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  • 1
    Publication Date: 2018-07-04
    Description: Publication date: Available online 2 July 2018 Source: Earth-Science Reviews Author(s): C. Thomazo, A. Brayard, S. Elmeknassi, E. Vennin, N. Olivier, G. Caravaca, G. Escarguel, E. Fara, K.G. Bylund, J.F. Jenks, D.A. Stephen, B. Killingsworth, P. Sansjofre, P. Cartigny The Early Triassic is generally portrayed as a time of various, high ecological stresses leading to a delayed biotic recovery after the devastating end-Permian mass extinction. This interval is notably characterized by repeated biotic crises (e.g., during the late Smithian), large-scale fluctuations of the global carbon, nitrogen and sulfur cycles as well as harsh marine conditions including a combination of ocean acidification, anoxia, extreme seawater temperatures and shifting productivity. Observations from different paleolatitudes suggest that sulfidic (H 2 S-rich) conditions may have developed widely during the Early Triassic, possibly reaching up to ultra-shallow environments in some places. However, the existence and the spatio-temporal extent of such redox swings remain poorly constrained. In order to explore Early Triassic paleoceanographic redox changes and their potential influences on the biotic recovery, we analyzed multiple sulfur isotopes ( 32 S, 33 S, 34 S, and 36 S) of sedimentary pyrite and carbonate associated sulfate (δ 34 S CAS ) from the Mineral Mountains section, Utah. Sediments from this section were mainly deposited in shallow waters and span the Smithian and lower Spathian. We report a 68‰ range of variations in δ 34 S py associated with Δ 33 S py varying from −0.01‰ to +0.12‰, whereas the δ 34 S CAS varies between +19.5‰ and + 34.8‰. We interpret the observed signal of multiple sulfur isotopes as reflecting the operation of pore-water synsedimentary microbial sulfate reduction in open system with respect to sulfates before the late Smithian, evolving to a closed system, sulfate limited, Rayleigh-type distillation across the Smithian/Spathian boundary (SSB) and immediately after the SSB. We argue that this marked change is driven by the effectiveness of the connection between the sedimentary pore waters and the overlying water column, which is, in our case, controlled by the local sedimentological conditions such as the bioturbation intensity and the sedimentation rate. Therefore, our results suggest that changes in the sulfur cycle before and across the SSB at Mineral Mountains is probably a local consequence of the loss of the mixed sedimentary layer during the late Smithian extinction event, as opposed to reflecting the development of a lethal anoxic ocean at the global scale.
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    Electronic ISSN: 1872-6828
    Topics: Geography , Geosciences
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  • 2
    Publication Date: 2018-07-02
    Description: Publication date: Available online 30 June 2018 Source: Earth-Science Reviews Author(s): Remus Prăvălie Forests are among the most important terrestrial ecological systems in terms of the multitude of ecosystem functions and services they provide. These biotic systems are vital not only for ensuring the wellbeing of human society and for preserving global biodiversity, but also for regulating the climate system, decarbonizing the atmosphere via carbon sequestration (in biomass or underlying soil carbon pools) and evaporative cooling processes that mitigate climate warming. However, forest ecosystems are currently being subjected to a wide range of natural and anthropic disturbances that pose a real threat not only to forest health and the various benefits forests provide for human society, but also to the overall functioning of the global system. This paper is a review that aims to analyse, in a brief and holistic manner, the main perturbations Earth forest ecosystems are currently facing, both the obvious (e.g. deforestation) and discrete/silent ones (e.g. defaunation) that have generally not yet been tackled strictly as ecological forest issues in the international scientific literature. At the same time, the paper aims to highlight the possible effects generated by forest perturbations in the global warming process, through carbon fluxes and biogeophysical feedbacks between these terrestrial systems and the atmosphere. Upon analysis of a vast scientific bibliography, it was found there currently are 12 major forest disturbances that can be grouped into three categories based on the prevalence of triggering causes, i.e. climatic (phenological shifts, range shifts, die-off events, insect infestations), anthropic (deforestation, fragmentation, air pollution) and mixed (defaunation, fires, composition shifts, net primary productivity shifts, biogeochemical shifts) perturbations. These ecological issues, which occur frequently, intensely and on large spatial scales, are able to significantly disrupt forest productivity and therefore strongly erode the forests’capacity to stabilize the climate system. All identified disturbances can amplify global warming in various ways, including by means of many positive feedback mechanisms in the case of climatic perturbations. Finally, this review paper proposes five major anthropogenic strategies to fight this multidimensional forest crisis – mitigate, adapt, repair, protect and research actions, which, if implemented rapidly, efficiently and on a large scale via international policies, can successfully stabilize these terrestrial ecosystems and, implicitly, the climate system in the 21st century.
