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  • PANGAEA  (484)
  • Springer Nature  (9)
  • AGU (American Geophysical Union)  (7)
  • Nature Publishing Group  (5)
Publikationsart
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Erscheinungszeitraum
  • 1
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    Simulating climate and stable water isotopes during the Last Interglacial using a coupled climate-isotope model (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Advances in Modeling Earth Systems, 9 (5). pp. 2027-2045.
    Details
    Publikationsdatum: 2018-12-17
    Beschreibung: Understanding the dynamics of warm climate states has gained increasing importance in the face of anthropogenic climate change, and while it is possible to simulate warm interglacial climates, these simulated results cannot be evaluated without the aid of geochemical proxies. One such proxy is δ18O, which allows for inference about both a climate state's hydrology and temperature. We utilize a stable water isotope equipped climate model to simulate three stages during the Last Interglacial (LIG), corresponding to 130, 125, and 120 kyr before present, using forcings for orbital configuration as well as greenhouse gases. We discover heterogeneous responses in the mean δ18O signal to the climate forcing, with large areas of depletion in the LIG δ18O signal over the tropical Atlantic, the Sahel, and the Indian subcontinent, and with enrichment over the Pacific and Arctic Oceans. While we find that the climatology mean relationship between δ18O and temperature remains stable during the LIG, we also discover that this relationship is not spatially consistent. Our results suggest that great care must be taken when comparing δ18O records of different paleoclimate archives with the results of climate models as both the qualitative and quantitative interpretation of δ18O variations as a proxy for past temperature changes may be problematic due to the complexity of the signals.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2017MS001056
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  • 2
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    Ocean temperature thresholds for Last Interglacial West Antarctic Ice Sheet collapse (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 43 (6). pp. 2675-2682.
    Details
    Publikationsdatum: 2019-02-01
    Beschreibung: The West Antarctic Ice Sheet (WAIS) is considered the major contributor to global sea level rise in the Last Interglacial (LIG) and potentially in the future. Exposed fossil reef terraces suggest sea levels in excess of 7 m in the last warm era, of which probably not much more than 2 m are considered to originate from melting of the Greenland Ice Sheet. We simulate the evolution of the Antarctic Ice Sheet during the LIG with a 3‐D thermomechanical ice sheet model forced by an atmosphere‐ocean general circulation model (AOGCM). Our results show that high LIG sea levels cannot be reproduced with the atmosphere‐ocean forcing delivered by current AOGCMs. However, when taking reconstructed Southern Ocean temperature anomalies of several degrees, sensitivity studies indicate a Southern Ocean temperature anomaly threshold for total WAIS collapse of 2–3°C, accounting for a sea level rise of 3–4 m during the LIG. Potential future Antarctic Ice Sheet dynamics range from a moderate retreat to a complete collapse, depending on rate and amplitude of warming.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2016GL067818
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  • 3
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    Abrupt climate and weather changes across time scales (2020)
    AGU (American Geophysical Union)
    Details
    Publikationsdatum: 2023-02-08
    Beschreibung: The past provides evidence of abrupt climate shifts and changes in the frequency of climate and weather extremes. We explore the non‐linear response to orbital forcing and then consider climate millennial variability down to daily weather events. Orbital changes are translated into regional responses in temperature, where the precessional response is related to nonlinearities and seasonal biases in the system. We question regularities found in climate events by analyzing the distribution of inter‐event waiting times. Periodicities of about 900 and 1150 years are found in ice cores besides the prominent 1500‐years cycle. However, the variability remains indistinguishable from a random process, suggesting that centennial‐to‐millennial variability is stochastic in nature. New numerical techniques are developed allowing for a high resolution in the dynamically relevant regions like coasts, major upwelling regions, and high latitudes. Using this model, we find a strong sensitivity of the Atlantic meridional overturning circulation depending on where the deglacial meltwater is injected into. Meltwater into the Mississippi and near Labrador hardly affect the large‐scale ocean circulation, whereas subpolar hosing mimicking icebergs yields a quasi shutdown. The same multi‐scale approach is applied to radiocarbon simulations enabling a dynamical interpretation of marine sediment cores. Finally, abrupt climate events also have counterparts in the recent climate records, revealing a close link between climate variability, the statistics of North Atlantic weather patterns, and extreme events.
