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  • Articles  (1,471,851)
  • 2015-2019  (1,471,851)
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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 294 (1992), S. 466-478 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 317 (1993), S. 474-484 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2019-01-22
    Repository Name: EPIC Alfred Wegener Institut
    Type: PANGAEA Documentation , NonPeerReviewed
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  • 4
    Publication Date: 2019-03-21
    Description: The early life-history stages of polar marine invertebrates are understudied, particularly in deep water. We present the results from a long-term (1999 – 2017) colonization experiment at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in the Fram Strait (Arctic Ocean, 79⁰ N, 04⁰ E, 2500 m water depth). Recruitment panels were constructed from plastic and brick and deployed attached to a metal frame in 1999. The experiment was monitored using an ROV in 2003 and 2011 and recovered in 2017. Recruitment was very low, with only foraminiferans being visible after 4 years (2003) and one metazoan species, the hydroid Halisiphonia arctica, being visible on the panels after 12 years (2011). After 18 years underwater, panels were colonized by 13 metazoan species as well as calcareous and agglutinating foraminiferans. Recruitment was higher on brick panels than on plastic, but while some species were more common on panels at higher altitude (H. arctica and the crinoid Bathycrinus carpenterii), others were more common on panels closer to the seafloor (serpulid polychaetes, agglutinating foraminifera) or on panels in line with the predominant bottom current (small round white sponge). The most common recruiting species can be described as opportunistic and are rare or absent in older communities on natural substrata nearby. Meanwhile, large hexactinellid sponges that are common in natural communities did not recruit to our panels. These results suggest that succession in the Arctic deep sea takes decades and involves early dominance by opportunistic species, with slower-growing, structureforming species appearing later on.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 5
    Publication Date: 2019-01-28
    Repository Name: EPIC Alfred Wegener Institut
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  • 6
    Publication Date: 2019-01-29
    Description: Rapid declines in Arctic sea ice have captured attention and pose significant challenges to a variety of stakeholders. There is a rising demand for Arctic sea ice prediction at daily to seasonal time scales, which is partly a sea ice initial condition problem. Thus, a multivariate data assimilation that integrates sea ice observations to generate realistic and skillful model initialization is needed to improve predictive skill of Arctic sea ice. Sea ice data assimilation is a relatively new research area. In this review paper, we focus on two challenges for implementing multivariate data assimilation systems for sea ice forecast. First, to address the challenge of limited spatiotemporal coverage and large uncertainties of observations, we discuss sea ice parameters derived from satellite remote sensing that (1) have been utilized for improved model initialization, including concentration, thickness and drift, and (2) are currently under development with the potential for enhancing the predictability of Arctic sea ice, including melt ponds and sea ice leads. Second, to strive to generate the “best” estimate of sea ice initial conditions by combining model simulations/forecasts and observations, we review capabilities and limitations of different data assimilation techniques that have been developed and used to assimilate observed sea ice parameters in dynamical models.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 7
    Publication Date: 2019-03-24
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
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    Unknown
    Springer International Publishing
    Publication Date: 2019-02-24
    Description: The aim of this book is to review and analyse the goods and services of bivalve shellfish. How they are defined, what determines the ecological functions that are the basis for the goods and services, what controversies in the use of goods and services exist, and what is needed for sustainable exploitation of bivalves from the perspective of the various stakeholders. The book is focused on the goods and services, and not on impacts of shellfish aquaculture on the benthic environment, or on threats like biotoxins; neither is it a shellfish culture handbook although it can be used in evaluating shellfish culture. The reviews and analysis are based on case studies that exemplify the concept, and show the strengths and weaknesses of the current applications. The multi-authored reviews cover ecological, economic and social aspects of bivalve goods and services. The book provides new insights for scientists, students, shellfish producers, policy advisors, nature conservationists and decision makers.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , NonPeerReviewed
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  • 9
    Publication Date: 2019-02-25
    Repository Name: EPIC Alfred Wegener Institut
    Type: Thesis , NonPeerReviewed
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  • 10
    Publication Date: 2019-02-26
    Description: The submerged valley of the paleo Elbe River forms one of the most prominent structures of the German North Sea (~1.000 ha). The valley developed to its present form during the Weichselian sea-level lowstand (130 m below present). Melt waters that discharged in north-westerly directions along the Scandinavian Ice Sheet fed the paleo Elbe at that time. During the Holocene the valley drowned in the rising sea. We will present an area-wide high resolution map of the seafloor (~1,600 km²), high-resolution shallow seismic data and sediment coring data along the paleo Elbe River to explain historical process of sedimentary valley infill and coastal evolution with the successive Holocene sea level rise. At the eastern levee of the valley (which belongs to a nature conservation area) complex sequences of glacio-fluvial and sub-glacial deposits are still present at the seafloor surface. The glacial deposits, consisting mainly of coarse sediments (such as coarse sands, gravel and boulders) are a unique habitat of the otherwise sandy North Sea. The new backscatter map highlights a much higher heterogeneity and complexity in sediment and habitat distribution as assumed before. The presence of only relative thin and patchy Holocene marine fine sand layers indicates strong hydrodynamic processes. Shallow seismic data show the base of the paleo Elbe valley and conspicuous internal seismic reflectors above the base, inclined in northeastern direction. Core data indicate a change in current regime and the development from a terrigenous towards a marine environment.
    Repository Name: EPIC Alfred Wegener Institut
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  • 11
    Publication Date: 2019-04-08
    Description: The deglacial history of CO2 release from the deep North Pacific remains unresolved. This is due to conflicting indications about subarctic Pacific ventilation changes based on various marine proxies, especially for Heinrich Stadial 1 (HS-1) when a rapid atmospheric CO2 rise occurs. Here, we use a complex Earth System Model to investigate the deglacial North Pacific overturning and its control on ocean stratification. Our results show an enhanced intermediate-to-deep ocean stratification coeval with intensified North Pacific Intermediate Water (NPIW) formation during HS-1, compared to the Last Glacial Maximum. The stronger NPIW formation causes lower salinities and higher temperatures at intermediate depths. By lowering NPIW densities, this enlarges vertical density gradient and thus enhances intermediate-to-deep ocean stratification during HS-1. Physically, this process prevents the North Pacific deep waters from a better communication with the upper oceans, thus prolongs the existing isolation of glacial Pacific abyssal carbons during HS-1.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 12
    Publication Date: 2019-02-25
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 13
    Publication Date: 2019-02-26
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 14
    Publication Date: 2019-03-22
    Repository Name: EPIC Alfred Wegener Institut
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  • 15
    Publication Date: 2019-03-12
    Repository Name: EPIC Alfred Wegener Institut
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  • 16
    Publication Date: 2019-03-15
    Description: We revisit the challenges and prospects for ocean circulation models following Griffies et al. (2010). Over the past decade, ocean circulation models evolved through improved understanding, numerics, spatial discretization, grid configurations, parameterizations, data assimilation, environmental monitoring, and process-level observations and modeling. Important large scale applications over the last decade are simulations of the Southern Ocean, the Meridional Overturning Circulation and its variability, and regional sea level change. Submesoscale variability is now routinely resolved in process models and permitted in a few global models, and submesoscale effects are parameterized in most global models. The scales where nonhydrostatic effects become important are beginning to be resolved in regional and process models. Coupling to sea ice, ice shelves, and high-resolution atmospheric models has stimulated new ideas and driven improvements in numerics. Observations have provided insight into turbulence and mixing around the globe and its consequences are assessed through perturbed physics models. Relatedly, parameterizations of the mixing and overturning processes in boundary layers and the ocean interior have improved. New diagnostics being used for evaluating models alongside present and novel observations are briefly referenced. The overall goal is summarizing new developments in ocean modeling, including: how new and existing observations can be used, what modeling challenges remain, and how simulations can be used to support observations.
