Local hydroclimate alters interpretation of speleothem δO records.

Oxygen isotopes (δO) are the most commonly utilized speleothem proxy and have provided many foundational records of paleoclimate. Thus, understanding processes affecting speleothem δO is crucial. Yet, prior calcite precipitation (PCP), a process driven by local hydrology, is a widely ignored control of speleothem δO. Here we investigate the effects of PCP on a stalagmite δO record from central Vietnam, spanning 45 - 4 ka. We employ a geochemical model that utilizes speleothem Mg/Ca and cave monitoring data to correct the δO record for PCP effects. The resulting record exhibits improved agreement with regional speleothem δO records and climate model simulations, suggesting that the corrected record more accurately reflects precipitation δO (δO). Without considering PCP, our interpretations of the δO record would have been misleading. To avoid misinterpretations of speleothem δO, our results emphasize the necessity of considering PCP as a significant driver of speleothem δO.