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    Publication Date: 2018-01-11
    Description: Arctic sea ice has displayed significant thinning as well as an increase in drift speed in recent years. Taken together this suggests an associated rise in sea ice deformation rate. A winter and spring expedition to the sea ice covered region north of Svalbard–the Norwegian young sea ICE2015 expedition (N-ICE2015)—gave an opportunity to deploy extensive buoy arrays and to monitor the deformation of the first-year and secondyear ice now common in the majority of the Arctic Basin. During the 5 month long expedition, the ice cover underwent several strong deformation events, including a powerful storm in early February that damaged the ice cover irreversibly. The values of total deformation measured during N-ICE2015 exceed previously measured values in the Arctic Basin at similar scales: At 100 km scale, N-ICE2015 values averaged above 0.1 d-1, compared to rates of 0.08 d-1 or less for previous buoy arrays. The exponent of the power law between the deformation length scale and total deformation developed over the season from 0.37 to 0.54 with an abrupt increase immediately after the early February storm, indicating a weakened ice cover with more free drift of the sea ice floes. Our results point to a general increase in deformation associated with the younger and thinner Arctic sea ice and to a potentially destructive role of winter storms.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
    Format: application/pdf
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  • 3
    Publication Date: 2019-11-25
    Description: The progress of science is tied to the standardization of measurements, instruments, and data. This is especially true in the Big Data age, where analyzing large data volumes critically hinges on the data being standardized. Accordingly, the lack of community‐sanctioned data standards in paleoclimatology has largely precluded the benefits of Big Data advances in the field. Building upon recent efforts to standardize the format and terminology of paleoclimate data, this article describes the Paleoclimate Community reporTing Standard (PaCTS), a crowdsourced reporting standard for such data. PaCTS captures which information should be included when reporting paleoclimate data, with the goal of maximizing the reuse value of paleoclimate data sets, particularly for synthesis work and comparison to climate model simulations. Initiated by the LinkedEarth project, the process to elicit a reporting standard involved an international workshop in 2016, various forms of digital community engagement over the next few years, and grassroots working groups. Participants in this process identified important properties across paleoclimate archives, in addition to the reporting of uncertainties and chronologies; they also identified archive‐specific properties and distinguished reporting standards for new versus legacy data sets. This work shows that at least 135 respondents overwhelmingly support a drastic increase in the amount of metadata accompanying paleoclimate data sets. Since such goals are at odds with present practices, we discuss a transparent path toward implementing or revising these recommendations in the near future, using both bottom‐up and top‐down approaches.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2015-09-06
    Description: Morphologic features, 600 to 1,100 m across and elevated up to 30 m above the surrounding seafloor, interpreted to be mud volcanoes were investigated on the continental slope in the Beaufort Sea in the Canadian Arctic. Sediment cores, detailed mapping with an autonomous underwater vehicle and exploration with a remotely operated vehicle show that these are young and actively forming features experiencing ongoing eruptions. Biogenic methane and low-chloride, sodium-bicarbonate-rich waters are extruded with warm sediment that accumulates to form cones and low relief circular plateaus. The chemical and isotopic compositions of the ascending water indicate that a mixture of meteoric water, seawater, and water from clay dehydration has played a significant role in the evolution of these fluids. The venting methane supports extensive siboglinid tubeworms communities and forms some gas hydrates within the near seafloor. We believe that these are the first documented living chemosynthetic biological communities in the continental slope of the western Arctic Ocean. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2015-12-02
    Description: Parasites are a major force in evolution, and understanding how host life history affects parasite pressure and investment in disease resistance is a general problem in evolutionary biology. The threat of disease may be especially strong in social animals, and ants have evolved the unique metapleural gland (MG), which in many taxa produce antimicrobial compounds that have been argued to have been a key to their ecological success. However, the importance of the MG in the disease resistance of individual ants across ant taxa has not been examined directly. We investigate experimentally the importance of the MG for disease resistance in the fungus-growing ants, a group in which there is interspecific variation in MG size and which has distinct transitions in life history. We find that more derived taxa rely more on the MG for disease resistance than more basal taxa and that there are a series of evolutionary transitions in the quality, quantity, and usage of the MG secretions, which correlate with transitions in life history. These shifts show how even small clades can exhibit substantial transitions in disease resistance investment, demonstrating that host–parasite relationships can be very dynamic and that targeted experimental, as well as large-scale, comparative studies can be valuable for identifying evolutionary transitions. Attine ants show substantial variations in their investment into both the quality and quantity of their antimicrobial secretions across their phylogeny. These differences may be related to transitions in colony size and other life-history traits within the group.
