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  • 1
    Book
    Book
    Variabilität von CH2O (Formaldehyd) : untersucht mit Hilfe der solaren Absorptionsspektroskopie und Modellen : determined by solar absorption spectroscopy and model studies = Variability of CH2O (Formaldehyde) (2001)
    Bremerhaven : Alfred-Wegener-Inst. für Polar- und Meeresforschung
    Details Availability
    Keywords: Air Pollution ; Polar regions ; Formaldehyde Environmental aspects ; Polar regions ; Spectrum, Solar ; Arktis ; Dissertation ; Spurengas ; Atmosphäre ; Hochschulschrift ; Atmosphäre ; Formaldehydbelastung
    Type of Medium: Book
    Pages: VII, 131 S. , graph. Darst., Kt.
    Series Statement: Berichte zur Polar- und Meeresforschung 401
    URL: https://www.gbv.de/dms/tib-ub-hannover/335737153.pdf
    RVK:
    RY 20075
    Language: German , English
    Note: Literaturverz. S. 107 - 127 , Intermediärsprache: Englisch , Zugl.:Berlin, Freie Univ., Diss., 2001 u.d.T.: Albrecht, Torsten: @Variationen von CH2O - untersucht mit Hilfe der solaren Absorptionsspektroskopie und Modellen
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  • 2
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    PISM glacial cycle sensitivity experiments of the Antarctic Ice Sheet (2019)
    PANGAEA
    In:  Supplement to: Albrecht, Torsten; Winkelmann, Ricarda; Levermann, Anders (2020): Glacial-cycle simulations of the Antarctic Ice Sheet with the Parallel Ice Sheet Model (PISM) - Part 1: Boundary conditions and climatic forcing. The Cryosphere, 14(2), 599-632, https://doi.org/10.5194/tc-14-599-2020
    Details
    Publication Date: 2023-10-28
    Description: This dataset contains PISM simulation results (http://www.pism-docs.org) of the Antarctic Ice Sheet based on code release v1.0-paleo-ensemble (https://doi.org/10.5281/zenodo.3574033). PISM is the open-source Parallel Ice Sheet Model developed mainly at UAF, USA and PIK, Germany. With the help of added python scripts, all figures can be reproduced as in the journal publication: - Albrecht et al., 2020, doi:10.5194/tc-14-599-2020. --- Data: Find PISM results as netCDF data. See 'README.md' for a list of all performed experiment. All forcing input data for the experiments and plots can be downloaded and remapped via https://github.com/pism/pism-ais. Some of the original input data files are freely available, for others please contact the author or the corresponding data publisher. Figure plotting scripts (jupyter notebook based on python, see https://jupyter.org) in 'plot_scripts' access the uploaded PISM results in 'model_data' and save the plots to 'final_figures'. Jupyter notebook can be run in the browser and shared, see https://nbviewer.jupyter.org/url/www.pik-potsdam.de/~albrecht/notebooks/paleo_paper/paleo_paper_final.ipynb. --- Contact: Albrecht, Torsten (albrecht@pik-potdam.de) ; Potsdam-Institute for Climate Impact Research (PIK), Potsdam, Germany
    Keywords: Antarctica; Antarctic Ice Sheet; Glacial cycles; glacial isostatic adjustment; paleo modeling; pan-Antarctica; Parallel Ice Sheet Model; PISM; Priority Programme 1158 Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas; SPP1158
    Type: Dataset
    Format: application/zip, 1.8 GBytes
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    DATA PANGAEA
  • 3
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    PISM parameter ensemble analysis of Antarctic Ice Sheet glacial cycle simulations - additional data (2022)
    PANGAEA
    Details
    Publication Date: 2024-04-20
