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  • 1
    Publication Date: 2015-12-22
    Description: Evidence from the joint interpretation of proxy data as well as geodynamical and biogeochemical modeling results point to complex interactions between sea level drawdown, volcanic degassing, and atmospheric CO2 that hampered the climate system’s decent into the last ice age. Ice core data shows that atmospheric CO2 dropped abruptly into glacial Marine Isotope Stage (MIS) 4 at ~71 ka, while Antarctic temperatures display a more gradual decline between ~85 ka to ~71 ka across the MIS 5/4 transition. Based on 2D and 3D geodynamical simulations, we show that a ~60-100 m sea level drop associated with the MIS 5/4 transition led to a significant increase in magma and possibly CO2 flux at mid-ocean ridges (MOR) and oceanic hotspot volcanoes. The MOR signal is assessed with 2D thermomechanical models that account for mantle melting and resolve the flux of incompatible carbon dioxide. These models have been run at different spreading rates and integrated with the global distribution of opening rates to compute global variations in magma and CO2 flux across the MIS 5/4 transition. 3D plume models have been used to quantify the impact of a dropping sea level on oceanic hotspot melting and CO2 release. Here a wide range of simulations with differing plume fluxes, lithospheric thicknesses as well as speeds, and plume excess temperatures have been integrated with data from ~40 hotspots in order to compute a global signal. Biogeochemical carbon cycle modeling shows that the predicted increase in volcanic emissions is likely to have raised atmospheric CO2 by up to 15 ppmv, sufficient to explain the bulk of the decoupling between temperature and atmospheric CO2 during the global change to pronounced glacial conditions across the MIS 5/4 transition.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 2
    Publication Date: 2016-03-15
    Description: Increasing evidences point to a more important role of volcanic CO2 outgassing in the carbon cycle than previously thought. Here we present two examples, where data or models indicate that only volcanic CO2 outgassing might explain some observed phenomena. (1) The paleo data show that atmospheric CO2 and Antarctic temperature changes are surprisingly synchronous on both millennial and orbital time scale, although there are some still unexplained exceptions. Here we show that the decoupling of temperature and CO2 around the transition into full glacial conditions around the MIS 5/4 boundary (~75kyr BP) might have been caused by the volcanic CO2 degassing, that itself was triggered by the sea level fall of 60-100m within ~10kyr. An additional volcanic CO2 release from mid ocean ridges and hotspots calculated with a state-of-the- art 3D geodynamical model to ~500 to 900 GtCO2 might explain the bulk of the ~18 ppm CO2 anomaly, that is associated with this decoupling of CO2 and temperature on orbital time scales. (2) Radiocarbon (14C) is widely used to detect the carbon that has been transferred from the atmosphere to the deep ocean during the LGM. New 14C data from a depth transect indicate that this carbon might be found at mid water depths (~3 km) in the South Pacific. However, the maximum observed anomaly in deep ocean Δ14C to the atmosphere of -1000permil can only be explained if a realistic increase in reservoir age and a hydrothermal influx of 14C-free CO2 from mid ocean ridges are considered together.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 3
    Publication Date: 2008-03-01
    Description: We present a generic algorithm for automating sedimentary basin reconstruction. Automation is achieved through the coupling of a two-dimensional thermotectonostratigraphic forward model to an inverse scheme that updates the model parameters until the input stratigraphy is fitted to a desired accuracy. The forward model solves for lithospheric thinning, flexural isostasy, sediment deposition, and transient heat flow. The inverse model updates the crustal- and mantle-thinning factors and paleowater depth. Both models combined allow for automated forward modeling of the structural and thermal evolution of extensional sedimentary basins. The potential and robustness of this method is demonstrated through a reconstruction case study of the northern Viking Graben in the North Sea. This reconstruction fits present stratigraphy, borehole temperatures, vitrinite reflectance data, and paleowater depth. The predictive power of the model is illustrated through the successful identification of possible targets along the transect, where the principal source rocks are in the oil and gas windows. These locations coincide well with known oil and gas occurrences. The key benefits of the presented algorithm are as follows: (1) only standard input data are required, (2) crustal- and mantle-thinning factors and paleowater depth are automatically computed, and (3) sedimentary basin reconstruction is greatly facilitated and can thus be more easily integrated into basin analysis and exploration risk assessment. Lars Helmuth Rüpke is a professor for sea-floor resources at the research cluster “The Future Ocean” at IFM-GEOMAR in Kiel, Germany. Before moving to Kiel, he was a senior researcher at Physics of Geological Processes at Oslo University, Norway. His present research focuses on passive margins, sedimentary basins, and fluid migration pattern through the Earth's crust. Stefan Markus Schmalholz is a senior researcher and lecturer at the Geological Institute of the Eidgenössische Technische Hochschule (ETH) Zurich, Switzerland. His present research focuses on folding and necking instabilities in rocks, low-frequency wave propagation in porous rocks, and numerical modeling of rock deformation. He holds a Ph.D. in natural sciences and a diploma in earth sciences both from ETH Zurich. Daniel Walter Schmid is a senior researcher and coordinator of the microstructures group at the Physics of Geological Processes at Oslo University, Norway. His present research focuses on small-scale rock deformation, coupling between chemical reactions and deformation, and the development of efficient numerical models. He holds a Ph.D. in geology from the ETH Zurich, Switzerland. Yuri Y. Podladchikov is a professor at Oslo University and Physics of Geological Processes.
