Fluctuation of marine osmium isotope ratio during the Quaternary climate cycles

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Author Correction: Fish proliferation and rare-earth deposition by topographically induced upwelling at the late Eocene cooling event (Scientific Reports, (2020), 10, 1, (9896), 10.1038/s41598-020-66835-8)

金沢大学理工研究域地球社会基盤学系An amendment to this paper has been published and can be accessed via a link at the top of the paper. © 2020, The Author(s)

Fish proliferation and rare-earth deposition by topographically induced upwelling at the late Eocene cooling event

金沢大学理工研究域地球社会基盤学系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. Much fish debris was deposited in the western North and central South Pacific sites roughly 34.4 million years ago, concurrent with a late Eocene event, a temporal expansion of Antarctic ice preceding the Eocene–Oligocene climate transition. The enhanced northward flow of bottom water formed around Antarctica probably caused upwelling of deep-ocean nutrients at topographic highs and stimulated biological productivity that resulted in the proliferation of fish in pelagic realms. The abundant fish debris is now a highly concentrated source of industrially critical rare-earth elements. © 2020, The Author(s)

アワ メイショ ズエ ニオケル ビザン ノ シゼン ト ケイカン

In this paper the nature and the landscape of the Mt. Bizan are investigated based on “Awa meisho zue” which was a guidebook of Awa (Tokushima) published about 200 years ago. In the picture entitled “Mt. Bizan” a tower at the Jimyoin Temple and two buildings are drawn in the mountain. The mountain is covered with pine trees, and there is a waterfall near the tower. Besides pine trees, three types of trees, Japanese cedar and/or Japanese cypress, trees that presumably cherry, and unknown broadleaf trees are drawn in Mt. Otakiyama that is a part of Mt. Bizan based on the picture entitled “Otakisan Jimyoin”. Other historical records in Edo era coincide with the composition of plant species in Mt. Bizan. Though the vegetation of Mt. Bizan was efended by laws throughout Edo era, it was deforested and the mountain became bald after the Meiji Restoration. Afterwards, it was protected by specifying it as the protection forest and by making it as a park. Now, pine trees and Japanese cedar and/or Japanese cypress have almost been lost, and pasania and live oak are well growing in the mountain. The tower at Jimyoin was burned down by the air raid in the World War II, and the waterfall has thinned. On the other hand, mountain trails and a ropeway were made, and a lot of buildings were built at the top of the mountain. Thus, the nature and the landscape of Mt. Bizan greatly changed in 200 years. However, citizens are still familiar with it as the symbol of Tokushima City

The tremendous potential of deep-sea mud as a source of rare-earth elements

金沢大学理工研究域地球社会基盤学系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. Here, we estimated the resource amount in REY-rich mud with Geographical Information System software and established a mineral processing procedure to greatly enhance its economic value. The resource amount was estimated to be 1.2 Mt of rare-earth oxide for the most promising area (105 km2 × 0-10 mbsf), which accounts for 62, 47, 32, and 56 years of annual global demand for Y, Eu, Tb, and Dy, respectively. Moreover, using a hydrocyclone separator enabled us to recover selectively biogenic calcium phosphate grains, which have high REY content (up to 22,000 ppm) and constitute the coarser domain in the grain-size distribution. The enormous resource amount and the effectiveness of the mineral processing are strong indicators that this new REY resource could be exploited in the near future. © 2018 The Author(s)

Stratigraphic Variations of Fe–Mn Micronodules and Implications for the Formation of Extremely REY-Rich Mud in the Western North Pacific Ocean

The origin of deep-sea sediments in the western North Pacific Ocean, which are significantly enriched in rare-earth elements and yttrium (REY), and its paleoceanographic implications have been poorly constrained. Here, we investigated stratigraphic variations in the chemical compositions and textures of ferromanganese (Fe–Mn) micronodules separated from western North Pacific sediments. The characteristics of the micronodules of an extremely REY-rich mud layer vary from almost purely diagenetic to relatively hydrogenetic. This indicates the abundant supply of organic matter to the sediment together with fish debris that accumulates REY at the onset of the REY-enrichment of the mud, followed by the exposure of the seafloor to oxic water masses during the latter half of the formation of the REY-rich mud. These results support a previously proposed formation mechanism based on which enhanced bottom water currents caused pelagic fish proliferation via the upwelling of nutrients and fish debris was physically sorted and selectively accumulated on the seafloor. After the main REY-enrichment, the micronodules exhibit varying diagenetic signatures, suggesting changes in the bottom current intensities after the main REY-enrichment. However, the bulk REY contents do not increase. This implies that a sufficient increase in the fish productivity is an essential factor affecting the formation of REY-rich mud