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    Electronic ISSN: 1872-6828
    Topics: Geography , Geosciences
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  • 3
    Publication Date: 2018-07-02
    Description: Publication date: Available online 30 June 2018 Source: Earth-Science Reviews Author(s): Zhaoliang Song, Congqiang Liu, Karin Müller, Xiaomin Yang, Yuntao Wu, Hailong Wang The terrestrial biogeochemical silicon (Si) cycle may significantly influence the stabilization of soil organic carbon (SOC), and thus plays an important role in regulating the global carbon (C) balance and climate change. Processes involved in Si-enhanced SOC stability at a decadal or centennial scale include protection of SOC through amorphous Si and interactions of Si-iron (Fe) and Si-aluminum (Al). Strategic manipulation of the Si cycle in terrestrial ecosystems offers a new opportunity to enhance soil C sequestration. Rock powder amendment, establishment of Si-rich plant buffer strips and innovative management practices that return Si-rich biomass materials to soil can be implemented as strategies to enhance soil C sequestration through regulating the terrestrial Si cycle. However, quantifying (i) the contribution of different processes to enhance soil dissolved Si and secondary Si minerals, (ii) the relative importance of different SOC stabilization mechanisms, and (iii) the potential and cost of different measures has not been attempted.
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    Electronic ISSN: 1872-6828
    Topics: Geography , Geosciences
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  • 4
    Publication Date: 2018-07-02
    Description: Publication date: Available online 30 June 2018 Source: Earth-Science Reviews Author(s): G. Cassinis, C. Perotti, G. Santi In the Italian regions the stratigraphic successions of the Verrucano s.l. consist essentially of continental alluvial plain to coastal-neritic siliciclastic redbeds, deposited at different times in the Alps (Mid? –Late Permian), the Northern Apennines (Mid?–Late Triassic p.p ., locally in Southern Tuscany also followed by the Jurassic Pseudoverrucano Complex) and the ‘Calabro-Peloritani Arc’ (Mid?-Late Triassic, exceptionally reaching earliest Jurassic), whereas in Sardinia the recognition of the Verrucano succession is still a topic of discussion. The most typical metamorphic lithofacies, in the Pisan Mts. of Tuscany, is represented by the Verrucano s.s. conglomerates and breccias, including quartz clasts and minor metamorphic and volcanic lithics, grading laterally and vertically to quartzitic sandstones and pelites. In the Pisa Symposium the term ‘Verrucano’ was suggested only for those detrital deposits laid down, in the Alpine-Mediterranean areas, after the final act of the Variscan orogeny, and also to use local geographical names. Consequently, the typical terms ‘Verrucano Toscano’, the ‘Verrucano Lombardo’, the ‘Verrucano Briançonnais’ and other similar deposits, being linked to the Variscan belt, were generally accepted. The ages of these ‘Verrucanos’, since they are devoid of fossils, can only be interpreted indirectly. The Verrucano Lombardo of central Southern Alps was recently ascribed to a Mid? –Late Permian interval (Late Guadalupian?