    Repository Name: EPIC Alfred Wegener Institut
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  • 17
    Publication Date: 2019-03-18
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
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  • 18
    Publication Date: 2019-03-19
    Repository Name: EPIC Alfred Wegener Institut
    Type: Miscellaneous , NonPeerReviewed
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  • 19
    Publication Date: 2019-03-20
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 20
    Publication Date: 2019-03-25
    Repository Name: EPIC Alfred Wegener Institut
    Type: Data Processing Reports , NonPeerReviewed
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  • 21
    Publication Date: 2019-03-25
    Description: ABSTRACT The region situated between the mountain area and the lowlands in NE Romania (East-Central Europe) is experiencing increased competition for water resources triggered by a growing population, intensification of agriculture, and industrial development. To better understand hydrological cycling processes in the region, a study was conducted using stable isotopes of water and atmospheric trajectory data to characterize regional precipitation and vapour sources derived from the Atlantic Ocean, Mediterranean and Black Seas, as well as recycled continental moisture, and to assess and partition these contributions to recharge of surface and groundwater. Atmospheric moisture in the lowlands is found to be predominantly delivered along easterly trajectories, while mountainous areas appear to be dominated by North Atlantic Ocean sources, with moisture transported along mid-latitude, westerly storm tracks. Large-scale circulation patterns affect moisture delivery, the North Atlantic Oscillation being particularly influential in winter and the East Atlantic pattern in summer. Winter precipitation is the main contributor to river discharge and aquifer recharge. As winter precipitation amounts are projected to decrease over the next decades, and water abstraction is expected to steadily increase, a general reduction in water availability is projected for the region.
    Repository Name: EPIC Alfred Wegener Institut
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  • 22
    Publication Date: 2019-03-21
    Repository Name: EPIC Alfred Wegener Institut
    Type: PANGAEA Documentation , NonPeerReviewed
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  • 23
    Publication Date: 2019-03-22
    Repository Name: EPIC Alfred Wegener Institut
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  • 24
    Publication Date: 2019-03-21
    Repository Name: EPIC Alfred Wegener Institut
    Type: PANGAEA Documentation , NonPeerReviewed
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  • 25
    Publication Date: 2019-03-29
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 26
    Publication Date: 2019-03-28
    Description: Thermokarst results from the thawing of ice-rich permafrost and alters the biogeochemical cycling in the Arctic by reworking soil material and redistributing soil organic carbon (SOC) and total nitrogen (TN) along uplands, hillslopes, and lowlands. Understanding the impact of this redistribution is key to better estimating the storage of SOC in permafrost terrains. However, there are insufficient studies quantifying long-term impacts of thaw processes on the distribution of SOC and TN along hillslopes. We address this issue by providing estimates of SOC and TN stocks along the hillslopes of three valleys located on Herschel Island (Yukon, Canada), and by discussing the impact of hillslope thermokarst on the variability of SOC and TN stocks. We found that the average SOC and TN 0–100 cm stocks in the valleys were 26.4 ± 8.9 kg C m-2 and 2.1 ± 0.6 kg N m-2. We highlight the strong variability in the soils physical and geochemical properties within hillslope positions. High SOC stocks were found at the summits, essentially due to burial of organic matter by cryoturbation, and at the toeslopes due to impeded drainage which favored peat formation and SOC accumulation. The average carbon-to‑nitrogen ratio in the valleys was 12.9, ranging from 9.7 to 18.9, and was significantly higher at the summits compared to the backslopes and footslopes (p 〈 0.05), suggesting a degradation of SOC downhill. Carbon and nitrogen contents and stocks were significantly lower on 16% of the sites that were previously affected by hillslope thermokarst (p 〈 0.05). Our results showed that lateral redistribution of SOC and TN due to hillslope thermokarst has a strong impact on the SOC storage in ice-rich permafrost terrains.
    Repository Name: EPIC Alfred Wegener Institut
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  • 27
    Publication Date: 2019-03-28
    Repository Name: EPIC Alfred Wegener Institut
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  • 28
    Publication Date: 2019-03-29
    Description: n 2016 the International Ocean Discovery Program (IODP) Expedition 361 (“SAFARI”) recovered complete high-resolution Plio-/Pleistocene sediment sections at six drilling locations on the southeast African margin and at the oceanic connection between the Indian and South Atlantic Oceans. Site U1475 is locatedon the southern flank of the Agulhas Plateau, proximal to the entrance of North Atlantic Deep Water (NADW) to the Southern Ocean and South Indian Ocean. The site was drilled into a sediment drift in 2669 m water depth and comprises a complete carbonate rich (74 –85%) stratigraphic section of the last ~7 Ma. The contourite deposits hold detailed information on past changes in the bottom water flow history in the Indian-Atlantic ocean gateway. Here we present results from the integration of physical properties, seismic reflection data, and major element records. The whole spliced sediment record (292 meters) of Site U1475 was measured using an X-ray fluorescence (XRF) core scanner to derive multi-centennial resolution records of major element intensities. Based on these measurements it is possible to derive biogenic (e.g. %CaCO3) and siliciclastic (e.g. TiO2, K2O) mineral phases. Elemental log-ratios, such as Ca/Ti and K/Fe, reflect variations in biogenic (CaCO3) vs. terrigenous supply and variability of theterrigenous provenance, respectively. While long-term changes in physical properties and elemental ratios can be linked to the seismic reflection patterns associated with deep water circulation changes, short-term cyclicities reflect Plio-Pleistocene climate variations at Milanlovitch-frequencies. Evolutionary spectra show that the orbital control on sediment composition was variable over time. During the last 4 Ma energy is concentrated at the 41ka band of obliquity and at lower frequencies. In contrast, the orbital precession cycle (19-23ka) is very prominent in a peculiar high sedimentation rate interval in the early Pliocene (~4 to 5 Ma) that is bounded by seismic reflectors and characterized by the development of sediment waves.
    Repository Name: EPIC Alfred Wegener Institut
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  • 29
    Publication Date: 2019-03-25
    Description: Die Messung von ganzjährigen CO2-, Wasser- und Energieflüssen zwischen Erdoberfläche und Atmosphäre in arktischen Regionen wird bisher nur an wenigen Standorten durchgeführt. Derartige Messungen sind aber insbesondere insofern relevant, als dass arktische Tundren bedeutende CO2-Senken darstellen, unter einem sich erwärmenden Klima möglicherweise aber zukünftig im Permafrost gespeicherten Kohlenstoff freisetzen. Durch den Einsatz bodengebundener in situ Messungen können Kohlenstoff- und Energiedynamik bilanziert werden. Des Weiteren sind die gemessenen Gas- und Energieflüsse wertvoll für die Kalibration und Validierung globaler Klimamodelle. Eine Messstation in der europäischen Arktis ist die Bayelva-Messstation (78� 55‘ N, 11� 50‘ O) nahe Ny Ålesund auf Spitzbergen. Der starke Einfluss des Nordatlantikstroms führt dort zu einem maritimen Klima mit kühlen Sommertemperaturen von durchschnittlich 5 °C im Juli und relativ milden Wintertemperaturen von -13 °C im Januar. Es handelt sich somit um eine vergleichsweise warme Permafrostregion mit Jahresmitteltemperaturen von etwa -2.5 °C. Der Jahresniederschlag liegt bei etwa 400 mm und die schneefreie Zeit beträgt typischerweise drei Monate. An der Bayelva-Station fanden von 2007 bis 2017 Messungen von Wasserdampf- und CO2-Konzentrationen (mittels open-path LiCor LI-7500 CO2 und H2O Gasanalysierer) sowie dreidimensionale Messungen der Windgeschwindigkeit (mittels Campbell CSAT 3D sonic anemometer) mit einer Messfrequenz von 20 Hz statt. Mithilfe der Eddy-Kovarianz-Software TK3 ermitteln wir hieraus halbstündliche Gas- und Energieflüsse und führen Qualitätsprüfungen durch. Erste Ergebnisse für das Jahr 2008/2009 zeigen, dass die jährliche CO2-Bilanz des Standortes nahezu bei null liegt, was durch die lange, winterliche Freisetzung von CO2 in die Atmosphäre zu erklären ist. Allerdings sind die Prozesse, welche diese winterliche CO2-Emission bedingen bisher nicht untersucht. Unser Ziel besteht daher nun darin, die Analyse der Gas- und Energieflüsse auf den gesamten Messzeitraum von 2007 bis 2017 auszuweiten. Insbesondere für die Zeiträume Oktober 2012 bis August 2014 sowie Januar 2015 bis September 2016 sind die Messreihen nahezu komplett mit Datenlücken von nur wenigen Tagen pro Zeitraum. Auf der Grundlage der entstehenden Langzeit-Datenreihe können wir durch den Klimawandel bedingte Änderungen der CO2-Flüsse von zwischenjährlicher Variabilität unterscheiden sowie saisonale und jahreszeitliche Schwankungen bilanzieren. Außerdem ermöglicht es uns der mehrjährige Datensatz die Umstände der ablaufenden Prozesse genauer zu beschreiben und dadurch möglicherweise Rückschlüsse auf deren Auslöser zu ziehen. Im weiteren Verlauf ist es zudem vorstellbar Wechselwirkungen zwischen den beobachteten Gas- und Energieflüssen und weiteren Eigenschaften verschiedener Komponenten des Klimasystems wie zum Beispiel Wolkeneigenschaften zu untersuchen.
