted environmental water (from −136 to −117‰) of alasses. Lake methane relatively enriched in D is interpreted to be the result of depletion in the hydrogen pool in lake sediments. Methane in shallow lakes is somewhat enriched in 14C relative to modern biogenic methane and is produced from fresh, recently fixed organic matter. The 14C content of methane from deeper lakes is 10–20% less than that of shallow lake methane, indicating a greater contribution from older methane derived from deeper parts of the sediment. The mean 13C, D, and 14C of methane from the alasses in general are estimated to be −61.1 ± 4.4‰, −363 ± 20‰, and 104 ± 6 pMC, respectively. This corresponds to the reported mean isotopic composition of methane from wetlands for δ13C, but shows lower value for δD and 14C content.
Empirical model for μ scattering caused by field line curvature in a realistic magnetosphere
Authors: Young S. L. , Denton R. E. , Anderson B. J. , Hudson M. K.
Published: October 2002

The combination of magnetic field line curvature (FLC) and weak magnetic field strength affects charged particle motion in a magnetic field by causing changes of the particle's first adiabatic invariant, μ. In this paper we refer to these changes as FLC induced μ scattering or simply μ scattering. Both large single scatterings and the cumulative effects of many small scatterings (Δμ/μ ≪ 1) influence particle populations in the Earth's magnetosphere. Because FLC‐induced μ scattering is strongly dependent on the magnetic field geometry and strength, realistic magnetospheric models must be employed in order to gain a quantitative understanding of how μ scattering affects the evolution of these populations. This requires a μ‐scattering model that is accurate for many different magnetic field geometries. Though several μ‐scattering models have been developed previously, we demonstrate that their accuracy is limited to the simple field geometries for which they were derived. In realistic magnetic fields, there are regions where these μ‐scattering models depart from Lorentz integration results by a factor of 2 or greater. The source of these discrepancies is attributed to the fact that the only magnetic field information used is the field line curvature RC and magnetic field strength B both evaluated at a single point, the magnetic equator. To generalize the analytical representation of μ scattering to a range of magnetic field geometries, we have developed a new μ‐scattering model that uses two additional parameters. These are proportional to the second derivatives of the field line curvature, ∂2RC/∂S2, and the field intensity, ∂2B /∂S2, where S is the distance along the field line and the derivatives are evaluated at the magnetic equator. We have defined an error parameter that measures the fit between the model and Lorentz integration results. Using this parameter, we show that the difference between our model Δμ values and those based on Lorentz integration is, on average, only 4%; this is at least a factor of 5 less than the difference using previous analytical models. Our new model will greatly facilitate quantitative analysis of μ scattering for realistic magnetospheric magnetic field geometries including active as well as quiet conditions.
Flow angle dependence of 1‐m ionospheric plasma wave turbulence for near‐threshold radar echo electric fields
Authors: Timofeev E. E. , Vallinkoski M. K. , Pollari P. , Kangas J. , Virdi T. , Williams P. J. S. , Nielsen E.
Published: October 2002

