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  • ENSO atmospheric teleconnections and their response to greenhouse gas forcing
    Rev. Geophys. (IF 12.34) Pub Date : 2018-01-15
    Sang-Wook Yeh, Wenju Cai, Seung-Ki Min, Michael J. McPhaden, Dietmar Dommenget, Boris Dewitte, Matthew Collins, Karumuri Ashok, Soon-Il An, Bo-Young Yim, Jong-Seong Kug

    AbstractEl Niño and Southern Oscillation (ENSO) is the most prominent year-to-year climate fluctuation on Earth, alternating between anomalously warm (El Niño) and cold (La Niña) sea surface temperature (SST) conditions in the tropical Pacific. ENSO exerts its impacts on remote regions of the globe through atmospheric teleconnections, affecting extreme weather conditions worldwide. However, these teleconnections are inherently nonlinear and sensitive to ENSO SST anomaly patterns and amplitudes. In addition, teleconnections are modulated by variability in the oceanic mean state outside the tropics and by land and sea-ice extent. The character of ENSO as well as the ocean mean state have changed since the 1990s, which might be due to either natural variability, or anthropogenic forcing, or their combined influences. This has resulted in changes in ENSO atmospheric teleconnections in terms of precipitation and temperature in various parts of the globe. In addition, changes in ENSO teleconnection patterns have affected their predictability and the statistics of extreme events. However, the short observational record does not allow us to clearly distinguish which changes are robust and which are not. Climate models suggest that ENSO teleconnections will change because the mean atmospheric circulation will change due to anthropogenic forcing in the 21st century, which is independent of whether ENSO properties change or not. However, future ENSO teleconnection changes do not currently show strong inter-model agreement from region to region, highlighting the importance of identifying factors that affect uncertainty in future model projections.

    更新日期:2018-01-16
  • Projection of future runoff change using climate elasticity method derived from Budyko framework in major basins across China
    Glob. Planet. Change (IF 3.915) Pub Date : 2018-01-13
    Wanqiu Xing, Weiguang Wang, Shan Zou, Chao Deng

    This study established a climate elasticity method based on Budyko hypothesis and enhanced it by selecting the most effective Budyko-type formula to strengthen the runoff change prediction reliability. The spatiotemporal variations in hydrologic variables (i.e., runoff, precipitation and potential evaporation) during historical period were revealed first and the climate elasticities of runoff were investigated. The proposed climate elasticity method was also applied to project the spatiotemporal variations in future runoff and its key influencing factors in 35 watersheds across China. Wherein, the future climate series were retrieved by consulting the historical series, informed by four global climate models (GCMs) under representative concentration pathways from phase five of the Coupled Model Intercomparison Project. Wang-Tang equation was selected as the optimal Budyko-type equation for its best ability in reproducing the runoff change (with a coefficient of determination and mean absolute error of 0.998 and 1.36 mm, respectively). Observed runoff presents significant decreasing trends in the northern and increasing trends in the southern regions of China, and generally its change is identified to be more sensitive to climatic variables in Hai River Basin and lower Yellow River Basin. Compared to the runoff during the reference period, positive change rates in the north and negative change rates in the south of China in the mid-21st century can be practically generalized from the majority of GCMs projections. This maybe resulted from the increasing precipitation, especially in parts of northern basins. Meanwhile, GCMs project a consistently upward trend in potential evaporation although significant decreasing trends occur in the majority of catchments for the historical period. The results indicate that climate change will possibly bring some changes to the water resources over China in the mid-21st century and some countermeasures of water resources planning and management should be taken.

    更新日期:2018-01-13
  • Interannual sea level variability in the Pearl River Estuary and its response to El Niño–Southern Oscillation
    Glob. Planet. Change (IF 3.915) Pub Date : 2018-01-12
    Linlin Wang, Qiang Li, Xian-zhong Mao, Hongsheng Bi, Peng Yin

    The South China coast, especially the Pearl River Estuary (PRE) region, is prosperous and densely populated, but vulnerable to sea level changes. Sea level anomalies (SLA) during 1954–2012 from tide gauge station data and regional SLAs during 1993–2012 from satellite altimetry are analyzed and compare to the El Niño–Southern Oscillation (ENSO). Results show that sea level declines during El Niño events and rises during La Niña. Sea level in the PRE responds to ENSO with ~3–month lag. The ENSO can cause sea level in the PRE to fluctuate from −8.70 to 8.11 cm. Sea level cycles of 3 and 5 years are related to ENSO. The ENSO mechanism affecting sea level in the PRE was analyzed by identifying dominant regional and local forces. Weak/strong SLAs in most El Niño/La Niña events may be attributed to less/more seawater transport driven by anomalously weak/strong north winds and local anomalously high/low sea level pressure. Wind-driven coastal current is the predominant factor. It generated coastal seawater volume transport along a ~160 km wide cross section to decrease by 21.07% in a typical El Niño period (January 2010) and increase by 44.03% in a typical La Niña period (January 2011) as compared to an ENSO neutral situation (January 2013). Results of sea level rise and its potential mechanism provide insight for disaster protection during extreme El Niño/La Niña events.

    更新日期:2018-01-13
  • Soil creep: The driving factors, evidence and significance for biogeomorphic and pedogenic domains and systems – A critical literature review
    Earth Sci. Rev. (IF 7.051) Pub Date : 2018-01-12
    Łukasz Pawlik, Pavel Šamonil

    Soil and regolith creep have been analyzed for at least the last 140 years, using many methodological configurations and temporal and spatial scales. The general concept of creeping soil and its mechanism, first proposed by W.M. Davis and G.K. Gilbert at the end of the 19th century, evolved since the 1940s towards theoretical models and precise short- and long-term field measurements. This fruitful epoch continued with results enhanced at the turn of the 20th century by the application of new research methods (e.g. radiometry) and a redefinition of the term soil creep to encompass the sum of stochastic shallow subsurface and near-surface processes causing net downslope movement of soil or regolith. Simultaneously, another possibility of creep detection was noticed in dendrochronology, and since the 1970s, in the formally defined discipline of dendrogeomorphology, indirect evaluations of creep activity were performed based on tree-ring analyses of bent trees. This method found many followers, but was also heavily criticized as imprecise and lacking in evidence of which kind of tree trunk curvature (e.g. “pistol-butt”- like deformation, S-shape curvature) could be ascribed to creep movement. From the beginning, soil creep was associated with the activity of living organisms on hillslopes. However, this aspect of creep studies has never been fully developed, in spite of the solid foundations and directions of potential studies pointed out by Charles Darwin at the end of the 19th century. In this paper we focus on the historical context of soil creep studies, and highlight forest ecosystems as probably the most active environment of biogenic creep, mainly due to tree uprooting and other biomechanical effects of living and dead trees (root channel infilling, tree root mounding etc.) that are a factors in biotransport. In the final sections the position of biogenic creep in the structure of biogeomorphic systems is discussed in relation to such important conceptual frameworks as the biogeomorphic ecosystem, biogeomorphic feedback window and ecosystem engineering. We also describe several hypotheses that should be carefully tested in the future, and propose several research methods that have the ability to further our knowledge about soil creep: radiometry, laser scanning and soil micromorphology.

    更新日期:2018-01-12
  • The Nile's journey through space and time: A geological perspective
    Earth Sci. Rev. (IF 7.051) Pub Date : 2018-01-12
    Mohamed G. Abdelsalam

    This synthesis summarizes the geography, geomorphology, and regional tectonics of the Nile drainage system (henceforth the Nile System) as well as outlines the important features and geological events in its different segments. The Nile System assembled from different drainage systems that were shaped by different tectonic and environmental events. The drainage systems at its two sources, the Lake Plateau and the Northwestern Ethiopian Plateau are shaped since ~30 Ma by tectonic uplift related to mantle plume(s) activities, eruption of the Ethiopian Large Igneous Province and the opening of the East African Rift System (EARS). Downstream from its 5000–2000 m high sources, the evolution of the Nile System was largely influenced by the White Nile paleo-lakes (and possibly a smaller paleo-lake within the Sudd Nile – the Lake Sudd) and the development of major low-angle alluvial fans (the Lol, the El Fula, the Bahr el Jebel, the Gezira, and the Abu Habil) within the flat plains of South Sudan and central Sudan. The drainage evolution of these regions of the Nile System ultimately ended with the emergence of the Blue Nile and the White Nile which meet in Khartoum to form the Cataract Nile which carves its way northward until the Sudanese-Egyptian boarder through Precambrian crystalline rocks and Mesozoic sandstones exposed within the Sahara. Here, recent uplift of the Nubian Swell diverted the river to flow southwestward before resuming a north course forming the Great Bend of the Nile. In Egypt, carving of the Eonile Canyon during the Messinian Salinity Crisis signaled the birth of the Egyptian Nile which possibly connected to the rest of the Nile System only ~2.5–~2.0 Ma ago. This synthesis proposes five phases for the assembly of the Nile System. (1) The period immediately before 6.0 Ma which is characterized by the presence of the Paleo-lake Obweruka along the Western Branch of the EARS, head-ward incision of the Blue Nile (and possibly the Tekeze – Atbara River) into the Northwestern Ethiopian Plateau, and the domination of the Ancestral Egyptian Nile drainage system. (2) The period between 6.0 Ma and 5.4 Ma which witnessed the appearance of the Lake Tana as well as the carving of the Eonile Canyon and its subsequent flooding by the Mediterranean Sea water to turn it into a gulf. (3) The period between 2.5 Ma and 0.5 Ma in which witnessed in the Lake Plateau the segmentation of the Western Branch of the EARS turning the Paleo-lake Obweruka into the Lake Albert and the Lake Edward and establishing the eastward directed drainage system (the Kifa, the Katonga, and the Kagera). This period also witnessed the carving of the Blue Nile its way through the Sahara to connect with the Egyptian Nile. (4) The period between 0.5 and 15 ka witnessed the appearance of the Lake Victoria in the Lake Plateau as well as the intermittent appearance of the White Nile paleo-lakes and possibly the Lake Sudd. It is also possibly the period when the Tushka – Kharga paleo-lakes were formed west of the Modern Egyptian Nile. This period also witnessed the continuation of the development of alluvial fans in the lowlands of South Sudan and central Sudan. Also during this period, uplift of the Nubian Swell in northern Sudan and southern Egypt produced the Great Bend of the Nile. (5) The period between 15 ka and Present witnessed drainage re-organization and the most recent overflow of the lakes of the Lake Plateau Nile to re-connect with the Sudd Nile, White Nile, and the Cataract Nile. This tentative model can be refined by better constraints on the tectonic uplift history of the sources of the Nile System, sediment budget of the system, and timing of connectivity between its different segments.

