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Akira Taniguchi Kazutoshi Saito Akio Koyama Mitsuo Fukuchi 《Journal of Oceanography》1976,32(3):99-106
Vertical distribution of phytoplankton in early warming season in the eastern Bering Sea and adjacent sea areas was investigated. In the surface layer which was under the influence of newly melted sea ice in the shelf water region of the Bering Sea in May, remarkably dense populations ofThalassiosira hyalina andT. nordenskiöldii and relatively large populations ofFragilaria andNavicula occupied large part of phytoplankton community. In June, although theThalassiosira populations sunk into the bottom layer and withered, a certain part of theFragilaria-Navicula populations was still suspended in subsurface layer. Thus,Fragilaria-Navicula were the leading components of the June community in the shelf region.In the Bering Basin region, no dense phytoplankton populations were developed until a shallow thermocline was established. In June when the shallow thermocline developed near shelf edge,Thalassiosira decipiens burst out. As the shallow thermocline extended from near shelf to central part of the Basin region with surface warming, the areas of blooming also shifted from near shelf to the central part.Contribution No. 73 from the Research Institute of North Pacific Fisheries, Hokkaido University. 相似文献
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Japanese fisheries production in the Japan/East Sea between 1958 and 2003 increased to their peak (1.76 million tons) in the late 1980s and decreased abruptly with the collapse of Japanese sardine. Catch results for 58 fisheries and various environmental time-series data sets and community indices, including mean trophic level (MTL) and Simpson’s diversity index (DI), were used to investigate the impacts of fishing and climate changes on the structure of the fish community in the Tsushima warm current (TWC) region of the Japan/East Sea. The long-term trend in fisheries production was largely dependent on the Japanese sardine that, as a single species, contributed up to 60% of the total production in the Japanese waters of the Japan/East Sea during the late 1980s. Excluding Japanese sardine, production of the small pelagic species was higher during 1960s and 1990s but lower during 1970s and 1980s. This variation pattern generally corresponds with the trend in water temperature, warmer before early 1960s and after 1990s but colder during 1970s and 1980s. The warm-water, large predatory fishes and cold water demersal species show opposite responses to the water temperature in the TWC region, indicating the significant impact of oceanic conditions on fisheries production of the Japan/East Sea. Declines in demersal fishes and invertebrates during 1970s and 1980s suggested some impact of fishing. MTL and DI show a similar variation pattern: higher during 1960s and 1990s but lower during 1970s and 1980s. In particular, the sharp decline during the 1980s resulted from the abundant sardine catches, suggesting that dominant species have a large effect on the structure of the fish community in the Japan/East Sea. Principal component analysis for 58 time-series data sets of fisheries catches suggested that the fish community varied on inter-annual to inter-decadal scales; the abrupt changes that occurred in the mid-1970s and late 1980s seemed to correspond closely with the climatic regime shifts in the North Pacific. These results strongly suggest that the structure of the fish community in the Japan/East Sea was largely affected by climatic and oceanic regime shifts rather than by fishing. There is no evidence showing “fishing down food webs” in the Japan/East Sea. However, in addition to the impacts of abrupt shifts that occurred in the late 1980s, the large predatory and demersal fishes seem to be facing stronger fishing pressure with the collapse of the Japanese sardine. 相似文献
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Tsuneo Odate Toru Hirawake Atsushi Tanimura Mitsuo Fukuchi 《Journal of Oceanography》2000,56(2):185-196
Surface temperature, salinity, concentrations of silicate (Si) and nitrate + nitrite (N), and in vivo fluorescence (Fluor) were investigated in the marginal ice zone (MIZ) and the seasonally open oceanic zone (SOOZ) (32–40°E, 64–69°S) from February 23 to 28 1992. In the MIZ the mean Si and N were 67.8 ± 2.2 M and 32.5 ± 1.7 M, respectively. There was a trend that low N values coincided with high Fluor values. Observation conducted at one point (64°S, 38°E) revealed a diel variation pattern in Fluor. Applying this pattern of deviation from noon value, all Fluor data were normalized to value at local noon. In the MIZ a significant negative correlation was observed between the normalized Fluor and N but not Si. On the other hand, Si decreased continuously from south to north in the SOOZ and was negatively correlated with the normalized Fluor. Difference in Si concentration was about 30 M between the sea around 64°S and the MIZ, while the difference in N concentration was estimated as less than 10 M. If diatoms take up silicate and nitrogen at an approximate ratio of 1:1, additional nitrogenous nutrients other than nitrate and nitrite (e.g. ammonia, urea etc.) would be required. In this case, an f-ratio of lower than 33% is obtained. It is suggested that in the MIZ abundance of phytoplankton community dominated by non-diatom increases utilizing nitrate while in the SOOZ abundance of phytoplankton community dominated by diatoms increases consuming Si and regenerated nitrogen. 相似文献
