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  • 1
    Call number: AWI G3-19-93211 ; AWI G3-19-93211(2. Ex.)
    Type of Medium: Dissertations
    Pages: viii, 220 Seiten , Illustrationen
    Language: English
    Note: Dissertation, Universität Potsdam, 2019 , Table of Contents Abstract Zusammenfassung 1 Introduction 1.1 Scientific background 1.1.1 Permafrost - terrestrial and subsea 1.1.2 Subsea permafrost distribution 1.1.3 Relevance in the context of a changing Arctic 1.1.4 Influences on subsea permafrost 1.2 Hypotheses and objectives 1.3 Thesis organization 2 Detection of subsea permafrost degradation rates 2.1 An overview of geophysical methods and studies in subsea permafrost 2.2 Geophysical objectives 2.3 Passive seismic techniques 2.3.1 H/V passive seismics 2.3.2 Passive seismic interferometry 2.4 Instrument design & marine tests on Sylt 2.5 Arctic feasibility test site around Muostakh Island 2.6 Arctic deployment for wide area detection around Muostakh Island 3 Modelling of subsea permafrost degradation processes 3.1 An overview on subsea permafrost modelling 3.2 Salt distribution- mechanisms beyond diffusional transport 3.3 Open questions in salt transport and permafrost degradation 3.4 Modelling objectives 3.5 Study sites 3.5.1 Primary study site: Cape Mamontov Klyk 3.5.2 Secondary study sites: Buor Khaya & Muostakh Island 3.6 Developing a model for subsea permafrost 3.6.1 Thermal regime of the subsurface: governing equations of conductive heat transfer 3.6.2 Model definitions: concentration and thaw depth 3.6.3 Saline effect on the state of permafrost 3.6.4 Salt transport: governing equation & parameterizations 3.6.5 Modelling approach 3.6.6 Model testing 3. 7 Results: Influence of model parameters on subsea permafrost degradation 3.8 Discussion and implications 3.8.1 Modelled inundation parameters 3.8.2 Further factors affecting subsea permafrost degradation 3.8.3 Implications 4 From local to regional scale: Amending sparsely distributed temperature records 4.1 An overview of borehole temperature reconstruction . 4.2 On the transferability of ground to air temperatures . 4.3 Reconstruction objectives 4.4 Borehole sites and climate 4.5 Borehole temperatures 4.6 Inversion method 4.6.1 Forward model 4.6.2 Optimization 4.6.3 Sensitivity analysis 4.7 Results and discussion of the reconstruction from the permafrost boreholes 4.7.1 Recoverable period 4.7.2 Optimization 4.7.3 Surface temperature reconstructions and fit 4.7.4 Inversion method's impact on character of solution & sensitivity to temperature history parameterization 4.8 Discussion of spatial differences and implications 4.8.1 Comparison to other temperature data 4.8.2 Site differences 4.8.3 Methodological considerations 4.8.4 Implications 5 Conclusion and outlook 5.1 Outlook Appendices A Modelling tests for H/V method configuration Bibliography Acknowledgements
    Location: AWI Reading room
    Location: AWI Reading room
    Branch Library: AWI Library
    Branch Library: AWI Library
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  • 2
    Publication Date: 2019-09-10
    Description: Warming of the Arctic led to an increase of permafrost temperatures by about 0.3 °C during the last decade. Permafrost warming is associated with increasing sediment water content, permeability and diffusivity and could on the long-term alter microbial community composition and abundance even before permafrost thaws. We studied the long-term effect (up to 2500 years) of submarine permafrost warming on microbial communities along an onshore-offshore transect on the Siberian Arctic Shelf displaying a natural temperature gradient of more than 10 °C. We analysed the in-situ development of bacterial abundance and community composition through total cell counts (TCC), quantitative PCR of bacterial gene abundance and amplicon sequencing, and correlated the microbial community data with temperature, pore water chemistry and sediment physicochemical parameters. On time-scales of centuries, permafrost warming coincided with an overall decreasing microbial abundance while millennia after warming microbial abundance was similar to cold onshore permafrost and DOC content was least. Based on correlation analysis TCC unlike bacterial gene abundance showed a significant rank-based negative correlation with increasing temperature while both TCC and bacterial gene copy numbers showed a negative correlation with salinity. Bacterial community composition correlated only weakly with temperature but strongly with pore-water stable isotope signatures and depth, while it showed no correlation with salinity. Microbial community composition showed substantial spatial variation and an overall dominance of Actinobacteria, Chloroflexi, Firmicutes, Gemmatimonadetes and Proteobacteria which are amongst the microbial taxa that were found to be active in other frozen permafrost environments as well. We suggest that, millennia after permafrost warming by over 10 °C, microbial community composition and abundance show some indications for proliferation but mainly reflect the sedimentation history and paleo-environment and not a direct effect through warming.
    Language: English
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 3
    Publication Date: 2017-03-16
    Description: The composition of perennially frozen deposits holds information on the palaeo-environment during and following deposition. In this study, we investigate late Pleistocene permafrost at the western coast of the Buor Khaya Peninsula in the south-central Laptev Sea (Siberia), namely the prominent eastern Siberian Yedoma Ice Complex (IC). Two Yedoma IC exposures and one drill core were studied for cryolithological (i.e. ice and sediment features), geochemical, and geochronological parameters. Borehole temperatures were measured for 3 years to capture the current thermal state of permafrost. The studied sequences were composed of ice-oversaturated silts and fine-grained sands with considerable amounts of organic matter (0.2 to 24 wt %). Syngenetic ice wedges intersect the frozen deposits. The deposition of the Yedoma IC, as revealed by radiocarbon dates of sedimentary organic matter, took place between 54.1 and 30.1 kyr BP. Continued Yedoma IC deposition until about 14.7 kyr BP is shown by dates from organic matter preserved in ice-wedge ice. For the lowermost and oldest Yedoma IC part, infrared-stimulated luminescence dates on feldspar show deposition ages between 51.1 ± 4.9 and 44.2 ± 3.6 kyr BP. End-member modelling was applied to grain-size-distribution data to determined sedimentation processes during Yedoma IC formation. Three to five robust end-members were detected within Yedoma IC deposits, which we interpret as different modes of primary and reworked unconfined alluvial slope and fan deposition as well as of localized eolian and fluvial sediment, which is overprinted by in situ frost weathering. The cryolithological inventory of the Yedoma IC preserved on the Buor Khaya Peninsula is closely related to the results of other IC studies, for example, to the west on the Bykovsky Peninsula, where formation time (mainly during the late Pleistocene marine isotope stages (MIS) 3 interstadial) and formation conditions were similar. Local freezing conditions on Buor Khaya, however, differed and created solute-enriched (salty) and isotopically light pore water pointing to a small talik layer and thaw-bulb freezing after deposition. Due to intense coastal erosion, the biogeochemical signature of the studied Yedoma IC represents the terrestrial end-member, and is closely related to organic matter currently being deposited in the marine realm of the Laptev Sea shelf.
    Language: English
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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