Global-scale proxy system modeling of oxygen isotopes in lacustrine carbonates: 2 new insights from isotope-enabled-model proxy-data comparison

Proxy System Modelling (PSM) is now recognised as a crucial step in comparing climate model output with proxy records of past environmental change. PSMs filter the climate signal from the model, or from meteorological data, based on the physical, chemical and biological processes of the archive and proxy system under investigation. Here we use a PSM of lake carbonate δ18O to forward model pseudoproxy time-series for every terrestrial grid square in the SPEEDY-IER isotope enabled General Circulation Model (GCM), and compare the results with 31 records of lake δ18O data from the Americas in the NOAA Paleoclimate Database. The model-data comparison shows general patterns of spatial variability in the lake δ18O data are replicated by the combination of SPEEDY-IER and the PSM, with differences largely explained by known biases in the models. The results suggest improved spatial resolution/coverage of climate models and proxy data, respectively, is required for improved data-model comparison, as are increased numbers of higher temporal resolution proxy time series (sub decadal or better) and longer GCM runs. We prove the concept of data-model comparison using isotope enabled GCMs and lake isotope PSMs and outline potential avenues for further work