Spatial distributions and seasonal variations of features related to a venting process at high southern latitudes observed by the MOC camera

A distinctive terrain named cryptic region which is characterized by regions of low albedo and low temperature has been identified on the Martian south polar cap. In this zone, many fan- and spider-shaped features of km-scale appeared following the sublimation of the CO₂ frost layer. These peculiar features were apparently caused by a wind-blown system of dust-laden jets. During the warming period starting at L_s∼180°, the seasonal ice cap regresses and fans and spiders appear in sequence. These surface features are repeatable events that tend to occupy the same areas from year to year. In this study, we use the Mars Orbiter camera (MOC) narrow-angle images to produce a statistical study of the time distributions of the fans and spiders as functions of L_s and as functions of the topography. The time variations and spatial distributions of these features are further correlated with the CO₂ ice coverage measured by the Mars Orbiter laser altimeter (MOLA) instrument. We have documented that most of the fans are found in the early spring with L_s<230° and the fans and spiders coexist at L_s=250°±20°. It is also found that there is a strong dependence on latitude and altitude with fans and spiders most often observed at high latitude (>83°S) and high altitude (>2500 m). Our statistical result also indicates that the occurrence of fans is highly correlated with the thickness of the CO₂ frost thus providing support for the venting model.     

An Examination of the Oxidation of Elemental Mercury in the Presence of Halide Surfaces

Recent field investigations in polar regions, and over the ocean, have suggested that elemental mercury (Hg⁰) can be photochemically oxidized in the presence of reactive halogen species that are formed in the presence of salt particles, typically through a reactive catalytic cycle involving ozone destruction. Furthermore, these studies have suggested that the Hg⁰ oxidation reaction involves the reaction with reactive bromine species such as Br, BrO, and Br₂. To investigate these reactions in more detail, we performed experiments using a quartz reactive chamber so that the oxidation of Hg⁰, and the formation of ionic Hg products, could be examined in detail under different reaction scenarios, but at realistic levels of Hg. To examine if the reactions were enhanced by the presence of deliquescent salt surfaces, as has been postulated to be the case for the formation of reactive halogens, one surface of the cell was coated with either NaCl or NaBr for some experiments. In addition to laboratory experiments with a Xenon lamp, outdoor experiments under natural light were also conducted. The results of these studies showed that oxidation of Hg⁰ did not occur in the dark, except in the presence of a deliquescent NaBr salt surface. The rate of oxidation was slow in the absence of salt surfaces, and in the absence of low wavelength light (<324 nm). In the presence of NaCl surfaces, oxidation rates were at least two orders of magnitude faster, but the rate was further increased in the presence of NaBr, by a further factor of 25. With outdoor light, while the rates of oxidation were lower, the results were similar overall. The results are discussed in terms of the reactions occurring and the mechanisms of Hg⁰ oxidation. Finally, the implications of these reactions to the overall global Hg cycle are discussed.     

Crustal movement along a collision boundary of plates (case of eastern Taiwan)

Recent crustal movements in eastern Taiwan were investigated based on geodetic and seismological data as a case study of the tectonics along a colliding plate boundary. Secular horizontal strain along the Longitudinal Valley, a probable arc-continent collision boundary between the Philippine Sea and Eurasion plates, is compressive with a large rate of 2 microstrains/year, and the maximum compression axis trends in NW-SE direction. This means that nearly two-thirds of the convergence rate between the two plates is consumed in the narrow zone along the valley and confirms the view that the valley is the plate boundary between the two. The amount of uplift in the Central Range, deduced from trigonometric leveling, reaches more than one meter during the past 60 years. Such active orogeny is caused by the high strain rate in this area. Horizontal displacement of the Coastal Range, a leading edge of the Philippine Sea plate, has a left-lateral component, suggesting that the boundary is a region of oblique collision and the range moves toward the north, producing subduction of the Philippine Sea plate off the Coast of northeastern Taiwan.An extensional strain pattern is found northeastern Taiwan near Hualien, in northern Taiwan near Ilan, and in southeastern Taiwan south Taitung. In northeastern Taiwan, the direction of the maximum extension axis is nearly parallel to the isodipth contours of deep-focus earthquakes that occurred under the southern part of the Ryukyu Trench. From a model calculation using a finite-element method, this pattern of strain is interpreted as an edge effect of the collision-subduction junction in northeastern Taiwan. The direction of the maximum extension in northern Taiwan forms high angles with the direction of the tectonic line near Ilan stretching from the Okinawa Trough. This fact is harmonious with the view that the Okinawa Trough is spreading. Extensional strain observed in southeastern Taiwan may be related to the eastward subduction since the area is situated on a transition zone, from collision to subduction.     

