ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • American Institute of Physics (AIP)  (241,950)
  • Wiley  (127,181)
Collection
Language
Years
  • 1
    Publication Date: 2019-03-08
    Description: As one of the most abundant and ubiquitous representatives of marine and brackish coastal macrophytobenthos communities, the genus Ulva is not only an important primary producer but also of ecological and morphogenetic interest to many scientists. Ulva mutabilis became an important model organism to study morphogenesis and mutualistic interactions of macroalgae and microorganisms. Here, we report that our collections of Ulva compressa Linnaeus (1753) from Germany are conspecific with the type strains of the model organism U. mutabilis Føyn (1958), which were originally collected at Olhão on the south coast of Portugal and have from that time on been maintained in culture as gametophytic and parthenogenetic lab strains. Different approaches were used to test conspecificity: (i) comparisons of vegetative and reproductive features of cultured material of U. mutabilis and German U. compressa demonstrated a shared morphological pattern; (ii) gametes of U. compressa and U. mutabilis successfully mated and developed into fertile sporophytic first‐generation offspring; (iii) molecular phylogenetics and species delimitation analyses based on the Generalized Mixed Yule‐Coalescent method showed that U. mutabilis isolates (sl‐G[mt+]) and (wt‐G[mt‐]) and U. compressa belong to a unique Molecular Operational Taxonomic Unit. According to these findings, there is sufficient evidence that U. mutabilis and U. compressa should be regarded as conspecific.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: image
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Publication Date: 2019-04-15
    Description: Genetic data have great potential for improving fisheries management by identifying the fundamental management units—that is, the biological populations—and their mixing. However, so far, the number of practical cases of marine fisheries management using genetics has been limited. Here, we used Atlantic cod in the Baltic Sea to demonstrate the applicability of genetics to a complex management scenario involving mixing of two genetically divergent populations. Specifically, we addressed several assumptions used in the current assessment of the two populations. Through analysis of 483 single nucleotide polymorphisms (SNPs) distributed across the Atlantic cod genome, we confirmed that a model of mechanical mixing, rather than hybridization and introgression, best explained the pattern of genetic differentiation. Thus, the fishery is best monitored as a mixed-stock fishery. Next, we developed a targeted panel of 39 SNPs with high statistical power for identifying population of origin and analyzed more than 2,000 tissue samples collected between 2011 and 2015 as well as 260 otoliths collected in 2003/2004. These data provided high spatial resolution and allowed us to investigate geographical trends in mixing, to compare patterns for different life stages and to investigate temporal trends in mixing. We found similar geographical trends for the two time points represented by tissue and otolith samples and that a recently implemented geographical management separation of the two populations provided a relatively close match to their distributions. In contrast to the current assumption, we found that patterns of mixing differed between juveniles and adults, a signal likely linked to the different reproductive dynamics of the two populations. Collectively, our data confirm that genetics is an operational tool for complex fisheries management applications. We recommend focussing on developing population assessment models and fisheries management frameworks to capitalize fully on the additional information offered by genetically assisted fisheries monitoring.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Publication Date: 2019-04-03
    Description: Peat plateaus and palsas are characteristic morphologies of sporadic permafrost, and the transition from permafrost to permafrost‐free ground typically occurs on spatial scales of meters. They are particularly vulnerable to climate change and are currently degrading in Fennoscandia. Here we present a spatially distributed data set of ground surface temperatures for two peat plateau sites in northern Norway for the year 2015–2016. Based on these data and thermal modeling, we investigate how the snow depth and water balance modulate the climate signal in the ground. We find that mean annual ground surface temperatures are centered around 2 to 2.5 °C for stable permafrost locations and 3.5 to 4.5 °C for permafrost‐free locations. The surface freezing degree days are characterized by a noticeable threshold around 200 °C.day, with most permafrost‐free locations ranging below this value and most stable permafrost ones above it. Freezing degree day values are well correlated to the March snow cover, although some variability is observed and attributed to the ground moisture level. Indeed, a zero curtain effect is observed on temperature time series for saturated soils during winter, while drained peat plateaus show early freezing surface temperatures. Complementarily, modeling experiments allow identifying a drainage effect that can modify 1‐m ground temperatures by up to 2 °C between drained and water accumulating simulations for the same snow cover. This effect can set favorable or unfavorable conditions for permafrost stability under the same climate forcing.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2019-05-09
    Description: Genetic divergence among populations arises through natural selection or drift and is counteracted by connectivity and gene flow. In sympatric populations, isolating mechanisms are thus needed to limit the homogenizing effects of gene flow to allow for adaptation and speciation. Chromosomal inversions act as an important mechanism maintaining isolating barriers, yet their role in sympatric populations and divergence with gene flow is not entirely understood. Here, we revisit the question of whether inversions play a role in the divergence of connected populations of the marine fish Atlantic cod (Gadus morhua), by exploring a unique data set combining whole-genome sequencing data and behavioural data obtained with acoustic telemetry. Within a confined fjord environment, we find three genetically differentiated Atlantic cod types belonging to the oceanic North Sea population, the western Baltic population and a local fjord-type cod. Continuous behavioural tracking over 4 year revealed temporally stable sympatry of these types within the fjord. Despite overall weak genetic differentiation consistent with high levels of gene flow, we detected significant frequency shifts of three previously identified inversions, indicating an adaptive barrier to gene flow. In addition, behavioural data indicated that North Sea cod and individuals homozygous for the LG12 inversion had lower fitness in the fjord environment. However, North Sea and fjord-type cod also occupy different depths, possibly contributing to prezygotic reproductive isolation and representing a behavioural barrier to gene flow. Our results provide the first insights into a complex interplay of genomic and behavioural isolating barriers in Atlantic cod and establish a new model system towards an understanding of the role of genomic structural variants in adaptation and diversification.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2019-01-24
    Description: Reconstruction of early Cenozoic deep‐water circulation is one of the keys to modelling Earth's greenhouse‐to‐icehouse surface evolution, but it has long been hampered by the paucity of information from the central South Pacific. To help overcome this knowledge gap, we present new micropalaeontological data from dredged carbonates (R/V Sonne Expedition SO193) at several eastern volcanic salients of the Manihiki Plateau. Interestingly, despite appreciable longitudinal separations among the dredged sites, ages indicated by the foraminiferal assemblages are consistently around the Middle Eocene [including mixed Turonian (Late Cretaceous)/Eocene at a single site], suggesting widespread post‐Eocene cessation of the pelagic sedimentation. By integrating with independent seismic and chronostratigraphic data (Deep Sea Drilling Project Leg 33) for large‐scale erosion of top‐Eocene–Oligocene sedimentary units on the eastern Manihiki Plateau, our results can be viewed as novel physical evidence for the intensification of central South Pacific deep‐water circulation since the Eocene/Oligocene climatic transition.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2019-02-25
    Description: We characterize the differences in the upward planetary‐scale wave propagation during observed weak polar vortex (WPV) events between heavy‐ and light‐sea‐ice years in the Barents‐Kara Sea based on a composite analysis for the period of 1979–2015. Upward wave propagation during WPV events in heavy‐ice years is dominated by the wavenumber 1 component. In contrast, WPV events occurring in light‐ice years are characterized by stronger wavenumber 2 propagation, which is caused by the tropospheric wavenumber 2 response to sea‐ice reduction in the Barents‐Kara Sea. The above observed features are supported by an Atmospheric General Circulation Model experiment. Thus, under present climate conditions, Arctic sea‐ice loss is a possible factor modulating the wave propagation during the WPV events. We also find that the WPV events in light‐ice years have stronger stratosphere‐troposphere coupling, followed by colder midlatitude surface conditions particularly over Eurasia.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2019-04-29
    Description: Sedimentary architecture and morphogenetic evolution of a polar bay-mouth gravel-spit system are revealed based on topographic mapping, sedimentological data, radiocarbon dating and ground-penetrating radar investigations. Data document variable rates of spit progradation in reaction to atmospheric warming synchronous to the termination of the last glacial re-advance (LGR, 0.45–0.25 ka BP), the southern hemisphere equivalent of the Little Ice Age cooling period. Results show an interruption of spit progradation that coincides with the proposed onset of accelerated isostatic rebound in reaction to glacier retreat. Spit growth resumed in the late 19th century after the rate of isostatic rebound decreased, and continues until today. The direction of modern spit progradation, however, is rotated northwards compared with the growth axis of the early post-LGR spit. This is interpreted to reflect the shift and strengthening in the regional wind field during the last century. A new concept for the interplay of polar gravel-spit progradation and glacio-isostatic adjustment is presented, allowing for the prediction of future coastal evolution in comparable polar settings.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    facet.materialart.
    facet.materialart.
    Wiley
    In:  Drug Development Research, 80 (1). pp. 24-27.
