Phytoplankton community adaptation to changing light levels in the southern Beaufort Sea,Canadian Arctic

The chlorophyll a specific absorption coefficient of phytoplankton, a_φ^∗(λ) is an important parameter to determine for primary production models and for the estimation of phytoplankton physiological condition. Knowledge of this parameter at high latitudes where nutrient rich cold water submitted to low incident light is a common environment is almost nonexistent. To address this issue, we investigated the light absorption properties of phytoplankton as a function of irradiance, temperature, and nutrients using a large data set in the southern Beaufort Sea during the open water to ice cover transition period. The a_φ^∗(λ) tended to increase from autumn when open water still existed to early winter when sea ice cover was formed, resulting from a biological selection of smaller-size phytoplankton more efficient to absorb light. There was no significant correlation between a_φ^∗(λ) and irradiance or temperature for both seasons. However, a_φ^∗(λ) showed a significant positive correlation with NO₃ + NO₂. Implications of the results for phytoplankton community adaptation to changing light levels are discussed.     

Clinopyroxene-perovskite phase transition of FeGeO3 under high pressure and room temperature

In order to confirm the possible existence of FeGeO₃ perovskite, we have performed in situ X-ray diffraction measurements of FeGeO₃ clinopyroxene at pressures up to 40 GPa at room temperature. The transition of FeGeO₃ clinopyroxene into orthorhombic perovskite is observed at about 33GPa. The cell parameters of FeGeO₃ perovskite are a=4.93(2) Å, b=5.06(6) Å, c=6.66(3) Å and V=166(3) ų at 40 GPa. On release of pressure, the perovskite phase transformed into lithium niobate structure. The previously reported decomposition process of clino-pyroxene into Fe₂GeO₄ (spinel)+GeO₂ (rutile) or FeO (wüstite) +GeO₂ (rutile) was not observed. This shows that the transition of pyroxene to perovskite is kinetically accessible compared to the decomposition processes under low-temperature pressurization.     

Seasonal variation of <Superscript>228</Superscript>Ra/<Superscript>226</Superscript>Ra ratio in surface water from the East China Sea and the Tsushima Strait

A total of 21 surface water samples were collected on the east side of the East China Sea (ECS) (3 sites) and at the Tsushima Strait (1 site), and ²²⁶Ra and ²²⁸Ra activities were measured using low-background γ-spectrometry. The ²²⁸Ra/²²⁶Ra ratios among the samples exhibited notable seasonal variation (²²⁸Ra/²²⁶Ra = 0.2–2.6) accompanying changes of salinity (31.7–34.7). Seasonal water circulation within the ECS is hypothesized to cause the change by altering the mixing ratio of ²²⁸Ra-rich continental shelf water and ²²⁸Ra-poor Kuroshio water.     

基于远场参考的超低频(ULF)地震地磁数据处理——以2003年1月日本茨城县5.1级地震为例

野外观测和室内试验表明,地震孕育和发生过程中可能产生电磁信号。地震电磁现象在防震减灾中具有潜在的应用价值,已成为21世纪国内外地学研究热点之一。由于地震电磁信号较弱,通常混杂于空间场源信号及人文噪音中,不易在观测数据中提取出来。以2003年1月日本茨城县5.1级地震为例,探讨远场参考在超低频(ULF)地震地磁数据处理中的应用,进而检测震前局部磁场异常。在此基础上,讨论远场参考法的优势及可能存在的不足。分析结果表明,2003年1月日本茨城县5.1级地震发生前存在局部磁场异常,验证了远场参考方法的有效性,相关成果可为地震地磁数据处理提供有益参考。     

A Transit of Venus Possibly Misinterpreted as an Unaided-Eye Sunspot Observation in China on 9 December 1874

Solar Physics - Large sunspots can be observed with the unaided eye under suitable atmospheric seeing conditions. Such observations are of particular value because the frequency of their appearance...     

Tethyan and Indian subduction viewed from the Himalayan high- to ultrahigh-pressure metamorphic rocks

The Himalayan range is one of the best documented continent-collisional belts and provides a natural laboratory for studying subduction processes. High-pressure and ultrahigh-pressure rocks with origins in a variety of protoliths occur in various settings: accretionary wedge, oceanic subduction zone, subducted continental margin and continental collisional zone. Ages and locations of these high-pressure and ultrahigh-pressure rocks along the Himalayan belt allow us to evaluate the evolution of this major convergent zone.

(1) Cretaceous (80–100 Ma) blueschists and possibly amphibolites in the Indus Tsangpo Suture zone represent an accretionary wedge developed during the northward subduction of the Tethys Ocean beneath the Asian margin. Their exhumation occurred during the subduction of the Tethys prior to the collision between the Indian and Asian continents.

(2) Eclogitic rocks with unknown age are reported at one location in the Indus Tsangpo Suture zone, east of the Nanga Parbat syntaxis. They may represent subducted Tethyan oceanic lithosphere.

(3) Ultrahigh-pressure rocks on both sides of the western syntaxis (Kaghan and Tso Morari massifs) formed during the early stage of subduction/exhumation of the Indian northern margin at the time of the Paleocene–Eocene boundary.

