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141.
We define for observational study two subsets of all polar zone filaments, which we call polemost filaments and polar filament bands. The behavior of the mean latitude of both the polemost filaments and the polar filament bands is examined and compared with the evolution of the polar magnetic field over an activity cycle as recently distilled by Howard and LaBonte (1981) from the past 13 years of Mt. Wilson full-disk magnetograms. The magnetic data reveal that the polar magnetic fields are built up and maintained by the episodic arrival of discrete f-polarity regions that originate in active region latitudes and subsequently drift to the poles. After leaving the active-region latitudes, these unipolar f-polarity regions do not spread equatorward even though there is less net flux equatorward; this indicates that the f-polarity regions are carried poleward by a meridional flow, rather than by diffusion. The polar zone filaments are an independent tracer which confirms both the episodic polar field formation and the meridional flow. We find:
- The mean latitude of the polemost filaments tracks the boundary of the polar field cap and undergoes an equatorward dip during each arrival of additional polar field.
- Polar filament bands track the boundary latitudes of the unipolar regions, drifting poleward with the regions at about 10 m s-1.
- The Mt. Wilson magnetic data, combined with a simple model calculation, show that the filament drift expected from diffusion alone would be slower than observed, and in some cases would be equatorward rather than poleward.
- The observation that filaments drift poleward along with the magnetic regions shows that fields of both polarities are carried by the meridional flow, as would be expected, rather than only the f-polarity flux which dominates the strength. This leads to the prediction that in the mid-latitudes during intervals between the passage of f-polarity regions, both polarities are present in nearly equal amounts. This prediction is confirmed by the magnetic data.
142.
The base of the Clun Forest Formation at Clun, Shropshire, has previously been taken to correlate with the base of the Downton Castle Sandstone Formation (Přídolí Series, upper Silurian) on the basis of brachiopod, bivalve, gastropod and ostracod faunas. The detailed distribution of microfossils (acritarchs, chitinozoans, conodonts and ostracods) is documented at Nantyrhynau Quarry, Clun, Shropshire, to test this correlation. Three new species of chitinozoans, Eisenackitina clunensis, Eisenackitina kerria and Angochitina paucispinosa, are described from the quarry. Macrofossil and ostracod distributions suggest that the correlation is correct. However, a typical Ludlow acritarch flora is present throughout the section and suggests that the basal part of the Clun Forest Formation is Ludlow in age. The mixture of characteristic Ludlow and Přídolí microfossils at Nantyrhynau Quarry may be the result of differing environmental conditions between the Ludlow (shelf) and Clun (basinal) areas at this time. Alternatively, the strata exposed at Nantyrhynau Quarry may represent a period towards the end of the Ludlow Series when there are no strata represented in corresponding shelf sections due to non-deposition or erosion. © 1997 John Wiley & Sons, Ltd. 相似文献
143.
Depositional environments and maturity evaluated by biomarker analyses of sediments deposited across the Cenomanian–Turonian boundary in the Yezo Group,Tomamae area,Hokkaido, Japan
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Takuto Ando Ken Sawada Hideto Nakamura Keita Omatsu Reishi Takashima Hiroshi Nishi 《Island Arc》2017,26(1)
Biomarker analyses for evaluating maturity of organic matter and depositional environments such as redox conditions, were performed in sediments across the Cenomanian–Turonian boundary (CTB) in the Saku Formation of the Yezo Group distributed along the Shumarinai‐gawa River and the Omagari‐zawa River, both in the Tomamae area, Hokkaido, Japan. Maturity indicators using steranes and hopanes, show that organic matter in sediments from the Shumarinai‐gawa and Omagari‐zawa sections are of lower maturity than those from the Hakkin‐gawa section (Oyubari area). Moreover, the ββ hopane ratios clearly show that the maturity of the Shumarinai‐gawa samples is lower than that of the Omagari‐zawa samples. These variations in the maturity of organic matter presumably reflect the difference in their burial histories. The results for the pristane/phytane (Pr/Ph) ratios suggest that the Shumarinai‐gawa samples were deposited under dysoxic to anoxic environments across the CTB, while the depositional environments of the Omagari‐zawa samples were relatively oxic. By another paleoredox indicator using C35 homohopanoids including a homohopene index (HHenI), higher values are observed in the Shumarinai‐gawa section, particularly in the horizons of the preceding period and an early stage of the first negative shift phase and the latest oceanic anoxic event 2 (OAE2) interval. These results suggest that the Shumarinai‐gawa samples record dysoxic to anoxic environments across the CTB. In contrast, the signals for the C35 homohopanoid index values show a relatively oxic condition in the Omagari‐zawa section. The trends of stratigraphic variations in redox conditions are different from those in the OAE2 interval in the proto‐Atlantic and Tethys regions as reported previously. Hence, the redox variations in the Tomamae area were basically related to a local environmental setting rather than global anoxia. However, the prominent anoxic emphasis observed in the HHenI profile of the Shumarinai‐gawa section can be a distinctive, and possibly global, event in the North‐West Pacific just before the OAE2. 相似文献
144.
