Collaborative Research: Common Era Climate Variability from Marine Proxy Surrogate Reconstructions

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The density-driven Atlantic meridional overturning circulation (AMOC), which can influence climate on regional and global scales, is poorly constrained by brief observational records. This adds considerable uncertainty to the interpretation of modern climate trends and to forecasts of future change. The proposed work will extend the instrumental record by generating quantitative reconstructions of AMOC variability over the past 2,000 years within the physically consistent framework of coupled ocean-atmosphere general circulation model (AOGCM) simulations. The project will identify the significant patterns of AMOC variability that emerge from proxy data and their most likely causes. Synthetic pseudoproxies will be used to evaluate the skill of these results and identify sites that might reduce uncertainty in the future. Results from this work will provide a valuable baseline for natural AMOC-climate relationships, giving context to recent trends that will inform future climate change forecasts. The research will combine a network of marine proxy records spanning the past two millennia, compiled during Phase 1 of the PAGES Ocean2K initiative, with Climate Model Intercomparison Project (CMIP) isotope enabled AOGCMs to estimate AMOC using proxy surrogate reconstructions (PSRs). The uncertainty in the PSR method arising from methodological choices, data type, proxy distribution and observational error will be evaluated based, in part, on pseudoproxy experiments (PPEs). PSRs represent completely consistent physical systems, allowing AMOC strength and pattern in skillful PSRs to be compared with atmospheric circulation, external radiative forcing and other variables to evaluate their dynamical links. Confidence in PSRs will likely increase as the proxy network expands in the future, and a PPE will be used to identify additional locations from which additional data might reduce the uncertainty in PSR-based estimates of AMOC (and other variables), providing a target for future work. In addition to the broader scientific relevance of advancing the international Oceans2K and model intercomparison project efforts, other notable impacts include support of an early career researcher with no prior NSF support, research opportunities for undergraduates, and involvement of both researchers in local education initiatives for minorities and high school students.