Impact of the thermal state of the tropical western Pacific on onset date and process of the South China Sea summer monsoon

Since the early or late onset of the South China Sea summer monsoon （SCSM） has a large impact on summer monsoon rainfall in East Asia, the mechanism and process of early or late onset of the SCSM are an worthy issue to study. In this paper, the results analyzed by using the observed data show that the onset date and process of the SCSM are closely associated with the thermal state of the tropical western Pacific in spring. When the tropical western Pacific is in a warming state in spring, the western Pacific subtropical high shifts eastward, and twin cyclones are early caused over the Bay of Bengal and Sumatra before the SCSM onset. In this case, the cyclonic circulation located over the Bay of Bengal can be early intensified and become into a strong trough. Thus, the westerly flow and convective activity can be intensified over Sumatra, the Indo-China Peninsula and the South China Sea （SCS） in mid-May. This leads to early onset of the SCSM. In contrast, when the tropical western Pacific is in a cooling state, the western Pacific subtropical high anomalously shifts westward, the twin cyclones located over the equatorial eastern Indian Ocean and Sumatra are weakened, and the twin anomaly anticyclones appear over these regions from late April to mid-May. Thus, the westerly flow and convective activity cannot be early intensified over the Indo-China Peninsula and the SCS. Only when the western Pacific subtropical high moves eastward, the weak trough located over the Bay of Bengal can be intensified and become into a strong trough, the strong southwesterly wind and convective activity can be intensified over the Indo-China Peninsula and the SCS in late May. Thus, this leads to late onset of the SCSM. Moreover, in this paper, the influencing mechanism of the thermal state of the tropical western Pacific on the SCSM onset is discussed further from the Walker circulation anomalies in the different thermal states of the tropical western Pacific.     

Covariations in oceanic dimethyl sulfide,its oxidation products and rain acidity at Amsterdam Island in the Southern Indian Ocean

Simultaneous measurements of rain acidity and dimethyl sulfide (DMS) at the ocean surface and in the atmosphere were performed at Amsterdam Island over a 4 year period. During the last 2 years, measurements of sulfur dioxide (SO₂) in the atmosphere and of methane sulfonic acid (MSA) and non-sea-salt-sulfate (nss-SO₄ ^2-) in rainwater were also performed. Covariations are observed between the oceanic and atmospheric DMS concentrations, atmospheric SO₂ concentrations, wet deposition of MSA, nss-SO₄ ^2-, and rain acidity. A comparable summer to winter ratio of DMS and SO₂ in the atmosphere and MSA in precipitation were also observed. From the chemical composition of precipitation we estimate that DMS oxidation products contribute approximately 40% of the rain acidity. If we consider the acidity in excess, then DMS oxidation products contribute about 55%.     

Reliability index in geotechnics

In this paper, the reliability index β is examined for its applicability in geotechnics. A statistical finite difference scheme is proposed to evaluate partial derivatives of the limit state function, enabling the computation of the reliability index β. Through illustrative examples, it is demonstrated that the proposed procedure gives results in excellent agreement with those obtained by the Monte Carlo simulation method, and yet it involves considerable savings in computing time. Extension of the reliability index method to cover many classes of problems involving correlated variables is highlighted.     

Palaeo-hydrogeological control on groundwater As levels in Red River delta,Vietnam

To study the geological control on groundwater As concentrations in Red River delta, depth-specific groundwater sampling and geophysical logging in 11 monitoring wells was conducted along a 45 km transect across the southern and central part of the delta, and the literature on the Red River delta’s Quaternary geological development was reviewed. The water samples (n = 30) were analyzed for As, major ions, Fe²⁺, H₂S, NH₄, CH₄, δ¹⁸O and δD, and the geophysical log suite included natural gamma-ray, formation and fluid electrical conductivity. The SW part of the transect intersects deposits of grey estuarine clays and deltaic sands in a 15–20 km wide and 50–60 m deep Holocene incised valley. The NE part of the transect consists of 60–120 m of Pleistocene yellowish alluvial deposits underneath 10–30 m of estuarine clay overlain by a 10–20 m veneer of Holocene sediments. The distribution of δ¹⁸O-values (range −12.2‰ to −6.3‰) and hydraulic head in the sample wells indicate that the estuarine clay units divide the flow system into an upper Holocene aquifer and a lower Pleistocene aquifer. The groundwater samples were all anoxic, and contained Fe²⁺ (0.03–2.0 mM), Mn (0.7–320 μM), SO₄ (<2.1 μM–0.75 mM), H₂S (<0.1–7.0 μM), NH₄ (0.03–4.4 mM), and CH₄ (0.08–14.5 mM). Generally, higher concentrations of NH₄ and CH₄ and low concentrations of SO₄ were found in the SW part of the transect, dominated by Holocene deposits, while the opposite was the case for the NE part of the transect. The distribution of the groundwater As concentration (<0.013–11.7 μM; median 0.12 μM (9 μg/L)) is related to the distribution of NH₄, CH₄ and SO₄. Low concentrations of As (?0.32 μM) were found in the Pleistocene aquifer, while the highest As concentrations were found in the Holocene aquifer. PHREEQC-2 speciation calculations indicated that Fe²⁺ and H₂S concentrations are controlled by equilibrium for disordered mackinawite and precipitation of siderite. An elevated groundwater salinity (Cl range 0.19–65.1 mM) was observed in both aquifers, and dominated in the deep aquifer. A negative correlation between aqueous As and an estimate of reduced SO₄ was observed, indicating that Fe sulphide precipitation poses a secondary control on the groundwater As concentration.     

