Research articles

Fjords line mountainous continental margins where icesheets and glaciers once stood. A two-dimensional model simulation suggests that fjords can be eroded within one million years, primarily in response to topographic ice steering and erosion from ice discharge. Subsequent glaciers that form on these landscapes are smaller and exhibit greater responses to climate change.

Overlapping subduction of the Pacific and Philippines Sea plates leads to an enhanced fluid flux to the mantle source of arc volcanoes in central Japan. Spatial variability in the amount of fluid that each plate contributes is determined by the configuration of the subducting plates.

Reconstructions of palaeosecular variation suggest that the Earth’s magnetic field reversed less frequently 2.82 to 2.45 billion years ago, relative to the Cenozoic era. This suggests a long-term trend of decreasing geodynamo stability since the Archaean eon.

On geological timescales, carbon dioxide enters the atmosphere through volcanism and organic matter oxidation and is removed through mineral weathering and carbonate burial. An analysis of ice-core CO₂ records and marine carbonate chemistry indicates a tight coupling between these processes during the past 610,000 years, which suggests that a weathering feedback driven by atmospheric CO₂ leads to a mass balance between CO₂ sources and sinks on long timescales.

Submarine groundwater discharge, estimated from a ²²⁸Ra inventory across the upper Atlantic Ocean, provides a flux of 2–4×10¹³ m³ yr⁻¹, equivalent to 80–160% of the influx from rivers into the Atlantic Ocean.

Tropospheric ozone contributes significantly to human-induced greenhouse warming. Calculations from satellite measurements of spectral radiance suggest that ozone in the upper troposphere caused an average reduction in clear-sky outgoing long-wave radiation over the oceans of 0.48±0.14 W m⁻² for the year 2006 between 45^∘ S and 45^∘ N.

The Eocene–Oligocene transition is the largest global cooling in the Cenozoic period. A comparison of three independent proxies from the continental shelf and deep ocean reveals a three-step transition to cold glacial conditions, with ice sheets 25% larger than their present size.

Using experimental conditions approximating those of the early Earth, the partition coefficient for palladium was found to be sufficiently low to explain the palladium content of the Earth’s mantle in terms of an early equilibration of the mantle with core-forming metals, rather than requiring the addition of a ‘late veneer’ of chondritic material after core formation.

Nitryl chloride, an active halogen, can be produced through the night-time reaction of dinitrogen pentoxide with chloride-containing aerosol in the polluted marine boundary, and has been measured at levels that are sufficient to affect the photochemistry of oxidants off the southwestern US coast and near Houston, Texas.

Temperature changes with depth do not appear to be a primary control for either slow slip or fault-locking processes at the Hikurangi margin, North Island, New Zealand. Both slow-slip events and the geodetically observed transition from fault locking to free slip at depth occur at temperatures as low as 100 ^∘C.

The largest earthquakes often cause rupture for hundreds of kilometres along a single subducting plate, and often begin or end at structural boundaries on the overriding plate. But the Solomons earthquake on 1 April 2007 ruptured across a triple junction, where the Australian and Woodlark plates subduct beneath the overriding Pacific plate.

The main Ethiopian rift has evolved in two stages, with successive activation of differently oriented fault systems. Analogue modelling of the Earth’s lithosphere demonstrates that such a rift evolution requires neither magma weakening nor a change in plate kinematics.

Biological availability of molybdenum and vanadium is facilitated by siderophores that are produced by cultures of the bacterium Azotobacter vinelandii during the fixation of atmospheric nitrogen. This suggests that the production of strong binding compounds may be a widespread strategy for metal acquisition by bacteria and implies that the availability of molybdenum and vanadium may be critical for the nitrogen cycle of terrestrial ecosystems.

Destruction of the Earth’s ozone shield due to the release of hydrogen sulphide and methane has been suggested as a cause of mass extinctions during periods of ocean anoxia over the past two billion years. This mechanism does not explain the end-Permian mass extinction, according to simulations with a two-dimensional atmospheric chemistry-transport model, which show that the ozone shield remains intact even with massive releases of hydrogen sulphide and methane.

Blue jets, gigantic jets, cloud-to-cloud discharges and cloud-to-ground lightning are all electrical discharges from thunderclouds. An analysis of numerical simulations and observations of these phenomena places them all in a unifying framework.

At nanometre scales, organic matter forms in soil are spatially, rather than chemically, complex, according to X-ray spectromicroscopy studies of thin sections of entire and intact free microaggregates. Organic matter forms detected at this spatial scale have no similarity to organic carbon forms of total soil.

Numerical simulations suggest that lobate scarps on the surface of Mercury could have resulted from compressive stresses induced by convection within the planet’s mantle, in addition to those generated by global contraction.

Attaching a ‘floating’ tree-ring chronology to ice core records that cover the abrupt Younger Dryas cold interval during the last glacial termination provides a better estimate of the onset and duration of the radiocarbon anomaly. The chronology suggests that marine records may be biased by changes in the concentration of radiocarbon in the ocean, which may affect the accuracy of a popular radiocarbon calibration program during this interval.

In the year AD 365, an earthquake and tsunami destroyed much of the eastern Mediterranean coastal regions. The distribution of uplift at the time suggests that the earthquake occurred on a fault within the overriding plate at the subduction zone beneath Crete, and not on the subduction interface itself.

Arc-shaped scours, sandwaves and channels on the Hudson Bay seafloor suggest that the catastrophic drainage of lake Agassiz–Ojibway occurred as a subglacial flood beneath the Laurentide Ice Sheet, which covered northern North America.