Research articles

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.

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.

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 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.

Estimates for sea level three million years ago, a period with similar atmospheric CO₂ levels to today, vary from 10 to 40 m above present. Glacial isostatic adjustment modelling suggests that variations in the height of palaeoshorelines result from the residual adjustment of continental flexure following recent glaciations.

Monomethylmercury is a neurotoxin that accumulates in marine organisms. Incubation experiments suggest that methylation of inorganic mercury accounts for around half of the monomethylmercury present in polar marine waters.

Two types of mountain-forming systems exist on Earth — external orogens form during oceanic–continental plate collisions and internal orogens form where continental plates collide. Hafnium isotope data from orogens worldwide show that each has produced a distinctive signature over the past 550 Myr, reflecting the contrasting subduction geometry in each setting.

Individual rock units are predicted by tectonic models to undergo numerous, complex cycles of subduction. Analysis of high-pressure rocks exposed in the Sesia zone, Italian Western Alps, suggest that slices of the crust underwent two distinct episodes of subduction to mantle depths in fewer than 20 million years.

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.

Melting glaciers in the Patagonian Icefields are thought to have contributed 10% of the sea-level rise attributable to mountain glaciers over the past 50 years. A reconstruction of Patagonian glacier decline since ad 1650 suggests that melt rates increased markedly in the twentieth century.

The subduction of topographic features has been linked both to earthquake generation and the segmentation of faults. Seismic imaging reveals a seamount subducted to 40-km depth below Sumatra that is associated with an aseismic zone, suggesting that at this location, the seamount reduces coupling of the slab and overriding plate.

The areal extent of mangrove forests has declined by 30–50% over the past half century. An analysis of mangrove forests across the Indo-Pacific suggests that mangrove deforestation generates losses of 0.02–0.12 Pg C yr⁻¹, equivalent to up to 10% of carbon emissions from global deforestation.

Trace elements and their isotopes have been explored as tracers for the movement of water masses. Measurements of the high-field-strength elements Zr, Hf, Nb and Ta along two meridional sections of the Pacific Ocean suggest higher ratios of Zr/Hf and Nb/Ta than expected, suggesting that these ratios will be useful for tracking water masses.

Rock fabrics record the formation, compaction and deformation history of that rock. High-resolution mapping of tiny grains in the Allende CV meteorite reveals preservation of a spherical fabric that may have formed in the solar nebula, and could be the oldest rock fabric to have formed in the Solar System.

Earthquakes trigger damaging aftershocks in nearby regions, but whether they also trigger large earthquakes over significant distances has been unclear. Analysis of seismic data since 1979 suggests that earthquakes triggered more large shocks only over distances of about 1,000 km, and did not increase the seismic hazard risk on a global scale.

Volcanism observed far from plate boundaries, in the interior of oceanic and continental plates, may result from flow in the underlying mantle. Comparison between a numerical model of mantle flow and the spatial distribution of intraplate volcanism indicates that rapid shear motion in the mantle may drive melting that causes intraplate eruptions.

Submarine melting has been suggested as a trigger for the widespread acceleration of tidewater glaciers in Greenland. An analysis of oceanographic data from the fjord off Helheim Glacier, Greenland, suggests the presence of light Arctic and dense Atlantic waters in the fjord and that the melting circulation is more complex than thought.

The 2010 Haiti earthquake was initially thought to have ruptured the Enriquillo–Plantain Garden fault, but previously unrecognized faults were later implicated. Radar imaging of surface deformation caused by the earthquake reveals uplift of alluvial fans and subsidence of mountains, consistent with reverse motion on a blind thrust fault.

The timing and style of magmatism and extension during the final stages of continental breakup are uncertain. Analysis of ongoing rifting processes in Ethiopia reveals that after a protracted period of extension by magma intrusion, late-stage breakup is characterized by a final phase of plate stretching and voluminous basalt extrusion.