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排序方式: 共有225条查询结果,搜索用时 125 毫秒
1.
Bethany Behrens Yosuke Miyairi Adam D. Sproson Masako Yamane Yusuke Yokoyama 《第四纪科学杂志》2019,34(8):603-608
Understanding Antarctic Ice Sheet dynamics related to global climate change is of scientific and societal interest as the future behaviour of the ice sheet under the currently changing climate is unknown. We present beryllium‐10 (10Be) analysis of a high‐resolution marine sediment core from the Adélie Basin near the eastern Wilkes Land margin, which is susceptible to marine ice sheet instability due to the low‐lying nature and down‐sloping trough of the Wilkes Subglacial Basin. Combined with a newly constructed age model using compound specific radiocarbon dates, the data reveal three events associated with high meteoric 10Be at ca. ~10 ka, ca. ~6.5 ka and from ca. ~4 ka. We interpret these high meteoric 10Be events to be derived from the deposition of 10Be released from the ice sheet during meltwater discharge. In particular, the shift to higher meteoric 10Be concentration at~4 ka may correspond to changes in climate patterns at this time. Copyright © 2019 John Wiley & Sons, Ltd. 相似文献
2.
Re-Os isotope systematics and fractionation of siderophile elements in metal phases from CBa chondrites 下载免费PDF全文
Nao Nakanishi Tetsuya Yokoyama Satoki Okabayashi Tomohiro Usui Hikaru Iwamori 《Meteoritics & planetary science》2018,53(5):1051-1065
We report Os isotope compositions of metal grains in two CBa chondrites (Bencubbin and Gujba) determined using a micromilling sampling coupled with thermal ionization mass spectrometry, together with the abundances of major and trace siderophile elements obtained by electron probe microanalysis and femtosecond laser ablation inductively coupled plasma–mass spectrometry. The CBa metal grains presented 187Os/188Os ratios akin to carbonaceous chondrites with limited variations (0.1257–0.1270). Most of the CBa metal grains were scattered along a 187Re-187Os reference isochron of IIIAB iron meteorites, indicating that the CBa metals experienced limited Re-Os fractionation at the time of their formation. The Re/Os ratios of sampling spots for the CBa metals, recast from the observed 187Os/188Os ratios, had a positive correlation with their Os/Ir ratios. In addition, the metal grains showed a positive correlation in a Pd/Fe versus Ni/Fe diagram. These correlations suggest that the CBa metal grains have formed via equilibrium condensation or evaporation from a gaseous reservoir at ~10−4 bar with enhanced metal abundances. Compared to the Bencubbin metals, the Gujba metals are characterized by having systematically lower Pd/Fe and Ni/Fe ratios that span subchondritic values. Such a difference was most likely induced by the compositionally heterogeneous impact plume from which the metals were condensed. 相似文献
3.
Itaru Yamashita Adichat Surinkum Yutaka Wada Makoto Fujihara Masao Yokoyama Haider Zaman Yo-ichiro Otofuji 《Journal of Asian Earth Sciences》2011,40(3):784-796
Jurassic to Cretaceous red sandstones were sampled at 33 sites from the Khlong Min and Lam Thap formations of the Trang Syncline (7.6°N, 99.6°E), the Peninsular Thailand. Rock magnetic experiments generally revealed hematite as a carrier of natural remanent magnetization. Stepwise thermal demagnetization isolates remanent components with unblocking temperatures of 620–690 °C. An easterly deflected declination (D = 31.1°, I = 12.2°, α95 = 13.9°, N = 9, in stratigraphic coordinates) is observed as pre-folding remanent magnetization from North Trang Syncline, whereas westerly deflected declination (D = 342.8°, I = 22.3°, α95 = 12.7°, N = 13 in geographic coordinates) appears in the post-folding remanent magnetization from West Trang Syncline. These observations suggest an occurrence of two opposite tectonic rotations in the Trang area, which as a part of Thai–Malay Peninsula received clockwise rotation after Jurassic together with Shan-Thai and Indochina blocks. Between the Late Cretaceous and Middle Miocene, this area as a part of southern Sundaland Block experienced up to 24.5° ± 11.5° counter-clockwise rotation with respect to South China Block. This post-Cretaceous tectonic rotation in Trang area is considered as a part of large scale counter-clockwise rotation experienced by the southern Sundaland Block (including the Peninsular Malaysia, Borneo and south Sulawesi areas) as a result of Australian Plate collision with southeast Asia. Within the framework of Sundaland Block, the northern boundary of counter-clockwise rotated zone lies between the Trang area and the Khorat Basin. 相似文献
4.
