Encystment and excystment of <Emphasis Type="Italic">Gyrodinium instriatum</Emphasis> Freudenthal et Lee

In the present study, we have investigated the conditions influencing encystment and excystment in the dinoflagellate Gyrodinium instriatum under laboratory conditions. We incubated G. instriatum in modified whole SWM-3 culture medium and in versions of modified SWM-3 from which NO₃ ⁻, PO₄ ³⁻, NO₃ ⁻ + PO₄ ³⁻, or Si had been omitted and observed encystment. Percentage encystment was high in the media without N and without P, while the percentage encystment in the medium lacking both N and P was highest. Moreover, to investigate N or P concentration which induced the encystment, Gyrodinium instriatum was also incubated in media with different concentrations of inorganic N and P; the concentrations of NO₂ ⁻ + NO₃ ⁻ and PO₄ ³⁻ were measured over time. The precursors of cysts appeared within 2 or 3 days of a decrease in NO₂ ⁻ + NO₃ ⁻ or PO₄ ³⁻ concentration to values lower than 1 μM or 0.2 μM, respectively. When cysts produced in the laboratory were incubated, we observed excystment after 8–37 days, without a mandatory period of darkness or low temperature. We incubated cysts collected from nature at different temperatures or in the dark or light and observed excystments. Natural cysts excysted at temperatures from 10 to 30°C, in both light and dark, but excystment was delayed at low temperatures. These studies indicate that G. instriatum encysts in low N or P concentration and excysts over a wide temperature range, regardless of light conditions, after short dormancy periods.     

O<Subscript>2</Subscript> consumption rate and its isotopic fractionation factor in the deep water of the Philippine Sea

Concentration and stable isotopic compositions (δ ¹⁸O) of dissolved O₂ were measured in seawater samples collected from the Philippine Sea in June 2006. The in-situ O₂ consumption rate and the isotopic fractionation factor (α _r ) during dissolved O₂ consumption were obtained from field observations by applying a vertical one-dimensional advection diffusion model to the deep water mass of about 1000–4000 m. The average O₂ consumption rate and α _r were, respectively, 0.11 ± 0.07 μmol kg⁻¹yr⁻¹ and 0.990 ± 0.001. These estimated values agree well with values from earlier estimations of Pacific deep water. The in-situ O₂ consumption rates are two or more times higher north of 20°N, although the value of α _r was not significantly different between the north and south. Its levels varied rapidly in the water mass of less about 2000 m depth. These results suggest that organic matter from the continent imparts a meaningful contribution to the upper water in the northern part of the area; it might produce the strong O₂ minimum that is evident in the water mass from about 1000–2000 m in the northern part of the Philippine Sea.     

Influence of Surface-Based Stable Layer Development on Asian Dust Behaviour Over Tokyo

The relationship between local meteorological fields and the behaviour of airborne Asian dust that arrived in the Tokyo metropolitan area on 1 April 2007 with the passage of a synoptic-scale cold front has been investigated through Doppler lidar observations, experiments using a regional atmospheric numerical model, and analyses of surface and upper-air meteorological observations. Results of the Doppler lidar observations showed that the Asian dust passed above the metropolitan area with strong south-westerly winds with speeds of 15–26 m s⁻¹. Meteorological fields reproduced by the numerical experiments showed the development of a surface-based stable layer in the metropolitan area caused by nocturnal radiational cooling near the ground surface and south-westerly warm air advection at upper levels. The blocking effect of the mountainous region located to the west of the metropolitan area induced an area of stagnant air inside the metropolitan area and promoted the stable layer development. Although strong downdrafts prevailed in the upper air, the airborne Asian dust did not spread to the ground when the stable layer was formed. These results strongly indicate that the developed stable layer prevented strong downdrafts from spreading to the ground, acting as an obstacle to the transport of the Asian dust particles from the upper air towards the ground. This is considered to be one of the main causes of the low appearance frequency of Asian dust phenomena near the ground in the Tokyo metropolitan area and eastern Japan.     

A Simple Method for Precise Determination of 23 Trace Elements in Granitic Rocks by ICP-MS after Lithium Tetraborate Fusion

Abstract. An improved alkali fusion method followed by HF-HNO₃-HC1O₄ treatment is performed for simultaneous determination of 23 trace elements (Sr, Y, Zr, Nb, Ba, Hf, Ta, Th, U, and REE) by ICP-MS in rock reference materials: basaltic rocks (JB-2, JB-3) and granitic rocks (JG-la, JG-2, JG-3). Our improved method offers several advantages including: (1) suppression of whitish precipitates probably composed of insoluble fluorides by addition of HCIO4, (2) simple and reliable preparation procedure, (3) instrument calibration which enables straightforward simultaneous multi-elemental analysis, and (4) the very low background levels by using pure lithium tetraborate flux. We obtained the analytical results with a reproducibility of mostly <2 % (1) for the basaltic rocks and <7 % for the granitic rocks. The higher relative standard deviation (RSD) values for granitic rocks may be attributed to sample heterogeneity of coarse-grained granitic rocks. The analytical results of the granitic rocks demonstrate that Zr and Hf abundances are consistent with the compiled values and that REE concentrations agree well with recently published data, suggesting that the Li₂B₄O₇ fusion method applied in the present study is suitable for the analysis of the granitic rocks.     

