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  • Skewed demographics
    Nat. Geosci. (IF 13.941) Pub Date : 2017-09-05

    Scientists based in North America and men are overrepresented in our authors' reviewer suggestions.

    更新日期:2017-09-05
  • Cryospheric science: Asia's glacier changes
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-07
    Daniel Farinotti

    Mass changes in High Mountain Asia's glaciers have been under dispute for almost a decade. An analysis of satellite data archives provides an observation-based mass budget for every single glacier in the region.

    更新日期:2017-09-05
  • Acts of God, human influence and litigation
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-28
    Sophie Marjanac, Lindene Patton, James Thornton

    Developments in attribution science are improving our ability to detect human influence on extreme weather events. By implication, the legal duties of government, business and others to manage foreseeable harms are broadening, and may lead to more climate change litigation.

    更新日期:2017-09-05
  • Plate tectonics: Crustal recycling evolution
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-21
    Valentina Magni

    The processes that form and recycle continental crust have changed through time. Numerical models reveal an evolution from extensive recycling on early Earth as the lower crust peeled away, to limited recycling via slab break-off today.

    更新日期:2017-09-05
  • Venus: Jet-setting atmosphere
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-28
    Alain Hauchecorne

    A fast equatorial jet in the Venusian cloud layer has been revealed by the Akatsuki orbiter by tracking cloud movement in near-infrared images. The findings suggest that the Venusian atmosphere is more variable than previously thought.

    更新日期:2017-09-05
  • Metal availability and the expanding network of microbial metabolisms in the Archaean eon
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-28
    Eli K. Moore, Benjamin I. Jelen, Donato Giovannelli, Hagai Raanan, Paul G. Falkowski

    Life is based on energy gained by electron-transfer processes; these processes rely on oxidoreductase enzymes, which often contain transition metals in their structures. The availability of different metals and substrates has changed over the course of Earth's history as a result of secular changes in redox conditions, particularly global oxygenation. New metabolic pathways using different transition metals co-evolved alongside changing redox conditions. Sulfur reduction, sulfate reduction, methanogenesis and anoxygenic photosynthesis appeared between about 3.8 and 3.4 billion years ago. The oxidoreductases responsible for these metabolisms incorporated metals that were readily available in Archaean oceans, chiefly iron and iron–sulfur clusters. Oxygenic photosynthesis appeared between 3.2 and 2.5 billion years ago, as did methane oxidation, nitrogen fixation, nitrification and denitrification. These metabolisms rely on an expanded range of transition metals presumably made available by the build-up of molecular oxygen in soil crusts and marine microbial mats. The appropriation of copper in enzymes before the Great Oxidation Event is particularly important, as copper is key to nitrogen and methane cycling and was later incorporated into numerous aerobic metabolisms. We find that the diversity of metals used in oxidoreductases has increased through time, suggesting that surface redox potential and metal incorporation influenced the evolution of metabolism, biological electron transfer and microbial ecology.

    更新日期:2017-09-05
  • Deep mantle: Enriched carbon source detected
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-21
    Peter H. Barry

    Estimates of carbon in the deep mantle vary by more than an order of magnitude. Coupled volcanic CO2 emission data and magma supply rates reveal a carbon-rich mantle plume source region beneath Hawai'i with 40% more carbon than previous estimates.

    更新日期:2017-09-05
  • Tidal controls on river delta morphology
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-31
    A. J. F. Hoitink, Z. B. Wang, B. Vermeulen, Y. Huismans, K. Kästner

    River delta degradation has been caused by extraction of natural resources, sediment retention by reservoirs, and sea-level rise. Despite global concerns about these issues, human activity in the world’s largest deltas intensifies. Harbour development, construction of flood defences, sand mining and land reclamation emerge as key contemporary factors that exert an impact on delta morphology. Tides interacting with river discharge can play a crucial role in the morphodynamic development of deltas under pressure. Emerging insights into tidal controls on river delta morphology suggest that—despite the active morphodynamics in tidal channels and mouth bar regions—tidal motion acts to stabilize delta morphology at the landscape scale under the condition that sediment import during low flows largely balances sediment export during high flows. Distributary channels subject to tides show lower migration rates and are less easily flooded by the river because of opposing non-linear interactions between river discharge and the tide. These interactions lead to flow changes within channels, and a more uniform distribution of discharge across channels. Sediment depletion and rigorous human interventions in deltas, including storm surge defence works, disrupt the dynamic morphological equilibrium and can lead to erosion and severe scour at the channel bed, even decades after an intervention.

    更新日期:2017-09-05
  • Equatorial jet in the lower to middle cloud layer of Venus revealed by Akatsuki
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-28
    Takeshi Horinouchi, Shin-ya Murakami, Takehiko Satoh, Javier Peralta, Kazunori Ogohara, Toru Kouyama, Takeshi Imamura, Hiroki Kashimura, Sanjay S. Limaye, Kevin McGouldrick, Masato Nakamura, Takao M. Sato, Ko-ichiro Sugiyama, Masahiro Takagi, Shigeto Watanabe, Manabu Yamada, Atsushi Yamazaki, Eliot F. Young

    The Venusian atmosphere is in a state of superrotation where prevailing westward winds move much faster than the planet’s rotation. Venus is covered with thick clouds that extend from about 45 to 70 km altitude, but thermal radiation emitted from the lower atmosphere and the surface on the planet’s nightside escapes to space at narrow spectral windows of the near-infrared. The radiation can be used to estimate winds by tracking the silhouettes of clouds in the lower and middle cloud regions below about 57 km in altitude. Estimates of wind speeds have ranged from 50 to 70 m s−1 at low to mid-latitudes, either nearly constant across latitudes or with winds peaking at mid-latitudes. Here we report the detection of winds at low latitude exceeding 80 m s−1 using IR2 camera images from the Akatsuki orbiter taken during July and August 2016. The angular speed around the planetary rotation axis peaks near the equator, which we suggest is consistent with an equatorial jet, a feature that has not been observed previously in the Venusian atmosphere. The mechanism producing the jet remains unclear. Our observations reveal variability in the zonal flow in the lower and middle cloud region that may provide clues to the dynamics of Venus’s atmospheric superrotation.

    更新日期:2017-09-05
  • Snow precipitation on Mars driven by cloud-induced night-time convection
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-21
    Aymeric Spiga, David P. Hinson, Jean-Baptiste Madeleine, Thomas Navarro, Ehouarn Millour, François Forget, Franck Montmessin

    Although it contains less water vapour than Earth’s atmosphere, the Martian atmosphere hosts clouds. These clouds, composed of water-ice particles, influence the global transport of water vapour and the seasonal variations of ice deposits. However, the influence of water-ice clouds on local weather is unclear: it is thought that Martian clouds are devoid of moist convective motions, and snow precipitation occurs only by the slow sedimentation of individual particles. Here we present numerical simulations of the meteorology in Martian cloudy regions that demonstrate that localized convective snowstorms can occur on Mars. We show that such snowstorms—or ice microbursts—can explain deep night-time mixing layers detected from orbit and precipitation signatures detected below water-ice clouds by the Phoenix lander. In our simulations, convective snowstorms occur only during the Martian night, and result from atmospheric instability due to radiative cooling of water-ice cloud particles. This triggers strong convective plumes within and below clouds, with fast snow precipitation resulting from the vigorous descending currents. Night-time convection in Martian water-ice clouds and the associated snow precipitation lead to transport of water both above and below the mixing layers, and thus would affect Mars’ water cycle past and present, especially under the high-obliquity conditions associated with a more intense water cycle.

