Abstract
Sodium chloride (NaCl) is an important, commonly used pressure medium and pressure calibrant in diamond-anvil cell (DAC) experiments. Its thermal conductivity at high pressure–temperature (
...P–T
) conditions is a critical parameter to model heat conduction and temperature distribution within an NaCl-loaded DAC. Here we couple ultrafast optical pump-probe methods with the DAC to study thermal conductivity and compressional velocity of NaCl in B1 and B2 phase to 66 GPa at room temperature. Using an externally-heated DAC, we further show that thermal conductivity of NaCl-B1 phase follows a typical
T
−1
dependence. The high
P–T
thermal conductivity of NaCl enables us to confirm the validity of Leibfried-Schlömann equation, a commonly used model for the
P–T
dependence of thermal conductivity, over a large compression range (~ 35% volume compression in NaCl-B1 phase, followed by ~ 20% compression in the polymorphic B2 phase). The compressional velocities of NaCl-B1 and B2 phase both scale approximately linearly with density, indicating the applicability of Birch’s law to NaCl within the density range we study. Our findings offer critical insights into the dominant physical mechanism of phonon transport in NaCl, as well as important data that significantly enhance the accuracy of modeling the spatiotemporal evolution of temperature within an NaCl-loaded DAC.
Hydrogen (H2) is the most abundant constituent in giant planets, but its thermal conductivity Λ under extreme pressure‐temperature (P‐T) conditions remains largely unknown. Here we report the Λ of H2 ...from ambient to 60.2 GPa at 300 K and from 300 to 773 K at 2.1 GPa. At 300 K, the Λ of liquid H2 fluctuates at ∼0.7–1.1 W m−1 K−1. Upon crystallization to H2‐I phase, the Λ jumps to 5.5 W m−1 K−1 at 7.2 GPa, and monotonically increases with pressure to ∼27 W m−1 K−1 at 60.2 GPa. Upon heating, the Λ of liquid H2 at 2.1 GPa scales with T0.68. Moreover, the density (ρ)‐dependent compressional sound velocity (Vp) of liquid and solid H2 derived from Brillouin frequency data both follow the Birch's law. Besides the novel insights into the physics of thermal transport in H2 under extreme conditions, our results significantly advance the modeling of Λ‐Vp‐ρ relationship in a planet with H2.
Plain Language Summary
Hydrogen is the most abundant element in the universe and is also the major constituent in the giant plants (Jupiter, Saturn, Uranus and Neptune) in the solar system. Although most of the surface temperatures of those giant planets are colder than Earth's, their interior temperatures are actually able to reach several thousand degrees Kelvin. The heat flows within these giant planets are very active, while knowledge of heat conduction and propagation are largely unknown. This study investigates the high‐pressure thermal conductivity of H2 at room temperature and high temperature conditions. Our results show that the liquid H2 exhibits low thermal conductivity, in the range of 0.7–1.1 W m−1 K−1 at high pressures and room temperature. However, appearance of solid H2 will increase thermal conductivity significantly and reach ∼27 W m−1 K−1 at 60.2 gigapascals and room temperature. Based on our model, the low thermal conductivity of liquid H2‐He mixture may suppress the heat loss of the giant planets and explain why their surfaces are cold, but interiors are hot.
Key Points
Thermal conductivity of liquid H2 varies in the range of 0.7–1.1 W m−1 K−1 at high pressures and room temperature
Thermal conductivity of solid H2‐I increases from 5.5 W m−1 K−1 at 7.2 GPa to 27 W m−1 K−1 at 60.2 GPa
Our model suggests that the thermal conductivity of liquid H2‐He mixture is in the range of 0.70–1.0 W m−1 K−1 at 300K
Abstract
Earth’s core is composed of iron (Fe) alloyed with light elements, e.g., silicon (Si). Its thermal conductivity critically affects Earth’s thermal structure, evolution, and dynamics, as it ...controls the magnitude of thermal and compositional sources required to sustain a geodynamo over Earth’s history. Here we directly measured thermal conductivities of solid Fe and Fe–Si alloys up to 144 GPa and 3300 K. 15 at% Si alloyed in Fe substantially reduces its conductivity by about 2 folds at 132 GPa and 3000 K. An outer core with 15 at% Si would have a conductivity of about 20 W m
−1
K
−1
, lower than pure Fe at similar pressure–temperature conditions. This suggests a lower minimum heat flow, around 3 TW, across the core–mantle boundary than previously expected, and thus less thermal energy needed to operate the geodynamo. Our results provide key constraints on inner core age that could be older than two billion-years.