(4) Granulitized eclogites in the Lesser Himalaya Sequence in southern Tibet formed during the Paleogene underthrusting of the Indian margin beneath southern Tibet, and were exhumed in the Miocene.

These metamorphic rocks provide important constraints on the geometry and evolution of the India–Asia convergent zone during the closure of the Tethys Ocean. The timing of the ultrahigh-pressure metamorphism in the Tso Morari massif indicates that the initial contact between the Indian and Asian continents likely occurred in the western syntaxis at 57 ± 1 Ma. West of the western syntaxis, the Higher Himalayan Crystallines were thinned. Rocks equivalent to the Lesser Himalayan Sequence are present north of the Main Central Thrust. Moreover, the pressure metamorphism in the Kaghan massif in the western part of the syntaxis took place later, 7 m.y. after the metamorphism in the eastern part, suggesting that the geometry of the initial contact between the Indian and Asian continents was not linear. The northern edge of the Indian continent in the western part was 300 to 350 km farther south than the area east of the Nanga Parbat syntaxis. Such “en baionnette” geometry is probably produced by north-trending transform faults that initially formed during the Late Paleozoic to Cretaceous Gondwana rifting. Farther east in the southern Tibet, the collision occurred before 50.6 ± 0.2 Ma. Finally, high-pressure to ultrahigh-pressure rocks in the western Himalaya formed and exhumed in steep subduction compared to what is now shown in tomographic images and seismologic data.     

Wind-Tunnel Experiment on Logarithmic-Layer Turbulence under the Influence of Overlying Detached Eddies

A wind-tunnel experiment was carried out to test a hypothesis that the turbulence characteristics in the near-neutral surface layer are largely determined by detached eddies from above. The surrogate detached eddies were generated by using an active turbulence grid installed at the front of the test section and the parameters of the grid were chosen such that the fully developed logarithmic layer downstream consists of a turbulent flow that has similar normalized intensity to that typically observed in the near-neutral atmospheric surface layer. The effects of the detached eddies on turbulence characteristics were investigated by comparison with a second experiment without detached eddies. The influence of the detached eddies on the logarithmic layer was mostly on the coherent structures; the logarithmic layer with the detached eddies revealed a multi-layer structure similar to that found in the atmosphere where the lower part of the surface layer is dominated by sweep-like events and the upper part by ejection-like events. Our experiments show that the mean velocity gradient and the Reynolds shear stress were, however, not affected significantly by the detached eddies and hence the eddy viscosity.     

Grain size dependence of far-infrared extinction spectra of amorphous fine grains

The far-infrared extinction spectra of fused silica grains with the size range from 1.8 m to 60 Å were measured. The spectra depend clearly on the grain size. For large grain sizes (from 1.8 m to 400 Å) the spectra show almost the ^–2 dependence ( is the wavelength), which resembles that of the bulk material. For fine grains (70 and 60 Å) the spectra are less steep, the wavelength dependence being ^–1. This grain size dependence of extinction spectra agrees essentially with the prediction of Seki and Yamamoto.     

A study on the distribution of total bacteria,bacterial aggregates and heterotrophic bacteria in the sea

The concentrations of total bacteria, bacterial aggregates and so-called heterotrophic bacteria were compared and discussed with special reference to the watermasses that vertically layered at the western North Pacific central region and the subarctic Pacific region.The concentrations of bacterial aggregates, having cells more than 25, were considerably uniform throughout the ocean depths. This was also shown indirectly by the measurements of size spectrum and organic constituents of particles, especially in the subsurface and deep watermasses. The so-called heterotrophic bacteria decreased in their concentration in deeper watermass, and the decrease was not obvious within each watermass but obvious among watermasses.     

Spatial Heterogeneity in Distributions of Chlorophyll a Derivatives in the Subarctic North Pacific during Summer

The distribution of chlorophyll a derivatives was examined in samples collected from the subarctic North Pacific during July to September 1997. Pheophorbide a, pheophytin a and pyropheophorbide a as determined by high performance liquid chromatography (HPLC) were the major derivatives recorded. The distribution patterns of chlorophyll a and its derivatives showed a strong vertical and horizontal heterogeneity. Patches with high concentration of derivatives seemed to be associated with high concentration of chlorophyll a. A clear east-west gradient was observed in both chlorophyll a and pheophorbide a integrated from the surface to 100 m depth with significantly higher amounts of both the pigments in the Western Subarctic Gyre and in the Bering Sea than in the Alaskan Gyre. In contrast, no apparent gradient was observed in the integrated pyropheophorbide a and pheophytin a. Grazing experiments conducted with the copepod (Neocalanus cristatus) and salp (Cyclosalpa bakeri) fed on five species of phytoplankton cultures, showed a marked difference in the composition of the derivatives in their fecal pellets. Pyropheophorbide a was dominant in the copepod fecal pellet regardless of the phytoplankton species fed on. In the salp, however, pheophytin a and pheophorbide a were found in the fecal pellets, the relative concentrations varying with the algal food. Spatial heterogeneity in the distribution of the derivatives is considered to reflect local variations in dominant herbivorous processes.