    Materialart: Article , PeerReviewed
    Format: text
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  • 4
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    Climate Noise Influences Ice Sheet Mean State (2019)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 46 (16). pp. 9690-9699.
    Details
    Publikationsdatum: 2022-01-31
    Beschreibung: Evidence from proxy records indicates that millennial‐scale abrupt climate shifts, called Dansgaard‐Oeschger events, happened during past glacial cycles. Various studies have been conducted to uncover the physical mechanism behind them, based on the assumption that climate mean state determines the variability. However, our study shows that the Dansgaard‐Oeschger events can regulate the mean state of the Northern Hemisphere ice sheets. Sensitivity experiments show that the simulated mean state is influenced by the amplitude of the climatic noise. The most likely cause of this phenomenon is the nonlinear response of the surface mass balance to temperature. It could also cause the retreat processes to be faster than the buildup processes within a glacial cycle. We propose that the climate variability hindered ice sheet development and prevented the Earth system from entering a full glacial state from Marine Isotope Stage 4 to Marine Isotope Stage 3 about 60,000 years ago.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2019GL083717
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  • 5
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    On timescales and reversibility of the ocean's response to enhanced Greenland Ice Sheet melting in comprehensive climate models (2022)
    AGU (American Geophysical Union) | Wiley
    Details
    Publikationsdatum: 2024-02-07
    Beschreibung: Warming of the North Atlantic region in climate history often was associated with massive melting of the Greenland Ice Sheet. To identify the meltwater’s impacts and isolate these from internal variability and other global warming factors, we run single-forcing simulations including small ensembles using three complex climate models differing only in their ocean components. In 200-year long pre-industrial climate simulations, we identify robust consequences of abruptly increasing Greenland runoff by 0.05 Sv: sea-level rise of 44±10 cm, subpolar North Atlantic surface cooling of 0.7˚C and a moderate AMOC decline of 1.1–2.0 Sv. The latter two emerge in under three decades—and reverse on the same timescale after the perturbation ends in year 100. The ocean translates the step-change perturbation into a multi-decadal to centennial signature in the deep overturning circulation. In all simulations, internal variability creates notable uncertainty in estimating trends, time of emergence and duration of the response.
    Materialart: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
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  • 6
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    No Consistent Simulated Trends in the Atlantic Meridional Overturning Circulation for the Past 6,000 Years (2023)
    AGU (American Geophysical Union) | Wiley
    Details
    Publikationsdatum: 2024-02-07
    Beschreibung: The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the North Atlantic with global ocean impacts. The AMOC's response to past changes in forcings during the Holocene provides important context for the coming centuries. Here, we investigate AMOC trends using an emerging set of transient simulations using multiple global climate models for the past 6,000 years. Although some models show changes, no consistent trend in overall AMOC strength during the mid-to-late Holocene emerges from the ensemble. We interpret this result to suggest no overall change in AMOC, which fits with our assessment of available proxy reconstructions. The decadal variability of the AMOC does not change in ensemble during the mid- and late-Holocene. There are interesting AMOC changes seen in the early Holocene, but their nature depends a lot on which inputs are used to drive the experiment.