    更新日期:2017-09-05
  • Large sulfur isotope fractionations in Martian sediments at Gale crater
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-07
    H. B. Franz, A. C. McAdam, D. W. Ming, C. Freissinet, P. R. Mahaffy, D. L. Eldridge, W. W. Fischer, J. P. Grotzinger, C. H. House, J. A. Hurowitz, S. M. McLennan, S. P. Schwenzer, D. T. Vaniman, P. D. Archer Jr, S. K. Atreya, P. G. Conrad, J. W. Dottin III, J. L. Eigenbrode, K. A. Farley, D. P. Glavin, S. S. Johnson, C. A. Knudson, R. V. Morris, R. Navarro-González, A. A. Pavlov, R. Plummer, E. B. Rampe, J. C. Stern, A. Steele, R. E. Summons, B. Sutter

    Variability in the sulfur isotopic composition in sediments can reflect atmospheric, geologic and biological processes. Evidence for ancient fluvio-lacustrine environments at Gale crater on Mars and a lack of efficient crustal recycling mechanisms on the planet suggests a surface environment that was once warm enough to allow the presence of liquid water, at least for discrete periods of time, and implies a greenhouse effect that may have been influenced by sulfur-bearing volcanic gases. Here we report in situ analyses of the sulfur isotopic compositions of SO2 volatilized from ten sediment samples acquired by NASA’s Curiosity rover along a 13 km traverse of Gale crater. We find large variations in sulfur isotopic composition that exceed those measured for Martian meteorites and show both depletion and enrichment in 34S. Measured values of δ34S range from −47 ± 14‰ to 28 ± 7‰, similar to the range typical of terrestrial environments. Although limited geochronological constraints on the stratigraphy traversed by Curiosity are available, we propose that the observed sulfur isotopic signatures at Gale crater can be explained by equilibrium fractionation between sulfate and sulfide in an impact-driven hydrothermal system and atmospheric processing of sulfur-bearing gases during transient warm periods.

    更新日期:2017-09-05
  • The strength of the meridional overturning circulation of the stratosphere
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-28
    Marianna Linz, R. Alan Plumb, Edwin P. Gerber, Florian J. Haenel, Gabriele Stiller, Douglas E. Kinnison, Alison Ming, Jessica L. Neu

    The distribution of gases such as ozone and water vapour in the stratosphere—which affect surface climate—is influenced by the meridional overturning of mass in the stratosphere, the Brewer–Dobson circulation. However, observation-based estimates of the global strength of this circulation are difficult to obtain. Here we present two calculations of the mean strength of the meridional overturning of the stratosphere. We analyse satellite data that document the global diabatic circulation between 2007–2011, and compare these to three reanalysis data sets and to simulations with a state-of-the-art chemistry–climate model. Using measurements of sulfur hexafluoride (SF6) and nitrous oxide, we calculate the global mean diabatic overturning mass flux throughout the stratosphere. In the lower stratosphere, these two estimates agree, and at a potential temperature level of 460 K (about 20 km or 60 hPa in tropics) the global circulation strength is 6.3–7.6 × 109 kg s−1. Higher in the atmosphere, only the SF6-based estimate is available, and it diverges from the reanalysis data and simulations. Interpretation of the SF6-data-based estimate is limited because of a mesospheric sink of SF6; however, the reanalyses also differ substantially from each other. We conclude that the uncertainty in the mean meridional overturning circulation strength at upper levels of the stratosphere amounts to at least 100%.

    更新日期:2017-09-05
  • A spatially resolved estimate of High Mountain Asia glacier mass balances from 2000 to 2016
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-07
    Fanny Brun, Etienne Berthier, Patrick Wagnon, Andreas Kääb, Désirée Treichler

    High Mountain Asia hosts the largest glacier concentration outside the polar regions. These glaciers are important contributors to streamflow in one of the most populated areas of the world. Past studies have used methods that can provide only regionally averaged glacier mass balances to assess the glacier contribution to rivers and sea level rise. Here we compute the mass balance for about 92% of the glacierized area of High Mountain Asia using time series of digital elevation models derived from satellite stereo-imagery. We calculate a total mass change of −16.3 ± 3.5 Gt yr−1 (−0.18 ± 0.04 m w.e. yr−1) between 2000 and 2016, which is less negative than most previous estimates. Region-wide mass balances vary from −4.0 ± 1.5 Gt yr−1 (−0.62 ± 0.23 m w.e. yr−1) in Nyainqentanglha to +1.4 ± 0.8 Gt yr−1 (+0.14 ± 0.08 m w.e. yr−1) in Kunlun, with large intra-regional variability of individual glacier mass balances (standard deviation within a region ~0.20 m w.e. yr−1). Specifically, our results shed light on the Nyainqentanglha and Pamir glacier mass changes, for which contradictory estimates exist in the literature. They provide crucial information for the calibration of the models used for projecting glacier response to climatic change, as these models do not capture the pattern, magnitude and intra-regional variability of glacier changes at present.

    更新日期:2017-09-05
  • Small fraction of marine cloud condensation nuclei made up of sea spray aerosol
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-14
    P. K. Quinn, D. J. Coffman, J. E. Johnson, L. M. Upchurch, T. S. Bates

    Sea spray aerosols impact Earth’s radiation balance by directly scattering solar radiation. They also act as cloud condensation nuclei, thereby altering cloud properties including reflectivity, lifetime and extent. The influence of sea spray aerosol on cloud properties is thought to be particularly strong over remote ocean regions devoid of continental particles. Yet the contribution of sea spray aerosol to the population of cloud condensation nuclei in the marine boundary layer remains poorly understood. Here, using a lognormal-mode-fitting procedure, we isolate sea spray aerosols from measurements of particle size and abundance over the Pacific, Southern, Arctic and Atlantic oceans to determine the contribution of sea spray aerosol to the population of cloud condensation nuclei in the marine boundary layer. On a global basis, with the exception of the high southern latitudes, sea spray aerosol makes a contribution of less than 30% to the cloud condensation nuclei population for air that is supersaturated at 0.1 to 1.0%—the supersaturation range typical of marine boundary layer clouds. Instead, the cloud condensation nuclei population between 70° S and 80° N is composed primarily of non-sea-salt sulfate aerosols, due to large-scale meteorological features that result in entrainment of particles from the free troposphere.

    更新日期:2017-09-05
  • Rapid post-seismic landslide evacuation boosted by dynamic river width
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-14
    Thomas Croissant, Dimitri Lague, Philippe Steer, Philippe Davy

    Mass wasting caused by large-magnitude earthquakes chokes mountain rivers with several cubic kilometres of sediment. The timescale and mechanisms by which rivers evacuate small to gigantic landslide deposits are poorly known, but are critical for predicting post-seismic geomorphic hazards, interpreting the signature of earthquakes in sedimentary archives and deciphering the coupling between erosion and tectonics. Here, we use a new 2D hydro-sedimentary evolution model to demonstrate that river self-organization into a narrower alluvial channel overlying the bedrock valley dramatically increases sediment transport capacity and reduces export time of gigantic landslides by orders of magnitude compared with existing theory. Predicted export times obey a universal non-linear relationship of landslide volume and pre-landslide valley transport capacity. Upscaling these results to realistic populations of landslides shows that removing half of the total coarse sediment volume introduced by large earthquakes in the fluvial network would typically take 5 to 25 years in various tectonically active mountain belts, with little impact of earthquake magnitude and climate. Dynamic alluvial channel narrowing is therefore a key, previously unrecognized mechanism by which mountain rivers rapidly digest extreme events and maintain their capacity to incise uplifted rocks.

