Nature Geoscience contents: May 2014 Volume 7 Number 5 pp321-388

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TABLE OF CONTENTS May 2014 Volume 7, Issue 5 Editorial Commentaries Research Highlights News and Views Letters Articles Subscribe   Facebook   RSS   Recommend to library   Twitter   Advertisement Nature Publishing Index 2013 Asia-Pacific The Nature Publishing Index 2013 Asia-Pacific supplement provides institutional league tables and regional commentary based on articles published by Asia-Pacific researchers between 1 January 2013 and 31 December 2013. How does your institution compare?    Editorial Top Farm and bench   p321 doi:10.1038/ngeo2163 Climate change could compromise food security over the coming century. Scientists working towards mitigation and adaptation have to win over those who work on the land. Commentaries Top Communication in a divided world   pp322 - 324 Joseph M. Craine doi:10.1038/ngeo2151 Livestock production accounts for a significant fraction of global anthropogenic greenhouse gas emissions. Progress in mitigating the adverse environmental impacts of this industry can be improved by shifting research emphases and fostering communication between researchers and ranchers. The land and its people   pp324 - 325 Paolo D'Odorico and Maria Cristina Rulli doi:10.1038/ngeo2153 Large tracts of agricultural land are being bought up by external investors. Turning the land into a commodity can have detrimental effects, for generations to come, on the local communities that sell or lease the land. Biochar by design   pp326 - 327 S. Abiven, M. W. I. Schmidt and J. Lehmann doi:10.1038/ngeo2154 Biochar has been heralded as a solution to a number of agricultural and environmental ills. To get the most benefit from its application, environmental and social circumstances should both be considered. Research Highlights Top Planetary science: Saving sulphur | Biogeochemistry: Lake carbon | Climate change: Walker uncertainty | Geodynamics: Mantle stages News and Views Top Planetary science: Into thin martian air   pp329 - 330 Sanjoy M. Som doi:10.1038/ngeo2145 A dense early atmosphere has been invoked to explain the strong greenhouse effect inferred for early Mars. Yet an analysis of the smallest impact craters suggests that the atmospheric pressure on Mars 3.6 billion years ago was surprisingly low. See also: Letter by Kite et al. Geodynamics: Mantle plume chemical diversity   pp330 - 331 Frédéric Deschamps doi:10.1038/ngeo2117 Ocean island lavas have complex geochemical signatures. Numerical simulations suggest that these signatures may reflect the entrainment and transport to Earth's surface of both primordial material and recycled oceanic crust by deeply rooted mantle plumes. See also: Letter by Li et al. Climate science: Autopsy of two mega-heatwaves   pp332 - 333 Erich M. Fischer doi:10.1038/ngeo2148 Record-breaking heatwaves in 2003 and 2010 surprised both the public and experts. Observations provide new insights into how temperatures escalated to unprecedented values through the interaction of boundary-layer dynamics and land surface drying. See also: Letter by Miralles et al. Geochemistry: A piece of the deep carbon puzzle   pp333 - 334 Craig E. Manning doi:10.1038/ngeo2152 Carbon loss from subducting slabs is thought to be insufficient to balance carbon dioxide emissions at arc volcanoes. Analyses of ancient subducted rocks in Greece suggest that fluid dissolution of slab carbonate can help solve this carbon-cycle conundrum. See also: Letter by Ague & Nicolescu Geoscience JOBS of the week Professor in Biogeochemistry Stockholm University More Science jobs from Geoscience EVENT Annual International Conference on Earth and Environmental Sciences 14.07.14 Athens, Greece More science events from Letters Top Low palaeopressure of the martian atmosphere estimated from the size distribution of ancient craters   pp335 - 339 Edwin S. Kite, Jean-Pierre Williams, Antoine Lucas and Oded Aharonson doi:10.1038/ngeo2137 The martian atmosphere has progressively thinned, allowing increasingly smaller meteorites to survive unscathed and impact the surface. The distribution of small craters in ancient river deposits on Mars suggests an atmospheric pressure less than that needed to warm the martian surface above freezing 3.5 billion years ago, when rivers presumably flowed. See also: News and Views by Som Tropospheric ozone variations governed by changes in stratospheric circulation   pp340 - 344 Jessica L. Neu, Thomas Flury, Gloria L. Manney, Michelle L. Santee, Nathaniel J. Livesey et al. doi:10.1038/ngeo2138 The downward transport of stratospheric air can deliver