THREE NEW GSJ ROCK REFERENCE SAMPLES: RHYOLITE JR-3, GABBRO JGB-2 AND HORNBLENDITE JH-1

Three new rock reference samples, Rhyolite JR-3, Gabbro JGb-2 and Hornblendite JH-1 have been prepared by the Geological Survey of Japan for collaborative studies on their chemical composition. Twenty-eight major, minor and trace elements were determined and presented. The results of homogeneity tests showed that all elements are considered to be distributed homogeneously in each reference sample. Geological and mineralogical characteristics are also described.     

Cosmic-ray-produced40K and50V in the metal phase of chondrites

Cosmic-ray-produced⁴⁰K in the metal phase of six chondrites and⁵⁰V in that of one chondrite were determined using a surface ionization mass spectrometer. The²²Ne_total/⁴⁰K_metal ratios of the chondrites are explained in part by shielding effects during cosmic-ray irradiation. The wide variation of this ratio in some groups of meteorites is explained in terms of partial loss of rare-gas nuclides. Radiation ages for the chondrites were determined using⁴⁰K measurements and production-rate estimates from thick target calculations.     

http://www.sciencedirect.com/science/article/pii/S1674987115000870

Cap Carbonates overlie the Marinoan Snowball Earth-related glacial diamictite,and possibly record the drastic surface environmental change and biological evolution after the Snowball Earth.We conducted on-land drilling from the Liantuo Formation,through the Nantuo,to the lower Doushantuo Formation in the Three Gorges area of South China to collect fresh,continuous samples in the Three Gorges area.We obtained high-resolution chemostratigraphies of δ~(13)C and δ~(18)O values of carbonates from the topmost part of the Nantuo Formation to the Cap Carbonate,in order to decode the detailed surface environmental change in the shallow marine setting.The δ~(13)C chemostratigraphy possesses some unique characteristics:(1) stable δ~(13)C values as a whole,but ubiquitous low δ~(13)C anomalies through the Cap Carbonate,(2) increase of the δ~(13)C values from-3 to +5‰ across the C2/C3 boundary,(3) no δ~(13)C anomaly between the C1 and C2 boundary,and(4) presence of an anomalous high δ~(13)C value(+2.3‰)and a faint positive correlation between δ~(13)C and δ~(18)O values in the C1 unit.Evidence of quite low δ~(13)C anomalies(with a nadir of-41‰),ubiquitous negative δ~(13)C anomalies through the Cap Carbonate,and a high δ~(13)C anomaly accompanied with a faint positive correlation between δ~(13)C and δ~(18)O values in the C1 unit supports decomposition and formation of methane hydrate during Cap Carbonate formation.The drastic increase of δ~(13)C values from the upper C2 to C3 units indicates enhancement of primary productivity and organic carbon burial,possibly due to high continental fluxes after the Snowball Earth event,evidenced by high Sr isotope values.The increase is restricted to the proximal side of the inner shelf in South China,and the timing of the increase of δ~(13)C values of carbonates is earlier at Three Gorges area than any other area,suggesting that the enhancement of primary productivity started in the proximal environment because of higher continental influxes.The increase in oxygen contents of seawater due to the enhanced primary productivity possibly resulted in the emergence of multicellular animals soon after Cap Carbonate deposition.     

Ca isotopic compositions of dolomite, phosphorite and the oldest animal embryo fossils from the Neoproterozoic in Weng'an, South China

Deciphering the drastic changes of surface environment and the emergence of animals after the Neoproterozoic Snowball Earth event are important for understanding the changes of surface environment and its influence on the evolution of life through geologic time. Especially, the emergence of two types of Metazoan animals such as animal embryo fossils, cnidarians or sponges, and Ediacaran fauna in the late Neoproterozoic was one of the critical turning points in the biological evolution.Calcium is one of the essential elements for the growth of most animals. In this study, in order to evaluate the Ca cycles in the Neoproterozoic, we have measured Ca isotopic ratios (⁴⁴Ca/⁴²Ca and ⁴³Ca/⁴²Ca) for phosphorite, dolostone and phosphatic animal embryo fossils with a multiple collector, inductively coupled plasma-mass spectrometer (MC-ICP-MS). The resulting ⁴⁴Ca/⁴²Ca ratio defined by the relative deviation from the ratio of NIST SRM915a (δ^44/42Ca_NIST915) for phosphorite and dolostone ranges from 0.83 to 0.95‰, demonstrating that the fractionation between phosphorite/dolostone and seawater was very small. This evidence indicates that at the emergence of the Weng'an biota seawater was deficient in Ca probably due to mass deposition of phosphorite/dolostone and to the beginning of Ca-biomineralization.Three phosphatic animal embryo fossils have lower δ^44/42Ca values than the phosphorite and dolomite, implying that the precursor of the phosphatic embryo fossils was able to fractionate Ca isotopes through Ca-biomineralization, consistent with marine gastropods.     

