Particulate flux in the water column overlying Santa Monica Basin     

Michael R. Landry  Willis K. Peterson  Christine C. Andrews 《Progress in Oceanography》1992,30(1-4)

Fluxes of particulate carbon, nitrogen, phytoplankton pigments, biogenic silica and dry mass were measured using free-floating and moored sediment trap arrays in the Santa Monica Basin during the period from October 1985 to August 1990 as part of the California Basin Study (CaBS) Program. In field testing for potential sources of sediment trap biases, we found little significant or consistent difference in rate estimates between short-term drifting traps and long-term moored traps, between preserved and unpreserved traps in short-term experiments, between different preservatives (mercury or formalin) in long-term experiments, between different designs of small cylindrical traps, and between deep-moored cylindrical traps and large conical traps. We did, however, find that sediment trap samples collected and analyzed on 0.45 μm silver filters gave estimates of carbon and nitrogen fluxes about 25% higher than samples collected on GF/F glass-fiber filters. Concurrent trap deployments at two stations 18km apart revealed low mesoscale variability in flux estimates. Seasonal patterns in carbon and nitrogen flux were not evident in our data, but strong seasonality, with spring maxima and summer minima, were observed for fluxes of phaeopigments and biogenic silica out of the euphotic zone.Time-averaged rates of particulate flux for long-term trap deployments from January to August 1990, were 121, 18.8, 1.5, 67 and 633mg m⁻²d⁻¹ at 110–135m for carbon, nitrogen, phaeopigment, biogenic silica and mass, respectively. Flux estimates to the basin floor (835–860m) were 50, 6.5, 0.64, 41.6 and 575mg m⁻²d⁻¹ for the same parameters. The former estimates are constrained by and in good agreement with independent assessments of new production from nitrate uptake in the euphotic zone. The latter agree with rates previously inferred from the sedimentary record using ²¹⁰Pb as a tracer. In addition, the difference in carbon estimates in the water column between the euphotic zone and the basin floor is consistent with the requirements for bacterial growth and metabolism at intermediate depths as measured by the thymidine method.  相似文献   

Uncertainties in field-line tracing in the magnetosphere. Part II: the complete internal geomagnetic field     

D. M. Willis  J. Robin Singh  K. S. C. Freeman 《Annales Geophysicae》1997,15(2):181-196

The discussion in the preceding paper is restricted to the uncertainties in magnetic-field-iine tracing in the magnetosphere resulting from published standard errors in the spherical harmonic coefficients that define the axisymmetric part of the internal geomagnetic field (i.e. g_n⁰ ± g_n⁰). Numerical estimates of these uncertainties based on an analytic equation for axisymmetric field lines are in excellent agreement with independent computational estimates based on stepwise numerical integration along magnetic field lines. This comparison confirms the accuracy of the computer program used in the present paper to estimate the uncertainties in magnetic-field-line tracing that arise from published standard errors in the full set of spherical harmonic coefficients, which define the complete (non-axisymmetric) internal geomagnetic field (i.e. g_n^m ± g_n^m and h_n^m ± h_n^m). An algorithm is formulated that greatly reduces the computing time required to estimate these uncertainties in magnetic-field-line tracing. The validity of this algorithm is checked numerically for both the axisymmetric part of the internal geomagnetic field in the general case (1 n 10) and the complete internal geomagnetic field in a restrictive case (0 m n, 1 n 3). On this basis it is assumed that the algorithm can be used with confidence in those cases for which the computing time would otherwise be prohibitively long. For the complete internal geomagnetic field, the maximum characteristic uncertainty in the geocentric distance of a field line that crosses the geomagnetic equator at a nominal dipolar distance of 2 R_E is typically 100 km. The corresponding characteristic uncertainty for a field line that crosses the geomagnetic equator at a nominal dipolar distance of 6 R_E is typically 500 km. Histograms and scatter plots showing the characteristic uncertainties associated with magnetic-field-line tracing in the magnetosphere are presented for a range of illustrative examples. Finally, estimates are given for the maximum uncertainties in the locations of the conjugate points of selected geophysical observatories. Numerical estimates of the uncertainties in magnetic-field-line tracing in the magnetosphere, including the associated uncertainties in thelocations of the conjugate points of geophysical observatories, should be regarded as first approximations in the sense that these estimates are only as accurate as the published standard errors in the full set of spherical harmomic coefficients. As in the preceding paper, howerver, all computational techniques developed in this paper can be used to derive more realistic estimates of the uncertainties in magnetic-field-line tracing in the magnetosphere, following further progress in the determination of more accurate standard errors in the spherical harmonic coefficients.Also Visiting Reader in Physics, University of Sussex, Palmer, Brighton, BN1 9QH, UK  相似文献   