    Publication Date: 2019-03-08
    Description: Natural products and derivatives thereof are of considerable importance in the discovery of new pharmaceuticals, for example, for the treatment of cancer, diabetes, inflammation diseases, and infection diseases caused by bacteria, fungi, viruses, or parasites. The great biodiversity of marine microorganisms is reflected in their huge chemical diversity, which provides a rich source of biologically active compounds. An increasing interest in marine microorganisms as promising producers of new compounds with potential medical applications has raised increasing interest in the sustainable exploration of marine microbial resources for the discovery of new antibiotics, which is highlighted. The bottlenecks in the development of drugs using the large marine natural product pipeline are also discussed.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2019-03-08
    Description: In order to understand the effect of global change on marine fishes, it is imperative to quantify the effects on fundamental parameters such as survival and growth. Larval survival and recruitment of the Atlantic cod (Gadus morhua) were found to be heavily impaired by end-of-century levels of ocean acidification. Here, we analysed larval growth among 35–36 days old surviving larvae, along with organ development and ossification of the skeleton. We combined CO2treatments (ambient: 503 µatm, elevated: 1,179 µatm) with food availability in order to evaluate the effect of energy limitation in addition to the ocean acidification stressor. As expected, larval size (as a proxy for growth) and skeletogenesis were positively affected by high food availability. We found significant interactions between acidification and food availability. Larvae fed ad libitum showed little difference in growth and skeletogenesis due to the CO2 treatment. Larvae under energy limitation were significantly larger and had further developed skeletal structures in the elevated CO2 treatment compared to the ambient CO2 treatment. However, the elevated CO2 group revealed impairments in critically important organs, such as the liver, and had comparatively smaller functional gills indicating a mismatch between size and function. It is therefore likely that individual larvae that had survived acidification treatments will suffer from impairments later during ontogeny. Our study highlights important allocation trade-off between growth and organ development, which is critically important to interpret acidification effects on early life stages of fish.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2019-04-16
    Description: Environmental enrichment aims for a deliberate increase in structural complexity in otherwise plain rearing units, helping to reduce aberrant traits and promote welfare of fish kept in captivity. Before putting enrichment protocols into practice, however, practitioners like hatchery managers need clear guidelines on enrichment measures and on the substrates used. In the present study, we used rainbow trout as a model species for salmonid rearing and investigated the use of a single layer of three different gravel types, i.e., small (4–8 mm), medium (8–16 mm) and large (16–32 mm), for environmental enrichment during egg incubation, endogenous and first feeding of rainbow trout and compared this to a barren control. From the egg stage onwards, we determined mortality, fungal prevalence as well as growth of larvae and fingerlings. We found that gravel size significantly affected mortality and fungal prevalence with the smallest gravel size and the control showing the lowest incidents. Growth of larvae and fingerlings was not affected by gravel, both when compared between gravel types and to the barren control. When using gravel for environmental enrichment in salmonid hatcheries, a small gravel size should be used. Small gravel provides the fish with a more natural environment without compromising practical feasibility of enrichment in hatcheries, still allowing for easy visual inspection and manual control of the reared fish.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 11
    Publication Date: 2019-03-08
    Type: Article , PeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 12
    Publication Date: 2019-05-13
    Description: Thawing of subsea permafrost can impact offshore infrastructure, affect coastal erosion, and release permafrost organic matter. Thawing is usually modeled as the result of heat transfer, although salt diffusion may play an important role in marine settings. To better quantify nearshore subsea permafrost thawing, we applied the CryoGRID2 heat diffusion model and coupled it to a salt diffusion model. We simulated coastline retreat and subsea permafrost evolution as it develops through successive stages of a thawing sequence at the Bykovsky Peninsula, Siberia. Sensitivity analyses for seawater salinity were performed to compare the results for the Bykovsky Peninsula with those of typical Arctic seawater. For the Bykovsky Peninsula, the modeled ice‐bearing permafrost table (IBPT) for ice‐rich sand and an erosion rate of 0.25 m/year was 16.7 m below the seabed 350 m offshore. The model outputs were compared to the IBPT depth estimated from coastline retreat and electrical resistivity surveys perpendicular to and crossing the shoreline of the Bykovsky Peninsula. The interpreted geoelectric data suggest that the IBPT dipped to 15–20 m below the seabed at 350 m offshore. Both results suggest that cold saline water forms beneath grounded ice and floating sea ice in shallow water, causing cryotic benthic temperatures. The freezing point depression produced by salt diffusion can delay or prevent ice formation in the sediment and enhance the IBPT degradation rate. Therefore, salt diffusion may facilitate the release of greenhouse gasses to the atmosphere and considerably affect the design of offshore and coastal infrastructure in subsea permafrost areas.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 13
    Publication Date: 2019-05-15
    Description: 1. Epimicrobial communities on seaweed surfaces usually contain not only potentially pathogenic but also potentially beneficial micro‐organisms. Capacity of terrestrial plants for chemically mediated recruitment, that is, “gardening” of bacterial communities in the rhizosphere was recently demonstrated. Empirical evidence directly linking such chemical “gardening” with the beneficial role of gardened microbes in terrestrial plants is rare and largely missing for aquatic macrophytes. 2. Here, we demonstrate that our model invasive seaweed holobiont Agarophyton vermiculophyllum possesses beneficial microbiota on its surface that provide protection from bacterial pathogens. Metabolites from the algal holobiont’s surface reduced settlement of opportunistic pathogens but attracted protective epibacterial settlement. 3. We tested 58 different bacterial species (isolated from the surface of A. vermiculophyllum) individually in tip bleaching assays. Kordia algicida was identified as a “significant pathogen” inducing a bleaching disease. In addition, nine other species significantly reduced the risk of algal bleaching and were thus “significantly protective”. Additionally, two “potential pathogens” and 10 “potential protectors” were identified. When 19 significant and potential protectors and 3 significant and potential pathogens were tested together, the protective strains fully prevented bleaching, suggesting that a component of A. vermiculophyllum’s epimicrobiome provides an associational defence against pathogens. Chemically mediated selective recruitment of microbes was demonstrated in bioassays, where A. vermiculophyllum surface metabolites attracted the settlement of protective strains, but reduced settlement of pathogens. 4. Synthesis. The capacity of an aquatic macrophyte to chemically “garden” protective micro‐organisms to the benefit of strengthened disease resistance is demonstrated for the first time. Such a role of surface chemistry in “gardening” of microbes as found in the current study could also be applicable to other host plant—microbe interactions. Our results may open new avenues towards manipulation of the surface microbiome of seaweeds via chemical “gardening,” enhancing sustainable production of healthy seaweeds.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 14
    Publication Date: 2019-05-21
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 15
    Publication Date: 2019-05-24
    Description: Due to strong mean state‐biases most coupled models are unable to simulate equatorial Atlantic variability. Here, we use the Kiel Climate Model to assess the impact of bias reduction on the seasonal prediction of equatorial Atlantic sea surface temperature (SST). We compare a standard experiment (STD) with an experiment that employs surface heat flux correction to reduce the SST bias (FLX) and, in addition, apply a correction for initial errors in SST. Initial conditions for both experiments are generated in partially coupled mode, and seasonal hindcasts are initialized at the beginning of February, May, August and November for 1981–2012. Surface heat flux correction generally improves hindcast skill. Hindcasts initialized in February have the least skill, even though the model bias is not particularly strong at that time of year. In contrast, hindcasts initialized in May achieve the highest skill. We argue this is because of the emergence of a closed Bjerknes feedback loop in boreal summer in FLX that is a feature of observations but is missing in STD.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 16
    Publication Date: 2019-05-24
    Description: Aim: Numerous regions worldwide are highly impacted by anthropogenic activities and globalization, with climate change and species introductions being among the greatest stressors to biodiversity and ecosystems. A main donor region of non‐indigenous species (NIS) for numerous European water bodies, as well as in the North American Great Lakes is the Ponto‐Caspian region (i.e., Black, Azov and Caspian Seas), with some of those species having significant impact on local communities and ecosystem functioning. Location: Northern European, Ponto‐Caspian and North American regions. Methods: To determine environmental tolerance of native species and related NIS under current and future global warming scenarios of the Baltic Sea, we conducted common garden experiments to test temperature tolerance of three euryhaline gammarid species: one Baltic (Gammarus oceanicus), one Ponto‐Caspian (Pontogammarus maeoticus) and one North American species (Gammarus tigrinus) in two different salinities. Results: Our results determined that mortality of P. maeoticus in all temperature treatments (i.e., increased, control, and decreased) at the end of both experiments (i.e., conducted in salinities of 10 and 16 g/kg) was lower when compared to mortality of G. oceanicus and (c) G. tigrinus. The highest mortality was observed for G. oceanicus, reaching 100% in both experiments in the increased temperature treatment. Main conclusions: Due to the high environmental tolerance of the Ponto‐Caspian species tested in this study, as well as the fact that Ponto‐Caspian species evolved in environmentally variable habitats and currently inhabit warmer waters than species from North America and Northern Europe, we suggest that species from the Ponto‐Caspian region may benefit from global warming when invading new areas. Those new invasions may, in the best case scenario, increase biodiversity of the Baltic Sea. However, if notorious invaders arrive, they may have a significant impact on local communities and ecosystem functioning.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 17
    Publication Date: 2019-05-21
    Description: Increasing global energy demands have led to the ongoing intensification of hydrocarbon extraction from marine areas. Hydrocarbon extractive activities pose threats to native marine biodiversity, such as noise, light, and chemical pollution, physical changes to the sea floor, invasive species, and greenhouse gas emissions. Here, we assessed at a global scale the spatial overlap between offshore hydrocarbon activities and marine biodiversity (〉25,000 species, nine major ecosystems, and marine protected areas), and quantify the changes over time. We discovered that two-thirds of global offshore hydrocarbon activities occur in areas within the top 10% for species richness, range rarity, and proportional range rarity values globally. Thus, while hydrocarbon activities are undertaken in less than one percent of the ocean's area, they overlap with approximately 85% of all assessed species. Of conservation concern, 4% of species with the largest proportion of their range overlapping hydrocarbon activities are range restricted, potentially increasing their vulnerability to localized threats such as oil spills. While hydrocarbon activities have extended to greater depths since the mid-1990s, we found that the largest overlap is with coastal ecosystems, particularly estuaries, saltmarshes and mangroves. Furthermore, in most countries where offshore hydrocarbon exploration licensing blocks have been delineated, they do not overlap with marine protected areas (MPAs). Although this is positive in principle, many countries have far more licensing block areas than protected areas, and in some instances, MPA coverage is minimal. These findings suggest the need for marine spatial prioritization to help limit future spatial overlap between marine conservation priorities and hydrocarbon activities. Such prioritization can be informed by the spatial and quantitative baseline information provided here. In increasingly shared seascapes, prioritizing management actions that set both conservation and development targets could help minimize further declines of biodiversity and environmental changes at a global scale.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 18
    Publication Date: 2019-06-16
    Description: Satellite‐derived data suggest an increase in annual primary production following the loss of summer sea ice in the Arctic Ocean. The scarcity of field data to corroborate this enhanced algal production incited a collaborative project combining six annual cycles of sequential sediment trap measurements obtained over a 17‐year period in the Eurasian Arctic Ocean. Here we present microalgal fluxes measured at ~200 m to reflect the bulk of algal carbon production. Ice algae contributed to a large proportion of the microalgal carbon export before complete ice melt and possible detection of their production by satellites. In the northern Laptev Sea, annual microalgal carbon fluxes were lower during the 2007 minimum ice extent than in 2006. In 2012, early snowmelt led to early microalgal carbon flux in the Nansen Basin. Hence, a change in the timing of snowmelt and ice algae release may affect productivity and export over the Arctic basins.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 19
    Publication Date: 2019-06-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 20
    Publication Date: 2019-06-23
    Description: Age control and paleoceanographic evidence of marine sediment records might be challenged if authors solely build their stratigraphy on visual correlation to apparently well‐dated records from the same ocean basin, using, for example, highly resolved X‐ray fluorescence‐based element‐count records and correlation tools such as AnalySeries. While per se perfectly reasonable, this approach bears the risk of missing stratigraphic gaps in the sedimentary record and thus might result in imprecise and/or flawed interpretations. Here we present a unique series of 14 planktic 14C ages from a 7‐cm section of East Pacific Rise core PS75/059‐2. The ages suggest a 14‐ky‐long period of low‐to‐zero deposition during Last Glacial Maximum, mainly marked by continuous redistribution of winnowed foraminifers, probably the result of enhanced bottom currents, moreover, by some bioturbational mixing. On the basis of this data we demonstrate the impact of the hiatus on a South Pacific transect of apparent benthic ventilation ages (ΔΔ14C values) and their meaning for estimates of CO2 stored in Last Glacial Maximum Pacific deep waters.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 21
    Publication Date: 2019-07-04
    Description: Rationale Boron (B) is an essential micronutrient in plants and its isotope variations are used to gain insights into plant metabolism, which is important for crop plant cultivation. B isotope variations were used to trace intraplant fractionation mechanisms in response to the B concentration in the irrigation water spanning the range from B depletion to toxic levels. Methods A fully validated analytical procedure based on MC‐ICP‐MS, sample decomposition and B matrix separation was applied to study B isotope fractionation. The validation was accomplished by establishing a complete uncertainty budget and by applying reference materials, yielding expanded measurement uncertainties of 0.8 ‰ for pure boric acid solutions and ≤ 1.5 ‰ for processed samples. With this validated procedure SI traceable B isotope amount ratios were determined in plant reference materials for the first time. Results The B isotope compositions of irrigation water and bell pepper samples suggest passive diffusion of the heavy 11B isotope into the roots during low to high B concentrations while uptake of the light 10B isotope was promoted during B depletion, probably by active processes. A systematic enrichment of the heavy 11B isotope in higher located plant parts was observed (average Δ11Bleaf‐roots = 20.3 ± 2.8 ‰ (1 SD)), possibly by a facilitated transport of the heavy 11B to growing meristems by B transporters. Conclusions B isotopes can be used to identify plant metabolism in response to the B concentration in the irrigation water and during intraplant B transfer. The large B isotope fractionation within the plants demonstrates the importance of biological B cycling for the global B cycle.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 22
    Publication Date: 2019-07-05
