Grain abundance in the primordial atmosphere of the Earth

For models of planetary accumulation in the presence of solar nebular gas, the initial surface temperature of the Earth is controlled by the grain opacity of the atmosphere. The surface temperature in turn controls the quantity of neon dissolved and trapped within the interior of the Earth. To compare accumulation theory with observation calculations have been made of the grain opacity expected to be associated with accumulation in a gaseous nebula. There are two parameters that are in principle determined by the theory, but actually are at present uncertain: the mean eccentricity e of the planetesimal swarm, and the fraction ξ of the accretional energy that is expended in the release of grains into the atmosphere by ablation of the incoming planetesimal. It is found that if the eccentricity of swarm is low (10^?3), rather low values of ξ(10^?5) are required to match the observed neon data. In contrast higher values of ξ are required (10^?1) for the most probable case, intermediate eccentricity (10^?2). For the high eccentricity case (e ～ 0.1) ξ must be >10^?2. The results show that avoidance of excess trapped neon of solar composition places restrictive, but not necessarily impossible, conditions on the parameters of the accumulation theory.     

Large but variable particulate flux in the Antarctic Ocean and its significance for the chemistry of Antarctic water

Settling particles were collected at 1,460 m and 3,760 m depth in the Antarctic Ocean with sediment traps of time series type. The total deployment period of 40 days was divided into four terms of 10 days each. Seawater samples were collected both at deployment and retrieval of the traps at each site. During the 42 days the concentration of silicate in the surface water decreased by 32%, whereas those of nitrate and phosphate decreased by only 4–5%. The total particulate flux in the Antarctic Ocean is the largest among those hitherto observed in the world ocean. The time variation of the particulate flux at 1,460 m depth almost coincided with that at 3,760 m. The settling particles were comprised roughly of 80% biogenic silica, 15% organic matter and 5% other substances including sea salt. The clay fraction was only 0.05% at 1,460 m depth. The settling flux of biogenic silica agrees fairly well with the calculated rate of change in the concentration of silicate in the surface 100 m. Thus it is concluded that preferential propagation of diatoms reduces the concentration of silicate prior to other nutrients in the Antarctic Ocean.     

Simultaneous vertical measurements of in situ pH and CO2 in the sea using spectrophotometric profilers

We have developed new systems capable of profiling to >1000 m for measuring in situ pH and fugacity of CO₂ (fCO₂) in the ocean using spectrophotometric analysis (pH and CO₂ profilers). The in situ pH is determined by detecting the color change of the pH indicator (m-cresol purple). It can withstand ambient pressure to 1000 m depth. The CO₂ profiler analyzed in situ fCO₂ by detecting the change of pH in an inner solution, equilibrated with the seawater through a gas permeable membrane. It can be operated to 2500 m depth. We used an amorphous fluoropolymer tubing form of AF-2400 for the gas permeable membrane due to its high gas permeability coefficients. The inner solution was a mixture of 2 μM bromocresol purple (BCP) and 5 μM sodium hydroxide. This system gave us a response time of 1 minute, which is twice as fast as previous systems. The precisions of pH and CO₂ profilers were within 0.002 and 2.5% respectively. We have used these profilers to study the North Pacific, obtaining good agreement with the difference between the data from profilers and a discrete bottle of 0.002 ± 0.005 pH (SE, n = 25) and −0.4 ± 3 μatm (SE, n = 31).     

Early Variscan magmatism in the Western Carpathians: U–Pb zircon data from granitoids and orthogneisses of the Tatra Mountains (Slovakia)