The carbonate system in the East China Sea in winter

Measurements of dissolved inorganic carbon (DIC), pH, total alkalinity (TA), and partial pressure of CO₂ (pCO₂) were conducted at a total of 25 stations along four cross shelf transects in the East China Sea (ECS) in January 2008. Results showed that their distributions in the surface water corresponded well to the general circulation pattern in the ECS. Low DIC and pCO₂ and high pH were found in the warm and saline Kuroshio Current water flowing northeastward along the shelf break, whereas high DIC and pCO₂ and low pH were mainly observed in the cold and less saline China Coastal Current water flowing southward along the coast of Mainland China. Difference between surface water and atmospheric pCO₂ (ΔpCO₂), ranging from ~ 0 to ? 111 μatm, indicated that the entire ECS shelf acted as a CO₂ sink during winter with an average flux of CO₂ of ?13.7 ± 5.7 (mmol C m^? 2 day^? 1), and is consistent with previous studies. However, pCO₂ was negatively correlated with temperature for surface waters lower than 20 °C, in contrast to the positive correlation found in the 1990s. Moreover, the wintertime ΔpCO₂ in the inner shelf near the Changjiang River estuary has appreciably decreased since the early 1990s, suggesting a decline of CO₂ sequestration capacity in this region. However, the actual causes for the observed relationship between these decadal changes and the increased eutrophication over recent decades are worth further study.     

Removal fluxes of Mn and Fe from the nearshore waters along the west coast of Taiwan

Dissolved and particulate Mn and Fe in the nearshore waters were determined at 27 stations along the west coast of Taiwan during 19-23 November 2004. The latitudinal distributions of Mn and Fe were very similar; however, the concentration in the dissolved phase was lower, whereas that in the particulate phase was higher in the northern regime. The higher percentage of Fe than Mn that was associated with particles resulted in a two-order of magnitude higher particle-water partition coefficient for Fe, K_d(Fe), than that for Mn, K_d(Mn). The removal fluxes of Mn and Fe could be estimated by multiplying the particulate ²³⁴Th removal flux with the Mn/²³⁴Th and Fe/²³⁴Th ratios in suspended particles, which ranged from 0.1 to 3.8 mmol m⁻² d⁻¹ for Mn, and from 3.4 to 194.5 mmol m⁻² d⁻¹ for Fe. Residence times ranged from 1 to 20 days for Mn and Fe were estimated in the nearshore.     

Recognition of an Elastic–Plastic Constitutive Law by a Multiobjective Evolutionary Algorithm

This study presents the recognition of an elastic–plastic constitutive law by a multiobjective evolutionary algorithm (MOEA). This idea is illustrated by the identification of ellipse aspect ratio and plastic modulus of a reported bounding surface model. Based on the multi-goals of well predicting all available drained or undrained stress–strain behaviors simultaneously, the compromising solutions of these two parameters are found by a strength Pareto evolutionary algorithm 2 (SPEA2). Their fittest values are then determined by additionally introducing the Akaike information criterion. Experimental data for the Ottawa sand are used to test such processes. The results show that an MOEA is an efficient and automatic tool to identify the fittest form of an elastic–plastic constitutive law from a large amount of experimental data. However, sufficient data are required to determine the correct searching range of parameters to be identified.     

Deformations resulting from the movements of a shear or tensile fault in an anisotropic half space

Earlier solutions (Bull. Seismol. Soc. Amer. 1985; 75 :1135–1154; Bull. Seismol. Soc. Amer. 1992; 82 :1018–1040) of deformations caused by the movements of a shear or tensile fault in an isotropic half-space for finite rectangular sources of strain nucleus have been extended for a transversely isotropic half-space. Results of integrating previous solutions (Int. J. Numer. Anal. Meth. Geomech. 2001; 25 (10): 1175–1193) of deformations due to a shear or tensile fault in a transversely isotropic half-space for point sources of strain nucleus over the fault plane are presented. In addition, a boundary element (BEM) model (POLY3D:A three-dimensional, polygonal element, displacement discontinuity boundary element computer program with applications to fractures, faults, and cavities in the Earth's crust. M.S. Thesis, Stanford University, Department of Geology, 1993; 62) is given. Different from similar researches (e.g. Thomas), the Akaike's view on Bayesian statistics (Akaike Information Criterion Statistics. D. Reidel Publication: Dordrecht, 1986) is applied for inverting deformations due to a fault to obtain displacement discontinuities on the fault plane. An example is given for checking displacements predicted by proposed analytical expressions. Another example is generated for the use of proposed BEM model. It demonstrates the effectiveness of this model in exploring displacement behaviours of a fault. Copyright © 2004 John Wiley & Sons, Ltd.     

