Transformation of arsenic compounds in modern intertidal sediments of Iriomote Island, Japan

The arsenic accumulation process in intertidal sediments of Iriomote Island, Japan, is analyzed as a naturally balanced arsenic-fixation system. Major and minor element chemistry is analyzed by X-ray fluorescence photometry, mineralogy is investigated by X-ray diffractometry, and four arsenic compounds are characterized by hydrogen-generated atomic absorption photometry. It is found that arsenic is accumulated by iron hydroxides/oxides precipitated following the decomposition of humic acids in the shallower sediment, and is subsequently incorporated into iron sulfide minerals at depth. The arsenic is immobile during incorporation into arsenic-bearing phases, suggesting that arsenic is unlikely to be released into the porewater under natural conditions in early diagenesis. The formation and decomposition of arsenic-bearing organic compounds appear to be associated with the formation and decomposition of arsenic in oxyhydroxides/oxides, suggesting that microbial activity may play an important role in controlling the behavior of arsenic and arsenic-bearing phases in the sediment column.     

Petrology and geochemistry of Northwest Africa 5480 diogenite and evidence for a basin‐forming event on Vesta

We performed a petrological and geochemical study of an olivine diogenite, Northwest Africa (NWA) 5480. NWA 5480 is a crystalline stone, but shows a heterogeneous texture. Olivine aggregates and grains of olivine and chromite display resorption textures set in a crystalline pyroxene matrix. Large olivine aggregates are penetrated by pyroxene matrix. Flow textures are observed near olivine aggregates. Olivine, chromite, and pyroxene show minor chemical zoning, implying relatively rapid cooling. NWA 5480 contains a significant amount of platinum group elements with chondritic relative proportions. All this evidence supports that NWA 5480 is an impact‐melt breccia from a target composed of olivine and pyroxene‐rich lithologies. Such impact melt would have formed by melting crustal materials, possibly during one of the impacts that formed the South Pole basins on Vesta.     

两个相连湖泊的微生态系统——云南高原湖泊中浅水的星云湖和深水的抚仙湖研究

抚仙湖是中国云南省的一个深水湖，连接着富营养化的浅水湖－－星云湖，星云湖排放含绿藻的水进入抚仙湖。两湖位于省会昆明附近，由于地方文化、集约化农业、以及旅游业的发展，两湖已经富营养化。因为湖泊体积容量的级别差异，深水湖的富营养化几乎没被注意，抚仙湖秋季下层滞水带缺氧已经关注了20年，似乎下层滞水带是深水湖富营养化的指标或趋势。抚仙湖看起来目前情况尚好，可以说寡营养，然而，外界负荷是潜在的，且是以稳定的加速度进行的。在此对浅水湖富营养化的原因进行了讨论，包括在其它云南湖泊观察到富营养化的过程，再者，对两个连相湖的藻和蓝藻碎片的大小构成进行比照。为了与深水的抚仙湖状况进行比较，简略介绍了一个日本的深湖及其径流系统。其中，涡流和它的微生态系统，在两者中相关性很好。对于以涡流生态系统的见解判断微生态系统的深水湖富营养化问题将给予概括。     

