Volume 5 Issue 10, October 2012

Estimates of stream and river area have relied on observations at coarse resolution. Consideration of the smallest and most dynamic streams could reveal a greater role for river networks in global biogeochemical cycling than previously thought.

Clay minerals on Mars have been interpreted as an indication for a warm, wet early climate. A new hypothesis proposes that the minerals instead formed during brief periods of magmatic degassing, diminishing the prospects for signs of life in these settings.

Climate change is likely to offset some of the improvements in air quality expected from reductions in pollutant emissions. A comprehensive analysis of future air quality over North America suggests that, on balance, the air will still be cleaner in coming decades.

Shallow magma bodies that feed regularly erupting volcanoes are usually considered enduring features that grow steadily between eruptions. Measurements of deformation at Santorini, however, reveal sudden rapid magma accumulation after half a century of rest.

Tracking diffuse, shearing deformation of continents is difficult. Numerical modelling of drainage evolution in the Southern Alps, New Zealand, suggests that rivers can act as dynamic markers of tectonic deformation over geological timescales.

Climate model projections of future precipitation extremes in the tropics are highly uncertain. Observations of year-to-year variations in extremes of present-day climate help to narrow down these projections to a rise in extreme rainfall by 6–14% per °C of warming.

Climate change is governed by changes to the global energy balance. A synthesis of the latest observations suggests that more longwave radiation is received at the Earth's surface than previously thought, and that more precipitation is generated.

Precipitation extremes increase in intensity over many regions of the globe in simulations of a warming climate, but not always consistently. Observational constraints, together with a close relationship between model responses to interannual variability and climate change, suggest a high sensitivity of tropical extreme precipitation to warming.

Boundary-layer clouds modify the near-surface climate and interact with the water and carbon cycles. Biophysical modelling suggests that rising atmospheric CO₂ levels and the associated closing of plant stomata may suppress boundary-layer cloud formation in the mid-latitudes, and demonstrates how biological and physical aspects of the climate system are intertwined.

Increased temperatures and declines in water availability have influenced the productivity of mountain forests over the past half century. An analysis of 25 years of observational and satellite data suggests that mid-elevation forest greenness is strongly regulated by snow accumulation.

Glaciers store and transform organic carbon, which, on release, could support downstream microbial life. An analysis of 26 glaciers in the European Alps suggests that a significant fraction of glacier organic matter is available for microbial consumption.

Nitrous oxide is a potent greenhouse gas that destroys stratospheric ozone. Measurements of nitrous oxide emissions from a Canadian river suggest that future increases in nitrate export to rivers will not necessarily lead to higher nitrous oxide emissions, but more widespread hypoxia most likely will.

Permafrost soils contain almost twice as much carbon as the current atmospheric carbon pool. Climate model simulations suggest that the feedback generated by future permafrost carbon release could lead to a further warming of 0.13–1.69 °C by 2300.

Life on land dates back at least 2.7 billion years, but the effects of this early terrestrial biosphere on biogeochemical cycling are poorly constrained. Marine sulphur data and geochemical modelling suggest that microbial pyrite weathering has transferred a substantial amount of sulphur to the oceans for at least 2.5 billion years.

Subducting slabs can influence mantle flow, but the importance of neighbouring continental cratons is little understood. Geodynamical modelling, constrained by seismic data that identify regions of mantle flow beneath the Caribbean–South American Plate margin, shows that the deep-rooted South American craton acts to deflect and enhance mantle flow into a narrow channel.

Slow earthquakes in subduction zones have been linked to high pore-fluid pressures. Laboratory measurements reveal a high permeability contrast between crust and mantle rocks, implying that water released from the subducting slab could accumulate at the crust–mantle boundary of the overlying plate, raising pore-fluid pressures and generating slow earthquakes.

Seamount chains in the southeast Atlantic Ocean are thought to have formed above plumes sourced from the deep mantle. Dating of lavas erupted along the trails show that the formation and distribution of the seamount chains is also controlled by the motion and structure of the African Plate.

Hydrous clay minerals detected on the ancient martian crust have been proposed to have formed by aqueous weathering on a warm, wet early Mars. However, analyses of terrestrial clay minerals and comparisons to Mars suggest that the Noachian clays could have alternatively formed by precipitation from magmatic fluids.

The persistence of dendritic drainage patterns implies that rivers reorganize after a tectonic perturbation, preserving no long-term record of that tectonic event. Numerical simulations of the evolution of drainage patterns in the Southern Alps, New Zealand, however, reveal rivers that resist reorganization and thus preserve a record of plate tectonic strain over 10 million years.

Santorini Volcano in Greece was thought to be continually charged by small injections of magma. Measurements of surface deformation show that magma equivalent to 10–50% of that emitted in previous small eruptions has been injected beneath Santorini since January 2011, implying that the volcano is instead charged by rapid, episodic fluxes of melt.

Rivers connect the highest mountains with the ocean's depth, carving up the land as they flow. En route, they transport and transform large quantities of terrestrial material, and exchange elements with the atmosphere, land and sea. In this web focus we present opinion pieces and research articles that examine the topographic, biogeochemical and cultural significance of rivers.