Groundwater δ18O Distribution Pattern and Spatial Inconsistency Over China During the Last Glacial-Holocene Cycle

The understanding of precipitation δ¹⁸O variation at the glacial scale has been controversial in paleoclimatology. Groundwater δ¹⁸O might help provide clarity as they are a widely distributed record of annual weighted mean precipitated δ¹⁸O. Here, groundwater δ¹⁸O during the last glacial maximum (LGM) and late Holocene (LH) are first illustrated throughout China based on 158 archived δ¹⁸O and ¹⁴C measurements. Between LGM and LH, the magnitude of changes in groundwater δ¹⁸O is higher in North China (NC > 2‰) than South China (SC < 0.5‰). This spatial inconsistency is similar to the seasonal precipitation δ¹⁸O variations in China caused by changes in atmospheric circulation patterns. Likewise, the difference of groundwater δ¹⁸O between LGM and LH in NC and SC is attributed to changes in the East Asian summer monsoon (EASM): during the LGM, the EASM was weaker in significantly affecting NC, whereas during the LH, the EASM was stronger and moved northward into NC. This illustrates that although the monsoon strengthens, the higher δ¹⁸O values in groundwater in NC are still found during the LH than that during the LGM. Furthermore, this spatial difference between NC and SC highlights the importance of moisture sources in affecting precipitation δ¹⁸O values, implying that the explanation for paleoclimate reconstruction based on stable isotope effects might need careful examination.