Volume 3 Issue 5, May 2010

A multitude of organisms makes soils the fertile factories of food and fibre production, decomposition and nutrient cycling that they are. But tying changes in soil biodiversity to shifts in ecosystem function is a daunting task.

Between 1960 and 2000, Asian and Latin American food production tripled, thanks to the use of high-yielding varieties of crops. Africa can follow suit, but only if depletion of soil nutrients is addressed.

Increasing temperatures stimulate the decomposition of soil organic matter in the short term. But a shift in microbial carbon allocation could mitigate this response over longer periods of time.

The amount of pore space in most unweathered granite is too small to support a plant-based ecosystem. But porosity grows as intact rock interacts with surface waters beneath the soil.

The organic matter stored in frozen Arctic soils could release significant quantities of carbon dioxide and methane on thawing. Now, laboratory experiments show that re-wetting of previously thawed permafrost could increase nitrous oxide production by 20-fold.

The formation and flow of deep water around Antarctica contributes to the global ocean circulation. New measurements report the strongest flow speeds recorded so far in a current below 3,000 m depth, and help to document a pathway for Antarctic Bottom Water.

Soils are the main terrestrial reservoir of nutrients such as nitrogen and phosphorus, and of organic carbon. Data synthesis reveals that soil erosion can result in lateral fluxes of these nutrients at comparable magnitudes to those induced by fertilizer application and crop removal.

The use of fossil fuels and fertilizers has increased the amount of biologically reactive nitrogen in the atmosphere over the past century. A meta-analysis suggests that nitrogen deposition typically impedes the decomposition of carbon in forest soils, significantly reducing carbon dioxide emissions to the atmosphere.

The sedimentary deposits at Meridiani Planum on Mars were formed in acidic surface waters. Geochemical calculations show that the oxidation of dissolved iron and the precipitation of oxidized iron minerals in the surface waters could be sufficient to generate the inferred acidity.

Deep western boundary currents east of the Antarctic Peninsula and the Kerguelen plateau are important pathways for transporting deep Antarctic water masses to the global ocean. An array of moored current meters, used to quantify the water transport in this system, reveals a flow that is stronger than any measured in a deep western boundary current at similar depths so far.

The impact of thawing permafrost on the nitrogen cycle is uncertain. Laboratory experiments using permafrost cores from northeast Greenland reveal that rewetting of thawed permafrost increases nitrous oxide production over 20-fold.

The loss of carbon dioxide from soils increases initially under climate warming, but tends to decline to control levels within a few years. Simulations of the soil-carbon response to warming with a microbial-enzyme model show that a decline in both microbial biomass and the production of degrading enzymes can explain this attenuation response.

Nitrous oxide is a potent atmospheric greenhouse gas that is thought to be produced in soils through biological processes. Field measurements reveal nitrous oxide fluxes near Don Juan Pond, Antarctica — of comparable magnitude to those found in tropical soils — which may result from abiotic water–rock reactions.

Natural petroleum seepage emits large volumes of oil and methane to the oceans every year, accompanied by the formation of asphalt volcanoes on the sea floor. The discovery of seven asphalt volcanoes off the coast of southern California may help to explain high methane emissions recorded during the late Pleistocene.

The 100,000-year glacial cycles are generally thought to be driven by the eccentricity of the Earth’s orbit. Statistical analyses of climate variability and orbital forcing over the past five million years indicate that the glacial cycles are the result of an internal climate oscillation phase locked to the 100,000-year eccentricity cycle.

The cause of the Laramide phase of mountain building remains uncertain. Modelling and plate reconstructions show that Laramide events coincide with subduction of the Shatsky oceanic plateau, implicating surface rebound after removal of the subducting plateau in Laramide uplift.

Deformation of the Himalaya and Tibet is thought to relate to flow within a weak crustal channel at depth. Magnetotelluric imaging of the Earth’s subsurface reveals a complex pattern of deformation, with two distinct weak crustal channels at 20–40 km depth.

Seismotectonic studies seek to provide ways of assessing the timing, magnitude and spatial extent of future earthquakes. Numerical simulations of seismic and aseismic fault slip in a fully dynamical numerical model open the possibility of predicting a fault system’s seismic rupture patterns from observations of its slip properties.

Vladimir Samarkin, Michael Madigan and colleagues travelled to Don Juan Pond in Antarctica, in an attempt to understand life on Mars. Instead, they discovered an unexpected link between the geosphere and atmosphere.

Soil is one of the most precious resources on the planet. As the global population grows, and the climate continues to warm, the structure and function of soils could change. In this focus issue we have gathered articles — ranging from primary research to opinion pieces — that explore the sensitivity of soils to climate and land use change, and that highlight the key role that soils play in shaping the environment and human society.