Iron may critically influence the physical properties and thermochemical structures of Earth’s lower mantle. Its effects on thermal conductivity, with possible consequences on heat transfer and ...mantle dynamics, however, remain largely unknown. We measured the lattice thermal conductivity of lower-mantle ferropericlase to 120 GPa using the ultrafast optical pump-probe technique in a diamond anvil cell. The thermal conductivity of ferropericlase with 56% iron significantly drops by a factor of 1.8 across the spin transition around 53 GPa, while that with 8–10% iron increases monotonically with pressure, causing an enhanced iron substitution effect in the low-spin state. Combined with bridgmanite data, modeling of our results provides a self-consistent radial profile of lower-mantle thermal conductivity, which is dominated by pressure, temperature, and iron effects, and shows a twofold increase from top to bottom of the lower mantle. Such increase in thermal conductivity may delay the cooling of the core, while its decrease with iron content may enhance the dynamics of large low shear-wave velocity provinces. Our findings further show that, if hot and strongly enriched in iron, the seismic ultralow velocity zones have exceptionally low conductivity, thus delaying their cooling.
SUMMARY
Heat transfer through Earth's mantle is sensitive to mantle thermal conductivity and its variations. Thermal conductivities of lower mantle minerals, bridgmanite (Bm) and ferropericlase (Fp), ...depend on pressure, temperature, and composition. Because temperature and composition are expected to strongly vary in the deep mantle, thermal conductivity may also vary laterally. Here, we compile self-consistent data on lattice thermal conductivities of Bm and Fp at high pressure to model lower mantle thermal conductivity and map its possible lateral variations. Importantly, our data set allows us to quantify the influence of iron content on mantle conductivity. At the bottom of the mantle, the thermal conductivity for a pyrolitic mantle calculated along an adiabat with potential temperature 2000 K is equal 8.6 W m–1 K–1. Using 3-D thermochemical models from probabilistic tomography, which include variations in temperature, iron content, and bridgmanite fraction, we then calculate possible maps of conductivity anomalies at the bottom of the mantle. In regions known as low shear-wave velocity provinces, thermal conductivity is reduced by up to 26 per cent compared to average mantle, which may impact mantle dynamics in these regions. A simple analysis of threshold and saturation effects related to the iron content shows that our estimates of thermal conductivity may be considered as upper bounds. Quantifying these effects more precisely however requires additional mineral physics measurements. Finally, we estimate variations in core–mantle boundary heat flux, and find that that these variations are dominated by lateral temperature anomalies and are only partly affected by changes in thermal conductivity.
Earth’s water cycle enables the incorporation of water (hydration) in mantle minerals that can influence the physical properties of the mantle. Lattice thermal conductivity of mantle minerals is ...critical for controlling the temperature profile and dynamics of the mantle and subducting slabs. However, the effect of hydration on lattice thermal conductivity remains poorly understood and has often been assumed to be negligible. Here we have precisely measured the lattice thermal conductivity of hydrous San Carlos olivine (Mg0.9Fe0.1)₂SiO₄ (Fo90) up to 15 gigapascals using an ultrafast optical pump–probe technique. The thermal conductivity of hydrous Fo90 with ∼7,000 wt ppm water is significantly suppressed at pressures above ∼5 gigapascals, and is approximately 2 times smaller than the nominally anhydrous Fo90 at mantle transition zone pressures, demonstrating the critical influence of hydration on the lattice thermal conductivity of olivine in this region. Modeling the thermal structure of a subducting slab with our results shows that the hydration-reduced thermal conductivity in hydrated oceanic crust further decreases the temperature at the cold, dry center of the subducting slab. Therefore, the olivine–wadsleyite transformation rate in the slab with hydrated oceanic crust is much slower than that with dry oceanic crust after the slab sinks into the transition zone, extending the metastable olivine to a greater depth. The hydration-reduced thermal conductivity could enable hydrous minerals to survive in deeper mantle and enhance water transportation to the transition zone.
