Research articles

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.

A large lens-shaped feature bounded by shear zones characterizes the remnant slab beneath the Hindu Kush region. Rather than dripping by viscous flow, the slab is actively stretching and might eventually break off before descending further into the underlying mantle.

Long linear ridges in the Valles Marineris region of Mars most likely represent fault zones that have been cemented by water-deposited minerals. This implies that water in the Martian crust could have traversed long distances via faults and fractures.

Dust input to alpine lakes in the western United States has risen dramatically following westward expansion of human settlements and increased livestock grazing over the past two centuries. The increased dust flux deposits additional nutrients and minerals to the lakes, with important implications for water chemistry, productivity and nutrient cycling.

Over the last twenty years, changes in the shoreline between the Amazon and Orinoco rivers have largely been controlled by the 18.6 year tidal cycle. By 2015 AD, the tidal cycle will account for 90 metres of shoreline retreat in French Guiana and 6 centimetres of sea level rise.

Extensive damage to coastal Louisiana from Hurricane Katrina in 2005 was largely attributed to high rates of relative sea-level rise caused by coastal subsidence. An examination of the underlying Holocene sediments shows that the compaction of peat-rich deposits contributes significantly to Mississippi Delta subsidence rates of up to 5 mm per year.

Eddy activity in the North Atlantic ocean produces fluctuations in ocean-wide volume transport on the order of 20×10⁶ cubic metres per second, on multi-year timescales. Such background noise makes it impossible to detect possible trends in the ocean circulation due to a changing climate without multi-decadal observations in three spatial dimensions.