    更新日期:2018-01-12
  • Assessing structural, functional and effective hydrologic connectivity with brain neuroscience methods: State-of-the-art and research directions
    Earth Sci. Rev. (IF 7.051) Pub Date : 2018-01-12
    Michael Rinderer, Genevieve Ali, Laurel Larsen

    While the concept of connectivity has gained popularity in fields like hydrology and ecology, little agreement exists on its definition, which hinders its use in both scientific and legal contexts. In contrast, neuroscientists have developed not only strong conceptualizations of connectivity but also tools to quantify it: a clear distinction is made between structural connectivity, which is determined from brain anatomy; functional connectivity, which is estimated based on statistical dependencies between neuronal electric timeseries; and effective connectivity, which infers causal relations from the same timeseries based on the assumption that “true” interactions occur with a certain time delay. The motivation of this review arose from the hypothesis that connectivity-related statistical techniques, which are applied to timeseries of electrical currents measured by placing electrodes on the scalp of the human brain, could also apply to high-frequency hydrological timeseries acquired to characterize catchment response to precipitation. Here we bring together existing conceptualizations of structural, functional and effective connectivity in hydrology and ecology and compare them with those used in brain neuroscience. We then summarize the most important brain connectivity measures and their associated mathematical frameworks before evaluating the potential of those measures to help advance our understanding of hydrologic connectivity properties – in terms of the frequency, magnitude, timing, duration and rate of water movement linking two disparate locations. Lastly, we present a short case study where a selection of brain connectivity measures is applied to 35 groundwater and streamflow timeseries from a Swiss catchment to infer subsurface flow-driven hydrologic connectivity. Our literature review combined with our short case study suggest that an ensemble of functional and effective connectivity measures should be used and constrained not only by structural connectivity measures but also by interpretation thresholds in order to make results parsimonious. We highlight challenges associated with transferring brain connectivity measures to hydrology, especially those related to choosing the appropriate length and sampling frequency of input timeseries when assessing perennial versus ephemeral connectivity, appropriately detecting and differentiating noisy from indirect connections, and interpreting unbounded connectivity measures. We then offer recommendations for future research and propose that hydrologists use a common classification system encompassing all potential connectivity assessment approaches and measures in order to facilitate scientific communication.

    更新日期:2018-01-12
  • The chronology of Late Pleistocene thermal contraction cracking derived from sand wedge OSL dating in central and southern France
    Glob. Planet. Change (IF 3.915) Pub Date : 2018-01-12
    Eric Andrieux, Mark D. Bateman, Pascal Bertran

    Much of France remained unglaciated during the Late Quaternary and was subjected to repeated phases of periglacial activity. Numerous periglacial features have been reported but disentangling the environmental and climatic conditions they formed under, the timing and extent of permafrost and the role of seasonal frost has remained elusive. The primary sandy infillings of relict sand-wedges and composite-wedge pseudomorphs record periglacial activity. As they contain well-bleached quartz-rich aeolian material they are suitable for optically stimulated luminescence dating (OSL). This study aims to reconstruct when wedge activity took place in two regions of France; Northern Aquitaine and in the Loire valley. Results from single-grain OSL measurements identify multiple phases of activity within sand wedges which suggest that wedge activity in France occurred at least 11 times over the last 100 ka. The most widespread events of thermal contraction cracking occurred between ca. 30 and 24 ka (Last Permafrost Maximum) which are concomitant with periods of high sand availability (MIS 2). Although most phases of sand-wedge growth correlate well with known Pleistocene cold periods, the identification of wedge activity during late MIS 5 and the Younger Dryas strongly suggests that these features do not only indicate permafrost but also deep seasonal ground freezing in the context of low winter insolation. These data also suggest that the overall young ages yielded by North-European sand-wedges likely result from poor record of periglacial periods concomitant with low sand availability and/or age averaging inherent with standard luminescence methods.

    更新日期:2018-01-12
  • Abundance and sources of phthalic acids, benzene-tricarboxylic acids and phenolic acids in PM2.5 at urban and suburban sites in Southern China
    ACS Earth Space Chem. Pub Date : 2018-01-11
    Xiao He, X. H. Hilda Huang, Ka Shing Chow, Qiongqiong Wang, Ting Zhang, Dui Wu, Jian Zhen Yu

    The organic composition of airborne fine particulate matter (PM2.5, aerodynamic diameter less than 2.5 micrometers) at a molecular level has yet to be achieved, hindering a full understanding of the climatic impacts and health effects of PM2.5. Compounds containing aromatic rings are closely associated with optically active brown carbon and toxicologically important quinones. In this work, a group of ten aromatic organic acids including three phthalic acids, four phenolic acids and three benzene-tricarboxylic acids (BTCAs) in PM2.5 were studied for their abundance and potential sources through quantifying their ambient concentrations at four sites in the Pearl River Delta (PRD) region in Southern China, where biomass burning and anthropogenic emissions are both significant PM sources. Average concentrations of individual aromatic acids in a total of 240 PM2.5 samples collected throughout 2012 were in the order of 0.1-20 ng/m3, with p-and o-phthalic acid being the most abundant. Inter-species correlation analysis with known PM source tracers reveals different source origins for the ten aromatic acids. The four phenolic acids, all possessing partial lignin structures, are highly correlated with levoglucosan, indicating their association with biomass burning emissions. Specific lignin tracer ratios characteristic of different types of biomass fuels (i.e., cinnamyl- to vanillyl-phenol ratio) revealed significant influence of crop burning emissions in the PRD region. The three BTCAs have moderate correlation with sulfate but no correlation with levoglucosan, suggesting a strong association with secondary formation origins while negating a strong link with biomass burning. The three phthalic acids are moderately correlated with sulfate, levoglucosan, and a number of polycyclic aromatic hydrocarbons (PAHs), indicating multiple significant sources. This study provides a valuable data set towards establishing quantitative links between molecular composition of organic matter and the optical and toxicological properties of PM2.5 as well as assisting identification of tracers for PM2.5 sources.

    更新日期:2018-01-12
  • Phase transitions and hygroscopic growth of Mg(ClO4)2, NaClO4, and NaClO4∙H2O: implications for the stability of aqueous water in hyperarid environments on Mars and on Earth
    ACS Earth Space Chem. Pub Date : 2018-01-11
    Xiaohong Jia, Wenjun Gu, Yongjie Li, Peng Cheng, Yujing Tang, Liya Guo, Xinming Wang, Mingjin Tang

    In general pure liquid water is not thermodynamically stable on Mars due to the extremely cold and dry environment. The presence in the soil of perchlorates, which could lower the freezing point of water and form aqueous solutions by taking up water vapor even under subsaturated conditions, has been proposed to explain the possible existence of liquid water on Mars and in some hyperarid environments on Earth. In this work, the phase transitions and hygroscopic growth of Mg(ClO4)2, NaClO4, and NaClO4∙H2O were investigated between 278 and 303 K. In this temperature range, we found that anhydrous Mg(ClO4)2 was completely converted to Mg(ClO4)2∙6H2O at RH as low as <1%. In contrast, anhydrous NaClO4 was stable at RH below 20%, and NaClO4∙H2O was completely transformed to anhydrous NaClO4 at <1% RH; when RH was increased to 30%, anhydrous NaClO4 was transformed to NaClO4∙H2O. We also found that the deliquescence relative humidity (DRH) of NaClO4∙H2O decreased from ~51.5% at 278 K to ~43.5% at 303 K, exhibiting a negative dependence on temperature. In addition, the amounts of water in the NaClO4 solution were quantitatively determined as a function of RH at 278, 288, and 298 K. This work considerably furthers our understanding of the hygroscopic properties of perchlorates under different conditions, as well as the hydrological cycles on Mars and in other hyperarid environments, such as the Atacama Desert on Earth.

    更新日期:2018-01-12
  • Drought vulnerability assessment of maize in Sub-Saharan Africa: Insights from physical and social perspectives
    Glob. Planet. Change (IF 3.915) Pub Date : 2018-01-11
    Bahareh Kamali, Karim C. Abbaspour, Bernhard Wehrli, Hong Yang

    Drought as a slow-onset phenomenon inflicts important losses to agriculture where the degree of vulnerability depends not only on physical variables such as precipitation and temperature, but also on societal preparedness. While the scopes of physical and social vulnerability are very different in nature, studies distinguishing these two aspects have been lacking. In this study we address the physical and social aspects of drought vulnerability of maize (CDVIphy and CDVIsoc) in Sub-Saharan Africa (SSA). To quantify vulnerability, we applied a probabilistic framework combining a Drought Exposure Index (DEI) with a physical or social Crop Failure Index, CFIphy or CFIsoc, respectively. DEI was derived from the exceedance probability of precipitation. Maize yields, simulated using the Environmental Policy Integrated Climate (EPIC) model, were used to build CFIphy, whereas the residual of simulated and FAO recorded yields were used to construct CFIsoc. The results showed that southern and partially central Africa are more vulnerable to physical drought as compared to other regions. Central and western Africa, however, are socially highly vulnerable. Comparison of CDVIphy and CDVIsoc revealed that societal factors cause more vulnerability than physical variables in almost all SSA countries except Nigeria and South Africa. We conclude that quantification of both drought vulnerabilities help a better characterization of droughts and identify regions where more investments in drought preparedness are required.

    更新日期:2018-01-12
  • The Early Toarcian oceanic anoxic event: Paleoenvironmental and paleoclimatic change across the Alpine Tethys (Switzerland)
    Glob. Planet. Change (IF 3.915) Pub Date : 2018-01-11
    Alicia Fantasia, Karl B. Föllmi, Thierry Adatte, Jorge E. Spangenberg, Jean-Carlos Montero-Serrano

    Paleoenvironmental and paleoclimatic change associated with the Toarcian oceanic anoxic event (T-OAE) was evaluated in five successions located in Switzerland. They represent different paleogeographic settings across the Alpine Tethys: the northern shelf (Gipf, Riniken and Rietheim), the Sub-Briançonnais basin (Creux de l'Ours), and the Lombardian basin (Breggia). The multi-proxy approach chosen (whole-rock and clay mineralogy, phosphorus, major and trace elements) shows that local environmental conditions modulated the response to the T-OAE across the Alpine Tethys. On the northern shelf and in the Sub-Briançonnais basin, high kaolinite contents and detrital proxies (detrital index, Ti, Zr, Si) in the T-OAE interval suggest a change towards a warmer and more humid climate coupled with an increase in the chemical weathering rates. In contrast, low kaolinite content in the Lombardian basin is likely related to a more arid climate along the southern Tethys margin and/or to a deeper and more distal setting. Redox-sensitive trace-element (V, Mo, Cu, Ni) enrichments in the T-OAE intervals reveal that dysoxic to anoxic conditions developed on the northern shelf, whereas reducing conditions were less severe in the Sub-Briançonnais basin. In the Lombardian basin well-oxygenated bottom water conditions prevailed. Phosphorus (P) speciation analysis was performed at Riniken and Creux de l'Ours. This is the first report of P speciation data for T-OAE sections, clearly suggesting that high P contents during this time interval are mainly linked to the presence of an authigenic phases and fish remains. The development of oxygen-depleted conditions during the T-OAE seems to have promoted the release of the organic-bound P back into the water column, thereby further sustaining primary productivity in a positive feedback loop.