Coordinated STARE–EISCAT data from the E‐region Rocket and Radar Instability Study (ERRRIS) campaign are used to study the flow angle distributions of threshold (signal‐to‐noise ratio [SNR] ≤ 1 dB) ionospheric parameters controlling the STARE radar echo appearance for either radar above Tromsø. Altogether, there are 64 measurements for the Finnish radar and 128 for the Norwegian radar. For the Finnish radar, the threshold E‐field strength is drift‐aligned with minimum‐to‐maximum ratio of the electron drift velocities of about 3. The strengths tend to decrease when going from positive to negative flow angles. For the Norwegian radar, the threshold electric fields are practically independent of flow angle. For the Finnish radar, the STARE line‐of‐sight Doppler velocities are exclusively positive, large, and well correlated with the corresponding EISCAT plasma velocity components. The Norwegian radar Doppler velocities are randomly distributed around zero and are practically uncorrelated. For either radar, the N(h) profiles have permanent upward vertical density gradients within the echo layers. The jet averaged threshold E‐fields are lower in the westjet than within the eastjet, but the averaged threshold electron densities are higher in the westjet than in the eastjet. For the Norwegian radar, the jet averaged turbulence level is about two times higher within the eastjet. The flow angle distributions of the plasma wave turbulence level are different. The westjet distribution is of the equilibrium type with a maximum at small flow angles and a minimum at large angles. The eastjet distribution is consistent with a flat one and can be kept stationary only if there is a damping of the turbulence for small flow angles and an enhancement for large angles. It is then conjectured that Finnish radar threshold echoes are generated by the Farley–Buneman instability, but the Norwegian echoes by a nonlinear gradient drift or/and wind‐driven mechanism. The gradient drift instability, due to the permanent vertical gradients in the lower part of the N(h) profile and the meridional component of the ionospheric E‐field, is suggested to be the mechanism responsible for the turbulence level enhancement in the eastjet and damping in the westjet.
Premonitory spreading of seismicity over the faults' network in southern California: Precursor Accord
Authors: Zaliapin I. , Keilis‐Borok V. , Axen G.
Published: October 2002

We establish a connection between geometry of the faults' network in a region and seismicity preceding the strong earthquakes in the intermediate‐term timescale of years. Previous studies of observed and computer‐simulated seismicity demonstrated that strong earthquakes are preceded in that timescale by the rise of seismic activity in a lower magnitude range. Here, we explore a complementary phenomenon: spreading of activity over the fault network. This phenomenon is depicted by the seismicity pattern Accord, defined as a simultaneous rise of seismicity in a sufficiently large number of fault zones (hence its name). Pattern Accord has been found recently in synthetic seismicity generated by the colliding cascades (CC) model. The present study demonstrates this pattern in observed seismicity of southern California. We applied to observations a prediction algorithm based on the pattern Accord. Scaled to the target magnitude 7.5, the pattern Accord emerges within a few years before each of the three largest earthquakes in southern California (Kern County, 1952; Landers, 1992; and Hector Mine, 1999) and at no other time. Scaled to the target magnitude interval from 6.5 to 7.4, the pattern Accord precedes six out of nine earthquakes. The duration of alarms in both cases is about 30% of the time considered. We repeated prediction with different combinations of adjustable numerical parameters of the algorithm, summing up the success and error scores on an error diagram. This numerical experiment shows that the prediction results are stable under moderate variations of adjustable parameters. The final test would be, as always, an advance prediction. The pattern Accord has a simple physical explanation connected with equilibrium of the crustal blocks' system under the impact of tectonic driving forces. At the same time, Accord is a manifestation of a broader phenomenon: premonitory increase of earthquakes' correlation range. The latter phenomenon was found for the first time in the CC model, although it was hypothesized by one of the authors much earlier.
Paleomagnetic dating of the smectite‐to‐illite conversion: Testing the hypothesis in Jurassic sedimentary rocks, Skye, Scotland
Authors: Woods Sharon D. , Elmore R. D. , Engel M. H.
Published: October 2002

A hypothesized connection between clay diagenesis and magnetite authigenesis is supported by the results of paleomagnetic, rock magnetic, geochemical, and petrographic studies on Jurassic sedimentary rock of Skye, Scotland. The results have implications for understanding remagnetization mechanisms and for the development of a paleomagnetic method to date clay diagenesis. Previous diagenetic studies indicate that rock in north Skye contains abundant detrital smectite, whereas the clays in the same age rock in south Skye have altered to illite because of Tertiary igneous activity. Geochemical (87Sr/86Sr, δ13C, δ18O) studies confirm that sedimentary rocks in south Skye are altered. The magnetization in the rocks in north Skye is weak and unstable. In contrast, the rocks in south Skye contain a multicomponent magnetization. At intermediate temperatures (225°–450°C) a magnetization with southerly declinations and negative inclinations or its antipodal equivalent is present. At higher temperatures (450°–580°C) a magnetization with northerly declinations and positive inclinations or its antipodal equivalent is removed. Both magnetizations have directions similar to Tertiary igneous rocks on Skye. Rock magnetic studies indicate the presence of pyrrhotite and magnetite. The intermediate‐temperature component resides in pyrrhotite and/or magnetite and is interpreted as a thermoviscous remanent magnetization or a thermochemical remanent magnetization related to the heat and/or hydrothermal activity associated with the igneous activity. The high‐temperature component resides in magnetite and is a chemical remanent magnetization (CRM). The presence‐absence test and the timing of acquisition for this CRM suggest that magnetite authigenesis is related to the smectite‐to‐illite conversion and that clay diagenesis is a viable remagnetization mechanism.
Modeling of nutation and precession: Effects of electromagnetic coupling
Authors: Buffett B. A. , Mathews P. M. , Herring T. A.
Published: October 2002

