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  • 11
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    In:  EPIC3International Symposium on Cryospheric Indicators of Global Climate Change. Cambridge, England 25 August 2006., 21
    Publication Date: 2019-07-16
    Description: A major focus of the VISA project (validation and interpretaion of satellite data in Antarctica) is an enhanced knowledge of the ice-mass changes in Antarctica and validation of new satellite data with detailed groundborne measurements.We present a spatial and temporal analysis of accumulation data from the Antarctic expedition VISA-Ground 2003/2004 on the Potsdam Glacier in Dronning Maud Land, Antarctica. High-frequency GPR profiles of a total length of ca. 100 km were carried out along and perpendicular to the main glacier flow line in order to detect internal reflection horizons. Firn cores and snow pits were deployed at five selected locations of the GPR profiles. Three continuous reflection horizons of isochronic origin were tracked in the processed GPR data throughout several profiles. Firn-core analysis covered dielectric profiling (DEP), density measurements, and determination of the content of delta-O18. From the density profiles a cumulative mass-depth relation was established. The velocity distribution of the radar waves with depth was derived from the DEP data. With these models the tracked horizons were converted from travel time to depth and to cumulative mass, respectively. Annual-layer counting of 18O peaks yielded an age-depth relation that was used for dating two of the horizons. Combining the data sets allows us to determine the mean annual accumulation rate and its variation in the investigation area. The accumulation rate shows a high spatial variability with pronounced maxima and minima, with a mean of 143 kg m-2 a-1 with a standard deviation of 47%. This is less than the value of 200-250 kg m-2a-1 reported before in this region. These features can at least partly be explained by the surface topography and the surface slope indicating that windborne redistribution of snow significantly contributes to the accumulation.Generally, the accumulation decreases along the main flow line in the direction of glacier flow, indicating an ablation area further downwards. Our results provide new insight in local featuresinfluencing the accumulation rate in this area and can be used to validate satellite data aiming at the temporal and spatial variation of different physical variables being related to climatic conditions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 12
    Publication Date: 2019-07-16
    Description: Abstract:We will present preliminary results from geophysical and glaciological measurements on Potsdam Glacier, south of the Schirmacher Oasis, Central Dronning Maud Land, East Antarctica.The data were retrieved during the Antarctic summer season 2003/2004 and consist of ground penetrating radar (GPR) surveys as well as shallow firn cores and snow pits.The GPR surveys were carried out using a central frequency of 500 MHz on the main flow line of Potsdam Glacier and perpendicular to that line. The total length of the GPR profiles was about 100 km, thus covering an area of ca. 400 km2 . Traces were recorded each 0.5 m and the time window was chosen such that the upper 25-30 m of the snow pack could be covered in high resolution.The processed radar data show several internal reflection horizons indicating a change of density (or conductivity) in the subsurface.These horizons were traced throughout the profiles and will be dated by the results of the firn core analyses.The firn cores were drilled at five locations on the radar profile lines, each core being 12-13 m in length. At the same locations snow pits were digged with a depth of 2 m and a sampling interval of 5cm, giving 40 snow samples per pit.On the firn cores dielectric profiling measurements were carried out in the laboratory to determine the real part of the dielectric permittivity and the conductivity. Furthermore the density was measured as well as the content of oxygen isotope, δ18O. From the snow samples density and δ18O were determined as well.Combining the geophysical and glaciologicaldata sets gives information about the accumulation pattern and internal structures in the upper snowpack. From the firn core data models were derived giving an estimation of the distribution of the radar velocity with depth. Using these models the radar data can be converted from traveltime- to depth-sections so the depths of the different horizons are known. Furthermore mass-depth relations were established yielding information about tht cumulative snow mass for the respective radar detected layers.Δ18O-peaks in the firn core data indicating summer times help to derive annual cycles covered by the firn cores.Comparing the depths of the radar horizons with the dated firn cores allows dating of the horizons. From the cumulative snow mass of the different reflection horizons and their respective ages the mean accumulation along the radar survey lines can be estimated.So the combination of geophysical and glaciological studies provides a powerfull tool for the determination of the accumulation pattern. On Potsdam Glacier the data indicate a high spatial variability of accumulation rate along the main flow line.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 13
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    In:  EPIC3DFG Colloquim of the Priority Program "Mass transport and mass distribution in the Earth system" (SPP 1257), Potsdam.10.2010., 14
    Publication Date: 2019-07-16
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 14
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    PERGAMON-ELSEVIER SCIENCE LTD
    In:  EPIC3Journal of Geodynamics, PERGAMON-ELSEVIER SCIENCE LTD, ISSN: 0264-3707
    Publication Date: 2019-07-16
    Description: Estimation of ocean circulation is investigated via assimilation of satellite measurements of the dynamic ocean topography (DOT) into the global finite-element ocean model (FEOM). The DOT was obtained by means of a geodetic approach from carefully cross-calibrated multi-mission altimeter data and GRACE gravity fields. The spectral consistency was achieved by consistently filtering both, the sea surface and the geoid. The filter length is determined by the spatial resolution of the gravity field and corresponds to approximately 241 km half width for the GRACE-based gravity field model ITG-Grace03s. The assimilation of the geodetic DOT was performed by employing a local singular evolutive interpolated Kalman (SEIK) filter in combination with the method of weighting of observations. It is shown that this approach leads to a successful assimilation technique that reduced the RMS difference between the model and the data from 16 cm to 5 cm during one year of assimilation. The ocean model returns an optimized mean dynamic ocean topography. The effects of assimilation on transport estimates across several hydrographic World Ocean Circulation Experiment (WOCE) sections show improvements compared to the FEOM run without data assimilation. As a result of the assimilation, DOT estimates are available in the polar or coastal regions where the geodetic estimates from satellite data alone are not adequate. Furthermore, more realistic features of the ocean can be seen in these areas compared to those obtained using the filtered data fields.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 15