    Repository Name: EPIC Alfred Wegener Institut
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  • 30
    Publication Date: 2019-04-29
    Description: Crystal Orientation Fabric (COF) of c-axes in ice cores reveals information about deformation within ice sheets. While this is a well established analysis technique for deep ice cores from ice divides, information about COF in ice streams is just now becoming available: the EastGRIP ice core is situated inside the largest ice stream in Greenland, the North East Greenland Ice Stream (NEGIS). With the ongoing analysis of samples from the EastGRIP ice core, COF is now available down to 1714 m, revealing an extremely more rapid evolution of COF anisotropy with depth compared to all other ice cores. This enables us to study the ability of polarimetric radar measurements to infer an overall pattern of COF from measurements conducted at the surface. Depending on whether the COF is isotropic or anisotropic, a radar signal is reflected differently in terms of angle dependence and polarization. We conducted these polarimetric measurements around the EastGRIP drill site and we compare them to COF data obtained from 778 thin sections, prepared and measured at EastGRIP drill site. We investigate the hypothesis that the same pattern of COF can be retrieved from the polarimetric measurements as is available from the ice core. If confirmed, this would provide an addition constraint on the (an)isotropy at locations where no ice core is available. This would potentially provide quasi spatial coverage and greatly improve our understanding of the evolution of anisotropy over from ice divides to outlet glaciers.
    Repository Name: EPIC Alfred Wegener Institut
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  • 31
    Publication Date: 2019-04-08
    Repository Name: EPIC Alfred Wegener Institut
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  • 32
    Publication Date: 2019-04-02
    Description: oraminifera are commonly used in paleoclimate reconstructions as they occur throughout the world's oceans and are often abundantly preserved in the sediments. Traditionally, foraminifera‐based proxies like δ18O and Mg/Ca are analyzed on pooled specimens of a single species. Analysis of single specimens of foraminifera allows reconstructing climate variability on timescales related to El Niño‐Southern Oscillation (ENSO) or seasonality. However, quantitative calibrations between the statistics of individual foraminiferal analyses (IFA) and climate variability are still missing. We performed Mg/Ca and δ18O measurements on single specimens from core‐top sediments from different settings to better understand the signal recorded by individual foraminifera. We used three species of planktic foraminifera (G. ruber (s.s.), T. sacculifer, and N. dutertrei) from the Indo‐Pacific Warm Pool (IPWP) and one species (G. ruber (pink)) from the Gulf of Mexico (GoM). Mean values for the different species of Mg/Ca vs calculated δ18O temperatures agree with published calibration equations. IFA statistics (both mean and standard deviation) of Mg/Ca and δ18O between the different sites show a strong relationship indicating that both proxies are influenced by a common factor, most likely temperature variations during calcification. This strongly supports the use of IFA to reconstruct climate variability. However, our combined IFA data for the different species only show a weak relationship to seasonal and interannual temperature changes, especially when seasonal variability increases at a location. This suggests that the season and depth habitat of the foraminifera strongly affect IFA variability, such that ecology needs to be considered when reconstructing past climate variability.
    Repository Name: EPIC Alfred Wegener Institut
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  • 33
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    Alfred Wegener Institute for Polar and Marine Research
    Publication Date: 2019-04-02
    Repository Name: EPIC Alfred Wegener Institut
    Type: "Berichte zur Polar- und Meeresforschung" , NonPeerReviewed
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  • 34
    Publication Date: 2019-04-25
    Description: Die vom Permafrost dominierten Gebiete der Arktis sind von der globalen Erwärmung besonders betroffen. Als Folge der höheren Temperaturen nehmen die Dicke der Auftauschicht und die Anzahl der frostfreien Tage im Jahr immer weiter zu, wodurch der Ausstoß von Treibhausgasen durch erhöhte Bakterienaktivität steigt. Wenn Infrastruktur in diesen Gebieten vorhanden ist oder angelegt werden soll, muss sie im Permafrost gegründet sein, um dauerhaft stabil zu sein. Somit ist es sowohl für die Klimamodellierung als auch für die Infrastruktur wichtig, die Auftautiefe der oberen Bodenschicht flächendeckend zu kennen. Zu diesem Zweck wurde im August 2018 eine große Feldkampagne rund um Inuvik, NW-Kanada, durchgeführt. Das Gebiet ist durch Permafrost geprägt, die Mächtigkeit der Auftauschicht liegt zwischen 30cm und 2m. Die Vegetation wechselt zwischen offener Tundra, strauchdominierter Tundra und Taiga (Nadelwald). Während der Feldarbeiten hat ein Team im Gelände die Vegetation, die Bodeneigenschaften und die Dicke der Auftauschicht punktuell erfasst, sowie GPR-Messungen mit 200 MHz Antennen zur Kartierung der Auftauschicht und geoelektrische Messungen zur Charakterisierung des Permafrostkörpers durchgeführt. Ein zweites Team hat mittels flugzeuggestützter Messungen mit der Polar 5 des Alfred-Wegener-Instituts das Gebiet großflächig kartiert. Bei niedrigen Flügen in ca. 300m Höhe über Grund wurden GPR Messungen zur Erfassung der Dicke der Auftauschicht durchgeführt. Das verwendete Radarsystem ist ein FMCW Radar mit einem Frequenzbereich von 400 – 800 MHz, wodurch eine hohe vertikale und horizontale Auflösung gegeben ist. Die Ausbreitungsgeschwindigkeit im Untersuchungsgebiet ist variabel mit einer durchschnittlichen Geschwindigkeit von 0,044m/ns in der Auftauschicht. Auf höheren Flügen (ca. 1000m über Grund) wurden unter anderem eine VIS+NIR und eine SWIR-Hyperspektralkamera (AISA EAGLE und HAWK) sowie ein RIEGL Laserscanner betrieben, womit Vegetation und Geomorphologie charakterisiert werden können. Um die Ergebnisse auf das gesamte Untersuchungsgebiet zu übertragen, werden zusätzlich Satellitendaten des Gebiets ausgewertet. Somit ist eine umfassende Charakterisierung des aktuellen Zustands aller Faktoren des Ökosystems, die den Permafrostkörper und die Auftauschicht betreffen, möglich. Hier präsentieren wir erste Ergebnisse der GPR Messungen aus den Befliegungen sowie vom Boden und ordnen diese in die räumliche Struktur des Untersuchungsgebiets ein.
    Repository Name: EPIC Alfred Wegener Institut
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  • 35
    Publication Date: 2019-02-25
    Description: Extreme ocean warming events, known as marine heatwaves (MHWs), have been observed to perturb significantly marine ecosystems and fisheries around the world. Here, we propose a detection method for long-lasting and large-scale summer MHWs, using a local, climatological 99th percentile threshold, based on present-climate (1976–2005) daily SST. To assess their future evolution in the Mediterranean Sea we use, for the first time, a dedicated ensemble of fully-coupled Regional Climate System Models from the Med-CORDEX initiative and a multi-scenario approach. The models appear to simulate well MHW properties during historical period, despite biases in mean and extreme SST. In response to increasing green- house gas forcing, the events become stronger and more intense under RCP4.5 and RCP8.5 than RCP2.6. By 2100 and under RCP8.5, simulations project at least one long-lasting MHW every year, up to three months longer, about 4 times more intense and 42 times more severe than present-day events. They are expected to occur from June-October and to affect at peak the entire basin. Their evolution is found to occur mainly due to an increase in the mean SST, but increased daily SST variability also plays a noticeable role. Until the mid-21st century, MHW characteristics rise independently of the choice of the emission scenario, the influence of which becomes more evident by the end of the period. Further analysis reveals e change responses in certain configurations, more likely linked to their driving global climate model rather to the individual model biases.