The presence of an internal magnetic field influences of the Earth's nutation through the effects of electromagnetic torques at the boundaries of the fluid core. We calculate the effect of electromagnetic torques on nutation by combining a solution for the full hydromagnetic response of the fluid core with the nutation theory of Mathews et al. [2002]. The coupling of the fluid outer core to the mantle and solid inner core is described by two complex constants, KCMB and KICB, that characterize the electromagnetic torques at the core‐mantle boundary (CMB) and the inner core boundary (ICB). Predictions for KCMB and KICB are compared with estimates inferred from observations of the Earth's nutation. The estimate of KCMB can be explained by the presence of a thin conducting layer at the base of the mantle with a total conductance of 108 S. The overall root‐mean‐square (RMS) radial field at the CMB is 0.69 mT, which is partitioned into a dipole component (0.264 mT) and a nondipole component (0.64 mT). (The latter is represented using a uniform radial field.) The estimate of KICB can be explained with a mixture of dipole and nondipole components. The overall RMS field at the ICB is 7.17 mT, though smaller values are inferred when small adjustments are made to the dynamic ellipticity of the inner core and/or the fluid density at the boundary. The minimum RMS radial field required to explain the nutation observations is 4.6 mT.
Fracture of Antarctic shelf ice
Authors: Rist M. A. , Sammonds P. R. , Oerter H. , Doake C. S. M.
Published: October 2002

We have investigated the fracture of Antarctic shelf ice core using two fracture mechanics test methods: the chevron‐notched short‐rod specimen loaded in tension and the chevron‐notched round‐bar specimen loaded in three‐point bending. These tests have been used to measure the fracture initiation toughness, Kinit, at which crack growth starts, on samples taken through the entire thickness of the Ronne Ice Shelf, from low‐density firn through consolidated meteoric ice to basal marine ice. The fracture data are presented together with depth profiles of relevant physical and mechanical properties derived from the test specimens: temperature, density, elastic modulus, and grain size. It is found that the trend in measured fracture toughness closely reflects changes in ice density and elastic modulus. We augment the experimental study by presenting a fracture mechanics analysis of ice shelf surface and basal crevassing which directly incorporates our measurements. For the examined ice shelf profiles, basal crevasses are found to be inherently unstable unless an external restraining force is imposed, which has important implications for overall ice shelf stability. On the other hand, surface crevassing is shown to be innately stable at depth. Our fracture mechanics model is used to predict local ice shelf back stresses in the vicinity of basal crevassing and is validated directly against field observations of crevasse penetration on the Ronne Ice Shelf.
Three‐dimensional nonplanar simulation of the 1992 Landers earthquake
Authors: Aochi Hideo , Fukuyama Eiichi
Published: October 2002

We have simulated the rupture process of the 1992 Landers, California, earthquake using a realistic nonplanar fault geometry, including fault bends and branches, through a three‐dimensional boundary integral equation method. Considering an external loading system due to local tectonics as well as a nonplanar fault structure, we could reproduce the characteristic features of this earthquake such as spontaneous rupture transfer between faults, pattern of slip distribution, and propagation of rupture front without assuming any laterally heterogeneous distribution of parameters. We could also reproduce seismic waveforms near the faults, especially in the forward direction of rupture propagation, where rupture directivity controlled by rupture transfer between faults significantly affects ground motion.
Effects of melt migration on the dynamics and melt generation of diapirs ascending through asthenosphere
Authors: Ghods Abdolreza , Arkani‐Hamed Jafar
Published: October 2002