    Description: The dense AlpArray network allows studying seismic wave propagation with high spatial resolution. Here we introduce an array approach to measure arrival angles of teleseismic Rayleigh waves. The approach combines the advantages of phase correlation as in the two-station method with array beamforming to obtain the phase-velocity vector. 20 earthquakes from the first two years of the AlpArray project are selected, and spatial patterns of arrival-angle deviations across the AlpArray are shown in maps, depending on period and earthquake location. The cause of these intriguing spatial patterns is discussed. A simple wave-propagation modelling example using an isolated anomaly and a Gaussian beam solution suggests that much of the complexity can be explained as a result of wave interference after passing a structural anomaly along the wave paths. This indicates that arrival-angle information constitutes useful additional information on the Earth structure, beyond what is currently used in inversions.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 23
    Publication Date: 2019-07-09
    Description: Parasites are one of the strongest selective agents in nature. They select for hosts that evolve counter‐adaptive strategies to cope with infection. Helminth parasites are special because they can modulate their hosts’ immune responses. This phenomenon is important in epidemiological contexts, where coinfections may be affected. How different types of hosts and helminths interact with each other is insufficiently investigated. We used the three‐spined stickleback (Gasterosteus aculeatus) – Schistocephalus solidus model to study mechanisms and temporal components of helminth immune modulation. Sticklebacks from two contrasting populations with either high resistance (HR) or low resistance (LR) against S. solidus, were individually exposed to S. solidus strains with characteristically high growth (HG) or low growth (LG) in G. aculeatus. We determined the susceptibility to another parasite, the eye fluke Diplostomum pseudospathaceum, and the expression of 23 key immune genes at three time points after S. solidus infection. D. pseudospathaceum infection rates and the gene expression responses depended on host and S. solidus type and changed over time. Whereas the effect of S. solidus type was not significant after three weeks, T regulatory responses and complement components were upregulated at later time points if hosts were infected with HG S. solidus. HR hosts showed a well orchestrated immune response, which was absent in LR hosts. Our results emphasize the role of regulatory T cells and the timing of specific immune responses during helminth infections. This study elucidates the importance to consider different coevolutionary trajectories and ecologies when studying host‐parasite interactions.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 24
    Publication Date: 2019-07-10
    Description: The East Antarctic Ice Sheet (EAIS) is underlain by a series of low‐lying subglacial sedimentary basins. The extent, geology, and basal topography of these sedimentary basins are important boundary conditions governing the dynamics of the overlying ice sheet. This is particularly pertinent for basins close to the grounding line wherein the EAIS is grounded below sea level and therefore potentially vulnerable to rapid retreat. Here we analyze newly acquired airborne geophysical data over the Pensacola‐Pole Basin (PPB), a previously unexplored sector of the EAIS. Using a combination of gravity and magnetic and ice‐penetrating radar data, we present the first detailed subglacial sedimentary basin model for the PPB. Radar data reveal that the PPB is defined by a topographic depression situated ~500 m below sea level. Gravity and magnetic depth‐to‐source modeling indicate that the southern part of the basin is underlain by a sedimentary succession 2–3 km thick. This is interpreted as an equivalent of the Beacon Supergroup and associated Ferrar dolerites that are exposed along the margin of East Antarctica. However, we find that similar rocks appear to be largely absent from the northern part of the basin, close to the present‐day grounding line. In addition, the eastern margin of the basin is characterized by a major geological boundary and a system of overdeepened subglacial troughs. We suggest that these characteristics of the basin may reflect the behavior of past ice sheets and/or exert an influence on the present‐day dynamics of the overlying EAIS.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 25
    Publication Date: 2019-07-10
    Description: Here we evaluate five atmospheric reanalyses in an Arctic gateway during late summer. The reanalyses include ERA5, ERA-Interim, JRA-55, CFSv2 and MERRA-2. We use observations from 50 radiosondes launched in the Fram Strait around 79-80˚N, between 25 August – 11 September 2017. Crucially, data from 27 radiosondes were not transmitted to the Global Telecommunications System (GTS), and therefore not assimilated into any reanalysis. In most reanalyses, the magnitude of wind speed and humidity errors are similar for profiles with and without data assimilation. In cases without data assimilation, correlation coefficients (R) exceed 0.88 for temperature, wind speed and specific humidity, in all reanalyses. Overall, the newly released ERA5 has higher correlation coefficients than any other reanalyses as well as smaller biases and root mean square errors, for all three variables. The largest improvements identified in ERA5 are in its representation of the wind field, and temperature profiles over warm water.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 26
    Publication Date: 2019-07-08
    Description: Marine species tend to have extensive distributions, which are commonly attributed to the dispersal potential provided by planktonic larvae and the rarity of absolute barriers to dispersal in the ocean. Under this paradigm, the occurrence of marine microendemism without geographic isolation in species with planktonic larvae poses a dilemma. The recently described Maya hamlet (Hypoplectrus maya, Serranidae) is exactly such a case, being endemic to a 50-km segment of the Mesoamerican Barrier Reef System (MBRS). We use whole-genome analysis to infer the demographic history of the Maya hamlet and contrast it with the sympatric and pan-Caribbean black (H. nigricans), barred (H. puella) and butter (H. unicolor) hamlets, as well as the allopatric but phenotypically similar blue hamlet (H. gemma). We show that H. maya is indeed a distinct evolutionary lineage, with genomic signatures of inbreeding and a unique demographic history of continuous decrease in effective population size since it diverged from congeners just ~3,000 generations ago. We suggest that this case of microendemism may be driven by the combination of a narrow ecological niche and restrictive oceanographic conditions in the southern MBRS, which is consistent with the occurrence of an unusually high number of marine microendemics in this region. The restricted distribution of the Maya hamlet, its decline in both census and effective population sizes, and the degradation of its habitat place it at risk of extinction. We conclude that the evolution of marine microendemism can be a fast and dynamic process, with extinction possibly occurring before speciation is complete.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 27
    facet.materialart.
    facet.materialart.
    Wiley
    In:  Geophysical Prospecting, 67 (6). pp. 1557-1570.
    Publication Date: 2019-07-08
    Description: Although narrow‐azimuth towed‐streamer data provides good image quality for structural interpretation, it is generally accepted that for wide‐azimuth marine surveys seabed receivers deliver superior seismic reflection measurements and seismically derived reservoir attributes. However, seabed surveys are not widely used due to the higher acquisition costs when compared to streamer acquisition. In recent years, there have been significant engineering efforts to automate receiver deployment and retrieval in order to minimize the cost differential and conduct cost‐efficient seabed receiver seismic surveys. These engineering efforts include industrially engineered nodes, nodes‐on‐a‐rope deployment schemes and even robotic nodes, which swim to and from the deployment location. This move to automation is inevitable, leading to robotization of seismic data acquisition for exploration and development activities in the oil and gas industry. We are developing a robotic‐based technology, which utilizes autonomous underwater vehicles as seismic sensors without the need of using a remotely operated vehicle for deployment and retrieval. In this paper, we describe the autonomous underwater vehicle evolution throughout the project years from initial heavy and bulky nodes to fully autonomous light and flexible underwater receivers. Results obtained from two field pilot tests using different generations of autonomous underwater vehicles indicate that the seismic coupling, and navigation based on underwater acoustics are very reliable and robust.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 28
    Publication Date: 2019-07-08
    Description: A marine seismic method based on continuous source and receiver wavefields has been developed. The method requires continuous recording of the seismic data. The source that may consist of multiple source elements can emit signals continuously while moving. The ideal source wavefield to be used with this method should be as white as possible both in a temporal and a spatial sense to avoid deep notches in the spectrum enabling a stable multi‐dimensional deconvolution. White noise has such properties. However, equipment that can generate white noise does not exist. In order to generate a continuous source wavefield that is approaching the properties of white noise using existing equipment onboard marine seismic vessels, individual air‐guns can be triggered with short randomized time intervals in a near‐continuous fashion. The main potential benefits with the method are to reduce the environmental impact of marine seismic surveys and to improve acquisition efficiency. The peak sound pressure levels are significantly reduced by triggering one air‐gun at a time compared to conventional marine seismic sources. Sound exposure levels are also reduced in most directions. Since the method is based on continuous recording of seismic data and the air‐guns are triggered based on time and not based on position, there are less vessel speed limitations compared to conventional marine seismic data acquisition. Also, because the source wavefield is spread out in time, the wavefields emitted from source elements in different cross‐line positions can be designed such that the emitted wavefield is spatially white in this direction. This means that source elements in multiple cross‐line positions can be operated simultaneously, potentially improving the cross‐line sampling and/or the acquisition efficiency.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 29
    facet.materialart.
    facet.materialart.
    Wiley
    In:  Annals of the New York Academy of Sciences, 1436 (1). pp. 54-69.
    Publication Date: 2019-07-08
    Description: Regional climate modeling bridges the gap between the coarse resolution of current global climate models and the regional-to-local scales, where the impacts of climate change are of primary interest. Here, we present a review of the added value of the regional climate modeling approach within the scope of paleoclimate research and discuss the current major challenges and perspectives. Two time periods serve as an example: the Holocene, including the Last Millennium, and the Last Glacial Maximum. Reviewing the existing literature reveals the benefits of regional paleo climate modeling, particularly over areas with complex terrain. However, this depends largely on the variable of interest, as the added value of regional modeling arises from a more realistic representation of physical processes and climate feedbacks compared to global climate models, and this affects different climate variables in various ways. In particular, hydrological processes have been shown to be better represented in regional models, and they can deliver more realistic meteorological data to drive ice sheet and glacier modeling. Thus, regional climate models provide a clear benefit to answer fundamental paleoclimate research questions and may be key to advance a meaningful joint interpretation of climate model and proxy data.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 30
    Publication Date: 2019-07-15
    Description: Sea ice dynamics determine the drift and deformation of sea ice. Nonlinear physics, usually expressed in a viscous‐plastic rheology, makes the sea ice momentum equations notoriously difficult to solve. At increasing sea ice model resolution the nonlinearities become stronger as linear kinematic features (leads) appear in the solutions. Even the standard elastic‐viscous‐plastic (EVP) solver for sea ice dynamics, which was introduced for computational efficiency, becomes computationally very expensive, when accurate solutions are required, because the numerical stability requires very short, and hence more, subcycling time steps at high resolution. Simple modifications to the EVP solver have been shown to remove the influence of the number of subcycles on the numerical stability. At low resolution appropriate solutions can be obtained with only partial convergence based on a significantly reduced number of subcycles as long as the numerical procedure is kept stable. This previous result is extended to high resolution where linear kinematic features start to appear. The computational cost can be strongly reduced in Arctic Ocean simulations with a grid spacing of 4.5 km by using modified and adaptive EVP versions because fewer subcycles are required to simulate sea ice fields with the same characteristics as with the standard EVP.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 31
    Publication Date: 2019-07-15
    Description: Quaternary East Asian winter monsoon (EAWM) evolution has long been attributed to high‐latitude Northern Hemisphere climate change. However, it cannot explain the distinct relationships of the EAWM in the northern and southern East Asian marginal sea in paleoclimatic records. Here we present an EAWM record of the northern East China Sea over the past 300 ka and a transient climate simulation with the Kiel Climate Model through the Holocene. Both proxy record and simulation suggest anticorrelated long‐term EAWM evolution between the northern East China Sea and the South China Sea. We suggest that this spatial discrepancy of EAWM can be interpreted as El Niño–Southern Oscillation (ENSO)‐like controlling, which generates cyclonic/anticyclonic wind anomalies in the northern/southern East Asian marginal sea. This research explains much of the controversy in nonorbital scale variability of Quaternary EAWM records in the East Asian marginal sea and supports a potent role of tropical forcing in East Asian winter climate change.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 32
    Publication Date: 2019-07-15
    Description: It is fundamentally important for many animal ecologists to quantify the costs of animal activities, although it is not straightforward to do so. The recording of triaxial acceleration by animal-attached devices has been proposed as a way forward for this, with the specific suggestion that dynamic body acceleration (DBA) be used as a proxy for movement-based power. Dynamic body acceleration has now been validated frequently, both in the laboratory and in the field, although the literature still shows that some aspects of DBA theory and practice are misunderstood. Here, we examine the theory behind DBA and employ modelling approaches to assess factors that affect the link between DBA and energy expenditure, from the deployment of the tag, through to the calibration of DBA with energy use in laboratory and field settings. Using data from a range of species and movement modes, we illustrate that vectorial and additive DBA metrics are proportional to each other. Either can be used as a proxy for energy and summed to estimate total energy expended over a given period, or divided by time to give a proxy for movement-related metabolic power. Nonetheless, we highlight how the ability of DBA to predict metabolic rate declines as the contribution of non-movement-related factors, such as heat production, increases. Overall, DBA seems to be a substantive proxy for movement-based power but consideration of other movement-related metrics, such as the static body acceleration and the rate of change of body pitch and roll, may enable researchers to refine movement-based metabolic costs, particularly in animals where movement is not characterized by marked changes in body acceleration.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 33
    Publication Date: 2019
    Description: Abstract Aim Poleward range shifts of species are among the most obvious effects of climate change on biodiversity. As a consequence of these range shifts, species communities are predicted to become increasingly composed of warm‐dwelling species, but this has only been studied for a limited number of taxa, mainly birds, butterflies and plants. As species groups may vary considerably in their adaptation to climate change, it is desirable to expand these studies to other groups, from different ecosystems. Freshwater macroinvertebrates, such as dragonflies (Odonata), have been ranked among the species groups with highest priority. In this paper, we investigate how the occurrence of dragonflies in Europe has changed in recent decades, and if these changes are in parallel with climate change. Location Europe. Methods We use data from 10 European geographical regions to calculate occupancy indices and trends for 99 (69%) of the European species. Next, we combine these regional indices to calculate European indices. To determine if changes in regional dragonfly communities in Europe reflect climatic warming, we calculate Species Temperature Indices (STI), Multi‐species Indicators (MSI) and Community Temperature Indices (CTI). Results 55 of 99 considered species increased in occupancy at European level, 32 species remained stable, and none declined. Trends for 12 species are uncertain. MSI of cold‐dwelling and warm‐dwelling species differ in some of the regions, but increased at a similar rate at European level. CTI increased in all regions, except Cyprus. The European CTI increased slightly. Main conclusions European dragonflies, in general, have expanded their distribution in response to climate change, even though their CTI lags behind the increase in temperature. Furthermore, dragonflies proved to be a suitable species group for monitoring changes in communities, both at regional and continental level.