    Repository Name: EPIC Alfred Wegener Institut
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  • 36
    Publication Date: 2019-04-04
    Repository Name: EPIC Alfred Wegener Institut
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  • 37
    Publication Date: 2019-04-08
    Description: IODP Expedition 370 (Temperature Limit of the Deep Biosphere off Muroto) established Site C0023 down to 1180 mbsf in the Nankai Trough off Shikoku Island, Japan, to explore the upper temperature limit of microbial life in deep subseafloor sediments. Part of the scientific program is to investigate the availability of nutrients and energy substrates and to identify unique geochemical and microbial signatures that differentiate the biotic and abiotic realms and/or their transitions (Heuer et al., 2017). Iron (Fe) reduction is considered one of the most ancient forms of microbial respiration (Vargas et al., 1998). In addition, Fe reducers can grow under high temperature and pressure conditions (Kashefi and Lovley, 2003), suggesting that microbes that use Fe oxides as energy substrates are potential candidates to survive close to the temperature limit of the deep biosphere. In this study, we aim at assessing the role of Fe oxides for microbial respiration and the related diagenetic alterations in deep sediments of Site C0023 by applying sequential extractions of Fe oxide and sulfide minerals. Volcanic ash layers, which are ubiquitous in sediments of Site C0023, are of particular interest as they have been identified earlier as hotspots for microbial life (e.g., Inagaki et al., 2003). Torres et al. (2015) further showed that ash layers at a different site in the Nankai Trough are typically rich in Fe and Mn oxides. Their results support the findings of Treude et al. (2014) who postulate a coupling of microbial processes to mineralogy. In addition, on-board measurements show a release of dissolved Fe into the pore water in the depth interval associated with volcanic ash layers (Heuer et al., 2017), suggesting that the observed liberation of dissolved Fe is related to an alteration of Fe phases in these ash layers. Our results show that the total Fe content in sediments of Site C0023 is relatively constant at ~4.2 wt%. The reactive Fe oxide content represents 25% of the total Fe. Based on sequential extractions, the fraction associated with amorphous Fe oxide such as ferrihydrite and lepidocrocite is the dominant Fe fraction with ~0.7 wt%. Mineralogical analyses are currently conducted in order to determine specific Fe mineral phases within this fraction. The total Fe contents in the ash layer samples strongly vary between 1.4 and 6.8 wt%. However, most samples generally contain less total Fe than the surrounding sediments. Similarly, the contents of the reactive Fe oxides are significantly lower. Thus, reactive Fe oxides in ash layers at Site C0023 do not seem to represent the energy substrate for microbial Fe reduction. As one of the next steps, stable Fe isotope (δ56Fe) analyses will be performed on (1) pore-water samples, the (2) different Fe oxide phases and (3) sediment residues remaining after sequential extractions in order to trace the source and reaction pathway for the observed release of dissolved Fe into the pore water. Diagenetic Fe cycling, in particular the reductive dissolution of Fe oxides driven by the reaction with hydrogen sulfide, may lead to the transformation of reactive Fe oxides to Fe sulfides such as pyrite (e.g., Berner 1970). Fe monosulfide contents are below detection limit in sediments of Site C0023. Pyrite, in contrast, occurs over the whole core interval with strongly varying contents. Three significant peaks with contents up to 0.5 wt% could be observed at 552, 707 and 1033 mbsf. The pyrite profile generally mimics the total sulfur profile, which suggests that most of bulk sulfur is present as pyrite. Fe bound in pyrite (Fepyrite), however, only represents less than 5% of the total Fe pool, except for the interval with elevated pyrite contents where Fepyrite accounts for ~10% of bulk Fe. This indicates that sulfidation does not affect the whole Fe oxide pool in sediments of Site C0023. The reductive dissolution of primary ferrimagnetic Fe oxides and the formation of secondary paramagnetic pyrite is generally known to modify rock magnetic properties such as magnetic susceptibility (e.g., Berner, 1970). Thus, our geochemical results are presented in combination with post-cruise generated magnetic susceptibility data. By combining the geochemical methods, including sequential Fe oxide and sulfide extractions and subsequent δ56Fe analyses, with rock magnetic measurements, we intend to decipher the role of Fe mineral phases in maintaining deep subsurface life at Site C0023. Acknowledgements - This research used samples and data provided by the International Ocean Discovery Program (IODP). We would like to thank all personnel involved in the operations aboard the DV Chikyu during Expedition 370 and the support team at the Kochi Core Center. We further would like to thank the German Research Foundation (DFG) for funding this project (project number: 388260220) in the framework of the priority program 527 (Bereich Infrastruktur – International Ocean Discovery Program). References: Berner, R.A., 1970. Sedimentary pyrite formation. AJS 268: 1-23. Heuer, V.B., Inagaki, F., Morono, Y., Kubo, Y., Maeda, L., and the Expedition 370 Scientists, 2017. Expedition 370 Preliminary Report: Temperature Limit of the Deep Biosphere off Muroto. International Ocean Discovery Program. Inagaki, F., Suzuki, M., Takai, K., Oida, H., Sakamoto, T., Aoki, K., Nealson K.H., Horikoshi, K., 2003. Microbial communities associated with geological horizons in coastal subseafloor sediments from the Sea of Okhotsk. AEM 69: 7224-7235. Kashefi, K., Lovley, D.R., 2003. Extending the upper temperature limit of life. Science 301: 934. Torres, M.E., Cox, T., Hong, W.-L., McManus, J., Sample, J.C., Destrigneville, C., Gan, H.M., Gan, H.Y., Moreau J.W., 2015. Crustal fluid and ash alteration impacts on the biosphere of Shikoku Basin sediments, Nankai Trough, Japan. Geobiology 13: 562-580. Treude, T., Krause, S., Maltby, S., Dale, A.W., Coffin, R., Hamdan, L.J., 2014. Sulfate reduction and methane oxidation activity below the sulfate-methane transition zone in Alaskan Beaufort Sea continental margin sediments: Implications for deep sulfur cycling. GCA 144: 217-237. Vargas, M., Kashefi, K., Blunt-Harris, E.L., Lovley, D.E., 1998. Microbiological evidence for Fe(III) reduction on early Earth. Nature 395: 65-67.
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  • 38
    Publication Date: 2019-04-03
    Description: Species of the planktonic dinoflagellates Azadinium and Amphidoma are small, inconspicuous and difficult, if not impossible to be identified and differentiated by light microscopy. Within this group, there are some species that produce the marine biotoxin azaspiracid (AZA) while others are non-toxigenic, therefore a requirement exists for precise species identification. A quantitative polymerase chain reaction (qPCR) assay for molecular detection and quantification of one of the toxigenic species, Amphidoma languida, was designed and extensively tested. The assay was highly specific and sensitive to detect and quantify down to 10 target gene copies (corresponding to ca. 0.05 cells) per reaction. DNA cell quota and copy number cell−1 were constant for four different Am. languida strains, and for one strain they were shown to be stable at various time points throughout the growth cycle. Recovery of known cell numbers of Am. languida spiked into natural samples was 95–103%, and the assay was successfully tested on field samples collected from Irish coastal waters. This new qPCR assay is a valuable tool for routine monitoring for the prevention of AZA-shellfish-poisoning caused by the consumption of contaminated shellfish and is a supportive tool for studies on the biogeography of this AZA-producing species.
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  • 39
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    Publication Date: 2019-04-08
    Repository Name: EPIC Alfred Wegener Institut
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  • 40
    Publication Date: 2019-04-09
    Repository Name: EPIC Alfred Wegener Institut
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  • 41
    Publication Date: 2019-04-09
    Description: Late Miocene to Recent sediments offshore from the Antarctic Peninsula are predominantly lithogenic, having originated through glacial erosion. Sediments that accumulated during interglacial periods commonly have a greater biogenic component, but deposits in which this constitutes a substantial fraction are rare. Only a small fraction of the continental block is above sea level and even during interglacial periods temperatures are only warm enough to generate significant melt at low elevations for a few weeks each summer, so sediment input to the sea from surface runoff is minor. Sediment transport to the continental margin takes place mainly at the ice bed during glacial periods when the grounding line advances to the shelf edge. On the Pacific margin, downslope transport from the shelf edge region occurs mainly through gravitational mass transport processes. These processes are likely most active during glacial periods when rapid delivery of glacial sediment leads to instability on the uppermost slope and discharge of sediment-laden subglacial meltwater at the shelf edge grounding line initiates turbidity currents. The lack of obvious large slide scars along most of the relatively steep continental slope suggests that most individual failures are small in volume. Dendritic networks of small channels on the lower slope feed into large turbidity current channels that run out across the continental rise for hundreds of kilometres. Between the channels are giant sediment drifts, some with more than a kilometre of relief, which are composed predominantly of finely-bedded silt and clay layers. The drifts have been produced through entrainment of the fine-grained components of turbidity currents in the ambient bottom current that flows southwestward along the margin. Results from Ocean Drilling Program Leg 178 showed that these drifts contain high-resolution records of ice sheet and oceanographic changes, although unfortunately insufficient core material was recovered to generate continuous composite sections. During a 2015 research cruise on RRS James Clark Ross (JR298) we obtained new data over several of the drifts and channels, including high-resolution multichannel seismic reflection data, piston cores and box cores. We will present results from these new data, interpreting them in terms of sedimentary processes that operated during the development of the giant sediment drifts, and links between depositional systems on the continental rise, palaeo-ice-sheet dynamics and palaeoceanographic processes.
