Long-lived partial melt beneath Cascade Range volcanoes
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Gravitational stability of iron-rich peridotite melt at Mars’ core-mantle boundary
Possible existence of dense iron-rich silicate melt layer above Mars’ core is important in understanding the nature and evolution of Mars. However, gravitational stability of iron-rich silicate melt in the Mars’ interior has not been well constrained, due to experimental difficulties in measuring density of iron-rich peridotitic melt. Here we report density measurements of iron-rich peridotitic melts up to 2465 K by using electrostatic levitation furnace at the International Space Station. Our experimentally obtained densities of iron-rich peridotitic melts are markedly higher than those calculated by first principles simulation, and are distinct from those estimated by extrapolating a density model for SiO2-rich basaltic melts. Our determined density model suggests that peridotitic melt with the Fe/(Mg+Fe) ratio more than 0.4-0.5 has higher density than that at the base of the Mars’ mantle, which indicates gravitational stability of the iron-rich peridotitic melt at the core-mantle boundary in Mars.
Revealing the mechanism of cold metal transfer
Cold metal transfer (CMT) is a pioneering feeding system widely used in wire-arc additive manufacturing (WAAM) and welding. However, process optimisation remains challenging. Although CMT has been extensively applied in various industrial sectors, its underlying mechanism is poorly understood because of the complex physics of the interactions between the wire and molten material and the wire’s highly dynamic motion. To elucidate the complexity and features of CMT, we explore the dynamic behaviour and anatomy of molten materials during wire motions (withdrawal and dipping cycles) using high-speed photography at a timescale of microseconds. We reveal a crucial driving force in the melt pool and the frequent ejection of streams or particles during CMT. This study contributes to WAAM and welding by presenting the influential features of ultra-high-dynamics CMT and facilitating the progression of process optimisation.
Active ice sheet conservation cannot stop the retreat of Sermeq Kujalleq glacier, Greenland
Active conservation of an ice sheet seeks to reduce ice sheet mass loss and sea level rise. Here we explore the response of Sermeq Kujalleq in Greenland to limiting warm water inflow to the fjord it terminates by raising the sill by an artificial barrier at its mouth. We asynchronously couple an ice sheet model with a fjord model, and simulate glacier evolution with varying climate scenarios from the year 2020 to 2100. The tallest barrier cools the fjord water and reduces melt at the ice front. But this has minor impacts on glacier retreat under SSP5-8.5 and SSP2-4.5. Cooling the atmospheric forcing to 1990s levels reduces glacier retreat, but even reducing water temperatures with a barrier cannot stabilize the glacier. The glacier seems to be in an unstoppable phase of marine ice sheet instability on a rapidly deepening retrograde sloping bed and in water much deeper than in 2000s.
Escalation of caldera unrest indicated by increasing emission of isotopically light sulfur
Calderas are depressions formed by some of the largest volcanic eruptions. Their long-lived inter-eruptive periods are occasionally interrupted by phases of unrest, in which escalating seismicity, ground deformation and gas emissions raise concerns of potential volcano reawakening. However, interpretation of such physico-chemical signals is complicated by few examples of monitored unrest that culminated into eruption and by our fragmentary understanding of the drivers and timescales of caldera reactivation. Here we show that multi-decadal gas observations at the restless Campi Flegrei caldera in Italy record an unprecedented increase in isotopically light sulfur release from fumaroles since 2018. We then use hydrothermal gas equilibria and numerical simulations of magmatic degassing to propose that such a change in sulfur emissions results from decompression-driven degassing of mafic magma at ≥6 km depth, along with some extent of sulfur remobilization from hydrothermal minerals. Examination of a global dataset indicates that, despite the diversity in eruptive behaviour and tectonic setting, increasing sulfur output may be a common process during unrest escalation at calderas generally. Hence, our observations and models of sulfur behaviour may inform interpretations of unrest and hazard assessment at reawakening calderas and hydrothermal active volcanoes worldwide.
Winter subglacial meltwater detected in a Greenland fjord
The interaction between glacier fronts and ocean waters is one of the key uncertainties for projecting future ice mass loss. Direct observations at glacier fronts are sparse, but studies indicate that the magnitude and timing of freshwater fluxes are crucial in determining fjord circulation, ice frontal melt and ecosystem habitability. In particular, wintertime dynamics are severely understudied due to inaccessible conditions, leading to a bias towards summer observations. Here we present in situ observations of temperature and salinity acquired in late winter in Greenland at the front of a marine-terminating glacier and in surrounding fjords. Our observations indicate the existence of an anomalously fresh pool of water by the glacier front, suggesting that meltwater generated at the bed of the glacier discharges during winter. The results suggest that warm Atlantic water and nutrients are entrained at the glacier front, leading to enhanced frontal melt and increased nutrient levels. Our findings have implications for understanding the heat exchange between glacier fronts and ocean waters, glacier frontal melt rates, ocean mixing and currents, and biological productivity.
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