Deformations caused by the movements of shear and tensile faults

Earlier solutions of deformations resulting from the movements of shear and tensile faults in a half space (Bull. Seismol. Soc. Amer. 1985; 75 :1135, 1992; 82 :1018) have been revised in view of cross‐anisotropic stress–strain relationships. The dislocation theory (Canad. J. Phys. 1958; 36 :192) is reviewed and the displacement field due to a concentrated force in an anisotropic half space is solved analytically for developing the current research. A fault is simulated as a point source of strain nuclei in applying the dislocation theory. Data (Terr. Atmos. Oceanic Sci. 2000; 11 (3):591, 631) that were used to study the Chi‐Chi earthquake (M_L=7.3; 1999/9/21 AM 1:47) are introduced to compare the solution with the isotropic results. Results indicate that the anisotropy of stress–strain relationships does affect the results of predicted deformations. Copyright © 2001 John Wiley & Sons, Ltd.     

Prediction of Probabilistic Settlements by the Perturbation-Based Spectral Stochastic Meshless Local Petrov–Galerkin Method

Originating an attempt of understanding the reliability and serviceability of foundations, an interest of comparing the difference between settlements predicted with and without considering the uncertainty in such as the spatial variability of soil properties is born. This study selectively compares between settlements predicted with and without considering the uncertainty in the spatial variability of Young’s modulus. The tool is a coupling of perturbation expansions of Young moduli and a two-dimensional meshfree weak-strong form in elastostatics. Two further examples show that the spatial variability of Young’s modulus causes apparent difference between probabilistic and deterministic settlement components along the direction of a surcharge. We can derive an autocorrelation function to describe the spatial variability of Young’s modulus and understand how it affects predicted settlements depending upon autocorrelation function values. In addition, the spectral stochastic meshless local Petrov–Galerkin method is a time-saving tool for predicting probabilistic settlements with the uncertainty in the spatial variability of soil properties.     

Carbonate chemistry and projected future changes in pH and CaCO3 saturation state of the South China Sea

To study the dissolved carbonate system in the South China Sea (SCS) and to understand the water mass exchange between the SCS and the West Philippine Sea (WPS), pH, total alkalinity and total CO₂ were measured aboard the R/V Ocean Researcher 1. Because of the sill that separates these two seas in the Luzon Strait with a maximum depth of 2200 m, the SCS Deep Water has characteristics similar to those of water at about 2200 m in the WPS. The minimum pH and the maxima of normalized alkalinity and total CO₂ commonly found in the open oceans at mid-depth also prevail in the WPS but are, however, very weak in the SCS. Rivers and inflows from Kuroshio Surface and Deep Waters through the Luzon Strait as well as those through the Mindoro Strait transport carbon to the SCS year-round. Meanwhile, the outflowing Taiwan Strait water as well as the SCS Surface and Intermediate Waters of the Luzon Strait transports carbon out of the SCS year-round. The Sunda Shelf is also a channel for carbon transport into the SCS in the wet season and out of the SCS in the dry season.fCO₂ data and mass balance calculations indicate that the SCS is a weak CO₂ source in the wet season but an even weaker CO₂ sink in the dry season. With these facts taken together, the SCS is likely a very weak CO₂ source. Anthropogenic CO₂ penetrates to about 1500 m in depth in the SCS, and the entire SCS contains 0.60 ± 0.15 × 10¹⁵ g of excess carbon. Typical profiles of pH as well as the degree of saturation of each of calcite and aragonite in 1850 and 1997 are presented, and those for 2050 AD are projected. The maximum decrease in pH is estimated to be 0.16 pH units in the surface layer when the amount of CO₂ is doubled. It is anticipated that aragonite in the upper continental slope will likely start to dissolve, thereby neutralizing excess CO₂ by around 2050 AD. This paper is unique in that it presents the results of the first attempt ever to estimate the past, present and future physico-chemical properties of the world's largest marginal sea.