Publications by authors named "Kazutaka Yasukawa"

Rock and sediment samples were collected from petit-spots in the northwestern Pacific. The sampling was conducted using deep-submergence vehicle (DSV) Shinkai 6500 and its mother ship, research vessel (RV) Yokosuka during YK20-14S and YK21-07S cruises. The collected rock samples are basalt and peperite.

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The solid earth plays a major role in controlling Earth's surface climate. Volcanic degassing of carbon dioxide (CO) and silicate chemical weathering are known to regulate the evolution of climate on a geologic timescale (> 10 yr), but the relationship between the solid earth and the shorter (< 10 yr) fluctuations of Quaternary glacial-interglacial cycles is still under debate. Here we show that the seawater osmium isotope composition (Os/Os), a proxy for the solid earth's response to climate change, has varied during the past 300,000 years in association with glacial-interglacial cycles.

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The deep-sea clay that covers wide areas of the pelagic ocean bottom provides key information about open-ocean environments but lacks age-diagnostic calcareous or siliceous microfossils. The marine osmium isotope record has varied in response to environmental changes and can therefore be a useful stratigraphic marker. In this study, we used osmium isotope ratios to determine the depositional ages of pelagic clays extraordinarily rich in fish debris.

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Meteorite impacts have caused catastrophic perturbations to the global environment and mass extinctions throughout the Earth's history. Here, we present petrographic and geochemical evidence of a possible impact ejecta layer, dating from about 11 Ma, in deep-sea clayey sediment in the Northwest Pacific. This clay layer has high platinum group element (PGE) concentrations and features a conspicuous negative Os isotope anomaly (Os/Os as low as ~0.

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Potential risks of supply shortages for critical metals including rare-earth elements and yttrium (REY) have spurred great interest in commercial mining of deep-sea mineral resources. Deep-sea mud containing over 5,000 ppm total REY content was discovered in the western North Pacific Ocean near Minamitorishima Island, Japan, in 2013. This REY-rich mud has great potential as a rare-earth metal resource because of the enormous amount available and its advantageous mineralogical features.

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Multiple transient global warming events occurred during the early Palaeogene. Although these events, called hyperthermals, have been reported from around the globe, geologic records for the Indian Ocean are limited. In addition, the recovery processes from relatively modest hyperthermals are less constrained than those from the severest and well-studied hothouse called the Palaeocene-Eocene Thermal Maximum.

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Deep-sea sediments have attracted much attention as a promising resource for rare-earth elements and yttrium (REY). In this study, we show statistically independent components characterising REY-enrichment in the abyssal ocean that are decoded by Independent Component Analysis of a multi-elemental dataset of 3,968 bulk sediment samples from 101 sites in the Pacific and Indian oceans. This study for the first time reconstructs the spatiotemporal variations of the geochemical signatures, including hydrothermal, hydrogenous, and biogenic calcium phosphate components that were closely involved in the formation of REY-rich mud over the past 65 million years.

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Extinctions within major pelagic groups (e.g., radiolarians and conodonts) occurred in a stepwise fashion during the last 15 Myr of the Triassic.

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