Digital Twin for Paleoclimate
Funding programm: AWI INSPIRES, International Science Program for Integrative Research in Earth Systems
Cost (Kostenstelle): PS 87010201
Project duration: 2021 - 2027
Principal investigator: Prof. Dr. Gerrit Lohmann
co-PIs: Gregor Knorr, Johann Klages, Thomas Jung, Karsten Gohl
PhD Candidate: Alexander Thorneloe
The aim is to evaluate the processes leading to Antarctic and Southern Ocean warming, deep-water formation, and to examine the feedbacks on long time scales. This will include the explicit simulation of the geometry of the cavities, vertical stratification and surface ocean processes. We will use the paleoclimatic information to assess further the impact of external forcing (solar insolation, CO2 and tectonic changes) as well as on internal variability and extremes in the atmosphere-ocean-ice system (Lohmann et al., 2020). The dynamics in high-resolution simulations has a completely different structure including eddies than the structure in coarse-resolution models. With this, we will evaluate how the system has reacted regionally differently under different forcing mechanisms (e.g., circumpolar deep-water shelf incursions). Small-scale eddies play an important role in preconditioning and re-stratifying the water column before and after mixing events, thereby affecting deep water formation, melt rates, the regional and large-scale surface ocean and climate. To improve the quality of the climate model, high spatial model resolution is required around the coasts and ice shelves, which makes traditional ocean-climate models with uniform meshes impractical. Recent developments have considerably improved the computational efficiency and scalability of high-resolution unstructured-mesh approaches on high-performance computing systems (e.g., Streffing et al., 2022; Danek et al., 2023).
Hypothesis: The dynamics current in high-resolution simulations has a completely different structure including eddies than the structure in coarse-resolution models. With this, we will evaluate how the system has reacted regionally differently under different forcing mechanisms (e.g., CDW shelf incursions). Small-scale eddies play an important role in preconditioning and restratifying the water column before and after mixing events, thereby affecting deep water formation, melt rates, the regional and large-scale surface ocean and climate.
Timeliness & method: To improve the quality of the model, high spatial model resolution is required around the coasts and ice shelves, which makes traditional ocean-climate models with uniform meshes impractical. Recent developments have considerably improved the computational efficiency and scalability of high-resolution unstructured-mesh approaches on high-performance computing systems (e.g., Streffing et al., 2022; Danek et al., 2023). Pioneering work has been performed in the Climate Dynamics section at AWI facilitated by the considerable increase in computational capacity. The application to the past is the logical next step, providing the opportunity to harvesting low-hanging fruits. Eddy-resolving (up to 5 km local horizontal resolution) ocean model FESOM coupled to 25 km resolution atmosphere openIFS will provide a step change for paleoclimate models. Acceleration methods will be applied to bridge the required time scales for selected periods (e.g., Lorenz and Lohmann, 2004).
POF relevance: This project has a broad scientific disciplinary scope with several sections involved (Climate Dynamics, Marine Geology, Geophysics, etc.). It corresponds explicitly to the aims of ST2.1 (Warming Climates), ST2.3 (Sea Level), and ST2.4 (Model development). Our approach provides valuable out-of-sample tests for the tools used to simulate future climate and environmental changes suitable for integration to IPCC and policy frameworks.
Average (1948–2009, March) local EKE changes of low- (left) and high-resolution (right) FESOM setups in the Labrador Sea. (a, b) Eddy wind work at the sea surface FeKe. Solid red and dashed magenta contours show the modeled and observed (EN4, Good et al.,2013) 2 km MLD (σϴ threshold 0.125 kg m−3), blue contours the depth-integrated 5 (solid) and 20 (dashed) m3 s−2 EKE and thick dashed black lines the LS interior index region. (c, d) Horizontal barotropic HRS and (e, f) baroclinic PeKe instabilities (depth-integrated; positive values indicate EKE generation). Arrows show sea surface velocity direction and magnitude greater or equal 5 cm s−1 and black contours the 1, 2 and 3 km isobaths.