    更新日期:2017-09-05
  • Fluid-driven metamorphism of the continental crust governed by nanoscale fluid flow
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-14
    Oliver Plümper, Alexandru Botan, Catharina Los, Yang Liu, Anders Malthe-Sørenssen, Bjørn Jamtveit

    The transport of fluids through the Earth’s crust controls the redistribution of elements to form mineral and hydrocarbon deposits, the release and sequestration of greenhouse gases, and facilitates metamorphic reactions that influence lithospheric rheology. In permeable systems with a well-connected porosity, fluid transport is largely driven by fluid pressure gradients. In less permeable rocks, deformation may induce permeability by creating interconnected heterogeneities, but without these perturbations, mass transport is limited along grain boundaries or relies on transformation processes that self-generate transient fluid pathways. The latter can facilitate large-scale fluid and mass transport in nominally impermeable rocks without large-scale fluid transport pathways. Here, we show that pervasive, fluid-driven metamorphism of crustal igneous rocks is directly coupled to the production of nanoscale porosity. Using multi-dimensional nano-imaging and molecular dynamics simulations, we demonstrate that in feldspar, the most abundant mineral family in the Earth’s crust, electrokinetic transport through reaction-induced nanopores (<100 nm) can potentially be significant. This suggests that metamorphic fluid flow and fluid-mediated mineral transformation reactions can be considerably influenced by nanofluidic transport phenomena.

    更新日期:2017-09-05
  • Anatomy of a meltwater drainage system beneath the ancestral East Antarctic ice sheet
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-21
    Lauren M. Simkins, John B. Anderson, Sarah L. Greenwood, Helge M. Gonnermann, Lindsay O. Prothro, Anna Ruth W. Halberstadt, Leigh A. Stearns, David Pollard, Robert M. DeConto

    Subglacial hydrology is critical to understand the behaviour of ice sheets, yet active meltwater drainage beneath contemporary ice sheets is rarely accessible to direct observation. Using geophysical and sedimentological data from the deglaciated western Ross Sea, we identify a palaeo-subglacial hydrological system active beneath an area formerly covered by the East Antarctic ice sheet. A long channel network repeatedly delivered meltwater to an ice stream grounding line and was a persistent pathway for episodic meltwater drainage events. Embayments within grounding-line landforms coincide with the location of subglacial channels, marking reduced sedimentation and restricted landform growth. Consequently, channelized drainage at the grounding line influenced the degree to which these landforms could provide stability feedbacks to the ice stream. The channel network was connected to upstream subglacial lakes in an area of geologically recent rifting and volcanism, where elevated heat flux would have produced sufficient basal melting to fill the lakes over decades to several centuries; this timescale is consistent with our estimates of the frequency of drainage events at the retreating grounding line. Based on these data, we hypothesize that ice stream dynamics in this region were sensitive to the underlying hydrological system.

    更新日期:2017-09-05
  • Emergence of silicic continents as the lower crust peels off on a hot plate-tectonic Earth
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-21
    Priyadarshi Chowdhury, Taras Gerya, Sumit Chakraborty

    The rock record and geochemical evidence indicate that continental recycling has been occurring since the early history of the Earth. The stabilization of felsic continents in place of Earth’s early mafic crust about 3.0 to 2.0 billion years ago, perhaps due to the initiation of plate tectonics, implies widespread destruction of mafic crust during this time interval. However, the physical mechanisms of such intense recycling on a hotter, (late) Archaean and presumably plate-tectonic Earth remain largely unknown. Here we use thermomechanical modelling to show that extensive recycling via lower crustal peeling-off (delamination but not eclogitic dripping) during continent–continent convergence was near ubiquitous during the late Archaean to early Proterozoic. We propose that such destruction of the early mafic crust, together with felsic magmatism, may have caused both the emergence of silicic continents and their subsequent isostatic rise, possibly above the sea level. Such changes in the continental character have been proposed to influence the Great Oxidation Event and, therefore, peeling-off plate tectonics could be the geodynamic trigger for this event. A transition to the slab break-off controlled syn-orogenic recycling occurred as the Earth aged and cooled, leading to reduced recycling and enhanced preservation of the continental crust of present-day composition.

    更新日期:2017-09-05
  • Abundant carbon in the mantle beneath Hawai‘i
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-21
    Kyle R. Anderson, Michael P. Poland

    Estimates of carbon concentrations in Earth’s mantle vary over more than an order of magnitude, hindering our ability to understand mantle structure and mineralogy, partial melting, and the carbon cycle. CO2 concentrations in mantle-derived magmas supplying hotspot ocean island volcanoes yield our most direct constraints on mantle carbon, but are extensively modified by degassing during ascent. Here we show that undegassed magmatic and mantle carbon concentrations may be estimated in a Bayesian framework using diverse geologic information at an ocean island volcano. Our CO2 concentration estimates do not rely upon complex degassing models, geochemical tracer elements, assumed magma supply rates, or rare undegassed rock samples. Rather, we couple volcanic CO2 emission rates with probabilistic magma supply rates, which are obtained indirectly from magma storage and eruption rates. We estimate that the CO2 content of mantle-derived magma supplying Hawai‘i’s active volcanoes is 0.97−0.19+0.25 wt%—roughly 40% higher than previously believed—and is supplied from a mantle source region with a carbon concentration of 263−62+81 ppm. Our results suggest that mantle plumes and ocean island basalts are carbon-rich. Our data also shed light on helium isotope abundances, CO2/Nb ratios, and may imply higher CO2 emission rates from ocean island volcanoes.

    更新日期:2017-09-05
  • Progress from catastrophe
    Nat. Geosci. (IF 13.941) Pub Date : 2017-08-01

    Natural disasters can devastate local communities. However, these rare events also often trigger new ways of thinking, and provide a treasure trove of data that must be used to reduce vulnerability.

    更新日期:2017-08-02
  • Geomorphology: Origins of low-relief plateaus
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-10
    Annina Margreth

    Relatively flat, low-relief plateaus contrast with glacially carved, deep fjords. Computational experiments suggest that these astonishing landscapes are formed exclusively by glaciers.

    更新日期:2017-08-02
  • Biogeochemistry: Warmer Arctic weakens vegetation
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-10
    Ana Bastos

    Warm conditions in the Arctic Ocean have been linked to cold mid-latitude winters. Observations and simulations suggest that warm Arctic anomalies lead to a dip in CO2 uptake capacity in North American ecosystems and to low crop productivity.

    更新日期:2017-08-02
  • Planetary science: Bypassing the habitable zone
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-31
    Andrew P. Ingersoll

    In our own solar system, Venus is too hot, Mars is too cold and Earth is just right. Simulations show that making an icy planet habitable is not as simple as melting its ice: many icy bodies swing from too cold to too hot, bypassing just right.

    更新日期:2017-08-02
  • National baselines for the Sustainable Development Goals assessed in the SDG Index and Dashboards
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-17
    Guido Schmidt-Traub, Christian Kroll, Katerina Teksoz, David Durand-Delacre, Jeffrey D. Sachs

    The Sustainable Development Goals map out a broad spectrum of objectives. Analytical tools in form of the Index and Dashboards provide a starting point to set national baselines, and allow comparison of the SDGs with other indices of well-being.

