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The high-temperature compression behavior of lithium fluoride (LiF) has been determined to ~80 GPa and 2300 K by means of high-resolution synchrotron-based x-ray diffraction in a laser-heated diamond-anvil cell. The room-temperature Vinet equation of state (EOS) for LiF yields an isothermal room-temperature, ambient-pressure lattice parameter a0 = 4.028 (±0.003) Å, volume V0 = 65.35 (±0.03) Å3, bulk modulus K0 = 67.57 (±0.34) GPa, and its pressure derivative K0’ = 4.64 (±0.03). This expanded experimental dataset is in good agreement with the LiF thermal equation of state by Myint et al. (2019) up to ~2300 K and 25 GPa. At higher pressures and temperatures our data shows reduced thermal expansion compared to the prediction and may be particularly important for experiments at more extreme conditions. 

Abstract Phase transitions in the mantle control its internal dynamics and structure. The post-spinel transition marks the upper–lower mantle boundary, where ringwoodite dissociates into bridgmanite plus ferropericlase, and its Clapeyron slope regulates mantle flow across it. This interaction has previously been assumed to have no lateral spatial variations, based on the assumption of a linear post-spinel boundary in pressure and temperature. Here we present laser-heated diamond anvil cell experiments with synchrotron X-ray diffraction to better constrain this boundary, especially at higher temperatures. Combining our data with results from the literature, and using a global analysis based on machine learning, we find a pronounced nonlinearity in the post-spinel boundary, with its slope ranging from –4 MPa/K at 2100 K, to –2 MPa/K at 1950 K, and to 0 MPa/K at 1600 K. Changes in temperature over time and space can therefore cause the post-spinel transition to have variable effects on mantle convection and the movement of subducting slabs and upwelling plumes. 

Abstract Iceberg calving is a major contributor to Greenland’s ice mass loss. Ice mélange, tightly packed sea ice and icebergs, has been hypothesized to buttress the calving fronts. However, quantifying the mélange buttressing force from field observations remains a challenge. Here we show that such quantification can be achieved with a single field measurement: thickness of mélange at the glacier terminus. We develop a three-dimensional discrete element model of mélange along with a simple analytical model to quantify the mélange buttressing using mélange thickness data from ArcticDEM over 32 Greenland glacier termini. We observed a strong seasonality in mélange thickness: thin mélange (averaged thickness$$3{4}_{-15}^{+17}$$ $34_{-15}^{+17}$ m) in summertime when terminus retreats, and thick mélange (averaged thickness$$11{9}_{-37}^{+31}$$ $119_{-37}^{+31}$ m) in wintertime when terminus advances. The observed seasonal changes of mélange thickness strongly coincide with observed Greenland calving dynamics and the modeled buttressing effects. 

Abstract On the Greenland Ice Sheet, hydrofracture connects the supraglacial and subglacial hydrologic systems, coupling surface runoff dynamics and ice velocity. In recent decades, the growth of low-permeability ice slabs in the wet snow zone has expanded Greenland's runoff zone, but observations suggest that surface-to-bed connections are rare, because meltwater drains through crevasses into the porous firn beneath ice slabs. However, there is little quantitative evidence confirming the absence of surface-to-bed fracture propagation. Here, we use poromechanics to investigate whether water-filled crevasses in ice slabs can propagate vertically through an underlying porous firn layer. Based on numerical simulations, we develop an analytical estimate of the water injection-induced effective stress in the firn given the water level in the crevasse, ice slab thickness, and firn properties. We find that the firn layer substantially reduces the system's vulnerability to hydrofracture because much of the hydrostatic stress is accommodated by a change in pore pressure, rather than being transmitted to the solid skeleton. This result suggests that surface-to-bed hydrofracture will not occur in ice slab regions until all pore space proximal to the initial flaw has been filled with solid ice. 

