Seasonal and interannual variability of chlorophyll a concentration in the Japan/East Sea (JES) was detected spatially by ocean color satellite remote sensing. Start timing of the spring bloom was different spatially. The spring bloom started at the subpolar front and southward of it in March, northward of subpolar front, along the Primorye coast and off Hokkaido in April and in the middle of the Japan Basin in May. The start of the spring bloom showed interannual variability that corresponded with the wind speed in the area. The spring bloom in 1998 and 2002 appeared about four weeks earlier than in 1997, 1999 and 2001, and it corresponded with weak winds that can lead to an early development of the thermocline. The bloom was late in 1999 and 2001 in the Japan Basin and along the Primorye coast, and in the southern area in 2000. It corresponded with stronger wind stress that delayed seasonal thermocline formation. The bloom along the Primorye coast appeared later in 1999, and it corresponded with stronger wind stress, and at the same time, it seemed to be related with the delay of melting of sea ice in Mamiya Strait. The fall bloom appeared from early October to early December, and it did not have a clear temporal transition. The area where chlorophyll a concentration exceeded 0.8 μg l−1 was wider in the western area than in the eastern area every year. The magnitude of the fall bloom was different between years, but it did not show a correlation with average wind speed in fall. Those results indicated that the timing of the seasonal bloom in the JES is largely affected by the variability of global climate such as ENSO events. 相似文献
We report the first study of sperm whale‐fall ecosystems, based on mass sinking of whale carcasses at shelf depths in the northwest Pacific. We conducted three observations over a 2‐year period on replicate sperm‐whale carcasses implanted at depths of 219–254 m off the southern part of Japan from July 2003 to August 2005. The study was made possible by a mass stranding of sperm whales in January 2002, and the subsequent sinking of 12 carcasses in the waters off Cape Nomamisaki. Dense aggregations of unique chemosynthesis‐based fauna had formed around the whale carcasses after 18 months (July 2003). The mytilid mussel Adipicola pacifica was the most abundant macrofaunal species and covered most of the exposed bone surfaces. The general composition of the fauna was similar to that of deep‐water reducing habitats, but none of the species appearing in this study has been found at hydrothermal vents, cold seeps or deep‐water whale falls. A new species of lancelet, which was the first record of the subphylum Cephalochordata from reducing environments, a new species of Osedax; a rarely encountered benthic ctenophore, and a rare gastropod species were discovered at this sperm whale‐fall site. Benthic communities were similar across all the carcasses studied, although the body sizes of the whales were very different. The succession of epifaunal communities was relatively rapid and the sulphophilic stage was considerably shorter than that of other known whale falls. 相似文献
The Global Imager (GLI) aboard the Advanced Earth Observing Satellite-II (ADEOS-II) made global observations from 2 April
2003 to 24 October 2003. In cooperation with several institutes and scientists, we obtained quality controlled match-ups between
GLI products and in-situ data, 116 for chlorophyll-a concentration (CHLA), 249 for normalized water-leaving radiance (nLw) at 443 nm, and 201 for
aerosol optical thickness at 865 nm (Tau_865) and Angstrom exponent between 520 and 865 nm (Angstrom). We evaluated the GLI
ocean color products and investigated the causes of errors using the match-ups. The median absolute percentage differences
(MedPD) between GLI and in-situ data were 14.1–35.7% for nLws at 380–565 nm, 52.5–74.8% nLws at 625–680 nm, 47.6% for Tau_865, 46.2% for Angstrom, and 46.6%
for CHLA, values that are comparable to the ocean-color products of other sensors. We found that some errors in GLI products
are correlated with observational conditions; nLw values were underestimated when nLw at 680 nm was high, CHLA was underestimated
in absorptive aerosol conditions, and Tau_865 was overestimated in sunglint regions. The error correlations indicate that
we need to improve the retrievals of the optical properties of absorptive aerosols and seawater and sea surface reflection
for further applications, including coastal monitoring and the combined use of products from multiple sensors. 相似文献
The spatial and seasonal variability of primary production in the Japan Sea from 1998 to 2002 was estimated using a satellite
primary production model. A size-fractionated primary production model was validated by in situ primary production data measured in the Japan Sea. Estimated primary production and in situ primary production showed a good positive correlation. Estimated primary production showed spatial variability. Annual primary
production levels were 170, 161, 191 and 222 gC m−2year−1 at the Russian coast, in the middle of the Japan Basin, the southeastern area and the southwestern area, respectively. It