    Print ISSN: 1366-9516
    Electronic ISSN: 1472-4642
    Topics: Biology
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 34
    Publication Date: 2019
    Description: Abstract Aim Fisheries bycatch is a major threat to populations of protected species such as marine mammals, seabirds and sea turtles, and static management approaches are often unsuccessful in mitigating bycatch of these highly mobile species. Combining species distribution models (SDMs) with oceanographic data has been proposed as a means of predicting when and where bycatch is likely to occur. However, studies assessing whether SDMs can accurately predict fisheries bycatch using independent data are lacking. Assessing model performance using independent data is necessary to test whether a model is generalizable, and this is particularly important for models with management applications. Here, we use short‐finned pilot whale (Globicephala macrorhynchus) bycatch in a pelagic longline fishery as a case study to inform efforts to mitigate fisheries bycatch. Location Offshore waters, north‐east United States. Methods We integrated telemetry and oceanographic data using mixed‐effects generalized additive models to predict pilot whale occurrence and assessed model performance using k‐folds cross‐validation. We then evaluated the model's ability to predict pilot whale bycatch using data from independent on‐board observers. Results The model performed well, and predictions were strongly and significantly correlated with observed rates of bycatch in space and time. Temperature and proximity to mesoscale oceanographic features (thermal fronts and sea level anomalies) were important predictors of pilot whale occurrence, and as a result, spatial predictions of the risk of bycatch varied through time. Main conclusions Our findings demonstrate that SDMs can be used to accurately predict times and places with a high risk of bycatch, and illustrate that models using dynamic oceanographic variables can identify smaller, more specific focal management regions than static management approaches. Combining SDMs with near real‐time or forecasted environmental conditions could provide a promising tool for decreasing bycatch and will be valuable in developing adaptive management strategies to mitigate fisheries bycatch of protected species.
    Print ISSN: 1366-9516
    Electronic ISSN: 1472-4642
    Topics: Biology
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 35
    Publication Date: 2019
    Description: Embodied approaches to urban water in/security bring attention to the body as a critical site and scale of analysis, pushing academic and policy work to go beyond quantity/quality approaches to water to examine the ways water insecurity is tied to a host of additional inequities and vulnerabilities. In recent years, emerging scholarship has advanced embodied approaches to urban water in/security, inequality and infrastructure. This new literature is broadly informed by political ecology studies of water, which critique depoliticized approaches to water scarcity, insecurity and inequality and give attention to the socially differentiated experiences of the urban waterscape. Recent interventions to bring feminist and embodied approaches to water's urban political ecology analyze the site and scale of the body as critical for understanding everyday urban water access and inequality. Drawing from these frameworks, I summarize three contributions of an embodied urban political ecology approach for addressing water in/security. These include analytical approaches that give attention to (1) the scale of the body within multi‐scalar approaches to water, (2) intersectionality and gender/class/race/ethno‐religious relations in shaping patterns of water inequality and insecurity, and (3) everyday practices and politics, in relation to both governance and citizens, which reveal under‐theorized dimensions of water insecurity and inequality. Embodied approaches to urban water insecurity are poised to expand and deepen work on the everyday politics and lived experiences of insufficient, insecure, and unequal water that profoundly shape urban life for city‐dwellers. This article is categorized under: Engineering Water 〉 Planning Water Human Water 〉 Water Governance Human Water 〉 Rights to Water
    Electronic ISSN: 2049-1948
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 36
    Publication Date: 2019
    Description: Nares Strait, a major connection between the Arctic Ocean and Baffin Bay, was blocked by coalescent Innuitian and Greenland ice sheets during the last glaciation. This paper focuses on the events and processes leading to the opening of the strait and the environmental response to establishment of the Arctic‐Atlantic throughflow. The study is based on sedimentological, mineralogical and foraminiferal analyses of radiocarbon‐dated cores 2001LSSL‐0014PC and TC from northern Baffin Bay. Radiocarbon dates on benthic foraminifera were calibrated with ΔR = 220±20 years. Basal compact pebbly mud is interpreted as a subglacial deposit formed by glacial overriding of unconsolidated marine sediments. It is overlain by ice‐proximal (red/grey laminated, ice‐proximal glaciomarine unit barren of foraminifera and containing 〉2 mm clasts interpreted as ice‐rafted debris) to ice‐distal (calcareous, grey pebbly mud with foraminifera indicative of a stratified water column with chilled Atlantic Water fauna and species associated with perennial and then seasonal sea ice cover) glacial marine sediment units. The age model indicates ice retreat into Smith Sound as early as c. 11.7 and as late as c. 11.2 cal. ka BP followed by progressively more distal glaciomarine conditions as the ice margin retreated toward the Kennedy Channel. We hypothesize that a distinct IRD layer deposited between 9.3 and 9 (9.4–8.9 1σ) cal. ka BP marks the break‐up of ice in Kennedy Channel resulting in the opening of Nares Strait as an Arctic‐Atlantic throughflow. Overlying foraminiferal assemblages indicate enhanced marine productivity consistent with entry of nutrient‐rich Arctic Surface Water. A pronounced rise in agglutinated foraminifers and sand‐sized diatoms, and loss of detrital calcite characterize the uppermost bioturbated mud, which was deposited after 4.8 (3.67–5.55 1σ) cal. ka BP. The timing of the transition is poorly resolved as it coincides with the slow sedimentation rates that ensued after the ice margins retreated onto land.
    Print ISSN: 0300-9483
    Electronic ISSN: 1502-3885
    Topics: Geography , Geosciences
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 37
    Publication Date: 2019
    Description: Abstract Regionally extensive parasequences in the upper McMurray Formation, Grouse Paleovalley, north‐east Alberta, Canada, preserve a shift in depositional processes in a paralic environment from tide domination, with notable fluvial influence, through to wave domination. Three stacked parasequences form the upper McMurray Formation and are separated by allogenic flooding surfaces. Sediments within the three parasequences are grouped into three facies associations: wave‐dominated/storm‐dominated deltas, storm‐affected shorefaces to sheltered bay‐margin and fluvio‐tidal brackish‐water channels. The two oldest parasequences comprise dominantly tide‐dominated, wave‐influenced/fluvial‐influenced, shoreface to bay‐margin deposits bisected by penecontemporaneous brackish‐water channels. Brackish‐water channels trend approximately north‐west/south‐east, which is perpendicular to the interpreted shoreline trend, and this implies the basinward and progradational direction was towards the north‐west during deposition of the upper McMurray Formation in Grouse Paleovalley. The youngest parasequence is interpreted as amalgamated wave‐dominated/storm‐dominated delta lobes. The transition from tide‐dominated deposition in the oldest two parasequences to wave‐dominated deposition in the youngest is attributed mainly to drowning of carbonate highlands to the north and north‐west of the study area, and potentially to relative changes in accommodation space and deposition rate. The sedimentological, ichnological and regional distribution of the three facies associations within each parasequence are compared to modern and Holocene analogues that have experienced similar shifts in process dominance. Through this comparison it is possible to consider how shifts in depositional processes are expressed in the rock record. In particular, this study provides one of few ancient examples of preservation of depositional process shifts and showcases how topography impacts the character and architecture of marginal‐marine systems. This article is protected by copyright. All rights reserved.
    Print ISSN: 0037-0746
    Electronic ISSN: 1365-3091
    Topics: Geosciences
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 38
    Publication Date: 2019
    Description: Abstract Spatiotemporal heterogeneity in soil water content is recognized as a common phenomenon, but heterogeneity in the hydrogen and oxygen isotope composition of soil water, which can reveal processes of water cycling within soils, has not been well studied. New advances are being driven by measurement approaches allowing sampling with high density in both space and time. Using in situ soil water vapor probe techniques, combined with conventional soil and plant water vacuum distillation extraction, we monitored the hydrogen and oxygen stable isotopic composition of soil and plant waters at paired sites dominated by grasses and Gambel's oak (Quercus gambelli) within a semi‐arid montane ecosystem over the course of a growing season. We found that sites spaced only 20 m apart had profoundly different soil water isotopic and volumetric conditions. We document patterns of depth‐ and time‐explicit variation in soil water isotopic conditions at these sites, and consider mechanisms for the observed heterogeneity. We found that soil water content and isotopic variability was damped under Quercus gambelli, perhaps due in part to hydraulic redistribution of deep soil water or groundwater by Quercus gambelli in these soils relative to the grass‐dominated site. We also found some support for H isotope discrimination effects during water uptake by Quercus gambelli. In this ecosystem, the soil water content was higher than that at the neighboring grass site, and thus 25% more water was available for transpiration by Quercus gambelli compared to the grass site. This work highlights the role of plants in governing soil water variation and demonstrates that they can also strongly influence the isotope ratios of soil water. The resulting fine‐scale heterogeneity has implications for the use of isotope tracers to study soil hydrology and evaporation and transpiration fluxes to improve understanding of water cycling through the soil‐plant‐atmosphere continuum.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 39
    Publication Date: 2019
    Description: On behalf of the authors and readers of Reviews of Geophysics, the American Geophysical Union (AGU), and the broader scientific community, the Editors wish to wholeheartedly thank those who reviewed the manuscripts for Reviews of Geophysics in 2018. Reviews of Geophysics is the top rated journal in Geophysics and Geochemistry and it could not exist without your investment of time and effort, lending your expertise to ensure that the papers published in this journal meet the standards that the research community expects for it. We sincerely appreciate the time spent reading and commenting on manuscripts, and we are very grateful for your willingness and readiness to serve in this role. Reviews of Geophysics published 20 review papers and an editorial in 2018, covering most of the AGU Section topics, and for this we were able to rely on the efforts of 85 dedicated reviewers from 20 countries. Many reviewers answered the call multiple times. Thank you again. We look forward to a 2019 of exciting advances in the field and communicating those advances to our community and to the broader public.
