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101.
Tomoyuki Shikata Sou Nagasoe Tadashi Matsubara Yasuhiro Yamasaki Yohei Shimasaki Yuji Oshima Takuji Uchida Ian R. Jenkinson Tsuneo Honjo 《Journal of Oceanography》2008,64(3):355-365
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. 相似文献
102.
C. Mizota H. Doi E. Kikuchi S. Shikano T. Kakegawa N. Yurlova A.K. Yurlov 《Applied Geochemistry》2009
The Lake Chany complex and nearby lakes in western Siberia (Russian Federation) were studied to constrain the S cycle in these terrestrial lake environments. Surface water chemistry was characterized by Na–SO4–Cl composition, comparable to other inland basins in semi-arid climatic zones associated with marine evaporite-bearing formations at depth. Dissolved sulfates showed elevated δ34S (up to +32.3‰). These values are quite distinct from those in similar saline lakes in northern Kazakhstan, the Aral Sea, Lake Barhashi, and a gypsum deposit in the Altai Mountains. The localized distribution of such a unique S isotopic signature in dissolved SO4 negates both aeolian and catastrophic flooding hypotheses previously suggested for the genesis of the dissolved salts. The probable source of the dissolved SO4 in Lake Chany basin is inherited from hidden saline groundwaters (whose location and origins remain unclear) from eastern Paleozoic ranges with Upper Devonian formations with heavy S isotope values. Post-depositional enrichment of heavy S in the dissolved SO4 from saline sediments may be caused by local activity of SO4-reducing bacteria under the ambient supply of electron donors (dissolved river load organic matter and decaying bacterial mats) in the lake complex. Such microbial processes can remove up to ca. 60% of SO4 from the system. Extensive and intensive evaporation of lake fluids, ca. 40%, was indicated by the progressive enrichment of δ18O values in meteoric water samples collected along the river and lake system. This evaporation process compensates the microbial loss of SO4 dissolved in the incoming river water. 相似文献
103.
In the Precambrian, parts of the Oklo, Okélobondo and Bangombé uranium deposits of the Republic of Gabon, central Africa, functioned as natural fission reactors. Many elements in the Oklo and Bangombé uranium deposits show variations in isotopic composition caused by a combination of nuclear fission, neutron capture and radioactive decay. Isotopic studies provide useful information to understand the behavior of radionuclides in geological media. In our recent work, in situ REE, Pb and U isotopic analyses of individual tiny minerals in and around reactor zones have been performed using a SHRIMP (Sensitive High Resolution Ion Microprobe). The isotopic results of the SHRIMP analyses on micro-minerals found in and around the Oklo and Bangombé natural reactors are reviewed in this paper. The data suggest the selective uptake behavior of (1) Ra into illite, and (2) Pu into apatite, (3) the formation process of secondary minerals bearing fissiogenic REE and depleted U, (4) evidence of nuggets (?-particles) bearing fissiogenic platinum group elements (PGE), and (5) from the U–Pb systematics of highly altered zircons, the redistribution of U and Pb. 相似文献
104.
105.
Spatio-temporal changes in macrozoobenthic assemblage structure were monitored at 8 stations in a river-affected temperate lagoon (Idoura Lagoon, Japan) from May 1997 to May 1998 to assess animal–environment relationships in estuarine soft-bottom habitats. A total of 29 taxa occurred with a predominance of a few polychaete species including Heteromastus cf. similis, Hediste spp., Pseudopolydora cf. kempi and Prionospio japonica. The community structure differed significantly among four habitat types that were characterized by different salinity, sediment characteristics, and/or bottom elevation. For each habitat, macrozoobenthic community structure changed significantly with time, which was discriminated mostly by the lower density of polyhaline opportunistic species such as P. cf. kempi in warmer period. The salinity in the study area was much lower from May to September, mainly due to irrigation discharge from paddy fields, which seemed to be a lethal factor for the polyhaline species. C/N ratio and δ13C value of the sediment implied the accumulation of river-derived organic matters during the high river flow period. Present results showed the significant effects of fluctuating river discharge on the estuarine soft-bottom habitats, suggesting a linkage among terrestrial, riverine and estuarine ecosystems. 相似文献
106.