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  • 42
    Publication Date: 2019-04-10
    Description: Our knowledge on distribution, habitats and behavior of Southern Ocean fishes living at water depths beyond scuba-diving limits is still sparse, as it is difficult to obtain quantitative data on these aspects of their biology. Here, we report the results of an analysis of seabed images to investigate species composition, behavior, spatial distribution and preferred habitats of demersal fish assemblages in the southern Weddell Sea. Our study was based on a total of 2736 high-resolution images, covering a total seabed area of 11,317 m2, which were taken at 13 stations at water depths between 200 and 750 m. Fish were found in 380 images. A total of 379 notothenioid specimens were recorded, representing four families (Nototheniidae, Artedidraconidae, Bathydraconidae, Channichthyidae), 17 genera and 25 species. Nototheniidae was the most speciose fam- ily, including benthic species (Trematomus spp.) and the pelagic species Pleuragramma antarctica, which was occasionally recorded in dense shoals. Bathydraconids ranked second with six species, followed by artedidraconids and channichthyids, both with five species. Most abundant species were Trematomus scotti and T. lepidorhinus among nototheniids, and Dol- loidraco longedorsalis and Pagetopsis maculatus among artedidraconids and channichthyids, respectively. Both T. lepi- dorhinus and P. maculatus preferred seabed habitats characterized by biogenous debris and rich epibenthic fauna, whereas T. scotti and D. longedorsalis were frequently seen resting on fine sediments and scattered gravel. Several fish species were recorded to make use of the three-dimensional structure formed by epibenthic foundation species, like sponges, for perching or hiding inside. Nesting behavior was observed, frequently in association with dropstones, in species from various families, including Channichthyidae (Chaenodraco wilsoni and Pagetopsis macropterus) and Bathydraconidae (Cygnodraco mawsoni).
    Repository Name: EPIC Alfred Wegener Institut
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  • 43
    Publication Date: 2019-04-18
    Description: Multilayer clouds (MLCs) occur more often in theArctic than globally. In this study we present the results of a detection algorithm applied to radiosonde and radar datafrom an 1-year time period in Ny-Ålesund, Svalbard. Multi-layer cloud occurrence is found on 29 % of the investigated days. These multilayer cloud cases are further analysed regarding the possibility of ice crystal seeding, meaning that an ice crystal can survive sublimation in a subsaturated layer between two cloud layers when falling through this layer. For this we analyse profiles of relative humidity with respect to ice to identify super- and subsaturated air layers. Then the sublimation of an ice crystal of an assumed initial size of r=400 μm on its way through the subsaturated layer is calculated. If the ice crystal still exists when reaching a lower supersaturated layer, ice crystal seeding can potentially take place. Seeding cases are found often, in 23 % of the investigated days (100 % includes all days, as well as non-cloudy days). The identification of seeding cases is limited by the radar signal inside the subsaturated layer. Clearly separated multilayer clouds, defined by a clear interstice in the radar image, do not interact through seeding (9 % of the investigated days). There are various deviations between the relative humidity profiles and the radar images, e.g. due to the lack of ice-nucleating particles (INPs) and cloud condensation nuclei (CCN). Additionally, horizontal wind drift of the radiosonde and time restriction when comparing radiosonde and radar data cause further deviations. In order to account for some of these deviations, an evaluation by manual visual inspection is done for the non-seeding cases.
    Repository Name: EPIC Alfred Wegener Institut
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  • 44
    Publication Date: 2019-04-16
    Description: Marine benthic organisms living in shelf seas of the Siberian Arctic are impacted severely by the pronounced consequences of climate change. Polar ecosystems are used to stable conditions and even small changes could influence benthic communities, food webs, and ecosystem functions. Regional patterns in community composition result from the interaction between marine organisms and their local environment. In this study, these relationships are investigated in order to understand how climate change affect Arctic biodiversity in particular.
    Repository Name: EPIC Alfred Wegener Institut
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  • 45
  • 46
    Publication Date: 2019-04-18
    Description: The concept of multi-use of the sea has gained popularity in recent years as a result of ocean space (coastal areas and regions with relatively small sea space in particular) becoming increasingly crowded due to the development of the maritime economy. Competing claims for space can be a source of conflict, however this may also lead to mutual benefits for different users when sustainable combinations are sought. Despite increasing European-wide efforts, on-the-ground knowledge and practice of multi-use are still limited. Therefore, with the aim of investigating opportunities for multi-use development in the European seas, 10 case studies were selected, involving different site-specific contexts. This study analyses the characteristics and development potential for ocean multi-use, integrating results from desk analysis and stakeholder perceptions from different sectors in each of the case study locations. Similarities and differences between various combinations of sea uses are also identified. The results show a high heterogeneity of multi-use opportunities between case studies, with a range of combinations identified. The investigated combinations of maritime uses share an overall balance between factors promoting (drivers) and hindering (barriers) multi-use development. Based on stakeholder opinions, expected benefits (added values) of multi-use implementation outweigh potential negative impacts. Management actions are also proposed to further exploit multi-use potential at a local, regional (sub-national) and national levels.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
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  • 47
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    Alfred Wegener Institute for Polar and Marine Research
    Publication Date: 2019-03-08
    Repository Name: EPIC Alfred Wegener Institut
    Type: "Berichte zur Polar- und Meeresforschung" , NonPeerReviewed
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  • 48
    Publication Date: 2019-04-09
    Repository Name: EPIC Alfred Wegener Institut
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  • 49
    Publication Date: 2019-01-31
    Description: Stratospheric ozone loss inside the Arctic polar vortex for the winters between 2004–2005 and 2012–2013 has been quantified using measurements from the space-borne Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). For the first time, an evaluation has been performed of six different ozone loss estimation methods based on the same single observational dataset to determine the Arctic ozone loss (mixing ratio loss profiles and the partial-column ozone losses between 380 and 550 K). The methods used are the tracer-tracer correlation, the artificial tracer correlation, the average vortex profile descent, and the passive subtraction with model output from both Lagrangian and Eulerian chemical transport models (CTMs). For the tracer-tracer, the artificial tracer, and the average vortex profile descent approaches, various tracers have been used that are also measured by ACE-FTS. From these seven tracers investigated (CH4, N2O, HF, OCS, CFC-11, CFC-12, and CFC-113), we found that CH4, N2O, HF, and CFC-12 are the most suitable tracers for investigating polar stratospheric ozone depletion with ACE-FTS v3.5. The ozone loss estimates (in terms of the mixing ratio as well as total column ozone) are generally in good agreement between the different methods and among the different tracers. However, using the average vortex profile descent technique typically leads to smaller maximum losses (by approximately 15–30 DU) compared to all other methods. The passive subtraction method using output from CTMs generally results in slightly larger losses compared to the techniques that use ACE-FTS measurements only. The ozone loss computed, using both measurements and models, shows the greatest loss during the 2010–2011 Arctic winter. For that year, our results show that maximum ozone loss (2.1–2.7 ppmv) occurred at 460 K. The estimated partial-column ozone loss inside the polar vortex (between 380 and 550 K) using the different methods is 66–103, 61–95, 59–96, 41–89, and 85–122 DU for March 2005, 2007, 2008, 2010, and 2011, respectively. Ozone loss is difficult to diagnose for the Arctic winters during 2005–2006, 2008–2009, 2011–2012, and 2012–2013, because strong polar vortex disturbance or major sudden stratospheric warming events significantly perturbed the polar vortex, thereby limiting the number of measurements available for the analysis of ozone loss.