    Print ISSN: 8755-1209
    Electronic ISSN: 1944-9208
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 40
    Publication Date: 2019
    Description: Abstract We present a model of the electrical resistivity structure of the lithosphere in the Central Andes between 20°S and 24°S from 3‐D inversion of 56 long‐period magnetotelluric sites. Our model shows a complex resistivity structure with significant variability parallel‐ and perpendicular to the trench direction. The continental forearc is characterized mainly by high electrical resistivity (〉1000 Ωm), suggesting overall low volumes of fluids. However, low resistivity zones (LRZs, 〈5 Ωm) were found in the continental forearc below areas where major trench‐parallel faults systems intersect NW‐SE transverse faults. Forearc LRZs indicate circulation and accumulation of fluids in highly permeable fault zones. The continental crust along the arc shows three distinctive resistivity domains, which coincide with segmentation in the distribution of volcanoes. The northern domain (20°‐20.5°S) is characterized by resistivities 〉1000 Ωm and the absence of active volcanism, suggesting the presence of a low‐permeability block in the continental crust. The central domain (20.5°‐23°S) exhibits a number of LRZs at varying depths, indicating different levels of a magmatic plumbing system. The southern domain (23°‐24°S) is characterized by resistivities 〉1000 Ωm, suggesting the absence of large magma reservoirs below the volcanic chain at crustal depths. Magma reservoirs located below the base of the crust or in the back‐arc may fed active volcanism in the southern domain. In the subcontinental mantle, the model exhibits LRZs in the forearc mantle wedge and above clusters of intermediate‐depth seismicity, likely related to fluids produced by serpentinization of the mantle and eclogitization of the slab, respectively.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 41
    Publication Date: 2019
    Description: Abstract Peer review is an act of serving the community. Each act of peer review leads to sharper, more accurate, more impactful science, and clearer communication. Reviews from independent colleagues help bring the strengths and opportunities for improvement in scientific work into focus. Each year in planetary science, new ideas and places are explored, new understanding of our planet, its neighbors, and distant exoplanets are uncovered. Ensuring that the lessons of those discoveries can lead to new breakthroughs rests on the accuracy and accessibility of science we share. In 2018, we were humbled by the 756 peer reviews from 461 individuals that JGR: Planets received. Thank you for your efforts, your insights, and your service on behalf of the planetary science community.
    Print ISSN: 2169-9097
    Electronic ISSN: 2169-9100
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 42
    Publication Date: 2019
    Description: Abstract Surrogate species are commonly used in conservation science due to the fact that it is not feasible to measure and manage each component of biodiversity independently; yet, there is much debate about their efficacy. We use long‐term monitoring data from six national park units in northern California and southern Oregon to test the focal species approach, wherein a suite of species is selected whose habitat requirements collectively encompass those of co‐occurring species. Specifically, we examine how well existing Partners in Flight (PIF) habitat‐based focal species lists and empirically derived focal species lists represent vegetation and three avian assemblages of interest: the entire assemblage, species of concern, and common species in steep decline. Existing PIF focal species lists were significantly correlated with the three alternative matrices of avian assemblages and vegetation, but not all parks and alternate matrices performed with equal correlative strength and/or significance. For example, existing PIF focal species lists were significantly correlated to the entire assemblage at five of the six parks and had ecologically meaningful correlations (〉0.70) at four. However, PIF focal species list correlations with park specific species of concern and common species in steep declined varied widely, with correlations between 0.040–0.943 and 0.210–0.556, respectively. Averaged across park units the empirical focal species lists developed to represent both vegetation metrics and species of concern improved correlation with all alternative matrices of avian assemblages and vegetation metrics. We found that the focal species approach generally represented the entire avian community, but did not adequately represent suites of species of concern or common species in decline. Empirical testing is a critical step in validating or refining suites of focal species at management relevant scales, and in some instances, a more refined focal species list may increase overall utility of the surrogate species approach.
    Print ISSN: 1051-0761
    Electronic ISSN: 1939-5582
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 43
    Publication Date: 2019
    Description: Abstract Quantification of allogenic controls in rift basin‐fills requires analysis of multiple depositional systems because of marked along‐strike changes in depositional architecture. Here, we compare two coeval Early‐Middle Pleistocene syn‐rift fan deltas that sit 6 km apart in the hangingwall of the Pirgaki‐Mamoussia Fault, along the southern margin of the Gulf of Corinth, Greece. The Selinous fan delta is located near the fault tip, and the Kerinitis fan delta towards the fault centre, but Selinous and Kerinitis have comparable overall aggradational stacking patterns. Selinous comprises fifteen cyclic stratal units (~25 m thick), whereas at Kerinitis eleven (~60 m thick) are present. Eight facies associations are identified. Fluvial and shallow water, conglomeratic facies dominate the major stratal units in the topset region, with shelfal fine‐grained facies constituting ~2 m thick intervals between major topsets units, and thick conglomeratic foresets building down‐dip. It is possible to quantify delta build times (Selinous: 615 kyrs; Kerinitis: 〉450 kyrs), and average subsidence and equivalent sedimentation rates (Selinous: 0.65 m/kyrs; Kerinitis: 〉1.77 m/kyrs). The presence of sequence boundaries at Selinous, but their absence at Kerinitis, enables sensitivity analysis of the most uncertain variables using a numerical model, ‘Syn‐Strat’, supported by an independent unit thickness extrapolation method. Our study has three broad outcomes: 1) the first estimate of lake level change amplitude in Lake Corinth for the Early‐Middle Pleistocene (10‐15 m), which can aid regional palaeoclimate studies and inform broader climate‐system models; 2) demonstration of two complementary methods to quantify faulting and base level signals in the stratigraphic record – forward modelling with Syn‐Strat and a unit thickness extrapolation ‐ which can be applied to other rift basin‐fills; and 3) a quantitative approach to the analysis of stacking patterns and key surfaces that could be applied to stratigraphic pinch‐out assessment and cross‐hole correlations in reservoir analysis. This article is protected by copyright. All rights reserved.
    Print ISSN: 0950-091X
    Electronic ISSN: 1365-2117
    Topics: Geosciences
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 44
    Publication Date: 2019
    Description: Abstract The interactions between climate and land use change are dictating the distribution of flora and fauna and reshuffling biotic community composition around the world. Tropical mountains are particularly sensitive because they often have a high human population density, a long history of agriculture, range‐restricted species, and high‐beta diversity due to a steep elevation gradient. Here we evaluated the change in distribution of woody vegetation in the tropical Andes of South America for the period 2001 to 2014. For the analyses we created annual land cover/land use maps using MODIS satellite data at 250‐m pixel resolution, calculated the cover of woody vegetation (trees and shrubs) in 9,274 hexagons of 115.47 km2, and then determined if there was a statistically significant (p 〈0.05) 14‐year linear trend (positive – forest gain, negative – forest loss) within each hexagon. Of the 1,308 hexagons with significant trends, 36.6% (n=479) lost forests and 63.4% (n=829) gained forests. We estimated an overall net gain of ~500,000 ha in woody vegetation. Forest loss dominated the 1000‐1499 m elevation zone and forest gain dominated above 1500 m. The most important transitions were forest loss at lower elevations for pastures and croplands, forest gain in abandoned pastures and cropland in mid elevation areas, and shrub encroachment into highland grasslands. Expert validation confirmed the observed trends, but some areas of apparent forest gain were associated with new shade coffee, pine, or eucalypt plantations. In addition, after controlling for elevation and country, forest gain was associated with a decline in the rural population. Although we document an overall gain in forest cover, the recent reversal of forest gains in Colombia demonstrates that these coupled natural‐human systems are highly dynamic and there is an urgent need of a regional real‐time land use, biodiversity, and ecosystem services monitoring network. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 45
    Publication Date: 2019
    Description: High winds and storm surges associated with torrential rain from tropical cyclones (TCs) cause massive destruction to property and cost the lives of many people. The coastline of the Bay of Bengal (BoB) ranks as one of the most susceptible to storm surges in the world due to low‐lying elevation and a high frequency of TC occurrence. This study uses data from 1885 to 2011 and a bivariate statistical copula to describe the relationship and dependency between empirical TC storm surge and reported wind speed before landfall at the BoB. Among the copulas and their families, an Archimedean, Gumbel copula with margins defined by the empirical distributions is specified as the most appropriate choice for the BoB. The model provides return periods for pairs of TC storm surge and 12‐hour pre‐landfall wind along the BoB coastline. On the shortest time scale, the BoB can expect a TC with 12‐hour pre‐landfall winds of at least 24 m s−1 and surge heights of at least 4.0 m, on average, once every 3.9 years. On the other hand, the long‐term, worst case scenario suggests the BoB can expect 12‐hour pre‐landfall winds of 62 m s−1 and surge heights of at least 8.0 m, on average, once every 311.8 years. Using a copula to model the combined frequency of cyclone wind speeds along with storm surges along the BoB coastline increases the understanding of the dangerous TC characteristics in this region, which can reduce fatalities and monetary losses. This article is protected by copyright. All rights reserved.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 46
    Publication Date: 2019
    Description: Choosing downscaling techniques is crucial in obtaining accurate and reliable climate change predictions, allowing for detailed impact assessments of climate change at regional and local scales. Traditional statistical methods are likely inefficient in downscaling precipitation data from multiple sources or complex data patterns, so using deep learning, a form of non‐linear models, could be a promising solution. In this study, we proposed to use deep learning models, the so‐called Long Short‐Term Memory (LSTM) and Feedforward Neural Network (FNN) methods, for precipitation downscaling for the Vietnamese Mekong Delta. Model performances were assessed with the 2036 – 2065 period, using original climate projections from five climate models under the Coupled Model Intercomparison Project Phase 5 (CMIP5), for two Representative Concentration Pathways scenarios (RCPs 4.5 and 8.5). The results exhibited that there were good correlations between the modeled and observed values of the testing and validating periods at two long‐term meteorological stations (Can Tho and Chau Doc). We then analyzed extreme indices of precipitation, including the annual maximum wet day frequency (Prcp), 95th percentile of precipitation (P95p), maximum 5‐day consecutive rain (R5d), total number of wet days (Ptot), wet day precipitation (SDII) and annual maximum dry day frequency (Pcdd) to evaluate changes in extreme precipitation events. All the five models under the two scenarios predicted that precipitation would increase in the wet season (June – October) and decrease in the dry season (November – May) in the future compared to the present‐day scenario. On average, the means of multi‐annual wet season precipitation would increase by 20.4% and 25.4% at Can Tho and Chau Doc, respectively, but in the dry season, these values were projected to decrease by 10% and 5.3%. All the climate extreme indices would increase in the period of 2036 – 2065 in comparison to the baseline. Overall, the developed downscaling models can successfully reproduce historical rainfall patterns and downscale projected precipitation data. This article is protected by copyright. All rights reserved.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 47
    Publication Date: 2019
    Description: The spring Sudan low and its Red Sea Trough (RST) were detected objectively using sea level pressure (SLP) data obtained from an NCEP/NCAR reanalysis dataset spanning the period from 1955 to 2014. The climatology of the detected lows suggested that the Sudan low was active for approximately 69.5% of the spring and that approximately 56.2% of this time the Sudan low developed into the RST. Furthermore, three main genesis regions of the RST, which generated 95.25% of the RST, were identified over Sudan, South Sudan and the Red Sea, approximately 61.76% of which was over South Sudan. Additionally, three main outermost areas of the RST, which received 94.1% of the RST, were specified to the west, east and north of the Red Sea, approximately 54.88% of which was in the eastern region. Synoptically, the orientations of the detected RST around the Red Sea are strongly influenced by the Siberian and Azores high systems. The RST is directed along the western side of the Red Sea if the Siberian high extends westward and the Azores high shrinks westward, whereas the RST is oriented to the east if the Siberian high shrinks eastward and the Azores high extends eastward. The RST extends directly northward if the Siberian and Azores high systems withdraw eastward and westward, respectively. These results also demonstrate that the core position and strength of the upper maximum winds play an important role in the generation of RST. The selected case studies have confirmed the synoptic climate results and indicate that the Sudan low will not develop into RST when the northern region has been affected by a high‐pressure system and the core of the upper maximum wind is located over the northern Arabian Peninsula. This article is protected by copyright. All rights reserved.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 48
    Publication Date: 2019
    Description: The aim of the article was to provide a detailed analysis of pressure conditions, employing the anomalies of geopotential heights, during the occurrence of heat waves in Central Europe, but also in the days preceding and following their occurrence. The study uses data from 1966 to 2015 from the Institute of Meteorology and Water Management – National Research Institute, Deutscher Wetterdienst and the National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR). A heat wave was defined as a sequence of at least 3 days with a maximum daily air temperature of 〉30°C. The study showed an increase in the number of hot days, which was statistically significant in the majority of the area. In the analysed years, an increasing number of heat waves was recorded, and this occurrence was associated with high pressure systems. Anticyclonic blocking in the summer inhibits the zonal flow of air masses and intensifies meridional flow, which in Central Europe in the summer means the presence of polar continental and tropical air masses. During heat waves, there were positive anomalies of isobaric surface heights over the study area with a maximum in the upper troposphere. On average, anomalies at the 300 hPa pressure level began to form over the Atlantic Ocean. Determining atmospheric preconditions of persisting blocking events in summer resulting in heat waves may be helpful in predicting thereof. This article is protected by copyright. All rights reserved.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 49