    更新日期:2018-01-12
  • Thermal history of the northern Olympic Domain, Gawler Craton; correlations between thermochronometric data and mineralising systems
    Gondwana Res. (IF 6.959) Pub Date : 2018-01-10
    James W. Hall, Stijn Glorie, Anthony J. Reid, Alan S. Collins, Fred Jourdan, Martin Danišík, Noreen Evans
    更新日期:2018-01-10
  • Assessment of regional downscaling simulations for long term mean, excess and deficit Indian Summer Monsoons
    Glob. Planet. Change (IF 3.915) Pub Date : 2018-01-10
    Hamza Varikoden, M. Mujumdar, J.V. Revadekar, K.P. Sooraj, M.V.S. Ramarao, J. Sanjay, R. Krishnan

    This study undertakes a comprehensive assessment of dynamical downscaling of summer monsoon (June–September; JJAS) rainfall over heterogeneous regions namely the Western Ghats (WG), Central India (CI) and North-Eastern Region (NER) for long term mean, excess and deficit episodes for the historical period from 1951 to 2005. This downscaling assessment is based on six Coordinated Regional Climate Downscaling Experiments (CORDEX) for South Asia (SAS) region, their five driving Global Climate Models (GCM) simulations along with observations from India Meteorological Department (IMD) and Asian Precipitation Highly Resolved Observational Integrated Towards Evaluation for Water Resources (APHRODITE). The analysis reveals an overall reduction of dry bias in rainfall across the regions of Indian sub-continent in most of the downscaled CORDEX-SAS models and in their ensemble mean as compared to that of driving GCMs.The interannual variabilities during historical period are reasonably captured by the ensemble means of CORDEX-SAS simulations with an underestimation of 0.43%, 38% and 52% for the WG, CI and NER, respectively. Upon careful examination of the CORDEX-SAS models and their driving GCMs revealed considerable improvement in the regionally downscaled rainfall. The value addition of dynamical downscaling is apparent over the WG in Regional Climate Model (RCM) simulations with an improvement of more than 30% for the long term mean, excess and deficit episodes from their driving GCMs. In the case of NER, the improvement in the downscaled rainfall product is more than 10% for all the episodes. However, the value addition in the CORDEX-SAS simulations for CI region, dominantly influenced by synoptic scale processes, is not clear. Nevertheless, the reduction of dry bias in the complex topographical regions is remarkable. The relative performance of dynamical downscaling of rainfall over complex topography in response to local forcing and orographic lifting depict the value addition (30% over WG and 10% over NER, with a statistical significance of more than 5% level), when compared with the synoptic scale system induced rainfall over the plains of central-India.

    更新日期:2018-01-10
  • Infragravity waves: from driving mechanisms to impacts
    Earth Sci. Rev. (IF 7.051) Pub Date : 2018-01-09
    Xavier Bertin, Anouk de Bakker, Ap van Dongeren, Giovanni Coco, Gael André, Fabrice Ardhuin, Philippe Bonneton, Frédéric Bouchette, Bruno Castelle, Wayne C. Crawford, Mark Davidson, Martha Deen, Guillaume Dodet, Thomas Guerin, Kris Inch, Fabien Leckler, Robert McCall, Héloïse Muller, Maitane Olabarrieta, Dano Roelvink, Gerben Ruessink, Damien Sous, Éléonore Stutzmann, Marion Tissier

    Infragravity (hereafter IG) waves are surface ocean waves with frequencies below those of wind-generated “short waves” (typically below 0.04 Hz). Here we focus on the most common type of IG waves, those induced by the presence of groups in incident short waves. Three related mechanisms explain their generation: (1) the development, shoaling and release of waves bound to the short-wave group envelopes (2) the modulation by these envelopes of the location where short waves break, and (3) the merging of bores (breaking wave front, resembling to a hydraulic jump) inside the surfzone. When reaching shallow water (O(1-10 m)), IG waves can transfer part of their energy back to higher frequencies, a process which is highly dependent on beach slope. On gently sloping beaches, IG waves can dissipate a substantial amount of energy through depth-limited breaking. When the bottom is very rough, such as in coral reef environments, a substantial amount of energy can be dissipated through bottom friction. IG wave energy that is not dissipated is reflected seaward, predominantly for the lowest IG frequencies and on steep bottom slopes. This reflection of the lowest IG frequencies can result in the development of standing (also known as stationary) waves. Reflected IG waves can be refractively trapped so that quasi-periodic along-shore patterns, also referred to as edge waves, can develop. IG waves have a large range of implications in the hydro-sedimentary dynamics of coastal zones. For example, they can modulate current velocities in rip channels and strongly influence cross-shore and longshore mixing. On sandy beaches, IG waves can strongly impact the water table and associated groundwater flows. On gently sloping beaches and especially under storm conditions, IG waves can dominate cross-shore sediment transport, generally promoting offshore transport inside the surfzone. Under storm conditions, IG waves can also induce overwash and eventually promote dune erosion and barrier breaching. In tidal inlets, IG waves can propagate into the back-barrier lagoon during the flood phase and induce large modulations of currents and sediment transport. Their effect appears to be smaller during the ebb phase, due to blocking by countercurrents, particularly in shallow systems. On coral and rocky reefs, IG waves can dominate over short-waves and control the hydro-sedimentary dynamics over the reef flat and in the lagoon. In harbors and semi-enclosed basins, free IG waves can be amplified by resonance and induce large seiches (resonant oscillations). Lastly, free IG waves that are generated in the nearshore can cross oceans and they can also explain the development of the Earth’s “hum” (background free oscillations of the solid earth).

    更新日期:2018-01-10
  • Isotopic Characterization of Mercury in Natural Gas via Analysis of Mercury Removal Unit Catalysts
    ACS Earth Space Chem. Pub Date : 2018-01-08
    Spencer J. Washburn, Joel D. Blum, Marcus W. Johnson, Jodie M. Tomes, Peter J. Carnell
    更新日期:2018-01-09
  • Adjoint-Based Climate Model Tuning: Application to the Planet Simulator
    J. Adv. Model. Earth Syst. (IF 4.189) Pub Date : 2018-01-08
    Guokun Lyu, Armin Köhl, Ion Matei, Detlef Stammer

    AbstractThe adjoint method is used to calibrate the medium complexity climate model “Planet Simulator” through parameter estimation. Identical twin experiments demonstrate that this method can retrieve default values of the control parameters when using a long assimilation window of the order of 2 months. Chaos synchronization through nudging, required to overcome limits in the temporal assimilation window in the adjoint method, is employed successfully to reach this assimilation window length. When assimilating ERA-Interim reanalysis data, the observations of air temperature and the radiative fluxes are the most important data for adjusting the control parameters. The global mean net longwave fluxes at the surface and at the top of the atmosphere are significantly improved by tuning two model parameters controlling the absorption of clouds and water vapor. The global mean net shortwave radiation at the surface is improved by optimizing three model parameters controlling cloud optical properties. The optimized parameters improve the free model (without nudging terms) simulation in a way similar to that in the assimilation experiments. Results suggest a promising way for tuning uncertain parameters in non-linear coupled climate models.

    更新日期:2018-01-09
  • Ocean Tide Influences on the Antarctic and Greenland Ice Sheets
    Rev. Geophys. (IF 12.34) Pub Date : 2018-01-08
    Laurie Padman, Matthew R. Siegfried, Helen A. Fricker

    AbstractOcean tides are the main source of high-frequency variability in the vertical and horizontal motion of ice sheets near their marine margins. Floating ice shelves, which occupy about half the perimeter of Antarctica and the termini of four outlet glaciers in northern Greenland, rise and fall in synchrony with the ocean tide. Lateral motion of floating and grounded portions of ice sheets near their marine margins can also include a tidal component. These tide-induced signals provide insight into the processes by which the oceans can affect ice-sheet mass balance and dynamics. In this review, we summarize in situ and satellite-based measurements of the tidal response of ice shelves and grounded ice are described, and spatial variability of ocean tide heights and currents around the ice sheets. We review sensitivity of tide heights and currents as ocean geometry responds to variations in sea level, ice shelf thickness, and ice sheet mass and extent. We then describe coupled ice-ocean models and analytical glacier models that quantify the effect of ocean tides on lower frequency ice-sheet mass loss and motion. We suggest new observations and model developments to improve the representation of tides in coupled models that are used to predict future ice-sheet mass loss and the associated contribution to sea level change. The most critical need is for new data to improve maps of bathymetry, ice shelf draft, spatial variability of the drag coefficient at the ice-ocean interface, and higher resolution models with improved representation of tidal energy sinks.

    更新日期:2018-01-08
  • Integrated global stratigraphy and geologic timescales, with some future directions for stratigraphy in China
    Earth Sci. Rev. (IF 7.051) Pub Date : 2018-01-06
    James G. Ogg

    Our knowledge of the history of our planet comes from deciphering the sedimentary record of biologic, ecologic, geochemical, climatic, physical and other systems using a vast array of tools and innovative techniques. To synthesize these trends and events into a coherent global history requires six inter-connected international efforts: (1) documentation and access to major research reference sections, including standardization of convenient and precise terminology for divisions of geologic time (e.g., Global Boundary Stratotype Section and Point (GSSPs) and within-stage levels), (2) inter-calibration of these marine and terrestrial records both within and among different regions to compile a global integrated scale, (3) improving and applying age models to understand cause-effect relationships and rates of processes, (4) public databases and syntheses, (5) international efforts and centers, and (6) Earth-systems geo-education that emphases relationships among fields in addition to training in particular specializations. In the past two decades, the careful analysis of the sedimentary records in China's marine and terrestrial basins have enabled major leaps in our understanding of Earth's history, such as major excursions of the carbon cycle during the Cambrian, “lethal” temperature excursions in Early Triassic, Cretaceous evolution of birds, and catastrophic impacts of large igneous eruptions. China has provided more reference sections for the international definition of GSSPs than any other country. It is vital to put those records from the China basins into a larger global context.