    Repository Name: EPIC Alfred Wegener Institut
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  • 50
    Publication Date: 2019-03-11
    Repository Name: EPIC Alfred Wegener Institut
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  • 51
    Publication Date: 2019-03-17
    Description: Modern global warming and their possible contribution to sea level rise and flooding of low lying coastal areas has moved both Antarctic and Greenland ice sheets into the focus of public and scientific interest. Research has concentrated on reconstructing the dynamics of the ice sheets in order to understand their vulnerability to a changing climate by collecting multi-disciplinary data and numerical simulations. Synchronous changes in ice sheet extent along its margin are assumed by a number of authors. The study presented here analyses the regional and chronological appearance, distribution, and modification of sedimentary features and structures identified at the slope and rise off the West Antarctic Ice Sheet margin to test whether this assumption is correct. In general, a synchronous West Antarctic Ice Sheet dynamic is not supported by the analysis presented here but rather a West-East trend with an early Miocene ice advance in the Amundsen Sea, while a glacial advance in the Bellingshausen Sea occurs only post-15 Ma. For the Bellingshausen Sea a stronger variability in sediment flux is observed indicating stronger variability in ice extent. The dominance of down-/along-slope sediment transport is on opposing trends between the two seas, which also reflects the advance/retreat of the local ice sheet and thus an increase/decrease in sediment input from the continent and a modification in intensity and relocation of the bottom current pathways. A possible reason for this West-East trend in ice sheet dynamics may be the local geology (hinterland and basal), basal geomorphology, and the geometry of the local ice sheets.
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  • 52
    Publication Date: 2018-11-08
    Repository Name: EPIC Alfred Wegener Institut
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  • 53
    Publication Date: 2019-01-29
    Description: We conducted multiple small (2011–2012) and one large sampling campaign (2013) at selected profiles along the Elbe River. With the data we were able to outline spatial and temporal variability of methane concentration, oxidation and emissions in one of the major rivers of Central Europe. The highest methane concentrations were found in human-altered riverine habitats, i.e., in a harbor (1,888 nmol L−1), in a lock and weirs (1409 ± 1545 nmol L−1), and in general in the whole “impounded” river segment (383 ± 215 nmol L−1). On the other hand, the lowest methane concentrations were found in the “lowland” river segment (86 ± 56 nmol L−1). The methane oxidation rate was more efficient in the “natural” segment (71 ± 113 nmol L−1day−1, which means a turnover time of 49 ± 83 day−1) than in the “lowland” segment (4 ± 3 nmol L−1day−1, which means a turnover time of 39 ± 45 day−1). Methane emissions from the surface water into the atmosphere ranged from 0.4 to 11.9 mg m−2 day−1 (mean 2.1 ± 0.6 mg m−2 day−1) with the highest CH4 emissions at the Meissen harbor (94 kg CH4 year−1). Such human-altered riverine habitats (i.e., harbors and similar) have not been taken into consideration in the CH4 budget before, despite them being part of the river ecosystems, they may be significant CH4 hot-spots. The total CH4 diffusive flux from the whole Elbe was estimated to be approximately 97 t CH4 year−1.
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  • 54
    Publication Date: 2018-11-19
    Description: The present study is based on a series of two-dimensional simple shear numerical simulations of two-phase non-linear viscous materials used to investigate the mechanical behaviour of two-phase aggregates representing partially molten rocks. These simulations couple viscoplastic deformation with dynamic recrystallisation (DRX). The aim of these simulations is to investigate the competition between deformation and recrystallisation, and how they affect the mechanical behaviour and resulting microstructures of the deforming material. We systematically vary the melt to solid rock ratio, the dihedral angle of melt and the ratio of DRX vs. deformation. The results show that the amount of DRX and the dihedral angle have a first-order impact on the bulk rheology and the melt distribution in the aggregate. The numerical results allow defining two regimes, depending on the relative contribution of deformation and DRX: (1) a deformation-dominated regime at high strain rates (i.e., with a low ratio of recrystallisation vs. viscoplastic deformation) and (2) a recrystallisation-dominated regime at low strain rates (i.e., with a high ratio of recrystallisation vs. viscoplastic deformation). The first case results in systems bearing large connected melt pockets whose viscous flow controls the deformation of the aggregate, while disconnected smaller melt pockets develop in models where dynamic recrystallisation dominates. The results of this study allow us to better understand the development of connected melt pockets, which may focus melt flow. The distribution of the melt phase plays a key role in the formation of larger-scale melt-enriched shear bands, which in turn has a direct influence on large-scale convective mantle flow.
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  • 55
    Publication Date: 2019-04-05
    Description: The 77th cruise of the RV MARIA S. MERIAN contributed to various large national and international research and infrastructure projects (FRAM, ARCHES, INTAROS, ICOS, SIOS) as well as to the research programme PACES-II (Polar Regions and Coasts in the changing Earth System) of the Alfred-Wegener-Institute Helmholtz-Center for Polar and Marine Research (AWI). Investigations within Work Package 4 (Arctic sea ice and its interaction with ocean and ecosystems) of the PACES-II programme, aim at assessing and quantifying ecosystem changes from surface waters to the deep ocean in response to the retreating sea ice, and at exploring the most important (feedback) processes determining temporal and spatial variability. Contributions to the PACES-II Work Package 6 (Large scale variability and change in polar benthic biota and ecosystem functions) include the identification of spatial patterns and temporal trends in relevant benthic community functions, and the development of a comprehensive science community reference collection of observational data. Work carried out within WPs 4 and 6 will support the time-series studies at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN (Fig. 1.1), where we document Global Change induced environmental variations on a polar deep-water ecosystem. This work is carried out in close co-operation between the HGF-MPG Joint Research Group on Deep-Sea Ecology and Technology and the PEBCAO Group (Phytoplankton Ecology and Biogeochemistry in the Changing Arctic Ocean) at AWI as well as the working group Microbial Geochemistry at the GEOMAR and the HGF Young Investigators Group SEAPUMP (Seasonal and regional food web interactions with the biological pump).
    Repository Name: EPIC Alfred Wegener Institut
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  • 56
    Publication Date: 2019-02-11
    Description: Oceans cover 〉70% of the earth and encompass variable habitats concerning salinity, temperature, pressure, light availability. The deep sea (〉1000 m water depth) constitutes more than 60% of the ocean´s biosphere and harbors an unparalleled biodiversity. It constitutes an extreme habitat due to high pressure, darkness and often low nutrient and oxygen concentrations. In order to ensure their survival, microorganisms thriving in such environments have to develop unique metabolic adaptations, thus represent an interesting resource for the discovery of new molecules. However, due to access difficulties to deep-sea habitats and the lack of suitable and affordable sampling techniques, deep-sea microorganisms have remained untapped for their potential in marine biodiscovery. In this study, we obtained deep-sea sediment samples from Arctic Ocean (-2432 m), sampled by an ROV during RV Polarstern expedition 108. Isolation of microorganisms has been performed using two specific media for bacteria and fungi, respectively. Isolates were identified by amplification of the 16S rRNA gene (bacteria) and ITS1-2 region (fungi) followed by Sanger sequencing. In total, 70 bacterial isolates were identified covering four phyla (52 Firmicutes, 1 Actinobacteria, 11 Proteobacteria and 6 Bacteroidetes) and seven fungal strains from two different phyla (6 Ascomycota and 1 Basidiomycota). Selected isolates were cultivated in two different media, followed by solvent (EtOAc) extraction and bioactivity screenings against a panel of clinically relevant microbial pathogens and six cancer cell lines. At 100 µg/mL concentration, three bacterial extracts showed antitumor activity (〉70%), whereas 17 exhibited activity (〉65%) against methicillin-resistant Staphylococcus aureus (MRSA). Notably, only one fungus showed a cultivation medium dependent-high antifungal activity (〉90%), highlighting the impact of culture media on the production of bioactive secondary metabolites.
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  • 57
    Publication Date: 2018-11-28
    Description: Life cycle and reproduction of Calanus hyperboreus were studied during a year of record low ice cover in the southeastern Beaufort Sea. Stages CIV, adult females and CV dominated the overwintering population, suggesting a 2- to 3-year life cycle. Within two spring-summer months in the upper water column females filled their energy reserves before initiating their downward seasonal migration. From February to March, vigorous reproduction (20–65 eggs f−1 d−1) delivered numerous eggs (29 000 eggs m−2) at depth and nauplii N1-N3 (17 000 ind. m−2) in the water column. However, CI copepodite recruitment in May, coincident with the phytoplankton bloom, was modest in Amundsen Gulf compared to sites outside the gulf. Consequently, C. hyperboreus abundance and biomass stagnated throughout summer in Amundsen Gulf. As a mismatch between the first-feeding stages and food was unlikely under the favourable feeding conditions of April-May 2008, predation on the egg and larval stages in late winter presumably limited subsequent recruitment and population growth. Particularly abundant in Amundsen Gulf, the copepods Metridia longa and C. glacialis were likely important consumers of C. hyperboreus eggs and nauplii. With the ongoing climate-driven lengthening of the ice-free season, intensification of top-down control of C. hyperboreus recruitment by thriving populations of mesopelagic omnivores and carnivores like M. longa may counteract the potential benefits of increased primary production over the Arctic shelves margins for this key prey of pelagic fish, seabirds and the bowhead whale.
