Paleoclimatic interpretation of the past 30 ka from isotopic studies of the deep confined aquifer of the North China plain

The δ18O and δD values in the deep confined aquifer beneath the North China Plain which is located at 112 deg. 30'E-119 deg. 30'E and 34 deg. 46'N-40 deg. 25'N, reflect differences in paleoclimatic conditions between the Holocene and the late Pleistocene. Groundwater samples whose 14C ages are between 12 and 25 ka B.P have ranges of -9.4 to -11.7 per mille for δ18O and -76 per mille to -85 per mille for δD values. These very negative δ18O and δD values reflect the cold and arid climate in the last glacial period. The temperature estimated in this period is 6-9 deg. C cooler than that of the present. The entire ranges of δ18O and δD values for samples with 14C dating from 7 ka B.P to present are -7.7 per mille to -10.2 per mille and -63 per mille to -73 per mille, respectively. The greater δ18O and δD enrichments of these samples indicate a period of relatively humid and warm climate in the Holocene. However, the wide ranges of δ18O (-9.0 per mille to -11.1 per mille) and δD (-66 per mille to -80 per mille) values for samples with 14C age ranging from 12 to 7 ka B.P. imply an unstable climatic condition of rapidly increasing temperature, which marks the transition from the Pleistocene to the Holocene