Seasonal succession in the diatom community of Sendai Bay,northern Japan,following the 2011 off the Pacific coast of Tohoku earthquake

Sendai Bay in northern Japan suffered serious damage from massive tsunamis generated by the 2011 off the Pacific coast of Tohoku earthquake. The physical disturbance caused by a tsunami may affect the coastal ecosystem, including the planktonic diatom community. We investigated seasonal changes in the diatom community structure at a coastal and an offshore station in Sendai Bay, from June 2011 (3 months after the tsunami) to April 2014. Diatom abundance increased at both stations during the spring. Sporadic increases were also recorded at the coastal station during the summer because of silicate input from river discharge. Seasonal succession of the diatom communities was similar at both the coastal and offshore stations. The onset of the spring bloom consisted mainly of Chaetoceros spp. when water temperatures were low. Subsequently, species such as Skeletonema costatum s.l. became dominant as salinity and nutrient concentrations decreased. Cell density decreased from summer into early winter. Leptocylindrus danicus became dominant in the summer, but was replaced by Thalassiosira cf. mala from autumn into winter. Redundancy analysis (RDA) showed that most of the variation in the diatom community could be explained by temperature, salinity, NO₃ ^?, NO₂ ^?, PO₄ ^3?, and SiO₂. In addition, the occurrence of diatom species before the tsunami showed a similar pattern to that after the tsunami, suggesting that the tsunami did not have a serious impact on the diatom community in Sendai Bay.     

Estimating of gas transfer velocity using triple isotopes of dissolved oxygen

The atmosphere-ocean exchange of climatically important gases is determined by the transfer velocity (k) and concentration gradient across the interface. Based on observations in the northwestern subarctic Pacific and Sagami Bay, we report here the results of the first ever application of the natural abundance of triple isotopes of dissolved oxygen (¹⁶O, ¹⁷O and ¹⁸O) for direct estimation of k and propose a new relationship with wind speed. The k values estimated from nighttime variations in oxygen isotopes are found to be higher than the direct estimations at low wind speed (<5 m s⁻¹) and lower at high wind speeds (>13 m s⁻¹) and showed significant spatial variability. The method presented here can be used to derive seasonal and spatial variations in k and the influence of surface conditions on the value, leading to improved estimates of biogenic/anthropogenic gas exchange at the air-sea interface.     

Relationship between sinking organic matter and minerals in the shallow zone of the western Subarctic Pacific

We used time-series sediment trap data for four major components, organic matter and ballast minerals (CaCO₃, opal, and lithogenic matter) from 150, 540, and 1000 m in the western subarctic Pacific (WSAP), where opal is the predominant mineral in sinking particles, to develop four simple models for settling particles, including the “ballast model”. The ballast model is based on the concept that most of the organic matter “rain” in the deep sea is carried by the minerals. These four models are designed to simultaneously reproduce the flux of each major component of settling particles at 540 and 1000 m by using the data for each component at 150 m as initial values. Among the four models, the ballast model, which considers the sinking velocity increase with depth, was identified as the best using the Akaike information criterion as a measure of the model fit to data. This model successfully reproduced the flux of organic matter at 540 and 1000 m, indicating that the ballast model concept works well in the shallow zone of the WSAP on a seasonal timescale. This also suggests that ballast minerals not only physically protect the organic matter from degradation during the settling process but also enhance the sinking velocity and reduce the degree of decomposition.     

A comparison of observed and calculated directional wave spectra in the East China Sea

Directional wave spectra measured by a cloverleaf buoy in the East China Sea during AMTEX '75 have been compared with those calculated with the operational numerical MRI wave model developed at the Meteorological Research Institute of the Japan Meteorological Agency (J.M.A.). It is shown that the numerical wave model MRI can predict rather well, not only the frequency spectrum, but also the angular distribution function of the spectrum. The frequency dependence of the calculated angular distribution function is quite similar to that observed; the angular distribution is narrower for the spectral components near the peak spectral frequency but widens toward high frequencies and approaches the cos²-distribution.     

Seasonal changes in the mesozooplankton biomass and community structure in subarctic and subtropical time-series stations in the western North Pacific

Seasonal changes in mesozooplankton biomass and their community structures were observed at time-series stations K2 (subarctic) and S1 (subtropical) in the western North Pacific Ocean. At K2, the maximum biomass was observed during the spring when primary productivity was still low. The annual mean biomasses in the euphotic and 200- to 1000-m layers were 1.39 (day) and 2.49 (night) g C m^?2 and 4.00 (day) and 3.63 (night) g C m^?2, respectively. Mesozooplankton vertical distribution was bimodal and mesopelagic peak was observed in a 200- to 300-m layer; it mainly comprised dormant copepods. Copepods predominated in most sampling layers, but euphausiids were dominant at the surface during the night. At S1, the maximum biomass was observed during the spring and the peak timing of biomass followed those of chlorophyll a and primary productivity. The annual mean biomasses in the euphotic and 200- to 1000-m layers were 0.10 (day) and 0.21 (night) g C m^?2 and 0.47 (day) and 0.26 (night) g C m^?2, respectively. Copepods were dominant in most sampling layers, but their mean proportion was lower than that in K2. Mesozooplankton community characteristics at both sites were compared with those at other time-series stations in the North Pacific and with each other. The annual mean primary productivities and sinking POC fluxes were equivalent at both sites; however, mesozooplankton biomasses were higher at K2 than at S1. The difference of biomasses was probably caused by differences of individual carbon losses, population turnover rates, and trophic structures of communities between the two sites.