–Lopingian p.p .), taking into account that the connected Val Gardena Sandstones of the nearby Venetian region are interdigitated with the Late Permian Bellerophon Fm. The Verrucano Briançonnais of the Maritime Alps is again mostly related to Late Permian, being covered by the Lower Triassic alluvial-deltaic quartzites. In the easternmost Ligurian Apennines, near La Spezia, the Mesozoic section of Punta Bianca, which begins with a fluvial conglomerate, transgressive and unconformable on a metamorphosed Paleozoic Variscan Basement, is composed of two main cycles, of which the upper one correlates to the typical Pisan Verrucano s.s . and the overlying Mt. Serra Quartzites, the latter yielding Carnian pelecypods and vertebrate footprints. The Verrucano from the Mid-Tuscan Ridge to Mt. Leoni and in the Argentario promontory is delimited above by the Tocchi Formation and presumably developed from Middle (Late? Ladinian) up to Late Triassic (Carnian) times; in contrast, in Calabria ( e.g. the Longobucco unit of Sila Grande) and in Sicily ( e.g. the Taormina-Longi Unit of Peloritani Mts.) the so-called (Pseudo-) Verrucano deposits pertain to Mid? –Late Triassic and are capped by a basal Jurassic succession, determined by the discovery of an Early Hettangian palynoflora. All over their distribution areas, the above-mentioned Alpine Verrucanos rest, through an unconformity marked by a gap of varying and imprecise duration, on Late Paleozoic volcanic/sedimentary successions or directly on the underlying Variscan metamorphic basement. Schematically, the post-Variscan succession in Italy can be subdivided into three main tectono-sedimentary megacycles: the first generally ranges from the Late Carboniferous to, or slightly above the Early Permian, the second from Mid? –Late Permian to Middle Triassic , while the third cycle begins with the Mid?-Late Triassic p.p., attaining the Jurassic in some parts of Southern Tuscany and the ‘Calabro-Peloritani Arc’. After the Late Carboniferous and Early Permian transtensional tectonics represented by many strike-slip continental basins (cycle I), widespread Middle Permian geodynamic reorganization (‘Mid-Permian Episode’ Auctt. ) led to the development of a dominant extensional regime, and the birth of tectonic plates and oceans (Neotethys, Meliata-Maliak, etc.) between Africa and Europe. The erosion of the Variscan relief was followed by ingression from S-E sectors of shallow-marine branches of Neotethys (cycle II). The major rifting events that led to the Jurassic birth of the Ligurian-Piedmont Ocean started during the Middle–Late Triassic, and were related to the eastern opening of the Atlantic Ocean. These rifting events gave rise to the development of the Adria and Europe-Corsica-Sardinia conjugate passive margins, characterized by an asymmetric structural and sedimentary evolution. In this geological context, the Verrucano-like deposits of Italy can be interpreted as a discontinuous and asynchronous ‘tectofacies’ that marks the final dismantling of the SE border of the Variscan chain.
