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1.
Abstract Magnetic measurements were carried out to investigate rock magnetic properties and paleomagnetic directions of late and middle Miocene sediments recovered from the land side of the Japan Trench during the Ocean Drilling Program Leg 186. Because the low coercive component in natural remanent magnetization (NRM) normalized by anhysteretic remanent magnetization shows that the drilling‐induced magnetization is severe in the sections obtained by the advanced hydraulic piston coring method, careful analyses of demagnetization of NRM using the ‘demagnetization plane’ were carried out to decompose the direction and intensity. Magnetostratigraphic correlation down to the upper Miocene, supplemented by biostratigraphic data, revealed that the sedimentation rates are characterized by drastic changes, with the early Pliocene having the highest rate. This high sedimentation rate is related to the subsidence of the southern deep‐sea terrace of the Japan Trench. 相似文献
2.
Miho Hirose Toshiya Katano Yuichi Hayami Atsushi Kaneda Takeshi Kohama Hidetaka Takeoka Shin-ichi Nakano 《Estuarine, Coastal and Shelf Science》2008
The Bungo Channel in southwestern Japan receives both warm, called Kyucho, and cold deep-water intrusions (bottom intrusion) from the Pacific Ocean. Abundances of Prochlorococcus, Synechococcus, and eukaryotic picophytoplankton were monitored from 18 July to 17 August 2001 to clarify whether advected picophytoplankton from the Pacific Ocean can grow in the channel or not. Synechococcus cells were further discriminated into low- and high-PUB types according to their fluorescence property in flow cytometry. From 18 to 25 July, the water temperature decreased by 3 °C at a 5-m depth at all stations, indicating the occurrence of a bottom intrusion. From 25 July to 4 August, a Kyucho occurred and the water temperature rapidly increased. From 4 to 17 August, a bottom intrusion and a Kyucho both occurred twice, although the intensities were smaller than those occurring until 4 August. From 18 to 30 July, the abundance of both Prochlorococcus and a high-PUB type of Synechococcus drastically decreased because of a bottom intrusion; however, the abundances rapidly increased due to the advection by a Kyucho. These advected cells increased from 4 to 17 August in the channel and Kitanada Bay. Changes in the abundance of low-PUB type of Synechococcus and eukaryotic picophytoplankton were less noticeable than those in the abundance of Prochlorococcus and high-PUB type. The present study demonstrated that oceanic picophytoplankton advected by the Kyucho could grow in the channel. However, abundances of low-PUB type and eukaryotic picophytoplankton increased higher than those of Prochlorococcus and high-PUB type did. Thus, these oceanic phytoplankters will be excluded when Kyucho does not occur for a long time. The co-occurrence of various types of picophytoplankton found in the channel is probably achieved by both Kyucho event and their growth capability in the channel. 相似文献
3.
Hiroshi Ishida Yutaka W. Watanabe Joji Ishizaka Toshiya Nakano Naoki Nagai Yuji Watanabe Akifumi Shimamoto Nobuhiro Maeda Michimasa Magi 《Journal of Oceanography》2009,65(2):179-186
Our analysis of the last three decades of retrospective data of vertical distributions and size composition of chlorophyll-a
(Chl-a) over the western North Pacific has revealed significant changes of three indices related to Chl-a during summer season,
as follows: (1) decreasing linear trend of the proportion of Chl-a in surface layer to that of the whole water column by 0.4
and 2.3% year−1 in the subtropical area along 137°E (STA137) during 1972 to 1997 and in the Kuroshio Extension area along 175°E (KEA175) during 1990 to 2001; (2) increasing linear trend of the depth of subsurface Chl-a maximum (DCM) by 0.4 and 2.6 m year−1 in STA137 and KEA175; and (3) decreasing linear trend of larger-size Chl-a (>3 μm) by 0.1 and 2.5% year−1 in STA137 and KEA175, respectively. Water density (σ
θ
) at 75 m depth had also decreased by 0.006 and 0.05 year−1 in STA137 and KEA175, respectively. The ratio of biogenic opal to biogenic CaCO3 in the sinking flux decreased by 0.015 year−1 in the subtropical region from 1997 to 2005. These findings may indicate that the subsurface chlorophyll maximum is deepening
and larger phytoplankton such as diatoms has been decreasing during the past decade, associated with the decreasing density
of surface water caused by warming in the western North Pacific, especially in the summer. 相似文献
4.
By means of in situ observation, the nucleation and growth of triclinic, pseudo-orthorhombic and pseudo-hexagonal CaAl2Si2O8 were investigated and their relative stabilities established. Pseudo-hexagonal and pseudo-orthorhombic CaAl2Si2O8 nucleate prior to anorthite and grow in a supercooled anorthite melt before the latter appears. They either dissolve or transform to anorthite once the latter nucleates and starts to grow. Corundum and mullite also nucleate metastably prior to anorthite in this melt. The liquidus temperatures of the four metastably nucleated phases were determined precisely by in situ measurements of the transformation temperatures from a polyhedral to a rounded morphology. On the basis of the supercooling thus determined, the growth rate versus supercooling relations were measured and analysed for the respective phases. The growth rate of the stable phase is one order of magnitude higher than those of any metastable phases. However, the growth rates of the three CaAl2Si2O8 polymorphs normalized by the viscosities are nearly the same. 相似文献
5.