    Print ISSN: 0149-1423
    Electronic ISSN: 1943-2674
    Topics: Geosciences
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  • 4
    Publication Date: 2019-08-13
    Description: Following Milankovitch's theory the incoming insolation or summer energy at 65°N is typically analysed to predict the waxing or waning of land ice. We here use a model-based deconvolution of the LR04 benthic-d18O stack into land ice distribution (de Boer et al., 2014, Köhler et al., 2015) to verify if the latitudinal focal point of land ice dynamics has changed over the last 2 Myr or whether this choice of 65°N in orbital data is indeed well justified. We find that the 5°-latitudinal band which contributes most to land ice albedo radiative forcing (ΔR_[LI]) is 70-75°N between 2.0-1.5 Myr, which is then until 1.0 Myr gradually substituted by 65-70°N. During the last 1 Myr both 60-65°N and 65-70°N dominate ΔR_[LI] and contribute approximately the same amount, while the relative importance of 70-75°N is shrinking. Our analyses illustrates that the choice of 65°N seems for the last 1 Myr to be well justified, while for earlier parts of the last 2 Myr the dominant land ice changes seems to happen up to 10° further to the north. Focusing on the last 800 kyr (the time for which precise data on atmospheric CO2 concentration exists) we furthermore find that the multi-millennial land ice growth and proxy-based reconstruction of global cooling (= the glaciation) appear synchronously to each other and to decreasing obliquity, but diverge from CO2. This suggests that the global cooling associated with Earth's way into an ice age as deduced in the reconstructions has to be mainly caused by the land ice albedo feedback, and is not dominated by the CO2 greenhouse forcing. One way of perceiving this CO2-glaciation divergence in reconstructions is that the reduced incoming insolation at high latitudes causes land ice growth and cooling, while there is a coexisting process that keeps CO2 at a relatively constant level. Solid Earth modeling experiments have indicated that falling sea level might lead to enhanced magma and CO2 production at mid-ocean ridges. Hasenclever et al. (2017) suggested that the combination of marine volcanism at mid-ocean ridges and at hot spot island volcanoes might react to decreasing sea level and be a potential cause for this CO2-glaciation divergence. This CO2-glaciation divergence needs to be considered, when using paleo data to quantify paleoclimate sensitivity: periods with diverging CO2 and global temperature change should be filtered out when approximating the relationship between global temperature rise and CO2 concentrations (Köhler et al., 2018). References: de Boer et al. (2014). https://doi.org/10.1038/ncomms3999. Köhler et al. (2015). https://doi.org/10.5194/cp-11-1801-2015. Hasenclever et al. (2017). https://doi.org/10.1038/ncomms15867. Köhler et al. (2018). https://doi.org/10.1029/2018GL077717.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Format: application/pdf
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  • 5
    Publication Date: 2008-03-01
    Print ISSN: 0149-1423
    Electronic ISSN: 1943-2674
    Topics: Geosciences
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  • 6
    Publication Date: 2009-10-01
    Print ISSN: 0950-091X
    Electronic ISSN: 1365-2117
    Topics: Geosciences
    Published by Wiley
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