The local structure of Ca-Na pyroxenes. I. XANES study at the Na K-edge

 X-ray absorption Na K-edge spectra have been recorded on synthetic endmember jadeite and on a series of natural Ca-Na pyroxenes compositionally straddling the Jd-Di join. The C2/c members of the series are systematically different from the P2/n members. Differences can be interpreted and explained by comparing the experimental spectra with theoretical spectra. These have been calculated by the multiple-scattering formalism from the atomic positional parameters determined by single-crystal X-ray diffraction structure refinement on the same samples. In the full multiple scattering region of the spectra (1075 to 1090 eV) C-pyroxenes exhibit three features which reflect the 6-2 configuration of the O back-scattering atoms around the Na absorber located at the center of the cluster (site M2 of the jadeite structure). P-pyroxenes show more complicated spectra in which at least four (possibly five) features can be recognized; they reflect the two types of configuration (6-2 and 4-2-2) of O around Na in the two independent M2 and M21 eight-fold coordinated sites of the omphacite structure. A weak, sometimes poorly resolved peak at 1079 eV is diagnostic and discriminates C- from P-pyroxenes. The Garnet Ridge C2/c impure jadeite exhibits a spectrum which is intermediate between those of jadeite and omphacite. The Hedin-Lundqvist potential proves best for these insulating materials and allows multiple-scattering calculations agreeing well with experiments. Received: July 11, 1996/Revised, accepted: October 21, 1996     

Precipitation chemistry and ozone and sulfate concentrations in the ocean atmosphere observed by multi-year cruising in East Asia and West Oceania (35°N–35°S, 100–135°E) in August and September

A comprehensive study on the chemistry of deposition and the concentration of tropospheric ozone and particulate sulfate in the ocean atmosphere was carried out for the data sets in 1990’s. It is important to study the atmospheric situation over the past years as well as the latest, especially in the East Asian region where emission amount of anthropogenic air pollutants have increased year by year due to rapid economic growth. The survey was conducted for 5 years in East Asia and West Oceania (35°N–35°S, 100–135°E) in August and September in 1990’s. The purpose of the survey was to study and understand the chemistry of deposition and the concentration of tropospheric ozone and particulate sulfate in the ocean atmosphere comprehensively in one project. Rainfall over the ocean was insufficiently neutralized. Gas and aerosol over the ocean were mature, i.e., well-mixed, during the period of the transportation. The characteristic latitudinal dependence was observed in the tropospheric ozone concentration, namely, higher in the southern hemisphere and lower in the northern hemisphere (approximately 25 ppb in the 10–40°S region and 5–15 ppb in the 20–40°N region). On the other hand, high concentrations of tropospheric ozone of over 30 ppb were observed in the northern hemisphere, which was attributable to the long-range transportation. The TSP concentration was approximately under the level of 40 μg m^?3 irrespectively of the latitude; in contrast, the nss-SO₄ ^2- concentration showed a clear latitudinal dependence, i.e., higher in the northern hemisphere and lower in the southern hemisphere. The background levels of the nss-SO₄ ^2- concentration were approximately 0.5 μg m^?3 in the 10–40°S region and 2–3 μg m^?3 and 4–5 μg m^?3 in the 0–20°N and 20–40°N regions, respectively.     

Circulation and Material Transport in Suo-Nada during Spring and Summer

An attempt was made to reproduce the circulation pattern in Suo-Nada, Japan during spring and summer season in order to elucidate the water exchange mechanism in the basin. Two hydrographic surveys at the end of each season were conducted covering the entire Suo-Nada area. A three-dimensional hydrodynamic Princeton Ocean Model (POM) was used to compute the current resulting from the observed density and wind field. During spring, a very pronounced counter clockwise gyre is situated near the opening of the basin. This is replaced by a clockwise circulation which seemed to occupy the whole domain during summer. Within each season, however, the vertical distribution of current does not show any remarkable differences, indicating the dominance of horizontal current and a very weak estuarine flow. These observational and numerical results were used to estimate the remnant function and the corresponding average residence time of permanently dissolved matter (PDM) and transformable matter (TM). The results revealed a small difference in the average residence times of materials within each season but a large seasonal variability between spring and summer. Furthermore, calculations based on climatological density fields have indicated a similar trend of variation between the seasonal values of average residence times. This revised version was published online in July 2006 with corrections to the Cover Date.     