    Description: This dataset contains PISM simulation results of the Antarctic Ice Sheet based on code release v1.0-paleo-ensemble (https://doi.org/10.5281/zenodo.3574033). PISM is the open-source Parallel Ice Sheet Model developed mainly at UAF, USA and PIK, Germany. See documentation in https://www.pism.io. These are additional netCDF data from the same ensemble simulations already stored in doi:10.1594/PANGAEA.909728. 1) 1000-year snapshots since 125000 years before present, of ice thickness, bed topography, change in bed topography, floating/grounded mask, surface elevation, basal melt rate and vertically averaged velocity magnitude (SIA+SSA) (16GB) 2) 5000-year snapshots since 125000 years before present, SSA velocity components in x and y direction (8GB)
    Keywords: Antarctic Ice Sheet; Binary Object; Binary Object (File Size); Binary Object (MD5 Hash); Ensemble Analysis; Glacial cycles; glacial isostatic adjustment; Paleo Modelling; PalMod; pan-Antarctica; Parallel Ice Sheet Model; PISM; Priority Programme 1158 Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas; SPP1158
    Type: Dataset
    Format: text/tab-separated-values, 2 data points
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    DATA PANGAEA
  • 4
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    PISM parameter ensemble analysis of Antarctic Ice Sheet glacial cycle simulations (2019)
    PANGAEA
    In:  Supplement to: Albrecht, Torsten; Winkelmann, Ricarda; Levermann, Anders (2020): Glacial-cycle simulations of the Antarctic Ice Sheet with the Parallel Ice Sheet Model (PISM) - Part 2: Parameter ensemble analysis. The Cryosphere, 14(2), 633-656, https://doi.org/10.5194/tc-14-633-2020
    Details
    Publication Date: 2024-04-20
    Description: This dataset contains PISM simulation results of the Antarctic Ice Sheet based on code release v1.0-paleo-ensemble (https://doi.org/10.5281/zenodo.3574033). PISM is the open-source Parallel Ice Sheet Model developed mainly at UAF, USA and PIK, Germany. See documentation in http://www.pism-docs.org. With the help of the added jupyter notebook (Python 2.7.3), all figures can be reproduced as published in the article: - Albrecht et al., 2020, doi:10.5194/tc-14-633-2020. --- Data: Find PISM results as netCDF data. See 'README.md' for a list of all performed experiment. All forcing input data for the experiments and plots can be downloaded and remapped via https://github.com/pism/pism-ais. Some of the original input data files are freely available, for others please contact the author or the corresponding data publisher. The jupyter notebook (https://jupyter.org) paleo_paper2_final.ipynb (based on python) in 'plot_scripts' accesses the uploaded PISM results in 'model_data' or 'supplement' and saves the plots as vector and pixel graphics to 'final_figures'. Edit header for changing work paths. Jupyter notebook can be run in the browser and shared, see https://nbviewer.jupyter.org/url/www.pik-potsdam.de/~albrecht/notebooks/paleo_paper/paleo_paper2_final.ipynb. --- Methods: The scoring scheme with respect to modern and paleo data based on Python 2.7.3 can be downloaded from (https://doi.org/10.5281/zenodo.3585118). The ensemble analysis calculates misfits to the paleo constraint database AntICEdat (Briggs & Tarasov, 2013) and to RAISED Consortium (2014) as well as to modern ice geometry from Bedmap2 (Fretwell et al., 2013), ice speed (Rignot et al., 2011) an GPS (Whitehouse et al., 2011). The analysis is based on Pollard et al., (2016) and Briggs et al., (2014). --- Contact : Albrecht, Torsten (albrecht@pik-potdam.de) ; Potsdam-Institute for Climate Impact Research (PIK), Potsdam, Germany
    Keywords: Antarctic Ice Sheet; Ensemble Analysis; Glacial cycles; glacial isostatic adjustment; pan-Antarctica; Parallel Ice Sheet Model; PISM; Priority Programme 1158 Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas; SPP1158
    Type: Dataset
    Format: application/zip, 5.5 GBytes
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    DATA PANGAEA
  • 5
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    Antarctic sub-shelf melt rates via PICO (2018)
    Copernicus Publications (EGU)
    In:  The Cryosphere, 12 (6). pp. 1969-1985.
