Magma erupted at subduction-zone volcanoes contains mantle rocks and a mixture of fluids and sediments derived from the subducted slab. A synthesis of work over past years provides an integrated physico-chemical framework for subduction zones with mixing at the slab-mantle interface and transport towards the surface volcanoes by buoyant diapirs. The image shows a thin-section microphotograph of a chlorite schist sample from the island of Syros, Greece, that displays a mélange zone.

Review Article p862

COVER IMAGE: HORST R. MARSCHALL

COVER DESIGN: DAVID SHAND

Recent changes in the Southern Annular Mode are associated with warmer, drier conditions in the Southern Hemisphere. An analysis of tree-ring records there suggests that these changes have significantly altered tree growth. The image shows a millennial-aged cypress tree of the species Austrocedrus chilensis in the northern Patagonian Andes.

Letter p793; News & Views p764

COVER IMAGE: DUNCAN CHRISTIE

COVER DESIGN: KAREN MOORE

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 tens of millions of years. The image shows a shaded digital elevation model of the Alpine Fault in the Southern Alps of New Zealand.

Article p744; News & Views p688

COVER IMAGE: SéBASTIEN CASTELLTORT, UNIVERSITY OF GENEVA

COVER DESIGN: DAVID SHAND

The mantles of the terrestrial planets contain elemental abundances that suggest accretion continued at a late stage, after core formation. Geochemical data of meteorites from differentiated asteroids are consistent with such a late accretion event, suggesting that the phenomenon occurred throughout the Solar System and was related to planet formation. The image shows the olivine- and orthopyroxene-bearing meteorite Miller Range 07001 in cross-polarized light.

Letter p614; News & Views p591

COVER IMAGE: J. DAY

COVER DESIGN: DAVID SHAND

The Bonnet Carré Spillway diverts floodwaters from the Mississippi River to Lake Pontchartrain, and was opened for 42 days during the 2011 flood. According to measurements of the newly deposited sediments, at least 31-46% of the river's sand load was diverted into the spillway at this time, suggesting that such diversions can help mitigate coastal wetland loss. The image shows sand waves in the Bonnet Carré Spillway after the 2011 Mississippi flood, with the spillway structure and Mississippi River in the background.

Letter p534; News & Views p521

COVER IMAGE: JEFF NITTROUER

COVER DESIGN: DAVID SHAND

Many terrestrial surfaces are covered by photoautotrophic communities, which are capable of synthesizing their own food from inorganic substances using sunlight. According to an analysis of previously published data, these communities account for nearly half of the biological nitrogen fixation on land. The image shows such a community, consisting of common orange lichen (Xanthoria parietina) and other species that colonize twigs on a tree near Thann in the Vosges mountains (Alsace, France).

Letter p459; News & Views p443

IMAGE CREDIT: WOLFGANG ELBERT, MPI FOR CHEMISTRY

COVER DESIGN: DAVID SHAND

Both marine- and land-terminating glaciers in southeast Greenland have experienced dramatic recent retreat. An 80-year record of historical aerial photographs and satellite imagery shows that many land-terminating glaciers in this region retreated more rapidly in the 1930s than today, whereas marine-terminating glaciers have retreated more quickly in the 2000s. The image shows the Heinkel hydroplane in a southeast Greenlandic fjord.

Article p427; News & Views p369; Editorial p365

COVER IMAGE: DANISH ARCTIC INSTITUTE

COVER DESIGN: DAVID SHAND

Ocean acidification may seriously impair marine calcifying organisms. Emiliania huxleyi, the world's single most important calcifying organism, may be able to evolve in response to ocean acidification conditions, according to laboratory selection experiments. The image shows micrometre-sized Emiliania huxleyi cells thriving in the sunlit surface layer of the ocean.

Article p346; News & Views p310

COVER IMAGE: LENNART T. BACH, JULIA GOLDHAMMER AND KAI T. LOHBECK

COVER DESIGN: DAVID SHAND

Rates of crust formation at midocean ridges are expected to vary with rates of plate spreading. U-Pb dating of zircon minerals from the fast-spreading East Pacific Rise reveals protracted formation of gabbroic rocks over timescales comparable with slow-spreading mid-ocean ridges, suggesting similar timescales of magmatic processes at slow- and fast-spreading ridges. The image shows grains of the mineral zircon that formed in the oceanic crust at the East Pacific Rise, each about 200 μm long. The grains are analysed using cathodoluminescence (grey) and the distribution of the element yttrium (colour).

Letter p275; News & Views p235

COVER IMAGE: ERIC HELLEBRAND AND C. JOHAN LISSENBERG

COVER DESIGN: DAVID SHAND

Glacier-derived dissolved organic matter represents a quantitatively significant source of ancient, but bioavailable, carbon to downstream ecosystems. Anthropogenic aerosols supply glaciers with aged organic matter, according to an analysis of organic matter from glaciers in Alaska. The image shows the upper slopes of Mendenhall Glacier near Juneau, southeast Alaska as seen during fieldwork.

Letter p198; News & Views p167

COVER IMAGE: ARON STUBBINS.

WWW.SKIO.USG.EDU/PEOPLE/STUBBINS/

COVER DESIGN: DAVID SHAND

In the roots of the ocean crust, mantle-derived rocks are progressively hydrated by hydrothermal circulation. Raman spectroscopic analyses of hydrated rocks sampled from the ocean floor reveal accumulations of organic matter, which point to the hydration process as a possible energy source. The image shows carbon accumulations that result from the activity of microbial communities in the oceanic crust.

Letter p133

COVER IMAGE: B. MENEZ,

V. PASINI, D. BRUNELLI

COVER DESIGN: DAVID SHAND

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. The image shows the thick loess mountains in the Jingyuan section of the northwestern Chinese Loess Plateau.

Letter p46

COVER IMAGE: YOUBIN SUN

COVER DESIGN: DAVID SHAND