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| Obrochta, Stephen P.; Crowley, Thomas J.; Channell, James E. T.; Hodell, David A.; Baker, Paul A.; Seki, Arisa; Yokoyama, Yusuke. |
| A composite North Atlantic record from DSDP Site 609 and IODP Site U1308 spans the past 300,000 years and shows that variability within the penultimate glaciation differed substantially from that of the surrounding two glaciations. Hematite-stained grains exhibit similar repetitive down-core variations within the Marine Isotope Stage (MIS) 8 and 4-2 intervals, but little cyclic variability within the MIS 6 section. There is also no petrologic evidence, in terms of detrital carbonate-rich (Heinrich) layers, for surging of the Laurentide Ice Sheet through the Hudson Strait during MIS 6. Rather, very high background concentration of iceberg-rafted debris (IRD) indicates near continuous glacial meltwater input that likely increased thermohaline disruption... |
| Tipo: Text |
Palavras-chave: Insolation; IRD; Heinrich Event; MIS 6; MIS 8; AMOC. |
| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00289/40050/38793.pdf |
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| Felis, Thomas; Mcgregor, Helen V.; Linsley, Braddock K.; Tudhope, Alexander W.; Gagan, Michael K.; Suzuki, Atsushi; Inoue, Mayuri; Thomas, Alexander L.; Esat, Tezer M.; Thompson, William G.; Tiwari, Manish; Potts, Donald C.; Mudelsee, Manfred; Yokoyama, Yusuke; Webster, Jody M.. |
| Tropical south-western Pacific temperatures are of vital importance to the Great Barrier Reef (GBR), but the role of sea surface temperatures (SSTs) in the growth of the GBR since the Last Glacial Maximum remains largely unknown. Here we present records of Sr/Ca and delta O-18 for Last Glacial Maximum and deglacial corals that show a considerably steeper meridional SST gradient than the present day in the central GBR. We find a 1-2 degrees C larger temperature decrease between 17 degrees and 20 degrees S about 20,000 to 13,000 years ago. The result is best explained by the northward expansion of cooler subtropical waters due to a weakening of the South Pacific gyre and East Australian Current. Our findings indicate that the GBR experienced substantial... |
| Tipo: Text |
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| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00290/40136/39239.pdf |
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| Pace, Aurelie; Bourillot, Raphael; Bouton, Anthony; Vennin, Emmanuelle; Galaup, Serge; Bundeleva, Irina; Patrier, Patricia; Dupraz, Christophe; Thomazo, Christophe; Sansjofre, Pierre; Yokoyama, Yusuke; Franceschi, Michel; Anguy, Yannick; Pigot, Lea; Virgone, Aurelien; Visscher, Pieter T.. |
| Microbialites are widespread in modern and fossil hypersaline environments, where they provide a unique sedimentary archive. Authigenic mineral precipitation in modern microbialites results from a complex interplay between microbial metabolisms, organic matrices and environmental parameters. Here, we combined mineralogical and microscopic analyses with measurements of metabolic activity in order to characterise the mineralisation of microbial mats forming microbialites in the Great Salt Lake (Utah, USA). Our results show that the mineralisation process takes place in three steps progressing along geochemical gradients produced through microbial activity. First, a poorly crystallized Mg-Si phase precipitates on alveolar extracellular organic matrix due to a... |
| Tipo: Text |
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| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00347/45852/45517.pdf |
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| Chang, Yuan-pin; Wang, Wei-lung; Yokoyama, Yusuke; Matsuzaki, Hiroyuki; Kawahata, Hodaka; Chen, Min-te. |
| High resolution planktic foraminifer fauna assemblage data are used to reconstruct the millennial-scale sea surface temperature (SST) variability of the past 40000 years at an IMAGES core site (MD012404) in the Okinawa Trough in the East China Sea (ECS). The fauna assemblages in core MD012404 are dominated by five species - Globigerinoides ruber, Globigerina bulloides, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globigerinita glutinata, which account for > 70% in relative abundance. Our Q-mode factor analysis decomposed the fauna abundance data into three factors, which indicate cold water mass, warm water mass, and possibly coastal water flow with low salinity in the ECS. The MD012404 fauna data show abrupt changes at similar to 16... |
| Tipo: Text |
Palavras-chave: Planktic foraminifer; Sea surface temperature; ITCZ; East China Sea; Okinawa Trough; IMAGES. |
| Ano: 2008 |
URL: https://archimer.ifremer.fr/doc/00237/34818/33684.pdf |
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| Chang, Yuan-pin; Chen, Min-te; Yokoyama, Yusuke; Matsuzaki, Hiroyuki; Thompson, William G.; Kao, Shuh-ji; Kawahata, Hodaka. |
| We analyzed the high-resolution foraminifer isotope records, total organic carbon (TOC), and opal content from an Okinawa Trough core MD012404 in order to estimate the monsoon hydrography and productivity changes in the East China Sea (ECS) of the tropical western Pacific over the past 100,000 years. The variability shown in the records on orbital time scales indicates that high TOC intervals coincide with the increases of boreal May-September insolation driven by precession cycles (similar to 21 ka), implying a strong connection to the variations in monsoons. We also observed possibly nearly synchronous, millennial-scale changes of the ECS surface hydrography (mainly driven by salinity changes but also by temperature effects) and productivity coincident... |
| Tipo: Text |
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| Ano: 2009 |
URL: https://archimer.ifremer.fr/doc/00218/32929/31435.pdf |
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| Kan, Hironobu; Urata, Kensaku; Nagao, Masayuki; Hori, Nobuyuki; Fujita, Kazuhiko; Yokoyama, Yusuke; Nakashima, Yosuke; Ohashi, Tomoya; Goto, Kazuhisa; Suzuki, Atsushi. |
| Submerged tropical karst features were discovered in Nagura Bay on Ishigaki Island in the southern Ryukyu Islands, Japan. The coastal seafloor at depths shallower than similar to 130 m has been subjected to repeated and alternating subaerial erosion and sedimentation during periods of Quaternary sea-level lowstands. We conducted a broadband multibeam survey in the central area of Nagura Bay (1.85 x 2.7 km) and visualized the high-resolution bathymetric results over a depth range of 1.6-58.5 m. Various types of humid tropical karst landforms were found to coexist within the bay, including fluviokarst, doline karst, cockpit karst, polygonal karst, uvalas, and mega-dolines. Although these submerged karst landforms are covered by thick postglacial reef and... |
| Tipo: Text |
Palavras-chave: Submerged karst; Coral reef; Multibeam echosounder; SCUBA; Ryukyu Islands; Japan. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00352/46285/45961.pdf |
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