    更新日期:2018-01-07
  • Phase Diagram of the Ternary Water-Tetrahydrofuran-Ammonia System at Low Temperatures. Implications for Clathrate Hydrates and Outgassing on Titan
    ACS Earth Space Chem. Pub Date : 2018-01-05
    M. Victoria Munoz-Iglesias, Mathieu Choukroun, Tuan H. Vu, Robert Hodyss, Ahmed Mahjoub, William D Smythe, Christophe Sotin

    Titan’s icy shell is expected to contain predominantly methane clathrate hydrates, water ice Ih, and possibly ammonia hydrates, beneath a cover of diverse organics formed via atmospheric photochemistry. The dissociation of clathrate hydrates has long been inferred as a potential replenishment mechanism for atmospheric methane, however pure methane clathrates would be stable all the way to the surface. The melting of ammonia hydrates and subsequent interaction with methane clathrates could favor the dissociation of clathrates at much lower temperatures, due to the strong antifreeze effect of ammonia. In order to better understand the phase behavior of clathrate hydrates in presence of ammonia, we have developed phase diagrams for the ternary system water-ammonia-tetrahydrofuran at 1 bar and in the temperature range 77-280 K via differential scanning calorimetry and Raman spectroscopy. We have been able to determine how ammonia promotes the start of a partial dissociation of THF-clathrates at temperatures far colder than the liquidus. We have also established that this ternary system exhibits a complex chemistry, with multiple phases forming in thermodynamic equilibrium because of a phase separation between a THF-dominated liquid and a H2O-NH3 dominated liquid. In addition to the expected THF-clathrates, we report the formation of other mineral phases such as ammonia hydrates, a new THF-NH3-rich phase, and potentially mixed THF-NH3 clathrates. Partial dissociation of ~ 10% of the clathrate reservoir would release to Titan’s atmosphere methane amounts sufficient to sustain the hydrocarbon cycle for 650 My, which is commensurate with the age of the present atmosphere.

    更新日期:2018-01-06
  • Drivers and trajectories of land cover change in East Africa: Human and environmental interactions from 6000 years ago to present
    Earth Sci. Rev. (IF 7.051) Pub Date : 2018-01-06
    Rob Marchant, Suzi Richer, Claudia Capitani, Colin Courtney-Mustaphi, Mary Prendergast, Daryl Stump, Oli Boles, Paul Lane, Stephanie Wynne-Jones, Cruz Ferro Vázquez, David Wright, Nicole Boivin, Carol Lang, Andrea Kay, Leanne Phelps, Dorian Fuller, Mats Widgren, Paramita Punwong, Julius Lejju, Marie-Jose Gaillard-Lemdahl, Kathleen D. Morrison, Jed Kaplan, Jacquiline Benard, Alison Crowther, Aida Cuní-Sanchez, Gijs de Cort, Nicolas Deere, Anneli Ekblom, Jennifer Farmer, Jemma Finch, Lindsey Gillson, Esther Githumbi, Tabitha Kabora, Rebecca Kariuki, Rahab Kinyanjui, Elizabeth Kyazike, Veronica Muiruri, Cassian Mumbi, Rebecca Muthoni, Alfred Muzuka, Emmanuel Ndiema, Chantal Nzaba, Dan Olago, Isaya Onjala, Annemiek Pas Schrijver, Nik Petek, Phillip J. Platts, Stephen Rucina, Anna Shoemaker, Senna Thornton-Barnett

    East African landscapes today are the result of the cumulative effects of climate and land-use change over millennial timescales. In this review, we compile archaeological and palaeoenvironmental data from East Africa to document land cover change, environmental, subsistence and land use transitions over the past 6000 years. Throughout East Africa there have been a series of relatively rapid and high magnitude environmental shifts characterised by changing hydrological budgets during the Holocene. For example, pronounced environmental shifts that manifested as a marked change in the rainfall or seasonality and subsequent hydrological budget throughout East Africa occurred around 4000, 800 and 300 radiocarbon years before present (yr BP). The past 6000 years have also seen numerous shifts in human interactions with East African ecologies. From the mid Holocene, anthropogenic land use has both diversified and increased exponentially associated with the arrival of new subsistence systems, crops, migrants and technologies, giving rise to a sequence of significant phases of land cover change. The first large scale human influences began to occur around 4000 yr BP, associated with the introduction of domesticated livestock and the expansion of pastoral communities. The first widespread and intensive forest clearances were associated with the arrival of iron-using early farming communities around 2500 yr BP, particularly in productive and easy to clear mid-altitudinal areas. Extensive and pervasive land cover change has been associated with population growth, immigration and movement of people. The expansion of trading routes between the interior and the coast starting around 1300 yr BP and intensifying in the 18th and 19th centuries, was one such process. These caravan routes possibly acted as conduits for spreading New World crops such as maize (Zea mays), tobacco and tomatoes, although the processes and timing of their introduction remains poorly documented. The introduction of SE Asian domesticates, especially banana, rice, taro, and chicken, via transoceanic biological transfers around and across the Indian Ocean, from at least around 1300 yr BP, and potentially significantly earlier, also had profound social and ecological consequences across parts of the region. Through an interdisciplinary synthesis of information, we explore the different drivers and directions of land cover change, the associated environmental history and multiple interactions with the distribution of various cultures, technologies, and subsistence strategies through time and across space in East Africa. This review suggests topics for targeted future research that focus on areas and/or time periods where our understanding of the interaction between people, the environment and land cover change are most contentious and/or poorly resolved. The review also critiques how this perspective on regional land use change can be used to inform and provide perspective for contemporary issues such as climate and ecosystem change models, conservation and the achievement of nature based solutions to development.

    更新日期:2018-01-06
  • 更新日期:2018-01-05
  • Atmospheric Reactivity of Fullerene (C60) Aerosols
    ACS Earth Space Chem. Pub Date : 2018-01-05
    Dhruv Mitroo, Jiewei Wu, Peter F. Colletti, Seung Soo Lee, Michael J. Walker, William H. Brune, Brent J. Williams, John D. Fortner
    更新日期:2018-01-05
  • An Environmentally Forced Tropical Cyclone Hazard Model
    J. Adv. Model. Earth Syst. (IF 4.189) Pub Date : 2018-01-05
    Chia-Ying Lee, Michael K. Tippett, Adam H. Sobel, Suzana J. Camargo

    AbstractA new statistical-dynamical model is developed for estimating the long-term hazard of rare, high impact tropical cyclones events globally. There are three components representing the complete storm lifetime: an environmental index-based genesis model, a beta-advection track model and an autoregressive intensity model. All three components depend upon the local environmental conditions, including potential intensity, relative sea surface temperature, 850 and 250 hPa steering flow, deep-layer mean vertical shear, 850 hPa vorticity, and midlevel relative humidity. The hazard model, using 400 realizations of a 32-year period (approximately 3000 storms per realization), captures many aspects of tropical cyclone statistics, such as genesis and track density distribution. Of particular note, it simulates the observed number of rapidly intensifying storms, a challenging issue in tropical cyclone modeling and prediction. Using the return period curve of landfall intensity as a measure of local tropical cyclone hazard, the model reasonably simulates the hazard in the western north Pacific (coastal regions of the Philippines, China, Taiwan, and Japan) and the Caribbean islands. In other regions, the observed return period curve can be captured after a local landfall frequency adjustment that forces the total number of landfalls to be the same as that observed while allowing the model to freely simulate the distribution of intensities at landfall.

    更新日期:2018-01-05
  • Seasonal drought prediction: advances, challenges, and future prospects
    Rev. Geophys. (IF 12.34) Pub Date : 2018-01-05
    Zengchao Hao, Vijay P. Singh, Youlong Xia

    AbstractDrought prediction is of critical importance to early warning for drought managements. This review provides a synthesis of drought prediction based on statistical, dynamical and hybrid methods. Statistical drought prediction is achieved by modeling the relationship between drought indices of interest and a suite of potential predictors, including large scale climate indices, local climate variables, and land initial conditions. Dynamical meteorological drought prediction relies on seasonal climate forecast from General Circulation Models (GCMs), which can be employed to drive hydrological models for agricultural and hydrological drought prediction with the predictability determined by both climate forcings and initial conditions. Challenges still exist in drought prediction at long lead time and under a changing environment resulting from natural and anthropogenic factors. Future research prospects to improve drought prediction include, but are not limited to, high-quality data assimilation, improved model development with key processes related to drought occurrence, optimal ensemble forecast to select or weight ensembles, and hybrid drought prediction to merge statistical and dynamical forecasts.

    更新日期:2018-01-05
  • Human impact on sediment in the Yangtze River: A review and new perspectives
    Glob. Planet. Change (IF 3.915) Pub Date : 2018-01-05
    H.F. Yang, S.L. Yang, K.H. Xu, J.D. Milliman, H. Wang, Z. Yang, Z. Chen, C.Y. Zhang

    Changes in riverine suspended and riverbed sediments have environmental, ecological and social implications. Here, we provide a holistic review of water and sediment transport and examine the human impact on the flux, concentration and size of sediment in the Yangtze River in recent decades. We find that most of the fluvial sediment has been trapped in reservoirs, except for the finest portion. Furthermore, soil-conservation since the 1990s has reduced sediment yield. From 1956 to 1968 (pre-dam period) to 2013–2015 (post-dams and soil-conservation), the sediment discharge from the sub-basins decreased by 91%; in the main river, the sediment flux decreased by 99% at Xiangjiaba (upper reach), 97% at Yichang (transition between upper and middle reaches), 83% at Hankou (middle reach), and 77% at Datong (tidal limit). Because the water discharge was minimally impacted, the suspended sediment concentration decreased to the same extent as the sediment flux. Active erosion of the riverbed and coarsening of surficial sediments were observed in the middle and lower reaches. Fining of suspended sediments was identified along the river, which was counteracted by downstream erosion. Along the 700-km-long Three Gorges Reservoir, which retained 80% of the sediment from upstream, the riverbed gravel or rock was buried by mud because of sedimentation after impoundment. Along with these temporal variations, the striking spatial patterns of riverine suspended and riverbed sediments that were previously exhibited in this large basin were destroyed or reversed. Therefore, we conclude that the human impacts on sediment in the Yangtze River are strong and systematic.