    Details
    Publication Date: 2018-12-17
    Description: Ocean-induced melting below ice shelves is one of the dominant drivers for mass loss from the Antarctic Ice Sheet at present. An appropriate representation of sub-shelf melt rates is therefore essential for model simulations of marine-based ice sheet evolution. Continental-scale ice sheet models often rely on simple melt-parameterizations, in particular for long-term simulations, when fully coupled ice–ocean interaction becomes computationally too expensive. Such parameterizations can account for the influence of the local depth of the ice-shelf draft or its slope on melting. However, they do not capture the effect of ocean circulation underneath the ice shelf. Here we present the Potsdam Ice-shelf Cavity mOdel (PICO), which simulates the vertical overturning circulation in ice-shelf cavities and thus enables the computation of sub-shelf melt rates consistent with this circulation. PICO is based on an ocean box model that coarsely resolves ice shelf cavities and uses a boundary layer melt formulation. We implement it as a module of the Parallel Ice Sheet Model (PISM) and evaluate its performance under present-day conditions of the Southern Ocean. We identify a set of parameters that yield two-dimensional melt rate fields that qualitatively reproduce the typical pattern of comparably high melting near the grounding line and lower melting or refreezing towards the calving front. PICO captures the wide range of melt rates observed for Antarctic ice shelves, with an average of about 0.1m a−1 for cold sub-shelf cavities, for example, underneath Ross or Ronne ice shelves, to 16m a−1 for warm cavities such as in the Amundsen Sea region. This makes PICO a computationally feasible and more physical alternative to melt parameterizations purely based on ice draft geometry.
    Type: Article , PeerReviewed
    Format: text
    Format: archive
    DOI: 10.5194/tc-12-1969-2018
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    The role of history and strength of the oceanic forcing in sea level projections from Antarctica with the Parallel Ice Sheet Model (2020)
    Copernicus Publications (EGU)
    In:  The Cryosphere, 14 (9). pp. 3097-3110.
    Details
    Publication Date: 2021-01-08
    Description: Mass loss from the Antarctic Ice Sheet constitutes the largest uncertainty in projections of future sea level rise. Ocean-driven melting underneath the floating ice shelves and subsequent acceleration of the inland ice streams are the major reasons for currently observed mass loss from Antarctica and are expected to become more important in the future. Here we show that for projections of future mass loss from the Antarctic Ice Sheet, it is essential (1) to better constrain the sensitivity of sub-shelf melt rates to ocean warming and (2) to include the historic trajectory of the ice sheet. In particular, we find that while the ice sheet response in simulations using the Parallel Ice Sheet Model is comparable to the median response of models in three Antarctic Ice Sheet Intercomparison projects – initMIP, LARMIP-2 and ISMIP6 – conducted with a range of ice sheet models, the projected 21st century sea level contribution differs significantly depending on these two factors. For the highest emission scenario RCP8.5, this leads to projected ice loss ranging from 1.4 to 4.0 cm of sea level equivalent in simulations in which ISMIP6 ocean forcing drives the PICO ocean box model where parameter tuning leads to a comparably low sub-shelf melt sensitivity and in which no surface forcing is applied. This is opposed to a likely range of 9.1 to 35.8 cm using the exact same initial setup, but emulated from the LARMIP-2 experiments with a higher melt sensitivity, even though both projects use forcing from climate models and melt rates are calibrated with previous oceanographic studies. Furthermore, using two initial states, one with a previous historic simulation from 1850 to 2014 and one starting from a steady state, we show that while differences between the ice sheet configurations in 2015 seem marginal at first sight, the historic simulation increases the susceptibility of the ice sheet to ocean warming, thereby increasing mass loss from 2015 to 2100 by 5 % to 50 %. Hindcasting past ice sheet changes with numerical models would thus provide valuable tools to better constrain projections. Our results emphasize that the uncertainty that arises from the forcing is of the same order of magnitude as the ice dynamic response for future sea level projections.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.5194/tc-14-3097-2020
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century (2020)
    Copernicus Publications (EGU)
    In:  The Cryosphere, 14 (9). pp. 3033-3070.