    Electronic ISSN: 2045-7758
    Topics: Biology
    Published by Wiley
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  • 6
    Publication Date: 2015-10-03
    Description: Using a global multi-fluid MHD model, we demonstrate the effects of magnetospheric O + on bursty magnetotail flows. We carry out two simulations without ionospheric outflow to use as baseline, one driven by real solar wind data and one driven by idealized solar wind. Solar wind data from 1 October 2001 is used as a stormtime solar wind driver. During this event, the plasma sheet was observed to be rich in O + , making the event of interest for a model analysis of the effects of ionospheric origin O + on magnetospheric dynamics. We carry out outflow comparison simulations for both the realistic and the idealized solar wind drivers using a simple empirical model that places auroral outflow in regions where downward-propagating Poynting flux and electron precipitation are present, combined with a low-flux thermal-energy O+ outflow over the entire polar region. We demonstrate the effects of O + on magnetotail structure and the occurrence rate and strength of bursty, fast Earthward flows. The addition of O + to the magnetotail stretches the tail and increases the velocity of bursty Earthward flows. This increase is shown to be produced by reconnection events in an extended current sheet created by tail stretching.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 2015-10-11
    Description: We present a new time-slice reconstruction of the Eurasian ice sheets (British–Irish, Svalbard–Barents–Kara Seas and Scandinavian) documenting the spatial evolution of these interconnected ice sheets every 1000 years from 25 to 10 ka, and at four selected time periods back to 40 ka. The time-slice maps of ice-sheet extent are based on a new Geographical Information System (GIS) database, where we have collected published numerical dates constraining the timing of ice-sheet advance and retreat, and additionally geomorphological and geological evidence contained within the existing literature. We integrate all uncertainty estimates into three ice-margin lines for each time-slice; a most-credible line, derived from our assessment of all available evidence, with bounding maximum and minimum limits allowed by existing data. This approach was motivated by the demands of glaciological, isostatic and climate modelling and to clearly display limitations in knowledge. The timing of advance and retreat were both remarkably spatially variable across the ice-sheet area. According to our compilation the westernmost limit along the British–Irish and Norwegian continental shelf was reached up to 7000 years earlier (at c.  27–26 ka) than the eastern limit on the Russian Plain (at c.  20–19 ka). The Eurasian ice sheet complex as a whole attained its maximum extent (5.5 Mkm 2 ) and volume (~24 m Sea Level Equivalent) at c.  21 ka. Our continental-scale approach highlights instances of conflicting evidence and gaps in the ice-sheet chronology where uncertainties remain large and should be a focus for future research. Largest uncertainties coincide with locations presently below sea level and where contradicting evidence exists. This first version of the database and time-slices (DATED-1) has a census date of 1 January 2013 and both are available to download via the Bjerknes Climate Data Centre and PANGAEA ( www.bcdc.no ; http://doi.pangaea.de/10.1594/PANGAEA.848117 ).
    Print ISSN: 0300-9483
    Electronic ISSN: 1502-3885
    Topics: Geography , Geosciences
    Published by Wiley
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  • 8
    Publication Date: 2015-10-08
    Description: Key Point Students questions about reconnection are summarized.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Publication Date: 2015-10-21
    Description: During the four decades of Keith Beven's career there have been many developments in the science of hydrological modelling. Some have focused on the links between hydrological process understanding and the structure and complexity of hydrological models, others on the related issues of modelling uncertainty. The southern Africa region continues to be generally less well endowed with the resources required to contribute to these research developments, but they are critical for successful water resources management decision-making in data scarce areas, and go beyond academic interest. Consequently, the focus in the region has been on adding a local context to northern hemisphere research as well as trying to put it into practice. The challenge in southern Africa has always been to extrapolate from published research ideas and decide how they can be effectively used in larger scale practical applications in data-poor areas. The paper examines the issues of model complexity, links with process understanding and the broad topic of model uncertainty estimation in the context of data scarce areas and how the science questions relate to improvements in water resources decision making. The conclusions suggest that the southern African region has benefited a great deal from several decades of northern hemisphere research (including those by Beven) and that some value has been added through the focus on practical implementation. The region should also embrace the opportunities presented by the need to link realistic uncertainty estimates with risk-based water resources decision-making, thereby contributing to the international debate on this important topic.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 10
    Publication Date: 2015-11-25
    Description: With increasing demands on limited water resources, regulation of larger river systems continues to increase and so too does the need for accurate water accounting and prediction in these systems. River system models are either calibrated manually or automatically on a reach–by–reach basis, i.e. each reach is calibrated as a separate entity with little or no consideration of fluxes at other locations within the river system. While this is a practical approach, simulation errors can propagate downstream to make calibration or prediction difficult at those locations. Likewise parameters may suffer from over-fitting especially where observations are erroneous. We developed and implemented a system calibration strategy in a portion of the Murrumbidgee River, Australia, where parameters for 11 gauges (36 parameters) were calibrated together. Parameter values, model states and model goodness of fit were compared to reach–by–reach calibration. The system calibration produced a better goodness of fit across the whole system relative to reach-by-reach calibration. Additionally, model system states were more realistic than reach-by-reach optimized models. Over-fitting was obvious using the reach-by-reach method for one reach/gauge in particular. This was avoided with system calibration method, with improved goodness of fit at all gauges downstream of the problem gauge. The results here suggest that the system calibration approach provides more hydrologically consistent states, improved overall fit and avoids over–fitting at problem gauges. This article is protected by copyright. All rights reserved.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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