    更新日期:2018-01-05
  • Human impacts on 20th century fire dynamics and implications for global carbon and water trajectories
    Glob. Planet. Change (IF 3.915) Pub Date : 2018-01-05
    Fang Li, David M. Lawrence, Ben Bond-Lamberty

    Fire is a fundamental Earth system process and the primary ecosystem disturbance on the global scale. It affects carbon and water cycles through changing terrestrial ecosystems, and at the same time, is regulated by weather and climate, vegetation characteristics, and, importantly, human ignitions and suppression (i.e., the direct human effect on fire). Here, we utilize the Community Land Model version 4.5 (CLM4.5) to quantify the impacts of changes in human ignition and suppression on fire dynamics and associated carbon and water cycles. We find that the impact is to significantly reduce the 20th century global burned area by a century average of 38 Mha/yr and by 103 Mha/yr at the end of the century. Land carbon gain is weakened by 17% over the 20th century, mainly due to increased human deforestation fires and associated escape fires (i.e., degradation fires) in the tropical humid forests, even though the decrease in burned area in many other regions due to human fire suppression acts to increase land carbon gain. The direct human effect on fire weakens the upward trend in global runoff throughout the century by 6% and enhances the upward trend in global evapotranspiration since ~ 1945 by 7%. In addition, the above impacts in densely populated, highly developed (if population density > 0.1 person/km2), or moderately populated and developed regions are of opposite sign to those in other regions. Our study suggests that particular attention should be paid to human deforestation and degradation fires in the tropical humid forests when reconstructing and projecting fire carbon emissions and net atmosphere-land carbon exchange and estimating resultant impacts of direct human effect on fire.

    更新日期:2018-01-05
  • Fusion of pixel and object-based features for weed mapping using unmanned aerial vehicle imagery
    Int. J. Appl. Earth Obs. Geoinf. (IF 3.93) Pub Date : 2018-01-04
    Junfeng Gao, Wenzhi Liao, David Nuyttens, Peter Lootens, Jürgen Vangeyte, Aleksandra Pižurica, Yong He, Jan G. Pieters
    更新日期:2018-01-05
  • Tropical Cyclone Activity in the High-Resolution Community Earth System Model and the Impact of Ocean Coupling
    J. Adv. Model. Earth Syst. (IF 4.189) Pub Date : 2018-01-04
    Hui Li, Ryan L. Sriver

    AbstractHigh resolution Atmosphere General Circulation Models (AGCMs) are capable of directly simulating realistic tropical cyclone (TC) statistics, providing a promising approach for TC-climate studies. Active air-sea coupling in a coupled model framework is essential to capturing TC-ocean interactions, which can influence TC-climate connections on interannual to decadal time scales. Here we investigate how the choices of ocean coupling can affect the directly simulated TCs using high resolution configurations of the Community Earth System Model (CESM). We performed a suite of high resolution, multi-decadal, global scale CESM simulations in which the atmosphere (∼0.25˚ grid spacing) is configured with three different levels of ocean coupling: prescribed climatological sea surface temperature (SST) (ATM), mixed layer ocean (SLAB), and dynamic ocean (CPL). We find that different levels of ocean coupling can influence simulated TC frequency, geographical distributions, and storm intensity. ATM simulates more storms and higher overall storm intensity than the coupled simulations. It also simulates higher TC track density over the eastern Pacific and the North Atlantic, while TC tracks are relatively sparse within CPL and SLAB for these regions. Storm intensification and the maximum wind speed are sensitive to the representations of local surface flux feedbacks in different coupling configurations. Key differences in storm number and distribution can be attributed to variations in the modeled large-scale climate mean state and variability that arise from the combined effect of intrinsic model biases and air-sea interactions. Results help to improve our understanding about the representation of TCs in high resolution coupled Earth system models, with important implications for TC-climate applications.

    更新日期:2018-01-05
  • A MIS 9/MIS 8 speleothem record of hydrological variability from Macedonia (F.Y.R.O.M.)
    Glob. Planet. Change (IF 3.915) Pub Date : 2018-01-04
    Eleonora Regattieri, Giovanni Zanchetta, Ilaria Isola, Petra Bajo, Chiara Boschi, Natale Perchiazzi, Russell N. Drysdale, John C. Hellstrom, Alexander Francke, Bernd Wagner

    The period corresponding to Marine Isotope Stages 9 (MIS 9) offers the opportunity to study orbital and sub-orbital scale climate variability under boundary conditions different from those of better studied intervals such as the Holocene and the Last Interglacial. Yet, it is poorly represented in independently-dated continental archives around the Mediterranean Region. Here, we present a speleothem stable isotope record (δ18O and δ13C) from the Former Yugoslavian Republic of Macedonia (F.Y.R.O.M., southern Balkans), which consists of two periods of growth broadly covering the ca. 332 to 292 ka and the ca. 264 to 248 ka intervals (MIS 9e-b and late MIS 8). We interpret the speleothem δ18O as mostly related to regional hydrology, with variations that can be interpreted as due to changes in rainfall amount, with higher/lower values associated to drier/wetter condition. This interpretation is corroborated by a change in mineralogical composition between aragonite and calcite at ca. 328 ka, which marks increasing precipitation at the onset of MIS 9 and occurs within a trend of decreasing δ18O values. Also the comparison with the multiproxy climate record available from the nearby Lake Ohrid seems to support the proposed interpretation. The MIS 9e interglacial appears to be characterized by wettest conditions between ca. 326 and 321 ka, i.e. lasting ca. 5 kyr. Decreasing precipitation and enhanced millennial scale variability matches the glacial inception (MIS9 d to b), with drier events at ca. 319 ka (ca. 2 kyr long) and 310 ka (ca. 1 kyr long), and a major rainfall reduction between 306 and 298 ka. The latter is followed by a prominent wetter period between 298 and 295 ka, for which carbon data values suggest high infiltration rate. Rainfall decreases again after 295 ka, and remain low until the growth interruption at ca. 292 ka. Resumption of the growth and progressive soil development, expressed by the carbon isotope record, occurred during the late part of MIS 8. Despite the rather high temporal uncertainty (average 6 ka), the speleothem hydrological record complements the environmental information provided by the Lake Ohrid record and also fits well to the framework of regional and extra-regional variability, showing similarities with pollen records from southern and western Europe, both at orbital and at sub-orbital time scale.

    更新日期:2018-01-04
  • Variability of orogenic magmatism during Mediterranean-style continental collisions: A numerical modelling approach
    Gondwana Res. (IF 6.959) Pub Date : 2018-01-04
    N. Andrić, K. Vogt, L. Matenco, V. Cvetković, S. Cloetingh, T. Gerya

    The relationship between magma generation and the tectonic evolution of orogens during subduction and subsequent collision requires self-consistent numerical modelling approaches predicting volumes and compositions of the produced magmatic rocks. Here, we use a 2D magmatic-thermomechanical numerical modelling procedure to analyse rapid subduction of a narrow ocean, followed by Mediterranean style collision, which is characterized by the gradual accretion of lower plate material and slab migration towards the orogenic foreland. Our results suggest that magmatism has a large-scale geodynamic effect by focusing deformation throughout the entire subduction and collision process. The rheological structure and compositional layering of the crust impose a key control on the distribution of magmatic rocks within the orogen. Compared to previous simplified homogeneous crustal models, a compositionally layered crust causes an increase in felsic material influx during continental collision and results in shallower magmatic sources that migrate with time towards the foreland. Changes in the deformation style may be locally driven by magma emplacement rather than by slab movement. Our modelling also demonstrates that the migration pattern of the deformation front and the magmatic arc relative to the location of the suture zone may be driven by lower crustal indentation in the overriding plate during early stages of collision. The modelling predicts a gradual change in magma source composition with time from typical calc-alkaline to ones associated with relamination and eduction during subduction, collision and slab detachment. This transition explains the compositional changes of magma their temporal and spatial migration, as well as the observed link with deformation in the Dinarides orogen of Central Europe selected as a case study.

    更新日期:2018-01-04
  • Urban heat island effect: A systematic review of spatio-temporal factors, data, methods, and mitigation measures
    Int. J. Appl. Earth Obs. Geoinf. (IF 3.93) Pub Date : 2018-01-03
    Kaveh Deilami, Md. Kamruzzaman, Yan Liu

    Despite research on urban heat island (UHI) effect has increased exponentially over the last few decades, a systematic review of factors contributing to UHI effect has scarcely been reported in the literature. This paper provides a systematic and overarching review of different spatial and temporal factors affecting the UHI effect. UHI is a phenomenon when urban areas experience a higher temperature than their surrounding non-urban areas and is considered as a critical factor contributing to global warming, heat related mortalities, and unpredictable climatic changes. Therefore, there is a pressing need to identify the spatio-temporal factors that contribute to (or mitigate) the UHI effect in order to develop a thorough understanding of their causal mechanism so that these are addressed through urban planning policies. This paper systematically identified 75 eligible studies on UHI effect and reviews the nature and type of satellite images used, the techniques applied to classify land cover/use changes, the models to assess the link between spatio-temporal factors and UHI effect, and the effects of these factors on UHI. The review results show that: a) 54% of the studies used Landsat TM images for modelling the UHI effect followed by Landsat ETM (34%), and MODIS (28%); b) land cover indices (46%), followed by supervised classification (17%) were the dominant methods to derive land cover/use changes associated with UHI effect; c) ordinary least square regression is the most commonly applied method (68%) to investigate the link between different spatio-temporal factors and the UHI effect followed by comparative analysis (33%); and d) the most common factors affecting the UHI effect as reported in the reviewed studies, include vegetation cover (44%), season (33%), built-up area (28%), day/night (25%), population density (14%), water body (12%) together with others. This research discusses the findings in policy terms and provides directions for future research.

    更新日期:2018-01-04
  • 更新日期:2018-01-03
  • Ethnocentrism as a defence
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-02
    Jenn Richler

    Ethnocentrism as a defence Ethnocentrism as a defence, Published online: 02 January 2018; doi:10.1038/s41558-017-0047-z Ethnocentrism as a defence

    更新日期:2018-01-03
  • How to spend a dwindling greenhouse gas budget
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-02
    Michael Obersteiner, Johannes Bednar, Fabian Wagner, Thomas Gasser, Philippe Ciais, Nicklas Forsell, Stefan Frank, Petr Havlik, Hugo Valin, Ivan A. Janssens, Josep Peñuelas, Guido Schmidt-Traub

    How to spend a dwindling greenhouse gas budget How to spend a dwindling greenhouse gas budget, Published online: 02 January 2018; doi:10.1038/s41558-017-0045-1 The Paris Agreement is based on emission scenarios that move from a sluggish phase-out of fossil fuels to large-scale late-century negative emissions. Alternative pathways of early deployment of negative emission technologies need to be considered to ensure that climate targets are reached safely and sustainably.

    更新日期:2018-01-03
  • African tropical forest carbon
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-02
    Alastair Brown

    African tropical forest carbon African tropical forest carbon, Published online: 02 January 2018; doi:10.1038/s41558-017-0052-2 African tropical forest carbon

    更新日期:2018-01-03
  • The price of fast fashion
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-02

    The price of fast fashion The price of fast fashion, Published online: 02 January 2018; doi:10.1038/s41558-017-0058-9 The fashion industry has changed rapidly in recent years with the increased prevalence of fast fashion, impacting the environment. Efforts to green this polluting industry require action from businesses and consumers.

