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

Abstract The understanding of precipitation δ 18 O variation at the glacial scale has been controversial in paleoclimatology. Groundwater δ 18 O might help provide clarity as they are a widely distributed record of annual weighted mean precipitated δ 18 O. Here, groundwater δ 18 O during the last glacial maximum (LGM) and late Holocene (LH) are first illustrated throughout China based on 158 archived δ 18 O and 14 C measurements. Between LGM and LH, the magnitude of changes in groundwater δ 18 O is higher in North China (NC > 2‰) than South China (SC < 0.5‰). This spatial inconsistency is similar to the seasonal precipitation δ 18 O variations in China caused by changes in atmospheric circulation patterns. Likewise, the difference of groundwater δ 18 O 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 δ 18 O 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 δ 18 O values, implying that the explanation for paleoclimate reconstruction based on stable isotope effects might need careful examination.