Carbonate Sediment Deposits on the Reef Front Around Oahu, Hawaii

Large sediment deposits on the reef front around Oahu are a possible resource for replenishing eroded beaches. High-resolution subbottom profiles clearly depict the deposits in three study areas: Kailua Bay off the windward coast, Makua to Kahe Point off the leeward coast, and Camp Erdman to Waimea off the north coast. Most of the sediment is in water depths between 20 and 100 m, resting on submerged shelves created during lowstands of sea level. The mapped deposits have a volume of about 4 × 10⁸ m³ in water depths less than 100 m, being thickest off the mouth of channels carved into the modern insular shelf, from which most of the sediment issues. Vibracore samples contain various amounts of sediment of similar size to the sand on Oahu beaches, with the most compatible prospects located off Makaha, Haleiwa, and Camp Erdman, and the least compatible ones located in Kailua Bay. Laboratory tests show a positive correlation of abrasion with Halimeda content: samples from Kailua Bay suffered high amounts of attrition, but others were comparable to tested beach samples. The common gray color of the offshore sediment, aesthetically undesirable for sand on popular tourist beaches, was diminished in the laboratory by soaking in heated hydrogen peroxide.     

The East Pacific Rise and its flanks 8–18° N: History of segmentation,propagation and spreading direction based on SeaMARC II and Sea Beam studies

SeaMARC II and Sea Beam bathymetric data are combined to create a chart of the East Pacific Rise (EPR) from 8°N to 18°N reaching at least 1 Ma onto the rise flanks in most places. Based on these data as well as SeaMARC II side scan sonar mosaics we offer the following observations and conclusions. The EPR is segmented by ridge axis discontinuities such that the average segment lengths in the area are 360 km for first-order segments, 140 km for second-order segments, 52 km for third-order segments, and 13 km for fourth-order segments. All three first-order discontinuities are transform faults. Where the rise axis is a bathymetric high, second-order discontinuities are overlapping spreading centers (OSCs), usually with a distinctive 3:1 overlap to offset ratio. The off-axis discordant zones created by the OSCs are V-shaped in plan view indicating along axis migration at rates of 40–100 mm yr^–1. The discordant zones consist of discrete abandoned ridge tips and overlap basins within a broad wake of anomalously deep bathymetry and high crustal magnetization. The discordant zones indicate that OSCs have commenced at different times and have migrated in different directions. This rules out any linkage between OSCs and a hot spot reference frame. The spacing of abandoned ridges indicates a recurrence interval for ridge abandonment of 20,000–200,000 yrs for OSCs with an average interval of approximately 100,000 yrs. Where the rise axis is a bathymetric low, the only second-order discontinuity mapped is a right-stepping jog in the axial rift valley. The discordant zone consists of a V-shaped wake of elongated deeps and interlocking ridges, similar to the wakes of second-order discontinuities on slow-spreading ridges. At the second-order segment level, long segments tend to lengthen at the expense of neighboring shorter segments. This can be understood if segments can be approximated by cracks, because the propagation force at a crack tip is directly proportional to crack length.There has been a counter-clockwise change in the direction of spreading on the EPR between 8 and 18° N during the last 1 Ma. The cumulative change has been 3°–6°, producing opening across the Orozco and Siqueiros transform faults and closing across the Clipperton transform. The instantaneous present-day Cocos-Pacific pole is located at approximately 38.4° N, 109.5° W with an angular rotation rate of 2.10° m.y.^–1 This change in spreading direction explains the predominance of right-stepping discontinuities of orders 2–4 along the Siqueiros-Clipperton and Orozco-Rivera segments, but does not explain other aspects of segmentation which are thought to be linked to patterns of melt supply to the ridge axis.There are 23 significant seamount chains in the mapped area and most are created very near the spreading axis. Nearly all of the seamount chains have trends which fall between the absolute and relative plate motion vectors.     

