Tree population dynamics of three altitudinal vegetation communities on Mount Cameroon (1989�C2004)

Changes in permanent sample plots in the lowland,submontane and montane forests on Mount Cameroon(4,095 m above sea level),an active volcano,are described for 15 years from 1989 to 2004.Throughout the study period,the stocking level of trees with a diameter at breast height(DBH) ≥ 10 cm in the three forests were lower than in pan-tropical stands suggesting a significant impact of volcanic and human-related activities on the vegetation communities on the mountain.Annual mortality rates in the submontane and montane forests were consistent with those reported for comparable altitudinal ranges in the Blue Mountains of Jamaica.The annual mortality rate was higher in the lowland forest than other lowland sites included.Divergence between recruitment and mortality rates was large suggesting that the three vegetation communities have not reached their climax.The seven-year difference in half-life of large trees(with a DBH ≥ 50 cm) in the submontane and montane forests suggests an altitudinal effect on turnover of larger trees that in turn contributes to the frequent small stature of high altitude forests.There was little evidence of an altitudinal effect on species turnover and growth rate.This finding supports generalizations about the zero effect of growth on the stature of high altitude trees.Understanding forest dynamics is crucially important in the management of tropical montane environmentsand in this instance particularly so given the recent creation of the Mount Cameroon National Park.     

Suspended sediment transport during tropical‐cyclone floods in Fiji

Flow records, rising‐stage sediment samplers, and a sand suspension model are used to examine suspended sediment concentrations during major floods caused by tropical cyclones TC Joni and TC Kina in the Rewa River, Fiji. The highest concentrations of total suspended solids were measured during the early stages of TC Kina. The suspension model predicts higher sand concentrations for TC Kina compared with TC Joni because of the larger slope and higher shear stresses during Kina. Extremely high wash load concentrations early in TC Kina are at least partly due to remobilization of fine sediment deposited during the earlier TC Joni flood. Samples from the TC Kina had volumetric concentrations larger than 5%, indicating hyperconcentrated streamflows. Mass‐density shear stresses in the hyperconcentrated flows are up 1·6 times larger than clear‐water shear stresses, but they occur early during low stages of the flood and probably do not result in severe bed erosion. Copyright © 2002 John Wiley & Sons, Ltd.     

Some useful approximations to generalized ray theory for regional distance seismograms

Summary . Seismograms recorded at regional distances (2°–12°) are quite complicated due to the waveguide nature of the crust. Generalized ray theory can be used to model the body waves in this distance range but a very large number of rays is required. Here I present a series of approximations to streamline generalized ray theory for the waveguide problem. If a layer over a half-space is used for the structure, then the de Hoop contour for a given ray is most strongly dependent on the fastest velocity of any leg of the ray. This results in analytic approximations to locate the contour. Each ray has two body wave arrivals (a headwave and a reflected arrival) so the displacement response of the ray need only be evaluated at a few points in time about the two arrival times and interpolated in between. A change in structure (increasing crustal thickness or Pn velocity) most strongly affects the relative timing of the headwave and the reflected arrival, so it is possible to 'stretch' or 'squeeze' the waveform of a representative model to simulate a whole suite of models.
Also discussed is the applicability of a single layer over a half-space structure for modelling the observed regional distance waveforms for shallow earthquakes. At periods greater than a few seconds crustal layering can be replaced by a single layer having the appropriate average velocities. Lateral variations in crustal thickness with scale lengths of less than about 100 km can also be modelled with a simple horizontal layer of appropriate average thickness.     

