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Recent studies show that oxygen three isotope measurement (16O, 17O, and 18O) of water provides additional information for investigating the hydrological cycle and paleoclimate. For determining the 18O/16O value of water, a conventional CO2-water equilibration method involves measurement of the ratios of CO2 isotopologues which were equilibrated with water. However, this long-established technique was not intended to measure the 17O/16O ratio, primarily because the historic ion correction scheme does not allow for possible deviations from a fixed (and mass-dependent) relationship between 17O/16O and 18O/16O isotope ratios. Here, we propose an improved method for obtaining the 17O/16O isotope ratio of fresh water by the equilibration method and measurement of the 45/44 CO2 ion abundance ratio. Equations which we formulated for 17O/16O measurement have two features: first, instead of absolute isotope ratio (R), all equations are formulated in δ values, measured by isotope ratio mass spectrometry. Second, we include two “assigned” δ values of water standards in the equations, because the δ18O are commonly measured against two working standards to normalize the span of the δ scale. This approach clarifies that the contribution from 17O (12C16O17O+) to the molecular ion current at mass-to-charge ratio m/z 45 signal depends not on the absolute 13C/12C ratio, but on the relative δ13C differences between the working standards and the sample. The pH value of water affects δ17O estimation because δ13C of CO2 was changed in the water-CO2 system. We reevaluated this effect using a set of equations, which explicitly includes CO2 partial pressure effect on pH value. Our new estimation of pH effect is significantly smaller than previously reported value, but it does not alter the main conclusions in the previous study. The method was verified by δ17O measurements of an international standard reference water (GISP) provided by the IAEA. We applied the method to investigate 17O-excess of the ice core drilled at the Dome Fuji station, Antarctica. A total of 1320 samples from a 130 m section around Marine Isotope Stage 9.3 (∼330,000 years before present) were measured. The error of a measurement for δ17O is 0.175‰ and that of 17O-excess is 184 per meg. Although these analytical uncertainties hampered accurate estimation of the changes in 17O-excess, the averaged data indicate that 17O-excess around MIS 9.3 was higher than during the subsequent glacial period. This approach can be applied only to fresh water samples, and additional improvements will be needed to measure samples which contains significant amount of carbonate minerals. 相似文献
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Shiro Kohshima Nozomu Takeuchi Jun Uetake Takayuki Shiraiwa Ryu Uemura Naohiro Yoshida Sumito Matoba Maria Angelica Godoi 《Global and Planetary Change》2007,59(1-4):236
Snow algae in a 45.97-m-long ice core from the Tyndall Glacier (50°59′05″S, 73°31′12″W, 1756 m a.s.l.) in the Southern Patagonian Icefield were examined for potential use in ice core dating and estimation of the net accumulation rate. The core was subjected to visual stratigraphic observation and bulk density measurements in the field, and later to analyses of snow algal biomass, water isotopes (18O, D), and major dissolved ions. The ice core contained many algal cells that belonged to two species of snow algae growing in the snow near the surface: Chloromonas sp. and an unknown green algal species. Algal biomass and major dissolved ions (Na+, K+, Mg2+, Ca2+, Cl−, SO42−) exhibited rapid decreases in the upper 3 m, probably owing to melt water elution and/or decomposition of algal cells. However, seasonal cycles were still found for the snow algal biomass, 18O, D-excess, and major ions, although the amplitudes of the cycles decreased with depth. Supposing that the layers with almost no snow algae were the winter layers without the melt water essential to algal growth, we estimated that the net accumulation rate at this location was 12.9 m a− 1 from winter 1998 to winter 1999, and 5.1 m from the beginning of winter to December 1999. These estimates are similar to the values estimated from the peaks of 18O (17.8 m a− 1 from summer 1998 to summer 1999 and 11.0 m from summer to December 1999) and those of D-excess (14.7 m a− 1 from fall 1998 to fall 1999 and 8.6 m a− 1 from fall to December 1999). These values are much higher than those obtained by past ice core studies in Patagonia, but are of the same order of magnitude as those predicted from various observations at ablation areas of Patagonian glaciers. 相似文献
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Mutsuo Inoue H. Uemura H. Kofuji K. Fujimoto H. Takata Y. Shirotani N. Kudo S. Nagao 《Journal of Oceanography》2017,73(5):571-584
