Some effects of sewage discharge upon phytoplankton in Hong Kong

The coastal waters of Hong Kong constitute a transition from estuarine conditions in the west to more oceanic conditions in the east, with a major discharge of untreated sewage located at the mid-point. Chlorophyll a was determined and net phytoplankton was sampled at 45 stations throughout this transition. Over a period of 20 months, chlorophyll a values rarely exceeded 2 μg l.^?1 in unpolluted coastal waters. Estuarine waters generally contained 2–6 μg l.^?1 and, in waters influenced by sewage discharge, values sometimes exceeded 20 μg l.^?1. There was no evidence of a reduction in taxonomic diversity in polluted areas except in summer, when the net phytoplankton was dominated by Chaetoceros spp. In the autumn and early winter, Skeletonema costatum was abundant in the central polluted areas.     

Origin of CFB Magmatism: Multi-tiered Intracrustal Picrite-Rhyolite Magmatic Plumbing at Spitzkoppe, Western Namibia, during Early Cretaceous Etendeka Magmatism

Early Cretaceous tholeiitic picrite-to-rhyolite dykes aroundSpitzkoppe, western Namibia, are part of the extensive HentiesBay–Outjo swarm, penecontemporaneous with 132 Ma Etendekalavas 100 km to the NW. Although only intermediate to rhyoliticdykes contain clinopyroxene phenocrysts, the behaviour of Ca,Al and Sc in the dyke suite shows that liquidus clinopyroxene—togetherwith olivine—was a fractionating phase when MgO fell to9 wt %. Both a plot of CIPW normative di–hy–ol–ne–Qand modelling using (p)MELTS show that a mid-crustal pressureof 0·6 GPa is consistent with this early clinopyroxenesaturation. Sr, Nd, Hf and Pb isotope variations all show trendsconsistent with AFC contamination (assimilation linked to fractionalcrystallization), involving Pan-African Damara belt continentalcrust. The geochemical variation, including isenthalpic AFCmodelling using (p)MELTS, suggests that the picrites (olivine-richcumulate suspensions) were interacting with granulite-faciesmetamorphic lower crust, the intermediate compositions withamphibolite-facies middle crust, and the rhyolitic dykes (anda few of the basalts) with the Pan-African granites of the uppercrust. The calculated densities of the magmas fall systematicallyfrom picrite to rhyolite and suggest a magmatic system resemblinga stack of sills throughout the crust beneath Spitzkoppe, withthe storage and fractionation depth of each magma fraction controlledby its density. Elemental and isotopic features of the 20 wt% MgO picrites (including Os isotopes) suggest that their parentalmelts probably originated by fusion of mid-ocean ridge basalt(MORB) source convecting mantle, followed by limited reactionwith sub-continental lithospheric mantle metasomatized justprior to the formation of the parental magmas. Many of the distinctivefeatures of large-volume picritic–basaltic magmas maynot be derived from their ultimate mantle sources, but may insteadbe the results of complex polybaric fractional crystallizationand multi-component crustal contamination. KEY WORDS: flood basalts; Spitzkoppe; picrite; trace elements; hafnium isotopes; Etendeka     

Reducing Drift and Bias of a Global Ocean Model by Frequency-Dependent Nudging

Frequency-dependent nudging is applied to a coarse resolution (nominal 1°) global ocean model to suppress its drift and bias, and the impact of the nudging on the skill of the model is assessed. The nudging is applied to temperature and salinity in frequency bands centred on 0 and 1 cycles per year. As expected, the nudging significantly reduces the biases in the long-term mean and annual cycle of temperature, salinity, and sea level. By comparing the simulated (i) sea surface temperature with operational analyses based on observations, (ii) vertical profiles of temperature and salinity with observations made by Argo floats, and (iii) sea level with altimeter observations, it is shown that the skill of the model in simulating variability about the annual cycle is also improved. The potential benefit of applying frequency-dependent nudging to the ocean component of a coupled atmosphere–ocean model is discussed.     

Passive interference localization within the GNSS environmental monitoring system (GEMS): TDOA aspects

Due to their low power levels, global positioning system (GPS) signals are very susceptible to interference from intentional and unintentional sources. With ever increasing reliance on global navigation satellite systems (GNSS) for everyday operation of safety–critical infrastructure, the detection, localization and elimination of interference to GNSS is of paramount importance. The GNSS environmental monitoring system (GEMS) II provides the capability to detect and localize interferers in real time in a given area. It consists of a number of spatially distributed sensor nodes connected to a central processing unit. Interference is localized using hybrid direction-of-arrival (DOA) and time-difference-of-arrival (TDOA) techniques. We describe the GEMS II environment and provide an in-depth analysis and evaluation of the TDOA aspects of the system. During evaluation, signals generated from Spirent GPS signal generators as well as data from actual field-test trials are used to provide extensive performance analysis and comparison, with a view to final system integration.     

Supermagnetic enhancement,superparamagnetism, and archaeological soils

A range of mineral magnetic measurements have been carried out on archaeological sediments from Orkney and Cyprus. In a soil profile from Orkney, a magnetic enhancement factor of over 200 is observed in susceptibility data between the bedrock and a Norse sediment. The magnetic enhancement is associated with an increase in superparamagnetic grains probably caused by burning. Until now it has proved difficult to confirm the presence of superparamagnetic grains in natural samples using room temperature magnetic measurements. However, clear differences are to be found between the hysteresis loops of various magnetic domain states, including superparamagnetism. An algorithm has been developed to unmix hysteresis loops in terms of constituent domain states of ferrimagnetic iron oxides. Unmixing 128 hysteresis loops of archaeological sediments has shown that the dominant domain state in all sediments is superparamagnetic. Remarkably uniform superparamagnetic grain sizes of between 80 and 95 Å were found for all 128 sediments. © 1999 John Wiley & Sons, Inc.     

The Big Circles in Jordan: First absolute ages using rock luminescence surface dating

In this study, we provide the first absolute ages for a Big Circle megalithic structure in Jordan, using rock surface luminescence dating of the buried surface of rocks collected from circle J4 in southern Jordan. Five rocks were used for this study. All rocks showed evidence of previous daylight exposure before being used in the construction of the circle. The exposure was sufficient to bleach the latent luminescence signal to a negligible level compared to the subsequent burial dose. Three rocks gave indistinguishable ages, and were last exposed to daylight in 1500 ± 100 BCE; this is very likely to be the date of circle construction. Two others gave younger ages, indicating later disturbance or reworking. These new results provide very strong evidence for construction during the Late Bronze Age, and refute the earlier hypothesis of construction during Umayyad period (661–750 CE) as a hunting trap.     

Melting relations of some oceanic basalts

The melting relations of a group of oceanic basalts—olivine basalts, tholeiitic to midly alkaline, and high-alumina tholeiites are determined. The liquidi of these rocks follow closely the course of the temperature—iron enrichment relationship of Kilauean thoeliitic basalts, ranging from 1430°C for an olivine enriched tholeiite, to a tholeiite of liquidus temperature of 1190°C, the liquidus phase of the assemblages being either olivine or plagioclase.     

folding and slumping in a layered gabbro

The layered gabbroic intrusion of Sarqata qaqa, Ubekendt Ejland, West Greenland contains numerous xenoliths of thermally metamorphosed picrite-basalt. Folding and slumping of the layering occurs adjacent to some of these blocks. It is postulated that the structures were formed by sloped lava xenoliths hitting the unconsolidated layers of crystals forming the floor of the magma chamber during the cooling history of the intrusion. The settling velocities of the xenoliths, and thickness and viscosity of the crystal mush are estimated and discussed.