    Publication Date: 2019
    Description: Abstract Linear aeolian bedforms are the most abundant bedform type in Earth's dune fields, and are very common in the Solar System. Despite their abundance, the long‐term development of these bedforms and its impact upon the resulting sedimentary architecture in the geological record is still poorly understood. The aim of this paper is to study the exposed record of an ancient linear megadune in order to discuss its development and the factors that impact the sedimentary architecture of aeolian linear bedforms. The outcrops of the ancient Troncoso Sand Sea (Barremian, Neuquén Basin, Argentina) provide a unique opportunity to study a preserved megadune record with an external body geometry that confirms its linear morphology. Architectural analysis reveals significant differences in cross‐stratified set bodies and bounding surfaces’ features and allows for the identification of three architectural complexes within the bedform's record. Analysis of deterministic models, sedimentary body relative chronology and distribution suggest that these architectural complexes result from distinctive phases in bedform development. It also clearly shows that construction of the megadune was achieved by expansion from a core, and that its development was characterized by sustained growth and strong longitudinal dynamics, without net accumulation. This study indicates how sustained bedform growth, rather than accretion, can be a critical factor conditioning linear bedform architecture towards a more ‘classic’ (bimodal bounding surface and cross‐bedding dip directions) concentric sedimentary architecture style. Furthermore, this research reveals how this style of architecture could only be relatively common in the geological record when related to bedform topography preservation. This article is protected by copyright. All rights reserved.
    Print ISSN: 0037-0746
    Electronic ISSN: 1365-3091
    Topics: Geosciences
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 50
    Publication Date: 2019
    Description: Abstract Aim Phenology of a wide diversity of organisms has a dependency on climate, usually with reproductive periods beginning earlier in the year and lasting longer at lower latitudes. Temperature and day length are known environmental drivers of the reproductive timing of many species. Hence, reproductive phenology is sensitive to warming and is important to be considered for reliable predictions of species distributions. This is particularly relevant for rapidly spreading non‐indigenous species (NIS). In this study, we forecast the future ranges of a NIS, the seaweed Sargassum muticum, including its reproductive phenology. Location Coastal areas of the Northern Hemisphere (Pacific and Atlantic oceans). Methods We used ecological niche modelling to predict the distribution of S. muticum under two scenarios forecasting limited (RCP 2.6) and severe (RCP 8.5) future climate changes. We then refined our predictions with a hybrid model using sea surface temperature constraints on reproductive phenology. Results Under the most severe climate change scenario, we predicted northward expansions which may have significant ecological consequences for subarctic coastal ecosystems. However, in lower latitudes, habitats currently occupied by S. muticum will no longer be suitable, creating opportunities for substantial community changes. The temperature constraints imposed by the reproductive window were shown to restrict the modelled future species expansion strongly. Under the RCP 8.5 scenario, the total range area was expected to increase by 61.75% by 2100, but only by 1.63% when the reproductive temperature window was considered. Main conclusions Altogether these results exemplify the need to integrate phenology better to improve the prediction of future distributional shifts at local and regional scales.
    Print ISSN: 1366-9516
    Electronic ISSN: 1472-4642
    Topics: Biology
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 51
    Publication Date: 2019
    Description: Abstract Measurements of electrons and ions in Saturn's ionosphere down to 1500 km altitudes as well as the ring crossing region above the ionosphere obtained by the Langmuir probe onboard the Cassini spacecraft are presented. Five nearly identical deep ionosphere flybys during the Grand Finale orbits and the Final plunge orbit revealed a rapid increase in the plasma densities and discrepancies between the electrons and ions densities (Ne and Ni) near the closest approach. The small Ne/Ni ratio indicates the presence of a dusty plasma, a plasma which charge carrier is dominated by negatively charged heavy particles. Comparison of the LP obtained density with the light ion density obtained by the Ion and Neutral Mass Spectrometer (INMS) confirmed the presence of heavy ions. An unexpected positive floating potential of the probe was also observed when Ne/Ni 〈〈 1. This suggests that Saturn's ionosphere near the density peak is in a dusty plasma state consisting of negatively and positively charged heavy cluster ions. The electron temperature (Te) characteristics in the ionosphere are also investigated and unexpectedly high electron temperature value, up to 5000 K, has been observed below 2500 km altitude in a region where electron‐neutral collisions should be prominent. A well‐defined relationship between Te and Ne/Ni ‐ratio was found, implying that the electron heating at low altitudes is related to the dusty plasma state of the ionosphere.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 52
    Publication Date: 2019
    Description: Abstract Using Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations over a ten‐year period from 2008 to 2017, we statistically investigate the thermodynamic properties for magnetosheath ions and their dependence on upstream interplanetary magnetic field (IMF) conditions. The thermodynamic properties for magnetosheath ions are estimated by using the polytropic index averaged over the subinterval that belongs to the same streamline ( ). The THEMIS observations show that the probability distribution of for magnetosheath ions has a major peak at ~1 (quasi‐isothermal conditions) with a longer left‐tail down to ~0 (quasi‐isobaric conditions). The spatial distributions of for two different types according to IMF spiral angle (i.e., Parker spiral and ortho‐Parker spiral IMF orientations) reveal that the ions in the downstream of a quasi‐perpendicular shock (quasi‐perpendicular magnetosheath) exhibit quasi‐isothermal processes, while those in the downstream of a quasi‐parallel shock (quasi‐parallel magnetosheath) show lower than unity (down to ~0.8) implying the anticorrelation between the ion temperature and the ion number density variations. Moreover, in the quasi‐parallel magnetosheath tends to decrease with increasing magnetic local time (MLT) distance from the magnetic local noon. These results indicate that the thermodynamic properties for magnetosheath ions depend on the bow shock geometry (quasi‐perpendicular bow shocks versus quasi‐parallel bow shocks) and are presumably controlled by a variety of instabilities, waves, and turbulence in the magnetosheath.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 53
    Publication Date: 2019
    Description: Abstract With the measurements of the Magnetospheric Multiscale (MMS) mission at the magnetopause, we investigated the electron distribution and the whistler waves associated with a series of six ion‐scale flux transfer events (FTEs). Based on the magnetic field signature, each FTE can be divided into the core region and the draping region. In the draping regions of the most FTEs, the low‐energy electrons displayed a bidirectional field‐aligned distribution. The medium‐energy electrons showed a field‐aligned or beam distribution in the leading part, while a pancake distribution was presented for the electrons in the trailing part of the draping region, which has never been reported previously. The close correlation between the pancake distribution and the compression of the localized magnetic field suggests that the pancake distribution may be due to the betatron acceleration. The whistler waves associated with the FTEs were observed and categorized into the lower and upper bands according to the frequency range. The lower‐band whistler waves propagated in variable directions and therefore could be generated locally. The trailing part of the draping region with the electron pancake distribution was considered to be one possible source region. On the contrary, the upper‐band whistler waves were all found in the core region and propagated antiparallel to the magnetic field, and therefore originated from the same source region. The observations confirmed that the FTEs are important channels for the mass and wave transport between the magnetosheath and the inner magnetosphere, and the electron dynamics can be modified during the FTE evolution.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 54
    Publication Date: 2019
    Description: Abstract We analyze three substorms that occur on 1) 9 March 2008 05:14 UT, 2) 26 February 2008 04:05 UT, and 3) 26 Feb 2008 04:55 UT. Using ACE solar wind velocity, IMF Bz values, we calculate the rectified (southward Bz) solar wind voltage propagated to the magnetosphere. The solar wind conditions for the two events were vastly different, 300 kV for 9 March 2008 substorm, compared to 50 kV for 26 February 2008. The voltage is input to a nonlinear physics based model of the magnetosphere called WINDMI. The output is the westward auroral electrojet current which is proportional to the auroral electrojet (AL) index from WDC Kyoto and the SuperMAG auroral electrojet index (SML). Substorm onset times are obtained from the superMAG substorm database, Pu et al. [2010], Lui [2011] and synchronized to THEMIS satellite data. The timing of onset, model parameters and intermediate state space variables are analyzed. The model onsets occurred about 5 to 10 mins earlier than the reported onsets. Onsets occurred when the geotail current in the WINDMI model reached a critical threshold of 6.2 MA for the 9 March 2008 event, while, in contrast, a critical threshold of 2.1 MA was obtained for the two 26 February 2008 events. The model estimates 1.99 PJ of total energy transfer during the 9 March 2008 event, with 0.95 PJ deposited in the ionosphere. The smaller events on 26 February 2008 resulted in a total energy transfer of 0.37 PJ according to the model, with 0.095 PJ deposited in the ionosphere.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 55
    Publication Date: 2019
    Description: Abstract This paper discusses the solar cycle variation of the DE3 and DE2 nonmigrating tides in the nitric oxide (NO) 5.3 μm and carbon dioxide (CO2) 15 μm infrared cooling between 100 and 150 km altitude and +/‐40 deg latitude. Tidal diagnostics of SABER NO and CO2 cooling rate data (2002‐2013) indicate DE3 (DE2) amplitudes during solar maximum are on the order of 1 (0.5) nW/m3 in NO near 125 km, and on the order of 60 (30) nW/m3 in CO2 at 100 km, which translates into roughly 15‐30% relative to the monthly zonal mean. The NO cooling shows a pronounced (factor of 10) solar cycle dependence (lower during solar minimum) while the CO2 cooling does not vary much from solar min to solar max. Photochemical modeling reproduces the observed solar cycle variability and allows one to delineate the physical reasons for the observed solar flux dependence of the tides in the infrared cooling, particularly in terms of warmer/colder background temperature versus smaller/larger tidal temperatures during solar max/min, in addition to cooling rate variations due to vertical tidal advection and tidal density variations. Our results suggest that (i) tides caused by tropospheric weather impose a substantial ‐ and in the NO 5.3 μm case solar cycle dependent‐ modulation of the infrared cooling, mainly due to tidal temperature (ii) observed tides in the infrared cooling are a suitable proxy for tidal activity including its solar cycle dependence in a part of Earth's atmosphere where direct global temperature observations are lacking.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 56
    Publication Date: 2019
    Description: Abstract We study characteristics of ion and electron beams observed during 101 crossings of the near‐separatrix region by ARTEMIS spacecraft in the magnetotail. We found that accelerated ion beams are observed under any level of geomagnetic activity. A duration of earthward moving ion beams is statistically longer (≤ 10 min) than a duration of tailward ion beams (≤ 4 min), which can be due to the transient character of ion acceleration in the vicinity of Near‐Earth Neutral Line (NENL). Energetic characteristics of earthward and tailward ion beams are similar indicating similar acceleration conditions at ion kinetic scales at both sides of an X‐line independently of its location. Conversely, electron velocity distributions observed near magnetic separatrix earthward of the Distant Neutral Line (DNL) differ from those observed tailward of the NENL. Earthward of the DNL a scattered and thermalized electron population without energetic field‐aligned beams is observed near the separatrix. On the contrary, tailward of the NENL field‐aligned electron beams accelerated to a few keVs are detected. These observations show that near DNL the electron scattering and thermalization dominate over the direct acceleration, whereas stronger electric fields in the NENL produce substantial population of field‐aligned keV‐electrons.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 57
    Publication Date: 2019
    Description: Abstract Question The existence of monodominant forest in highly diverse tropical rainforest has been the subject of much debate. One hypothesis suggests that the combination of advantageous traits and long periods of low disturbance is key for this forest persistence. Here we ask whether there is evidence for the long‐term presence of monodominant Gilbertiodendron forest in the absence of fire and climate change. Location Republic of Congo. Methods We extracted fossil pollen and macro‐charcoal from a sediment sequence collected in present‐day monodominant Gilbertiodendron forest stand that spans the last 2700 years. Climatic changes were inferred using other published palaeoecological records from Central Africa. We also looked at Gilbertiodendron dewevrei's present‐day ecological tolerances. Results Gilbertiodendron pollen was found in every sample covering the last 2700 years in similar percentages to present‐day soil surface samples. In addition, no statistically significant change in pollen composition was found during this time despite wetter and drier vegetation changes documented in nearby mixed‐forest cores over the same time period. No evidence of fire was found for a period of 2400 years. Only minimal burning occurred over the last 300 years in this monodominant stand. The analysis of ecological tolerances shows G. dewevrei has a broad niche for precipitation (1300 to 2460 mm). Conclusions Our pollen record is the first to describe the long‐term ecological history of an African monodominant forest. Our results show this monodominant stand existed over the past 2700 years mostly in the absence of fire, providing support for the low disturbance hypothesis as an explanation for monodominance persistence. However, the persistence of the monodominant forest at this site occurs despite evidence for climatic fluctuations in the immediate region. This combined with the broad tolerance of water requirements of the species suggests a potential resilience to future climate variability. However, additional pollen records from a wider area are needed to confirm this. This article is protected by copyright. All rights reserved.