    Details
    Publication Date: 2021-01-08
    Description: Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in response to different climate scenarios and assess the mass loss that would contribute to future sea level rise. However, there is currently no consensus on estimates of the future mass balance of the ice sheet, primarily because of differences in the representation of physical processes, forcings employed and initial states of ice sheet models. This study presents results from ice flow model simulations from 13 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015–2100 as part of the Ice Sheet Model Intercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climate model results. Simulations of the Antarctic ice sheet contribution to sea level rise in response to increased warming during this period varies between −7.8 and 30.0 cm of sea level equivalent (SLE) under Representative Concentration Pathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment with constant climate conditions and should therefore be added to the mass loss contribution under climate conditions similar to present-day conditions over the same period. The simulated evolution of the West Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica mass change varies between −6.1 and 8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional simulated mass loss of 28 mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared to simulations done under present-day conditions for the two CMIP5 forcings used and display limited mass gain in East Antarctica.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/tc-14-3033-2020
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    initMIP-Antarctica: an ice sheet model initialization experiment of ISMIP6 (2019)
    Copernicus Publications (EGU)
    In:  The Cryosphere, 13 (5). pp. 1441-1471.
    Details
    Publication Date: 2021-01-08
    Description: Ice sheet numerical modeling is an important tool to estimate the dynamic contribution of the Antarctic ice sheet to sea level rise over the coming centuries. The influence of initial conditions on ice sheet model simulations, however, is still unclear. To better understand this influence, an initial state intercomparison exercise (initMIP) has been developed to compare, evaluate, and improve initialization procedures and estimate their impact on century-scale simulations. initMIP is the first set of experiments of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), which is the primary Coupled Model Intercomparison Project Phase 6 (CMIP6) activity focusing on the Greenland and Antarctic ice sheets. Following initMIP-Greenland, initMIP-Antarctica has been designed to explore uncertainties associated with model initialization and spin-up and to evaluate the impact of changes in external forcings. Starting from the state of the Antarctic ice sheet at the end of the initialization procedure, three forward experiments are each run for 100 years: a control run, a run with a surface mass balance anomaly, and a run with a basal melting anomaly beneath floating ice. This study presents the results of initMIP-Antarctica from 25 simulations performed by 16 international modeling groups. The submitted results use different initial conditions and initialization methods, as well as ice flow model parameters and reference external forcings. We find a good agreement among model responses to the surface mass balance anomaly but large variations in responses to the basal melting anomaly. These variations can be attributed to differences in the extent of ice shelves and their upstream tributaries, the numerical treatment of grounding line, and the initial ocean conditions applied, suggesting that ongoing efforts to better represent ice shelves in continental-scale models should continue.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/tc-13-1441-2019
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2) (2020)
    Copernicus Publications (EGU)
    In:  Earth System Dynamics, 11 (1). pp. 35-76.