Miyuki Tahata Yusuke Sawaki Yuichiro Ueno Manabu Nishizawa Naohiro Yoshida Toshikazu Ebisuzaki Tsuyoshi Komiya Shigenori Maruyama 《地学前缘(英文版)》2015,6(1):121-136
Important ecological changes of the Earth(oxidization of the atmosphere and the ocean) increase in nutrient supply due to the break-up of the super continent(Rodinia) and the appearance of multi-cellular organisms(macroscopic algae and metazoan) took place in the Ediacaran period,priming the Cambrian explosion.The strong perturbations in carbon cycles in the ocean are recorded as excursions in carbonate and organic carbon isotope ratio(δ~(13)C_(carb) and δ~(13)C_(org)) from the Ediacaran through early Cambrian periods.The Ediacaran-early Cambrian sediment records of δ~(13)C_(carb) and δ~(13)C_(org),obtained from the drill-core samples in Three Gorges in South China,are compared with the results of numerical simulation of a simple one-zone model of the carbon cycle of the ocean,which has two reservoirs(i.e.,dissolved organic carbon(DOC) and dissolved inorganic carbon(DIC).The fluxes from the reservoirs are assumed to be proportional to the mass of the carbon reservoirs.We constructed a model,referred to here as the Best Fit Model(BFM),which reproduce δ~(13)C_(carb) and δ~(13)C_(org) records in the Ediacaran-early Cambrian period noted above.BFM reveals that the Shuram excursion is related to three major changes in the carbon cycle or the global ecological system of the Earth:(1) an increase in the coefficient of remineralization by a factor of ca.100,possibly corresponding to a change in the dominant metabolism from anaerobic respiration to aerobic respiration,(2) an increase of carbon fractionation index from 25‰ to 33‰,possibly corresponding to the change in the primary producer from rock-living cyanobacteria to free-living macro algae,and(3) an increase in the coefficient of the organic carbon burial by a factor of ca.100,possibly corresponding to the onset of a biological pump driven by the flourishing metazoan and zooplankton.The former two changes took place at the start of the Shuram excursion,while the third occurred at the end of the Shuram excursion.The other two excursions are explained by the tentative decrease in primary production due to cold periods,which correspond to the Gaskiers(ca.580 Ma) and Bikonor(ca.542 Ma) glaciations. 相似文献
5.
6.
Richard A. Staff Takeshi Nakagawa Gordon Schlolaut Michael H. Marshall Achim Brauer Henry F. Lamb Christopher Bronk Ramsey Charlotte L. Bryant Fiona Brock Hiroyuki Kitagawa Johannes van der Plicht Rebecca L. Payne Victoria C. Smith Darren F. Mark Alison Macleod Simon P. E. Blockley Jean‐Luc Schwenninger Pavel E. Tarasov Tsuyoshi Haraguchi Katsuya Gotanda Hitoshi Yonenobu Yusuke Yokoyama Suigetsu Project Members 《Boreas: An International Journal of Quaternary Research》2013,42(2):259-266
The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high‐resolution, multi‐proxy palaeoenvironmental data across the last glacial/interglacial cycle. In order to maximize the potential of this archive, a well‐constrained chronology is required. This paper outlines the multiple geochronological techniques being applied – namely varve counting, radiocarbon dating, tephrochronology (including argon–argon dating) and optically stimulated luminescence (OSL) – and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu (SG06) varve chronology and the absolute (IntCal09 tree‐ring) time scale, as derived using radiocarbon data from the uppermost (non‐varved) portion of the core. This tie‐point, defined as a distinct (flood) marker horizon in SG06 (event layer B‐07–08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 IntCal09 cal. years BP (68.2% probability range). 相似文献
7.