Formation of the Bencubbin polymict meteoritic breccia     

Gregory W. Kallemeyn  William V. Boynton  John Willis  John T. Wasson 《Geochimica et cosmochimica acta》1978,42(5):507-515

The Bencubbin meteorite is a polymict breccia consisting of a host fraction of ~60% metal and ~40% ferromagnesian silicates and a selection of carbonaceous, ordinary and ‘enstatite’ chondritic clasts. Concentrations of 27 elements were determined by neutron activation in replicate samples of the host silicates and the ordinary and carbonaceous chondritic clasts; 12 elements were determined in the host metal. Compositional data for the ordinary chondrite clast indicate a classification of LL4 ± 1. Refractory element data for the carbonaceous chondrite clast indicate that it belongs to the CI-CM-CO clan; its volatile element abundances are intermediate between those of CM and CO chondrites. Abundances of nonvolatile elements in the silicate host are similar to those in the carbonaceous chondrite clast and in CM chondrites; the rare earths are unfractionated. We conclude that it is not achondritic as previously designated, but chondritic and that it is probably related to the CI-CM-CO clan; its volatile abundances are lower than those in CO chondrites. Oxygen isotope data are consistent with these classifications. Host metal in Bencubbin and in the closely related Weatherford meteorite has low abundances of moderately volatile siderophiles; among iron meteorite groups its nearest relative is group IIIF.We suggest that Bencubbin and Weatherford formed as a result of an impact event on a carbonaceous chondrite regolith. The impact generated an ‘instant magma’ that trapped and surrounded regolithic clasts to form the polymict breccia. The parent of this ‘magma’ was probably the regolith itself, perhaps mainly consisting of the so-called ‘enstatite’ chondrite materials. Accretion of such a variety of materials to a small parent body was probably only possible in the asteroid belt.  相似文献   

Late Holocene sea-level changes and isostasy in western Denmark     

W. Roland Gehrels  Katie Szkornik  Jason R. Kirby  William A. Marshall  Jørn B.T. Pedersen 《Quaternary Research》2006,66(2):288-302

Cores and exposed cliff sections in salt marshes around Ho Bugt, a tidal embayment in the northernmost part of the Danish Wadden Sea, were subjected to ¹⁴C dating and litho- and biostratigraphical analyses to reconstruct paleoenvironmental changes and to establish a late Holocene relative sea-level history. Four stages in the late Holocene development of Ho Bugt can be identified: (1) groundwater-table rise and growth of basal peat (from at least 2300 BC to AD 0); (2) salt-marsh formation (0 to AD 250); (3) a freshening phase (AD 250 to AD 1600?), culminating in the drying out of the marshes and producing a distinct black horizon followed by an aeolian phase with sand deposition; and (4) renewed salt-marsh deposition (AD 1600? to present). From 16 calibrated AMS radiocarbon ages on fossil plant fragments and 4 calibrated conventional radiocarbon ages on peat, we reconstructed a local relative sea-level history that shows a steady sea-level rise of 4 m since 4000 cal yr BP. Contrary to suggestions made in the literature, the relative sea-level record of Ho Bugt does not contain a late Holocene highstand. Relative sea-level changes at Ho Bugt are controlled by glacio-isostatic subsidence and can be duplicated by a glacial isostatic adjustment model in which no water is added to the world's oceans after ca. 5000 cal yr BP.  相似文献   

'Dad says I'm tied to a shooting star!' Grounding (research on) British expatriate belonging   总被引：1，自引：0，他引：1  

Katie Walsh 《Area》2006,38(3):268-278

This paper analyses one British woman's everyday practices of belonging as she negotiates expatriate life in Dubai, United Arab Emirates. In doing so, it responds to widespread calls to ground research on processes of transnationalism and diaspora by drawing on 18 months of ethnographic research and adopting a three-stranded analytical framework to reflect on the significance of domesticity, intimacy and foreignness in expatriate belonging. The author focuses on a single research subject to draw attention to a particular British expatriate experience otherwise neglected in migration research and the paper resonates with theoretical literatures aiming to challenge the binary divisions of geographies of belonging, including attachment/detachment.  相似文献   

