Implementing climate proxy data from coralline algae in climate model evaluation: a Southern Hemisphere case study of New Zealand

• Applicants: Professor Dr. Thomas Mölg; Dr. Sebastian Teichert
• Subject Area: Physical Geography
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 453305163

Coupled atmosphere/ocean general circulation models, or global climate models (GCMs) in short, are our most important tools for projecting climate into the future. In addition, they provide input for regional atmospheric models that translate global climate change to regional and local scales where humans face the impacts. Owing to this importance, GCMs must be evaluated against the observed past climate as thoroughly as possible, where one focus is the so-called historical period from 1850 to present. However, the evaluation task is difficult for the period of World War II and earlier due to a lack of reliable observations. The outlined problem is exacerbated for the Southern Hemisphere, which has been notoriously understudied in comparison to the climate of the Northern Hemisphere. --- The present project proposes to utilize a rather recently discovered proxy archive (crustose coralline algae, CCA) for extending the observational record of the climatic environment of New Zealand back to before 1950, and exploit the new data set for the benefit of GCM evaluation, regional atmospheric modeling, and improved understanding of climate system functioning. CCA has a number of advantages compared to other proxy archives (e.g., easy retrieval, high temporal resolution, worldwide distribution). In the first part we will collect CCA offshore New Zealand and extract geochemical signals that allow us to reconstruct ocean temperatures 100 or more years back to the past (the large-scale signal). Second, this new information will be employed in GCM evaluation to reveal their skill of representing the larger-scale climate of New Zealand. And third, regional numerical atmospheric modeling will be conducted to test whether the addition of the CCA-based criterion to the GCM evaluation ultimately adds value to regional climate modeling. A focus here will be on high-altitude climate and glacier variability in the Southern Alps (the impact signal). The regional modeling will also allow us to unravel the physical mechanisms that determine the potential of CCA as a climate proxy in New Zealand. --- The proposed project bundles the expertise of three partners across the fields of paleoclimate, Southern Hemisphere climatology and measurements, and climate modeling, which strongly supports the project goals due to the collaboration. The implications of the potential results, however, will go beyond the specific case study. Results will demonstrate how to rigorously combine the GCM and climate proxy worlds in a systematic framework, highlighting the role of CCA, and how the said combination can enhance regional climate modeling down to the local scale. These points are of generic importance for climate modeling and climate impact research.

• DFG Programme: Research Grants
• International Connection: New Zealand
• Cooperation Partner: Dr. Nicholas Cullen