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  • 5
    Publication Date: 2018-06-29
    Description: Publication date: Available online 28 June 2018 Source: Earth-Science Reviews Author(s): M. Oliva, M. Žebre, M. Guglielmin, P.D. Hughes, A. Çiner, G. Vieira, X. Bodin, N. Andrés, R.R. Colucci, C. García-Hernández, C. Mora, J. Nofre, D. Palacios, A. Pérez-Alberti, A. Ribolini, J. Ruiz-Fernández, M.A. Sarıkaya, E. Serrano, P. Urdea, M. Valcárcel, J.C. Woodward, C. Yıldırım The relatively warm climate conditions prevailing today in the Mediterranean region limit cold geomorphological processes only to the highest mountain environments. However, climate variability during the Late Pleistocene and Holocene has led to significant spatio-temporal variations of the glacial and periglacial domain in these mountains, including permafrost conditions. Here, we examine the distribution and evolution of permafrost in the Mediterranean region considering five time periods: Last Glaciation, deglaciation, Holocene, Little Ice Age (LIA) and present-day. The distribution of inactive permafrost-derived features as well as sedimentary records indicates that the elevation limit of permafrost during the Last Glaciation was between 1000 m and even 2000 m lower than present. Permafrost was also widespread in non-glaciated slopes above the snowline forming rock glaciers and block streams, as well as meter-sized stone circles in relatively flat summit areas. As in most of the Northern Hemisphere, the onset of deglaciation in the Mediterranean region started around 19-20 ka. The ice-free terrain left by retreating glaciers was subject to paraglacial activity and intense periglacial processes under permafrost conditions. Many rock glaciers, protalus lobes and block streams formed in these recently deglaciated environments, though most of them became gradually inactive as temperatures kept rising, especially those at lower altitudes. Following the Younger Dryas glacial advance, the Early Holocene saw the last massive deglaciation in Mediterranean mountains accompanied by a progressive shift of permafrost conditions to higher elevations. It is unlikely that air temperatures recorded in Mediterranean mountains during the Holocene favoured the existence of widespread permafrost regimes, with the only exception of the highest massifs exceeding 2500-3000 m. LIA colder climate promoted a minor glacial advance and the spatial expansion of permafrost, with the development of new protalus lobes and rock glaciers in the highest massifs. Finally, post-LIA warming has led to glacial retreat/disappearance, enhanced paraglacial activity, shift of periglacial processes to higher elevations, degradation of alpine permafrost along with geoecological changes.
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  • 6
    Publication Date: 2018-06-28
    Description: Publication date: Available online 27 June 2018 Source: Earth-Science Reviews Author(s): Eric Desjardins, Marco Van De Wiel, Yannick Rousseau This paper brings a philosophical perspective on computer simulations in the field of geomorphology. The first part of our analysis presents a general framework within which to interpret and evaluate the adequacy of simulations models pursuing three broad epistemic goals (modes): prediction, explanation, and exploration. It also explains the diverse relationships existing between the phenomenon of equifinality and each one of these modes. The second part of the paper applies this framework to a case in fluvial geomorphology. This application enables further specification of the three modelling modes and shows how they can work together in the inquiry of natural phenomena. Finally, our analysis looks briefly at the path-dependent nature of model building, which highlights the importance of historical contingencies in model development and further support the pragmatic stance endorsed in the framework.
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  • 7
    Publication Date: 2018-06-28
    Description: Publication date: Available online 26 June 2018 Source: Earth-Science Reviews Author(s): Guido M. Gianni, Federico M. Dávila, Andrés Echaurren, Lucas Fennell, Jonathan Tobal, Cesar Navarrete, Paulo Quezada, Andrés Folguera, Mario Giménez This study synthesizes the tectonomagmatic evolution of the Andes between 35°30′S to 48°S with the aim to spotlight early contractional phases on Andean orogenic building and to analyze their potential driving processes. We examine early tectonic stages of the different fold-thrust belts that compose this Andean segment. Additionally, we analyzed the spatio-temporal magmatic arc evolution as a proxy of dynamic changes in Andean subduction during critical tectonic stages of orogenic construction. This revision proposes a hypothesis related the existence of a continuous large-scale flat subduction setting in Cretaceous times with a similar size to the present-largest flat-slab setting on earth. This potential process would have initiated diachronically in the late Early Cretaceous and achieved full development in Late Cretaceous to earliest Paleocene times, constructing a series of fold-thrust belts on the retro-arc zone from 35°30′S to 48°S. Moreover, we assess major paleogeographic changes that took place during flat-slab full development in Maastrichtian-Danian times. At this moment, an enigmatic Atlantic-derived marine flooding covered the Patagonian foreland reaching as far as the Andean foothills. Based on flexural and dynamic topography analyses, we suggest that focused dynamic subsidence at the edge of the flat-slab may explain sudden marine ingression previously linked to continental tilting and orogenic loading during a high sea level global stage. Finally, flat-subduction destabilization could have triggered massive outpouring of synextensional intraplate volcanic rocks in southern South America and the arc retraction in late Paleogene to early Neogene times.