Abstract Germanates are often used as structural analogs of planetary silicates. We have explored the high-pressure phase relations in Mg2GeO4 using diamond-anvil cell experiments combined with synchrotron X-ray diffraction and computations based on density functional theory. Upon room temperature compression, forsterite-type Mg2GeO4 remains stable up to 30 GPa. At higher pressures, a phase transition to a forsterite-III type (Cmc21) structure was observed, which remained stable to the peak pressure of 105 GPa. Using a third-order Birch Murnaghan fit to the experimental data, we obtained V0 = 305.1(3) Å3, K0 = 124.6(14) GPa, and K0′ = 3.86 (fixed) for forsterite-type Mg2GeO4 and V0 = 263.5(15) Å3, K0 = 175(7) GPa, and K0′ = 4.2 (fixed) for the forsterite-III type phase. The forsterite-III type structure was found to be metastable when compared to the stable assemblage of perovskite/post-perovskite + MgO, as observed during laser-heating experiments. Understanding the phase relations and physical properties of metastable phases is crucial for studying the mineralogy of impact sites, understanding metastable wedges in subducting slabs, and interpreting the results of shock compression experiments. 

Supp_dataset.docx lists the ArcticDEM tiles, ICESat-2, Landsat, Sentinel-1 and Sentinel-2 Imagery files used in this study.  Figures_MainText.zip contains the source data and MATLAB codes to reproduce Figure 1 to Figure 8 presented in the main text. The ReadMe.txt file in each folder includes instructions on how to reproduce the corresponding figure.  demo_codes_CodeOcean.zip contains the sample code and data file to reproduce Figure 13(a)(d) in the supplemental material (Melange surface elevation profile at Jakobshavn on 19 Apr 2014, from ArcticDEM). User can run the Hx_distribution.m file, which calls peakFit.m function and dpROI_Jakob_20140419.mat data file, and to obtain the figure. This folder has been uploaded to code ocean portal as well (https://codeocean.com/capsule/4948451/tree).  Termini_offset_tide.xlsx contains the elevation offsets applied on the 108 ArcticDEM strips for the 32 Greenland glacier termini, with corresponding ArcticDEM strip acquisition dates and Mosaic DEM tiles for coregistration. GlacierID_GlacierName.zip folders contain two types of files: 1) points_yymmdd.csv contains point ID, x and y coordinates in polar stereographic projection (EPSG: 3413). The first and second points (ID=1, 2) delineate the glacier terminus segment, and the third to the last points (ID=3, N) delineate the region of interest of proglacial melange from the corresponding ArcticDEM strip acquired on the same date (yymmdd); 2) dpROI_yymmdd.mat contains all data points from the ArcticDEM strip cropped by the melange region of interest. Every row represents one data point from ArcticDEM, the first to fourth column corresponds to i) x coordinate in polar stereographic projection (EPSG: 3413); ii) y coordinate in polar stereographic projection (EPSG: 3413); iii) elevation above mean sea level in meters before coregistration; and iv) distance of the data point from the terminus segment in meters. Column iii) and iv) are used to plot the melange surface elevation (or thickness) profile as a function of distance from terminus.  Hx_distribution.m is the MATLAB file (calling the function peakFit.m) that plots the melange surface elevation profile as a function of distance from terminus (Z(x)), providing the dpROI_yymmdd.mat file. ICESat-2_allData.zip folder contains the ICESat-2 data presented in Figure 2 in the main text (seasonal melange surface elevation profiles for Jakobshavn, Kangerlussuaq, and Store glaciers). Figure 2 in the main text can be reproduced by running the MATLAB code inside the folder (Fig_H_x_disToTerm.m), which includes the geoid and tidal corrections on the ICESat-2 raw data files.        

This dataset contains mélange surface elevation and related observational data used in Meng et al. (2024) "Seasonal Changes of Mélange Thickness Coincide With Greenland Calving Dynamics", supporting a comprehensive analysis of ice mélange variability and glacier calving behavior in Greenland. It compiles ArcticDEM elevation strips for 32 marine-terminating glaciers, ICESat-2 surface elevation measurements, and associated satellite imagery (Landsat and Sentinel). Accompanying MATLAB codes and scripts enable reproduction of key figures in Meng et al. (2024). The dataset also includes processed ICESat-2 measurements and tools to reconstruct mélange elevation profiles as a function of distance from termini, enabling quantitative investigation of the relationship between mélange thickness and terminus motion. These codes and datasets were used to mechanistically link seasonal mélange variability with glacier retreat and advance. Reference: Meng, Yue, Ching-Yao Lai, Riley Culberg, Michael G. Shahin, Leigh A. Stearns, Justin C. Burton, and Kavinda Nissanka. "Seasonal changes of mélange thickness coincide with Greenland calving dynamics." Nature Communications 16, no. 1 (2025): 573.