    Repository Name: EPIC Alfred Wegener Institut
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  • 58
    Publication Date: 2018-12-10
    Repository Name: EPIC Alfred Wegener Institut
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  • 59
    Publication Date: 2019-01-07
    Description: The rapid dissemination of microplastics in many habitats of the oceans has raised concerns about the consequences for marine biota and ecosystems. Many adverse effects of microplastics on marine invertebrates are consequences of ingestion. Accordingly, the identification of mechanisms that facilitate the uptake of microplastics is essential for the evaluation of possible implications for marine organisms and food webs. Gastropods produce mucus for locomotion. Gastropod pedal mucus naturally retains formerly suspended micro-organisms, such as bacteria, microalgae, and seaweed spores. The retained organisms are consumed by gastropods that forage on pedal mucus. Here, we investigated the potential of gastropod pedal mucus to retain suspended microplastic particles and make them available for ingestion by periwinkles that forage on the contaminated mucus. In laboratory experiments, mucus of the periwinkles Littorina littorea and Littorina obtusata efficiently retained microplastics. Retention of microplastics varied between mucus from conspecifics of different size but not between mucus from either species. The density of microplastics in mucus trails increased concomitantly with the experimental particle concentration but was independent of incubation time. Aging of mucus and, particularly, desiccation affected the retention of microplastics. Periwinkles ingested microplastics when foraging on the contaminated mucus. Our results reveal a functional link between biogenic accumulation of microplastics and their trophic transfer by marine benthic herbivores into marine food webs.
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  • 60
    Publication Date: 2019-03-25
    Repository Name: EPIC Alfred Wegener Institut
    Type: Data Processing Reports , NonPeerReviewed
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  • 61
    Publication Date: 2019-01-30
    Description: The purpose of this list of digital platforms is to facilitate the research of scientific data (articles, books, conferences, websites, indexers, etc.) by students of all undergraduate levels. The interface of platforms have similarities and because of this, low degree of difficulty of use. I emphasize that the key to an excellent literature search on digital platforms is to choose the right "keyword".
    Repository Name: EPIC Alfred Wegener Institut
    Type: PANGAEA Documentation , NonPeerReviewed
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  • 62
    Publication Date: 2019-01-17
    Description: Mumiyo deposits form in the vicinity of snow petrel (Pagodroma nivea) nesting sites and consist of fossil stomach oil (mumiyo), guano, and minerogenic material. Here we evaluate mumiyo deposits from the inland mountain ranges of central Dronning Maud Land as high-resolution archives for paleoenvironmental reconstructions in Antarctica. Investigation of internal structures and chemical composition shows that the lamination reflects progressive sedimentation, despite the irregular outer morphology of the deposits. Detailed radiocarbon analysis demonstrates that stratigraphies are intact: 14C ages become successively younger upwards in the deposits. Fatty acid and n-alcohol composition was determined on samples from eight mumiyo deposits. Dominance of low molecular weight compounds (C14 to C18) points to a dietary signal; however, the relatively low proportions of unsaturated compounds compared to fresh stomach oils indicates some postdepositional degradation. We found marine diatoms in the mumiyo, which potentially provide a proxy for sea ice conditions in the foraging habitat of the petrels. Age ranges of the investigated deposits suggest occupation of the analyzed sites by snow petrels from 17 ka to 〉58 ka. Changes in deposition rates point to higher occupation frequency in Petermann Range from 46 to 42 ka compared to the late marine isotope stage 3 and the Last Glacial Maximum.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 63
    Publication Date: 2019-01-23
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 64
    Publication Date: 2019-02-11
    Description: In this study 129I and 236U concentrations in seawater samples collected onboard R/V Polarstern during the PS100 expedition in the Fram Strait in 2016 are presented. The overall aim of the study was to investigate the distribution of these long‐lived radionuclides along the transect located at 79°N. The combination of both radionuclides was used for the first time in the Fram Strait to trace ocean circulation pathways of Atlantic waters. Results show that both 129I and 236U concentrations as well as 236U/238U ratios are about two times higher (〉 600 × 107 at kg(−1), 〉 20 × 106 at kg(−1), and 2.8 × 10−9, respectively) in the cold and fresh outflowing surface waters from the Arctic Ocean (Polar Surface Water, PSW) compared to inflowing Atlantic origin waters (300 × 107 at kg(−1) 129I, 12 × 106 at kg(−1) 236U, and 1.4 × 10−9 236U/238U). A comparison with the different 129I and 236U input functions for the Atlantic branches entering the Arctic Ocean reveals that the middepth Atlantic origin waters outflowing the Arctic Ocean show more influence of the Barents Sea Branch Water than the Fram Strait Branch Water. The high radionuclide concentrations observed in the PSW indicate substantial influence of the Norwegian Coastal Current. This current carries a significantly larger proportion of 129I and 236U releases from European reprocessing plants than the aforementioned Atlantic branches. We estimate surface water transit times from the northern Norwegian Coast through the Arctic to the PSW of 12–19 years, less than for the middepth Barents Sea Branch Water (16–23 years).
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 65
    Publication Date: 2019-02-25
    Description: We investigated the intracellular dynamics of calcite and sulfur in the large sulfur-oxidizing, calcite-accumulating bacterium Achromatium, with an emphasis on oxygen exposure as a physiological control. For this purpose, morphological changes and possible accretion mechanisms of calcite granules in cells that were freshly collected from natural Achromatium-containing sediment were compared to cells from the same source after prolonged exposure to atmospheric oxygen. Intracellular sulfur is oxidized and removed in response to oxygen exposure. Calcite granules also undergo distinct oxygen-related dynamics; they alternate between tightly packaged, smooth granules with narrow but sharply defined interstitial spaces in atmospheric oxygen-exposed cells, and more loosely packaged granules with irregular, bumpy surface texture and larger interstitial spaces in cells that were not artificially exposed to oxygen. These results suggest that morphological changes of the calcite granules reflect their changing physiological role inside the cell. Sulfur oxidation and calcite dissolution appear to be linked in that proton generation during sulfur oxidation is buffered by gradual calcite erosion, visible in the smooth, rounded surface morphology observed after oxygen exposure. Our results support the hypothesis that calcite dynamics buffer the intracellular pH fluctuations linked to electron acceptor limitation during proton-consuming sulfide oxidation to sulfur, and electron acceptor abundance during proton-generating sulfur oxidation to sulfate.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 66
    Publication Date: 2019-02-26
    Description: The demand for efficient stone detection techniques of stony areas (reefs) in the marine environment increased in the last years. This is especially important for seafloor areas with a patchy distribution of stones in an otherwise sand-dominated milieu. These hard substrates are hotspots of marine biodiversity; especially for benthic communities. For fishes, marine mammals and birds stony areas are important breeding and feeding places. Current research projects are dealing with the stone distribution and density to investigate e.g. species-habitat interactions. On the political level detailed distribution maps are relevant for resource assessments, coastal management and protection conventions. The detection of stony habitats in sublittoral environments is still a considerable challenge in spite of modern high resolution hydroacoustic techniques. Object detection on the seafloor is commonly done on the basis of hydroacoustic backscatter intensities recorded with e.g. sidescan sonar and multibeam echo sounder. Single objects such as stones can generally be recognized by the acoustic shadow behind the object. For small areas single objects can be easily identified manually; for large scale mapping automated techniques are required which are still under development. We collected a set of hydroacoustic data on the German continental shelf to compare and discuss the following approaches to detect and demarcate stony habitats: • manual detection on backscatter mosaics • automated detection on backscatter mosaics using machine learning techniques • seismo-acoustic approach (sediment echo sounder, sidescan sonar)
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 67
    Publication Date: 2019-02-21
    Description: The Association of Polar Early Career Scientists (APECS) is an important legacy of the International Polar Year (IPY). APECS continues to foster engagement in education, outreach and communication (EOC) activities relating to the polar regions and provide training for early career researchers (ECRs). We highlight opportunities for training, leadership and skills development, such as the annual Polar Weeks and Antarctica Day celebrations. Participation and engagement in EOC activities actively contributes to career development by enabling ECRs to develop valuable soft skills such as networking, communication and interdisciplinary knowledge. A pilot survey on EOC engagement highlighted that those who organise events also gain leadership skills such as team management. We discuss several factors contributing to the success of APECS in training the next generation of polar leaders. These include the geographical rather than discipline-specific focus of the organisation, utilisation of online resources, including social media, and the strong links with partner organisations. These examples demonstrate how the EOC legacy of IPY has continued due to APECS’ targeted efforts to create EOC opportunities and provide skills and leadership training for ECRs.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 68
    Publication Date: 2019-02-21