In 2014 and 2015, we examined the spatial distribution of cesium-134 (half-life: 2.06 years) from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in marine sediments within coastal–basin areas (water depths of 40–520 m) off central Honshu Island (the main island of Japan) in the Sea of Japan. The 134Cs concentrations in both the surface sediment (0–1 cm depth) and whole-core inventory exhibited wide variations, and were highest at the site closest to the Agano River Estuary area (6.7 Bq/kg-dry and 886 Bq/m2, respectively). This indicates that 134Cs in coastal areas was delivered by riverine suspended solids (SS). Given the spatial variation in 134Cs concentrations, we believe that 134Cs partially migrated northeastward within ~50 km along Honshu Island (at water depths shallower than ~140 m), and southwestward, including the Sado Basin area. This is predominantly attributable to the transport of SS by bottom currents and unsteady downward delivery onto the steep slopes of the basin. The total amount of 134Cs in the study area in 2014 was estimated at approximately 0.6 TBq (decay-corrected to March 11, 2011, date of FDNPP accident). 相似文献
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Morita Satoshi Uchida Yutaka Hirose Shigenobu Uemura Shuhei Yamaguchi Tomotaka 《Solar physics》2001,200(1-2):137-156
In February 1992, three flares, which we consider constitute a homologous flare series (flares having basically the same configuration repeating in the same situation), occurred in the active region NOAA 7070 and were observed by Yohkoh SXT. In the present paper, we first discuss the homology of these three flares, and derive the 3D structure by making use of the information obtained from the three different lines of sight at common phases. The result of this analysis made clear for the first time that the so-called `cusped arcade' at the maximum phase in the well-known 21 February 1992 flare is, contrary to the general belief, an `elongated arch' created at the beginning of the flare, seen with a shallow oblique angle. It is not the `flare arcade' seen on axis as widely conceived. This elongated arch roughly coincides with a diagonal of the main body of the soft X-ray arcade that came up later. The magnetic structure responsible for the flare as a whole turned out to be a structure with quadruple magnetic sources – with the third and fourth sources also playing essential roles. The observationally derived information in our paper provides strong restrictions to the theoretical models of the process occurring in arcade flares. 相似文献
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Subsurface temperatures were analyzed to evaluate the effects of urbanization and groundwater flow in Osaka, the second largest metropolitan in Japan. The temperature-depth profiles were classified into three (recharge, intermediate and discharge) types based on the thermal gradient, shape of the profiles, and temperature itself. The locations of the three types of profiles represent the places of regional and local groundwater flow systems in Osaka plain. The analyses of subsurface temperature using heat conduction-convection theory under the condition of surface warming showed that the depth of minimum temperature in the profile increased with the groundwater recharge rate and time lapse from the beginning of surface warming due to urbanization. Comparisons between observed and estimated temperature profiles showed that the surface warming due to urbanization is larger and occurred earlier in the middle of the city than those in surrounding area, which agreed with the air temperature records. 相似文献
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Y. Uchida S. Hirose S. Morita M. Torii T. Tanaka T. Yabiku T. Miyagoshi S. Uemura T. Yamaguchi 《Astrophysics and Space Science》1998,264(1-4):145-169
We discuss here some of the new aspects about solar flares and active regions found by the Solar X-ray Satellite Yohkoh, by
taking advantage of the wider dynamic range and higher cadence observations with higher spatial resolution compared with the
previous satellites. Those new aspects have lead us to new ways of understandings, with contradictions to the previous views
about flares and active regions that are widely conceived for a long time. We give some models that explain those newly revealed
observational results.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Analyses of gallium content were made by the fluorometric method on 57 samples of seaweeds which were composed of 30 species. As the result of it, the gallium content was found ranging from 0.02 to 0.64g g–1 and the average was 0.14g g–1 in the dried seaweeds.Generally, the gallium content in seaweeds had a close relationship to the aluminium and iron contents. The average weight ratio of Ga/Al was 3.8×10–4 and one of Ga/Fe was 4.0×10–4. The average Ga/Al weight ratio (3.8×10–4) was very similar to that reported for shallow-water deposits (2.1×10–4), but was definitely lower than that in sea water (1.5×10–2). 相似文献