华北平原深层地下水14C年龄的TDIC校正与对比

用14C确定地下水年龄需要进行多种校正。在系统测定华北平原深层地下水14C含量的基础上,应用TDIC(Total Dissolved Inorganic Carbon,即总溶解无机碳)校正地下水14C年龄。将补给区地下水样的14C和TDIC含量作为"初始14C活度"和"初始TDIC"含量,对其他样品进行"初始TDIC"的14C活度校正,并用CAL-IB5.0分别计算了样品校正年龄(14C校)和TDIC校正后的校正年龄(14CTDIC校)。华北平原深层地下水14C校正年龄变化比例达-27.5%~44.4%,TDIC校正对14C年龄影响明显,地下水样品进行14C定年时需要先进行TDIC校正。根据华北平原地下水14C校正年龄和Cl-含量分布,华北平原深层地下水受到明显的海水入侵的影响,衡水—河间—任丘一线西侧地下水14C校正年龄代表了其真实年龄,而衡水—献县—天津一线东侧地下水14C校正年龄不能代表其真实年龄,只是海水和地下水混合后的表观年龄。

Calibrating deep groundwater 14C ages of North China Plain with TDIC and a comparative study

Dating groundwater with 14C needs a variety of calibrations.Groundwater 14C age is calibrated with TDIC(Total Dissolved Inorganic Carbon) in North China Plain according to the results of systematic determination of 14C concentration.The 14C and TDIC concentrations of groundwater samples from recharge area are treated as "the initial 14C activity" and "Initial TDIC" content,and other groundwater samples are calibrated with the "Initial TDIC".Calibrated 14C age and calibrated 14C age after TDIC calibrating are calculated by CALIB 5.0,respectively.The variation of calibrated 14C age is up to-27.5% to 44.4%,TDIC calibrating has obvious impact on 14C age,so it is needed to calibrate age with TDIC first when dating groundwater by 14C.According to the distribution of deep groundwater 14C calibrated age and Cl-content,deep groundwater is obviously affected by seawater intrusion in North China Plain.The groundwater calibrated 14C age represents the real age for the west side of Hengshui-Hejian-Renqiu,but not the case for the east side of Hengshui-Xianxian-Tianjin because it presents a kind of mixture age of deep groundwater and seawater.