    Materialart: Article , PeerReviewed
    Format: text
    Format: text
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  • 7
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    Simulated response of the mid-Holocene Atlantic meridional overturning circulation in ECHAM6-FESOM/MPIOM (2016)
    AGU (American Geophysical Union) | Wiley
    Details
    Publikationsdatum: 2023-08-01
    Beschreibung: Changes of the Atlantic meridional overturning circulation (AMOC) in the mid‐Holocene compared to the preindustrial state are explored in different coupled climate models. Using time‐slice integrations by a newly developed global finite‐element model ECHAM6‐FESOM with unstructured mesh and high resolution, our simulations show an enhanced mid‐Holocene AMOC, accompanied by an increase in the ocean salinity over regions of deep water formation. We identify two different processes affecting the AMOC: (1) a more positive phase of North Atlantic Oscillation (NAO) increased water density over the Labrador Sea through anomalous net evaporation and surface heat loss; (2) a decreased import of sea ice from the Arctic causes a freshwater reduction in the northern North Atlantic Ocean. Using the coupled model ECHAM6‐MPIOM in T63GR15 and T31GR30 grids, we find that the simulated AMOC has significant discrepancy with different model resolutions. In detail, stronger‐than‐present mid‐Holocene AMOC is revealed by simulations with the T63GR15 grid, which resembles the result of ECHAM6‐FESOM, while a decline of the mid‐Holocene AMOC is simulated by the low resolution model with the T31GR30 grid. Such discrepancy can be attributed to different changes in Labrador Sea density which is mainly affected by (1) NAO‐induced net precipitation and deep water convection, (2) freshwater transport from the Arctic Ocean, and (3) the strength of AMOC itself. Finally, we analyzed available coupled climate models showing a diversity of responses of AMOC to mid‐Holocene forcings, most of which reveal positive AMOC changes related to northern high latitudes salinification.
    Materialart: Article , PeerReviewed
    Format: text
    Format: text
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  • 8
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    Biomarker data of four sediment cores from the Arctic Ocean (2017)
    PANGAEA
    In:  Supplement to: Stein, Ruediger; Fahl, Kirsten; Gierz, Paul; Niessen, Frank; Lohmann, Gerrit (2017): Arctic Ocean sea ice cover during the penultimate glacial and the last interglacial. Nature Communications, 8(1), 13 pp, https://doi.org/10.1038/s41467-017-00552-1
    Details
    Publikationsdatum: 2023-03-16
    Beschreibung: Coinciding with global warming, Arctic sea ice has rapidly decreased during the last four decades and climate scenarios suggest that sea ice may completely disappear during summer within the next about 50-100 years. Here we produce Arctic sea ice biomarker proxy records for the penultimate glacial (Marine Isotope Stage 6) and the subsequent last interglacial (Marine Isotope Stage 5e). The latter is a time interval when the high latitudes were significantly warmer than today. We document that even under such warmer climate conditions, sea ice existed in the central Arctic Ocean during summer, whereas sea ice was significantly reduced along the Barents Sea continental margin influenced by Atlantic Water inflow. Our proxy reconstruction of the last interglacial sea ice cover is supported by climate simulations, although some proxy data/model inconsistencies still exist. During late Marine Isotope Stage 6, polynya-type conditions occurred off the major ice sheets along the northern Barents and East Siberian continental margins, contradicting a giant Marine Isotope Stage 6 ice shelf that covered the entire Arctic Ocean.
    Schlagwort(e): AWI_Paleo; Paleoenvironmental Reconstructions from Marine Sediments @ AWI
    Materialart: Dataset
    Format: application/zip, 4 datasets
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    DATA PANGAEA
  • 9
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    COSMOS model simulations of NAO-like variability during middle Oligocene (2018)
    PANGAEA
    Details
    Publikationsdatum: 2023-03-16
    Schlagwort(e): AWI_Paleo; File format; File name; File size; Paleoenvironmental Reconstructions from Marine Sediments @ AWI; Uniform resource locator/link to file
    Materialart: Dataset
    Format: text/tab-separated-values, 12 data points
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    DATA PANGAEA
  • 10
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    Satellite derived and ice model data off Western Antarctic Peninsula (2020)
    PANGAEA
    Details
    Publikationsdatum: 2023-03-16
    Schlagwort(e): Antarctic sea ice; AWI_Envi; File content; File format; File name; File size; highly branched isoprenoids; IPSO25; Paleoclimate; Polar Terrestrial Environmental Systems @ AWI; sea ice proxy; Uniform resource locator/link to file
    Materialart: Dataset
    Format: text/tab-separated-values, 10 data points
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    DATA PANGAEA
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