Motoko Igisu Tsuyoshi Komiya Stanley M. Awramik Yuka Ikemoto Yechuan Geng Hiroki Uehara Ken Takai 《Island Arc》2019,28(5)
Conventional and synchrotron radiation‐based (SR) Fourier transform infrared microspectroscopies (micro‐FTIR) were applied to four types of ~ 810 Ma organic‐walled microfossils together with diffuse organic matter (OM) and one irregularly shaped structure from the Fifteenmile Group, in Yukon, Canada, for their chemical characterization. The microfossils comprised one filamentous type and three coccoidal types. Micro‐FTIR mapping analysis revealed the micrometer‐scale, spatial distribution of organic components (aliphatic C‐H bonds) and carbonate in the microfossils. Based on comparisons of CH3/CH2 peak height ratios (R3/2) and morphologies of the microfossils (without the diffuse OM) to those of previously described Proterozoic microfossils, possible affinities of the microfossils are suggested, as follows. Palaeolyngbya? and Glenobotrydion belong to bacteria. Myxococcoides is not clearly characterized due to the significant mixing with diffuse OM containing abundant aliphatic C‐H groups. The irregularly shaped structure may represent a eukaryote. The diffuse OM may represent a mixture of decomposed microbial cells and extracellular polymeric substances (EPS). SR micro‐FTIR measurements of two coccoid types (Glenobotrydion and Unnamed Coccoid Form D) revealed that the R3/2 values of the internal spots with wall structures are similar to those without wall structures in Glenobotrydion: those values from Unnamed Coccoid Form D were different. The results suggest that these two coccoids are different chemically as well as morphologically. Micro‐FTIR characterization of the organic‐walled microfossils together with morphological analysis provides new insight into their biological affinities. 相似文献
145.
146.
147.
Jessica E. Pilarczyk Yuki Sawai Dan Matsumoto Yuichi Namegaya Naohisa Nishida Ken Ikehara Osamu Fujiwara Chris Gouramanis Tina Dura Benjamin P. Horton 《Sedimentology》2020,67(3):1373-1392
Tsunami deposits preserved in the geological record provide a more comprehensive understanding of their patterns of frequency and intensity over longer timescales; but recognizing tsunami deposits can prove challenging due to post-depositional changes, lack of contrast between the deposits and surrounding sedimentary layers, and differentiating between tsunami and storm deposition. Modern baseline studies address these challenges by providing insight into modern spatial distributions that can be compared with palaeotsunami deposits. This study documents the spatial fingerprint of grain size and foraminifera from Hasunuma Beach and the Kujukuri shelf to provide a basis from which tsunami deposits can be interpreted. At Hasunuma Beach, approximately 50 km east of Tokyo, the spatial distribution of three common proxies (foraminiferal taxonomy, foraminiferal taphonomy and sediment grain size) for tsunami identification were mapped and clustered using Partitioning Around Medoids cluster analysis. Partitioning Around Medoids cluster analysis objectively discriminated two coastal zones corresponding to onshore and offshore sample locations. Results show that onshore samples are characterized by coarser grain sizes (medium to coarse sand) and higher abundances of Pararotalia nipponica (27 to 63%) than offshore samples, which are characterized by finer grain sizes (fine to medium sand), lower abundances of Pararotalia nipponica (2 to 19%) and Ammonia parkinsoniana (0 to 10%), higher abundances of planktonics (15 to 58%) and species with fragile tests including Uvigerinella glabra. When compared to grain-size and foraminiferal taxonomy, foraminiferal taphonomy; i.e. surface condition of foraminifera, a proxy not commonly used to identify tsunami deposits, was most effective in discriminating modern coastal zones (identified supratidal, intertidal and offshore environments) and determining sediment provenance for tsunami deposits at Kujukuri. This modern baseline study assists the interpretation of tsunami deposits in the geological record because it provides a basis for sediment provenance to be determined. 相似文献
148.