    Publication Date: 2019-07-17
    Description: Simulation characteristics from eighteen global ocean–sea-ice coupled models are presented with a focus on the mean Atlantic meridional overturning circulation (AMOC) and other related fields in the North Atlantic. These experiments use inter-annually varying atmospheric forcing data sets for the 60-year per- iod from 1948 to 2007 and are performed as contributions to the second phase of the Coordinated Ocean- ice Reference Experiments (CORE-II). The protocol for conducting such CORE-II experiments is summa- rized. Despite using the same atmospheric forcing, the solutions show significant differences. As most models also differ from available observations, biases in the Labrador Sea region in upper-ocean potential temperature and salinity distributions, mixed layer depths, and sea-ice cover are identified as contribu- tors to differences in AMOC. These differences in the solutions do not suggest an obvious grouping of the models based on their ocean model lineage, their vertical coordinate representations, or surface salinity restoring strengths. Thus, the solution differences among the models are attributed primarily to use of different subgrid scale parameterizations and parameter choices as well as to differences in vertica and horizontal grid resolutions in the ocean models. Use of a wide variety of sea-ice models with diverse snow and sea-ice albedo treatments also contributes to these differences. Based on the diagnostics con- sidered, the majority of the models appear suitable for use in studies involving the North Atlantic, but some models require dedicated development effort.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 16
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    Alfred Wegener Institute for Polar and Marine Research & German Society of Polar Research
    In:  EPIC3Polarforschung, Bremerhaven, Alfred Wegener Institute for Polar and Marine Research & German Society of Polar Research, 78(1/2), pp. 79-80, ISSN: 0032-2490
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: "Polarforschung" , peerRev
    Format: application/pdf
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  • 17
    Publication Date: 2021-09-21
    Description: Simulation characteristics from eighteen global ocean–sea-ice coupled models are presented with a focus on the mean Atlantic meridional overturning circulation (AMOC) and other related fields in the North Atlantic. These experiments use inter-annually varying atmospheric forcing data sets for the 60- 1 Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site year period from 1948 to 2007 and are performed as contributions to the second phase of the Coordinated Ocean-ice Reference Experiments (CORE-II). The protocol for conducting such CORE-II experiments is summarized. Despite using the same atmospheric forcing, the solutions show significant differences. As most models also differ from available observations, biases in the Labrador Sea region in upper-ocean potential temperature and salinity distributions, mixed layer depths, and sea-ice cover are identified as contributors to differences in AMOC. These differences in the solutions do not suggest an obvious grouping of the models based on their ocean model lineage, their vertical coordinate representations, or surface salinity restoring strengths. Thus, the solution differences among the models are attributed primarily to use of different subgrid scale parameterizations and parameter choices as well as to differences in vertical and horizontal grid resolutions in the ocean models. Use of a wide variety of sea-ice models with diverse snow and sea-ice albedo treatments also contributes to these differences. Based on the diagnostics considered, the majority of the models appear suitable for use in studies involving the North Atlantic, but some models require dedicated development effort.
    Description: U.S. National Science Foundation (NSF) NSF U.S. Department of Energy NOAA Climate Program Office under Climate Variability Predictability Program NA09OAR4310163 Department of Climate Change and Energy Efficiency Bureau of Meteorology CSIRO National Computational Infrastructure facility at the Australian National University Research Council of Norway through the EarthClim 207711/E10 NOTUR/NorStore projects Centre for Climate Dynamics at the Bjerknes Centre for Climate Research Italian Ministry of Education, University, and Research Italian Ministry of Environment, Land, and Sea under the GEMINA project BNP-Paribas foundation via the PRECLIDE project under the CNRS 30023488 WGOMD
    Description: Published
    Description: 76-107
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: open
    Keywords: Global ocean–sea-ice modelling ; Ocean model comparisons ; Atmospheric forcing ; Experimental design ; Atlantic meridional overturning circulation ; North Atlantic simulations ; 03. Hydrosphere::03.03. Physical::03.03.03. Interannual-to-decadal ocean variability
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 18
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/conferenceObject
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  • 19
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/conferenceObject
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  • 20
    Publication Date: 2020-05-14
    Description: A detailed and precise knowledge of ocean bottom topography is essential in many geoscientific and oceanographic applications. Shipborne echo sounding provides the only direct bathymetric method. However, even after decades of applying this technique only a fraction of the global ocean could be covered. Alternatively, gravity data inversion is a feasible method to infer ocean bottom topography since the gravity field correlates with topography at short to medium wavelengths. Gravity field observables are globally provided by dedicated satellite missions like GOCE, GRACE and GRACE-FO and, over the oceans, by satellite altimetry. Regional and local measurements are realised by means of ground-based, shipborne and airborne gravimetry. For the first time in Europe a jet aircraft was used for airborne gravimetry. During the GEOHALO flight campaign over Italy and the Tyrrhenian, Ionian and Adriatic seas in June 2012, the German research aircraft HALO carried an entire suite of geodetic-geophysical instrumentation, including gravity metres. The careful processing of the gravity data acquired by the CHEKAN-AM instrument of the German Research Centre for Geosciences allowed to achieve an accuracy at the mGal level. Subsequently, the Parker–Oldenburg inversion was applied to predict ocean bottom topography along the GEOHALO profiles flown over the ocean. To constrain the parameter space in the inversion we used the Crust1.0 model. Finally, the obtained results were compared to the General Bathymetric Chart of the Oceans in order to estimate the performance of the method. Our study demonstrates that airborne gravimetry aboard a jet aircraft is capable to provide valuable data for regional geoscientific studies.
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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