    Description: Global warming has a direct impact on the degradation of permafrost and the resulting ground subsidence. Thermokarst lakes develop. During the formation of thermokarst lakes, the thawing of permafrost releases methane and carbon, which was locked in the frozen ground before. As a result, the generation of thermokarst lakes is directly linked to climatic changes. The aim of this research is to reconstruct the initiation of lakes which are situated in the discontinuous permafrost of Goldstream Valley, Central Alaska. In course of an expedition in summer 2017, cores from eleven thermokarst lakes were taken from Goldstream Valley in Central Alaska. The samples were analysed for sedimentological and biochemical parameters. Additionally, macro remains were examined. There are three classes of thermokarst lakes within this research: Lakes which develop over a longer period of time and lakes which developed in less time. The third class includes lakes where the initiation phase was not caught within the selected transition zones, but it is assumed they also developed over a longer period of time and therefore belong to class one. A distinct peat layer is characteristic for lakes of class one. The analysed macro remains reflect the degree of degradation of the sediment except in one case. In case of biochemical analyses, the macro remains are only partly reflected. An implication of thermokarst lake development is a release of a high amount of methane and carbon dioxide while thermokarst lakes develop. So, the more time a lake needs to originate, the higher the emissions of methane and carbon dioxide are. Lakes that form within less time therefore emit less methane and carbon dioxide.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Thesis , NonPeerReviewed , info:eu-repo/semantics/other
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  • 69
    Publication Date: 2019-02-21
    Description: We discuss several forms of developmental plasticity exhibited by marine crabs, in the context of ecological developmental biology (EcoDevo), and seek to motivate research in EcoDevo by addressing some key questions of the field. We summarise the diversity of plastic developmental responses exhibited during crab development, identify gaps in knowledge and highlight the importance of EcoDevo research in the light of current climate change. Marine crabs show a suite of plastic responses including transgenerational plasticity (e.g., maternal effects), as well as developmental plasticity both within the larval phase and across the larval-juvenile life history transition (e.g., latent effects). Given the potential ecological and evolutionary consequences we think that there is much potential for research in the field of EcoDevo using brachyuran crabs as model organisms.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , NonPeerReviewed
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  • 70
    Publication Date: 2019-02-26
    Description: Sediment distribution maps are usually the basis for biotope mapping and modeling. The standard method to generate sediment maps is the interpretation of area-wide backscatter data from e.g. sidescan sonar or multibeam, or the interpretation of single beam data from acoustic ground discrimination systems (e.g. RoxAnn). In areas of homogeneous sediment distributions with clear sediment boundaries, one data set combined with ground truthing is often sufficient for the spatial demarcation of specific sediment types. Mapping campaigns in the offshore area of the German Bight, where the seafloor is characterized by moraine deposits partly covered by Holocene mobile fine sands, have shown that accurate mapping is only possible with high resolution backscatter data (at least 25 cm resolution). With low resolution data (1 m) it is principally possible to differentiate between sands (low backscatter) and coarse grained sediments (high backscatter). However, high resolution data show that the high backscatter areas can be further differentiated by means of texture analysis. Winnowed lag deposits (fine gravel) characterized by large ripples and moraine relict sediments (sand, gravel, stones) characterized by stone signatures are lying closely together. They differ in their biological functions and are thus worth to differentiate. Also ground discrimination data were not able to distinguish both coarse grained habitats. Since the acquisition of data with appropriate resolution is related to small beam swath widths and is thus very time intensive, we followed a multi-method approach by combining different simultaneous recorded data sets. The combination of low resolution sidescan sonar data and parametric sediment echo sounder data (used for detecting stones) enabled a fast and reproducible method to distinguish stony grounds from gravelly substrates in highly heterogeneous environments.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 71
    Publication Date: 2019-02-25
    Description: The Arctic has become a hot spot of climate change, but the nonlinear interactions between regional and global scales in the coupled climate system responsible for Arctic amplification are not well understood and insufficiently described in climate models. Here, we compare reanalysis data with model simulations for low and high Arctic sea ice conditions to identify model biases with respect to atmospheric Arctic–mid‐latitude linkages. We show that an appropriate description of Arctic sea ice forcing is able to reproduce the observed winter cooling in mid‐latitudes as result of improved tropospheric‐stratospheric planetary wave propagation triggering a negative phase of the Arctic Oscillation/North Atlantic Oscillation in late winter.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 72
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    2019 Springer Nature Publishing AG
    Publication Date: 2019-03-05
    Description: Food-chain length (FCL) is a fundamental ecosystem attribute, integrating information on both food web composition and ecosystem processes. It remains untested whether FCL also reflects the history of community assembly known to affect community composition and ecosystem functioning. Here, we performed microcosm experiments with a copepod (top predator), two ciliate species (intermediate consumers), and bacteria (producers), and modified the sequence of species introduction into the microcosm at four productivity levels to jointly test the effects of historical contingency and productivity on FCL. FCL increased when the top predator was introduced last; thus, the trophic position of the copepod reflected assembly history. A shorter FCL occurred at the highest productivity level, probably because the predator switched to feeding at the lower trophic levels because of the abundant basal resource. Thus, we present empirical evidence that FCL was determined by historical contingency, likely caused by priority effects, and by productivity.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 73
    Publication Date: 2019-04-23
    Description: Research on permafrost has intensified in recent years, due to enhanced warming in the Arctic and in alpine regions, and the direct feedbacks between thawing permafrost and climate. To explore how scientists build on existing knowledge on permafrost and identify which studies inspire more research, we analyzed scientific articles published over two decades, before (1998-2007) and after (2008-2017) the 4th International Polar Year (2007/2008). We compared this bibliometric data to results from an online survey in which respondents were asked to list the most influential and inspiring publications on permafrost in their view. While publications per year have more than doubled for multidisciplinary geosciences from 1998 to 2017, permafrost publications have increased more than six-fold for the same period, according to bibliometric data from Web of Science. Permafrost publications have increased the most in journals focusing on biogeosciences (e.g. Journal of Geophysical Research - Biogeosciences) but also in the broader geoscience and science journals (e.g. Geophysical Research Letters, Nature), reflecting a shift towards more carbon-cycle focused research in later years. From the survey, many listed books as the most influential publications and comments also revealed that conferences, photographs, movies and (non-science) books inspire permafrost researchers. Keeping track on how knowledge is collectively built within a scientific discipline and community, can help us to identify how to design impactful studies and how to coordinate research efforts in a time when high quality and impact research is badly needed.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 74
    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
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  • 75
    Publication Date: 2019-03-07
    Description: Aim: Most protist plankton are mixotrophic, with potential to engage in photoautotrophy and phagotrophy; however, the ecology of these organisms has been misdiagnosed for over a century. A large proportion of these organisms are constitutive mixotrophs (CMs), with an innate ability to photosynthesize. Here, for the first time, an analysis is presented of the biogeography of CMs across the oceans. Location: Global marine ecosystems. Time period: 1970–2018. Major taxa studied: Marine planktonic protists. Methods: Records for CM species, primarily from the Ocean Biogeographic Information System (OBIS), were grouped by taxonomy and size to evaluate sampling efforts across Longhurst's oceanic provinces. Biases were evaluated through nonparametric tests and multivariate analysis. Biogeographies of CMs from OBIS data were compared with data from studies that specifically targeted these organisms. Results: Constitutive mixotrophs of different taxonomic groups, across all size ranges, are ubiquitous. However, strong database biases were detected with respect to organism size, taxonomic groups and region. A strong bias was seen towards dinophytes. Species 〈 20 μm, especially non‐dinophytes, were least represented, with their recorded distribution limited to coastal regions and to temperate and polar seas. Studies specifically targeting these organisms revealed their distribution to be much wider. Such biases are likely to have occurred owing to a failure to capture and correctly identify these organisms in routine sampling protocols. Main conclusions: Constitutive mixotrophs are dominant members of organisms traditionally termed “phytoplankton”. However, lack of routine protocols for measuring phagotrophy in “phytoplankton” protists has led to widespread misrepresentation of the fundamental nature of marine planktonic primary producers; most express both “animal‐like” and “plant‐like” nutrition. Our results have implications for studies of the global biogeography of plankton, of food web dynamics (including models) and of biogeochemical cycling in the oceans.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 76
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    Publication Date: 2019-03-18
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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