This study presents the first U–Pb zircon data on granitoid basement rocks of the Tatra Mountains, part of the Western Carpathians (Slovakia). The Western Carpathians belong to the Alpine Carpathian belt and constitute the eastern continuation of the Variscides. The new age data thus provide important time constraints for the regional geology of the Carpathians as well as for their linkage to the Variscides. U–Pb single zircon analyses with vapour digestion and cathodoluminescence controlled dating (CLC-method) were obtained from two distinct granitoid suites of the Western Tatra Mountains. The resulting data indicate a Proterozoic crustal source for both rock suites. The igneous precursors of the orthogneisses (older granites) intruded in Lower Devonian (405 Ma) and were generated by partial melting of reworked crustal material during subduction realated processes. In the Upper Devonian (365 Ma), at the beginning of continent–continent collision, the older granites were affected by high-grade metamorphism including partial melting, which caused recrystallisation and new zircon growth. A continental collision was also responsible for the generation of the younger granites (350–360 Ma). The presented data suggest multi-stage granitoid magmatism in the Western Carpathians, related to a complex subduction and collision scenario during the Devonian and Carboniferous. Received: 19 February 1999 / Accepted: 3 December 1999     

Re–Os molybdenite dating of granite-related Sn–W–Mo mineralisation at Hnilec, Gemeric Superunit, Slovakia

Summary Re–Os molybdenite ages from the exocontact of the Hnilec granite-greisen body provide temporal constraints for tin, tungsten and molybdenite mineralisation in the Gemeric Superunit, Slovakia. Two molybdenite separates were taken from a representative sample of the Sn–W–Mo mineralisation at Hnilec and their Re–Os ages of 262.2 ± 0.9 and 263.8 ± 0.8 Ma (2-sigma) are in excellent agreement. The obtained Re–Os molybdenite ages are similar to recent but less precise electron microprobe monazite (276 ± 13 Ma) and U–Pb single zircon (250 ± 18 Ma) ages from the Hnilec granite intrusion, supporting a granite-related greisen origin for the Sn–W–Mo mineralisation. Our precise Re–Os molybdenite ages resolve the long time controversy over the timing of high-temperature mineralisation in the Gemeric Superunit. These Permian ages eliminate suggestions of an Alpine age. The sulphur isotope composition of the studied molybdenite is δ³⁴S_(CDT) = 1.71 ± 0.2‰ and is consistent with a magmatic sulphur source. Field observations indicate the lack of a broad contact aureole in the vicinity of the Hnilec granite body. Shallow level granite emplacement in schistose host rocks was accompanied by alteration and formation of tin-tungsten greisen in the upper part of the granite and exocontact molybdenite mineralisation, both commonly lacking in other granite bodies within the Gemeric Superunit.     

Tracking an upper limit of the “Carnian Crisis” and/or Carnian stage in the Western Carpathians (Slovakia)

International Journal of Earth Sciences - The Late Triassic timescale, especially the Carnian–Norian boundary, is poorly constrained mainly due to a paucity of high-precision radio-isotopic...     

The calibrated map of the HII region S237 in Hα emission

The difference of spatial distributions between the O-type stars, supernovae and red giant stars found by Riekeet al. (1980) in the nuclear region of M82 can be interpreted if the star formation has been triggered by shock waves expanding from the nucleus with velocities of 100 km s^–1 at 300 pc from the centre and if the explosions have recurrently occurred with time interval of about 2×10⁶ yr. The recurrent formation of such giant compressed gas layer makes the formation rate of massive stars efficient.     

Actigraphically evaluated sleep on the days surrounding the Great East Japan Earthquake

The present study examined actigraphically evaluated sleep on the days surrounding the greatest earthquake in Japanese history. The Great East Japan Earthquake occurred unexpectedly on the third day of a 1-week actigraphy measurement. The subjects were eight elderly (73.1 ± 4.3 years, mean ± SD) individuals living in Sendai city, one of the largest cities damaged by the earthquake. All of the subjects wore their actigraph devices until 2 days after the earthquake. The results showed that wake after sleep onset (WASO) was significantly increased (118 ± 29 min, mean ± SE) the first night after the earthquake compared with pre-earthquake values (35 ± 12 min). The subjects described being awoken by frequent aftershocks the first night. This sleep debt was recovered the next day through significant increases in daytime napping and the length of nocturnal sleep periods resulting from earlier bedtimes. An electrical blackout that lasted 2–3 days seemed to be associated with earlier bedtimes by inducing a dark and cold environment. One subject who evacuated to a school gymnasium after the earthquake suffered severely disturbed sleep due to cold temperatures (nocturnal WASO over 180 min). These findings suggest that the environmental factors related to disrupted infrastructure might have considerable impacts on sleep in the first several days after the catastrophic disaster. The findings should be considered for future disaster preparedness initiatives.     