运用聚丙烯酰胺凝胶电泳分析方法对中国卤虫(Artemia)同工酶变异的研究

本文提出运用聚丙烯酰胺凝胶电泳的方法,对我国山东半岛几个盐场中的卤虫的十一种同工酶变异进行分析。其中三种同工酶,乳酸脱氢酶(LDH),苹果酸脱氢酶(MDH),以及四唑氧化酶(TO),表现为多态酶,并且存在盐场内和盐场间的相对变异。该项技术将有助于基础科学的研究以及在水产养殖中用来筛选和辨别卤虫的不同品系。     

Long term changes in Zostera meadows in the Berre lagoon (Provence, Mediterranean Sea)

The Berre lagoon (Provence, France), one of the largest Mediterranean brackish lagoons (155 km²), was occupied, at the turn of the 20th century, by extensive Zostera meadows (Zostera marina and probably Zostera noltii; perhaps over 6000 ha). Subsequently, the lagoon was disturbed by urban and industrial pollution and, from 1966, by the diversion of the Durance River. This resulted in a 10–49-fold and 8–31-fold increase of the freshwater and silt inputs, respectively. By means of digital analysis of aerial photographs for the years 1944, 1992, 1998 and 2004, coupled with ground truth for the last three dates, we mapped the Zostera meadows. The replacement of Z. marina by Z. noltii, the latter species being already dominant in the 1970s, was completed in 1990. In parallel to this substitution, the Zostera beds underwent a dramatic decline. Their depth limit, which was (6–9) m in the early 20th century, withdrew to 3.5, 3, 1 and less than 1 m by 1944, the 1970s, 1992 and 1998, respectively. Since 1998, Zostera must be considered as functionally extinct. The total surface area of Zostera meadows was of the order of 1.5 ha in 2004. In an attempt to alleviate disturbance, the input of freshwater and silt from the Durance River was significantly reduced from the early 1980s and 1990s respectively. Similarly, from the 1970s to the 1990s, urban and domestic pollution was drastically reduced. Despite these steps, Zostera meadows continued to shrink to near extinction. The lagoon has shifted from a system dominated by seagrass beds to a system with bare silt bottoms, which now occupy most of the lagoon. The reasons could be, in addition to continuing nutrient inputs, the resuspension of silt, no longer trapped under the seagrass canopy, during wind episodes, which are frequent in the area, and/or the release of nutrients from the bare silt habitat, which would constitute an indication of a possible hysteresis of the system. However, since 2000, the establishment of the mussel Mytilus galloprovincialis, a drop in turbidity and a slight, inconspicuous progression of Z. noltii could be the harbinger of a reverse shift of the system.     

Improving the sampling strategy for point-to-point line-of-sight modelling in urban environments

Visibility modelling calculates what an observer could theoretically see in the surrounding region based on a digital model of the landscape. In some cases, it is not necessary, nor desirable, to compute the visibility of an entire region (i.e. a viewshed), but instead it is sufficient and more efficient to calculate the visibility from point to point, or from a point to a small set of points, such as computing the intervisibility of predators and prey in an agent-based simulation. This paper explores how different line-of-sight (LoS) sample ordering strategies increase the number of early target rejections, where the target is considered to be obscured from view, thereby improving the computational efficiency of the LoS algorithm. This is of particular importance in dynamic environments where the locations of the observers, targets and other surface objects are being frequently updated. Trials were conducted in three UK cities, demonstrating a robust fivefold increase in performance for two strategies (hop, divide and conquer). The paper concludes that sample ordering methods do impact overall efficiency, and that approaches which disperse samples along the LoS perform better in urban regions than incremental scan methods. The divide and conquer method minimises elevation interception queries, making it suitable when elevation models are held on disk rather than in memory, while the hopping strategy was equally fast, algorithmically simpler, with minimal overhead for visible target cases.     

