Interannual variation of rare earth element abundances in corals from northern coast of the South China Sea and its relation with sea-level change and human activities

Here we present interannual rare earth element (REE) records spanning the last two decades of the 20th century in two living Porites corals, collected from Longwan Bay, close to the estuarine zones off Wanquan River of Hainan Island and Hong Kong off the Pearl River Delta of Guangdong Province in the northern South China Sea. The results show that both coral REE contents (0.5-40 ng g?1 in Longwan Bay and 2-250 ng g?1 in Hong Kong for La-Lu) are characterized with a declining trend, which are significantly negative correlated with regional sea-level rise (9.4 mm a?1) from 1981 to 1996 in Longwan Bay, 13.7 mm a?1 from 1991 to 2001 in Hong Kong). The REE features are proposed to be resulted from seawater intrusion into the estuaries in response to contemporary sea-level rise. However, the tendency for the coral Er/Nd time series at Hong Kong site is absent and there is no significant relation between Er/Nd and total REEs as found for the coral at Longwan Bay site. The observations are likely attributed to changes of the water discharge and sediment load of Pearl River, which have been significantly affected by intense human activities, such as the construction of dams/reservoirs and riverbed sediment mining, in past decades. The riverine sediment load/discharge ratio of the Pearl River decreased sharply with a rate of 0.02 kg m?3 a?1, which could make significant contribution to the declining trend of coral REE. We propose that coastal corals in Longwan Bay and similar unexplored sites with little influences of river discharge and anthropogenic disruption are ideal candidates to investigate the influence of sea-level change on seawater/coral REE.     

ACTUAL ANALYSIS AND THEORETICAL SIMULATION ON POSITION OF SUBTROPICAL HIGHS OVER WESTERN PACIFIC

In this paper,using a nonlinear low-order barotropic system with orography and momentum forcing aswell as dissipation,we have theoretically calculated the two kinds of curves for the seasonal northward movementof subtropical highs.It has been shown that the theoretical results resemble basically with the analysed resultsof wave spectrum data.     

Composition and classification of clasts in the St. Mesmin LL chondrite breccia

Seven samples of the unique St. Mesmin meteorite have been analyzed by instrumental and radiochemical neutron activation analysis for Na, Ca, Sc, Cr, Mn, Fe, Co, Ni, Zn, Ga, Ge, Se, In, Sm, Yb, Ir and Au. St. Mesmin is unique in being the only ordinary chondrite known to contain an unmelted xenolith of another ordinary chondrite. Data for two host matrix samples and three light clasts are consistent with their classification as LL chondrite material. The composition of the large dark xenolith confirms earlier evidence that it is an H chondrite; volatile abundances are consistent with it being highly shocked, petrologic type-4 material. In an olivine microporphyry, siderophile abundances are mostly about 0.13 times LL abundances, an apparent indication of metal loss during the shock melting which produced the clast. As in other regolithic chondrites, the dark host has higher contents of highly volatile elements than do the light clasts. We suggest that this results from a combination of differences in intensity of preexisting metamorphism as well as a redistribution of volatiles during regolith gardening.The H-group xenolith in St. Mesmin is a relatively recent addition to the parent body (< 1.4 Ga ago), but it is argued that this does not require regolith activity at that time. Rather the view is supported that the regolith period occurred very early in the meteorite's history (&gsim;4.0 Ga ago) and may have been related to the growth of the parent body. The H-group fragment may be part of the projectile whose impact excavated the St. Mesmin meteoroid from the LL parent body.     

Spatial distribution of sponge spicules in sediments around Taiwan and the Sunda Shelf

Biogenic silica (BSi) in marine sediments is an important indicator of siliceous organism distributions and paleoproductivities. Organisms that have BSi skeletons include diatoms, silicoflagellates, radiolarians and sponges. This study presents, for the first time, the distribution of biogenic siliceous fragments in shallow water sediments around Taiwan and the Sunda Shelf, which belong to this rarely studied region of the South China Sea (SCS). Thirty-one surface sediment samples were collected from intertidal to depths of 1,100?m. Only sponge spicules were found in this study and the abundance varied in the range of 3?C7,910?n?g^?1 sediment. Combining previous studies with ours, from shallow to deep, it was observed that BSi composition in the surface sediment of this area changed from sponge spicules in the Sunda Shelf, followed by sponge spicules and radiolarians in the southwestern SCS, to sponge spicules, radiolarians and diatoms in the southern SCS. Based on this study, the abundance of sponge spicules correlated positively and negatively with water depth and sediment grain size when coral reef sites were excluded. The low spicule abundance in shallow waters may have resulted from local current conditions and the dilution effect through riverine input of terrestrial sediment. Other possible explanations for the varying spicule abundance among sites are the difference in local fauna, such as coral reefs which usually have high diversity and abundance of sponges. The findings provide additional information on the process of recent BSi deposition which may help future studies in sedimentology, paleogeography and paleoenvironments.     

Classification of and elemental fractionation among ureilites

Concentrations of Ni, Zn, Ga, Ge, Cd, In, Ir and Au in five ureilites can be combined with petrographie evidence to yield a well-defined suite extending from Goalpara (heavily shocked, low Ir concentration, low Ir/Ni ratio) through Haverö, Dyalpur, Novo-Urei to Kenna (moderately shocked, high Ir concentration, high Ir/Ni ratio). Arguments are presented indicating that this suite represents the sampling of a vertical section within the ureilitic parent body. The large range in Ir/Ni and Ir/Au ratios indicates greater efficiency of extraction of primitive, refractory metal in the Goalpara region than in the Kenna region, and implies that higher maximum temperatures prevailed in the former during the production of ureilitic ultramafic silicates by a partial melting process.

