青海湖全新世硬水效应随时间变化性及其对沉积物~(14)C年龄的校正

通过研究青海湖全新世硬水效应变化与大气~(14)C浓度(X_(atm))之间的关系,确定了湖水溶解无机碳(DIC)与大气~(14)C浓度之比值(X_(DIC)/X_(atm))约为0.790.利用已知X_(atm)随时间变化曲线重建了青海湖全新世的硬水效应,并对沉积物年龄作了相应校正.结果表明,青海湖全新世沉积物(有机质)~(14)C年龄偏老主要缘于湖泊硬水效应,从全新世早期的1000a左右升高到核爆近前的2300a左右,核爆效应之后2005AD又降至1500a左右,其变化至少在很大程度上受控于X_(atm)的波动(对应于以上3个时期,根据X_(atm)所恢复的硬水效应分别为1100a、2150a、1313a).在此基础上,利用硬水效应校正表对青海湖全新世沉积物~(14)C年龄进行了分阶段校正,基于此校正年龄的红度曲线较好地响应了9000-8000cal aBP、6000-5000cal aBP、4200-3800cal aBP、3500-2500cal aBP、1200-1000cal aBP和600-150cal aBP等全球性冷事件.

A corrected 14C age model for Lake Qinghai's sediment spanning the Holocene period,based on the reconstruction of temporal changes in hard water effect

The relationship between 14C levels in lake waters and in the atmosphere had been investigated by comparing the chan ges in hardwater effect ( HWE, expressed by XDIC; X: percent modem carbon; DIC: abbreviation of dissolved inorganic carbon) of lake waters with changes in atmospheric 14C levels ( Xatm). The XDIC/Xatm ratio of Lake Qinghai was found to be about 0.790. The reconstruction of HWE was established based on the XDIC/Xatm ratio and the well known changes of Xatm. The age model ( based on 5 14C dates) of QH-2000 sedimentary core was corrected by the temporal changes of HWE. It showed that the shifts toward old ages for 14 C dates of Lake Qinghai's sediment was mainly due to HWE and the reconstructed HWE was 1100a in the early Holocene, which slowly rose to 2150a in the latest Holocene ( pre-bomb era) and then shifted to 1313a in 2005 AD. It was also val idated by the measured HWE, which was determined to be ca. 1000a, 2300a and 1500a correspondingly. A "HWE correction table" was established for Lake Qinghai so as to transfer any given calendar age without HWE correction into a corrected calendar age. The published redness curve based on our corrected age model shows rapid climate changes (RCC) correlative to those indicated by many records all over the world. The RCCs include those occurred during 9000-8000 cal aBP, 6000-5000 cal aBP, 4200-3800 cal aBP, 3500-2500 cal aBP, 1200 -1000 cal aBP and 600 - 150 cal aBP.