Research articles

Hydrous magnesium-rich silicates play an important role in transporting water into the deep mantle when oceanic plates subduct as slabs, but were thought to dissociate at pressures of 44 GPa. In situ X-ray measurements in conjunction with a multi-anvil apparatus show that hydrous phases of magnesium-rich silicate are stable under lower mantle conditions up to 50 GPa, and may transport water to deeper layers of the mantle.

Changes in climate are amplified in the Arctic region. An analysis of the CMIP5 state-of-the-art climate models reveals that temperature feedbacks are the dominant factor in this amplification, whereas the change in reflectivity of the Earth’s surface as sea ice and snow melt makes only a secondary contribution.

Tropospheric ozone is a potent greenhouse gas, biological irritant and significant source of highly reactive hydroxyl radicals. Simulations with a chemistry climate model suggest that shifts in atmospheric circulation can account for the seasonally dependent trends in tropospheric ozone levels observed at Mauna Loa, Hawaii, over the past three decades.

Arctic sea ice is a key component of the modern climate system. Marine sediment analyses suggest that perennial sea ice in the Arctic Ocean first formed—transiently—about 44 million years ago.

The age of the Grand Canyon is fervently debated. Thermochronological reconstructions of canyon incision show that although parts of the canyon were carved more than 50 million years ago, two key segments formed less than 6 million years ago, implying that the canyon is a young feature.

The flux of methane from the sea bed to the overlying water column is mitigated by the sulphate-dependent anaerobic oxidation of methane by marine microbes. Laboratory experiments point to the equilibration of stable carbon isotopes during the anaerobic oxidation of methane under sulphate-limited conditions.

Upwelling mantle plumes are thought to be sheared by the motions of the overlying tectonic plates. Seismic imaging of a hotspot beneath the Galápagos Islands, however, identifies a plume that is not deflected in the direction of plate motion and whose characteristics are instead controlled by multistage melting processes.

Carbon is removed from the Earth’s surface through the formation and burial of carbon-bearing rocks and minerals. An analysis of pore water profiles collected from marine sediments around the globe suggests that the precipitation of authigenic calcium carbonate accounts for around 10% of the carbonate that accumulates in marine sediments globally.

During the Younger Dryas cold event about 12,800 years ago, environmental change in western Europe seems to occur 170 years after cooling over Greenland. Lake sediment analyses confirm this delay, and suggest European hydrological and vegetation change occurred only after the build-up of sea ice in the North Atlantic pushed the westerly wind system south.

The dynamics of Earth’s mantle are difficult to constrain. Analysis of GOCE satellite gravity data can be used to identify gravity anomalies to mid-mantle depths and hence to identify regions of tectonic-plate subduction and plume upwelling in the mantle.

Several periods of massive iceberg discharge into the North Atlantic and widespread cooling marked the last glacial period. Reconstructions of northward flow along the Florida margin suggest that not all cold events were associated with a change in the strength of the Atlantic meridional overturning circulation.

The dynamics of dune evolution under bimodal wind regimes are poorly understood owing to a lack of long-term wind records and the limitations of most experimental set-ups. A 4-year landscape-scale experiment in the Tengger Desert, Mongolia, demonstrates that the orientation of oblique dune crests is controlled by the wind regime.

The 2011 eruption of a 20-km-high volcanic plume from Grímsvötn Volcano, Iceland, led to the closure of northern European airspace. Geodetic measurements from the volcano reveal a correlation between plume height, surface deformation and magma-chamber pressure, with a delay of an hour, implying that volcanic-plume behaviour can be predicted before eruption onset.

Chlorine radicals function as a strong atmospheric oxidant, particularly in polar regions, where levels of hydroxyl radicals are low. Measurements in the Arctic reveal high levels of molecular chlorine during the day, consistent with a photochemical source.

The global frequency of volcanic eruptions is inversely proportional to the volume of magma erupted in a single event. Numerical modelling of magma reservoirs evolving in Earth’s crust shows that frequent, small eruptions are triggered by injections of magma into the reservoir, but rare, giant supervolcano eruptions are triggered by magma buoyancy.

Supervolcano eruptions dwarf all historical eruptions, but their trigger mechanisms are unclear. Experimental measurements of magma density at high pressures and temperatures show that the buoyancy of magma alone can impose sufficient pressure at the roof of a supervolcano magma chamber to induce an eruption.