Spatial distribution, diversity and composition of bacterial communities in sub-seafloor fluids at a deep-sea hydrothermal field of the Suiyo Seamount

Spatial distribution, diversity, and composition of bacterial communities within the shallow sub-seafloor at the deep-sea hydrothermal field of the Suiyo Seamount, Izu-Bonin Arc, Western Pacific Ocean, were investigated. Fluids were sampled from four boreholes in this area. Each borehole was located near or away from active vents, the distance ranging 2–40 m from active vents. In addition, fluids discharging from a natural vent and ambient seawater were sampled in this area. We extracted DNA from each sample, amplified bacterial 16S rRNA genes by PCR, cloned the PCR products and sequenced. The total number of clones analyzed was 348. Most of the detected phylotypes were affiliated with the phylum Proteobacteria, of which the detection frequency in each clone library ranged from 84.6% to 100%. The bacterial community diversity and composition were different between hydrothermal fluids and seawater, between fluids from the boreholes and the vent, and even among fluids from each borehole. The relative abundances of the phylotypes related to Thiomicrospira, Methylobacterium and Sphingomonas were significantly different among fluids from each borehole. The phylotypes related to Thiomicrospira and Alcanivorax were detected in all of the boreholes and vent samples. Our findings provide insights into bacterial communities in the shallow sub-seafloor environments at active deep-sea hydrothermal vent fields.     

Diel Vertical Migration of the Marine Cladoceran Podon Leuckarti: Variations with Reproductive Stage

Diel vertical migration (DVM) of the marine cladoceran Podon leuckarti was investigated with reference to their reproductive stages and size. Males and females, except for gamogenic females with an advanced resting egg (GA), aggregated at the near-bottom layer or at the surface during the day and dispersed into the water column at night. Both the near-bottom aggregation and the surface aggregation during daytime are suggested to be behavior that reduces the predation risk from visual predators. However, GA aggregated in the near-bottom layer during daytime and avoided the surface layer. The near-bottom aggregation might be more effective behavior for GAs to reduce risk of visual predation than the surface aggregation because of the conspicuous resting egg they carried. These results show that carrying an advanced resting egg influenced the DVM of P. leuckarti.     

Variability of Sea Surface Circulation in the Japan Sea

Composite sea surface dynamic heights (CSSDH) are calculated from both sea surface dynamic heights that are derived from altimetric data of ERS-2 and mean sea surface that is calculated by a numerical model. The CSSDH are consistent with sea surface temperature obtained by satellite and observed water temperature. Assuming the geostrophic balance, sea surface current velocities are calculated. It is found that temporal and spatial variations of sea surface circulation are considerably strong. In order to examine the characteristics of temporal and spatial variation of current pattern, EOF analysis is carried out with use of the CSSDH for 3.5 years. The spatial and temporal variations of mode 1 indicate the strength or weakness of sea surface circulation over the entire Japan Sea associated with seasonal variation of volume transport through the Tsushima Strait. The spatial and temporal variations of mode 2 mostly indicate the temporal variation of the second branch of the Tsushima Warm Current and the East Korean Warm Current. It is suggested that this variation is possibly associated with the seasonal variation of volume transport through the west channel of the Tsushima Strait. Variations of mode 3 indicate the interannual variability in the Yamato Basin.     

Measurement of evaporation from the forest floor in a deciduous forest throughout the year using microlysimeter and closed‐chamber systems

Evaporation from the forest floor (E_FF) in a deciduous broadleaf forest was measured using microlysimeter and closed‐chamber systems. The microlysimeter was used at six points in the experimental basin, and measurements gave different E_FF values at different points. This could be attributed to the local photoenvironment of each sampling point, rather than to litter conditions, if the spatial variation in air temperature (Ta) or vapour pressure deficit (VPD) at the forest floor was small within this basin. A detachable microlysimeter measured condensation in the litter layer during the night, indicating that the litter layer, as well as the mulch layer, played a role in preventing evaporation from the soil layer. The closed‐chamber system made it possible to continuously measure long‐term E_FF. E_FF was closely related to VPD; even during the night, when solar radiation was zero, E_FF amounted to 14·0% of the daily E_FF. The daily E_FF was 0·20 ± 0·13 mm day^?1 during the study period, with two seasonal peaks: in late spring (0·31 mm day^?1 in April) and early fall (0·22 mm day^?1 in September). The former peak has been reported from two deciduous forests in Japan and is strongly related to the solar radiation reaching the forest floor when the trees are dormant. Copyright © 2008 John Wiley & Sons, Ltd.     

HISTORICAL GEOGRAPHY IN JAPAN*

A regret frequently expressed at International Geographical Congresses concerns the lack of summary information about the nature of geographic research in the host country. During a discussion of this point with members of the Association of Japanese Geographers, the idea of publishing a series of reports on various aspects of Japanese research surfaced. The concept was later enthusiastically supported by the United States National Committee for the International Geographical Union. This first report, “Historical Geography in Japan,” has been modified for the benefit of the English-speaking readers of THE PROFESSIONAL GEOGRAPHER. Although the reports will be of particular interest to those planning to attend the 1980 IGC in Tokyo, they should prove of general interest as well.—H. Jesse Walker, Member, U.S. National Committee, IGU.     