Geochemical Features and Tectonic Setting of Greenstones from Kunimiyama, Northern Chichibu Belt, Central Shikoku, Japan

Abstract. We report whole‐rock chemical data for the greenstones from the Kunimiyama area in the Northern Chichibu Belt and their implications on the tectonic setting of these rocks. The Kunimiyama greenstones are associated with stratiform fer‐romanganese deposits or bedded cherts in the northern part of the study area, but are closely associated with a thick limestone block or bedded cherts in the southern part. The constituent minerals of greenstones are albitized plagioclase, clinopy‐roxene, chlorite, calcite, epidote, pumpellyite, prehnite, quartz, celadonite, sericite and opaque minerals such as iron oxyhy‐droxide and hematite. These mineral assemblages, epidote + pumpellyite + chlorite and chlorite + pumpellyite + prehnite, suggest that the metamorphic grade of greenstones from the Kunimiyama area is prehnite‐pumpellyite facies. The whole‐rock chemical compositions of greenstones associated with ferromanganese deposits are generally similar to those of normal mid‐ocean ridge basalt (N‐MORB). In contrast, the chemical compositions of the greenstones associated with the limestone block are comparable to those of ocean island alkaline basalt. Greenstones associated with bedded cherts are of enriched MORB and ocean island basalt, as well as N‐MORB origins, suggesting they probably formed as a result of plume‐related MOR volcanism in the Panthalassa Ocean in Early Permian and by tectonic mixing of ocean island basalts with oceanic ridge crustal fragments during accretion/subduction processes. These geological and geochemical lines of evidence suggest that the Kunimiyama greenstones are allochthonous blocks of accreted oceanic crust and seamounts. The ferromanganese deposits are frequently accompanied by reddish greenstones. Compared to common greenish greenstones, the reddish greenstones are characterized by high MnO and rare earth element contents and distinct negative Ce anomalies, implying a slight contribution of hydro thermal component forming the ferromanganese deposits.     

A GIS-based study toward forecast of suburban forest change

At a time when the concept of ‘human and environmental symbiosis’ has taken on much significance, protection of suburban forests (i.e. forests adjacent to or near developed areas) is a topic that has drawn much attention. Suburban forests have, since ancient times, been places where people have gathered firewood and cultured trees. As a result, the vegetation of suburban forests is only partially natural and continues to change as the forms of human activity in and around them changes. Accurate forecasts of how suburban forests will change are, therefore, an important element in the debate over how to protect them. In this study, a suburban forest was analyzed with laser radar sensing, multi-spectrum scanning, digital photogrammetry analysis, aerial photograph interpretation, and a field survey. Data gathered using these techniques were compiled on a GIS to forecast future changes in the forest. Aerial photographs taken over the past 50 years were analyzed to illuminate changes in the forest over that period. Specifically, comparisons of precise Digital Elevation Models (DEMs) measured by using digital photogrammetry workstations made it possible to estimate growth in forest height. The possible future conversion of such results to estimates of amounts of carbon dioxide consolidated by forests should be very significant for discussions of global environmental problems. This revised version was published online in July 2006 with corrections to the Cover Date.     

MEAN SEA LEVEL AND SEA SURFACE VARIABILITY OF NQRTHWEST PACIFIC OCEAN AND EASTERN CHINA SEAS FROM GEOSAT ALTIMETRY

Collinear analysis technique is widely used for determining sea surface variability with Geosat altimeterdata from its Exact Repeat Mission(ERM).But most of the researches have been only on global scaleor in oceans deeper than 2000 m.In shallow shelf waters this method is hampered by the inaccuracy ofocean tide data supplied with Geosat Geophysical Data Records(GDRs).This work uses a modified collinearanalysis technique characterized by simultaneous separation of mean sea level and ocean tide with theleast squares method,to compute sea surface variability in the Northwest Pacific Ocean and eastern ChinaSeas.The mean sea level map obtained contains not ouly bathymetric but also dynamic features such asamphidromes,indicating considerable improvement over previous works.Our sea surface variability mapsshow clearly the main current system,the well-known Zhejiang coastal upwelling,and a northern East Chi-na Sea meso-scale eddy in good agreement with satellite sea surface temperature(SST)observation and his-to     

Distribution of nitrate in groundwater affected by the presence of an aquitard at an agricultural area in Chiba, Japan

Geological and geographical parameters including land use, stratigraphic structure, groundwater quality, and N- and O-isotopic compositions of nitrate in groundwater were investigated to elucidate the mechanism of groundwater pollution by NO₃ ^? in the agricultural area of Katori, Chiba, Japan. An aquitard distributed in the western part of the study area has produced two unconfined aquifers. The average concentrations of NO₃ ^? and dissolved oxygen (DO) were high in the aquifer above the aquitard (7.5 and 7.6 mg/L, respectively) and in the aquifer of the eastern part of the study area that was not influenced by the aquitard (11.9 and 7.8 mg/L, respectively); however, the levels in the aquifer under the aquitard were relatively low (2.2 and 3.7 mg/L, respectively). The δ¹⁵N and δ¹⁸O values of NO₃ ^? generally increased exponentially in the groundwater that flowed into the aquifer under the aquitard as the concentration of NO₃ ^? decreased, although this decrease in NO₃ ^? also occasionally occurred without isotopic changes. These results indicated that the aquitard prevented the penetration of NO₃ ^?, DO, and gaseous O₂. Under the aquitard, denitrification and dilution with unpolluted water that entered from natural forested areas reduced the NO₃ ^? concentrations in the groundwater. The major sources of NO₃ ^? in groundwater in the study area were estimated to be NH₄-chemical fertilizer, livestock waste, and manure.