Geothermobarometry of UHP and HP eclogites and schists – an evaluation of equilibria among garnet–clinopyroxene–kyanite–phengite–coesite/quartz

Geothermometry of eclogites and other high pressure (HP)/ultrahigh‐pressure (UHP) rocks has been a challenge, due to severe problems related to the reliability of the garnet–clinopyroxene Fe–Mg exchange thermometer to omphacite‐bearing assemblages. Likewise, reliable geobarometers for eclogites and related HP/UHP rocks are scarce. In this paper, a set of internally consistent geothermobarometric expressions have been formulated for reactions between the UHP assemblage garnet–clinopyroxene–kyanite–phengite–coesite, and the corresponding HP assemblage garnet–clinopyroxene–kyanite–phengite–quartz. In the system KCMASH, the end members grossular (Grs) and pyrope (Prp) in garnet, diopside (Di) in clinopyroxene, muscovite (Ms) and celadonite (Cel) in phengite together with kyanite and coesite or quartz define invariant points in the coesite and quartz stability field, respectively, depending on which SiO₂ polymorph is stable. Thus, a set of net transfer reactions including these end members will uniquely define equilibrium temperatures and pressures for phengite–kyanite–SiO₂‐bearing eclogites. Application to relevant eclogites from various localities worldwide show good consistency with petrographic evidence. Eclogites containing either coesite or polycrystalline quartz after coesite all plot within the coesite stability field, while typical quartz‐bearing eclogites with no evidence of former coesite fall within the quartz stability field. Diamondiferous coesite–kyanite eclogite and grospydite xenoliths in kimberlites all fall into the diamond stability field. The present method also yields consistent values as compared with the garnet–clinopyroxene Fe–Mg geothermometer for these kinds of rocks, but also indicates some unsystematic scatter of the latter thermometer. The net transfer geothermobarometric method presented in this paper is suggested to be less affected by later thermal re‐equilibration than common cation exchange thermometers.     

The 2dF Galaxy Redshift Survey: galaxy luminosity functions per spectral type

We calculate the optical b _J luminosity function (LF) of the 2dF Galaxy Redshift Survey (2dFGRS) for different subsets defined by their spectral properties. These spectrally selected subsets are defined using a new parameter, η , which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter η identifies the average emission- and absorption-line strength in the galaxy rest frame spectrum, and hence is a useful indicator of the present star formation. We use a total of 75 000 galaxies in our calculations, chosen from a sample of high signal-to-noise ratio, low-redshift galaxies observed before 2001 January. We find that there is a systematic steepening of the faint-end slope ( α ) as one moves from passive  ( α =-0.54)  to active  ( α =-1.50)  star-forming galaxies, and that there is also a corresponding faintening of the rest frame characteristic magnitude   M *-5 log₁₀( h )  (from −19.6 to −19.2). We also show that the Schechter function provides a poor fit to the quiescent (Type 1) LF for very faint galaxies  [ M _{b J}-5 log₁₀( h )  fainter than −16.0], perhaps suggesting the presence of a significant dwarf population. The LFs presented here give a precise confirmation of the trends seen previously in a much smaller preliminary 2dFGRS sample, and in other surveys. We also present a new procedure for determining self-consistent k -corrections, and investigate possible fibre-aperture biases.     

The 2dF Galaxy Redshift Survey: the dependence of galaxy clustering on luminosity and spectral type

We investigate the dependence of galaxy clustering on luminosity and spectral type using the 2dF Galaxy Redshift Survey (2dFGRS). Spectral types are assigned using the principal-component analysis of Madgwick et al. We divide the sample into two broad spectral classes: galaxies with strong emission lines ('late types') and more quiescent galaxies ('early types'). We measure the clustering in real space, free from any distortion of the clustering pattern owing to peculiar velocities, for a series of volume-limited samples. The projected correlation functions of both spectral types are well described by a power law for transverse separations in the range  2<( σ / h ^-1 Mpc)<15  , with a marginally steeper slope for early types than late types. Both early and late types have approximately the same dependence of clustering strength on luminosity, with the clustering amplitude increasing by a factor of ∼2.5 between L * and 4 L *. At all luminosities, however, the correlation function amplitude for the early types is ∼50 per cent higher than that of the late types. These results support the view that luminosity, and not type, is the dominant factor in determining how the clustering strength of the whole galaxy population varies with luminosity.     