Are C1 chondrites chemically fractionated? a trace element study

Six C1 chondrite samples and a C2 xenolith from the Plainview H5 chondrite were analyzed by radiochemical neutron activation for the elements Ag, Au, Bi, Br, Cd, Ce, Cs, Eu, Ge, In, Ir, Lu, Nd, Ni, Os, Pd, Pt, Rb, Re, Sb, Se, Sn, Tb, Te, Tl, Yb, and Zn. The data were combined with 9 earlier analyses from this laboratory and examined for evidence of chemical fractionation in C1 chondrites.A number of elements (Br, Rb, Cs, Au, Re, Os, Ni, Pd, Sb, Bi, In, Te) show small but correlated variations. Those of the first 8 probably reflect hydrothermal alteration in the meteorite parent body, whereas those of Sb, Bi, In, and Te may at least in part involve nebular processes. Br and Au show systematic abundance differences from meteorite to meteorite, which suggests hydrothermal transport on a kilometer scale. The remaining elements vary from sample to sample, suggesting transport on a centimeter scale.There is no conclusive evidence for nebular fractionation affecting C1 's. Though C1 chondrites have lower $\text{Zr}\text{Hf}$ and $\text{Ir}\text{Re}$ ratios than do other chondrite classes, these ratios vary in other classes, suggesting that those classes rather than C1's are fractionated. Three fractionation-prone REE—Ce, Eu, and Yb have essentially the same relative abundances in C1's and all other chondrite classes, and hence apparently are not fractionated in C1's. We did not confirm the large Tb and Yb variations in C1's reported by other workers.We present revised mean C1 abundances for 35 elements, based on the new data and a critical selection of literature data. Changes are generally less than 10%, except for Br, Rb, Ag, Sb, Te, Au, and the REE.The Plainview C2 xenolith has normal trace element abundances, except for 3 elements falling appreciably above the C2 range: Rb, Cs, and Bi. Hydrothermal alteration may be the reason for all 3, though nebular fractionation remains a possibility for Bi.     

Analysis of change of red tide species in Yodo River estuary by the numerical ecosystem model

Occurrence number of red tides in Osaka Bay in Japan is more than 20 cases every year. Diatom red tide was dominant in Osaka Bay, but the non-diatom red tide was dominant in early 1990s. Therefore, the material cycling in Yodo River estuary in Osaka Bay during August from 1991 to 2000 was analyzed by using the numerical ecosystem model and field observation data to clarify the reasons of change in red tide species. Year-to-year variation in calculated concentration ratio of diatom to non-diatom corresponds to the variation in observed ratio of red tide days of diatom to non-diatom. Limiting nutrient of primary production is phosphate over the period. Diatom dominated from 1991 to 1993, but it was difficult for non-diatom to grow due to the limitation by physical condition. Non-diatom was able to grow because of good physical and nutrient conditions from 1994 to 1996. And diatom dominated again under the good physical condition, and phosphorus supply was not enough for non-diatom to grow from 1998 to 2000. Phosphate concentration in the lower layer of Yodo River estuary was important to the variation in red tide species in the upper layer of Yodo River estuary.     

Transfer of60Co from midwater squid to sperm whales

Sperm whales are notable squid-eaters. They feed mainly on medium to large-sized cephalopods at midwater levels and defecate near the surface. This suggests the existence of an upward transport of⁶⁰Co by sperm whales from the mesopelagic zone (150–1,200 m). To elucidate this squid-whale route for this artificial radionuclide,⁶⁰Co content was determined in squid and in predator whales captured by commercial whaling. In the Cephalopoda livers⁶⁰Co levels of 30–500 mBq kg^–1 wet were found and in the viscera of Odontoceti (toothed whales) 15–40 mBq kg^–1 wet. About 0.3% of⁸⁰Co ingested was estimated to be retained in a 23-year-old male sperm whale. In the livers of Bryde's whales,⁶⁰Co levels of 40–80 mBq kg^–1 wet were detected, but not in euphausiids and sardines, their possible prey. The level of Co in sperm whales was nearly the same as in Bryde's whales. Specific radioactivity⁶⁰Co/⁵⁹Co in mBq µg^–1 was several times higher in sperm whale (1.1–1.6) than in cephalopods (0.19–0.77). Eating prey with a high content of⁶⁰Co in the 1960's may have contributed to the present body burden in sperm whales with a long-life span. However, the origin of⁶⁰Co in Bryde's whales is unknown.     

