The fraction of NO2 in NO x emitted from European road transport is up to a factor of two smaller than used in policy projections, suggests an analysis of 130 million roadside observations. Roadside air quality standards may thus be obtained faster. The image shows traffic in London, UK.

See Grange et al. and News & Views by Gentner and Xiong

Interactions between narrow frontal currents and topography in the Drake Passage enhance bottom mixing, according to ocean glider observations. Such interactions between frontal currents and topography could help close Southern Ocean overturning. This image shows Neumayer Channel near the northwestern coast of the Antarctic Peninsula.

Article p840; News & Views p806

IMAGE: XIAOZHOU RUAN

COVER DESIGN: TULSI VORALIA

Unloading of the lithosphere due to evaporation and reduced sea level in the Mediterranean six million years ago may have triggered magmatism around the region, according to numerical models. The eruptions cannot be easily explained by tectonic processes. The image shows Messinian evaporites in the Realmonte salt mine in Sicily, Italy.

Article p783; News & Views p718

IMAGE: GIUSEPPE FALLICA

COVER DESIGN: TULSI VORALIA

Estimates of the carbon content of Earth's mantle and magmas vary. Analysis and modelling of gas emissions at Hawai'i indicate that the amount of carbon in the Hawaiian mantle plume and CO2 in Hawaiian lavas is 40% greater than previously thought. The image shows the summit caldera and lava lake of Klauea Volcano, Hawai'i on 4 July 2016.

Article p704; News & Views p625

IMAGE: ANDREW RICHARD HARA

COVER DESIGN: TULSI VORALIA

Microbes are expected to prefer substrates with the highest energy yield. Laboratory experiments demonstrate that a metabolically flexible archaeon exhibits preference for, and greater growth from, lower energy substrates. The image shows overlapping gradients in mineral substrates capable of supporting microbial metabolism in a hot spring outflow channel in Yellowstone National Park, Wyoming, USA.

Article p577

IMAGE: ERIC BOYD

COVER DESIGN: TULSI VORALIA

Many lakes in China are subject to eutrophication. Water quality analyses on 862 Chinese lakes reveal that better sanitation has reduced phosphorus inputs in the most populated areas, but aquaculture and livestock offset improvements elsewhere. The image shows traditional houses in the Jiangnan region, China.

Article p507; News & Views p469

IMAGE: SHIAN YUAN

COVER DESIGN: TULSI VORALIA

Models and proxy data diverge on the global temperature evolution of the Holocene, perhaps due to representation of the seasons. Isotopic analyses of stalagmites from the Ural Mountains suggest that winter climate dominated in the Eurasian interior. The image shows an active drip hanging from a soda-straw stalactite in Kinderlinskaya Cave, Russia, moments before it fell upon the stalagmite below.

Article p430

IMAGE: OLGA CHERVYATSOVA

COVER DESIGN: TULSI VORALIA

River piracy – the diversion of one stream's headwaters into another – has occurred on long timescales. An analysis of streamflow and digital elevation models documents river rerouting in response to glacier retreat in the Yukon, Canada in May 2016. The image shows dirty icebergs floating in turquoise proglacial Slims Lake at the rapidly disintegrating Kaskawulsh Glacier terminus, Kluane National Park and Preserve, Yukon, Canada.

Article p370; News & Views p327

IMAGE: DAN H. SHUGAR

COVER DESIGN: TULSI VORALIA

Planetary materials reveal variation in iron isotope composition across planetary bodies. Experiments suggest that this variation can be explained by varying degrees of fractionation during core formation, depending on temperature. The image shows a scanning electron microscope image of an iron isotope exchange experiment: a bright semi-spherical metal which simulates a planets core is found next to a grey, quenched silicate, representing a magma ocean. The black region is the graphite sample container.

Article p317

IMAGE: STEPHEN M. ELARDO

COVER DESIGN: TULSI VORALIA

Reconstructions of Holocene summer temperatures differ between models and vegetation based proxies. A quantitative reconstruction for the Mediterranean region based on fossil midge assemblages suggests warm summers, in line with climate models. The image shows the head capsule of a chironomid larva (Polypedilum nubeculosum-type), cleared to reveal structures and mouthparts that are examined in fossil specimens.

Article p207

IMAGE: OLIVER HEIRI

COVER DESIGN: TULSI VORALIA

Glaciers have been retreating almost globally over the past century. An analysis using signal-to-noise ratio as a metric of individual glacier change reveals that glacier retreat constitutes categorical evidence for regional climate change. The image shows a colour lithograph of an 1851 sketch of the Nigardsbreen glacier in Norway (one of the world's most well-measured glaciers), which has retreated approximately 4 km since 1850.

Article p95

IMAGE: NORWAY AND ITS GLACIERS; A&C BLACK, 1851

COVER DESIGN: TULSI VORALIA

Ocean acidification can affect growth and calcification rates of calcifying phytoplankton. Mesocosm experiments reveal that acidification can also cause declines in population size and inhibit bloom formation. The image shows a pelagic mesocosm, which is part of the KOSMOS (Kiel Off-Shore Mesocosms for Ocean Simulations) experimental platform.

Article p19

IMAGE: DAVID F. PENCE, UNIVERSITY OF HAWAI'I

COVER DESIGN: TULSI VORALIA