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Jeffrey M. Napp Christine T. Baier Richard D. Brodeur Kenneth O. Coyle Naonobu Shiga Kathy Mier 《Deep Sea Research Part II: Topical Studies in Oceanography》2002,49(26)
The southeastern Bering Sea shelf ecosystem is an important fishing ground for fin- and shellfish, and is the summer foraging grounds for many planktivorous seabirds and marine mammals. In 1997 and 1998, Northern Hemisphere climate anomalies affected the physical and biological environment of the southeastern Bering Sea shelf. The resulting anomalous conditions provided a valuable opportunity to examine how longer-term climate change might affect this productive ecosystem. We compared historical and recent zooplankton biomass and species composition data for the southeastern Bering Sea shelf to examine whether or not there was a response to the atmosphere–ocean–ice anomalies of 1997 and 1998. Summer zooplankton biomass (1954–1994) over the southeastern shelf did not exhibit a decline as previously reported for oceanic stations. In addition, zooplankton biomass in 1997 and 1998 was not appreciably different from other years in the time series. Spring concentrations of numerically abundant copepods (Acartia spp., Calanus marshallae, and Pseudocalanus spp.), however, were significantly higher during 1994–1998 than 1980–1981; spring concentrations of Metridia pacifica and Neocalanus spp. were not consistently different between the two time periods. Neocalanus spp. was the only taxon to have consistent differences in stage composition between the two time periods—CV copepodites were much more prevalent in May of the 1990s than early 1980s. Since relatively high zooplankton concentrations were observed prior to 1997, we do not attribute the high concentrations observed in the summers of 1997 and 1998 directly to the acute climate anomalies. With the present data it is not possible to distinguish between increased production (control from below) and decreased predation (control from above) to explain the recent increase in concentrations of the species examined. 相似文献
2.
Biomass distribution and trophodynamics in the oceanic ecosystem in the Oyashio region are presented and analyzed, combining
the seasonal data for plankton and micronekton collected at Site H since 1996 with data for nekton and other animals at higher
trophic levels from various sources. The total biomass of biological components including bacteria, phytoplankton, microzooplankton,
mesozooplankton, micronekton, fishes/squids and marine birds/mammals was 23 g C m−2, among which the most dominant component was mesozooplankton (34% of the total), followed by phytoplankton (28%), bacteria
(15%) and microzooplankton (protozoans) (14%). The remainder (9%) was largely composed of micronekton and fish/squid. Marine
mammals/birds are only a small fraction (0.14%) of the total biomass. Large/medium grazing copepods (Neocalaus spp., Eucalanus bungii and Metridia spp.) accounted for 77% of the mesozooplankton biomass. Based on information about diet composition, predators were assigned
broadly into mean trophic level 3–4, and carbon flow through the grazing food chain was established based on the estimated
annual production/food consumption balance of each trophic level. From the food chain scheme, ecological efficiencies as high
as 24% were calculated for the primary/secondary production and 21% for the secondary/tertiary production. Biomass and production
of bacteria were estimated as 1/10 of the respective values for phytoplankton at Site H, but the role of the microbial food
chain remains unresolved in the present analysis. As keystone species in the oceanic Oyashio region, Neocalanus spp. are suggested as a vital link between primary production and production of pelagic fishes, mammals and birds. 相似文献
3.
Astrophysics and Space Science - Analysis of the radial velocity curves of 12 DD Lacertae showns that the primary period is decreasing and the secondary is almost constant, confirming the... 相似文献
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Naonobu Sato 《Astrophysics and Space Science》1979,66(2):309-318
All the observational data of 12DD Lacertae obtained have been examined to find a clue to the problem of secular variation or pulsational stability. From the statistical consideration it is concluded that the mean brightness is almost constant within small irregular variation of a few hundredth of a magnitude and the -velocity also shows small irregular variation of a few km sec–1 during more than a half century; but a result from the least-squares solution is also discussed. No periodicity of the variation in mean magnitude and -velocity has been detected, and an expectation that the small variation in the -velocity might be caused by orbital motion is not confirmed. 相似文献
5.