    更新日期:2018-01-03
  • Photosynthesis in high definition
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-02
    Timothy W. Hilton

    Photosynthesis in high definition Photosynthesis in high definition, Published online: 02 January 2018; doi:10.1038/s41558-017-0040-6 Photosynthesis is the foundation for almost all known life, but quantifying it at scales above a single plant is difficult. A new satellite illuminates plants’ molecular machinery at much-improved spatial resolution, taking us one step closer to combined ‘inside–outside’ insights into large-scale photosynthesis.

    更新日期:2018-01-03
  • A sensible climate solution for the boreal forest
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-02
    Rasmus Astrup, Pierre Y. Bernier, Hélène Genet, David A. Lutz, Ryan M. Bright

    A sensible climate solution for the boreal forest A sensible climate solution for the boreal forest, Published online: 02 January 2018; doi:10.1038/s41558-017-0043-3 Climate change could increase fire risk across most of the managed boreal forest. Decreasing this risk by increasing the proportion of broad-leaved tree species is an overlooked mitigation–adaption strategy with multiple benefits.

    更新日期:2018-01-03
  • Looking to nature for solutions
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-02
    Will R. Turner

    Looking to nature for solutions Looking to nature for solutions, Published online: 02 January 2018; doi:10.1038/s41558-017-0048-y Completely stopping fossil fuel use may not be enough to avoid dangerous climate change. Recent research on the mitigation potential of conservation, restoration, and improved land management demonstrates that natural solutions can reduce emissions and remove atmospheric CO2 while safeguarding food security and biodiversity.

    更新日期:2018-01-03
  • Arctic storms
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-02
    Graham Simpkins

    Arctic storms Arctic storms, Published online: 02 January 2018; doi:10.1038/s41558-017-0050-4 Arctic storms

    更新日期:2018-01-03
  • Evaluating the capability of Landsat 8 OLI and SPOT 6 for discriminating invasive alien species in the African Savanna landscape
    Int. J. Appl. Earth Obs. Geoinf. (IF 3.93) Pub Date : 2018-01-02
    Mahlatse Kganyago, John Odindi, Clement Adjorlolo, Paidamoyo Mhangara

    Globally, there is paucity of accurate information on the spatial distribution and patch sizes of Invasive Alien Plants (IAPs) species. Such information is needed to aid optimisation of control mechanisms to prevent further spread of IAPs and minimize their impacts. Recent studies have shown the capability of very high spatial (<1 m) and spectral resolution (<10 nm) data for discriminating vegetation species. However, very high spatial resolution may introduce significant intra-species spectral variability and result in reduced mapping accuracy, while higher spectral resolution data are commonly limited to smaller areas, are costly and computationally expensive. Alternatively, medium and high spatial resolution data are available at low or no cost and have limitedly been evaluated for their potential in determining invasion patterns relevant for invasion ecology and aiding effective IAPs management. In this study medium and high resolution datasets from Landsat Operational Land Imager (OLI) and SPOT 6 sensors respectively, were evaluated for mapping the distribution and patch sizes of IAP, Parthenium hysterophorus in the savannah landscapes of KwaZulu-Natal, South Africa. Support Vector Machines (SVM) classifier was used for classification of both datasets. Results indicated that SPOT 6 had a higher overall accuracy (86%) than OLI (83%) in mapping P. hysterophorus. The study found larger distributions and patch sizes in OLI than in SPOT 6 as a result of possible P. hysterophorus expansion due to temporal differences between images and coarser pixels were insufficient to delineate gaps inside larger patches. On the other hand, SPOT 6 showed better capabilities of delineating gaps and boundaries of patches, hence had better estimates of distribution and patch sizes. Overall, the study showed that OLI may be suitable for mapping well-established patches for the purpose of large scale monitoring, while SPOT 6 can be used for mapping small patches and prioritising them for eradication to prevent further spread at a landscape scale.

    更新日期:2018-01-03
  • A modified temporal criterion to meta-optimize the extended Kalman filter for land cover classification of remotely sensed time series
    Int. J. Appl. Earth Obs. Geoinf. (IF 3.93) Pub Date : 2018-01-02
    B.P. Salmon, W. Kleynhans, J.C. Olivier, F. van den Bergh, K.J. Wessels

    Humans are transforming land cover at an ever-increasing rate. Accurate geographical maps on land cover, especially rural and urban settlements are essential to planning sustainable development. Time series extracted from MODerate resolution Imaging Spectroradiometer (MODIS) land surface reflectance products have been used to differentiate land cover classes by analyzing the seasonal patterns in reflectance values. The proper fitting of a parametric model to these time series usually requires several adjustments to the regression method. To reduce the workload, a global setting of parameters is done to the regression method for a geographical area. In this work we have modified a meta-optimization approach to setting a regression method to extract the parameters on a per time series basis. The standard deviation of the model parameters and magnitude of residuals are used as scoring function. We successfully fitted a triply modulated model to the seasonal patterns of our study area using a non-linear extended Kalman filter (EKF). The approach uses temporal information which significantly reduces the processing time and storage requirements to process each time series. It also derives reliability metrics for each time series individually. The features extracted using the proposed method are classified with a support vector machine and the performance of the method is compared to the original approach on our ground truth data.

    更新日期:2018-01-03
  • Accounting for the human factor
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-01
    Jonathan M. Gilligan

    Accounting for the human factorAccounting for the human factor, Published online: 01 January 2018; doi:10.1038/s41558-017-0038-0One of the greatest sources of uncertainty about future climate change is the path greenhouse gas emissions will take. Now research using a coupled model of human behaviour and climate finds that individual behaviour can significantly alter emissions trajectories and global temperature.

    更新日期:2018-01-01
  • Inverse relationship between present-day tropical precipitation and its sensitivity to greenhouse warming
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-01
    Yoo-Geun Ham, Jong-Seong Kug, Jun-Young Choi, Fei-Fei Jin, Masahiro Watanabe

    Future changes in rainfall have serious impacts on human adaptation to climate change, but quantification of these changes is subject to large uncertainties in climate model projections. To narrow these uncertainties, significant efforts have been made to understand the intermodel differences in future rainfall changes. Here, we show a strong inverse relationship between present-day precipitation and its future change to possibly calibrate future precipitation change by removing the present-day bias in climate models. The results of the models with less tropical (40° S–40° N) present-day precipitation are closely linked to the dryness over the equatorial central-eastern Pacific, and project weaker regional precipitation increase due to the anthropogenic greenhouse forcing1,2,3,4,5,6 with stronger zonal Walker circulation. This induces Indo-western Pacific warming through Bjerknes feedback, which reduces relative humidity by the enhanced atmospheric boundary-layer mixing in the future projection. This increases the air–sea humidity difference to enhance tropical evaporation and the resultant precipitation. Our estimation of the sensitivity of the tropical precipitation per 1 K warming, after removing a common bias in the present-day simulation, is about 50% greater than the original future multi-model projection.

    更新日期:2018-01-01
  • Elevated increases in human-perceived temperature under climate warming
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-01
    Jianfeng Li, Yongqin David Chen, Thian Yew Gan, Ngar-Cheung Lau

    Changes in air temperature (AT), humidity and wind speed (Wind) affect apparent temperature (AP), the human-perceived equivalent temperature1,2,3. Here we show that under climate warming, both reanalysis data sets and Global Climate Model simulations indicate that AP has increased faster than AT over land. The faster increase in AP has been especially significant over low latitudes and is expected to continue in the future. The global land average AP increased at 0.04 °C per decade faster than AT before 2005. This trend is projected to increase to 0.06 °C (0.03–0.09 °C; minimum and maximum of the ensemble members) per decade and 0.17 °C (0.12–0.25 °C) per decade under the Representative Concentration Pathway 4.5 scenario (RCP4.5) and RCP8.5, respectively, and reduce to 0.02 °C (0–0.03 °C) per decade under RCP2.6 over 2006–2100. The higher increment in AP in summer daytime is more remarkable than in winter night-time and is most prominent over low latitudes. The summertime increases in AT-based thermal discomfort are projected to balance the wintertime decreases in AT-based discomfort over low and middle latitudes, while the summertime increases in AP-based thermal discomfort are expected to outpace the wintertime decreases in AP-based thermal discomfort. Effective climate change mitigation efforts to achieve RCP2.6 can considerably alleviate the faster increase in AP.

    更新日期:2018-01-01
  • Linking models of human behaviour and climate alters projected climate change
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-01
    Brian Beckage, Louis J. Gross, Katherine Lacasse, Eric Carr, Sara S. Metcalf, Jonathan M. Winter, Peter D. Howe, Nina Fefferman, Travis Franck, Asim Zia, Ann Kinzig, Forrest M. Hoffman

    Although not considered in climate models, perceived risk stemming from extreme climate events may induce behavioural changes that alter greenhouse gas emissions. Here, we link the C-ROADS climate model to a social model of behavioural change to examine how interactions between perceived risk and emissions behaviour influence projected climate change. Our coupled climate and social model resulted in a global temperature change ranging from 3.4–6.2 °C by 2100 compared with 4.9 °C for the C-ROADS model alone, and led to behavioural uncertainty that was of a similar magnitude to physical uncertainty (2.8 °C versus 3.5 °C). Model components with the largest influence on temperature were the functional form of response to extreme events, interaction of perceived behavioural control with perceived social norms, and behaviours leading to sustained emissions reductions. Our results suggest that policies emphasizing the appropriate attribution of extreme events to climate change and infrastructural mitigation may reduce climate change the most.

    更新日期:2018-01-01
  • Keeping global warming within 1.5 °C constrains emergence of aridification
    Nat. Clim. Change (IF 19.304) Pub Date : 2018-01-01
    Chang-Eui Park, Su-Jong Jeong, Manoj Joshi, Timothy J. Osborn, Chang-Hoi Ho, Shilong Piao, Deliang Chen, Junguo Liu, Hong Yang, Hoonyoung Park, Baek-Min Kim, Song Feng

    Aridity—the ratio of atmospheric water supply (precipitation; P) to demand (potential evapotranspiration; PET)—is projected to decrease (that is, areas will become drier) as a consequence of anthropogenic climate change, exacerbating land degradation and desertification1,2,3,4,5,6. However, the timing of significant aridification relative to natural variability—defined here as the time of emergence for aridification (ToEA)—is unknown, despite its importance in designing and implementing mitigation policies7,8,9,10. Here we estimate ToEA from projections of 27 global climate models (GCMs) under representative concentration pathways (RCPs) RCP4.5 and RCP8.5, and in doing so, identify where emergence occurs before global mean warming reaches 1.5 °C and 2 °C above the pre-industrial level. On the basis of the ensemble median ToEA for each grid cell, aridification emerges over 32% (RCP4.5) and 24% (RCP8.5) of the total land surface before the ensemble median of global mean temperature change reaches 2 °C in each scenario. Moreover, ToEA is avoided in about two-thirds of the above regions if the maximum global warming level is limited to 1.5 °C. Early action for accomplishing the 1.5 °C temperature goal can therefore markedly reduce the likelihood that large regions will face substantial aridification and related impacts.