References
Danek, C., P. Scholz, G. Lohmann, 2023: Decadal variability of eddy temperature fluxes in the Labrador Sea. Ocean Modelling 182, 102170. doi:10.1016/j.ocemod.2023.102170
Lohmann, G., M. Butzin, N. Eissner, X. Shi, C. Stepanek, 2020: Abrupt climate and weather changes across timescales. Paleoceanography and Paleoclimatology 35 (9), e2019PA003782, https://doi.org/10.1029/2019PA003782
Streffing, J., Sidorenko, D., Semmler, T., Zampieri, L., Scholz, P., Andrés-Martínez, M., Koldunov, N., Rackow, T., Kjellsson, J., Goessling, H., Athanase, M., Wang, Q., Hegewald, J., Sein, D. V., Mu, L., Fladrich, U., Barbi, D., Gierz, P., Danilov, S., Juricke, S., Lohmann, G., and Jung, T.: AWI-CM3 coupled climate model: description and evaluation experiments for a prototype post-CMIP6 model, Geosci. Model Dev., 15, 6399–6427, 2022. https://doi.org/10.5194/gmd-15-6399-2022
Knorr G., Barker S., Zhang X., Lohmann G., Gong X., Gierz P., Stepanek C., and Stap L. B., 2021: A salty deep ocean as a prerequisite for glacial termination. Nature Geo 14, 930–936, doi:10.1038/s41561-021-00857-3
Lembke-Jene L., Tiedemann R., Nürnberg D., and Lohmann G., 2018: Rapid shift and millennial-scale variations in Holocene North Pacific Intermediate Water ventilation. PNAS 115 (21), 5365-5370, doi:10.1073/pnas.1714754115
Lorenz S. J., and Lohmann G., 2004: Acceleration technique for Milankovitch type forcing in a coupled atmosphere-ocean circulation model: method and application for the Holocene. Climate Dynamics 23, 727–743, doi:10.1007/s00382-004-0469-y
Klages J. P., Salzmann U., Bickert T., Hillenbrand C. D., Gohl K., Kuhn G., Bohaty M. S., Titschack J., Müller J., Frederichs T., Bauersachs T., Ehrmann W., Van de Flierdt T., Pereira P. S., Larter R. D., Lohmann G., Niezgodzki I., Uenzelmann-Neben G., Zundel M., Spiegel C., Mark C., Chew D., Francis J. E., Nehrke G., Schwarz F., Smith J. A., Freudenthal T., Esper O., Pälike H., Ronge T. A., Ricarda Dziadek R., and the Science Team of Expedition PS104, 2020: Temperate rainforests near the South Pole during peak Cretaceous warmth. Nature 580, 81–86, doi:10.1038/s41586-020-2148-5
Maier E., Zhang X., Abelmann A., Gersonde R., Mulitza S., Werner W., Méheust M., Ren J., Chapligin B., Meyer H., Stein R., Tiedemann R., and G. Lohmann G., 2018: North Pacific freshwater events linked to changes in glacial ocean circulation. Nature 559, 241–245, doi:10.1038/s41586-018-0276-y
Stein R., Fahl K., Gierz P., Niessen F, and Lohmann G., 2017: Arctic Ocean sea ice cover during the penultimate glacial and the last interglacial. Nature Communications 8, Article-Nr.: 373, doi:10.1038/s41467-017-00552-1
Streffing J., Sidorenko D., Semmler T., Zampieri L., Scholz P., Andrés-Martínez M., Koldunov N., Rackow T., Kjellsson J., Goessling H., Athanase M., Wang Q., Hegewald J., Sein D. V., Mu L., Fladrich U., Barbi D., Gierz P., Danilov S., Juricke S., Lohmann G., and Jung T., 2022: AWI-CM3 coupled climate model: description and evaluation experiments for a prototype post-CMIP6 model. Geoscientific Model Development 15, 6399–6427, doi:10.5194/gmd-15-6399-2022