Seismic anomalies observed in Earth's deep mantle are conventionally considered to be associated with thermal and compositional anomalies, and possibly partial melt of major lower‐mantle phases. ...However, through deep water cycle, impacts of hydrous minerals on geophysical observables and on the deep mantle thermal state and geodynamics remain poorly understood. Here we precisely measured thermal conductivity of δ‐(Al,Fe)OOH, an important water‐carrying mineral in Earth's deep interior, to lowermost mantle pressures at room temperature. The thermal conductivity varies drastically by twofold to threefold across the spin transition of iron, resulting in an exceptionally low thermal conductivity at the lowermost mantle conditions. As δ‐(Al,Fe)OOH is transported to the lowermost mantle, its exceptionally low thermal conductivity may serve as a local thermal insulator, promoting high‐temperature anomalies and the formation of partial melt and thermal plumes at the base of the mantle, strongly influencing thermo‐chemical profiles in the region and fate of Earth's deep water cycle.
Plain Language Summary
Hydrous minerals subducted to Earth's deep interior may critically affect the thermo‐chemical and seismic signatures observed at the bottom of the mantle. We measured thermal conductivity of δ‐(Al,Fe)OOH, an important water carrier in deep Earth, to the lowermost mantle pressures. Its thermal conductivity varies drastically across the spin transition of iron and approaches an exceptionally low value of ~5 W·m−1·K−1 at the lowermost mantle conditions, much smaller than the pyrolitic mantle. Such anomalous evolution of thermal conductivity would induce anomalies in heat flux and temperature profile in the lower mantle. It could create a local thermal insulating effect that heats up slab's crust at the lowermost mantle, facilitating dehydration melting of surrounding mantle and affecting thermo‐chemical features in the region.
Key Points
We combined ultrafast optics with diamond‐anvil cell to study high‐pressure thermal conductivity of δ‐(Al,Fe)OOH
Within the spin transition zone the thermal conductivity of δ‐(Al,Fe)OOH varies drastically with pressure
Its exceptionally low thermal conductivity at the lowermost mantle may induce thermal anomalies, altering local thermo‐chemical structures
The presence of water in minerals generally alters their physical properties. Ringwoodite is the most abundant phase in the lowermost mantle transition zone and can host up to 1.5–2 wt% water. We ...studied high‐pressure lattice thermal conductivity of dry and hydrous ringwoodite by combining diamond‐anvil cell experiments with ultrafast optics. The incorporation of 1.73 wt% water substantially reduces the ringwoodite thermal conductivity by more than 40% at mantle transition zone pressures. We further parameterized the ringwoodite thermal conductivity as a function of pressure and water content to explore the large‐scale consequences of a reduced thermal conductivity on a slab's thermal evolution. Using a simple 1‐D heat diffusion model, we showed that the presence of hydrous ringwoodite in the slab significantly delays decomposition of dense hydrous magnesium silicates, enabling them to reach the lower mantle. Our results impact the potential route and balance of water cycle in the lower mantle.
Plain Language Summary
The physical properties of minerals are determined by the interaction of atoms in the crystal lattice. Water can be incorporated into the crystal structure and alter its behavior. Ringwoodite is a high‐pressure mineral that can host large quantities of water and is expected to be abundant in the lower part of Earth's mantle transition zone, a region ranging from 520 to 660‐km depth. Here we studied ringwoodite thermal conductivity, describing how effectively heat is transported through solids. Based on our measurements we determined that water in ringwoodite significantly slows down heat propagation. We performed computer simulations to investigate the large‐scale implications of our findings. For this purpose, we modeled a cold oceanic plate, entirely made of ringwoodite, which is surrounded by warm mantle. The delayed heat transport is sufficient to maintain low temperatures in the inner part of the oceanic plate and potentially preserve the hydrous minerals for an extended period of time.