Mapping memorials for Edith Cavell on the colonial edge     

Katie Pickles 《New Zealand geographer》2006,62(1):13-24

Abstract:  This paper identifies and explains the pattern of memorialization in New Zealand for English nurse Edith Cavell, arguing that while the influences of empire and colonial mimicry provided a strong overarching framework, local context and parochial expressions were also strong at the colonial edge. In 1915 Cavell was executed by the occupying German forces in Belgium for her resistance work. The general transnational pattern of remembrance that resulted from the huge reaction to her death is explained. The paper then turns to the New Zealand memorialization of Cavell. With reference to monuments for other medical women, and addressing where Cavell does not appear in the landscape, the last section contextualizes Cavell's New Zealand memorialization.  相似文献   

Sex, politics and empire: A post-colonial geography - Richard Phillips     

Katie Pickles 《New Zealand geographer》2006,62(3):241-242

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NEGOTIATING DUALISMS: WOMEN, LOCALITY AND EMPLOYMENT OPPORTUNITIES IN OAXACA CITY, MEXICO     

Katie D. Willis 《Singapore journal of tropical geography》1997,17(2):195-212

This paper examines the validity of the public/private and reproductive/productive dichotomies commonly adopted in the analysis of gender and employment. It considers three aspects of the dualisms: spatial division, activity patterns and the construction of identities. The discussion is based on fieldwork undertaken in three districts of Oaxaca City, Mexico, between 1992 and 1995. While recognising the usefulness of spatial dualisms within Mexican cities, the paper seeks to identify the ways in which class and location within the urban space affect the construction of the boundary between “public” and “private”, women's “employment” experiences, and women's identities.  相似文献   

Statistics of the largest geomagnetic storms per solar cycle (1844–1993)     

D. M. Willis  P. R. Stevens  S. R. Crothers 《Annales Geophysicae》1997,15(6):719-728

A previous application of extreme-value statistics to the first, second and third largest geomagnetic storms per solar cycle for nine solar cycles is extended to fourteen solar cycles (1844–1993). The intensity of a geomagnetic storm is measured by the magnitude of the daily aa index, rather than the half-daily aa index used previously. Values of the conventional aa index (1868– 1993), supplemented by the Helsinki Ak index (1844–1880), provide an almost continuous, and largely homogeneous, daily measure of geomagnetic activity over an interval of 150 years. As in the earlier investigation, analytic expressions giving the probabilities of the three greatest storms (extreme values) per solar cycle, as continuous functions of storm magnitude (ad), are obtained by least-squares fitting of the observations to the appropriate theoretical extreme-value probability functions. These expressions are used to obtain the statistical characteristics of the extreme values; namely, the mode, median, mean, standard deviation and relative dispersion. Since the Ak index may not provide an entirely homogeneous extension of the aa index, the statistical analysis is performed separately for twelve solar cycles (1868–1993), as well as nine solar cycles (1868–1967). The results are utilized to determine the expected ranges of the extreme values as a function of the number of solar cycles. For fourteen solar cycles, the expected ranges of the daily aa index for the first, second and third largest geomagnetic storms per solar cycle decrease monotonically in magnitude, contrary to the situation for the half-daily aa index over nine solar cycles. The observed range of the first extreme daily aa index for fourteen solar cycles is 159–352 nT and for twelve solar cycles is 215–352 nT. In a group of 100 solar cycles the expected ranges are expanded to 137–539 and 177–511 nT, which represent increases of 108% and 144% in the respective ranges. Thus there is at least a 99% probability that the daily aa index willAlso Visiting Reader in Physics, University of Sussex, Palmer, Brighton, BN1 9QH, UK  相似文献   

Applications géodésiques du système DORIS à l'Institut géographique national     

Pascal Willis  Claude Boucher  Hervé Fagard  Zuheir Altamimi 《Comptes Rendus Geoscience》2005,337(7):653-662

IGN is in charge of the installation and maintenance of the DORIS orbit determination network. More recently, in collaboration with JPL, precise geodetic computations were performed. The goal of this paper is to recall the various historic contributions of IGN to the DORIS system in their international context and then to describe a new estimation technique developed for a multi-satellite mode, making full profit of a better modeling for satellites and ground clocks as well as tropospheric correction parameters. Derived geodetic results demonstrate a precision in the order of 1 cm for station positions. To cite this article: P. Willis et al., C. R. Geoscience 337 (2005).  相似文献