Trans-boundary and in-country transport of air pollutants observed in Kobe,Japan by high frequent filter pack sampling method

The seasonal intensive sampling of gases and particulate matter in ambient air was conducted at the site established in urban area of Japan to study the seasonal difference of the temporal variation of gases and particulate matter concentrations in urban atmosphere as well as to illustrate the different transport regimes that impacts air pollutants. The sample was collected by the four-stage filter-pack method with 6-h interval for one week in four seasons (spring, summer, autumn and winter). The trans-boundary transport of air pollutants with high concentration was characteristically observed in the spring sampling. On the other hand, we could successfully detect the in-country transports of air pollutants in the summer sampling. Four-season’s intensive survey considered, we could show the characteristic transport of air pollutants to provide the episodic high concentration for ambient air in the urban area of Japan, and successfully illustrate the seasonal-dependent transport regimes to impact on air pollutants.     

Methodology of analysis associating survey results by the filter-pack method with those of precipitation- Acid-base balance on acid-related and alkali-related chemical species in urban ambient air and its influence on the acidification of precipitation -

Continuous weekly monitoring on the concentration of gases and aerosols in urban ambient air by a four-stage filter-pack method was carried out for 7 years in order to study not only the acid-base balance of acid-related (HNO₃, NO₃ ⁻, and non-sea-salt-(nss-)SO₄ ²⁻) and alkali-related (NH₃, NH₄ ⁺, and nss-Ca²⁺) chemical species but also its influence on the acidification of precipitation. The concentrations of the total nitrate (= NO₃⁻ + HNO₃) and nss-SO₄²⁻ showed a similar seasonal variation: high in the summer and low in the winter. The total nitrate and nss-SO₄²⁻ accounted for 0.43 and 0.57 of the acid-related species, respectively, on an equivalent basis. The total ammonium (= NH₃ + NH₄⁺) accounted for more than 0.9 of the alkali-related species, except for a springtime nss-Ca²⁺ episodic peak. The alkali-related species were generally overabundant compared with the acid-related species in the HNO₃-NO₃⁻-nss-SO₄²⁻-NH₃-NH₄⁺-nss-Ca²⁺ system. The alkali-rich distribution was especially pronounced in the winter, but the acid-related species was comparable to the alkali-related species in the summer, which was attributed to the larger H⁺ deposition by precipitation in the summer. This study can provide a methodology to associate survey results obtained by a filter-pack method with those of precipitation.     

Electron probe microanalysis study on processes of low-temperature oxidation of titanomagnetite

Partially oxidized titanomagnetite grains in various kinds of volcanic rocks were investigated by electron probe microanalyzer (EPMA) in order to clarify the process of oxidation at low temperature. The following results were obtained by the present investigation: (1) Primary composition of titanomagnetite is homogeneous in individual grains, although variation in composition among different grains is observed on each thin section. (2) Migration of Fe cations during low-temperature oxidation is clearly seen in all oxidized grains. Some other constituent cations are also bleached and consequently the relative content of the remaining cations becomes large. (3) The detailed internal structures of titanomagnetite grains are observed as backscattered electron images (BEI) with an electronprobe microanalyzer, and it seems likely that the structures depend upon the degree of low-temperature oxidation. (4) The chemical and physical properties of oxidized titanomagnetites imply that low-temperature oxidation is not a simple process but a complex one. Such an oxidation process is correlatable to both the mobility of cation and the oxidation condition such as a circulation of some active hydrothermal materials at low temperature.     