significant quantities of ozone to the upper troposphere. An analysis of satellite data suggests that year-to-year variations in stratospheric circulation can account for around half of the interannual variability in tropospheric ozone levels in the northern mid-latitudes. Mega-heatwave temperatures due to combined soil desiccation and atmospheric heat accumulation   pp345 - 349 Diego G. Miralles, Adriaan J. Teuling, Chiel C. van Heerwaarden and Jordi Vilà-Guerau de Arellano doi:10.1038/ngeo2141 Extreme heatwave events are expected to become increasingly common as a consequence of climate change. Analyses of the 2003 and 2010 mega-heatwaves in Europe suggest that atmospheric boundary-layer dynamics and feedbacks with the drying land surface lead to the build-up of heat in the atmosphere and extremely hot temperatures. See also: News and Views by Fischer Sand as a stable and sustainable resource for nourishing the Mississippi River delta   pp350 - 354 Jeffrey A. Nittrouer and Enrica Viparelli doi:10.1038/ngeo2142 Dams have starved the lower Mississippi River of sediment over recent decades, suggesting that the drowning of the delta is inevitable. Analysis of the rivers suspended sediment load and morphodynamic modelling suggest that the amount of sand essential for land building has not significantly decreased since dam construction, with sand remaining available for several centuries. Carbon dioxide released from subduction zones by fluid-mediated reactions   pp355 - 360 Jay J. Ague and Stefan Nicolescu doi:10.1038/ngeo2143 The balance between carbonate subduction into the deep Earth and CO2 release through degassing at volcanoes is critical for the carbon cycle. Geochemical analyses of an exhumed subduction zone complex in Greece show that fluid-mediated reactions could liberate significant amounts of carbon from the subducting slab for later release at arc volcanoes. See also: News and Views by Manning Eastward expansion of the Tibetan Plateau by crustal flow and strain partitioning across faults   pp361 - 365 Qi Yuan Liu, Robert D. van der Hilst, Yu Li, Hua Jian Yao, Jiu Hui Chen et al. doi:10.1038/ngeo2130 The Tibetan Plateau is expanding eastwards, but the modes of deformation are poorly understood. High-resolution seismic images from the region identify localized zones of weak crustal rocks as well as deep faults, implying that deformation occurs through a combination of crustal flow and movement of rigid blocks of crust. Chemical complexity of hotspots caused by cycling oceanic crust through mantle reservoirs   pp366 - 370 Mingming Li, Allen K. McNamara and Edward J. Garnero doi:10.1038/ngeo2120 Lavas erupted at ocean island hotspots have complex geochemical signatures. Numerical simulations suggest that this complexity may result from the mixing of subducted oceanic crust with reservoirs of more primitive material in the deep mantle, with the resulting mixture entrained into rising mantle plumes. See also: News and Views by Deschamps Seismological evidence of mantle flow driving plate motions at a palaeo-spreading centre   pp371 - 375 Shuichi Kodaira, Gou Fujie, Mikiya Yamashita, Takeshi Sato, Tsutomu Takahashi et al. doi:10.1038/ngeo2121 At oceanic spreading centres, it is unclear whether plate motions drag the underlying mantle, or mantle flow pulls the overlying plates. Seismic imaging of a former speading centre in the Pacific Plate reveals strong seismic anisotropy that was generated by mantle flowing at speeds greater than plate motions, implying that mantle flow pulled this part of the plate. Articles Top Climate warming during Antarctic ice sheet expansion at the Middle Miocene transition   pp376 - 381 Gregor Knorr and Gerrit Lohmann doi:10.1038/ngeo2119 During the expansion of the Antarctic ice sheet about 14 million years ago, sea surface temperatures in the Southern Ocean rose. Climate model simulations suggest that this short-lived warming was related to changes in ocean-atmosphere circulation induced by the growth of the ice sheet. Carbon sequestration during the Palaeocene-Eocene Thermal Maximum by an efficient biological pump   pp382 - 388 Zhongwu Ma, Ellen Gray, Ellen Thomas, Brandon Murphy, James Zachos et al. doi:10.1038/ngeo2139 Globally increased temperatures and a perturbation of the carbon cycle and biosphere characterized the Palaeocene–Eocene Thermal Maximum about 55.9 million years ago, but its effect on ocean productivity is controversial. Records of marine barite accumulation rates suggest that carbon sequestration during the event could have been enhanced by an efficient biological pump. 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