A Comparison of Field Techniques for Confirming Dense Nonaqueous Phase Liquids

Dense nonaqueous phase liquids (DNAPLs) are immiscible fluids with a specific gravity greater than, water. When present, DNAPLs present a serious and long-term source of continued ground water and soil contamination (Pankow and Cherry 1996). Accurate characterization and delineation of DNAPL in the subsurface is critical for evaluating restoration potential and for remedy design at a site. However, obtaining accurate and definitive direct evidence of DNAPL is difficult. A field study was recently performed comparing several approaches to DNAPL characterization at a site where anecdotal and limited direct evidence of DNAPL exists. The techniques evaluated included a three-dimensional high-resolution seismic survey, field screening of soil cores with a flame ionization detector (FID)/organic vapor analyzer (OVA), hydrophobic (Sudan IV) dye-impregnated reactive FLUTe® (Flexible Liner Underground Technologies) liner material in combination with Rotasonic drill cores, centrifuged soil with Sudan IV dye, ultraviolet light (UV) fluorescence, a Geoprobe® Membrane Interface Probe (MIP®), and phase equilibrium partitioning evaluations based on laboratory analysis of soil samples. Sonic drilling provided reliable continuous cores from which minor soil structures could be evaluated and screened with an OVA, The screening provided reliable preliminary data for identifying likely DNAPL zones and for selecting samples for further analyses. The FLUTe liner material provided the primary direct evidence of the presence of DNAPL and reliable information on the thickness and nature of its occurrence (i.e., pooled or ganglia). The MIP system provided good information regarding the subsurface lithology and rapid identification and delineation of probable DNAPL areas. The three-dimensional seismic survey was of minimal benefit to this study, and the centrifuging of samples with Sudan IV dye and the use of UV fluorescence provided no benefit. Results of phase equilibrium partitioning concentration calculations for soil samples (to infer the presence of DNAPL) were in good agreement with the site screening data. Additionally, screening data compared well with previous ground water data and supported using 1% of the pure phase solubility limit of Freon 113 (2 mg/L) as an initial means to define the DNAPL study area. Based on the results of this study, the preferred approach for identifying and delineating DNAPL in the subsurface is to initially evaluate ground water data and define an area where dissolved concentrations of the target analyte(s) approach 1% of the pure phase solubility limit. Within this study area, the MIP device is used to more specifically identify areas and lithologic zones where DNAPL may have accumulated. Core samples (either Rotasonic or Geoprobe) are then collected from zones where MIP readings are indicative of the presence of DNAPL. Soil samples from the free-product portions of the core(s) are then submitted to a laboratory for positive analyte identification. Soil analyses are then combined with site-specific geotechnical information (i.e., fraction organic carbon, soil bulk density, and porosity) and equilibrium partitioning algorithms used to estimate concentrations of organic contaminants in soil samples that would be indicative of free product. Used in combination, the soil analysis and the MIP records appear to provide accurate DNAPL identification and delineation.     

Mean thermal and albedo behavior of the Mars surface and atmosphere over a Martian year

A Mars average data set (MADS) has been constructed from thermal and albedo measurements of the Viking Infrared Thermal Mapper; by merging information from all longitudes; and, ensuring reasonably complete longitudinal sampling, a representation of mean Mars behavior is obtained. Brightness temperatures at 7, 9, 11, 15, and 20 μm and albedo information in the band 0.3–3.0 μm have been binned using 2° latitude strips, 24 times of day, 3 emission angle intervals, and 23 nonoverlapping L_s periods covering 1.43 Mars years starting at L_s = 84°. The MADS is ideally suited to parametric study of latitudinal, diurnal, angular, and seasonal dependences. Data are presented for surface thermal and albedo behavior in clear and dusty atmospheric conditions; the thermal response of the atmospheric temperature to a major dust storm is found to be consistent with Mariner 9 data from the 1971 storm. Examples of use of the MADS, which is available through the Mars Consortium, indicate how averaged data reveal specific surface and atmospheric phenomena.