    Print ISSN: 1100-9233
    Electronic ISSN: 1654-1103
    Topics: Biology
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 58
    Publication Date: 2019
    Description: ABSTRACT Imaging in geological challenging environments has led to new developments, including the idea of generating reflection responses by means of interferometric redatuming at a given target datum in the subsurface, when the target datum lies beneath a complex overburden. One way to perform this redatuming is via conventional model‐based wave‐equation techniques. But those techniques can be computationally expensive for large‐scale seismic problems since the number of wave‐equation solves is equal to two‐times the number of sources involved during seismic data acquisition. Also conventional shot‐profile techniques require lots of memory to save full subsurface extended image volumes. Therefore, they only form subsurface image volumes in either horizontal or vertical directions. We now present a randomized singular value decomposition based approach built upon the matrix probing scheme, which takes advantage of the algebraic structure of the extended imaging system. This low‐rank representation enables us to overcome both the computational cost associated with the number of wave‐equation solutions and memory usage due to explicit storage of full subsurface extended image volumes employed by conventional migration methods. Experimental results on complex geological models demonstrate the efficacy of the proposed methodology and allow practical reflection‐based extended imaging for large‐scale 5D seismic data. This article is protected by copyright. All rights reserved
    Print ISSN: 0016-8025
    Electronic ISSN: 1365-2478
    Topics: Geosciences , Physics
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 59
    Publication Date: 2019
    Description: Abstract A significant portion of the production and consumption of trace gases (e.g. CO2, CH4, N2O, NH3, etc.) by world ecosystems occurs in areas without sufficient infrastructure or easily available grid power to run traditional closed‐path flux stations. Open‐path analyzer design allows such measurements with power consumption 10‐150 times below present closed‐path technologies, helping to considerably expand the global coverage and improve the estimates of gas emissions and budgets, informing the remote sensing and modeling communities and policy decisions, all the way to IPCC reports. Broad‐band NDIR devices have been used for open‐path CO2 and H2O measurements since the late 1970s, but since recently, a growing number of new narrow‐band laser‐based instruments are being rapidly developed. The new design comes with its own challenges, specifically: (i) mirror contamination, and (ii) uncontrolled air temperature, pressure and humidity, affecting both the gas density and the laser spectroscopy of the measurements. While the contamination can be addressed via automated cleaning, and density effects can be addressed via the Webb‐Pearman‐Leuning approach, the spectroscopic effects of the in‐situ temperature, pressure and humidity fluctuations on laser‐measured densities remain a standing methodological question. Here we propose a concept accounting for such effects in the same manner as Webb et al. (1980) proposed to account for respective density effects. Derivations are provided for a general case of flux of any gas, examined using a specific example of CH4 fluxes from a commercially available analyzer, and then tested using “zero‐flux” experiment. The proposed approach helps reduce errors in open‐path, enclosed, and temperature‐ or pressure‐uncontrolled closed‐path laser‐based flux measurements due to the spectroscopic effects from few percents to multiple folds, leading to methodological advancement and geographical expansion of the use of such systems providing reliable and consistent results for process‐level studies, remote sensing and Earth modeling applications, and GHG policy decision‐making. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 60
    Publication Date: 2019
    Description: Abstract Extreme events significantly impact ecosystems and are predicted to increase in frequency and/or magnitude with climate change. Generalized extreme value (GEV) distributions describe most ecologically‐relevant extreme events, including hurricanes, wildfires, exotic species outbreaks, and disease spread. In climate science, the GEV is widely used as an accurate and flexible tool over large spatial scales (〉〉 105 km2) to study how changes in climate shift extreme events. However, ecologists rarely use the GEV to study how climate change affects populations. Here we show how to estimate a GEV for hurricanes at an ecologically‐relevant (〈 103 km2) spatial scale, and use the results in a stochastic, empirically‐based matrix population model. As a case study, we use an understory shrub in southeast Florida with hurricane‐driven dynamics and measure the effects of change using the stochastic population growth rate. We use sensitivities to analyze how population growth rate is affected by changes in hurricane frequency and intensity, canopy damage levels, and canopy recovery rates. Our results emphasize the importance of accurately estimating location‐specific storm frequency. In a rapidly changing world, our methods show how to combine realistic extreme event and population models to assess ecological impacts and to prioritize conservation actions for at‐risk populations. This article is protected by copyright. All rights reserved.
    Print ISSN: 0012-9658
    Electronic ISSN: 1939-9170
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 61
    Publication Date: 2019
    Description: Abstract The Sentinel‐1 mission is part of the European Copernicus program aiming at providing observations for Land, Marine and Atmosphere Monitoring, Emergency Management, Security and Climate Change. It is a constellation of two (Sentinel‐1 A and B) Synthetic Aperture Radar (SAR) satellites. The SAR wave mode (WV) routinely collects high‐resolution SAR images of the ocean surface during day and night and through clouds. In this study, a subset of more than 37,000 SAR images is labelled corresponding to ten geophysical phenomena, including both oceanic and meteorologic features. These images cover the entire open ocean and are manually selected from Sentinel‐1A WV acquisitions in 2016. For each image, only one prevalent geophysical phenomenon with its prescribed signature and texture is selected for labelling. The SAR images are processed into a quick‐look image provided in the formats of PNG and GeoTIFF as well as the associated labels. They are convenient for both visual inspection and machine learning‐based methods exploitation. The proposed dataset is the first one involving different oceanic or atmospheric phenomena over the open ocean. It seeks to foster the development of strategies or approaches for massive ocean SAR image analysis. A key objective was to allow exploiting the full potential of Sentinel‐1 WV SAR acquisitions, which are about 60,000 images per satellite per month and freely available. Such a dataset may be of value to a wide range of users and communities in deep learning, remote sensing, oceanography and meteorology.
    Electronic ISSN: 2049-6060
    Topics: Geosciences
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 62
    Publication Date: 2019
    Description: Abstract The total electron content (TEC) recorded at two middle latitude stations Mohe and Beijing, four low latitude stations Xiamen, Guangzhou, Nanning and Kunming in the China sector, respectively, are analyzed to study the response of ionosphere during the sudden stratospheric warming event in February 2018. The TEC and deviation of TEC (ΔTEC) present remarkable perturbation after the reversal of zonal wind during the SSW period. The ΔTEC presents enhancement during the daytime and decreases after the sunset, especially around the temperature peak. Results of wavelet power spectra analysis show that the ΔTEC shows intensive semi‐diurnal and diurnal oscillations during the SSW period. The percentage of dTEC exhibits moderate correlation with solar geophysical drivers (such as solar wind speed, F10.7 and Ap index) during the period of 11‐26 February at low latitude stations. The significant correlation between equatorial electrojet (EEJ) with the percentage of dTEC monitored in low latitude indicates that the EEJ plays a key role on the anomaly perturbation and oscillation periodic of TEC, while it has a weak correlation in middle latitude.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 63
    Publication Date: 2019
    Description: Abstract Most of existing ground penetrating radar (GPR) imaging algorithms are only capable of imaging of targets under a single layer subsurface. In this paper, a generalized three‐dimensional (3‐D) fast imaging algorithm for GPR imaging of targets buried under multilayered subsurface is presented. The exploding reflection model is employed to simplify the imaging algorithm and then the layered media dyadic Green's function is expanded in spectral form to facilitate the easy implementation of the imaging algorithm with fast Fourier transform (FFT). The wave propagation effects through multilayered subsurface are efficiently taken into account and be properly compensated for in the imaging formulation through the multilayer media dyadic Green's function. The linearization of the inversion scheme and utilization of FFT resolve the time‐consuming challenge in 3‐D GPR imaging and make the imaging algorithm suitable in several applications concerning the diagnostics of large probed region. Representative numerical and experimental examples are presented to show the effectiveness and efficiency of the proposed algorithm for 3‐D GPR imaging through multilayered media.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 64
    Publication Date: 2019
    Description: Abstract The south Indian Ocean (SIO) is a region of strong air‐sea heat loss due to the unique ocean circulation pattern influenced by the Indonesian Throughflow. In this study, the seasonal variation of the surface layer heat budget in the eastern SIO is investigated using 2 years of measurements from a mooring at 25°S, 100°E, the only colocated upper ocean and surface meteorology time series in the subtropical Indian Ocean. The mooring data are combined with other in situ and satellite data to examine the role of air‐sea fluxes and ocean heat transport on the evolution of mixed layer temperature using heat budget diagnostic models. Results show that on seasonal timescales, mixed layer heat storage in the eastern SIO is mostly balanced by a combination of surface fluxes and turbulent entrainment with a contribution from horizontal advection at times. Solar radiation dominates the seasonal cycle of net surface heat flux, which warms the mixed layer during austral summer (67 Wm‐2) and cools it during austral winter (‐44 Wm‐2). Entrainment is in good agreement with the heat budget residual for most of the year. Horizontal advection is spatially variable and appears to be dominated by the presence of mesoscale eddies and possibly annual and semi‐annual Rossby waves propagating from the eastern boundary. Results from the 2‐year mooring‐based data analysis are in reasonably good agreement with a 12‐year regional heat budget analysis around the mooring location using ocean reanalysis products.