was higher to the south around 40°N than to the north, and higher in the western area than in the eastern one. Peaks of primary
production appeared twice, in spring and fall, in the southern area, while a single peak appeared in the northern area. Primary
production along the Russian coast was higher than in other areas during summer. The spring bloom contributed 42% to the annual
primary production in these four areas. Furthermore, estimated primary production showed an interannual variability that was
largest in spring. Primary production in fall also showed interannual variability, especially in the middle of the Japan Basin
and the southwestern area. This corresponded mainly to the size of the phytoplankton bloom in each year. Winter convection
by wind and the depth of nutrient-rich, cold subsurface water underlying the Tsushima Current may contribute to the nutrient
supply to upper layer and interannual variations of primary production in spring. 相似文献
Primary productivity was measured byin situ method using13C in the offshore Oyashio region in the spring (May) and summer (September) of 1990. Most of the values were within the range of 0.1 to 4 gC 1–1 h–1 although a very large value, 7.96 gC l–1 h–1, was observed in summer. Most daily primary production fell within the range of 372 to 633 mgC m–2 d–1 although a very large value, 2,109 mgC m–2 d–1, was observed around the frontal area in summer. Chlorophylla (Chl.a) exceeded 1 g l–1 in many cases, and the maximum was 4.61 g l–1 in spring and 7.53 g l–1 in summer. Most primary productivity per unit Chl.a (photosynthetic assimilation ratio) was within the range of 0.1 to 3 gC gChl.a–1 h–1 although higher values, 3–6 gC gChl.a–1 h–1, were observed where small-size phytoplanktons (<2 m) were dominant. These results were compared with results obtained until now in the Oyashio region. The values beyond the range obtained so far in the offshore region were also observed in this study. Furthermore, it was pointed out that the size composition of phytoplankton community has significant influence on the results of Chl.a and photosynthetic assimilation ratio in the Oyashio region. 相似文献
In order to determine quantitatively the reason for the high productivity in the Oyashio Region, which is the southwest part
of the Pacific Subarctic Region, the annual-mean vertical circulation of nitrogen in the region was estimated from the vertical
profiles of nitrate, dissolved oxygen and salinity, and sediment-trap data by adapting them to the balance equations. Estimates
of the upwelling velocity (1.7×10−5cm sec−1) and the vertical diffusivity (2.1 cm2 sec−1) in the abyssal zone and the primary and secondary productivities (44 and 4 mgN m−2day−1, respectively) in the euphotic zone were close to those of previous works. The estimated vertical circulation of nitrogen
strongly suggested that, since the divergence (5 mgN m−2day−1) is caused by the abyssal convergence (6 mgN m−2day−1) and the positive precipitation, the local new production (22 mgN m−2day−1) necessarily exceeds not only the sinking flux (10 mgN m−2day−1) itself but also the sum of the sinking flux and the downward diffusion of dissolved and particulate organic matter (7 mgN
m−2day−1) produced probably in the euphotic zone. The important roles of the abyssal circulation, the winter convection, and the metabolic
activity in the bathyal zone to support the high productivity in the euphotic zone were clarified quantitatively. 相似文献
Physical-scaled model testing under 1 g conditions is carried out in obtaining the vertical response of fixed head floating-inclined single piles embedded in dry sand. Practical pile inclinations of 5° and 10° besides a vertical pile (0°) subjected to static and dynamic vertical pile head loadings are considered. To account for the effects of soil nonlinearity as well as the soil–pile interface nonlinearity on the response of piles, a range of low-to-high magnitude of pile head displacements is considered for the static case while a varying amplitude of harmonic accelerations for a wide range of frequencies is considered for the dynamic case. Experimental results are obtained in the form of pile head stiffnesses and strains generated in the pile under both the static and dynamic loadings. Results suggest that the nonlinear behavior of soil as well as the nonlinearity generated at the interface between the soil and the pile as the result of applied loading considerably affect the response of piles. The soil–pile interface nonlinearity that governs the slippage of pile shows a clear influence on the pile head stiffnesses by providing two distinct values of stiffnesses corresponding to the push and the pull directional movement of piles; the two values are significantly different. Axial and bending strains generated in the piles show expected dependency on the amplitude of applied loading; the pile head-level bending strain increases almost linearly with the increase in the angle of pile inclination.