Applicability of CPT-based methods in predicting toe bearing capacities of driven piles in sand

This paper presents a study on applicability of predicting toe bearing capacities from cone penetration test (CPT) for PHC (pretensioned spun high-strength concrete) driven piles into deep sandy deposits in the Nakdong River deltaic area west of Busan City in South Korea. Using toe bearing capacities obtained from pile driving analyzer (PDA) tests as reference values, which were reliably calibrated by on-site O-cell tests, the applicability of the CPT-based methods was evaluated using a statistical rank index (RI). A total of 82 piezocone penetration test soundings and 190 PDA test piles were used for reliability analysis in this study. Three correction steps were applied to obtain reliable PDA and CPT data sets before ranking is carried out. The RI index is combined from four criteria: (1) the best-fit line, (2) the arithmetic mean and standard deviation, (3) the cumulative probabilities, and (4) the log-normal and histogram distributions. Based on these criteria the performance of some SPT-based methods in the literature is evaluated.     

Sublethal toxicity of orchard stormwater runoff in Sacramento splittail (Pogonichthys macrolepidotus) larvae

The sublethal effects of stormwater runoff from sections of a plum orchard treated with esfenvalerate or diazinon were evaluated in 7-day-old Sacramento splittail (Pogonichthys macrolepidotus) larvae. Fish were exposed to eight runoff samples using the USEPA standard static renewal method for 96 h acute toxicity testing, then transferred to clean water for three-month to assess the survival, growth, histopathological abnormalities, and heat stress proteins (hsp). No significant mortality was observed at 96 h in exposed fish. At one week, histopathological abnormalities included severe glycogen depletion, cytoplasmic protein droplets, vacuolar degeneration, and cell necroses in liver of all exposure groups. Pyknotic nerve cells were seen in brain of one exposure group. Significantly higher cumulative mortality, lower condition factor, and elevated hsp60 and hsp70 levels (p < 0.05) were occurred in several exposure groups. No histopathological abnormalities were observed after three months in any exposure group. This study confirms that standard acute toxicity tests have underestimated the toxicity of stormwater runoff, and although splittail larvae survived the 96 h exposure, they exhibited reduced survival and growth and showed signs of cellular stress even after a three month recovery period.     

Binding of thorium(IV) to carboxylate, phosphate and sulfate functional groups from marine exopolymeric substances (EPS)

Th(IV) isotopes are important proxies in oceanographic investigations, and are used as tracers of particle dynamics and particulate organic matter (POC) fluxes out of the euphotic zone through the use of ²³⁴Th/POC ratios. These approaches rely on empirically determined and variable POC to ²³⁴Th ratios, which might be controlled, in parts, by the abundance of exopolymeric substances (EPS). EPS contain acidic polysaccharides (APS) and are excreted by both phytoplankton and bacteria. To this end, radiotracer experiments with EPS from microbial cultures were conducted to determine the binding environment of ²³⁴Th(IV)-binding ligands in colloids and suspended particles in marine systems. In these experiments, the ²³⁴Th distribution during isoelectric focusing (IEF) and polyacrylamide gel electrophoresis (PAGE) was related to the functional group composition of EPS and of colloidal organic matter (COM) isolated from the Gulf of Mexico (GOM) using cross-flow ultrafiltration. EPS was extracted from phytoplankton (Emiliania huxleyi and Synechococcus elongatus) and bacteria (Sagittula stellata and Roseobacter gallaeciensis) cultures by repeated alcohol precipitation. Phosphate and sulfate concentrations were determined using ion chromatography (IC). IEF profiles indicated that 49% to 65% of the ²³⁴Th-labeled EPS from plankton and bacteria as well as COM samples from the GOM was found concentrated below pH of 4, near an isoelectric point, pH_IEP, of about 2. The carboxylic acid maxima for extracted EPS and COM samples appeared close to the pH_IEF of ²³⁴Th(IV). The phosphate maximum appeared at the same pH_IEF as ²³⁴Th(IV) for EPS from R. gallaeciensis and S. elongatus. The sulfate maximum was found at the same pH_IEF as ²³⁴Th(IV) for EPS from S. elongatus and COM. The molecular weight (MW) of the strongly Th(IV)-binding ligand varied from 1 to 14 kDa, depending on the species, but was about 10 kDa in COM. Thus, depending on the species of plankton or bacteria, the MW and specific functional group composition of the strongly ²³⁴Th(IV)-binding amphiphilic biomolecule can vary. Therefore, different acidic functional groups can, at times, contribute to the binding of Th(IV) to the EPS chelating ligand, which can also have different MWs. This implies that the binding environment for Th(IV), which is present at total concentrations at least a million times lower than the acid functional groups, consists of strong polydentate chelate complexes in clustered structures of carboxylate, sulfates and/or phosphates. The combination of strongly chelating groups and amphiphilicity gives this biomolecule the unique properties of a “sticky” ligand.