    Print ISSN: 2169-9275
    Electronic ISSN: 2169-9291
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 65
    Publication Date: 2019
    Description: Abstract Low‐δ26Mg basalts are commonly interpreted to represent melts derived from carbonated mantle sources. The mantle domain feeding low‐δ26Mg Cenozoic basalts in eastern China overlaps the so‐called Big Mantle Wedge (BMW) above the stagnant Pacific slab in the mantle transition zone, which indicates that the BMW is an important carbon reservoir generated by the slab. However, Mg isotopic composition in the nearby mantle beyond the BMW, and thus the spatial extent of carbonated components in the mantle beneath eastern Asia have not yet been extensively characterized. Therefore, it remains largely unconstrained if additional or alternative carbon reservoirs exist. Here we carried out a geochemical study on Cenozoic Huihe nephelinites, which crop out ~500 km west of the present‐day BMW. These rocks are characterized by negative K, Zr, Hf, and Ti anomalies, high Zr/Hf, Ca/Al ratios and low δ26Mg values, which suggest that they are derived from a carbonated mantle source. The composition of the nephelinites demonstrates that low δ26Mg mantle components exist at significant distances from the present‐day BMW, which highlights that in addition to the stagnant Pacific slab, other oceanic slab(s) also contribute carbonate‐bearing crustal materials into the mantle sources of eastern Asia's Cenozoic volcanism.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 66
    Publication Date: 2019
    Description: Abstract The 2016‐2017 Central Apennines earthquake sequence is a recent example of how damages from subsequent aftershocks can exceed those caused by the initial mainshock. Recent studies reveal that physics‐based aftershock forecasts present comparable skills to their statistical counterparts, but their performance remains a controversial subject. Here, we employ physics‐based models that combine the elasto‐static stress transfer with rate‐and‐state friction laws, and short‐term statistical ETAS models to describe the spatiotemporal evolution of the earthquake cascade. We then track the absolute and relative model performance using log‐likelihood statistics for a 1‐year horizon after the 24th August 2016 Mw=6.0 Amatrice earthquake. We perform a series of pseudo‐prospective experiments by producing 7 classes of Coulomb rate‐state (CRS) forecasts with gradual increase in data input quality and model complexity. Our goal is to investigate the influence of data quality on the predictive power of physics‐based models and to assess the comparative performance of the forecasts in critical time windows, such as the period following the 26th October Visso earthquakes leading to the 30th October Mw=6.5 Norcia mainshock. We find that (1) the spatiotemporal performance of the basic CRS models is poor and progressively improves as more refined data are used, (2) CRS forecasts are about as informative as ETAS when secondary triggering effects from M3+ earthquakes are included together with spatially variable slip models, spatially heterogeneous receiver faults, and optimized rate‐and‐state parameters. After the Visso earthquakes, the more elaborate CRS model outperforms ETAS highlighting the importance of the static stress transfer for operational earthquake forecasting.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 67
    Publication Date: 2019
    Description: Abstract Inelastic rheological behaviour, such as viscoelasticity, is increasingly utilised in the modelling of volcanic ground deformation, as elevated thermal regimes induced by magmatic systems may necessitate the use of a mechanical model containing a component of time‐dependent viscous behaviour. For the modelling of a given amplitude and footprint of ground deformation, incorporating a viscoelastic regime has been shown to reduce the magma reservoir overpressure requirements suggested by elastic models. This phenomenon, however, is restricted to pressure‐based analyses and the associated creep behaviour. Viscoelastic materials exhibit additional constitutive time‐dependent behaviours, determined by the stress and strain states, that are yet to be analysed in the context of volcanic ground deformation. By utilising a mechanically homogeneous model‐space and distinct reservoir evolutions, we provide a comparison of three viscoelastic rheological models, including the commonly implemented Maxwell and Standard Linear Solid configurations, and their time‐dependent behaviours from a fundamental perspective. We also investigate the differences between deformation timeseries resulting from a pressurisation or volume change; two contrasting approaches that are assumed to be equivalent through elastic modelling. Our results illustrate that the perceived influence of viscoelasticity is dependent on the mode of deformation, with stress‐based pressurisation models imparting enhanced deformation relative to the elastic models, thus reducing pressure requirements. Strain‐based volumetric models, however, exhibit reduced levels of deformation and may produce episodes of apparent ground subsidence induced by source inflation or vice versa, due to the relaxation of crustal stresses, dependent on whether the reservoir is modelled to be expanding or contracting, respectively.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 68
    Publication Date: 2019
    Description: Abstract Structures of sudden enhancements/depressions and associated interhemispheric asymmetry in low latitude total electron content (TEC) during main phase (MP) of geomagnetic storms have remained unpredictable majorly due to oscillating equatorial vertical ExB drifts and resultant redistribution of plasma in low latitudes in a given seasonal background. Robust analysis of 7 major and 30 moderate ionospheric storms during years 2000‐2018 is performed with comprehensive literature review encompassing various sources of asymmetry in magnetosphere‐ionosphere coupling. Taking advantage of simultaneous long term observations of ExB drift from Jicamarca, H‐component from magnetometers, GIM‐VTEC and TEC observations across the dip equator from the South American sector, simultaneous formation of peaks and valleys in VTEC and associated asymmetry are studied. Additionally a 3‐layer neural network based ExB drift model is developed using delta‐H observations that provides drift estimates in the absence of Jicamarca drifts. Main results establish simultaneous high magnitude short lived (1‐2 hours) enhancements and depression in VTEC during MP in daytime in both the hemispheres with varying differences of ‐30 to 100 TECU wrt quiet time mean and along with prominent existence of interhemispheric asymmetry in TEC during MP regardless of seasons. Maximum VTEC in the northern and southern low latitudes is found to occur at different times during storms. Large difference of VTEC is found ranging between 10 to 30 TECU between the near conjugate locations of the hemispheres. Coincident global episodic peaks marked by steep VTEC falls show dominance of episodic eastward and westward penetration electric field in low latitudes daytime ionosphere.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 69
    Publication Date: 2019
    Description: Abstract Convection under the due northward interplanetary magnetic field (IMF) is reproduced by the global simulation. The resulting magnetosphere is closed except in the XZ plane, and separated from the solar wind by the separatrix generated from cusp nulls. Inside the separatrix, there exist three plasma regimes of the cusp high‐pressure region, the low‐latitude boundary layer (LLBL) and the plasma sheet. In the ionosphere, the NBZ current and the reverse cell occur in higher latitudes than 80°, and the fun‐shaped arc‐like field‐aligned current (FAC) and the main oval occur in lower latitudes than 80°. Magnetic field lines in the anti‐sunward flow region of the reverse cell are connected to the LLBL that is accelerated to supersonic flow by the cusp pressure. Circulation on the reverse cell in the ionosphere is as a whole constructed to the interchange cycle in the magnetosphere. Convection is looked upon as the process to discharge stress generated by the dayside cusp reconnection. Magnetic stress generated by the reconnection is first converted to thermal energy in the cusp. This thermal energy is drained through three possible routes; release of plasma downtail through the LLBL, dissipation as electromagnetic energy through formation of the dynamo, and evacuation down to the ionosphere through the plasma sheet.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 70
    Publication Date: 2019
    Description: Abstract A hybrid gyrofluid‐kinetic electron model is adapted and used to simulate poloidal standing modes for different electron temperatures and azimuthal mode numbers. As in previous studies of toroidal standing modes, mirror force effects lead to increased parallel potential drops, monoenergetic electron energization and wave energy dissipation as the ambient electron temperature is increased. A similar trend is also observed when the electron temperature is held fixed and the azimuthal mode number increased ‐ owing to the narrowing of the azimuthal flux tube width which necessitates more electron energization to carry the increased parallel current density. In both cases, the increase in electron energization eventually leads to more rapid decreases in the parallel current with time because of the dissipation of wave energy.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 71
    Publication Date: 2019
    Description: Abstract A double peak structure in the peak height of ionospheric F2‐layer (hmF2) around ±10o geomagnetic latitudes similar to the equatorial ionization anomaly was recently reported. This unique feature was referred as the Equatorial Height Anomaly (EHA). In the present paper, a simulation study is carried out using the data‐driven artificial neural network based two dimensional ionospheric model (ANNIM‐2D) and the physics‐based thermosphere ionosphere electrodynamics general circulation model (TIEGCM) to understand the local time and latitudinal variation of EHA during the main phase of St. Patrick's Day geomagnetic storm. Both the ANNIM‐2D and TIEGCM consistently show pronounced EHA during the main phase of the geomagnetic storm. Further, the local time of EHA development on the storm day is much earlier (nearly 2 hours) than the quiet time over Brazilian sector (90oW). The TIEGCM simulation revealed that the storm time enhancement of the equatorial fountain associated with the enhanced equatorial zonal electric field is the main controlling factor for the pronounced EHA during the main phase. The storm time meridional neutral winds positively contribute to the development of EHA. This study revealed the direct manifestation of the storm time enhanced plasma fountain on the EHA.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 72
    Publication Date: 2019
    Description: Abstract Enceladus is characterised by a south polar hot spot associated with a large outflow of heat, the source of which remains unclear. We compute the heat generated via viscous dissipation resulting from tidal and (longitudinal) libration forcing in the moon's subsurface ocean using the linearised Navier‐Stokes equation in a 3‐dimensional spherical model. We conclude that libration is the dominant cause of dissipation at the linear order, providing up to ~0.001 GW of heat to the ocean, which remains insufficient to explain the ~10 GW observed by Cassini. We also illustrate how resonances with inertial modes can significantly augment the dissipation. Our work is an extension to Rovira‐Navarro et. al. (2019) to include the effects of libration and the presence of the icy crust. The model developed here is readily applicable to the study of other moons with a subsurface ocean and planets with a liquid core.
    Print ISSN: 2169-9097
    Electronic ISSN: 2169-9100
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 73
    Publication Date: 2019
    Description: Abstract We present a theoretical study focusing on exploring the possibility of controlling anthropogenic and natural seismicity. We actively control the pressure of injected fluids using a negative‐feedback control system. Our analysis is based on the spring‐slider model for modeling the earthquake instability. We use a general Coulomb‐type rheology for describing the frictional behavior of a fault system. This model leads to a non‐autonomous system, whose steady‐state and stability are studied using a double‐scale asymptotic analysis. This approach renders the dominant order of the system time invariant. Established tools from the classical mathematical theory of control are used for designing a proper stabilizing controller. We show that the system is stabilizable by controlling fluid pressure. This is a central result for industrial operations. A stabilizing controller is then designed and tested. The controller regulates in real‐time the applied pressure in order to assure stability, avoid unwanted seismicity and drive the system from unstable states of high potential energy, to stable ones of low energy. The controller performs well even in the absence of complete knowledge of the frictional properties of the system. Finally, we present two numerical examples (scenarios) and illustrate how anthropogenic and natural eart