Interannual variations of the Hawaiian Lee Countercurrent (HLCC) in the 2000s were investigated using satellite and Argo profiling
float observations. The satellite-observed sea surface height shows that the geostrophic eastward current was anomalously
strong to the west away from Hawaii in 2003 and 2005. However, the trade winds and the orographic wind curl dipole in the
lee of Hawaii that drives the climatological mean HLCC were not particularly strong in these years, suggesting that the accelerations
of the HLCC were not caused by the wind stress curl forcing around Hawaii and subsequent Rossby wave propagation. Using Argo
observations, we found negative potential vorticity (PV) anomalies in the subsurface north of the HLCC in these 2 years. The
pycnocline is lifted northward as low PV waters of different densities stack up in the vertical, and the HLCC is then accelerated
via the thermal wind. The intensification and/or southward intrusion of the eastern subtropical mode water and subtropical
mode water seem to have induced negative PV anomalies in 2003 and 2005, respectively. Using high-resolution ocean simulations,
we confirmed the migrations of PV anomalies and their contributions to the HLCC accelerations. Although the HLCC is located
away from the cores of major mode waters, our results suggest that interannual variations of the HLCC are affected by those
of mode waters. 相似文献
The Higashi-akaishi garnet-bearing ultramafic body in the Sanbagawa metamorphic belt, Southwest Japan, represents a rare example of oceanic-type ultrahigh-pressure metamorphism. The body of 2 km × 5 km is composed mostly of anhydrous dunite with volumetrically minor lenses of clinopyroxene-rich rocks. Dunite samples contain high Ir-type platinum group elements (PGE) and Cr in bulk rocks, high Mg and Ni in olivine, and high Cr in spinel. On the other hand, clinopyroxene-rich rocks contain low concentrations of Ir-type PGE and Cr, high concentrations of fluid-mobile elements in bulk rocks, and low Ni and Mg in olivine. Clinopyroxene is diopsidic with low Al2O3. The compositions of bulk rocks and mineral chemistry of spinel, olivine, and clinopyroxene suggest that the olivine-dominated rocks are residual mantle peridotites after high degrees of influx partial melting, and that the clinopyroxene-rich rocks are cumulates of subduction-related melts. Thus, the Higashi-akaishi ultramafic body originated from the interior of the mantle wedge, most likely the forearc upper mantle. It was then incorporated into the Sanbagawa subduction channel by a mantle flow, and underwent high pressure metamorphism to a depth greater than 100 km. Such a strong active flow in the mantle wedge is likely facilitated by the lack of serpentinites along the interface between the slab and the overlying mantle, as it was too hot for serpentine. These unusually hot conditions and strong active mantle flow may reflect conditions in the earliest stage of development of subduction, and may have been maintained by massive upwelling and subsequent eastward flow of asthenospheric mantle in the northeastern Asian continent in Cretaceous time when the Sanbagawa belt began to form. 相似文献