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  • 1
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    Sea level fall during glaciation stabilized atmospheric CO2 by enhanced volcanic degassing (2017)
    Nature Research
    In:  Nature Communications, 8 (15867).
    Details
    Publication Date: 2020-06-18
    Description: Paleo-climate records and geodynamic modelling indicate the existence of complex interactions between glacial sea level changes, volcanic degassing and atmospheric CO2, which may have modulated the climate system's descent into the last ice age. Between ∼85 and 70 kyr ago, during an interval of decreasing axial tilt, the orbital component in global temperature records gradually declined, while atmospheric CO2, instead of continuing its long-term correlation with Antarctic temperature, remained relatively stable. Here, based on novel global geodynamic models and the joint interpretation of paleo-proxy data as well as biogeochemical simulations, we show that a sea level fall in this interval caused enhanced pressure-release melting in the uppermost mantle, which may have induced a surge in magma and CO2 fluxes from mid-ocean ridges and oceanic hotspot volcanoes. Our results reveal a hitherto unrecognized negative feedback between glaciation and atmospheric CO2 predominantly controlled by marine volcanism on multi-millennial timescales of ∼5,000-15,000 years.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1038/ncomms15867
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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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
    Publication Date: 2018-12-17
    Description: 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.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2017MS001056
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Reconciling glacial Antarctic water stable isotopes with ice sheet topography and the isotopic paleothermometer (2018)
    Nature Research
    In:  Nature Communications, 9 (1). Art.Nr. 3537.
    Details
    Publication Date: 2021-02-08
    Description: Stable water isotope records from Antarctica are key for our understanding of Quaternary climate variations. However, the exact quantitative interpretation of these important climate proxy records in terms of surface temperature, ice sheet height and other climatic changes is still a matter of debate. Here we report results obtained with an atmospheric general circulation model equipped with water isotopes, run at a high-spatial horizontal resolution of one-by-one degree. Comparing different glacial maximum ice sheet reconstructions, a best model data match is achieved for the PMIP3 reconstruction. Reduced West Antarctic elevation changes between 400 and 800 m lead to further improved agreement with ice core data. Our modern and glacial climate simulations support the validity of the isotopic paleothermometer approach based on the use of present-day observations and reveal that a glacial ocean state as displayed in the GLAMAP reconstruction is suitable for capturing the observed glacial isotope changes in Antarctic ice cores.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/s41467-018-05430-y
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Arctic Ocean sea ice cover during the penultimate glacial and the last interglacial (2017)
    Nature Research
    In:  Nature Communications, 8 (1). Art.Nr. 373.
    Details
    Publication Date: 2020-02-06
    Description: 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.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/s41467-017-00552-1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Abrupt North Atlantic circulation changes in response to gradual CO2 forcing in a glacial climate state (2017)
    Nature Research
    In:  Nature Geoscience, 10 (7). pp. 518-523.
    Details
    Publication Date: 2020-02-06
    Description: Glacial climate is marked by abrupt, millennial-scale climate changes known as Dansgaard–Oeschger cycles. The most pronounced stadial coolings, Heinrich events, are associated with massive iceberg discharges to the North Atlantic. These events have been linked to variations in the strength of the Atlantic meridional overturning circulation. However, the factors that lead to abrupt transitions between strong and weak circulation regimes remain unclear. Here we show that, in a fully coupled atmosphere–ocean model, gradual changes in atmospheric CO2 concentrations can trigger abrupt climate changes, associated with a regime of bi-stability of the Atlantic meridional overturning circulation under intermediate glacial conditions. We find that changes in atmospheric CO2 concentrations alter the transport of atmospheric moisture across Central America, which modulates the freshwater budget of the North Atlantic and hence deep-water formation. In our simulations, a change in atmospheric CO2 levels of about 15 ppmv—comparable to variations during Dansgaard–Oeschger cycles containing Heinrich events—is sufficient to cause transitions between a weak stadial and a strong interstadial circulation mode. Because changes in the Atlantic meridional overturning circulation are thought to alter atmospheric CO2 levels, we infer that atmospheric CO2 may serve as a negative feedback to transitions between strong and weak circulation modes.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/NGEO2974
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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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
    Publication Date: 2019-02-01
    Description: 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.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2016GL067818
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    LakeCC: a tool for efficiently identifying lake basins with application to palaeogeographic reconstructions of North America (2020)
    Wiley
    Details
    Publication Date: 2023-02-08
    Description: Along the margins of continental ice sheets, lakes formed in isostatically depressed basins duringglacial retreat. Their shorelines and extent are sensitive to the ice margin and the glacial history of the region.Proglacial lakes, in turn, also impact the glacial isostatic adjustment due to loading, and ice dynamics by posing amarine‐like boundary condition at the ice margin. In this study we present a tool that efficiently identifies lake basinsand the corresponding maximum water level for a given ice sheet and topography reconstruction. This algorithm,called the LakeCC model, iteratively checks the whole map for a set of increasing water levels and fills isolated basinsuntil they overflow into the ocean. We apply it to the present‐day Great Lakes and the results show good agreement(∼1−4%) with measured lake volume and depth. We then apply it to two topography reconstructions of NorthAmerica between the Last Glacial Maximum and the present. The model successfully reconstructs glacial lakes suchas Lake Agassiz, Lake McConnell and the predecessors of the Great Lakes. LakeCC can be used to judge the quality ofice sheet reconstructions.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Challenges in the Paleoclimatic Evolution of the Arctic and Subarctic Pacific since the Last Glacial Period—The Sino–German Pacific–Arctic Experiment (SiGePAX) (2019)
    MDPI
    In:  Challenges, 10 (1). Art.Nr. 13.
    Details
    Publication Date: 2021-01-08
    Description: Arctic and subarctic regions are sensitive to climate change and, reversely, provide dramatic feedbacks to the global climate. With a focus on discovering paleoclimate and paleoceanographic evolution in the Arctic and Northwest Pacific Oceans during the last 20,000 years, we proposed this German–Sino cooperation program according to the announcement “Federal Ministry of Education and Research (BMBF) of the Federal Republic of Germany for a German–Sino cooperation program in the marine and polar research”. Our proposed program integrates the advantages of the Arctic and Subarctic marine sediment studies in AWI (Alfred Wegener Institute) and FIO (First Institute of Oceanography). For the first time, the collection of sediment cores can cover all climatological key regions in the Arctic and Northwest Pacific Oceans. Furthermore, the climate modeling work at AWI enables a “Data-Model Syntheses”, which are crucial for exploring the underlying mechanisms of observed changes in proxy records.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3390/challe10010013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Spatio-temporal variability of processes across Antarctic ice-bed–ocean interfaces (2018)
    Nature Research
    In:  Nature Communications, 9 (1). Art.Nr. 2289.
    Details
    Publication Date: 2021-02-08
    Description: Understanding how the Antarctic ice sheet will respond to global warming relies on knowledge of how it has behaved in the past. The use of numerical models, the only means to quantitatively predict the future, is hindered by limitations to topographic data both now and in the past, and in knowledge of how subsurface oceanic, glaciological and hydrological processes interact. Incorporating the variety and interplay of such processes, operating at multiple spatio-temporal scales, is critical to modeling the Antarctic’s system evolution and requires direct observations in challenging locations. As these processes do not observe disciplinary boundaries neither should our future research.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/s41467-018-04583-0
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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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
    Publication Date: 2024-02-07
    Description: 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.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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