Letters

Flow in the deep mantle is thought to create textures in the high-pressure mineral post-perovskite. Laboratory simulations of the transformation between lower-pressure perovskite and post-perovskite show that post-perovskite can also inherit textures from the perovskite phase, and vice versa.

Greenhouse warmth during the Cretaceous period was interrupted by several intervals of cooling. Marine sediment analyses and biogeochemical modelling suggest that a decline in the abundance of planktonic foraminifera and nannoconids 116–114 million years ago was linked to sea surface cooling.

Throughout the ocean, countless small animals swim to depth in the daytime, presumably to seek refuge from large predators. An analysis of backscatter data from acoustic Doppler profilers suggests that migration intensifies oxygen depletion in the upper margin of oxygen minimum zones.

Altimeter data suggest that sea level rose by about 2.4 mm per year from 2005 to 2011, but estimates of the relative contributions of ocean warming and increased ocean mass are equivocal. An analysis of ocean temperature and satellite gravity data suggests that the delivery of meltwater from ice sheets and mountain glaciers contributed 75% of the observed sea-level rise.

Stable fault slip, or creep, is thought to occur in unconsolidated sediments that form shallow parts of continental strike-slip faults. Numerical simulations show that creep events observed on faults in California also require the presence of a shallow, unstable layer of rock, the thickness of which influences the duration of the creep event.

Carbon is carried into the Earth at subduction zones. Geochemical analysis of subducted sediments now exhumed in Alpine Corsica, France, reveal the formation of graphite during shallow subduction, implying that carbonate transformation to graphite aids transport into the deeper Earth.

The development and termination of El Niño events seem to be coupled with the seasonal cycle. Statistical analyses suggest that this link reflects the presence of a combination climate mode with periods of 10 and 15 months.

Unusual minerals observed in lunar craters were thought to originate from beneath the Moon’s surface. Numerical simulations show that rather than being vaporized, much of the impactor material can survive in the crater, implying that the unusual minerals come from the impactor and may not be indigenous to the Moon.

Temperate and tropical rivers serve as a substantial source of carbon dioxide to the atmosphere. Organic matter measurements in the Amazon River suggest that terrestrial macromolecules contribute significantly to this outgassing.

The observed seismic anisotropy in the Earth’s inner core has been explained by the preferential alignment of grains by plastic deformation. Measurements of the strength of iron at core pressures suggest that the inner core is weaker than previously thought and deforms by dislocation creep.

Slow earthquakes form part of a spectrum of fault behaviour between steady creep and fast rupture during a normal earthquake. Laboratory simulations of slow slip in rock samples taken from the Nankai subduction zone, Japan, reveal similar characteristics to fast earthquakes, implying that some slow slip events could be prematurely arrested earthquakes.

Climate change can be thought of in terms of geographical shifts in climate properties. Tracking the geographical movement of analogous climate conditions between historical and future climate model simulations, and calculating the impact of such shifts on vegetation carbon storage, suggests that boreal forests will lose carbon as low-carbon ecosystems shift in.

The brightness and lifetime of clouds is determined by cloud droplet number concentration, which is in turn dictated by the number of available seed particles. Model simulations suggest that condensation of semi-volatile organic compounds enhances the formation of cloud droplets, with consequences for cloud dynamics.

Atmospheric aerosol particles can significantly influence the climate system. Analyses of observations and observation-based modelling data reveal that biogenic aerosol emissions soar in response to warming, exerting a cooling effect in a negative feedback loop.

Ridges on the down-going plate in a subduction zone can segment the seismogenic zone and influence earthquake occurrence, but the role of the overriding plate is unclear. InSAR and GPS satellite measurements indicate that segmentation of the subduction zone in northern Chile correlates with a 1-km-high coastal scarp, implying that overriding plate structure can influence seismicity.

Predicting the response of tropical rainfall to climate change remains a challenge. An analysis of climate model simulations suggests that in an emission scenario without mitigation, a large fraction of tropical precipitation change will be independent of global surface warming over the twenty-first century.

The growth of ice on Antarctica about 34 million years ago affected sea level. A combination of modelling and marine sediment analyses shows that sea level near the developing ice sheet first fell and then rose as a result of crustal deformation imposed by the ice growth.

Saturn is brighter than expected for a gas giant of its age. Calculations of Saturn’s thermal evolution show that the presence of layered convection in Saturn’s interior—much like that observed in the Earth’s oceans—would have slowed the planet’s cooling and may explain Saturn’s anomalous luminosity.

Whether changes in atmospheric circulation over West Antarctica during the past few decades are part of a longer-term trend is unclear. Ice cores reveal a significant increase in the oxygen isotopes from precipitation over the past 50 years, but the anomaly cannot be distinguished from natural climate variability.

The response of tropical precipitation to global warming varies spatially and the factors controlling the spatial patterns of precipitation changes are unclear. An analysis of climate model simulations shows that warm regions are projected to become wetter in annual mean, whereas seasonally high rainfall anomalies are expected in regions that are currently wet.