The conceptual model of paleoclimate data assimilation and commonly used proxies for paleoclimate reconstruction. (IMAGE)
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(A) The process begins with a randomly simulated climate model ensemble Xb. Using a proxy system model H, forward estimation is performed to map paleoclimate states (such as sea surface temperature, SST) onto the observational space of paleoclimate proxies (such as δ18O), yielding predicted proxy values Ye. The difference between the observed proxy values Yo and the predicted values Ye is referred to as the innovation introduced into the climate model ensemble. The ensemble Kalman filter framework then utilizes this innovation to update the climate state to Xa. The assimilation output (posterior, Xa) generally lies between the model ensemble (prior, Xb) and the observed values Yo, with reduced error. (B) The types of commonly used proxies and their sources include: δ18O, δ11B, Mg/Ca, and Δ47 from biogenic carbonates; CaCO3 content, Δ47, and δ13Corg from marine sediments; δ18O and δ2H from ice cores; archaeal biomarkers such as TEX86 , UK′37, and MBT′5Me; stomatal density index, tree ring width (TWR), and δ2H . Orange-bordered ovals indicate temperature proxies, green-bordered ovals indicate pCO2 proxies, and blue-bordered ovals indicate precipitation proxies.
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