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  • 8
    Publication Date: 2018-06-25
    Description: Publication date: Available online 23 June 2018 Source: Earth-Science Reviews Author(s): Wenchao Yu, Thomas J. Algeo, Jiaxin Yan, Jianghai Yang, Yuansheng Du, Xing Huang, Shenfu Weng The late Paleozoic Era was an interval of major tectonic and climatic changes, including formation of the supercontinent Pangea and the ~60-Myr-long Late Paleozoic Ice Age (LPIA). Although bauxite formation declined globally from the Carboniferous to the Permian in conjunction with global cooling, it was an interval of widespread bauxite formation in China. In South China, (1) the Jiujialu Formation bauxite deposits in central and northern Guizhou (Zunyi area) are of early-middle Visean age; (2) the Dazhuyaun Formation bauxite deposits in northern Guizhou (Wuchuan–Zheng'an–Daozheng area) to southern Chongqing (Nanchuan area) and southeastern Guizhou (Fuquan–Kaili area) are of Late Pennsylvanian–Early Permian age; and (3) the Heshan Formation bauxite deposits in western Guangxi to Yunnan are of Middle–Late Permian age. In North China, the Benxi Formation bauxite deposits are of Late Mississippian–Middle Pennsylvanian age. The contrasting trends in bauxite metallogenesis between China and the rest of the world imply different climatic patterns in the eastern Tethys (high annual humidity with seasonal dryness) and Pangea (aridification). This hypothesis is further supported by differences in the chemical index of alteration, or CIA (>80 in the eastern Tethys vs. ~50 in western Pangea), and in paleotemperatures (mean annual temperature, or MAT = ~20 °C in the eastern Tethys vs. ~4 °C in western Pangea) determined from Permo-Carboniferous siliciclastic deposits. Permo-Carboniferous bauxite deposits in South China formed in coastal plain and coastal karstic depression environments, in which the position of the groundwater table was related to sea-level changes. During the late Paleozoic, high-frequency eustatic fluctuations caused by waxing and waning of Gondwana icesheets controlled sedimentation in these coastal depositional systems, leading to cyclic accumulation of coal and bauxite deposits and cycles of vadose- and phreatic-type bauxite formation. The results of the present study show that, during interglacial stages, lateritization resulted from high p CO 2 , high sea-level and groundwater-table elevations, low precipitation, and limited vegetation cover, whereas during glacial stages, bauxitization of these ferralitic weathering products was promoted by low p CO 2 , low sea-level and groundwater-table elevations, high precipitation, and more extensive vegetation cover. Thus, a unique combination of geographic, climatic, and eustatic factors accounted for widespread formation of bauxite in South China during the LPIA.