Trish J. Lavery Catherine M. Kemper Ken Sanderson Christopher G. Schultz Peter Coyle James G. Mitchell Laurent Seuront 《Marine environmental research》2009,67(1):1-7
Metallothioneins (MT) concentration, renal damage, and bone malformations were investigated in 38 adult Tursiops aduncus carcasses to determine any associations with cadmium, copper, zinc, mercury, lead and selenium. Significantly higher concentrations of cadmium, copper, and zinc in the liver were observed in dolphins showing evidence of more advanced renal damage. No significant differences in metal or selenium concentrations in the liver were observed between groups differing in level of bone malformations. Some dolphins displayed evidence of toxicity and knowledge of metal toxicity pathways were used to elucidate the cause of these abnormalities. Two dolphins had high metal burdens, high MT concentrations, renal damage, and evidence of bone malformations, indicating possible severe and prolonged metal toxicity. One dolphin showed evidence of renal damage, but the lack of any other symptoms suggests that this was unlikely to be caused by metal toxicity. We recommend examining a range of metal toxicity symptoms simultaneously to aid in distinguishing metal toxicity from unrelated aetiologies. 相似文献
149.
Anil Kumar Vijayan Takashi Yoshikawa Shigeki Watanabe Hiroaki Sasaki Kazuhiko Matsumoto Sei-Ichi Saito Shigenobu Takeda Ken Furuya 《Journal of Oceanography》2009,65(2):245-258
Regional variations in the contribution of non-photosynthetic pigments (ā
np*) to the total light absorption of phytoplankton (ā
ph*) and its influence on the maximum quantum yield of photosynthesis (φ
m) were investigated. In the western equatorial Pacific, the surface ā
np* : ā
ph* ratio was higher in the western warm pool than that in the upwelling region. This difference appears to be attributable to
severe nitrate depletion and higher percentage of prokaryotes, which can accumulate very high concentrations of zeaxanthin
in the western warm pool. In the subarctic North Pacific, the ā
np* : ā
ph* ratio was expected to be higher in the Alaskan Gyre where the thermocline is sharper and iron limitation may possibly be
more severe than in the Western Subarctic Gyre. However, the ratio was actually higher in the Western Subarctic Gyre, contradictory
to our expectations. This east-west variation appears to be attributable to changes in the taxonomic composition; cyanobacteria
were more abundant in the Western Subarctic Gyre. The values of ā
np* : ā
ph* and its vertical variations were relatively small in the subarctic North Pacific compared to those in the western equatorial
Pacific. These inter-regional variations appear to be attributable to the lower solar radiation intensity, smaller percentage
of cyanobacteria, and relatively strong vertical mixing in the subarctic North Pacific. The spatial variations in ā
np* : ā
ph* significantly influence φ
m. In comparison with φ
m based on the total light absorption (φ
m ph), the values corrected for the contribution of non-photosynthetic pigments (φ
m ps) showed an increase in both the western equatorial Pacific and the subarctic North Pacific. 相似文献
150.
Temporal variation in phytoplankton composition related to water mass properties in the central part of Sagami Bay 总被引:1,自引:0,他引:1
Fuminori Hashihama Naho Horimoto Jota Kanda Ken Furuya Takashi Ishimaru Toshiro Saino 《Journal of Oceanography》2008,64(1):23-37
Temporal variations in water mass properties and the composition of phytoplankton pigments in the central part of Sagami Bay
were investigated by monthly observations from June 2002 to May 2004. Eleven pigments were quantified using high-performance
liquid chromatography (HPLC) from 100%, 20%, and 5% light depths relative to the surface; the class-specific composition of
phytoplankton community was then obtained by CHEMTAX analysis. The study area was influenced by the Kuroshio water for most
of the observation period. The mean contribution of diatoms in all samples was relatively low (29%), while that of flagellates,
mainly chlorophytes or cryptophytes, was quite high (60%). The phytoplankton composition at the three depths was uniform throughout
the observation period, indicating that the vertical structure of the phytoplankton community did not develop significantly
over time. A distinct temporal pattern was observed: flagellates dominated during the summer of 2002 and the winters of 2002–2003
and 2003–2004, while diatoms dominated during the summer of 2003. This pattern was associated with water mass changes. The
community in the summer of 2003 was influenced by coastal water. While no distinct spring bloom of phytoplankton was observed,
a weak increase in chlorophyll a was observed during the spring of 2004. Ocean color satellite data showed that fluctuations in chlorophyll a concentrations at time scales much shorter than a month occurred during the spring of 2003 and that the elevations in chlorophyll
a levels were not continuous. The fluctuations were probably associated with rapid flushing by the Kuroshio water, which has
low chlorophyll a content. 相似文献