Key Points
Ringwoodite thermal conductivity is reduced by 40% due to the presence of 1.73 wt% water in the crystal structure
Lower thermal conductivity of hydrous ringwoodite might delay the breakdown of hydrous phases hosted in a subducting slab
Hydrous ringwoodite acts as a heat propagation barrier, supporting preservation of hydrous minerals down to the lower mantle
Gout is an inflammatory disease manifested by the deposition of monosodium urate (MSU) crystals in joints, cartilage, synovial bursa, tendons or soft tissues. Gout is not a new disease, which was ...first documented nearly 5,000 years ago. The prevalence of gout has increased globally in recent years, imposing great disease burden worldwide. Moreover, gout or hyperuricemia is clearly associated with a variety of comorbidities, including cardiovascular diseases, chronic kidney disease, urolithiasis, metabolic syndrome, diabetes mellitus, thyroid dysfunction, and psoriasis. To prevent acute arthritis attacks and complications, earlier use of pharmacotherapeutic treatment should be considered, and patients with hyperuricemia and previous episodes of acute gouty arthritis should receive long‐term urate‐lowering treatment. Urate‐lowering drugs should be used during the inter‐critical and chronic stages to prevent recurrent gout attacks, which may elicit gradual resolution of tophi. The goal of urate‐lowering therapy should aim to maintain serum uric acid (sUA) level <6.0 mg/dL. For patients with tophi, the initial goal can be set at lowering sUA to <5.0 mg/dL to promote tophi dissolution. The goal of this consensus paper was to improve gout and hyperuricemia management at a more comprehensive level. The content of this consensus paper was developed based on local epidemiology and current clinical practice, as well as consensuses from two multidisciplinary meetings and recommendations from Taiwan Guideline for the Management of Gout and Hyperuricemia.
Complex seismic, thermal, and chemical features have been reported in Earth's lowermost mantle. In particular, possible iron enrichments in the large low shear‐wave velocity provinces (LLSVPs) could ...influence thermal transport properties of the constituting minerals in this region, altering the lower mantle dynamics and heat flux across core‐mantle boundary (CMB). Thermal conductivity of bridgmanite is expected to partially control the thermal evolution and dynamics of Earth's lower mantle. Importantly, the pressure‐induced lattice distortion and iron spin and valence states in bridgmanite could affect its lattice thermal conductivity, but these effects remain largely unknown. Here we precisely measured the lattice thermal conductivity of Fe‐bearing bridgmanite to 120 GPa using optical pump‐probe spectroscopy. The conductivity of Fe‐bearing bridgmanite increases monotonically with pressure but drops significantly around 45 GPa due to pressure‐induced lattice distortion on iron sites. Our findings indicate that lattice thermal conductivity at lowermost mantle conditions is twice smaller than previously thought. The decrease in the thermal conductivity of bridgmanite in mid‐lower mantle and below would promote mantle flow against a potential viscosity barrier, facilitating slabs crossing over the 1000 km depth. Modeling of our results applied to LLSVPs shows that variations in iron and bridgmanite fractions induce a significant thermal conductivity decrease, which would enhance internal convective flow. Our CMB heat flux modeling indicates that while heat flux variations are dominated by thermal effects, variations in thermal conductivity also play a significant role. The CMB heat flux map we obtained is substantially different from those assumed so far, which may influence our understanding of the geodynamo.
Key Points
We combine time domain thermoreflectance and diamond cell to measure lattice thermal conductivity of Fe‐bearing bridgmanite to 120 GPa
Thermal conductivity of Fe‐bearing bridgmanite drops around 45 GPa due to pressure‐induced lattice distortion
Modeling of LLSVP thermal conductivity and CMB heat flux provides insights to thermo‐chemical structure and dynamics of lowermost mantle
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