There has been limited previous research about Holocene climate variability in the Indian Sector of the Southern Ocean. Here we examine centennial‐scale changes in diatom assemblages and stable isotopic ratios since 10 000 cal a BP in a high‐accumulation‐rate sediment core from the Conrad Rise. Although abundances of dominant diatom taxa (Fragilariopsis kerguelensis and Thalassiothrix antarctica) are comparatively constant, relative abundances of secondary taxa fluctuate. Before c. 9900 cal a BP, winter sea‐ice and cold water covered the Conrad Rise. Following deglaciation the sea‐ice retreated from the Conrad Rise, lagging that of the Atlantic and eastern Indian Sectors by about 1500 a. The Polar Front moved southward during the early Holocene optimum and north Antarctic Zone waters covered the Conrad Rise for about 650 a. After 9300 cal a BP, solar insolation strongly influenced sea surface temperature and primary productivity in the Southern Ocean. In the high‐latitude Indian Sector, productivity increased 1500 a after the onset of late Holocene neoglaciation. Periodic δ18O and cold‐water diatom taxa spikes (at intervals of 200 and 300–500 a, respectively) occurred after 9300 cal a BP, probably associated with solar activity. Fluctuations in short‐term sea surface temperature and cold‐water taxa are synchronous with changes in δD observed in an east Antarctic ice core. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
8.
Yusuke Okazaki Osamu Seki Takeshi Nakatsuka Tatsuhiko Sakamoto Minoru Ikehara Kozo Takahashi 《Journal of Oceanography》2006,62(5):639-648
Cycladophora davisiana, a radiolarian species dwelling at mesopelagic depths, is known as a representative glacial fauna due to its unique distribution
during glacial periods. In the present ocean, abundant production of C. davisiana is only observed in the Okhotsk Sea, indicating an adaptation of C. davisiana for seasonal sea-ice covered conditions. We found pronounced abundant production of C. davisiana during the early to middle Holocene in the Okhotsk Sea, suggesting more favorable conditions for C. davisiana than the present Okhotsk Sea. In order to clarify the reason, oceanographic conditions during the Holocene were reconstructed
based on biomarkers, lithogenic grains including ice-rafted debris (IRD), biogenic opal, and total organic carbon (TOC) in
two sediment cores from the Okhotsk Sea. These indicators suggest that the pronounced C. davisiana production may be attributed to: 1) a supply to mesopelagic depths under intensified stratification of fine organic particles
derived from coccolithophorids, bacteria, and detrital materials; and 2) cold, well-ventilated intermediate water formation. 相似文献
9.
Roland Bibron Concèle Leger Jacques Tobailem Yfji Yokoyama Hisao Mabuchi Noëlle Baillard 《Geochimica et cosmochimica acta》1974,38(2):197-205
]The activities of 18 radionuclides in 4 samples from the Saint-Séverin meteorite have been measured after chemical separation. The results show that the DI sample from the D piece has been less irradiated than the samples B2, B3 and B4 from the B piece. This is based on activities of isotopes produced both by spallation as 26Al, 53Mn, 54Mn, 55Fe, 57Co and by thermal neutron capture as 59Ni and 60Co.Comparison of experimental values to calculated production rates suggests that the D piece was connected to the main body of the meteorite by a small surface, and that the DI sample in this piece was opposite to the main body of the meteorite. 相似文献
10.
Tetsuya Yokoyama Yusuke Ohkuma Keiji Nishikawa Koki Sumiya Ikshu Gautam 《Geostandards and Geoanalytical Research》2023,47(2):415-435
The Cr isotope ratios of terrestrial and extra-terrestrial materials are emerging as one of the most important tracers in geosciences. Previous studies on Cr isotopic measurements using TIMS have found that there is residual Cr isotopic fractionation between the mass-fractionation-corrected 53Cr/52Cr and 54Cr/52Cr ratios, which may cause an offset of obtained ratios from the reference values. The residual fractionation was thought to be caused by the evaporation of Cr-oxide species during thermal ionisation, but the mechanism by which this residual fractionation could be reduced remained unclear. Here we revisit the issue of residual fractionation and propose that this problem can be alleviated by utilising W filaments instead of conventionally used Re filaments for Cr ionisation. Using W filaments, the formation of CrO+ was suppressed during heating as the filament temperature was ~ 100 °C lower than when Re filaments were used. In repeated measurement of a carbonaceous chondrite, the intermediate precisions of 53Cr/52Cr and 54Cr/52Cr ratios in the W filament runs were two to three times better than those of the Re filament runs. Therefore, the new finding of this study will be of key importance for future studies of Cr isotopes for terrestrial and extra-terrestrial materials. 相似文献