Diffuse Emission of CO2 from Showa-Shinzan, Hokkaido, Japan: A Sign of Volcanic Dome Degassing 总被引:1,自引:0,他引:1
Pedro A. Hernández Kenji Notsu Hiromu Okada Toshiya Mori Masanori Sato Francisco Barahona Nemesio M. Pérez 《Pure and Applied Geophysics》2006,163(4):869-881
Two soil CO2 efflux surveys were carried out in September 1999 and June 2002 to study the spatial distribution of diffuse CO2 degassing and estimate the total CO2 output from Showa-Shinzan volcanic dome, Japan. Seventy-six and 81 measurements of CO2 efflux were performed in 1999 and 2002, respectively, covering most of Showa-Shinzan volcano. Soil CO2 efflux data showed a wide range of values up to 552 g m-2 d-1. Carbon isotope signatures of the soil CO2 ranged from -0.9‰ to -30.9‰, suggesting a mixing between different carbon reservoirs. Most of the study area showed CO2 efflux background values during the 1999 and 2002 surveys (B = 8.2 and 4.4 g m-2 d-1, respectively). The spatial distribution of CO2 efflux anomalies for both surveys showed a good correlation with the soil temperature, indicating a similar origin for the
extensive soil degassing generated by condensation processes and fluids discharged by the fumarolic system of Showa-Shinzan.
The total diffuse CO2 output of Showa-Shinzan was estimated to be about 14.0–15.6 t d-1 of CO2 for an area of 0.53 km2. 相似文献
6.
7.
Aoki Toshiya Katsura Shinya Koi Takashi Tanaka Yasutaka Yamada Takashi 《Landslides》2022,19(8):1813-1824
Landslides - The 2018 Hokkaido Eastern Iburi Earthquake triggered numerous shallow landslides on slopes covered with thick pyroclastic-fall deposits. The landslides occurred more frequently on... 相似文献
8.
A simple model of lower trophic level ecosystem has been created to analyze possible environmental control of primary production
in eight sub-areas of the Seto Inland Sea. The primary production rates observed by Hashimotoet al. (1997a) in these sub-areas are well reproduced by the model, including horizontal processes such as horizontal transport
of nutrients and vertical processes such as vertical mixing, light intensity and sinking of particulate matter. Without taking
account of horizontal processes the model also successfully reproduces the observed primary production rates in some areas,
but if fails to reproduce those in the others. This shows that the relative importance of the horizontal transport on the
primary production differs are by area. Two time scales,T
z andT
H, are introduced to explain this difference.T
z is a vertical cycling time of material, which is defined as the time during which the stock of the material in the water
column is utilized for primary production;T
H is the horizontal transit time of the material. The relative importance of the horizontal process is well explained by theT
H/T
z ratio; that is, the horizontal transport process is important in the areas where this ratio is small. Further the possible
mechanisms of nutrient supply for the primary production in each sub-area are investigated using this model. 相似文献
9.
Eitarou Oka Shota Katsura Hiroyuki Inoue Atsushi Kojima Moeko Kitamoto Toshiya Nakano Toshio Suga 《Journal of Oceanography》2017,73(4):479-490
The 137°E repeat hydrographic section for 50 winters during 1967–2016 has been analyzed to examine interannual to interdecadal variations and long-term changes of salinity and temperature in the surface and intermediate layers of the western North Pacific, with a particular focus on freshening in the subtropical gyre. Rapid freshening on both isobars and isopycnals began in the mid-1990s and persisted for the last 20 years in the upper main thermocline/halocline in the western subtropical gyre. In addition, significant decadal variability of salinity existed in the subtropical mode water (STMW), as previously reported for the shallower layers. An analysis of the 144°E repeat hydrographic section during 1984–2013 supplemented by Argo profiling float data in 2014 and 2015 revealed that the freshening trend and decadal variability observed at 137°E originated in the winter mixed layer in the Kuroshio Extension (KE) region and was transmitted southwestward to 137°E 1–2 years later in association with the subduction and advection of STMW. The mechanism of these changes and variations in the source region was further investigated. In addition to the surface freshwater flux in the KE region pointed out by previous studies, the decadal KE variability in association with the Pacific Decadal Oscillation likely contributes to the decadal salinity variability through water exchange between the subtropics and the subarctic across the KE. Interdecadal change in both the surface freshwater flux and the KE state, however, failed to explain the rapid freshening for the last 20 years. 相似文献
10.