Mario?UchimiyaEmail author Hideki?Fukuda Shigeto?Nishino Takashi?Kikuchi Hiroshi?Ogawa Toshi?Nagata 《Journal of Oceanography》2011,67(5):589-599
This study examined possible environmental factors that affect prokaryote variables in surface waters (upper 100 m of water
column) in the Canada Basin, western Arctic Ocean. We collected data on prokaryote abundance and heterotrophic production
([3H]leucine incorporation) at eight stations deployed along a slope-to-offshore transect during September 2009. Prokaryote production
and growth tended to increase with increasing chlorophyll a (Chl. a) and temperature and with decreasing salinity. The combination of Chl. a, temperature, and salinity accounted for a large fraction (74%) of the variability in prokaryote production, with the highest
contribution made by Chl. a (r
2 = 0.56), followed by salinity (r
2 = 0.14) and temperature (r
2 = 0.03). Similarly, the variability in prokaryote growth rate was largely accounted for by the combination of the three environmental
variables (overall r
2 of 0.64), with Chl. a making the largest contribution to variability (r
2 = 0.33), followed by salinity (r
2 = 0.27) and temperature (r
2 = 0.05). These data are consistent with the notion that organic matter supply associated with freshwater inputs to surface
layers can result in enhanced prokaryote production and growth in the Canada Basin. Our results provide insights into the
regulation of the microbial loop in the Canada Basin where freshening has been proceeding rapidly due to increasing river
discharge and sea-ice melting. 相似文献
107.
An assessment of Arctic Ocean freshwater content changes from the 1990s to the 2006-2008 period 总被引:2,自引:0,他引:2
Benjamin Rabe Michael KarcherUrsula Schauer John M. TooleRichard A. Krishfield Sergey PisarevFrank Kauker Rüdiger GerdesTakashi Kikuchi 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(2):173-185
Unprecedented summer-season sampling of the Arctic Ocean during the period 2006-2008 makes possible a quasi-synoptic estimate of liquid freshwater (LFW) inventories in the Arctic Ocean basins. In comparison to observations from 1992 to 1999, LFW content relative to a salinity of 35 in the layer from the surface to the 34 isohaline increased by 8400±2000 km3 in the Arctic Ocean (water depth greater than 500 m). This is close to the annual export of freshwater (liquid and solid) from the Arctic Ocean reported in the literature.Observations and a model simulation show regional variations in LFW were both due to changes in the depth of the lower halocline, often forced by regional wind-induced Ekman pumping, and a mean freshening of the water column above this depth, associated with an increased net sea ice melt and advection of increased amounts of river water from the Siberian shelves. Over the whole Arctic Ocean, changes in the observed mean salinity above the 34 isohaline dominated estimated changes in LFW content; the contribution to LFW change by bounding isohaline depth changes was less than a quarter of the salinity contribution, and non-linear effects due to both factors were negligible. 相似文献
108.
109.
The Wigner-Ville distribution (WVD) function was originally proposed by Wigner in quantum mechanics and Ville applied it for signal analysis. This method has made it possible to represent a signal's power density spectrum in the time-frequency domain as a natural extension of the Fourier transform method (FTM). Recently, it has attracted great interest for its validity to analyze time-varying signals accomplished by the development of high-speed digital signal processing, and it is used for analyzing nonstationary signals. Conventionally, a sonar beamformer is constructed using delay lines, but the development of the high-speed processor has made it possible to apply the FTM for sonar beamforming. However, the bearing resolution of the beamformer is not enough for discriminating small underwater objects on the sea bottom by this method. To solve this problem, we aim to apply the WVD method, which can represent finer structure of signals as a natural extension of the FTM, for sonar beamforming to obtain sharper beam patterns than those of the beamforming method by FTM. Simulation results by computational calculations to clarify the resolution by the WVD method, which is presented in this paper, becomes approximately twice as high as by conventional FTM. The results of an experiment at sea also show the performance of this method 相似文献
110.
Masahiro Kajikawa Katsuhiro Kikuchi Yoshio Asuma Yusuke Inoue Noboru Sato 《Atmospheric Research》2000,52(4):377
Supercooled drizzle (freezing drizzle) was observed at Inuvik, N.W.T., Canada (68°22′N, 133°42′W) on December 20, 21 and 27, 1995. Meteorological conditions in which the supercooled drizzle could form under low temperatures (colder than −20°C) in the mid-winter season of the Canadian Arctic were examined from the sounding data and data measured by a passive microwave radiometer at ground level. The following results were obtained. (1) Supercooled drizzle fell to the ground with ice pellets and frozen drops on snow crystals. (2) The maximum size of supercooled drizzle particles increased as the depth of cloud layer saturated with respect to water increased. (3) Because a layer of air temperature higher than 0°C was not detected from the sounding data at Inuvik, melting of snow particles was impossible. It was concluded, therefore, that supercooled drizzle was formed by the condensation–coalescence process below freezing temperature. 相似文献