An introduction to the South China Sea throughflow: Its dynamics, variability, and application for climate

The South China Sea throughflow (SCSTF) involves the inflow through the Luzon strait and the outflow through the Karimata, Mindoro, and Taiwan straits. Recent studies have suggested that the SCSTF act as a heat and freshwater conveyor, playing a potentially important role in regulating the sea surface temperature pattern in the South China Sea and its adjoining tropical Indian and Pacific Oceans. In this introductory paper, we attempt to convey the progress that has recently been made in understanding the SCSTF. We first provide an overview of existing observations, theories, and simulations of the SCSTF. Then, we discuss its interaction with the Pacific western boundary current and Indonesian throughflow. Finally, we summarize issues and questions that remain to be addressed, with special reference to the SCSTF's dynamics, variability, and implication for climate.     

Critical response of structures to multicomponent earthquake excitation

This paper aims to develop an improved understanding of the critical response of structures to multicomponent seismic motion characterized by three uncorrelated components that are defined along its principal axes: two horizontal and the vertical component. An explicit formula, convenient for code applications, has been derived to calculate the critical value of structural response to the two principal horizontal components acting along any incident angle with respect to the structural axes, and the vertical component of ground motion. The critical response is defined as the largest value of response for all possible incident angles. The ratio r_cr/r_srss between the critical value of response and the SRSS response—corresponding to the principal components of ground acceleration applied along the structure axes—is shown to depend on three dimensionless parameters: the spectrum intensity ratio γ between the two principal components of horizontal ground motion characterized by design spectra A(T_n) and γA(T_n); the correlation coefficient α of responses r_x and r_y due to design spectrum A(T_n) applied in the x‐ and y‐directions, respectively; and β = r_y/r_x. It is demonstrated that the ratio r_cr/r_srss is bounded by 1 and . Thus the largest value of the ratio is , 1.26, 1.13 and 1.08 for γ = 0, 0.5, 0.75 and 0.85, respectively. This implies that the critical response never exceeds times the result of the SRSS analysis, and this ratio is about 1.13 for typical values of γ, say 0.75. The correlation coefficient α depends on the structural properties but is always bounded between −1 and 1. For a fixed value of γ, the ratio r_cr/r_srss is largest if β = 1 and α = ±1. The parametric variations presented for one‐storey buildings indicate that this condition can be satisfied by axial forces in columns of symmetric‐plan buildings or can be approximated by lateral displacements in resisting elements of unsymmetrical‐plan buildings. Copyright © 2000 John Wiley & Sons, Ltd.     

Temporal shoreline change and infrastructure influences along the southern Red Sea coast of Saudi Arabia

Jizan is one of the Saudi Arabian coastal cities endowed with diverse natural settings, which includes Ash Shuqayq in the north, Turfah in the centre and Jizan in the South. This work analysed specific environmental characteristics, such as spits, sabkhas and wadis. Assessments used Landsat imagery to examine coastal change between 1973 and 2011. The cumulative temporal change identified regression trends given by coefficients of determination that explained a significant percentage of data variation for Jizan (R ² = 69%) and Turfah (R ² = 72%), while Ash Shuqayq was insignificant (R ² = 14%). Inter-survey results predicted future change, although trends were not significant, i.e. Jizan (R ² = 22%), Turfah (R ² = 14%) and Ash Shuqayq (R ² = 3 and 61% with outlying value removed). Aerial photos showed regional coastal changes, which included a maximum accretion of 36.4 m and maximum erosion of 12.9 m. These are scientifically effective techniques to monitor regional coastal change, i.e. erosion and accretion and identified rates of 0.59, 1.80 and 3.53 myr^?1 for Ash Shuqayq, Turfah and Jizan. Changes were linked to infrastructure developments, e.g. tourism, port development and natural causes, e.g. spit formations and wadi outfalls.     

Millennial-scale sea-level control on avulsion events on the Amazon Fan

The Late Quaternary Amazon deep-sea fan provides a modern analogue to ancient fan systems containing coarse-grained hydrocarbon reservoirs. Sand lenses deposited within the Amazon Fan, due to abrupt shifts in channel pathways called avulsion events, were drilled as part of ODP Leg 155. The hemipelagic sediment directly on top of the avulsion sands was dated using primarily AMS radio carbon dating. This dating shows that these large sand lobes (1 km³) are triggered by relatively small, millennial scale changes in marine transgression and regression (±5–10 m). Relative sea level also controls the architecture of the Channel–levee distributive systems within the Amazon Fan. For example prior to 22 k calendar years BP there is a tripartite channel system. After 22 ka there is only one active Channel–levee system. Transitions between the multi-channel and single channel configurations are related to variations in the volume of sediment supply resulting in aggradation or erosion of channel floor and levee growth in the canyon-channel transition area. The sensitivity of the Amazon deep-sea Fan sedimentation to relatively small changes in sea level supports one of the central assumptions of the theory of Sequence Stratigraphy. In addition this study demonstrates how traps for hydrocarbons may have been formed in ancient fan systems.     

