Volume 4 Issue 6, June 2011

The potential for earthquakes along the plate boundaries has been mapped with reasonable success. Our attention should now focus on the threat posed by unanticipated quakes located in the continental interiors.

Sulphur aerosols contribute to the regulation of the Earth's climate. Biogenic sulphur emissions from the Southern Ocean have been underestimated, and could be further enhanced owing to climate warming, according to observations and model simulations.

Gaseous pollutants such as ozone and carbon monoxide from Asia are lifted to altitudes of more than 10 km during the summer monsoon season. Satellite observations show that aerosol particles, too, can rise high and spread across thousands of kilometres.

Animals originated in a world with marine oxygen levels only a fraction of those found in today's oceans. Observations of microbial habitats in present-day lagoons suggest that early animals could have found refuge in oxygen-producing mats.

Observations from the Cassini–Huygens mission have produced potentially contradictory constraints on the origin of Titan's atmosphere. Experiments and a simple model demonstrate that a new mechanism for late formation is plausible.

Great earthquakes along the western, subduction zone boundary of the Andes Mountains in South America are expected. Measurements of surface motion along the eastern boundary highlight the potential for equally large earthquakes in the east.

The origin of Titan’s massive nitrogen atmosphere is largely unknown. Laser-gun experiments and numerical calculations suggest that the nitrogen could have been generated by conversion from ammonia during the period of Late Heavy Bombardment.

Mixing in the Southern Ocean plays an important part in large-scale ocean circulation and in climate. An analysis of high-resolution hydrographic profiles from the Argo float programme reveals that the seasonal cycle of mixing in the Southern Ocean is controlled by seasonal variations in the wind stress, in particular over flat topography.

Hydrothermal vents emit metals such as iron to the ocean. A chemical analysis of hydrothermal fluids suggests that up to 10% of the iron is present as stable, iron-bearing nanoparticles.

The evolution of marine complex animals about 635 million years ago took place in relatively low-oxygen waters. An analysis of a low-oxygen, hypersaline lagoon suggests these early animals may have obtained both oxygen and food from widespread microbial mats.

Carbonaceous minerals in 3.8-billion-year-old rocks from West Greenland have been used as evidence for early life on Earth. Geochemical analyses of similar carbon minerals in 3.75- to 4.2-billion-year-old rocks from Canada show that they can be derived from subsequent alteration more than a billion years after the initial formation.

The western margin of the Andes Mountains often experiences large earthquakes, but the potential size of earthquakes along the eastern margin is unknown. Analysis of GPS data shows that a substantial section of the eastern margin is locked and could rupture in an earthquake with a magnitude of up to 8.9.

Radiating seismic waves can generate tremor on faults that are far away from the original earthquake source. Analysis of seismic wave data from the San Andreas fault reveals episodes of tremor, triggered by far-off earthquakes, which record a prolonged creeping of the fault that could potentially trigger another earthquake.

The seismic hazard associated with individual faults can be assessed from the distribution of slip and the recurrence time of earthquakes. Analysis of the offsets of stream channels and terraces caused during five historical earthquakes on the Fuyun fault, China, reveals characteristic fault slip of about six metres for each event.

The geochemistry of lavas erupted at locations where mantle plumes interact with mid-ocean ridges reflects the mixing between the two sources. Analysis of lavas erupted above the Foundation hotspot, near the Pacific–Antarctic Ridge, reveal a geochemical signature indicative of both a primitive mantle plume source and a recycled oceanic lithosphere source.

The Pacific sector of Antarctica has experienced substantial warming in the past 30 years. Observations of global surface temperatures and atmospheric circulation data show that the warming in continental West Antarctica is linked to sea surface temperature changes in the tropical Pacific Ocean.

Slow slip of the down-going plate at subduction zones can generate seismic tremor. Analysis of recent large tremor and slip episodes along the Cascadia subduction zone reveals tremor signals that reverse and rapidly migrate back along the previously ruptured fault, implying that the initial fault slip weakened the plate interface.

Murray Gingras and colleagues examined lagoon goo for signs of life from the comfort of a moonlit rooftop in the Caribbean.