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Editorials

An epic voyage in the making p733

doi:10.1038/ngeo669

The plan to drill through the entire oceanic crust is ambitious and exciting, and well worth the expense.


Bridging the biodiversity gap p733

doi:10.1038/ngeo688

As climate change continues to erode biodiversity, the two disciplines need to improve their dialogue.


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Correspondence

Early twentieth-century warming pp735 - 736

Stefan Brönnimann

doi:10.1038/ngeo670


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Commentary

CO2 emissions from forest loss pp737 - 738

G. R. van der Werf, D. C. Morton, R. S. DeFries, J. G. J. Olivier, P. S. Kasibhatla, R. B. Jackson, G. J. Collatz & J. T. Randerson

doi:10.1038/ngeo671

Deforestation is the second largest anthropogenic source of carbon dioxide to the atmosphere, after fossil fuel combustion. Following a budget reanalysis, the contribution from deforestation is revised downwards, but tropical peatlands emerge as a notable carbon dioxide source.


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Research Highlights


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News and Views

Geodynamo: A matter of boundaries pp741 - 742

Bruce Buffett

doi:10.1038/ngeo673

The use of more realistic parameters in numerical geodynamo simulations tends to generate less Earth-like magnetic fields. This paradox could be resolved by considering uniform heat flux instead of uniform temperature at the core's surface.

Subject Categories: Structural geology, tectonics and geodynamics | Geomagnetism, palaeomagnetism and core processes

See also: Letter by Sakuraba & Roberts


Atmospheric science: Nitrous oxide delays ozone recovery pp742 - 743

Martyn Chipperfield

doi:10.1038/ngeo678

The stratospheric ozone layer has undergone severe depletion as a result of anthropogenic halocarbons. Although the Montreal Protocol has provided relief, anthropogenic emissions of another substance, nitrous oxide, are set to dominate ozone destruction.

Subject Category: Atmospheric science


Palaeoceanography: Tracking ancient sea ice pp743 - 744

Niels Nørgaard-Pedersen

doi:10.1038/ngeo676

Sea ice is an integral component of the climate system, but a difficult one to reconstruct. Biochemical tracers preserved in marine sediments now reveal the waxing and waning of sea ice since the Last Glacial Maximum in an Arctic Ocean gateway.

Subject Category: Palaeoclimate and palaeoceanography

See also: Letter by Müller et al.


Tectonics: Soaking slabs pp744 - 746

Magali I. Billen

doi:10.1038/ngeo674

Faults that develop in subducting slabs act as conduits for sea water. Numerical modelling indicates that pressure gradients resulting from the bending of slabs may then drive the water deep into their interior.

Subject Category: Structural geology, tectonics and geodynamics

See also: Letter by Faccenda et al.


Planetary science: Wet moon dry Earth p746

Ninad Bondre

doi:10.1038/ngeo679


Geomorphology: Rivers split as mountains grow pp747 - 748

Mikaël Attal

doi:10.1038/ngeo675

Mountain landscapes are shaped by tectonics and climate. A series of laboratory experiments has documented a mechanism by which mountain river networks split as the geometry of a mountain evolves in response to an orographic precipitation gradient.

Subject Category: Geomorphology

See also: Letter by Bonnet


Water pollution: Urban waste p748

Anna Armstrong

doi:10.1038/ngeo680


Atmospheric science: ENSO and the stratosphere pp749 - 750

Elisa Manzini

doi:10.1038/ngeo677

The El Niño/Southern Oscillation phenomenon is the most prominent source of climate variability. Emerging evidence suggests that its signature is not limited to the lower layers of the atmosphere.

Subject Category: Atmospheric science


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Correction

The dark side of marine carbon p750

doi:10.1038/ngeo664


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Progress Article

Interglacial diversity pp751 - 755

P. C. Tzedakis, D. Raynaud, J. F. McManus, A. Berger, V. Brovkin & T. Kiefer

doi:10.1038/ngeo660

Past interglacials can be thought of as a series of natural experiments in which boundary conditions varied considerably. Examination of the palaeoclimate record of the past 800,000 years reveals a large diversity among interglacials in terms of their intensity, duration and internal variability.

Subject Category: Palaeoclimate and palaeoceanography


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Letters

Emergence of sprite streamers from screening-ionization waves in the lower ionosphere pp757 - 760

Alejandro Luque & Ute Ebert

doi:10.1038/ngeo662

Sprite discharges above thunderclouds, at altitudes of 40–90 km, are usually created by a strong positive cloud-to-ground lightning flash. A numerical discharge model of the process suggests that sprite streamers are generated through the collapse of a downward-propagating screening-ionization wave in the lower ionosphere.

Subject Categories: Atmospheric science | Space physics


Sea surface cooling at the Equator by subsurface mixing in tropical instability waves pp761 - 765

J. N. Moum, R.-C. Lien, A. Perlin, J. D. Nash, M. C. Gregg & P. J. Wiles

doi:10.1038/ngeo657

Changes in the sea surface temperature of equatorial waters have critical effects on the large-scale atmospheric circulation. Shipboard measurements of turbulence kinetic-energy dissipation rate indicate that seasonal surface cooling in the central equatorial Pacific may be largely caused by mixing induced by tropical instability waves.

