The structures of eye and surrounding tissues of Longman's beaked whale,Indopacetus pacificus

Observations were made on one eye from a Longman’s beaked whale Indopacetus pacificus, which was probably one of the least known extant cetaceans. The whale died shortly after swimming aground on the coast in the Nishikata Beach, Sendai-shi, Kagoshima-ken Prefecture, Japan, on July 26, 2002. It was a mature female with body length 6.45 m. This paper documented the basic structural characteristics of her visual organ of the whale in order to better understand this animal.     

Timescale of magma chamber processes revealed by U–Pb ages,trace element contents and morphology of zircons from the Ishizuchi caldera,Southwest Japan Arc

U–Pb geochronology and trace element chemistry of zircons in a microscale analysis were applied to the Ishizuchi caldera in the Outer Zone of Southwest Japan in order to estimate the timescale of the magma process, in particular, the magma differentiation. This caldera is composed mainly of ring fault complexes, major pyroclastic flow deposits, and felsic intrusion including central plutons. Using SHRIMP‐IIe, our new U–Pb zircon ages obtained from the major pyroclastic flow deposits (Tengudake pyroclastic flow deposits), granitic rocks from central plutons (Soushikei granodiorite and Teppoishigawa quartz monzonite), and rhyolite from the outer ring dike (Tenchuseki rhyolite) and the inner ring dike (Bansyodani rhyolite) are 14.80 ±0.11 Ma, 14.56 ±0.10 Ma, 14.53 ±0.12 Ma, 14.55 ±0.11 Ma and 14.21 ±0.19 Ma, respectively. Based on the U–Pb ages, the Hf contents and the REE patterns of the zircons, three stages are recognized in the evolutionary history of the magma chamber beneath the Ishizuchi caldera: (i) climactic Tengudake pyroclastic flow eruption; (ii) Tenchuseki rhyolite intrusion into the outer ring dike and central pluton intrusion; and (iii) Bansyodani rhyolite intrusion in the inner ring dike. These results indicate a magma evolution history of the Ishizuchi caldera system which took at least ca 600 kyr from the climatic caldera‐forming eruption to the post‐caldera intrusions. Our new geochronological data suggest that the Ishizuchi caldera formed as part of the voluminous and episodic magmatism that occurred in the wide zone along the Miocene forearc basin of Southwest Japan during the inception of the young Philippine Sea Plate subduction.     

Does suspended matter drained from the Isahaya freshwater reservoir cause organic enrichment in the northern Ariake Bay?

The inner part of Isahaya Bay was converted to a freshwater reservoir following the closure of the land claim dike in 1997. Turbid water drains into Isahaya Bay when water levels increase. We investigated whether particulate organic matter (POM) from the reservoir in Isahaya Bay has caused bottom organic enrichment in the northern part of Ariake Bay. Using potential end-members from before to after the rainy seasons, during which a frequent discharge from the reservoir was expected, stable isotope analyses were performed on sediments collected from Isahaya Bay and northern Ariake Bay. Each end-member was isotopically differentiated by δ¹³C and δ¹⁵N (riverine POM: ?28.5 to ?27.2‰ and 3.3–4.6‰; reservoir POM: ?25.7 to ?25.3‰ and 7.4–8.4‰; marine POM: ?21.8 to ?19.7‰ and 6.7–7.6‰; microphytobenthos estimated from consumers: ?16.1 to ?15.9‰ and 5.2–6.1‰, respectively). Sediment isotopic signatures fell within the mixing space defined by the signatures of the end-members. Marine POM contributed greatly to bottom sediments in both seasons in Isahaya Bay and Ariake Bay, ranging from ca. 60–70 and 40–60%, respectively. Reservoir POM contributed around 10% to bottom sediments. This percentage slightly increased in the sediment of Isahaya Bay after the rainy season, but decreased in the sediment of Ariake Bay. Thus, most of the POM discharged from the reservoir would not reach the northern part of Ariake Bay and would not be a major contributor to organic enrichment. This study is the first to quantitatively describe the contribution of drained reservoir POM outside Isahaya Bay.     

