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  • 11
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    Sahel rainfall strength and onset improvements due to more realistic Atlantic cold tongue development in a climate model (2018)
    Nature Research
    In:  Scientific Reports, 8 (1). Art.No. 2569.
    Details
    Publication Date: 2021-03-19
    Description: The simulation of Sahel rainfall and its onset during the West African Monsoon (WAM) remains a challenge for current state-of-the-art climate models due to their persistent biases, especially in the tropical Atlantic region. Here we show that improved representation of Atlantic Cold Tongue (ACT) development is essential for a more realistic seasonal evolution of the WAM, which is due to a further inland migration of the precipitation maximum. The observed marked relationship between ACT development and Sahel rainfall onset only can be reproduced by a climate model, the Kiel Climate Model (KCM), when sufficiently high resolution in its atmospheric component is employed, enabling enhanced equatorial Atlantic interannual sea surface temperature variability in the ACT region relative to versions with coarser atmospheric resolution. The ACT/Sahel rainfall relationship in the model critically depends on the correct seasonal phase-locking of the interannual variability rather than on its magnitude. We compare the KCM results with those obtained from climate models participating in the Coupled Model Intercomparison Project phase 5 (CMIP5).
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.1038/s41598-018-20904-1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 12
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    Early Cretaceous South Atlantic opening - modelling the effects of geography, bathymetry and radiative forcing (2018)
    Details
    Publication Date: 2023-11-08
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Talk
  • 13
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    Early Cretaceous climate and South Atlantic opening in the Kiel Climate Model (2016)
    Details
    Publication Date: 2023-11-08
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Poster
  • 14
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    Global mean surface temperature and climate sensitivity of the early Eocene Climatic Optimum (EECO), Paleocene–Eocene Thermal Maximum (PETM), and latest Paleocene (2020)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2023-02-08
    Description: Accurate estimates of past global mean surface temperature (GMST) help to contextualise future climate change and are required to estimate the sensitivity of the climate system to CO2 forcing through Earth's history. Previous GMST estimates for the latest Paleocene and early Eocene (∼57 to 48 million years ago) span a wide range (∼9 to 23 ∘C higher than pre-industrial) and prevent an accurate assessment of climate sensitivity during this extreme greenhouse climate interval. Using the most recent data compilations, we employ a multi-method experimental framework to calculate GMST during the three DeepMIP target intervals: (1) the latest Paleocene (∼57 Ma), (2) the Paleocene–Eocene Thermal Maximum (PETM; 56 Ma), and (3) the early Eocene Climatic Optimum (EECO; 53.3 to 49.1 Ma). Using six different methodologies, we find that the average GMST estimate (66 % confidence) during the latest Paleocene, PETM, and EECO was 26.3 ∘C (22.3 to 28.3 ∘C), 31.6 ∘C (27.2 to 34.5 ∘C), and 27.0 ∘C (23.2 to 29.7 ∘C), respectively. GMST estimates from the EECO are ∼10 to 16 ∘C warmer than pre-industrial, higher than the estimate given by the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (9 to 14 ∘C higher than pre-industrial). Leveraging the large “signal” associated with these extreme warm climates, we combine estimates of GMST and CO2 from the latest Paleocene, PETM, and EECO to calculate gross estimates of the average climate sensitivity between the early Paleogene and today. We demonstrate that “bulk” equilibrium climate sensitivity (ECS; 66 % confidence) during the latest Paleocene, PETM, and EECO is 4.5 ∘C (2.4 to 6.8 ∘C), 3.6 ∘C (2.3 to 4.7 ∘C), and 3.1 ∘C (1.8 to 4.4 ∘C) per doubling of CO2. These values are generally similar to those assessed by the IPCC (1.5 to 4.5 ∘C per doubling CO2) but appear incompatible with low ECS values (〈1.5 per doubling CO2).