PETROLOGY OF THE YAMATO METEORITES (j), (k), (l), AND (m) FROM ANTARCTICA*

The Yamato (j), (k), (l), and (m) meteorites collected from near the Yamato Mountains in December, 1973, are respectively an H-4 and L-5 chondrite, a howardite, and an L-5 chondrite. Yamato (l), the howardite, is a polymict breccia of diogenite and eucrite clasts. Olivine in the chondrites ranges in composition from Fo₇₅ to Fo₈₀, whereas in the howardite, where it is rare, the composition is about Fo₆₀. Pyroxenes in the chondrites are mostly orthopyroxenes and (En₈₃), while the pyroxenes in the howardite are more complex, comprising orthopyroxene, pigeonite, augite, and rare clinohypersthene (in the order of decreasing abundance), with the range from En₈₀ to En₃₇. They form a definite trend, probably formed by the fractional crystallization of the parental magma of the achondrite, and later subjected to exsolution phenomena during the slow cooling. Plagioclase is high-temperature oligoclase in the chondrites, and anorthite in the howardite. Maskelynitization is sometimes observed. Other shock effects are also observed. Opaque phases consist mostly of nickel-iron, troilite, chromite, and rarely ilmenite. Intergrowth of these minerals are common. The accessory minerals comprise quartz, cristobalite, apatite, spinel, and rare uranium-bearing minerals. The bulk composition and genetic significance are discussed.     

Hypoxia in the Upper Gulf of Thailand: Hydrographic observations and modeling

We conducted hydrographic observations throughout the year to investigate seasonal variations of the hypoxic water mass distribution in the Upper Gulf of Thailand (UGoT). Hypoxic water masses were observed from June to November, with half of the UGoT occupied by hypoxic water in September. A hypoxic water mass appeared in the northeastern part of the UGoT in June and August, and moved westward over time. Low-salinity surface water moved from east to west as the rotational direction of surface circulation shifted with the reversal of monsoon winds. Westward movement of low-salinity water causes strong stratification in the northwestern part of the UGoT, leading to severe hypoxia. Numerical experiments showed high dissolved oxygen consumption rates around and offshore of river mouths, where hypoxic water is generated. This finding suggests that hypoxic water masses are transported to the south by physical processes. We examined how flooding affects hypoxic water mass formation. The volume of hypoxia in a flood year was approximately 2.5 times greater than in a normal year. In addition, hypoxia occurred in the dry season and extensive hypoxia was observed in the year after flooding. These results suggest that the hypoxic water mass persists for a long time after flooding.

     

Eutrophication and hypoxia in the upper Gulf of Thailand

In this study, we investigated the mechanism of eutrophication and hypoxia in the upper Gulf of Thailand from August 2014 to June 2015 based on field observation data, box model analysis, and the unscaled trophic status index (UNTRIX). Fresh water residence time derived from a simple box model was long (38.61 days) during the transition period between the southwest to northeast monsoon in September 2014. In contrast, fresh water residence time was short (2.63 days) during the late northeast monsoon in February 2015. Long residence time was related to the development of widespread strong hypoxia in near-bottom waters in over half of the gulf during the transition between the southwest and the northeast monsoon, when river discharge was also very large. UNTRIX is used to assess water trophic levels, and is based on water qualities including concentrations of chlorophyll-a (Chl-a), dissolved oxygen (DO), dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphorus (DIP). Hypertrophic and eutrophic conditions were observed at river mouths; their seasonal eutrophication was related to river discharge and circulation. Nutrients were mainly increased by river discharge. Water column stratification and long residence time were required for the development of severe hypoxia in the study area.

     

Ordered distribution of aluminum atoms in analcime

Based on the connectivity relations among tetrahedron sites and the NMR spectra, we propose an ordered distribution of aluminum atoms in the framework of analcime with space groups of Pbcb and Pcaa. The symmetries of the ordered distributions are formally the same as Pcca. These symmetries are much lower than those reported by others such as Ia3d, I4₁/acd, Ibca, and I2/a. The lowering of symmetry results apparently from the fact that aluminum atoms in the framework of analcime were strictly discriminated from silicon atoms. Dependence of the populations of Si(nAl)s upon Al content was estimated from ²⁹Si MAS NMR, and can be successfully simulated by the ordered distributions. In the simulation, a small number of defects in the Al distribution were introduced into the ordered distribution mainly to adjust the deviation of Al content per unit cell from the typical composition. Analysis of the powder X-ray diffraction patterns of analcime was carried out, which suggests that the space groups proposed in the present work offer a better fit than the ones reported previously. Received: 5 April 1997 / Revised, accepted: 12 March 1998     

Effects of temperature and chlorinity on the microdistribution ofFavella taraikaensis Hada (Ciliata) in Maizuru Bay

Continuous sampling of the plankton with a pump sampler was carried out along a 960 m straight-line course in Maizuru Bay. The 25 collections of plankton were successively obtained at a depth of 1.5 m along the course, each of the collections covering a horizontal distance of 38 m. Vertical samplings of the plankton were done at five different depths (90, 120, 150, 180 and 210 cm) at 13 stations along the course. In both kinds of samplings temperature and chlorinity were measured.In the horizontal distribution ofF. taraikaensis, it was demonstrated that the counts of plankton had no correlation with the temperature and chlorinityin situ. There was a correlation between the counts and the differences of temperature and chlorinity between two successive sampling stations. It seemed thatF. taraikaensis was most abundant in the locations where the temperature difference was greater than +0.2C and the chlorinity difference was greater than +0.04 . This species was more abundant around the steep thermocline and the steep halocline. When the vertical profiles of temperature and chlorinity did not show steep gradients, this species was more abundant near the surface.