    更新日期:2017-08-02
  • Abrupt climate transition of icy worlds from snowball to moist or runaway greenhouse
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-31
    Jun Yang, Feng Ding, Ramses M. Ramirez, W. R. Peltier, Yongyun Hu, Yonggang Liu

    Ongoing and future space missions aim to identify potentially habitable planets in our Solar System and beyond. Planetary habitability is determined not only by a planet’s current stellar insolation and atmospheric properties, but also by the evolutionary history of its climate. It has been suggested that icy planets and moons become habitable after their initial ice shield melts as their host stars brighten. Here we show from global climate model simulations that a habitable state is not achieved in the climatic evolution of those icy planets and moons that possess an inactive carbonate–silicate cycle and low concentrations of greenhouse gases. Examples for such planetary bodies are the icy moons Europa and Enceladus, and certain icy exoplanets orbiting G and F stars. We find that the stellar fluxes that are required to overcome a planet’s initial snowball state are so large that they lead to significant water loss and preclude a habitable planet. Specifically, they exceed the moist greenhouse limit, at which water vapour accumulates at high altitudes where it can readily escape, or the runaway greenhouse limit, at which the strength of the greenhouse increases until the oceans boil away. We suggest that some icy planetary bodies may transition directly to a moist or runaway greenhouse without passing through a habitable Earth-like state.

    更新日期:2017-08-02
  • Remote detection of widespread indigenous water in lunar pyroclastic deposits
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-24
    Ralph E. Milliken, Shuai Li

    Laboratory analyses of lunar samples provide a direct means to identify indigenous volatiles and have been used to argue for the presence of Earth-like water content in the lunar interior. Some volatile elements, however, have been interpreted as evidence for a bulk lunar mantle that is dry. Here we demonstrate that, for a number of lunar pyroclastic deposits, near-infrared reflectance spectra acquired by the Moon Mineralogy Mapper instrument onboard the Chandrayaan-1 orbiter exhibit absorptions consistent with enhanced OH- and/or H2O-bearing materials. These enhancements suggest a widespread occurrence of water in pyroclastic materials sourced from the deep lunar interior, and thus an indigenous origin. Water abundances of up to 150 ppm are estimated for large pyroclastic deposits, with localized values of about 300 to 400 ppm at potential vent areas. Enhanced water content associated with lunar pyroclastic deposits and the large areal extent, widespread distribution and variable chemistry of these deposits on the lunar surface are consistent with significant water in the bulk lunar mantle. We therefore suggest that water-bearing volcanic glasses from Apollo landing sites are not anomalous, and volatile loss during pyroclastic eruptions may represent a significant pathway for the transport of water to the lunar surface.

    更新日期:2017-08-02
  • Hemispheric climate shifts driven by anthropogenic aerosol–cloud interactions
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-17
    Eui-Seok Chung, Brian J. Soden

    The contrasting rainfall between the wet tropics and the dry subtropics largely determines the climate of the tropical zones. A southward shift of these rain belts has been observed throughout the latter half of the twentieth century, with profound societal consequences. Although such large-scale shifts in rainfall have been linked to interhemispheric temperature gradients from anthropogenic aerosols, a complete understanding of this mechanism has been hindered by the lack of explicit information on aerosol radiative effects. Here we quantify the relative contributions of radiative forcing from anthropogenic aerosols to the interhemispheric asymmetry in temperature and precipitation change for climate change simulations. We show that in model simulations the vast majority of the precipitation shift does not result from aerosols directly through their absorption and scattering of radiation, but rather indirectly through their modification of cloud radiative properties. Models with larger cloud responses to aerosol forcing are found to better reproduce the observed interhemispheric temperature changes and tropical rain belt shifts over the twentieth century, suggesting that aerosol–cloud interactions will play a key role in determining future interhemispheric shifts in climate.

    更新日期:2017-08-02
  • Reduced North American terrestrial primary productivity linked to anomalous Arctic warming
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-10
    Jin-Soo Kim, Jong-Seong Kug, Su-Jong Jeong, Deborah N. Huntzinger, Anna M. Michalak, Christopher R. Schwalm, Yaxing Wei, Kevin Schaefer

    Warming temperatures in the Northern Hemisphere have enhanced terrestrial productivity. Despite the warming trend, North America has experienced more frequent and more intense cold weather events during winters and springs. These events have been linked to anomalous Arctic warming since 1990, and may affect terrestrial processes. Here we analyse multiple observation data sets and numerical model simulations to evaluate links between Arctic temperatures and primary productivity in North America. We find that positive springtime temperature anomalies in the Arctic have led to negative anomalies in gross primary productivity over most of North America during the last three decades, which amount to a net productivity decline of 0.31 PgC yr−1 across the continent. This decline is mainly explained by two factors: severe cold conditions in northern North America and lower precipitation in the South Central United States. In addition, United States crop-yield data reveal that during years experiencing anomalous warming in the Arctic, yields declined by approximately 1 to 4% on average, with individual states experiencing declines of up to 20%. We conclude that the strengthening of Arctic warming anomalies in the past decades has remotely reduced productivity over North America.

    更新日期:2017-08-02
  • Microbial substrate preference dictated by energy demand rather than supply
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-03
    Maximiliano J. Amenabar, Everett L. Shock, Eric E. Roden, John W. Peters, Eric S. Boyd

    Growth substrates that maximize energy yield are widely thought to be utilized preferentially by microorganisms. However, observed distributions of microorganisms and their activities often deviate from predictions based solely on thermodynamic considerations of substrate energy supply. Here we present observations of the bioenergetics and growth yields of a metabolically flexible, thermophilic strain of the archaeon Acidianus when grown autotrophically on minimal medium with hydrogen (H2) or elemental sulfur (S°) as an electron donor, and S° or ferric iron (Fe3+) as an electron acceptor. Thermodynamic calculations indicate that S°/Fe3+ and H2/Fe3+ yield three- and fourfold more energy per mole of electrons transferred, respectively, than the H2/S° couple. However, biomass yields in Acidianus cultures provided with H2/S° were eightfold greater than when provided S°/Fe3+ or H2/Fe3+, indicating that the H2/S° redox couple is preferred. Indeed, cells provided with all three growth substrates (H2, Fe3+ and S°) grew preferentially by reduction of S° with H2. We conclude that substrate preference is dictated by differences in the energy demand of electron transfer reactions in Acidianus when grown with different substrates, rather than substrate energy supply.

    更新日期:2017-08-02
  • Microbial oxidation as a methane sink beneath the West Antarctic Ice Sheet
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-31
    Alexander B. Michaud, John E. Dore, Amanda M. Achberger, Brent C. Christner, Andrew C. Mitchell, Mark L. Skidmore, Trista J. Vick-Majors, John C. Priscu

    Aquatic habitats beneath ice masses contain active microbial ecosystems capable of cycling important greenhouse gases, such as methane (CH4). A large methane reservoir is thought to exist beneath the West Antarctic Ice Sheet, but its quantity, source and ultimate fate are poorly understood. For instance, O2 supplied by basal melting should result in conditions favourable for aerobic methane oxidation. Here we use measurements of methane concentrations and stable isotope compositions along with genomic analyses to assess the sources and cycling of methane in Subglacial Lake Whillans (SLW) in West Antarctica. We show that sub-ice-sheet methane is produced through the biological reduction of CO2 using H2. This methane pool is subsequently consumed by aerobic, bacterial methane oxidation at the SLW sediment–water interface. Bacterial oxidation consumes >99% of the methane and represents a significant methane sink, and source of biomass carbon and metabolic energy to the surficial SLW sediments. We conclude that aerobic methanotrophy may mitigate the release of methane to the atmosphere upon subglacial water drainage to ice sheet margins and during periods of deglaciation.

