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The lowermost mantle right above the core-mantle boundary is highly heterogeneous containing multiple poorly understood seismic features. The smallest but most extreme heterogeneities yet observed are ‘Ultra-Low Velocity Zones’ (ULVZ). We exploit seismic shear waves that diffract along the core-mantle boundary to provide new insight into these enigmatic structures. We measure a rare core-diffracted signal refracted by a ULVZ at the base of the Hawaiian mantle plume at unprecedentedly high frequencies. This signal shows remarkably longer time delays at higher compared to lower frequencies, indicating a pronounced internal variability inside the ULVZ. Utilizing the latest computational advances in 3D waveform modeling, here we show that we are able to model this high-frequency signal and constrain high-resolution ULVZ structure on the scale of kilometers, for the first time. This new observation suggests a chemically distinct ULVZ with increasing iron content towards the core-mantle boundary, which has implications for Earth’s early evolutionary history and core-mantle interaction.

Ultra-low velocity zones (ULVZs) are thin anomalous patches on the boundary between the Earth's core and mantle, revealed by their effects on the seismic waves that propagate through them. Here we map a broad ULVZ near the Galápagos hotspot using shear-diffracted waves. Forward modelling assuming a cylindrical shape shows the patch is ~600 km wide, ~20 km high, and its shear velocities are ~25% reduced. The ULVZ is comparable to other broad ULVZs mapped on the core-mantle boundary near Hawaii, Iceland, and Samoa.  Strikingly, all four hotspots where the mantle plume appears rooted by these ‘mega-ULVZs’, show similar anomalous isotopic signatures in He, Ne, and W in their ocean island basalts. This correlation suggests mega-ULVZs might be primordial or caused by interaction with the core, and some material from ULVZs is entrained within the plume. For the Galápagos, the connection implies the plume is offset to the west towards the base of the mantle.

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Natural phenethyl acetate (PEA), phenylacetic acid (PAA), ethyl phenylacetate (Et‐PA), and phenethyl phenylacetate (PE‐PA) are highly desirable aroma chemicals, but with limited availability and high price. Here, green, sustainable, and efficient bioproduction of these chemicals as natural products from renewable feedstocks was developed. PEA and PAA were synthesized from l‐phenylalanine (l‐Phe) via novel six‐ and five‐enzyme cascades, respectively. Whole‐cell‐based cascade biotransformation of 100 mm l‐Phe in a two‐phase system (aqueous/organic: 1 : 0.5 v/v) containing ethyl oleate or biodiesel as green solvent gave 13.6 g L−1 PEA (83.1 % conv.) and 11.6 g L−1 PAA (87.1 % conv.), respectively. Coupled fermentation and biotransformation approach produced 10.4 g L−1 PEA and 9.2 g L−1 PAA from glucose or glycerol, respectively. The biosynthesized PAA was converted to natural Et‐PA and PE‐PA by esterification using lipases with ethanol or 2‐phenylethanol derived from sugar, affording 2.7 g L−1 Et‐PA (83.1 % conv.) and 4.6 g L−1 PE‐PA (96.3 % conv.), respectively.

Abstract:As a new branch of MOFs which are composed of biocompatible metal ions and organic ligands, bio-metal-organic frameworks (bio-MOFs) have attracted much attention recently. Bio-MOFs feature multiple Lewis basic sites which have strong interaction with CO2 molecules, thus they have great potential in the separation and purification of gas mixtures containing CO2. In this work, molecular simulation studies were carried out to investigate the adsorption and diffusion behaviors of CO2/N2 gas mixtures in bio-MOF-11. Results show that bio-MOF-11 displays excellent adsorption selectivity towards CO2 in CO2/N2 gas mixtures which was dominated by electrostatic interaction between material and CO2. In addition, we found both CO2 and N2 molecules were preferably adsorbed around the pyrimidine ring and exocyclic amino and transferred to the secondary favorable adsorption sites (methyl groups) with increasing pressure. Bio-MOF-11 membranes show superior permeation selectivity, but low permeability for CO2/N2 gas systems. The reason is that the small pores restrict the movement of gas molecules, leading to the observed low permeability. The information obtained in this work can be applied to other theoretical and experimental studies of bio-MOFs adsorbents and membranes in the future.

The thermochemical boundary between Earth's core and mantle marks a profound change in composition, physical properties, and dynamics within the planet. The transfer of heat across this boundary represents up to a third of the Earth's surface heat flow Q surf (Lay et al., 2008). Convection in the mantle regulates the cooling of the planet, controlling the magnitude and spatial distribution of heat flow across the core-mantle boundary (CMB;Olson et al., 2015). The low-viscosity liquid outer core adjusts rapidly to changes in CMB heat flow (Jones, 2011), altering the power available to sustain the Earth's magnetic field (e.g., Nimmo, 2015a). Despite the importance of the CMB heat flow (hereafter called Q CMB ), there are large uncertainties on its present-day magnitude. Furthermore, recent upward revisions of the core thermal conductivity necessitate revisiting constraints on Q CMB (e.g., de Koker et al., 2012). To date, several approaches have been used to estimate Q CMB : petrological inferences on mantle potential temperature through time, simulations of Earth's magnetic field, and mantle convection simulations for different thermal gradients at the CMB. The allowable range of Q CMB is large when each approach is considered in isolation. By combining these approaches in a self-consistent way, we can better constrain the range of heat flow into the mantle from the core.To start, petrological observations of igneous rocks at the planet's surface point to trends in the melting conditions over geological time, and are used to establish rates of mantle cooling (Herzberg et al., 2010). A present-day cooling rate is combined with inventories of radiogenic elements in the mantle and crust to infer the Q CMB needed to account for the mantle heat budget for the present-day Q surf of ∼46 TW (Jaupart et al., 2015). Based on petrological arguments (discussed further in Section 2), Q CMB estimates fall in the range of 14-20 TW for a nominal Urey ratio of 0.3 and secular cooling rate of the mantle of 50-100 K/Ga (Herzberg et al., 2010;Korenaga & Karato, 2008).Several authors have investigated the Q CMB needed to account for the strength and morphology of the Earth's magnetic field. The upward revision of thermal conductivity in the liquid outer core (de Koker et al.