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  • 9
    Publication Date: 2018-06-24
    Description: Publication date: Available online 22 June 2018 Source: Earth-Science Reviews Author(s): Stefani Daryanto, Bojie Fu, Lixin Wang, Pierre-André Jacinthe, Wenwu Zhao The maintenance of soil health in agro-ecosystems is essential for sustaining agricultural productivity. Through its positive impacts on various soil physical and biological processes, cover cropping can be an important component of sustainable agricultural production systems. However, the practice of cover cropping can be complex, and possible trade-offs between the benefits and side effects of cover crops have not been examined. To evaluate these benefits and potential trade-offs, we quantitatively synthesized different ecosystem services provided by cover crops (e.g., erosion control, water quality regulation, soil moisture retention, accumulation of soil organic matter and microbial biomass, greenhouse gas (GHG) emission, weed and pest control, as well as yield of the subsequent cash crop) using data from previous publications. We used a simple indicator (δ), defined as the ratio of an observed variable (i.e., ecosystem service) under cover crop and under fallow condition, to evaluate the impacts of cover crops on a given ecosystem service. Our results showed that cover crops provided beneficial ecosystem services in most cases, except for an increase in GHG emission (δ CO2  = 1.46 ± 0.47 and δ N2 O  = 1.49 ± 1.22; x ¯  ± SD) and in pest (nematode) incidence (δ nematode abundance  = 1.29 ± 1.61). It is also important to highlight that, in some cases, tillage could offset the extent of ecosystem service benefits provided by cover crops. Based on this synthesis, we argue that cover crops should be incorporated into modern agricultural practices because of the many environmental benefits they offer, particularly the maintenance of soil and ecosystem health. More importantly, there was generally an increase in cash crop yield with cover cropping (δ yield  = 1.15 ± 0.75), likely due to improvement in various soil processes. Despite its benefits, the complexity of cover crop management should not be overlooked, and site-specific factors such as climate, soil type, cover crop species and tillage practices must be considered in order to optimize the benefits of cover cropping. In addition to crop yield, detailed economic analyses are needed to calculate the direct (e.g., reduction in the amount of chemical fertilizer) and indirect monetary benefits (e.g., the improvement of soil quality) of cover crops. Such a comprehensive analysis could serve as incentive for producers to integrate cover crops into their management practices.
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  • 10
    Publication Date: 2018-06-22
    Description: Publication date: Available online 21 June 2018 Source: Earth-Science Reviews Author(s): Jian Sun, Tiancai Zhou, Miao Liu, Youchao Chen, Hua Shang, Liping Zhu, Arshad Ali Shedayi, Huan Yu, Genwei Cheng, Guohua Liu, Ming Xu, Wei Deng, Jihui Fan, Xuyang Lu, Yukun Sha Future climate warming is expected to have a significant effect on the operation of Earth and Ecological systems. A key concern in the future is water resource availability. In regions such as the Tibet Plateau (TP) lakes and glaciers appear to be highly sensitive to climate forcing and variations in the size and extent of these system will have profound socio-economic and environmental consequences in South and Central Asia. Although the variety of glaciers and lake son the TP is a heavily researched and discussed topic the interaction between glaciers/lakes and climate change has not be thoroughly investigated. Here we present, through a review of existing studies and original remote sensing analysis, a reconstruction of changes in the spatial coverage of glaciers and lakes on the TP from 1990 to 2015 along with an analysis of climate data for the same period. The results revealed that these systems responded to changes in both temperature and precipitation but the nature of this response, and the controlling factor, was spatially diverse. During this interval the total number of lakes increased from 868 to 1207, thus a large number of new lakes (n = 339) formed. The total water surface area of the lakes increase from 38,823.3 km 2 in 1990 to 48,793.0 km 2 in 2015, at a rate of 383.5 km 2 yr -1 . Over this period intensive glacial shrinkage occurred, primarily driven by increasing average temperature, except in the Karakoram Mountains where a slight increase in glacier extent was explained by low and stable temperatures along with increasing precipitation. The expansion of lakes in the central and northeastern TP can, therefore, be explained by a trend of increasing precipitation and the accelerated melting of glaciers associated with rising temperatures, both of which contributed to the enhanced total basin runoff. The shrinkage of lake areas along the Himalayan Mountains is accounted for by low precipitation coupled with high evaporation and limited basin space. The lakes within the Qaidam Basin express a complex pattern of response in association with fluctuating precipitation and strong evaporation. The pattern of shrinking glaciers and expanding lakes indicate that water-cycle processes on the TP have been accelerating during the past 25 years. Under current climates, and future climate change, the shrinkage of glaciers and the enlargement of lakes may be expected to continue to accelerate until a “tipping point” is reached when the meltwater of declining glaciers can no longer sustain the enhanced lake levels. Such a scenario would have severe socio-economic and ecological consequences for this region making the continued study of water-cycle activity across the TP an urgent priority. Graphical abstract
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