    更新日期:2017-08-02
  • High levels of endocrine pollutants in US streams during low flow due to insufficient wastewater dilution
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-10
    Jacelyn Rice, Paul Westerhoff

    Wastewater discharges from publicly owned treatment works are a significant source of endocrine disruptors and other contaminants to the aquatic environment in the US. Although remaining pollutants in wastewater pose environmental risks, treated wastewater is also a primary source of stream flow, which in turn is critical in maintaining many aquatic and riparian wildlife habitats. Here we calculate the dilution factor—the ratio of flow in the stream receiving discharge to the flow of wastewater discharge—for over 14,000 receiving streams in the continental US using streamflow observations and a spatially explicit watershed-scale hydraulic model. We found that wastewater discharges make up more than 50% of in-stream flow for over 900 streams. However, in 1,049 streams that experienced exceptional low-flow conditions, the dilution factors in 635 of those streams fell so low during those conditions that the safety threshold for concentrations of one endocrine disrupting compound was exceeded, and in roughly a third of those streams, the threshold was exceeded for two compounds. We suggest that streams are vulnerable to public wastewater discharge of contaminants under low-flow conditions, at a time when wastewater discharges are likely to be most important for maintaining stream flow for smaller sized river systems.

    更新日期:2017-08-02
  • Formation of plateau landscapes on glaciated continental margins
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-10
    David L. Egholm, John D. Jansen, Christian F. Brædstrup, Vivi K. Pedersen, Jane L. Andersen, Sofie V. Ugelvig, Nicolaj K. Larsen, Mads F. Knudsen

    Low-relief plateaus separated by deeply incised fjords are hallmarks of glaciated, passive continental margins. Spectacular examples fringe the once ice-covered North Atlantic coasts of Greenland, Norway and Canada, but low-relief plateau landscapes also underlie present-day ice sheets in Antarctica and Greenland. Dissected plateaus have long been viewed as the outcome of selective linear erosion by ice sheets that focus incision in glacial troughs, leaving the intervening landscapes essentially unaffected. According to this hypothesis, the plateaus are remnants of preglacial low-relief topography. However, here we use computational experiments to show that, like fjords, plateaus are emergent properties of long-term ice-sheet erosion. Ice sheets can either increase or decrease subglacial relief depending on the wavelength of the underlying topography, and plateau topography arises dynamically from evolving feedbacks between topography, ice dynamics and erosion over million-year timescales. This new mechanistic explanation for plateau formation opens the possibility of plateaus contributing significantly to accelerated sediment flux at the onset of the late Cenozoic glaciations, before becoming stable later in the Quaternary.

    更新日期:2017-08-02
  • Dynamics and early post-tsunami evolution of floating marine debris near Fukushima Daiichi
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-03
    John Philip Matthews, Lev Ostrovsky, Yutaka Yoshikawa, Satoru Komori, Hitoshi Tamura

    The devastating tsunami triggered by the Tōhoku-Oki earthquake of 11 March 2011 caused a crisis at the Fukushima Daiichi nuclear power station where it overtopped the seawall defences. On retreating, the tsunami carried loose debris and wreckage seaward and marshalled buoyant material into extensive plumes. Widespread concern over the fate of these and numerous other Tōhoku tsunami depositions prompted attempts to simulate debris dispersion throughout the wider Pacific. However, the effects of locally perturbed wind and wave fields, active Langmuir circulation and current-induced attrition determine a complex and poorly understood morphology for large floating agglomerations. Here we show that the early post-tsunami evolution of marine-debris plumes near Fukushima Daiichi was also shaped by near-surface wind modifications that took place above relatively calm (lower surface roughness) waters covered by surface films derived from oil and other contaminants. High-spatial-resolution satellite tracking reveals faster-than-expected floating-debris motions and invigorated plume evolution within these regions, while numerical modelling of turbulent air flow over the low-drag, film-covered surface predicts typically metre-per-second wind strengthening at centimetric heights, sufficient to explain the observed debris-speed increases. Wind restructuring probably stimulates the dispersion of flotsam from both biological and anthropogenic sources throughout a global ocean of highly variable surface roughness.

    更新日期:2017-08-02
  • A reverse energy cascade for crustal magma transport
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-10
    Leif Karlstrom, Scott R. Paterson, A. Mark Jellinek

    Direct constraints on the ascent, storage and eruption of mantle melts come primarily from exhumed, long-frozen intrusions. These structures, relics of a dynamic magma transport network, encode how Earth’s crust grows and differentiates over time. Furthermore, they connect mantle melting to an evolving distribution of surface volcanism. Disentangling magma transport processes from the plutonic record is consequently a seminal but unsolved problem. Here we use field data analyses, scaling theory and numerical simulations to show that the size distribution of intrusions preserved as plutonic complexes in the North American Cordillera suggests a transition in the mechanical response of crustal rocks to protracted episodes of magmatism. Intrusion sizes larger than about 100 m follow a power-law scaling expected if energy delivered from the mantle to open very thin dykes and sills is transferred to intrusions of increasing size. Merging, assimilation and mixing of small intrusions into larger ones occurs until irreversible deformation and solidification dissipate available energy. Mantle magma supply over tens to hundreds of thousands of years will trigger this regime, a type of reverse energy cascade, depending on the influx rate and efficiency of crustal heating by intrusions. Identifying regimes of magma transport provides a framework for inferring subsurface magmatic processes from surface patterns of volcanism, information preservation in the plutonic record, and related effects including climate.

    更新日期:2017-08-02
  • Tsunamigenic structures in a creeping section of the Alaska subduction zone
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-24
    Anne Bécel, Donna J. Shillington, Matthias Delescluse, Mladen R. Nedimović, Geoffrey A. Abers, Demian M. Saffer, Spahr C. Webb, Katie M. Keranen, Pierre-Henri Roche, Jiyao Li, Harold Kuehn

    Segments of subduction zones that are capable of generating tsunamigenic earthquakes appear to have characteristic structural configurations. These structures include heterogeneous plate interfaces, a small wedge of deformed sediment at the toe of the overriding plate (the frontal prism), and splay faults in the crust of the overriding plate that root within the plate boundary megathrust. Here we use seismic reflection imaging to show that these features also exist within a creeping segment of the Alaska subduction zone, the Shumagin Gap. We identify an active crustal-scale normal fault system that dips landward and resembles that involved in the 2011 Tohoku-oki earthquake in Japan. We also find that the Shumagin Gap has a small frontal prism, a deep-water splay fault, and that the plate interface here is rough and thinly sedimented. We propose that lateral propagation of rupture from a neighbouring segment into the Shumagin Gap may explain a tsunamigenic earthquake that occurred there in 1788 and that tsunamigenic potential should be considered in hazard assessments for the region. Our results demonstrate that structural configurations similar to those in Tohoku may exist in other subduction zones, including within creeping segments or segments with no record of historical megathrust earthquakes, but are under-recognized. Identifying similar configurations globally may improve our ability to anticipate regions capable of generating large tsunamis.

    更新日期:2017-08-02
  • Planetary science: Bypassing the habitable zone
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-31

    In our own solar system, Venus is too hot, Mars is too cold and Earth is just right. Simulations show that making an icy planet habitable is not as simple as melting its ice: many icy bodies swing from too cold to too hot, bypassing just right.