Geotectonic framework of Permo–Triassic magmatism within the Korean Peninsula

This study presents sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon ages, and whole-rock chemical and isotopic (Sr-Nd) compositions of representative Triassic plutons from South Korea. The plutons from the Gyeonggi massif (Hongseong, Namyang, Yangpyeong and Odesan), the central Okcheon belt (Baeknok and Yongsan), and the Yeongnam massif (Sangju, Gimcheon, Hamyang and Macheon) yield zircon U–Pb ages of ca. 232–226 Ma, 227–226 Ma, and 240–228 Ma, respectively. Among the Triassic plutonic suite in South Korea, those within the Gyeonggi massif are dominated by granite, syenite, monzonite, monzodiorite and gabbro. Plutons within the Okcheon belt are mainly by granite to quartz monzodiorite. The Yeongnam massif mainly incorporates granite to granodiorite and minor monzodiorite intrusions. The geochemical signatures of the Triassic plutons are characterized by Ta–Nb troughs, depletion of P and Ti, and enrichment of LILE. Most plutons except Macheon monzodioritic pluton show high initial ⁸⁷Sr/⁸⁶Sr ratios (0.708248–0.714678) and strongly negative ε_Nd(T) (− 20.3 to − 7.7) values, suggesting contribution from middle to upper crust. In contrast, the Macheon monzodioritic pluton in the Yeongnam massif shows relatively low initial ⁸⁷Sr/⁸⁶Sr ratios (0.706547-0.706629) and negative ε_Nd(T) (− 4.43 to − 3.62) values. The Middle Triassic syenite–monzonite–granite–gabbro series in and around the Gyeonggi massif possess high-K calc-alkaline and shoshonitic affinity suggesting a post-collisional magmatic event following the Permo–Triassic collision between the North and South China blocks. The Triassic plutons in the Yeongnam massif and the Okcheon belt, together with a Permian Yeongdeok pluton in the Gyeongsang basin, show features typical of high- to medium-K calc-alkaline magmatism with LREE and LILE enrichments. This together with a depletion of Y and HREE suggests their formation in a subduction setting. Our results provide robust evidence to consider the Gyeonggi massif as an extension of the Qinling–Dabie–Sulu belt between the North and South China blocks in central China. The Okcheon belt and Yeongnam massif in South Korea, together with the continental margin of South China, are marked by a common Permian to Triassic magmatic episode, probably related to the paleo-Pacific slab subduction.     

Assessment of nitrogen loading from the Kiso-Sansen Rivers into Ise Bay using stable isotopes

Concentrations of particulate organic nitrogen (PN), dissolved inorganic nitrogen (DIN), and their nitrogen isotope ratios (δ ¹⁵N) in the Kiso-Sansen Rivers were determined from monthly observations over the course of a year to assess variations in the form and sources of riverine nitrogen discharged into Ise Bay. The δ ¹⁵N values of NO₃ ⁻ observed in the Kiso-Sansen Rivers showed a logarithmic decreasing trend from 8 to 0‰, which varied with the river discharge, indicating mixing between point sources with high δ ¹⁵N and non-point sources with low δ ¹⁵N. The influence of isotope fractionation of in situ biogeochemical processes (mainly DIN assimilation by phytoplankton) on δ ¹⁵N of NO₃ ⁻ was negligible, because sufficient concentrations of NH₄ ⁺ for phytoplankton demand would inhibit the assimilation of NO₃ ⁻. A simple relationship between river discharge and δ ¹⁵N of NO₃ ⁻ showed that the fraction of total NO₃ ⁻ flux arising from point sources increased from 4.0–6.3% (1.1–1.8 tN day⁻¹) during higher discharge (>600 m³ s⁻¹) to 30.2–48.3% (2.6–4.1 tN day⁻¹) during lower discharge (<300 m³ s⁻¹). Riverine NO₃ ⁻ discharge from the Kiso-Sansen Rivers can explain 75% of the variations in surface NO₃ ⁻ at the head of Ise Bay over the year.