    更新日期:2018-01-01
  • Global Boundary Stratotype Section and Point (GSSP) for the Anthropocene Series: Where and how to look for potential candidates
    Earth Sci. Rev. (IF 7.051) Pub Date : 2017-12-30
    Colin N. Waters, Jan Zalasiewicz, Colin Summerhayes, Ian J. Fairchild, Neil L. Rose, Neil J. Loader, William Shotyk, Alejandro Cearreta, Martin J. Head, James P.M. Syvitski, Mark Williams, Michael Wagreich, Anthony D. Barnosky, An Zhisheng, Reinhold Leinfelder, Catherine Jeandel, Agnieszka Gałuszka, Juliana A. Ivar do Sul, Felix Gradstein, Will Steffen, John R. McNeill, Scott Wing, Clément Poirier, Matt Edgeworth

    The Anthropocene as a potential new unit of the International Chronostratigraphic Chart (which serves as the basis of the Geological Time Scale) is assessed in terms of the stratigraphic markers and approximate boundary levels available to define the base of the unit. The task of assessing and selecting potential Global Boundary Stratotype Section and Point (GSSP) candidate sections, a required part of the process in seeking formalisation of the term, is now being actively pursued. Here, we review the suitability of different stratified palaeoenvironmental settings and facies as potential hosts for a candidate GSSP and auxiliary sections, and the relevant stratigraphical markers for correlation. Published examples are evaluated for their strengths and weaknesses in this respect. A marked upturn in abundance of radioisotopes of 239Pu or 14C, approximately in 1952 and 1954 CE respectively, broadly coincident with a downturn in δ13C values, is applicable across most environments. Principal palaeoenvironments examined include: settings associated with accumulations of anthropogenic material, marine anoxic basins, coral reefs, estuaries and deltas, lakes at various latitudes, peat bogs, snow/ice layers, speleothems and trees. Together, many of these geographically diverse palaeoenvironments offer annual/subannual laminae that can be counted and independently dated radiometrically (e.g. by 210Pb). Examples of possible sections offer the possibility of correlation with annual/seasonal resolution. From among such examples, a small number of potentially representative sites require the acquisition of more systematic and comprehensive datasets, with correlation established between sections, to allow selection of a candidate GSSP and auxiliary stratotypes. The assessments in this paper will help find the optimal locations for these sections.

    更新日期:2018-01-01
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  • 更新日期:2017-12-31
  • Binding geometries of silicate species on ferrihydrite surfaces
    ACS Earth Space Chem. Pub Date : 2017-12-29
    Xiaoming Wang, James David Kubicki, Jean-François Boily, Glenn Waychunas, Yongfeng Hu, Xionghan Feng, Mengqiang Zhu

    Silicate sorption on ferrihydrite surfaces, as monomers, oligomers, and polymers, strongly affects ferrihydrite crystallinity, thermodynamic stability, and surface reactivity. How these silicate species bind on ferrihydrite surfaces is, however, not well understood. We have determined silicate binding geometries using a combination of X-ray absorption spectroscopy (XAS), differential atomic pair distribution function (d-PDF) analysis, and density functional theory (DFT) calculations. Silicon K-edge absorption pre-edges and DFT-predicted energies indicate that silicate forms monomeric monodentate-mononuclear (MM) complexes at low silicate sorption loadings. With increasing silicate loading, the pre-edge peak shifts to higher energies, suggesting changes in silicate binding geometry towards multi-dentate complexation. The d-PDF analysis determines the Si–Fe interatomic distance to be ~ 3.25 Å for the high loading samples. The DFT calculations indicate that such distance corresponds to an oligomer in the bidentate-binuclear (BB) binding geometry. The transition of the silicate sorption geometry accompanied with polymerization can affect stability of ferrihydrite and its adsorption and redox reactivity, and increase the degree of Si isotopic fractionation upon silicate sorption on Fe oxides. Monodentate-mononuclear monomeric complexes and bidentate-binuclear oligomeric complexes should be used for surface complexation models predicting silicate sorption on Fe oxide surfaces.

    更新日期:2017-12-31
  • Effects of simultaneous application of ferrous iron and nitrate on arsenic accumulation in rice grown in contaminated paddy soil
    ACS Earth Space Chem. Pub Date : 2017-12-29
    Xiangqin Wang, Tongxu Liu, Fangbai Li, Bin Li, Chuanping Liu

    The objective of this study was to investigate the effects of simultaneous application of ferrous iron (Fe(II)) and nitrate (NO3–) on arsenic (As) accumulation in rice plants during the entire growth period. To this end, Fe(II) and NO3– were simultaneously applied to As-contaminated soil in a pot experiment conducted under climate-controlled greenhouse conditions. Compared with the control and the sole treatments with Fe(II), NO3–, or amorphous iron (Fe) oxides, the simultaneous application of Fe(II) and NO3– significantly reduced As bioavailability by enhancing As(V) immobilization in the soil and also significantly inhibited As accumulation in rice plants, especially that of iAs in the grain. The presence of Fe(II) and nitrate can decrease As releasing via inhibiting reductive dissolution of iron minerals, and the Fe(II) oxidation coupled with nitrate reduction can immobilize As via incorporating As into iron secondary minerals. Therefore, the simultaneous application of Fe(II) and NO3– effectively decreased As accumulation in rice plants by enhancing As oxidation/immobilization mediated by abiotic/biotic Fe redox transformation and mineralization. These findings provided new insights into the Fe/N/As biogeochemical cycles and are also important from the view of agronomic management of As toxicity and mitigation in As-contaminated paddy fields.

    更新日期:2017-12-31
  • Fracture Evolution in Multi-mineral Systems: The Role of Mineral Composition, Flow Rate and Fracture Aperture Heterogeneity
    ACS Earth Space Chem. Pub Date : 2017-12-29
    Hang Deng, Carl I. Steefel, Sergi Molins, Donald DePaolo

    Geochemical reactions add complexity to the characterization and prediction of fracture hydraulic properties because they depend on factors that are highly heterogeneous, such as mineral composition. But systematic analyses of fracture evolution in mineralogically heterogeneous systems are still limited. In this study, we investigated fracture evolution in multi-mineral systems using a reduced dimension reactive transport model. The model was developed and tested based on experimental studies and addresses the complex morphological and geochemical changes that arise from the presence of multiple minerals of different reactivity. Numerical experiments were performed using randomly generated initial fracture geometries based on representative geostatistics, different categories of mineral composition, and a range of flow rates that are relevant to geologic carbon storage systems. The simulation results showed distinct dissolution regimes at different flow rates, each of which produced characteristic dissolution patterns and temporal evolutions of chemical reactions and fracture hydraulic properties. Overall, as flow rate increases, fracture evolution shifts from compact dissolution to fracture channelization to uniform dissolution. The corresponding flow rate for a given dissolution regime, however, varies considerably with mineral composition. Fracture evolution, especially in the flow regime that induces fracture channelization, is also affected by initial fracture geometry. The numerical experiments were used to develop a multi-reaction Damköhler number (mDa) for the prediction of fracture evolution, and fracture channelization in particular, in multi-mineral systems. The multi-reaction Damköhler number also provides a useful framework for the evaluation of caprock integrity in geologic carbon storage systems.

    更新日期:2017-12-31
  • Low-δ18O mantle-derived magma in Panjal traps overprinted by hydrothermal alteration and Himalayan UHP metamorphism: Revealed by SIMS zircon analysis
    Gondwana Res. (IF 6.959) Pub Date : 2017-12-28
    Hafiz Ur Rehman, Kouki Kitajima, John W. Valley, Sun-Lin Chung, Hao-Yang Lee, Hiroshi Yamamoto, Tahseenullah Khan
    更新日期:2017-12-31
  • Permo-Triassic evolution of the southern margin of the Central Asian Orogenic Belt revisited: insights from Late Permian igneous suite in the Daheishan Horst, NE China
    Gondwana Res. (IF 6.959) Pub Date : 2017-12-28
    Zhi-Gang Song, Zuo-Zhen Han, Li-Hua Gao, Hong-Yan Geng, Xu-Ping Li, Fan-Xue Meng, Mei Han, Wen-Jian Zhong, Jing-Jing Li, Qing-Xiang Du, Jun-Lei Yan, Hui Liu

    The Daheishan Horst in Jilin Province, NE China, is the key geological unit that links the Solonker-Xar Moron-Changchun and Changchun-Yanji sutures, which are generally interpreted to mark the zone of closure of the Paleo-Asian Ocean along the southeastern margin of the Central Asian Orogenic Belt (CAOB). Here we investigate a suite of volcanic rocks from Daheishan and the Doushantouzi syenogranite intrusion to gain insights into the Permian–Triassic tectonic evolution of the eastern segment of the Paleo-Asian Ocean. Zircon U-Pb data and zircon rare earth element (REE) patterns indicate that the igneous suite formed during the Late Permian (ca. 253–256 Ma) and underwent late-stage alteration during Early Triassic tectono-thermal events. The presence of older magmatic zircon grains in this igneous suite suggest multiple pulses of magmatism during the Permian in this region. The Daheishan volcanic rocks predominantly consist of intermediate-felsic rocks, including andesite, rhyodacite and rhyolite with minor basaltic lava. Geochemically, the basaltic rocks belong to calc-alkaline series, whereas the intermediate-felsic rocks classify as calc-alkaline to high-K calc-alkaline series. The Doushantouzi syenogranites belong to peraluminous I-type granites, with the A/CNK ratio between 1.06 and 1.15. All these rocks have an arc-like affinity with enriched light rare earth elements (LREE) and large ion lithophile elements (LILE; e.g. Rb, Ba and U) and depleted high field strength elements (HFSE; e.g. Nb, Ta and Ti). The Daheishan intermediate-felsic rocks and Doushantouzi syenogranites have higher SiO2 contents but lower MgO contents and Mg# values and plot within the field of experimentally derived partial melts from metabasaltic rocks in MgO vs. SiO2 diagram. These geochemical features, together with the positive εNd(t) (+ 1.6 to + 4.6) and εHf(t) (+ 1.53 to + 7.41) values of zircon grains, indicate that the primary magma of these intermediate-felsic rocks likely originated from the partial melting of a juvenile metabasaltic lower crust. In contrast, the basaltic lavas were probably derived from the partial melting of a depleted mantle wedge that was metasomatized by fluids from a subducted slab, as suggested by their low initial 87Sr/86Sr ratios and depleted εNd(t) (+ 3.6 to + 4.4) values. These data, in conjunction with regional geological investigations, suggest that formation of this Late Permian igneous suite was related to the northward subduction of the Paleo-Asian oceanic plate beneath the Songliao-Xilinhot block and that the eastern segment of the Paleo-Asian Ocean did not close before the Late Permian.