Subject Category: Oceanography


Shrinking and splitting of drainage basins in orogenic landscapes from the migration of the main drainage divide pp766 - 771

Stephane Bonnet

doi:10.1038/ngeo666

Many mountain ranges have asymmetric topography and drainage patterns. Laboratory experiments show that tectonic uplift combined with a precipitation gradient will cause the drainage divide to migrate towards the drier side of the mountain range, thereby triggering the splitting of drainage basins on the dry side of the range.

Subject Category: Geomorphology

See also: News and Views by Attal


Variability of sea-ice conditions in the Fram Strait over the past 30,000 years pp772 - 776

Juliane Müller, Guillaume Massé, Rüdiger Stein & Simon T. Belt

doi:10.1038/ngeo665

Sea ice is a critical component of the climate and oceanographic system in the North Atlantic Ocean. A biomarker record reveals millennial-scale and glacial–interglacial fluctuations in sea-ice coverage in the northernmost Atlantic Ocean over the past 30,000 years.

Subject Categories: Cryospheric science | Palaeoclimate and palaeoceanography

See also: related Backstory | News and Views by Nørgaard-Pedersen


Warm and wet conditions in the Arctic region during Eocene Thermal Maximum 2 pp777 - 780

Appy Sluijs, Stefan Schouten, Timme H. Donders, Petra L. Schoon, Ursula Röhl, Gert-Jan Reichart, Francesca Sangiorgi, Jung-Hyun Kim, Jaap S. Sinninghe Damsté & Henk Brinkhuis

doi:10.1038/ngeo668

The Eocene Thermal Maximum 2 occurred 53.5 million years ago in response to elevated atmospheric carbon dioxide levels. Geochemical and microfossil analyses of Arctic sediments show that the during this event the surface of the Arctic Ocean warmed and freshened, and the coldest month mean temperatures did not fall below 8 °C.

Subject Category: Palaeoclimate and palaeoceanography


Generation of banded iron formations by internal dynamics and leaching of oceanic crust pp781 - 784

Yifeng Wang, Huifang Xu, Enrique Merino & Hiromi Konishi

doi:10.1038/ngeo652

Banded iron formations are plentiful in the rocks representing early Earth, but the mechanisms by which they formed remain controversial. Geochemical modelling indicates that the hydrothermal leaching of low-aluminium ocean crust and subsequent chemical reactions in iron- and silica-rich hydrothermal fluids could have triggered the alternating deposition of iron and silica-dominated sediments.

Subject Categories: Biogeochemistry | Volcanology, mineralogy and petrology


Distribution of melt beneath Mount St Helens and Mount Adams inferred from magnetotelluric data pp785 - 789

Graham J. Hill, T. Grant Caldwell, Wiebke Heise, Darren G. Chertkoff, Hugh M. Bibby, Matt K. Burgess, James P. Cull & Ray A. F. Cas

doi:10.1038/ngeo661

The cause of high electrical conductivity in the middle crust beneath the Pacific Northwest region of the US is not clear. New electrical-resistivity data reveal a connection between this regional conductor and a localized conductor beneath a prominent volcano in the region, suggesting that the anomalous conductivity is due to the presence of partial melts.

Subject Category: Structural geology, tectonics and geodynamics


Deep slab hydration induced by bending-related variations in tectonic pressure pp790 - 793

Manuele Faccenda, Taras V. Gerya & Luigi Burlini

doi:10.1038/ngeo656

Geophysical data reveal that at subduction zones oceanic plates could be pervasively hydrated for several kilometres below the crust–mantle boundary. Numerical experiments suggest that such deep hydration is facilitated by negative pressure gradients that lead to the downward pumping of water along bending-related normal faults.

Subject Category: Structural geology, tectonics and geodynamics

See also: News and Views by Billen


Weakening of calcium iridate during its transformation from perovskite to post-perovskite pp794 - 797

Simon A. Hunt, Donald J. Weidner, Li Li, Liping Wang, Nicolas P. Walte, John P. Brodholt & David P. Dobson

doi:10.1038/ngeo663

Magnesium silicate perovskite, the dominant mineral in the lower mantle, is thought to transform into a post-perovskite phase in the mantle's lowermost region. Laboratory experiments suggest substantial weakening could occur during the transformation from perovskite to post-perovskite, which could explain the anomalous physical properties of the lowermost mantle.

Subject Category: Structural geology, tectonics and geodynamics


Core formation and metal–silicate fractionation of osmium and iridium from gold pp798 - 801

James M. Brenan & William F. McDonough

doi:10.1038/ngeo658

Both core formation and the late addition of extraterrestrial material have been invoked to explain the abundances and relative proportions of iron-loving elements in the Earth's mantle. High-temperature experiments suggest that the concentration of gold is consistent with core formation, but the amounts of osmium and iridium require later inputs of extraterrestrial material.

Subject Category: Oceanography


Generation of a strong magnetic field using uniform heat flux at the surface of the core pp802 - 805

Ataru Sakuraba & Paul H. Roberts

doi:10.1038/ngeo643

Numerical simulations that assume realistic core-fluid viscosities have been unsuccessful in fully reproducing the unique characteristics of the Earth's geomagnetic field. An evaluation of boundary conditions suggests that the prescription of a uniform heat flux at the core's surface could generate a more Earth-like magnetic field.

Subject Category: Geomagnetism, palaeomagnetism and core processes

See also: News and Views by Buffett


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