Naonobu Sato 《Astrophysics and Space Science》1973,24(1):215-230
Analysis of the light curves of 12DD Lacertae obtained during the years 1918-'71 shows that the primary period,P
1, is decreasing at the rate of about 1 s per 500 yr. The secondary period,P
2, is nearly constant but the third and fourth periods,P
3 andP
4, appear unstable with some irregular changes in frequency and amplitude. It is confirmed that the color in the primary variation is bluest around the phase of a half quarter before maximum light, 0.
P
875. The third variation also shows a similar tendency in color, while the secondary and fourth variations do not seem to show any meaningful color change, presumably indicating that the latter two are different from the pulsational nature of the primary and third variations. The method of power spectrum analysis is further applied to examine the structure of the multiperiodicity in more details and to search for any unknown periods in the light variation. 相似文献
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Atsushi Tsuda Hiroshi Kiyosawa Akira Kuwata Mamiko Mochizuki Naonobu Shiga Hiroaki Saito Sanae Chiba Keiri Imai Jun Nishioka Tsuneo Ono 《Progress in Oceanography》2005,64(2-4):189
Phytoplankton species composition was analyzed inside and outside of the iron-enriched patch during the SEEDS experiment. Before the iron-enrichment, the phytoplankton community consisted of similar proportions of pico-, nano- and micro-sized phytoplankton, and the micro-phytoplankton was dominated by the pennate diatom Pseudo-nitzschia turgidula. Although all the diatoms, except the nano-sized Fragilariopsis sp., increased during the two weeks of the observation period, the flora in the patch dramatically changed with the increase of phytoplankton biomass to a centric diatom-dominated community. Neritic diatoms, especially Chaetoceros debilis, showed higher growth rates than other diatoms, without any delay in the initiation of growth after the enrichment, and accounted for 90% of the micro-phytoplankton after day 9. In contrast, the oceanic diatoms showed distinct delays in the initiation of growth. We conclude that the responses of the diatoms to the manipulation of iron concentration were different by species, and the fast and intensive response of the phytoplankton to iron-enrichment resulted from the presence of a small amount of neritic diatoms at the study site. The important factors that determine the dominant species in the bloom are the potential growth rates under an iron-replete condition and the growth lag. Abundant species in the patch are widely distributed in the North Pacific and their relative contributions in the Oyashio area and at Stn KNOT are high from spring to summer. However, a characteristic difference of species composition between the SEEDS bloom and natural blooms was the lack of Thalassiosira and Coscinodiscus species in the patch, which usually account for a major part of the phytoplankton community under blooming conditions in the western North Pacific. 相似文献
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Rashid S. Al-Maamari Akihiko Hirayama Tsuyoshi Shiga Mark N. Sueyoshi Mahfoodh Al-Shuely Osman A. E. Abdalla Anvar R. Kacimov 《Environmental Earth Sciences》2011,63(6):1189-1198
Water table dynamics, dissolved oxygen (DO) content, electrical resistivity (ER) in monitoring wells and air pressure in the vadose zone are monitored in air sparging (AS) accompanied by soil vapor extraction (SVE) at a hydrocarbon-contaminated groundwater site in Oman, where a diesel spillover affected a heterogeneous unconfined aquifer. The formation of a groundwater mound at the early stage of air injection and potential lateral migration of contaminants from the mound apex called for an additional hydrodynamic barrier constructed as a pair of pump-and-treat (P&T) wells whose recirculation zone encompassed the AS and SVE wells. In all monitored piezometers the phreatic surface showed a rapid and distinct peak, which is attributed to the time of air breakthrough from the injection point to the vadose zone and a relatively mild recession limb interpreted as a decay of the mound. Tracer tests showed a layer of a relatively low hydraulic conductivity at an intermediate depth of the screened interval of the wells. Increased levels of DO and borehole air pressure that have been observed (as far as 50 m away) are likely mitigated by SVE and P&T. Radius of influence can be indirectly inferred from ER and DO changes in the AS operation zone. Salt tracer tests have shown that groundwater velocity within the AS zone decreases with the increase of air injection rate. 相似文献
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