    更新日期:2017-07-31
  • Microbial oxidation as a methane sink beneath the West Antarctic Ice Sheet
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-31
    Alexander B. Michaud, John E. Dore, Amanda M. Achberger, Brent C. Christner, Andrew C. Mitchell, Mark L. Skidmore, Trista J. Vick-Majors, John C. Priscu

    Aquatic habitats beneath ice masses contain active microbial ecosystems capable of cycling important greenhouse gases, such as methane (CH4). A large methane reservoir is thought to exist beneath the West Antarctic Ice Sheet, but its quantity, source and ultimate fate are poorly understood. For instance, O2 supplied by basal melting should result in conditions favourable for aerobic methane oxidation. Here we use measurements of methane concentrations and stable isotope compositions along with genomic analyses to assess the sources and cycling of methane in Subglacial Lake Whillans (SLW) in West Antarctica. We show that sub-ice-sheet methane is produced through the biological reduction of CO2 using H2. This methane pool is subsequently consumed by aerobic, bacterial methane oxidation at the SLW sediment–water interface. Bacterial oxidation consumes >99% of the methane and represents a significant methane sink, and source of biomass carbon and metabolic energy to the surficial SLW sediments. We conclude that aerobic methanotrophy may mitigate the release of methane to the atmosphere upon subglacial water drainage to ice sheet margins and during periods of deglaciation.

    更新日期:2017-07-31
  • Abrupt climate transition of icy worlds from snowball to moist or runaway greenhouse
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-31
    Jun Yang, Feng Ding, Ramses M. Ramirez, W. R. Peltier, Yongyun Hu, Yonggang Liu

    Ongoing and future space missions aim to identify potentially habitable planets in our Solar System and beyond. Planetary habitability is determined not only by a planet’s current stellar insolation and atmospheric properties, but also by the evolutionary history of its climate. It has been suggested that icy planets and moons become habitable after their initial ice shield melts as their host stars brighten. Here we show from global climate model simulations that a habitable state is not achieved in the climatic evolution of those icy planets and moons that possess an inactive carbonate–silicate cycle and low concentrations of greenhouse gases. Examples for such planetary bodies are the icy moons Europa and Enceladus, and certain icy exoplanets orbiting G and F stars. We find that the stellar fluxes that are required to overcome a planet’s initial snowball state are so large that they lead to significant water loss and preclude a habitable planet. Specifically, they exceed the moist greenhouse limit, at which water vapour accumulates at high altitudes where it can readily escape, or the runaway greenhouse limit, at which the strength of the greenhouse increases until the oceans boil away. We suggest that some icy planetary bodies may transition directly to a moist or runaway greenhouse without passing through a habitable Earth-like state.

    更新日期:2017-07-31
  • Tsunamigenic structures in a creeping section of the Alaska subduction zone
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-24
    Anne Bécel, Donna J. Shillington, Matthias Delescluse, Mladen R. Nedimović, Geoffrey A. Abers, Demian M. Saffer, Spahr C. Webb, Katie M. Keranen, Pierre-Henri Roche, Jiyao Li, Harold Kuehn

    Segments of subduction zones that are capable of generating tsunamigenic earthquakes appear to have characteristic structural configurations. These structures include heterogeneous plate interfaces, a small wedge of deformed sediment at the toe of the overriding plate (the frontal prism), and splay faults in the crust of the overriding plate that root within the plate boundary megathrust. Here we use seismic reflection imaging to show that these features also exist within a creeping segment of the Alaska subduction zone, the Shumagin Gap. We identify an active crustal-scale normal fault system that dips landward and resembles that involved in the 2011 Tohoku-oki earthquake in Japan. We also find that the Shumagin Gap has a small frontal prism, a deep-water splay fault, and that the plate interface here is rough and thinly sedimented. We propose that lateral propagation of rupture from a neighbouring segment into the Shumagin Gap may explain a tsunamigenic earthquake that occurred there in 1788 and that tsunamigenic potential should be considered in hazard assessments for the region. Our results demonstrate that structural configurations similar to those in Tohoku may exist in other subduction zones, including within creeping segments or segments with no record of historical megathrust earthquakes, but are under-recognized. Identifying similar configurations globally may improve our ability to anticipate regions capable of generating large tsunamis.

    更新日期:2017-07-25
  • Remote detection of widespread indigenous water in lunar pyroclastic deposits
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-24
    Ralph E. Milliken, Shuai Li

    Laboratory analyses of lunar samples provide a direct means to identify indigenous volatiles and have been used to argue for the presence of Earth-like water content in the lunar interior. Some volatile elements, however, have been interpreted as evidence for a bulk lunar mantle that is dry. Here we demonstrate that, for a number of lunar pyroclastic deposits, near-infrared reflectance spectra acquired by the Moon Mineralogy Mapper instrument onboard the Chandrayaan-1 orbiter exhibit absorptions consistent with enhanced OH- and/or H2O-bearing materials. These enhancements suggest a widespread occurrence of water in pyroclastic materials sourced from the deep lunar interior, and thus an indigenous origin. Water abundances of up to 150 ppm are estimated for large pyroclastic deposits, with localized values of about 300 to 400 ppm at potential vent areas. Enhanced water content associated with lunar pyroclastic deposits and the large areal extent, widespread distribution and variable chemistry of these deposits on the lunar surface are consistent with significant water in the bulk lunar mantle. We therefore suggest that water-bearing volcanic glasses from Apollo landing sites are not anomalous, and volatile loss during pyroclastic eruptions may represent a significant pathway for the transport of water to the lunar surface.

    更新日期:2017-07-25
  • National baselines for the Sustainable Development Goals assessed in the SDG Index and Dashboards
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-17

    The Sustainable Development Goals map out a broad spectrum of objectives. Analytical tools in form of the Index and Dashboards provide a starting point to set national baselines, and allow comparison of the SDGs with other indices of well-being.

    更新日期:2017-07-18
  • Hemispheric climate shifts driven by anthropogenic aerosol–cloud interactions
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-17

    A southward shift of the tropical rainbelts over the late twentieth century has been attributed. Climate simulations suggest that the mechanism for this influence lies largely with the interaction of aerosols with clouds.

    更新日期:2017-07-18
  • Biogeochemistry: Warmer Arctic weakens vegetation
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-10
    Ana Bastos

    Warm conditions in the Arctic Ocean have been linked to cold mid-latitude winters. Observations and simulations suggest that warm Arctic anomalies lead to a dip in CO2 uptake capacity in North American ecosystems and to low crop productivity.

    更新日期:2017-07-11
  • Geomorphology: Origins of low-relief plateaus
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-10
    Annina Margreth

    Relatively flat, low-relief plateaus contrast with glacially carved, deep fjords. Computational experiments suggest that these astonishing landscapes are formed exclusively by glaciers.

    更新日期:2017-07-11
  • Formation of plateau landscapes on glaciated continental margins
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-10
    David L. Egholm, John D. Jansen, Christian F. Brædstrup, Vivi K. Pedersen, Jane L. Andersen, Sofie V. Ugelvig, Nicolaj K. Larsen, Mads F. Knudsen

    Low-relief plateaus separated by deeply incised fjords are hallmarks of glaciated, passive continental margins. Spectacular examples fringe the once ice-covered North Atlantic coasts of Greenland, Norway and Canada, but low-relief plateau landscapes also underlie present-day ice sheets in Antarctica and Greenland. Dissected plateaus have long been viewed as the outcome of selective linear erosion by ice sheets that focus incision in glacial troughs, leaving the intervening landscapes essentially unaffected. According to this hypothesis, the plateaus are remnants of preglacial low-relief topography. However, here we use computational experiments to show that, like fjords, plateaus are emergent properties of long-term ice-sheet erosion. Ice sheets can either increase or decrease subglacial relief depending on the wavelength of the underlying topography, and plateau topography arises dynamically from evolving feedbacks between topography, ice dynamics and erosion over million-year timescales. This new mechanistic explanation for plateau formation opens the possibility of plateaus contributing significantly to accelerated sediment flux at the onset of the late Cenozoic glaciations, before becoming stable later in the Quaternary.

