Meltwater discharge during the Holocene from the Wilkes subglacial basin revealed by beryllium isotope analysis of marine sediments     

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   

http://www.sciencedirect.com/science/article/pii/S1674987114000917     

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   

Theoretical and experimental evidence for the post-cotunnite phase transition in zirconia at high pressure     

Daisuke Nishio-Hamane  Haruhiko Dekura  Yusuke Seto  Takehiko Yagi 《Physics and Chemistry of Minerals》2015,42(5):385-392

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The multiple chronological techniques applied to the Lake Suigetsu SG06 sediment core,central Japan     

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   

Holocene migration of oceanic front systems over the Conrad Rise in the Indian Sector of the Southern Ocean     

Kota Katsuki  Minoru Ikehara  Yusuke Yokoyama  Masako Yamane  Boo‐Keun Khim 《第四纪科学杂志》2012,27(2):203-210

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   

Cycladophora davisiana (Radiolaria) in the Okhotsk Sea: A key for reconstructing glacial ocean conditions     

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   

Evaluation of the Residual Mass Fractionation in High-Precision Cr Isotopic Analysis with TIMS     

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   

Micro-X-ray fluorescence-based comparison of skeletal structure and P, Mg, Sr, O and Fe in a fossil of the cold-water coral Desmophyllum sp., NW Pacific     

Toshihiro Yoshimura  Atsushi Suzuki  Yusuke Tamenori  Hodaka Kawahata 《Geo-Marine Letters》2014,34(1):1-9

Micro-scale distributions of trace and minor elements in, for example, coral skeletons are crucial as geochemical tracers of past environmental conditions, because they have the inherent advantage of accounting for confounding diagenetic and physiological effects. To extract reproducible paleoceanographic records from coral skeletons, a selective measurement of specific ultrastructures at high spatial resolution is required. Compared to warm-water reef-building corals, such data are limited in cold-water corals and, to the best of the authors’ knowledge, the latter have to date not been examined by means of micro-X-ray fluorescence. This technique was used for micrometer-scale imaging of P, Mg, Sr, O, and Fe intensities (counts per unit time) in a fossil specimen (as yet unknown age) of the cold-water coral Desmophyllum sp. from surface sediments of the NW Pacific. Cross plots confirmed that the micro-XRF signals were associated with corresponding trends in elemental concentration (ppm). Two major structural components of the septum—centers of calcification (COCs) and the surrounding fibrous aragonite portion—differed in composition. The COCs were characterized by higher intensities of P and Mg (650 and 220 counts per 5 s, respectively), and lower intensities of Sr (2,800) and O (580; corresponding values for the fibrous aragonite are 370, 180, 3,300 and 620 counts per 5 s, respectively). Oxygen intensity values were mostly homogeneous, but slightly lower in COCs and substantially higher in a well-defined patch in the fibrous aragonite. The mostly homogeneous P signals in the fibrous aragonite confirm the utility of this structural component and of coral septa in general for tracer studies of oceanic P. Nevertheless, spot occurrences of elevated P (>950 counts per 5 s) spanning tens of micrometers in specific parts of the fibrous region of the septum would cause overestimates of oceanic P, and should evidently not be overlooked in future research. The distribution of Fe showed no correlation with P, indicating no significant contamination in the form of P-bearing diagenetic ferromanganese precipitates. Such hotspots plausibly reflect the presence of other mineral phases, such as crystalline hydroxylapatite inclusions or contamination with organic material. The P signal intensity was positively correlated with Mg (r=0.553, p<0.001), and negatively with Sr (r=–0.489, p<0.001) and O (r=–0.311, p<0.001). There was no discernible evidence of control by water temperature in the Sr distribution pattern. These findings establish micro-X-ray fluorescence as a highly suitable pre-screening tool in cold-water coral sclerochronology, which can serve to refine sampling strategies without sample damage, and complement other micrometer-scale spatial distribution analyses of elements (notably, Ca) based on well-known approaches involving micro-milling, electron microprobes, secondary ion mass spectrometry, and laser ablation.  相似文献   

Alkaline leaching characteristics of biogenic opal in Eocene sediments from the central Arctic Ocean: a case study in the ACEX cores     

Shinya Iwasaki  Kozo Takahashi  Yusuke Ogawa  Seiichiro Uehara  Christoph Vogt 《Journal of Oceanography》2014,70(3):241-249

Accurate knowledge of the extent of biogenic opal preservation in marine sediment cores is important for paleoceanographic reconstructions. The alkaline leaching method is widely employed for %biogenic opal analysis due to its ease and speed. In this study, a revised method for measuring %biogenic opal in sediment from arctic coring expedition samples was suggested. The studied middle Eocene sediments from the central Arctic Ocean presented a problem in insufficiently leaching biogenic opal with a Na₂CO₃ solution. Based on XRD analysis, it was suggested that such an alkaline resistance results from slight diagenesis of biogenic opal. In order to solve this problem, an alkaline leaching method utilizing a 2 M NaOH solution was suggested for the accurate measurement of %biogenic opal in the Eocene sediments from the central Arctic. Furthermore, dissolution rates from lithogenic matter by NaOH solution were measured in order to correct the %biogenic opal values.  相似文献   

Bayesian and Neural Network Approaches to Estimate Deep Temperature Distribution for Assessing a Supercritical Geothermal System: Evaluation Using a Numerical Model     

Ishitsuka  Kazuya  Kobayashi  Yosuke  Watanabe  Norihiro  Yamaya  Yusuke  Bjarkason  Elvar  Suzuki  Anna  Mogi  Toru  Asanuma  Hiroshi  Kajiwara  Tatsuya  Sugimoto  Takeshi  Saito  Ryoichi 《Natural Resources Research》2021,30(5):3289-3314

The temperature distribution at depth is a key variable when assessing the potential of a supercritical geothermal resource as well as a conventional geothermal resource. Data-driven estimation by a machine-learning approach is a promising way to estimate temperature distributions at depth in geothermal fields. In this study, we developed two methodologies—one based on Bayesian estimation and the other on neural networks—to estimate temperature distributions in geothermal fields. These methodologies can be used to supplement existing temperature logs, by estimating temperature distributions in unexplored regions of the subsurface, based on electrical resistivity data, observed geological/mineralogical boundaries, and microseismic observations. We evaluated the accuracy and characteristics of these methodologies using a numerical model of the Kakkonda geothermal field, Japan, where a temperature above 500 °C was observed below a depth of about 3.7 km. When using geological and geophysical knowledge as prior information for the machine learning methods, the results demonstrate that the approaches can provide subsurface temperature estimates that are consistent with the temperature distribution given by the numerical model. Using a numerical model as a benchmark helps to understand the characteristics of the machine learning approaches and may help to identify ways of improving these methods.

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