Characteristics of the Sôya Warm Current in the Okhotsk Sea

Characteristics of the Sôya Warm Current from Abashiri Bay to the area off the coast of the southern Kuril Islands are clarified by water mass analysis. The water flowing into the Okhotsk Sea as the Sôya Warm Current is divided into two: the Forerunner of the Sôya Warm Water (March to May) and the Sôya Warm Water (June to November). It is shown that in May the Sôya Warm Current flows in the subsurface layer (about 200–400m deep) in Abashiri Bay, and flows northeastward just off the coast of the Kuril Islands as a subsurface current reaching a region northwest of Etorofu Island by the end of May. The dissolved oxygen content is fairly effective in identifying the Forerunner of the Sôya Warm Water in the subsurface layer. The Sôya Warm Current shifts upwards to the surface layer in Abashiri Bay by early July, because the Sôya Warm Water with large thermosteric anomaly _t begins to flow into the Okhotsk Sea in June. It is shown that, in general, the major portion of the Sôya Warm Current flows northeastward just off the coast of the Kuril Islands during the summer season, although a minor branch of the current flows northward in the area off the Shiretoko Peninsula, and another minor branch flows out to the Pacific Ocean through the Nemuro Straits.     

Species and concentrations of selenium and nutrients in Tanabe Bay during red tide due toGymnodinium nagasakiense

A red tide due toGymnodinium nagasakiense was observed in August 1988 in Tanabe Bay, Wakayama Prefecture, Japan. The maximum cell concentration ofG. nagasakiense reached 1×10⁵ cells ml^–1 at the surface water. From May to September 1988, the following were monitored: water temperature, salinity, chlorophylla, D.O., dissolved nutrients (NO₂–N, NO₃–N, NH₄–N, PO₄–P DON, DOP), particulate nutrients (PON, POP) and three dissolved selenium species [Se(IV), Se(VI), Organic Se]. Dissolved inorganic nitrogen (NO₃–N, NH₄–N) decreased but PON, POP, DON, DOP and inorganic phosphate increased at the peak of the bloom. The concentration of organic selenium increased up to the bloom initiation period which started on 5 July, and then the concentration of Se(IV) increased as the concentration of organic selenium decreased at the peak of the bloom (3 August). The strong relationship was found between the concentration of Se(IV) and the cell concentration ofG. nagasakiense (r ²=0.98). The Se(IV) requirement ofG. nagasakiense was 2.89×10^–17 moles cell^–1, which was agreed well with 4.4×10^–17 moles cell^–1 found in a laboratory experiment onG. nagasakiense using selenium spiked artificial sea water medium. The average ratio of Se(IV) to dissolved inorganic nitrogen (DIN) during the red tide bloom was 11441, the ratio of Se(IV) to DIN at the surface with the maximum cell concentration ofG. nagasakiense of 1×10⁵ cells ml^–1 was 1137. These results suggested that selenium may play an important role in red tide outbreak ofG. nagasakiense.     

Step-like structure in temperature and salinity profiles,observed near icebergs trapped by fast ice,Antarctica

Step-like thermohaline structure was observed near icebergs trapped by fast ice in Lützow-Holm Bay, Antarctica. The structure was developed within the draft depth of the icebergs. The typical vertical distance between the succeeding step surfaces is 20–30 m, and the temperature and salinity differences across the step surface are about 0.05–0.06 deg and 0.06–0.10 psu, respectively. The structure appears to be generated by a sea-water/iceberg interaction, and is explainable by a simple model in which an ice wall is placed in the ocean linearly stratified by vertical salinity gradient.     

Characteristic seasonal variation of vertical air temperature profile in urban areas of Japan

The seasonality of the vertical air temperature profile in an urban area in the vicinity of the coast was studied. The vertical air temperature profile showed the characteristic seasonality. In the summer, the atmosphere was thermally stratified in the 60–100 m layer, while the 20–60 m layer was unstable or weakly stable throughout the day due to the strong solar radiation. On the other hand, no temperature inversion layer was observed in the winter presumably due to the heat supply from the sea as well as the strong wind speed in the vicinity of the coast. The vertical air temperature profiles at nighttime in the spring and autumn were transitional between the summer and the winter. In contrast, the vertical air temperature profile in the daytime in the spring was similar to that in the summer, while that in the autumn was comparable to that in the winter. Characteristic findings in the study due to the site location, i.e., in the vicinity of the coast, can be summarized as follows: (1) the elevated temperature inversion layer at noon was observed in the summer, and (2) no temperature inversion layer was observed in the winter.