    更新日期:2017-07-11
  • A reverse energy cascade for crustal magma transport
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-10
    Leif Karlstrom, Scott R. Paterson, A. Mark Jellinek

    Direct constraints on the ascent, storage and eruption of mantle melts come primarily from exhumed, long-frozen intrusions. These structures, relics of a dynamic magma transport network, encode how Earth’s crust grows and differentiates over time. Furthermore, they connect mantle melting to an evolving distribution of surface volcanism. Disentangling magma transport processes from the plutonic record is consequently a seminal but unsolved problem. Here we use field data analyses, scaling theory and numerical simulations to show that the size distribution of intrusions preserved as plutonic complexes in the North American Cordillera suggests a transition in the mechanical response of crustal rocks to protracted episodes of magmatism. Intrusion sizes larger than about 100 m follow a power-law scaling expected if energy delivered from the mantle to open very thin dykes and sills is transferred to intrusions of increasing size. Merging, assimilation and mixing of small intrusions into larger ones occurs until irreversible deformation and solidification dissipate available energy. Mantle magma supply over tens to hundreds of thousands of years will trigger this regime, a type of reverse energy cascade, depending on the influx rate and efficiency of crustal heating by intrusions. Identifying regimes of magma transport provides a framework for inferring subsurface magmatic processes from surface patterns of volcanism, information preservation in the plutonic record, and related effects including climate.

    更新日期:2017-07-11
  • Reduced North American terrestrial primary productivity linked to anomalous Arctic warming
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-10
    Jin-Soo Kim, Jong-Seong Kug, Su-Jong Jeong, Deborah N. Huntzinger, Anna M. Michalak, Christopher R. Schwalm, Yaxing Wei, Kevin Schaefer

    Warming temperatures in the Northern Hemisphere have enhanced terrestrial productivity. Despite the warming trend, North America has experienced more frequent and more intense cold weather events during winters and springs. These events have been linked to anomalous Arctic warming since 1990, and may affect terrestrial processes. Here we analyse multiple observation data sets and numerical model simulations to evaluate links between Arctic temperatures and primary productivity in North America. We find that positive springtime temperature anomalies in the Arctic have led to negative anomalies in gross primary productivity over most of North America during the last three decades, which amount to a net productivity decline of 0.31 PgC yr−1 across the continent. This decline is mainly explained by two factors: severe cold conditions in northern North America and lower precipitation in the South Central United States. In addition, United States crop-yield data reveal that during years experiencing anomalous warming in the Arctic, yields declined by approximately 1 to 4% on average, with individual states experiencing declines of up to 20%. We conclude that the strengthening of Arctic warming anomalies in the past decades has remotely reduced productivity over North America.

    更新日期:2017-07-11
  • High levels of endocrine pollutants in US streams during low flow due to insufficient wastewater dilution
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-10
    Jacelyn Rice, Paul Westerhoff

    Wastewater discharges from publicly owned treatment works are a significant source of endocrine disruptors and other contaminants to the aquatic environment in the US. Although remaining pollutants in wastewater pose environmental risks, treated wastewater is also a primary source of stream flow, which in turn is critical in maintaining many aquatic and riparian wildlife habitats. Here we calculate the dilution factor—the ratio of flow in the stream receiving discharge to the flow of wastewater discharge—for over 14,000 receiving streams in the continental US using streamflow observations and a spatially explicit watershed-scale hydraulic model. We found that wastewater discharges make up more than 50% of in-stream flow for over 900 streams. However, in 1,049 streams that experienced exceptional low-flow conditions, the dilution factors in 635 of those streams fell so low during those conditions that the safety threshold for concentrations of one endocrine disrupting compound was exceeded, and in roughly a third of those streams, the threshold was exceeded for two compounds. We suggest that streams are vulnerable to public wastewater discharge of contaminants under low-flow conditions, at a time when wastewater discharges are likely to be most important for maintaining stream flow for smaller sized river systems.

    更新日期:2017-07-11
  • Correction
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-04

    更新日期:2017-07-05
  • For people and planet
    Nat. Geosci. (IF 13.941) Pub Date : 2017-07-04

    The emerging field of geohealth links human well-being and ecosystem health. A deeper understanding of these linkages can help society mitigate the health costs of economic growth before they become crises.

    更新日期:2017-07-05
  • Biodiversity loss from deep-sea mining
    Nat. Geosci. (IF 13.941) Pub Date : 2017-06-26
    C. L. Van Dover, J. A. Ardron, E. Escobar, M. Gianni, K. M. Gjerde, A. Jaeckel, D. O. B. Jones, L. A. Levin, H. J. Niner, L. Pendleton, C. R. Smith, T. Thiele, P. J. Turner, L. Watling, P. P. E. Weaver

    更新日期:2017-07-05
  • Climate change narratives
    Nat. Geosci. (IF 13.941) Pub Date : 2017-06-26
    Richard D. Pancost

    Reconstructions of Earth's past are much more than benchmarks for climate models. They also help us comprehend risk by providing concrete narratives for diverse climates.

    更新日期:2017-07-05
  • Aquatic biogeochemistry: Cleaner Chinese lakes
    Nat. Geosci. (IF 13.941) Pub Date : 2017-06-12
    Jessica Corman

    Phosphorus loading can cause eutrophication of lakes. Analyses of lake chemistry in China reveal that policies have led to lower phosphorus levels overall, but increasing trends in some lakes suggest that expanded policies may be needed.

    更新日期:2017-07-05
  • Climate variability: The Atlantic's internal drum beat
    Nat. Geosci. (IF 13.941) Pub Date : 2017-05-29
    Sloan Coats, Jason E. Smerdon

    The North Atlantic region experiences climate variability on a range of timescales. A climate reconstruction suggests that large-magnitude, multidecadal internal variability was a robust feature over the past 1,200 years.

    更新日期:2017-07-05
  • The deep atmosphere of Venus and the possible role of density-driven separation of CO2 and N2
    Nat. Geosci. (IF 13.941) Pub Date : 2017-06-26
    Sebastien Lebonnois, Gerald Schubert

    The only temperature profile of the lowermost Venusian atmosphere appears unstable. Compositional heterogeneity due to density-driven separation of N2 from CO2 gas in the lower atmosphere of Venus may be a viable explanation.