Melting of a plume head can affect its dynamics by creating melt retention buoyancy. Melt migration controls the distribution of the melt retention buoyancy and affects the dynamics of the plume. We investigate in detail the effects of melt migration on the dynamics and partial melting of a 20‐km radius mantle diapir, using axisymmetric two‐phase flow models. We first study melt migration in a diapir with a 10% initial melt where no further melting is allowed. The diapir dynamics are modeled for permeable and impermeable cases. In the permeable model, melt migrates within the diapir, whereas no relative motion is allowed between melt and solid matrix in the impermeable model. The permeable model shows a progressive increase of melt fraction in the top portion and decrease in the bottom part of the diapir. This results in a melt buoyancy polarization that elongates the diapir and increases its upwelling velocity. We then model the dynamics of the permeable and impermeable diapirs allowing melting to occur. The velocity of the permeable diapir and its melt generation are significantly larger than that of the impermeable diapir. In general, the permeable diapirs lack the mushroom shape observed for the impermeable ones. Because of intensive computational demand of the two‐phase flow modeling, our detailed studies are limited to small diapirs. However, we also investigate a 200‐km‐diameter mantle plume and show that melt migration produces a nibble of higher melt fraction at the top of the plume that ascends much faster than the bulk of the plume.
Volcanic eruptions on mid‐ocean ridges: New evidence from the superfast spreading East Pacific Rise, 17°–19°S
Authors: Sinton John , Bergmanis Eric , Rubin Ken , Batiza Rodey , Gregg Tracy K. P. , Grönvold Karl , Macdonald Ken C. , White Scott M.
Published: October 2002

Side‐scan sonar, submersible observations and sampling of lava flows from the East Pacific Rise, 17°–19°S constrain the character and variability of submarine volcanic eruptions along mid‐ocean ridges. Nine separate lava sequences were mapped using relative age and lithological contrasts among recovered samples. Axial lengths activated during eruptive episodes range from ∼1 to >18 km; individual flow field areas vary from <1 to >19 km2. Estimated erupted volumes range from <1 to >200 × 106 m3. The largest unit is the chemically uniform Animal Farm lava near 18°37′S. The youngest lava is the Aldo‐Kihi flow field, 17°24′–34′S, probably erupted in the early 1990s from a fissure system extending >18 km along axis. Near 18°33′S two distinct lava compositions with uniform sediment cover were recovered from lava that buries older faulted terrain. The boundary in lava composition coincides with a change in depth to the top of an axial magma lens seismic reflector, consistent with magmas from two separate reservoirs being erupted in the same event. Chemical compositions from throughout the area indicate that lavas with identical compositions can be emplaced in separate volcanic eruptions within individual segments. A comparison of our results to global data on submarine mid‐ocean ridge eruptions suggests consistent dependencies of erupted volume, activated fissure lengths, and chemical heterogeneity with spreading rate, consistent with expected eruptive characteristics from ridges with contrasting thermal properties and magma reservoir depths.
Relation between surface velocity field and shear wave splitting in the South Island of New Zealand
Authors: Moore M. , England P. , Parsons B.
Published: October 2002

The relative motion between the Pacific and Australian plates across the central South Island of New Zealand, as measured by repeated GPS measurements, is distributed over a region more than 80 km wide. The surface distribution of velocity is fit almost equally well by a model in which deformation of the lower lithosphere is concentrated into very narrow slip zones below one or two major faults and by a model in which the lower lithosphere deforms in a broad shear zone. Observations of the splitting of SKS waves permit distinction between the two models on the basis of the finite strain they predict. Deformation in the deep lithosphere that was limited to narrow shear zones would not produce measurable splitting; hence any splitting observed should not correlate with surface tectonics. However, the distribution of fast propagation directions revealed by observations of shear wave splitting do reflect surface tectonics. In particular, the orientations of fast propagation directions are consistent with the finite strain calculated by assuming that the distribution of velocity at depth within the lithosphere resembles the distribution of velocity measured at the surface by GPS. The observed distribution of splitting can be reproduced with an RMS misfit of 15°, provided that the velocity field is integrated over at least the time interval since significant convergence across the Southern Alps began at about 6.5 Ma.
Deformation due to the 17 August 1999 Izmit, Turkey, earthquake measured from SPOT images
Authors: Michel Rémi , Avouac Jean‐Philippe
Published: October 2002