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 15
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    The impact of Early Cretaceous gateway evolution on ocean circulation and organic carbon burial in the emerging South Atlantic and Southern Ocean basins (2020)
    Elsevier
    Details
    Publication Date: 2023-02-08
    Description: Highlights • Nd isotope records from the South Atlantic and Southern Ocean. • New Early Cretaceous general circulation model. • Opening history of gateways on the Falkland Plateau. • Gateway opening controlled organic carbon burial. Organic carbon burial is an important driver of carbon cycle and climate dynamics on geological and shorter time scales. Ocean basins emerging during the Early Cretaceous break-up of Gondwana were primary sites of organic carbon burial, implying that their tectonic and oceanographic evolution may have affected trends and perturbations in global climate via changes in local organic carbon burial. Assessing the role of individual ocean basins in the global carbon-climate context requires a sound understanding of the processes that induced large-scale changes in carbon burial and the timing of these changes. Here we reconstruct the oceanographic evolution, and its links to organic carbon burial, in the Barremian to Albian South Atlantic and Southern Ocean basins, which may have acted as carbon sinks of global importance. Our reconstruction is based on combined seawater neodymium isotope and sedimentological records obtained from multiple deep sea drill sites and a new general circulation model. Deep water circulation within and between those basins was primarily controlled by the opening of the shallow Falkland Plateau Gateway (between ∼118 Ma and ∼113 Ma) and the deep Georgia Basin Gateway (by ∼110 Ma), for which we provide new age constraints based on biostratigraphic and carbon isotope data. The opening of these gateways was accompanied by local to basin-wide decreases in organic carbon burial, suggesting that ocean circulation affected the oxygenation state via changes in deep water ventilation. Although our data do not provide quantitative information on the impact of changes in regional organic carbon burial on the global carbon cycle, the synchronicity between the reduction of organic carbon burial in the South Atlantic basin and global warming during the Early Albian points to a strong causal relationship.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 16
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    Evidence for a regional warm bias in the Early Cretaceous TEX86 record (2020)
    Elsevier
    Details
    Publication Date: 2023-02-08
    Description: Highlights • New Early Cretaceous South Atlantic TEX86 samples and climate modelling. • Systematic differences in Cretaceous isoGDGT abundances. • Regional similarities to modern Mediterranean and Red Sea sediments. Regional TEX86-temperature calibration enables model-data congruence for OAE 1a. Abstract The Cretaceous Period (145-66 Ma) provides an opportunity to obtain insights into the adaptation of the climate system to increased atmospheric greenhouse gas concentrations. The organic paleothermometer TEX86 is one of the few proxies available for reconstructing quantitative estimates of upper ocean temperatures of this time period. Here we show that the sedimentary TEX86 signal in the Early Cretaceous North and South Atlantic shows systematic differences to other Cretaceous samples. In particular, the relative increase in the fractional abundances of the crenarchaeol isomer compared to crenarchaeol exhibits similarities with surface sediments from the modern Mediterranean and Red Sea. Dedicated climate model simulations suggest that the formation of warm and saline deep waters in the restricted North and South Atlantic may have influenced TEX86 export dynamics leading to a warm bias in reconstructed upper ocean temperatures. Applying a regional calibration from the modern Mediterranean and Red Sea to corresponding TEX86 data significantly improves the model-data fit for the Aptian Oceanic Anoxic Event 1a and the overall comparison with other temperature proxies for the Early Cretaceous. Our results demonstrate the need to consider regional and temporal changes of the TEX86-temperature relation for the reconstruction of deep-time ocean temperatures.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: other
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 17
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    Evolving ocean basins in the Early Cretaceous greenhouse: A climate model-proxy synthesis of circulation, surface temperatures and carbon burial (2019)
    In:  (PhD/ Doctoral thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 161 pp
    Details
    Publication Date: 2022-01-31
    Description: Greenhouse climates with global mean temperatures significantly higher than today prevailed during large parts of the geological history. They provide direct evidence for the adaptation of the climate system to enhanced greenhouse gas forcing during the past and represent the only possibility to constrain model-derived projections of future anthropogenic warming. The Early Cretaceous (~145-100.5 Ma) provides a special opportunity to test our understanding of past greenhouse dynamics, as the long-term warmth was punctuated by severe perturbations of the global carbon cycle and episodes of transient cooling. Young and restricted ocean basins, emerging from the break-up of Gondwana, are a possible driver of both short- and long-term carbon cycle dynamics due to their enhanced organic carbon burial potential. This thesis aims to better constrain the main drivers of the Early Cretaceous greenhouse climate and to assess how they differed from the present-day dynamics. Dedicated climate model simulations of the Early Cretaceous were integrated with paleoceanographic records of water mass mixing, surface temperatures and organic carbon burial to assess both the causes for the mean state warming, as well as to reconstruct the tectonically driven ocean circulation and carbon cycle changes.
    Type: Thesis , NonPeerReviewed
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    OceanRep: Thesis - not published by a publisher
  • 18
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    Periodic changes in the Cretaceous ocean and climate caused by marine redox see-saw (2019)
    Nature Research
    In:  Nature Geoscience, 12 (6). pp. 456-461.
    Details
    Publication Date: 2022-01-31
    Description: Periodic changes in sediment composition are usually ascribed to insolation forcing controlled by Earth’s orbital parameters. During the Cretaceous Thermal Maximum at 97–91 Myr ago (Ma), a 37–50-kyr-long cycle that is generally believed to reflect obliquity forcing dominates the sediment record. Here, we use a numerical ocean model to show that a cycle of this length can be generated by marine biogeochemical processes without applying orbital forcing. According to our model, the restricted proto-North Atlantic and Tethys basins were poorly ventilated and oscillated between iron-rich and sulfidic (euxinic) states. The Panthalassa Basin was fertilized by dissolved iron originating from the proto-North Atlantic. Hence, it was less oxygenated while the proto-North Atlantic was in an iron-rich state and better oxygenated during euxinic periods in the proto-North Atlantic. This redox see-saw was strong enough to create significant changes in atmospheric pCO2. We conclude that most of the variability in the mid-Cretaceous ocean–atmosphere system can be ascribed to the internal redox see-saw and its response to external orbital forcing.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1038/s41561-019-0359-x
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 19
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    Early Cretaceous Climate and South Atlantic opening in the Kiel Climate Model (2017)
    Details
    Publication Date: 2022-02-18
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Poster
  • 20
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    Cloud feedbacks maintain meridional temperature gradient during Early Cretaceous greenhouse climate (2017)
    In:  [Talk] In: GSA Annual Meeting 2017, 22.10.-25.10.2017, Seattle, Washington, USA .
    Details
    Publication Date: 2019-01-11
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
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