An anomalous eucrite,Dhofar 007, and a possible genetic relationship with mesosiderites

Abstract— We studied the texture, mineralogy, and bulk chemical composition of Dhofar 007, a basaltic achondrite. Dhofar 007 is a polymict breccia that is mostly composed of coarse‐grained granular (CG) clasts with a minor amount of xenolithic components, such as a fragment of Mg‐rich pyroxene. The coarse‐grained, relict gabbroic texture, mineral chemistry, and bulk chemical data of the coarse‐grained clast indicate that the CG clasts were originally a cumulate rock crystallized in a crust of the parent body. However, in contrast to monomict eucrites, the siderophile elements are highly enriched and could have been introduced by impact events. Dhofar 007 appears to have experienced a two‐stage postcrystallization thermal history: rapid cooling at high temperatures and slow cooling at lower temperatures. The presence of pigeonite with closely spaced, fine augite lamellae suggests that this rock was cooled rapidly from higher temperatures (>0.5 °C/yr at ˜1000 °C) than typical cumulate eucrites. However, the presence of the cloudy zone in taenite and the Ni profile across the kamacite‐taenite boundaries indicates that the cooling rate was very slow at lower temperatures (˜1–10 °C/Myr at <600–700 °C). The slow cooling rate is comparable to those in mesosiderites and pallasites. The two‐stage thermal history and the relative abundance of siderophile elements similar to those for metallic portions in mesosiderites suggest that Dhofar 007 is a large inclusion of mesosiderite. However, we cannot rule out a possibility that Dhofar 007 is an anomalous eucrite.     

Crustal partial melting on Vesta: Evidence from highly metamorphosed eucrites

We have performed a mineralogical and geochemical study of eight metamorphosed basaltic eucrites. These are classified into granulitic eucrites and type 4–7 eucrites on the basis of their textures and pyroxene mineralogy, and display mineralogical evidence for high temperature metamorphism, including partial melting. In particular, rare earth element (REE) patterns of a number of the eucrites studied show varying degrees of light REE depletion due to partial melting, with subsequent melt extraction. A simple correlation between metamorphic grade, as deduced from pyroxene mineralogy, and the degree of light REE depletion was not detected. This can be explained by the fact that homogenization, exsolution and inversion of pigeonite would have required prolonged heating at moderate temperatures (800–1000 °C), whereas partial melting would have taken place over a short time interval where temperatures exceeded that of the solidus. The eucrites studied therefore record a two stage thermal regime consisting of short, high temperature reheating events superimposed on long duration global crustal metamorphism. The short reheating events may have been caused by impact events and/or intrusions of hot magmas. The results of this study demonstrate that the thermal history of eucritic crust was more complex than can be explained by a simple burial model alone. In particular, the origin of Stannern trend eucrites requires contamination of Main-Group magmas by partial melts extracted from residual eucrites.     

Chemical characteristics of the lherzolitic shergottite Yamato 000097: magmatism on Mars inferred from the chemical compositions of shergottites

As a part of a consortium study, we analyzed the Martian meteorite Yamato (Y) 000097 by prompt gamma-ray analysis, instrumental neutron activation analysis, and instrumental photon activation analysis. For comparison, we also analyzed Allan Hills (ALH) 77005 using the same methods. The data confirm that Y000097 belongs to lherzolitic shergottites in terms of chemical composition. Although there exist slight differences in elemental abundances among lherzolitic shergottites due to differences in the modal abundances of constituent minerals, they have essentially the same chemical compositions, suggesting they are genetically related and experienced similar formation histories.Zr/Hf ratios obtained for Y000097 and ALH 77005 are subchondritic, consistent with values reported for other lherzolitic shergottites and olivine-phyric shergottites. Such fractionation can be explained by invoking clinopyroxene, ilmenite, or majorite in the petrogenesis of the shergottites' source material. CI-normalized Hf/Sm ratios obtained for Y000097 and ALH 77005 are 1.52 and 1.37, respectively, consistent with superchondritic Hf/Sm ratios reported for shergottites. Based on experimentally derived partition coefficients, majorite is the best candidate mineral for the fractionation of Hf and Sm in shergottites.