The geometry of the ruptured areas and the coseismic slip distribution data are key to highlighting the behavior of seismic faults. This information is generally retrieved from field investigations and geodetic measurements or synthetic aperture radar (SAR) interferometry. Here we show that SPOT images can also be used to accurately map the fault zone and to determine the slip distribution by subpixel correlation of images acquired before and after an earthquake. The measured slip includes the contribution of possible distributed shear that might not be clearly expressed in surface ruptures and smoothes out possible along‐strike variability due to near‐surface fault complexities. We apply the technique to the Ms = 7.4, 1999, Izmit earthquake. Our results reveal a <100‐m‐wide and very linear fault zone that can be traced for 70 km from Gölcük to Akyazi, along which supershear rupture has been inferred. The obtained slip distribution compares well with the field measurements and is consistent with ground deformation measured at some distance from the fault zone using SAR images. Very little deformation was accommodated off the main fault plane. Maximum slip is observed near Sapanca lake at a small fault jog that has probably influenced rupture propagation.
Nutrient supply to the surface waters of the North Atlantic: A model study
Authors: Oschlies Andreas
Published: October 2002

An eddy‐permitting coupled ecosystem‐circulation model with accurate descriptions of advection and turbulent mixing is used to estimate the nitrate supply to the euphotic zone in the North and equatorial Atlantic Ocean. The simulated annual mean input of nitrate into the euphotic zone is separated into different supply routes, namely, turbulent vertical mixing, vertical advection, and horizontal transport. Vertical mixing is found to be the dominant supply mechanism in the subpolar North Atlantic, while horizontal advection provides most of the simulated nitrate input into the subtropical gyre. Contributions by vertical advection are largest in the equatorial upwelling region and in the subpolar gyre. A comparison with observational estimates of nitrate flux into euphotic zone of the subtropical gyre reveals that the model can simultaneously fit the estimates by Lewis et al. [1986] and Jenkins [1988] that were previously thought to be contradictory. The simulated nitrate supply is, on the other hand, not consistent with estimates of export production based on oxygen consumption [Jenkins, 1982]. The model results are used to investigate to what extent the advective input of organic matter could possibly explain a local imbalance between new and export production. It turns out that the simulated advective input of organic matter alone, which in the model provides nitrogen at a rate similar to that arising from nitrate supply, is not sufficient to explain observed oxygen consumption rates.
Biological response to frontal dynamics and mesoscale variability in oligotrophic environments: Biological production and community structure
Authors: Lima Ivan D. , Olson Donald B. , Doney Scott C.
Published: October 2002

Two food web models, a single‐species and a multispecies formulation, are incorporated into a three‐dimensional eddy‐resolving model of an unstable frontal jet to investigate the effects of mesoscale instabilities on biological production and community structure in oligotrophic ocean environments. The growing instability wave triggers the formation of divergence and convergence and, consequently, upwelling and downwelling zones along the jet. Most of the biological production takes place near the surface on the cyclonic (northern) side of the front and on the upstream region of meander crests in response to nutrient upwelling. However, strong advection downstream and downward in the convergence regions (downstream side of meander crests) results in accumulation of biomass at depth on the anticyclonic (southern) side of the front, leading to spatial separation between regions of biological growth and regions of biomass accumulation. The large domain and long duration of the runs allow for investigation of diverse phenomena including eddy–eddy and eddy–front interactions for both cyclonic and anticyclonic features. In addition to the traditional cyclonic eddy pumping mechanism we observe enhanced primary production and biomass accumulation on the edges of anticyclonic eddies due to eddy–eddy interactions and biomass filaments trailing behind detached cyclonic eddies propagating away from the front. In the multispecies formulation the mesoscale dynamics drives a sustained shift in the phytoplankton community toward the large size classes that is consistent with observations and that has not been observed in previous similar process‐modeling studies. Because of the higher species diversity, nutrients are used more efficiently in the multispecies system, resulting in higher total plankton biomass for the same amount of total nitrogen in the domain. The fractional increase in total biomass is less pronounced inside the unstable front and eddies where species diversity is lower (large size classes dominate).
Thermal conductivity and heat transfer through the snow on the ice of the Beaufort Sea
Authors: Sturm Matthew , Perovich Donald K. , Holmgren Jon
Published: October 2002

