Paleoenvironmental changes of the Yellow Sea during the Late Quaternary

Based on stable isotope data and carbon and sulfur elemental analyses, the sedimentary environment of the Yellow Sea was significantly influenced by the sea level changes during the Late Quaternary. At the low sea level stand when the sea level was lower by 56?m, the salinity of seawater was reduced to about 7.6‰, and the sedimentation rate in the central part of the Yellow Sea was three times higher than the present rate. The high C/S ratio during the low sea level stand is strong evidence that sedimentation took place in a lower salinity environment than exists at present.     

Data assimilation using the particle filter for identifying the elasto‐plastic material properties of geomaterials

A computational method, incorporating the finite element model (FEM) into data assimilation using the particle filter, is presented for identifying elasto‐plastic material properties based on sequential measurements under the known changing traction boundary conditions to overcome some difficulties in identifying the parameters for elasto‐plastic problems from which the existing inverse analysis strategies have suffered. A soil–water coupled problem, which uses the elasto‐plastic constitutive model, is dealt with as the geotechnical application. Measured data on the settlement and the pore pressure are obtained from a synthetic FEM computation as the forward problem under the known parameters to be identified for both the element tests and the ground behavior during the embankment construction sequence. Parameter identification for elasto‐plastic problems, such as soil behavior, should be made by considering the measurements of deformation and/or pore pressure step by step from the initial stage of construction and throughout the deformation history under the changing traction boundary conditions because of the embankment or the excavation because the ground behavior is highly dependent on the loading history. Thus, it appears that sequential data assimilation techniques, such as the particle filter, are the preferable tools that can provide estimates of the state variables, that is, deformation, pore pressure, and unknown parameters, for the constitutive model in geotechnical practice. The present paper discusses the priority of the particle filter in its application to initial/boundary value problems for elasto‐plastic materials and demonstrates a couple of numerical examples. Copyright © 2012 John Wiley & Sons, Ltd.     

High precision SIMS oxygen three isotope study of chondrules in LL3 chondrites: Role of ambient gas during chondrule formation

We report high precision SIMS oxygen three isotope analyses of 36 chondrules from some of the least equilibrated LL3 chondrites, and find systematic variations in oxygen isotope ratios with chondrule types. FeO-poor (type I) chondrules generally plot along a mass dependent fractionation line (Δ¹⁷O ∼ 0.7‰), with δ¹⁸O values lower in olivine-rich (IA) than pyroxene-rich (IB) chondrules. Data from FeO-rich (type II) chondrules show a limited range of δ¹⁸O and δ¹⁷O values at δ¹⁸O = 4.5‰, δ¹⁷O = 2.9‰, and Δ¹⁷O = 0.5‰, which is slightly ¹⁶O-enriched relative to bulk LL chondrites (Δ¹⁷O ∼ 1.3‰). Data from four chondrules show ¹⁶O-rich oxygen isotope ratios that plot near the CCAM (Carbonaceous Chondrite Anhydrous Mineral) line. Glass analyses in selected chondrules are systematically higher than co-existing minerals in both δ¹⁸O and Δ¹⁷O values, whereas high-Ca pyroxene data in the same chondrule are similar to those in olivine and pyroxene phenocrysts.Our results suggest that the LL chondrite chondrule-forming region contained two kinds of solid precursors, (1) ¹⁶O-poor precursors with Δ¹⁷O > 1.6‰ and (2) ¹⁶O-rich solid precursors derived from the same oxygen isotope reservoir as carbonaceous chondrites. Oxygen isotopes exhibited open system behavior during chondrule formation, and the interaction between the solid and ambient gas might occur as described in the following model. Significant evaporation and recondensation of solid precursors caused a large mass-dependent fractionation due to either kinetic or equilibrium isotope exchange between gas and solid to form type IA chondrules with higher bulk Mg/Si ratios. Type II chondrules formed under elevated dust/gas ratios and with water ice in the precursors, in which the ambient H₂O gas homogenized chondrule melts by isotope exchange. Low temperature oxygen isotope exchange may have occurred between chondrule glasses and aqueous fluids with high Δ¹⁷O (∼5‰) in LL the parent body. According to our model, oxygen isotope ratios of chondrules were strongly influenced by the local solid precursors in the proto-planetary disk and the ambient gas during chondrule melting events.     

Effects of nitrogen and sulphide on macroinfaunal community: a microcosm study

A microcosm experiment was conducted to test the short-term effects of nitrogen (as TKN, total Kjeldahl nitrogen) and sulphide (as AVS, acid volatile sulphide) on macrobenthic infauna over a period of 8 weeks. The experiment consisted of four treatments using sediment cores (D: 8 cm, H: 20 cm) with addition of: I, nitrogen (N) to an in situ mean level of 0.48 mg Ng(-1) dw; II, sulphidic solution (S) to an in situ mean level of 318.8 microM S g(-1) dw; III, nitrogen and sulphidic solution (NS) to in situ mean levels of 0.45 mg Ng(-1) dw and 329.0 microM S g(-1) dw, respectively, and IV, control with no addition of N and S. Sediment cores were retrieved for analysis of infaunal composition after weeks 2, 4 and 8. A total of 646 specimens of macrobenthic infauna belonging to 27 species were recorded from the cores, in which polychaetes were the most abundant with respect to species and individual numbers. Mean species number and diversity H' of the control and N treatment was statistically higher than S and NS treatments, mean individual number of the S treatment was larger than the NS treatment, and mean evenness J of the S treatment was lower than the N and NS treatments as well as the control. Individual numbers also showed a significant increase from weeks 2 to 8, whereas evenness J decreased in weeks 4 and 8. Multivariate analyses of the faunal data suggested that benthic composition of the N treatment and control did not differ during the experimental period, but changes in benthic structure in S and NS treatments were evident. The present findings demonstrated the dose-response relationship of benthic species changes under controlled addition of N and S. The response to N and S additions in the sediment microcosms was in agreement with the general effects of organic enrichment on macrobenthic communities along a spatial gradient of organic pollution as described by Pearson and Rosenberg [Pearson, T.H., Rosenberg, R., 1978. Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanography and Marine Biology Annual Review 16, 229-311]. However, in the present experiment, community changes in the treatments were observable in a short, temporal scale.     

Sensitivity of global warming to the pattern of tropical ocean warming

The current generations of climate models are in substantial disagreement as to the projected patterns of sea surface temperatures (SSTs) in the Tropics over the next several decades. We show that the spatial patterns of tropical ocean temperature trends have a strong influence on global mean temperature and precipitation and on global mean radiative forcing. We identify the SST patterns with the greatest influence on the global mean climate and find very different, and often opposing, sensitivities to SST changes in the tropical Indian and West Pacific Oceans. Our work stresses the need to reduce climate model biases in these sensitive regions, as they not only affect the regional climates of the nearby densely populated continents, but also have a disproportionately large effect on the global climate.

---