    更新日期:2017-12-31
  • A North American Hydroclimate Synthesis (NAHS) of the Common Era
    Glob. Planet. Change (IF 3.915) Pub Date : 2017-12-28
    Jessica R. Rodysill, Lesleigh Anderson, Thomas M. Cronin, Miriam C. Jones, Robert S. Thompson, David B. Wahl, Debra A. Willard, Jason A. Addison, Jay R. Alder, Katherine H. Anderson, Lysanna Anderson, John A. Barron, Christopher E. Bernhardt, Steven W. Hostetler, Natalie M. Kehrwald, Nicole S. Khan, Julie N. Richey, Scott W. Starratt, Laura E. Strickland, Michael R. Toomey, Claire C. Treat, G. Lynn Wingard

    This study presents a synthesis of century-scale hydroclimate variations in North America for the Common Era (last 2000 years) using new age models of previously published multiple proxy-based paleoclimate data. This North American Hydroclimate Synthesis (NAHS) examines regional hydroclimate patterns and related environmental indicators, including vegetation, lake water elevation, stream flow and runoff, cave drip rates, biological productivity, assemblages of living organisms, and salinity. Centennial-scale hydroclimate anomalies are obtained by iteratively sampling the proxy data on each of thousands of age model realizations and determining the fractions of possible time series indicating that the century-smoothed data was anomalously wet or dry relative to the 100 BCE to 1900 CE mean. Results suggest regionally asynchronous wet and dry periods over multidecadal to centennial timescales and frequent periods of extended regional drought. Most sites indicate drying during previously documented multicentennial periods of warmer Northern Hemisphere temperatures, particularly in the western U.S., central U.S., and Canada. Two widespread droughts were documented by the NAHS: from 50 BCE to 450 CE and from 800 to 1100 CE. Major hydroclimate reorganizations occurred out of sync with Northern Hemisphere temperature variations and widespread wet and dry anomalies occurred during both warm and cool periods. We present a broad assessment of paleoclimate relationships that highlights the potential influences of internal variability and external forcing and supports a prominent role for Pacific and Atlantic Ocean dynamics on century-scale continental hydroclimate.

    更新日期:2017-12-31
  • A global framework for the Earth: Putting geological sciences in context
    Glob. Planet. Change (IF 3.915) Pub Date : 2017-12-28
    Benjamin van Wyk de Vries, Paul Byrne, Audray Delcamp, Pall Einarson, Oğuz Göğüş, Marie-Noelle Guilbaud, Miruts Hagos, Szabolcs Harangi, Dougal Jerram, Liviu Matenco, Sophie Mossoux, Karoly Nemeth, Mehran Maghsoudi, Michael S. Petronis, Vladislav Rapprich, William Rose, Erika Vye

    We propose a global framework for the Earth system to facilitate communication between the geoscience community, the public and policy makers. Geoscience research aims to understand the history and evolution of the Earth system. This combines the non-living and living parts of the Earth, especially through interactions of the lithosphere, biosphere and atmosphere as well as the other parts of the system, such as the asthenosphere, core and extraterrestrial influences. Such research considers a system that spans scales from microscopic (micrometer scale) to megascopic (many 1000 s of km scale), and from milliseconds to millions of years. To connect different parts of this immense system, we habitually use a wide range of ad hoc geological frameworks, systems and geological environment models, where different processes and features operate and combine. In consequence, one way to judge the significance of our work, and to increase its value, is to assess how the elements studied are integrated within the whole Earth system. This allows us to see what implications any study has for this greater Earth system. To do this successfully, our research needs a standard global framework to assess a study's relevance. However, such a global framework does not formally exist, and so this article looks at existing examples and proposes one that can systematically place research into a global geological context. This proposed framework has the advantage of being useful for communicating geological processes to other disciplines, and can be used for any type of Earth (or planetary) environment. This framework is a fundamental tool for geoscience communication and for outreach, especially through geological heritage (geoheritage). Geoheritage concerns the valuing and protection of geoscience and geological sites, and is a vital tool for communicating geoscience. It can be used to communicate our knowledge of global change, providing, through landscapes and outcrops, a story that renders the concepts and advances of geoscience accessible. Like our basic research, the concept of geoheritage evolves as our understanding of the Earth progresses, and these dual changes can be explained with the global framework. Geoheritage is a global activity and it needs a global framework to put sites into context. A revision of the UNESCO geological thematic studies was called for by the World Heritage Committee in 2014 (decision: 38 COM 8B.11), and this can be done with the input from the full geoscience community using this global geological framework. Thus, for research, geoscience policy and for geoheritage, a global framework is now needed. The proposed framework can place any site in its geological environment, related to its lithospheric plate tectonic setting and its history. The framework has a solid-earth bias (lithosphere), but includes all other spheres, such as the biosphere and anthropogenic activity. Extraterrestrial influences, like solar variations and impacts are included. The framework is phenomenological, due to the necessity of grouping the features that we see, but these phenomena provide evidence of processes that we cannot see. The basic format is a table, a sketch of the Earth and a system diagram, three complementary and most powerful ways of depicting a system. A timeline, or stratigraphic column can be included, to show the evolution of geological history, and the table can be used as a ‘game board’ where one site migrates across from one set of conditions to another over time. The global framework allows any research site, area or subject to be set in the Earth's system, in a way that gives it context, allows comparisons and provides significance. We suggest that it can be a template for an internationally accepted version used to consolidate the necessary geoscience – geoheritage link and promote outreach.

    更新日期:2017-12-31
  • Effects of a Simple Convective Organization Scheme in a Two-Plume GCM
    J. Adv. Model. Earth Syst. (IF 4.189) Pub Date : 2017-12-27
    Baohua Chen, Brian E. Mapes

    Abstract A set of experiments is described with the Community Atmosphere Model (CAM5) using a two-plume convection scheme. To represent the differences of organized convection from General Circulation Model (GCM) assumptions of isolated plumes in uniform environments, a dimensionless prognostic “organization” tracer Ω is invoked to lend the second plume a buoyancy advantage relative to the first, as described in Mapes and Neale (2011). When low-entrainment plumes are unconditionally available (Ω = 1 everywhere), deep convection occurs too easily, with consequences including premature (upstream) rainfall in inflows to the deep tropics, excessive convective vs. large-scale rainfall, poor relationships to the vapor field, stable bias in the mean state, weak and poor tropical variability, and midday peak in diurnal rainfall over land. Some of these are shown to also be characteristic of CAM4 with its separated deep and shallow convection schemes. When low-entrainment plumes are forbidden by setting Ω = 0 everywhere, some opposite problems can be discerned. In between those extreme cases, an interactive Ω driven by the evaporation of precipitation acts as a local positive feedback loop, concentrating deep convection: In areas of little recent rain, only highly entraining plumes can occur, unfavorable for rain production. This tunable mechanism steadily increases precipitation variance in both space and time, as illustrated here with maps, time-longitude series, and spectra, while avoiding some mean state biases as illustrated with process-oriented diagnostics such as conserved variable profiles and vapor-binned precipitation curves.

    更新日期:2017-12-28
  • Full Coupling Between the Atmosphere, Surface, and Subsurface for Integrated Hydrologic Simulation
    J. Adv. Model. Earth Syst. (IF 4.189) Pub Date : 2017-12-27
    Jason Hamilton Davison, Hyoun-Tae Hwang, Edward A. Sudicky, Derek V. Mallia, John C. Lin

    Abstract An ever increasing community of earth system modelers are incorporating new physical processes into numerical models. This trend is facilitated by advancements in computational resources, improvements in simulation skill, and the desire to build numerical simulators that represent the water cycle with greater fidelity. In this quest to develop a state-of-the-art water cycle model, we coupled HydroGeoSphere (HGS), a 3D control-volume finite element surface and variably-saturated subsurface flow model that includes evapotranspiration processes, to the Weather Research and Forecasting (WRF) Model, a 3D finite difference nonhydrostatic mesoscale atmospheric model. The two-way coupled model, referred to as HGS-WRF, exchanges the actual evapotranspiration fluxes and soil saturations calculated by HGS to WRF; conversely, the potential evapotranspiration and precipitation fluxes from WRF are passed to HGS. The flexible HGS-WRF coupling method allows for unique meshes used by each model, while maintaining mass and energy conservation between the domains. Furthermore, the HGS-WRF coupling implements a sub-time stepping algorithm to minimize computational expense. As a demonstration of HGS-WRF's capabilities, we applied it to the California Basin and found a strong connection between the depth to the groundwater table and the latent heat fluxes across the land surface.

    更新日期:2017-12-28
  • The Impact of Parametric Uncertainties on Biogeochemistry in the E3SM Land Model
    J. Adv. Model. Earth Syst. (IF 4.189) Pub Date : 2017-12-27
    Daniel Ricciuto, Khachik Sargsyan, Peter Thornton

    Abstract We conduct a global sensitivity analysis (GSA) of the Energy Exascale Earth System Model (E3SM), land model (ELM) to calculate the sensitivity of five key carbon cycle outputs to 68 model parameters. This GSA is conducted by first constructing a Polynomial Chaos (PC) surrogate via new Weighted Iterative Bayesian Compressive Sensing (WIBCS) algorithm for adaptive basis growth leading to a sparse, high-dimensional PC surrogate with 3000 model evaluations. The PC surrogate allows efficient extraction of GSA information leading to further dimensionality reduction. The GSA is performed at 96 FLUXNET sites covering multiple plant functional types (PFTs) and climate conditions. About 20 of the model parameters are identified as sensitive with the rest being relatively insensitive across all outputs and PFTs. These sensitivities are dependent on PFT, and are relatively consistent among sites within the same PFT. The five model outputs have a majority of their highly sensitive parameters in common. A common subset of sensitive parameters is also shared among PFTs, but some parameters are specific to certain types (e.g. deciduous phenology). The relative importance of these parameters shifts significantly among PFTs and with climatic variables such as mean annual temperature.

    更新日期:2017-12-28
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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