Volume 5 Issue 1, January 2012

Atmospheric CO₂ levels were much lower during the last glacial maximum than in the pre-industrial period. Ice-core data and biogeochemical modelling suggest that difference is partly due to the greater mass of inert carbon in glacial terrestrial biomes.

Mercury's spin and its orbit around the Sun are tied to each other in a unique arrangement. According to a set of calculations, random asteroid impacts may have aided the planet's evolution into the current spin-orbit pattern.

Formic acid exerts a significant influence on atmospheric chemistry and rainwater acidity. Satellite observations and model simulations suggest that terrestrial vegetation accounts for around 90% of the formic acid produced annually.

Mixed-phase clouds, comprising both ice and supercooled liquid water, have a large impact on radiative fluxes in the Arctic. Interactions between numerous local feedbacks sustain these complex cloud systems, leading to the development of a resilient mixed-phase cloud system.

The planet Mercury rotates three times about its spin axis for every two orbits around the Sun. Numerical modelling suggests that this unusual pattern could result from initial retrograde rotation that was captured into a stable synchronous orbit, and subsequent disturbance by a large impact.

The electric discharge of a thundercloud in the troposphere is often accompanied by upper-atmospheric electric discharges such as sprites or halos. Numerical simulations of the electric response of the mesosphere to lightning suggest that the process of electron associative detachment is fundamental to upper-atmospheric electrodynamics.

Formic acid contributes significantly to acid rain in remote environments. Satellite measurements combined with model simulations indicate that annual formic acid production is two to three times larger than current estimates suggest.

The formal detection of climate warming and its attribution to human influence has so far relied on the differences between natural and anthropogenic warming patterns. An alternative and entirely independent attribution method that relies on the principle of conservation of energy instead, confirms greenhouse gas warming by 0.85 °C since the mid-twentieth century, half of which was offset by aerosol cooling.

During the early twenty-first century, the Greenland Ice Sheet experienced the largest ice mass loss on instrumental record. An analysis of sand deposition in Sermilik Fjord, off Helheim Glacier in east Greenland, suggests that despite strong variability over the past 120 years, similarly high rates of iceberg calving have only occurred once before, in the 1930s.

Massive-turbidite deposits are common in deep-water environments. Numerical simulations suggest that when turbulence is extinguished as turbidity currents reach areas of minimal slope, sediment reworking ceases, which allows the deposition of massive units.

East Asian summer monsoon precipitation varied on millennial timescales during the last glacial period. Sediment records and climate modelling suggest that the winter monsoon was also affected by millenial scale variability, and that the abrupt changes were driven by changes in the strength of the Atlantic meridional overturning circulation.

Subduction modifies the cycling of Earth’s volatile elements. Geochemical analyses of fragments of mantle rocks collected above the Batan Island subduction zone, Philippines, suggest that wet sediment melts are released from the subducted slab, followed later by release of aqueous fluids, yet a significant amount of water is retained in the wedge.

Oceanic lithosphere contains a record of plate-spreading rates, but the oldest oceanic plates have been subducted into the mantle. Measurements of seismic wave velocities in the subducted part of the Cocos Plate beneath central Mexico reveal an anisotropy that was created when the plate formed, preserving an archive of ancient plate-spreading rates on Earth.

The timing of onset of modern-style plate tectonics on Earth is debated. Analysis of rocks in the West African metamorphic province, which is more than 2 Gyr old, reveals that some minerals formed under conditions similar to those in modern-day subduction zones, suggesting that subduction occurred on the Palaeoproterozoic Earth.

Wetlands cover more than 6% of the global ice-free land area, and represent an important arsenic sink. Laboratory experiments suggest that natural organic matter plays an active role in the immobilization of arsenic in anoxic wetlands.

Atmospheric carbon dioxide levels rose at the end of the last glacial period, but the sources of this carbon are uncertain. Ice-core data and carbon-cycle modelling suggest that the disappearance of a terrestrial inert carbon pool may have contributed to the rise.