Environmental controls on phytoplankton production in coastal ecosystems: A case study from Tokyo Bay

Phytoplankton biomass and primary production were examined in their environmental context, for a semi-enclosed bay (Tokyo Bay, Japan) using data from monthly samples collected over a three-year period. Heavy precipitation and high surface temperatures in the late spring and summer gave rise to a highly-stratified water-column and stimulated a series of phytoplankton blooms, whereas during the winter, a weakly-stratified and deeply-mixed water-column led to a rapid decline in phytoplankton biomass under light-limited growth conditions. By incorporating pigment, photophysiological and optical data into a primary production model we show that daily, water-column primary production ranges from ∼160 mg C m⁻² d⁻¹ to 7600 mg C m⁻² d⁻¹. High water turbidity and deep vertical mixing, both separately and in concert, limit the light available for algal growth over much of the year. Annual primary production varied from 370 to 580 g C m⁻² y⁻¹. The relative influences of nutrient limitation and light limitation are assessed. A model is developed that describes this in an explicit manner using photophysiological parameters.     

日本岛根县石见银矿区英安质火山岩中的黑云母矿物学特征及其K-Ar和40Ar-39Ar年代学研究

以显微镜、X射线衍射仪和电子探针等方法,对日本岛根县石见银矿区所产英安质火山岩中的黑云母进行了详细的研究．观察到部分黑云母经受了不同程度的热液蚀变作用。根据对未蚀变、或仅受到轻微蚀变作用的黑云母所进行的^40Ar-^39Ar同位素年龄测定,它们主要为第四纪产物。但是,从经受强热液蚀变作用的黑云母所获得的^40Ar-^39Ar同位素结果表明,后期的高温热液活动可以破坏晶体中的原始K—Ar同位素平衡,使得其。^40Ar-^39Ar同位素年龄与高于从未蚀变矿物所获得的结果,从而产生严重的年代失真。所以,对来自热液蚀变带的样品需要进行详细的矿物学研究。估计对黑云母的原始KAr同位素体系产生破坏的热扰动临界温度可能在200℃左右。     

The Weathering of Granodiorite Porphyry in the Thiel Mountains, Inland Antarctica

The weathering of granodiorite porphyry is examined in the extremely cold and dry environment of the inland part of Antarctica. Weathering features include granular disintegration, rock varnish, and sheeting. Sheeting has gradually proceeded since the exposing of the nunatak, but the other types of weathering have not actively advanced in recent times.
Granular disintegration primarily comprises the release of individual crystals. The mechanism of this release is that cracks are created along crystal boundaries and cleavages in phenocrysts mainly due to differential thermal expansion. Plagioclase and hypersthene are released more readily than quartz. Disintegration of plagioclase has produced many prism-shaped holes, 0.5 to 2.0 mm in length, while fine-grained quartz crystals, 0.05 to 0.1 mm in diameter, are incidentally released without cracking.
The reddish brown (10R4/4) rock varnishes result from oxidation and consist of limonite, which fills cracks and penetrates into crystals. Ferrous iron in hypersthene, biotite, ilmenite and magnetite is transformed into limonite by oxidation. Manganese is not found in the varnishes. Sulfur, which is important for oxidation and which may have originated from adhered snow, is concentrated on the surface of the rock.
Sheeting has precipitated rock falls, and has gradually formed a gray mosaic on the varnished wall. The sheeting was caused by gravitational body force, which is internal stress of the rock body due to the mass of the overburden.     

A Late Holocene geomagnetic secular variation record from Erhai Lake, southwest China

A secular variation record of the geomagnetic field direction for the last 6.5  kyr has been obtained from the magnetization of sediment cores from Erhai Lake, southwest China. In order to make a comparison with this record, secular variation in east-central China was investigated by combining available magnetic field data from historical records and archaeomagnetic measurements since about 350 bc . The secular variation in Erhai Lake shows features consistent with the combined record, except for the oldest three observed declination swings in Sian from 720 to 900 ad . Many features of declination and inclination in China also occur in Japan. From 500 to 1000 ad , declination was westerly ranging from about −20° to −5° in Erhai Lake, east-central China, and Japan.