Research articles

A whirling vortex has been observed in the atmosphere at the south pole of Venus. Cloud motions tracked by the Venus Express spacecraft suggest that the south polar vortex is long-lived, erratic and baroclinic in character.

Foreshocks precede some—but not all—earthquakes. Analysis of all earthquakes larger than magnitude 6.5 that occurred between 1999 and 2011 shows that earthquakes at plate boundaries are often preceded by increasing foreshock activity in the days leading up to the quake, whereas earthquakes in plate interiors often are not.

The sea floor at the easternmost Southwest Indian mid-ocean ridge is smooth, unlike that at other mid-ocean ridges. Sonar imaging and analysis of rock samples show that the sea floor here is composed almost entirely of sea-water-altered mantle rocks that have been brought to the surface by large faults on both sides of the ridge axis over the past 11 million years.

Lunar samples suggest that the inner Solar System was bombarded by asteroids about 4 Gyr ago. Radiometric ages of meteorites suggest an unusual number of high-velocity asteroids at this time, consistent with a dynamical origin of the bombardment in which the asteroids were pushed by outer planet migration onto highly eccentric orbits.

The continents are thought to insulate and heat the underlying mantle. Geochemical analyses of lava samples formed at a mid-ocean ridge in the Atlantic Ocean immediately after continental breakup show that the mantle was up to 150 °C hotter than today and took about 70 million years to cool.

The elemental composition of marine organic matter is used to infer a variety of oceanic ecosystem processes. A compilation of observational data suggests that elemental ratios differ substantially from the Redfield ratio, but exhibit a clear latitudinal trend.

Fluids flowing through cavities in Earth’s crust can deposit gold. Thermo-mechanical modelling of a fluid-filled cavity that expands suddenly during an earthquake shows that the drop in pressure would cause the fluid to vaporize and deposit the gold almost instantaneously.

Microbes regulate the decomposition of organic matter in marine sediments. Measurements at the deepest oceanic site on Earth reveal high rates of microbial activity, potentially fuelled by the deposition of organic matter.

The 100,000-year problem refers to an apparent mismatch between the strength of solar forcing associated with the 100,000-year cycle of eccentricity in the Earth’s orbit and the amplitude of glacial–interglacial cycles. Numerical analyses suggest that recent glacial–interglacial cycles can instead be explained by a phase locking between internal climate oscillations and the 413,000-year eccentricity cycle.

Assessing potential future carbon loss from tropical forests is important for evaluating the efficacy of programmes for reducing emissions from deforestation and degradation (REDD). An exploration of results from 22 climate models in conjunction with a land surface scheme suggests that in the Americas, Africa and Asia, the resilience of tropical forests to climate change is higher than expected, although uncertainties are large.

Aerosols scatter and absorb incoming solar radiation, with consequences for the energy balance of the atmosphere. An analysis of satellite data suggests that the regional redistribution of aerosols over the past decade had little net effect on the global radiative forcing of the atmosphere.

The micronutrient iron is thought to limit primary production in large regions of the global ocean. Meltwater measurements suggest that the Greenland ice sheet serves as a significant source of potentially bioavailable iron to the surrounding coastal ocean

The water vapour content of the atmosphere has increased as a result of global warming, strengthening the hydrological cycle. An analysis of observational data suggests that wet seasons have become wetter, and dry seasons drier, in recent decades.

Nitrite, a central intermediate in the marine nitrogen cycle, accumulates at the base of the sunlit surface ocean. Isotopic measurements suggest that ammonia oxidation is the primary source of nitrite in the primary nitrite maximum in the Arabian Sea.

The fast flow of glaciers in Greenland during the summer season has been attributed to seasonal increases in subglacial melt water. Tracking the flow of subglacial water using geochemical tracers reveals the establishment of an increasingly efficient drainage network as the melt season progresses.

Ridges of thick, raised crust on the Indian Ocean floor were thought to be mostly volcanic seamounts formed above the Réunion mantle plume. Dating of zircon minerals in Mauritian lavas, however, indicates that fragments of an ancient microcontinent may be preserved beneath the seamounts, contributing to the thickened crust.

Antarctic Bottom Water fills much of the global abyssal ocean, and is known to form in three main sites in the Southern Ocean. Data from instrumented elephant seals and moorings suggest an additional source of bottom-water formation in the Cape Darnley polynya that is driven by sea-ice production.

Oxygen minimum zones account for a significant fraction of oceanic nitrogen loss. Observational and experimental data suggest that marine nitrogen loss is strongly tied to organic matter export in the South Pacific oxygen minimum zone.

The intensity of extreme precipitation rises faster than the rate of increase in the atmosphere’s water-holding capacity. A combination of radar and rain gauge measurements over Germany with synoptic observations and temperature records reveals that convective precipitation, for example from thunderstorms, dominates events of extreme precipitation.

Water has been detected on the lunar surface and attributed to delivery by impacts and the solar wind to a dry early Moon. Spectroscopic detections of water in lunar anorthosites from the Apollo collection suggest that a significant amount of water is indigenous to the Moon.