Takafumi Yamamoto

A nearly water-saturated mantle transition zone inferred from mineral viscosity

The mantle transition zone contains 1 to 2 weight % water based on the viscosity difference between ringwoodite and bridgmanite. An open question for solid-earth scientists is the amount of water in Earth’s interior. The uppermost mantle and lower mantle contain little water because their dominant minerals, olivine and bridgmanite, have limited water storage capacity. In contrast, the mantle transition zone (MTZ) at a depth of 410 to 660 km is considered to be a potential water reservoir because its dominant minerals, wadsleyite and ringwoodite, can contain large amounts of water [up to 3 weight % (wt %)]. However, the actual amount of water in the MTZ is unknown. Given that water incorporated into mantle minerals can lower their viscosity, we evaluate the water content of the MTZ by measuring dislocation mobility, a property that is inversely proportional to viscosity, as a function of temperature and water content in ringwoodite and bridgmanite. We find that dislocation mobility in bridgmanite is faster by two orders of magnitude than in anhydrous ringwoodite but 1.5 orders of magnitude slower than in water-saturated ringwoodite. To fit the observed mantle viscosity profiles, ringwoodite in the MTZ should contain 1 to 2 wt % water. The MTZ should thus be nearly water-saturated globally.

Serum Amyloid A3 Gene Expression in Adipocytes is an Indicator of the Interaction with Macrophages

The infiltration of macrophages into adipose tissue and their interaction with adipocytes are essential for the chronic low-grade inflammation of obese adipose tissue. In this study, we identified the serum amyloid A3 (Saa3) gene as a key adipocyte-derived factor that is affected by interaction with macrophages. We showed that the Saa3 promoter in adipocytes actually responds to activated macrophages in a co-culture system. Decreasing C/EBPβ abundance in 3T3-L1 adipocytes or point mutation of C/EBPβ elements suppressed the increased promoter activity in response to activated macrophages, suggesting an essential role of C/EBPβ in Saa3 promoter activation. Bioluminescence based on Saa3 promoter activity in Saa3-luc mice was promoted in obese adipose tissue, showing that Saa3 promoter activity is most likely related to macrophage infiltration. This study suggests that the level of expression of the Saa3 gene could be utilized for the number of infiltrated macrophages in obese adipose tissue.

Generation of pressures over 40 GPa using Kawai-type multi-anvil press with tungsten carbide anvils

We have generated over 40 GPa pressures, namely, 43 and 44 GPa, at ambient temperature and 2000 K, respectively, using Kawai-type multi-anvil presses (KMAP) with tungsten carbide anvils for the first time. These high-pressure generations were achieved by combining the following pressure-generation techniques: (1) precisely aligned guide block systems, (2) high hardness of tungsten carbide, (3) tapering of second-stage anvil faces, (4) materials with high bulk modulus in a high-pressure cell, and (5) high heating efficiency.

Pressure generation to 65 GPa in a Kawai-type multi-anvil apparatus with tungsten carbide anvils

ABSTRACT We have expanded the pressure ranges at room and high temperatures generated in a Kawai-type multi-anvil apparatus (KMA) using tungsten carbide (WC) anvils with a high hardness of Hv = 2700 and a Young’s modulus of 660 GPa. At room temperature, a pressure of 64 GPa, which is the highest pressure generated with KMA using WC anvils in the world, was achieved using 1°-tapered anvils with a 1.5-mm truncation. Pressures of 48–50 GPa were generated at high temperatures of 1600–2000 K, which are also higher than previously achieved. Tapered anvils make wide anvil gaps enabling efficient X-ray diffraction. The present pressure generation technique can be used for studying the upper part of the Earth’s lower mantle down to 1200 km depth without sintered diamond anvils.

Deformation history of Pinatubo peridotite xenoliths: constraints from microstructural observation and determination of olivine slip systems

Abstract The deformation history of the Pinatubo peridotite xenoliths was estimated on the basis of the microstructural observations and the determination of olivine slip systems. The latter was performed by using three methods: lattice-preferred orientation (LPO), crystallographic analysis of subgrain boundaries, and direct characterization of dislocations. The Pinatubo peridotites are composed of coarse olivine grains containing numerous fluid inclusions and some fine aggregates of orthopyroxene and amphibole grains, which implies intense fluid–rock interaction. The development of euhedral fine recrystallized olivine grains along the healed cracks within the coarse olivine grains suggests that the strain-free grains were nucleated and grew during static recovery. The LPO patterns and the analyses of subgrain boundaries indicate the activation of a [100]{0kl} slip system that developed under high temperature, low pressure, and dry deformation conditions. Although dislocations showing the [100]{0kl} slip system are dominantly observed, the other slip systems which could be formed by the deformation under moderate–high water content and lower-temperature conditions are also developed. The discrepancy between the results of dislocation characterization and the other two methods might have been caused by fulfilling the von Mises criterion or overprinting dislocation microstructures. Either way, the possible deformation history of the Pinatubo peridotites can be explained by the following scenario. The peridotites plastically moved from the back-arc to the fore-arc adjacent region, where CO2-rich saline fluid was trapped, by the corner flow of a mantle wedge. They were then annealed and metasomatized during entrapment of the upwelling magma.

IκB kinase epsilon expression in adipocytes is upregulated by interaction with macrophages

Macrophage infiltration in the adipose tissue, and the interaction with adipocytes, is well documented to be involved in fat inflammation and obesity-associated complications. In this study, we isolated IκB kinase ε (IKKε) as a key adipocyte factor that is potentially affected by interaction with macrophages in adipose tissue in vivo. We showed that IKKε mRNA expression levels in white adipose tissue were increased in both genetic and diet-induced obese mouse. Furthermore, IKKε mRNA expression was decreased by the administration of vitamin B6, an anti-inflammatory vitamin, and that IKKε expression levels in adipose tissue were closely correlated with the numbers of infiltrating macrophages. In a co-culture system, we showed that IKKε expression in adipocytes was upregulated by interaction with activated macrophages. This study provides novel insight into IKKε, which is involved in adipose tissue inflammation during the development of obesity. Graphical Abstract IKKε mRNA levels in white adipose tissue were increased in both genetic and diet-induced obese mouse and closely correlated with the numbers of infiltrating macrophages.

Complete agreement of the post-spinel transition with the 660-km seismic discontinuity

The 660-km seismic discontinuity, which is a significant structure in the Earth’s mantle, is generally interpreted as the post-spinel transition, as indicated by the decomposition of ringwoodite to bridgmanite + ferropericlase. All precise high-pressure and high-temperature experiments nevertheless report 0.5–2 GPa lower transition pressures than those expected at the discontinuity depth (i.e. 23.4 GPa). These results are inconsistent with the post-spinel transition hypothesis and, therefore, do not support widely accepted models of mantle composition such as the pyrolite and CI chondrite models. Here, we present new experimental data showing post-spinel transition pressures in complete agreement with the 660-km discontinuity depth obtained by high-resolution in situ X-ray diffraction in a large-volume high-pressure apparatus with a tightly controlled sample pressure. These data affirm the applicability of the prevailing mantle models. We infer that the apparently lower pressures reported by previous studies are experimental artefacts due to the pressure drop upon heating. The present results indicate the necessity of reinvestigating the position of mantle mineral phase boundaries previously obtained by in situ X-ray diffraction in high-pressure–temperature apparatuses.