A major impact event injected a deposit of C-rich material into the ultramafic silicates. This C-rich material had a moderately high content of metal; there is no direct evidence that it contained volatiles other than the rare gases. High Ca contents of the ferromagnesian minerals indicate that the ultramafics were hot at the time the injection occurred; the zoning of these mineral grains also indicates high temperatures (ca. 1400 K) and low pressures (S 10atm) such that reaction between C and Fe₂SiO₄ could occur, but that cooling occurred too quickly to allow complete equilibration. The ureilitic C-rich material appears to represent an important type of primitive material.

Two siderophile-rich components are necessary to explain the relative siderophile trends in ureilites. We interpret the high-Ir component to be a refractory nebular condensate or residue that was retained during the partial melting event. The low-Ir component, which roughly resembles E4 chondrite siderophiles, is attributed to metal injected together with the vein material.     

Measuring the orbital periods of low mass X-ray binaries in the X-ray band

A low mass X-ray binary(LMXB) contains either a neutron star or a black hole accreting materials from its low mass companion star. It is one of the primary astrophysical sources for studying stellar-mass compact objects and accreting phenomena. As with other binary systems, the most important parameter of an LMXB is the orbital period, which allows us to learn about the nature of the binary system and constrain the properties of the system's components, including the compact object. As a result, measuring the orbital periods of LMXBs is essential for investigating these systems even though fewer than half of them have known orbital periods. This article introduces the different methods for measuring the orbital periods in the X-ray band and reviews their application to various types of LMXBs, such as eclipsing and dipping sources, as well as pulsar LMXBs.     

Distribution of contaminants in biota and sediments in the Musquash Estuary, Atlantic Canada, marine protected area site initiative and contaminant exclusion zone

The Musquash Estuary, one of the last ecologically intact estuaries in New Brunswick, has been designated an area of interest for a marine protected area (MPA) under the Oceans Act. The area has been assessed for contaminant background levels as required for establishing MPA environmental quality. American lobster (Homarus americanus), blue mussel (Mytilus edulis) and sediments were collected for assessing contaminant levels and distribution in the harbour. Levels of contaminants from the indicator species and the abiotic component have shown: (1) two extremes of high and low Cu and Ag in lobster from the area; and (2) lower metal levels in inner Musquash Harbour sediments and mussels than in those from the harbour mouth. These suggest that deposition of contaminants into the Musquash MPA site was due to transport of contaminants by coastal currents from upstream coastal industrial activities. This reverse trend with higher contaminant levels in the biotic and abiotic components in the outer harbour than in the inner harbour differs from a contaminated harbour and suggests that a contaminant exclusion zone should be considered for controlling contamination from nearby coastal and estuarine industrial sites to protect the sensitive habitats within the marine protected area.     

Hydrothermal studies in a new diamond anvil cell up to 10 GPa and from −190°C to 1200°C

The new hydrothermal diamond anvil cell (HDAC) has been designed for optical microscopy and X-ray diffraction at pressures up to 10 GPa and temperatures between –190°C and 1200°C. Laser light reffected from the top and bottom anvil faces and the top and bottom solid sample faces produce interference fringes that provide a very sensitive means of monitoring the volume of sample chamber and for observing volume and refractive index changes in solid samples due to transitions and reactions. Synchrotron radiation has been used to make X-ray diffraction patterns of samples under hydrothermal conditions. Individual heaters and individual thermocouples provide temperature control with an accuracy of ±0.5°C. Liquid nitrogen directly introduced into the HDAC has been used to reduce the sample temperature to –190°C. The - phase boundary of quartz has been used to calculate the transition pressures from measured transition temperatures. With this method we have redetermined 5 isochores of H₂O up to 850°C and 1.2 GPa at which the solution rate of the quartz became so rapid that the quartz dissolved completely before the - transition could be observed. When silica solutions were cooled, opal spherules and rods formed.     

A unified equation for calculating methane vapor pressures in the CH4-H2O system with measured Raman shifts

A unified equation has been derived by using all available data for calculating methane vapor pressures with measured Raman shifts of C-H symmetric stretching band (υ₁) in the vapor phase of sample fluids near room temperature. This equation eliminates discrepancies among the existing data sets and can be applied at any Raman laboratory. Raman shifts of C-H symmetric stretching band of methane in the vapor phase of CH₄-H₂O mixtures prepared in a high-pressure optical cell were also measured at temperatures between room temperature and 200 °C, and pressures up to 37 MPa. The results show that the CH₄υ₁ band position shifts to higher wavenumber as temperature increases. We also demonstrated that this Raman band shift is a simple function of methane vapor density, and, therefore, when combined with equation of state of methane, methane vapor pressures in the sample fluids at elevated temperatures can be calculated from measured Raman peak positions. This method can be applied to determine the pressure of CH₄-bearing systems, such as methane-rich fluid inclusions from sedimentary basins or experimental fluids in hydrothermal diamond-anvil cell or other types of optical cell.