Letters in 2010

The degradation of submerged Sphagnum mosses generates significant quantities of methane in peat bogs. A global survey of these mosses reveals the presence of an active population of methane-oxidizing bacteria.

Ocean eddies generated through instability of the mean flow are a vital component of the energy budget of the global ocean. Modelling combined with satellite altimetry data suggests that the energy from westward-propagating eddies is scattered and eventually dispersed when they reach the western boundary of an ocean basin.

Reconstructions of land and ocean temperatures over the past 18,000 years in the high southern latitudes have shown conflicting trends. Analyses of temperatures on Campbell Island, south of New Zealand, confirm this behaviour, and lead to the suggestion that it reflects changes in the position and intensity of the westerly winds.

At subduction zones, andesite lavas erupt in greater abundance than the individual magmas that mix to produce them. Textural and geochemical analyses of andesites from Mount Hood, Oregon, reveal that injection and mixing of iron- and magnesium-rich magma in the magma chamber can initiate the volcanic eruption.

Varying concentrations of atmospheric oxygen have affected the development of animals and the role of wildfire in ecosystems. Reconstructions of past oxygen concentrations from fossil charcoal constrain atmospheric oxygenation over the past 400 million years.

Black-carbon aerosols absorb solar radiation and are thought to be a significant source of global warming. Surface and aircraft measurements of aerosol plumes in China suggest that solar absorption increases with the ratio of black carbon to sulphate.

The reason for the spectacular curvature of the Banda subduction zone is debated. Tomographic images and plate reconstructions reveal subduction of a single slab. The ancient geometry of the Australian plate, as well as the interaction between the slab and the mantle, caused the deformation of the slab.

Dense water that formed over the Antarctic continental shelf spreads throughout the global ocean as Antarctic Bottom Water. Observations over eight years reveal a strong seasonal cycle in the flow of Weddell Sea bottom water northwards that is linked to winds over the western margin of the Weddell Sea.

Organic phosphorus is removed from the ocean by its conversion to phosphorite. Laboratory incubations suggest that bacteria catalyse phosphorite formation, and that the rate of conversion is greatest under anoxic conditions.

Modelling studies suggest that management of solar radiation could produce stabilized global temperatures and reduced global precipitation. An analysis of a large-ensemble simulation of 54 temperature-stabilization scenarios suggests that it may not be possible to achieve climate stabilization through management of solar radiation simultaneously in all regions.

Sea-level rise is not globally uniform. A combination of observations and climate-model simulations reveals a pattern of sea-level changes in the Indian Ocean, with a decrease in the southern tropical Indian Ocean and a rise elsewhere, that can be attributed to changes in the atmospheric overturning circulation.

The composition, structure and evolution of the Moon’s mantle is poorly constrained. A global survey of the Moon’s surface, using the spectral profiler onboard the lunar explorer SELENE/Kaguya, identifies a number of exposures of olivine in concentric regions around lunar craters, with a possible mantle origin.

Methylmercury is a neurotoxin that accumulates in food webs and poses a significant risk to human health. Laboratory experiments suggest that complexation of methylmercury with sulphur-containing ligands can stimulate its degradation.

Sequestration of carbon dioxide has been proposed for the mitigation of ongoing global warming. Projections with an Earth system model over 100,000 years suggest that leakage from carbon-storage reservoirs of no more than 1% per thousand years, or continuous resequestration, would be required to maintain conditions similar to a low-emissions scenario.

Some faults slip at high angles to the greatest principal compressive stress. The discovery of shear veins formed at angles of about 80 degrees relative to the greatest principal compressive stress in the Chrystalls Beach complex, New Zealand, suggests that slip can be facilitated by a pre-existing rock fabric under high fluid pressure.

Thinning ice in West Antarctica is currently contributing about 10% of the observed rise in global sea level. Observations obtained from an autonomous underwater vehicle operating beneath Pine Island Glacier, West Antarctica, reveal that the glacier was recently grounded on a transverse ridge in the sea floor, but now warm sea water flows through the widening gap above the ridge.

River canyons are thought to be cut slowly over millions of years. However, at Lake Canyon Gorge, Texas, a seven-metre-deep canyon was cut in just three days in 2002, providing insight into the erosion processes operating during megaflood events.

A large earthquake has been a national hazard concern for decades in the Tokai region of Japan. The 2009 Suruga Bay earthquake increased seismic stress in strongly locked patches of the Tokai fault plane, potentially increasing the likelihood of a major earthquake in the region.

The deposition of iron formations ceased about 1.84 billion years ago. Reconstructions of ocean chemistry suggest that the advent of euxinic conditions along ocean margins preferentially removed dissolved iron from the water column in the form of the mineral pyrite, inhibiting widespread iron-oxide mineral deposition.

Extension at mid-ocean ridges can be accommodated by detachment faults, forming oceanic core complexes that develop under low rates of magma intrusion. Modelling reveals that oceanic core complexes can also form under high rates of magma intrusion, if the magma is injected into the lower ductile layer of the crust.