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Satoshi?KitajimaEmail author Naoki?Iguchi Naoto?Honda Tatsuro?Watanabe Osamu?Katoh 《Journal of Oceanography》2015,71(3):287-296
We investigated the horizontal distribution of Nemopilema nomurai medusae using a midwater trawl in the southwestern Sea of Japan from September to October of each year from 2006 to 2012. Numerous medusae of this species found in 2006, 2007, and 2009 were mainly distributed far (>40 km) from the mainland of Japan in the western part of the survey area, but were distributed in the stations closest (<25 km) to the mainland in the eastern part, particularly in 2006 and 2009. These distribution patterns were associated with the path of the second branch of the Tsushima Warm Current (TWC) that flows offshore to the west of Oki Islands and usually approaches the mainland of Japan to the east of Oki Islands. Differences in jellyfish distribution across the survey periods were related to the distribution of the second branch being associated with types, position and intensity of eddies in the eastern part of the survey area. Hence, the formations of eddies and consequent variation in the path of the TWC would be responsible for transporting medusae from offshore to near the mainland to the east of Oki Islands. Individuals with large bells accumulated in the northwestern part of the survey area, where a cyclonic eddy was present downstream of the third branch of the TWC. This variation in bell size distribution may be ascribed to differences in the physical and/or biological factors among the three branches of the TWC. 相似文献
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Recent structural, tephrochronologic and magnetostratigraphic studies conducted along the northernmost border of the Philippine Sea (PHS) plate enable us to reconstruct the precise tectonic evolution along the convergent boundary between the PHS plate and the Northeast Japan (NEJ) plate or the North American (NAM) plate since about 1 Ma. The authors of the present study split the tectonic evolution into five stages and present the characteristics of each stage. A plate tectonic interpretation is proposed, based upon the tectonic evolution, with special reference to the mode of convergent motion. In brief, our interpretations are as follows: the relative motion between the PHS and the NEJ plates was not recognized geologically within the area studied from about 1.0 to 0.9 Ma (Stage 1), suggesting either none or small influence from the coupling between the two plates during that period of time. Convergence between the PHS and the NEJ plates was possibly in N-S direction from 0.9 to 0.5 Ma (Stage II), and probably north-northwestward since 0.5 Ma (Stages III to V). The mode of the convergent motion was that of buoyant subduction in Stages II and III. The mode changed gradually from buoyant subduction during Stage IV to collision in Stage V (0.07 Ma to the present). 相似文献
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Daiki Nomura Nobue Kasamatsu Kazu TateyamaSakae Kudoh Mitsuo Fukuchi 《Continental Shelf Research》2011,31(13):1377-1383
The combined concentration of total dimethylsulfoniopropionate and dimethylsulfide (DMSP+DMS) were measured in Antarctic fast ice on the coast of Lützow-Holm Bay, eastern Antarctica. High bulk-ice DMSP+DMS and chlorophyll a concentrations were found at the bottom of the sea ice, and these concentrations were higher than those in the under-ice water. The bulk-ice DMSP+DMS and chlorophyll a concentrations were highly correlated (r2=0.68, P<0.001), suggesting that the high bulk-ice DMSP+DMS concentrations were caused mainly by the presence of algae assemblages in the ice. The calculated brine DMSP+DMS concentrations were as high as 1100 nM in the bottom ice layer, and the vertical profile patterns of brine DMSP+DMS concentrations were almost the same as for the bulk ice, mainly because of the small amount of variability in the vertical brine volume fraction. DMSP+DMS and chlorophyll a concentrations in the under-ice water increased, whereas the salinity of the under-ice water decreased, during the sampling period. These results reflect the supply of freshwater containing high levels of DMSP+DMS to the water just under the ice as the ice melted. These results suggest that sea-ice melting could be important to sulfur cycling in coastal ice-covered regions of the polar oceans. 相似文献
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Tatsuro Watanabe Daisuke Simizu Kou Nishiuchi Toru Hasegawa Osamu Katoh 《Journal of Oceanography》2009,65(6):791-801
We examined the surface current structure in the Tsushima Warm Current (TWC) region of the Japan Sea based on a dataset from
satellite-tracked surface drifters, including our new deployments during 2004–2008. The gridded mean current velocity and
mean kinetic energy (KE) fields calculated from all available drifter data revealed the structure and seasonality of the three
branches of the TWC. By comparing the eddy kinetic energy (EKE) field to the KE field, we found four regions where the ratio
of EKE to KE was high. In particular, this ratio became extremely high east of the Oki Islands located between the first branch
of the TWC (FBTWC) and the second branch of the TWC (SBTWC). Our analysis suggests that the generation of alternate warm and
cold eddies east of the Oki Island induced this high ratio. The occurrence of a warm or cold eddy was related to the route—either
nearshore or offshore—of the SBTWC. When the offshore route of the SBTWC became dominant, a warm eddy was frequently generated
east of the Oki Islands. In contrast, when the nearshore route of the SBTWC became dominant, a cold eddy was more likely to
be generated. 相似文献