Book reviews

Third World politics: a concise introduction

J. Haynes, 1996

Blackwell, Oxford

15 × 23 cm, viii + 227pp., ISBN 0–631–19778–8, £14.99/US$19.95 (soft)

Thirdspace: journeys to Los Angeles and other real‐and‐imagined places

E.W. Soja, 1996

Blackwell, Cambridge, MA

17 × 25 cm, xii + 334pp., ISBN 1–55786–675–9, £14.99/US$20.95 (soft)

Alpine Tasmania: an illustrated guide to the flora and vegetation

J. Kirkpatrick, 1997

Oxford University Press, Melbourne

14 × 22 cm, xii+ 196 pp., ISBN 0–19–553753‐X, A$24.95

Spatial behavior: a geographic perspective

R.G. Golledge. & R.J. Stimson, 1997

The Guilford Press, New York

16 × 24 cm, xx + 620 pp., ISBN 1–57230–050–7, A$39.95 (soft)

Pacific Rim development: integration and globalisation in the Asia‐Pacific economy,(Studies in World Affairs XIII)

P.J. Rimmer (ed.), 1997

Allen & Unwin, Sydney

14 × 22 cm, xiii + 294 pp., ISBN 1–86373–978–5, A$24.95 (soft)     

Vibrational analysis of dioptase Cu6Si6O18 · 6(H2O) and its puckered six-membered ring

The normal modes of vibration and their frequencies are calculated for dioptase, a mineral whose crystal structure (space group R or C _3i ² ) consists of puckered six-membered silicate rings (Si₆O₁₈) linked by Cu²⁺ ions and H₂O groups. The calculation employs a valence force potential consisting of central interactions between nearest neighbors and bond-bending interactions centered at the Si⁴⁺ and Cu²⁺ ions. The force constants are determined by fitting the calculated frequencies to values obtained by measuring the single-crystal Raman spectra. The calculated frequencies are in reasonable agreement with experiment, permitting assignment of normal modes to the observed spectral frequencies. Considerable mixing of Cu and H₂O motions with those of the ring is found for the Raman-active modes below 430 cm^-1. The normal modes and frequencies of the hypothetical isolated ring with C _3i symmetry are determined by neglecting all interactions between the rings and the surrounding Cu and H₂O. The identification of normal modes characteristic of the puckered six-membered silicate rings and the effect of the environment on these modes may prove useful in the interpretation of the Raman spectra of amorphous silicates.     

Assessing disaster needs in megacities: Perspectives from developing countries

Megacities are extreme manifestations of urban complexity that present aid agencies with major disaster assessment challenges. Geographers can contribute to improving megacity disaster assessments by: 1) defining megacity disasters; 2) improving socioeconomic measures of disaster to allow for clearer differentiation of effects among different population sub-groups; 3) specifying criteria for identifying thresholds of disaster and trends in the status of disaster-affected populations; and 4) developing credible data collection and analysis methods appropriate for complex urban environments. In addition, long term research is needed to encourage the formulation of models of megacity life that provide better understanding of human survival under normal conditions of severe adversity.The views expressed herein are entirely those of the author and are not attributable to organizations which have sponsored the author's research.     

Particle size distribution of cataclastic fault materials from Southern California: A 3-D study

The particle size distributions of fault gouge from the San Andreas, the San Gabriel, and the Lopez Canyon faults in Southern California were measured using sieving and Coulter-Counter techniques over a range of particle sizes from 2 m to 16 mm. The distributions were found to be power law (fractal) for the smaller fragments and log-normal by mass for sizes near and above the peak size. The apparent fractal dimensionD of the smaller particles in gouge samples from the San Andreas fault, the San Gabriel fault and the Lopez Canyon gouge were 2.4–3.6, 2.6–2.9 and 2.4–3.0, respectively. The averageD for the Lopez Canyon gouge was 2.7±0.2, which is in agreement with earlier studies of this gouge using planar 2-D sections. The fractal dimension of the finer fragments from all three faults is observed to be correlated with the peak fragment size, with finer gouges tending to have a largerD. A computer automaton is used to show that this observation may be explained as resulting from a fragmentation process which has a grinding limit at which particle reduction stops.