Eighty‐nine point measurements of the thermal conductivity (ks) of the snow on the sea ice of the Beaufort Sea were made using a heated needle probe. Average values ranged from 0.078 W m−1 K−1 for new snow to 0.290 W m−1 K−1 for an ubiquitous wind slab. ks increased with increasing density, consistent with published equations, but could also be reliably estimated from the metamorphic state of the snow. Using measured values of ks and snow stratigraphy, the average bulk value for the full snowpack was 0.14 W m−1 K−1. In contrast, ks inferred from ice growth and temperature gradients in the snow was 0.33 W m−1 K−1. The mismatch arises in part because the second estimate is based on measurements from an aggregate scale that includes enhanced heat flow due to two‐ and three‐dimensional snow and ice geometry. A finite element model suggests that the complex geometry produces areas of concentrated heat loss at the snow surface. These “hot spots,” however, increase the apparent conductivity only by a factor of 1.4, not enough to fully explain the mismatch. Nonconductive heat transfer mechanisms, like natural and forced air convection, may also be operating in the snowpack, though the ubiquitous presence of low permeability wind slabs potentially limits their effectiveness. The relative contributions of effects due to snow and ice geometric and nonconductive processes within the snowpack remain uncertain.
Assessing ocean buoy shortwave observations using clear‐sky model calculations
Authors: Medovaya M. , Waliser D. E. , Weller R. A. , McPhaden M. J.
Published: October 2002

Comparison of ocean buoy observations and model calculations of incoming clear‐sky surface shortwave radiation is performed in order to assess the buoys' general reliability under operating conditions. The buoy data employed for this study come from several experimental and operational deployments conducted by Woods Hole Oceanographic Institution (WHOI) and Pacific Marine Environmental Laboratory (PMEL). WHOI deployments include the Frontal Air‐Sea Interaction Experiment, Marine Light Mixed Layer Experiment, Coupled Ocean‐Atmosphere Response, Subduction Experiment, Arabian Sea Experiment, Pan‐American Climate Study, and Biowatt. PMEL deployments include the Tropical Atmosphere Ocean moored buoy array in the tropical Pacific Ocean. These moorings and their associated shortwave measurements represent the vast majority of open‐ocean in situ shortwave observations available to date. Two separate schemes were used to filter the cloudy samples from the buoy shortwave time series, one based on satellite values of cloudiness and a second scheme based on the buoy observations themselves and on a number of additional constraints. The clear‐sky model calculations of surface shortwave were computed using the single‐column radiation code from the National Center for Atmospheric Research Community Climate Model, version 3. The primary uncertainty associated with the model calculations is the specification of the aerosol amount. In general, there was a fairly high level of agreement between the buoy and modeled values of clear‐sky surface shortwave. However, there were a few buoys that exhibited significant model‐data discrepancies (e.g., model‐data biases exceeding 10%, or ∼40 W m−2). The possible reasons for these discrepancies were investigated. In some cases, unaccounted for aerosol variability in the model was found to be the most probable cause, indicating that observations were likely to be reliable. In other cases, the discrepancies appeared to result from sensor tilt associated with wind, currents, or deployment/mounting problems and/or were possibly due to aerosol buildup on the sensor.