    Details
    Publication Date: 2021-01-08
    Description: The sea level contribution of the Antarctic ice sheet constitutes a large uncertainty in future sea level projections. Here we apply a linear response theory approach to 16 state-of-the-art ice sheet models to estimate the Antarctic ice sheet contribution from basal ice shelf melting within the 21st century. The purpose of this computation is to estimate the uncertainty of Antarctica's future contribution to global sea level rise that arises from large uncertainty in the oceanic forcing and the associated ice shelf melting. Ice shelf melting is considered to be a major if not the largest perturbation of the ice sheet's flow into the ocean. However, by computing only the sea level contribution in response to ice shelf melting, our study is neglecting a number of processes such as surface-mass-balance-related contributions. In assuming linear response theory, we are able to capture complex temporal responses of the ice sheets, but we neglect any self-dampening or self-amplifying processes. This is particularly relevant in situations in which an instability is dominating the ice loss. The results obtained here are thus relevant, in particular wherever the ice loss is dominated by the forcing as opposed to an internal instability, for example in strong ocean warming scenarios. In order to allow for comparison the methodology was chosen to be exactly the same as in an earlier study (Levermann et al., 2014) but with 16 instead of 5 ice sheet models. We include uncertainty in the atmospheric warming response to carbon emissions (full range of CMIP5 climate model sensitivities), uncertainty in the oceanic transport to the Southern Ocean (obtained from the time-delayed and scaled oceanic subsurface warming in CMIP5 models in relation to the global mean surface warming), and the observed range of responses of basal ice shelf melting to oceanic warming outside the ice shelf cavity. This uncertainty in basal ice shelf melting is then convoluted with the linear response functions of each of the 16 ice sheet models to obtain the ice flow response to the individual global warming path. The model median for the observational period from 1992 to 2017 of the ice loss due to basal ice shelf melting is 10.2 mm, with a likely range between 5.2 and 21.3 mm. For the same period the Antarctic ice sheet lost mass equivalent to 7.4 mm of global sea level rise, with a standard deviation of 3.7 mm (Shepherd et al., 2018) including all processes, especially surface-mass-balance changes. For the unabated warming path, Representative Concentration Pathway 8.5 (RCP8.5), we obtain a median contribution of the Antarctic ice sheet to global mean sea level rise from basal ice shelf melting within the 21st century of 17 cm, with a likely range (66th percentile around the mean) between 9 and 36 cm and a very likely range (90th percentile around the mean) between 6 and 58 cm. For the RCP2.6 warming path, which will keep the global mean temperature below 2 ∘C of global warming and is thus consistent with the Paris Climate Agreement, the procedure yields a median of 13 cm of global mean sea level contribution. The likely range for the RCP2.6 scenario is between 7 and 24 cm, and the very likely range is between 4 and 37 cm. The structural uncertainties in the method do not allow for an interpretation of any higher uncertainty percentiles. We provide projections for the five Antarctic regions and for each model and each scenario separately. The rate of sea level contribution is highest under the RCP8.5 scenario. The maximum within the 21st century of the median value is 4 cm per decade, with a likely range between 2 and 9 cm per decade and a very likely range between 1 and 14 cm per decade.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.5194/esd-11-35-2020
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    The hysteresis of the Antarctic Ice Sheet (2020)
    Nature Research
    Details
    Publication Date: 2023-02-08
    Description: More than half of Earth’s freshwater resources are held by the Antarctic Ice Sheet, which thus represents by far the largest potential source for global sea-level rise under future warming conditions1. Its long-term stability determines the fate of our coastal cities and cultural heritage. Feedbacks between ice, atmosphere, ocean, and the solid Earth give rise to potential nonlinearities in its response to temperature changes. So far, we are lacking a comprehensive stability analysis of the Antarctic Ice Sheet for different amounts of global warming. Here we show that the Antarctic Ice Sheet exhibits a multitude of temperature thresholds beyond which ice loss is irreversible. Consistent with palaeodata2 we find, using the Parallel Ice Sheet Model3,4,5, that at global warming levels around 2 degrees Celsius above pre-industrial levels, West Antarctica is committed to long-term partial collapse owing to the marine ice-sheet instability. Between 6 and 9 degrees of warming above pre-industrial levels, the loss of more than 70 per cent of the present-day ice volume is triggered, mainly caused by the surface elevation feedback. At more than 10 degrees of warming above pre-industrial levels, Antarctica is committed to become virtually ice-free. The ice sheet’s temperature sensitivity is 1.3 metres of sea-level equivalent per degree of warming up to 2 degrees above pre-industrial levels, almost doubling to 2.4 metres per degree of warming between 2 and 6 degrees and increasing to about 10 metres per degree of warming between 6 and 9 degrees. Each of these thresholds gives rise to hysteresis behaviour: that is, the currently observed ice-sheet configuration is not regained even if temperatures are reversed to present-day levels. In particular, the West Antarctic Ice Sheet does not regrow to its modern extent until temperatures are at least one degree Celsius lower than pre-industrial levels. Our results show that if the Paris Agreement is not met, Antarctica’s long-term sea-level contribution will dramatically increase and exceed that of all other sources.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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