Rapid coupling between solid earth and ice volume during the Quaternary.

The solid earth plays a major role in controlling Earth's surface climate. Volcanic degassing of carbon dioxide (CO2) and silicate chemical weathering are known to regulate the evolution of climate on a geologic timescale (> 106 yr), but the relationship between the solid earth and the shorter (< 105 yr) fluctuations of Quaternary glacial-interglacial cycles is still under debate. Here we show that the seawater osmium isotope composition (187Os/188Os), 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. Our marine Os isotope mass-balance simulation reveals that the observed 187Os/188Os fluctuation cannot be explained solely by global chemical weathering rate changes corresponding to glacial-interglacial climate changes, but the fluctuation can be reproduced by taking account of short-term inputs of (1) radiogenic Os derived from intense weathering of glacial till during deglacial periods and (2) unradiogenic Os derived from enhanced seafloor hydrothermalism triggered by sea-level falls associated with increases of ice sheet volume. Our results constitute the first evidence that ice sheet recession and expansion during the Quaternary systematically and repetitively caused short-term (< 105 yr) solid earth responses via chemical weathering of glacial till and seafloor magmatism. This finding implies that climatic changes on < 105 yr timescales can provoke rapid feedbacks from the solid earth, a causal relationship that is the reverse of the longer-term (> 106 yr) causality that has been conventionally considered.

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

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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

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.

A Miocene impact ejecta layer in the pelagic Pacific Ocean.

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 (187Os/188Os as low as ~0.2), indicating an influx of extraterrestrial material. It also contains abundant spherules that include pseudomorphs suggestive of porphyritic olivine as well as spinel grains with euhedral, dendritic and spherical forms and NiO contents as great as 23.3 wt%, consistent with impact ejecta. Osmium isotope stratigraphy suggests a most plausible depositional age of ~11 Ma (Miocene) for this layer, as determined by fitting with the seawater evolution curve. No large impact crater of this age is known on land, even within the relatively large uncertainty range of the relative Os age. Thus, we suggest that an unrecognised impact event in the middle or late Miocene produced the impact ejecta layer of the Northwest Pacific.

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

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.