Development and evaluation of Proxy Surrogate Reconstructions as a tool for characterizing Common Era climate variability.

Centennial-timescale variations in Common Era climate are poorly constrained by brief observational records, but can be inferred from the geochemical variations of biogenic material preserved in ocean sediments as well as realistically-forced atmosphere-ocean general circulation model (AOGCM) simulations. Both sources of paleoclimate information are imperfect however, suggesting that applying them in combination may better approximate the true evolution of the climate system, and better characterize the uncertainty in reconstructions. Here we describe how proxy surrogate reconstructions (PSRs) work toward this goal through a simple analog approach. We use Common Era Mg/Ca, alkenone unsaturation index, and oxygen isotope records, compiled as part of the PAGES Ocean2K and PAGES2k v2.0 databases, to reorder realistically forced isotope-enabled AOGCM simulations that have been observationally mapped via proxy system modeling (PSM), such that spatiotemporally local misfit to the paleoclimate observations are minimized. As part of this process, we present new, independently-validated, PSMs of Mg/Ca in four species based on globally-distributed core-top data. We demonstrate hows PSRs may be used to generate spatially complete climate fields not captured by sparse paleoclimate data networks, estimate dynamic variable such as the Atlantic Meridional Overturning Circulation (AMOC), and evaluate optimal targets for future data generation.