Old stellar population synthesis: new age and mass estimates for Mayall Ⅱ = G1

Mayall Ⅱ = G1 is one of the most luminous globular clusters (GCs) in M31. Here, we determine its age and mass by comparing multicolor photometry with theo-retical stellar population synthesis models. Based on far- and near-ultraviolet GALEX photometry, broad-band UBV RI, and infrared JHK8 2MASS data, we construct the most extensive spectral energy distribution of G1 to date, spanning the wavelength range from 1538 to 20000A. A quantitative comparison with a variety of simple stellar pop-ulation (SSP) models yields a mean age which is consistent with G1 being among the oldest building blocks of M31 and having formed within ～1.7Gyr after the Big Bang. Irrespective of the SSP model or stellar initial mass function adopted, the resulting mass estimates (of order 107M⊙) indicate that G1 is one of the most massive GCs in the Local Group. However, we speculate that the cluster's exceptionally high mass suggests that it may not be a genuine GC. Our results also suggest that G1 may contain, on average, (1.65±0.63) × 102L⊙ far-ultraviolet-bright, hot, extreme horizontal-branch stars, depend-ing on the adopted SSP model. In addition, we demonstrate that extensive multi-passband photometry coupled with SSP analysis enables one to obtain age estimates for old SSPs that have similar accuracies as those from integrated spectroscopy or resolved stellar pho-tometry, provided that some of the free parameters can be constrained independently.     

Empirical distributions of galactic λ spin parameters from the Sloan Digital Sky Survey

Using simple dimensional arguments for both spiral and elliptical galaxies, we present formulae to derive an estimate of the halo spin parameter λ for any real galaxy, in terms of common observational parameters. This allows a rough estimate of λ, which we apply to a large volume-limited sample of galaxies taken from the Sloan Digital Sky Survey data base. The large numbers involved (11 597) allow the derivation of reliable λ distributions, as signal adds up significantly in spite of the errors in the inferences for particular galaxies. We find that if the observed distribution of λ is modelled with a lognormal function, as often done for this distribution in dark matter haloes that appear in cosmological simulations, we obtain parameters  λ₀= 0.04 ± 0.005  and  σ_λ= 0.51 ± 0.05  , interestingly consistent with values derived from simulations. For spirals, we find a good correlation between empirical values of λ and visually assigned Hubble types, highlighting the potential of this physical parameter as an objective classification tool.     

A study of the chemistry of pore fluids and authigenic carbonates in methane seep environments: Kodiak Trench, Hydrate Ridge, Monterey Bay, and Eel River Basin

Analyses of the chemical and isotopic composition of carbonates rocks recovered from methane seepage areas of the Kodiak Trench, Hydrate Ridge, Monterey Bay Clam Flats, and the Eel River Basin, coupled with the studies of the chemistry of the pore fluids, have shown that these carbonates have grown within the sediment column. Geochemical profiles of pore fluids show that, in deep water seeps (Kodiak Trench—4450 m; Monterey Bay—1000 m; Hydrate Ridge—650 m), δ¹³C (DIC) values are low (isotopically light), whereas in the Eel River area ( 350–500 m), δ¹³C (DIC) values are much higher (isotopically heavier). In all cases, the δ¹³C values indicate that processes of methane oxidation, associated with sulfate reduction, are dominant in the shallow sediments. Data on the isotopic composition of authigenic carbonates found at sites in Kodiak Trench, Eel River Basin South, and Eel River Basin North indicate a variable composition and origin in different geochemical environments. Some of the authigenic carbonates from the study sites show a trend in their δ¹³C values similar to those of the pore fluids obtained in their vicinity, suggesting formation at relatively shallow depths, but others indicate formation at greater sediment depths. The latter usually consist of high magnesium calcite or dolomite, which, from their high values of δ¹³C (up to 23‰;) and δ¹⁸O (up to 7.5‰), suggest formation in the deeper horizons of the sediments, in the zone of methanogenesis. These observations are in agreement with observations by other workers at Hydrate Ridge, in Monterey Bay, and in the Eel River Basin.     

中国以外的世界天坑概览

就中国以外已发现的26个天坑的特征和成因进行了一般性的描述和讨论.此外,对其它类型的一些特大型塌陷漏斗也与天坑进行了比较.