    更新日期:2017-07-05
  • Causes of differences in model and satellite tropospheric warming rates
    Nat. Geosci. (IF 13.941) Pub Date : 2017-06-19
    Benjamin D. Santer, John C. Fyfe, Giuliana Pallotta, Gregory M. Flato, Gerald A. Meehl, Matthew H. England, Ed Hawkins, Michael E. Mann, Jeffrey F. Painter, Céline Bonfils, Ivana Cvijanovic, Carl Mears, Frank J. Wentz, Stephen Po-Chedley, Qiang Fu, Cheng-Zhi Zou

    In the early twenty-first century, satellite-derived tropospheric warming trends were generally smaller than trends estimated from a large multi-model ensemble. Because observations and coupled model simulations do not have the same phasing of natural internal variability, such decadal differences in simulated and observed warming rates invariably occur. Here we analyse global-mean tropospheric temperatures from satellites and climate model simulations to examine whether warming rate differences over the satellite era can be explained by internal climate variability alone. We find that in the last two decades of the twentieth century, differences between modelled and observed tropospheric temperature trends are broadly consistent with internal variability. Over most of the early twenty-first century, however, model tropospheric warming is substantially larger than observed; warming rate differences are generally outside the range of trends arising from internal variability. The probability that multi-decadal internal variability fully explains the asymmetry between the late twentieth and early twenty-first century results is low (between zero and about 9%). It is also unlikely that this asymmetry is due to the combined effects of internal variability and a model error in climate sensitivity. We conclude that model overestimation of tropospheric warming in the early twenty-first century is partly due to systematic deficiencies in some of the post-2000 external forcings used in the model simulations.

    更新日期:2017-07-05
  • Top-of-atmosphere radiative forcing affected by brown carbon in the upper troposphere
    Nat. Geosci. (IF 13.941) Pub Date : 2017-05-22
    Yuzhong Zhang, Haviland Forrister, Jiumeng Liu, Jack Dibb, Bruce Anderson, Joshua P. Schwarz, Anne E. Perring, Jose L. Jimenez, Pedro Campuzano-Jost, Yuhang Wang, Athanasios Nenes, Rodney J. Weber

    Carbonaceous aerosols affect the global radiative balance by absorbing and scattering radiation, which leads to warming or cooling of the atmosphere, respectively. Black carbon is the main light-absorbing component. A portion of the organic aerosol known as brown carbon also absorbs light. The climate sensitivity to absorbing aerosols rapidly increases with altitude, but brown carbon measurements are limited in the upper troposphere. Here we present aircraft observations of vertical aerosol distributions over the continental United States in May and June 2012 to show that light-absorbing brown carbon is prevalent in the troposphere, and absorbs more short-wavelength radiation than black carbon at altitudes between 5 and 12 km. We find that brown carbon is transported to these altitudes by deep convection, and that in-cloud heterogeneous processing may produce brown carbon. Radiative transfer calculations suggest that brown carbon accounts for about 24% of combined black and brown carbon warming effect at the tropopause. Roughly two-thirds of the estimated brown carbon forcing occurs above 5 km, although most brown carbon is found below 5 km. The highest radiative absorption occurred during an event that ingested a wildfire plume. We conclude that high-altitude brown carbon from biomass burning is an unappreciated component of climate forcing.

    更新日期:2017-07-05
  • Transition from high- to low-NOx control of night-time oxidation in the southeastern US
    Nat. Geosci. (IF 13.941) Pub Date : 2017-06-26
    P. M. Edwards, K. C. Aikin, W. P. Dube, J. L. Fry, J. B. Gilman, J. A. de Gouw, M. G. Graus, T. F. Hanisco, J. Holloway, G. Hübler, J. Kaiser, F. N. Keutsch, B. M. Lerner, J. A. Neuman, D. D. Parrish, J. Peischl, I. B. Pollack, A. R. Ravishankara, J. M. Roberts, T. B. Ryerson, M. Trainer, P. R. Veres, G. M. Wolfe, C. Warneke, S. S. Brown

    The influence of nitrogen oxides (NOx) on daytime atmospheric oxidation cycles is well known, with clearly defined high- and low-NOx regimes. During the day, oxidation reactions—which contribute to the formation of secondary pollutants such as ozone—are proportional to NOx at low levels, and inversely proportional to NOx at high levels. Night-time oxidation of volatile organic compounds also influences secondary pollutants but lacks a similar clear definition of high- and low-NOx regimes, even though such regimes exist. Decreases in anthropogenic NOx emissions in the US and Europe coincided with increases in Asia over the last 10 to 20 years, and have altered both daytime and nocturnal oxidation cycles. Here we present measurements of chemical species in the lower atmosphere from day- and night-time research flights over the southeast US in 1999 and 2013, supplemented by atmospheric chemistry simulations. We find that night-time oxidation of biogenic volatile organic compounds (BVOC) is NOx-limited when the ratio of NOx to BVOC is below approximately 0.5, and becomes independent of NOx at higher ratios. The night-time ratio of NOx to BVOC in 2013 averaged 0.6 aloft. We suggest that night-time oxidation in the southeast US is in transition between NOx-dominated and ozone-dominated.

    更新日期:2017-07-05
  • Hotspots of soil N2O emission enhanced through water absorption by plant residue
    Nat. Geosci. (IF 13.941) Pub Date : 2017-06-05
    A. N. Kravchenko, E. R. Toosi, A. K. Guber, N. E. Ostrom, J. Yu, K. Azeem, M. L. Rivers, G. P. Robertson

    N2O is a highly potent greenhouse gas and arable soils represent its major anthropogenic source. Field-scale assessments and predictions of soil N2O emission remain uncertain and imprecise due to the episodic and microscale nature of microbial N2O production, most of which occurs within very small discrete soil volumes. Such hotspots of N2O production are often associated with decomposing plant residue. Here we quantify physical and hydrological soil characteristics that lead to strikingly accelerated N2O emissions in plant residue-induced hotspots. Results reveal a mechanism for microscale N2O emissions: water absorption by plant residue that creates unique micro-environmental conditions, markedly different from those of the bulk soil. Moisture levels within plant residue exceeded those of bulk soil by 4–10-fold and led to accelerated N2O production via microbial denitrification. The presence of large (∅ >35 μm) pores was a prerequisite for maximized hotspot N2O production and for subsequent diffusion to the atmosphere. Understanding and modelling hotspot microscale physical and hydrologic characteristics is a promising route to predict N2O emissions and thus to develop effective mitigation strategies and estimate global fluxes in a changing environment.

    更新日期:2017-07-05
  • Substantial inorganic carbon sink in closed drainage basins globally
    Nat. Geosci. (IF 13.941) Pub Date : 2017-06-19
    Yu Li, Chengqi Zhang, Naiang Wang, Qin Han, Xinzhong Zhang, Yuan Liu, Lingmei Xu, Wangting Ye

    Arid and semi-arid ecosystems are increasingly recognized as important carbon storage sites. In these regions, extensive sequestration of dissolved inorganic carbon can occur in the terminal lakes of endorheic basins—basins that do not drain to external bodies of water. However, the global magnitude of this dissolved inorganic carbon sink is uncertain. Here we present isotopic, radiocarbon, and chemical analyses of groundwater, river water, and sediments from the terminal region of the endorheic Shiyang River drainage basin, in arid northwest China. We estimate that 0.13 Pg of dissolved inorganic carbon was stored in the basin during the mid-Holocene. Pollen-based reconstructions of basin-scale productivity suggest that the mid-Holocene dissolved inorganic carbon sink was two orders of magnitude smaller than terrestrial productivity in the basin. We use estimates of dissolved inorganic carbon storage based on sedimentary data from 11 terminal lakes of endorheic basins around the world as the basis for a global extrapolation of the sequestration of dissolved organic carbon in endorheic basins. We estimate that 0.152 Pg of dissolved inorganic carbon is buried per year today, compared to about 0.211 Pg C yr−1 during the mid-Holocene. We conclude that endorheic basins represent an important carbon sink on the global scale, with a magnitude similar to deep ocean carbon burial.

    更新日期:2017-07-05
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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